首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   28691篇
  免费   349篇
  国内免费   128篇
教育   20343篇
科学研究   3124篇
各国文化   198篇
体育   2276篇
综合类   17篇
文化理论   209篇
信息传播   3001篇
  2021年   207篇
  2020年   359篇
  2019年   565篇
  2018年   758篇
  2017年   726篇
  2016年   709篇
  2015年   439篇
  2014年   586篇
  2013年   5177篇
  2012年   585篇
  2011年   673篇
  2010年   463篇
  2009年   461篇
  2008年   572篇
  2007年   500篇
  2006年   567篇
  2005年   457篇
  2004年   426篇
  2003年   414篇
  2002年   439篇
  2001年   549篇
  2000年   525篇
  1999年   515篇
  1998年   264篇
  1997年   301篇
  1996年   346篇
  1995年   335篇
  1994年   265篇
  1993年   292篇
  1992年   433篇
  1991年   417篇
  1990年   417篇
  1989年   459篇
  1988年   423篇
  1987年   403篇
  1986年   395篇
  1985年   442篇
  1984年   388篇
  1983年   416篇
  1982年   337篇
  1981年   313篇
  1980年   303篇
  1979年   453篇
  1978年   354篇
  1977年   324篇
  1976年   290篇
  1975年   250篇
  1974年   264篇
  1973年   243篇
  1971年   211篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Part of the controversy about allowing examinees to review and change answers to previous items on computerized adaptive tests (CATs) centers on a strategy for obtaining positively biased ability estimates attributed to Wainer (1993) in which examinees intentionally answer items incorrectly before review and to the best of their abilities upon review. Our results, based on both simulated and live testing data, showed that there were instances in which the Wainer strategy yielded inflated ability estimates as well as instances in which it yielded deflated ability estimates. The success of the strategy in inflating ability estimates depended on the ability estimation method used (maximum likelihood versus Bayesian), the examinee's true ability level, the standard error of the ability estimate, the examinee's ability to implement the strategy, and the type of decision made from the ability estimate. We discuss approaches to dealing with the Wainer strategy in operational CAT settings.  相似文献   
992.
Rats were used in four experiments to study the effects on behavior and pain sensitivity of exposure to a context previously paired with footshock or injection of the emetic drug lithium chloride (LiCl). Exposure to a context previously paired with footshock or injection of LiCl provoked the species-typical defense response of freezing (Experiments 1A and 1B). Exposure to a context previously paired with footshock additionally produced hypoalgesia when rats were tested using the tailflick test (Experiment 1A). By contrast, exposure to a context previously paired with injection of LiCl produced hyperalgesia when rats were tested using the tailflick test (Experiment 1B). However, exposure to a context previously paired with injection of LiCl did provoke hypoalgesia when rats were tested for pain sensitivity using either the hotplate or formalin tests (Experiment 2), which was mediated by the release of endogenous opioid peptides (Experiment 3). These results are discussed with reference to the processes governing associative regulation of defensive behavior and pain control.  相似文献   
993.
This case study illustrates instruction in an urban 6th‐grade classroom in which students were learning about mass, volume, and density by attempting to layer (stack) three miscible solutions with differing densities atop one another. The study examines classroom discourse and interaction on the basis of four teaching goals: (a) reaching consensus about which stacks were possible, (b) developing persuasive arguments that separated data from noise, (c) establishing social norms for collective inquiry, and (d) appreciating the epistemological status of scientific knowledge. The study traces the fate of three stacks that students claimed were possible after initial investigations with the solutions. These claims underwent a process of collective validation in which consensus without coercion was the goal, which illustrates emergent standards for backing claims with evidence, as well as for replicability, among the students. Students were successful in achieving three of the four goals, with some qualifications. In relation to Goal 3, which required generalization to other situations, somewhat less success is reported. Limitations in the current standards, difficulties of time allotment in current curricula, and establishing classroom cultures of inquiry are discussed. © 1999 John Wiley & Sons, Inc. J Res Sci Teach 36: 179–199, 1999  相似文献   
994.
Conduct Disorder (CD) research is focusing on complex issues introduced by comorbidity because of its widespread existence, thoeretical importance and practical significance. This review provides critical examination of research published during the past ten years addressing CD and its comorbid conditions, specifically Attention‐Deficit Hyperactivity Disorder (ADHD), Oppositional Defiant Disorder (ODD), and internalizing disorders. It is concluded that comorbidity varies with age, gender, informant, diagnostic criteria, and nature of the sample (clinical vs. epidemiological). Implications of comorbidity for etiology, diagnosis, treatment, law, and policy and preventive efforts in work with children and adolescents with CD are offered for school psychologists. © 1999 John Wiley & Sons, Inc.  相似文献   
995.
Instruction in hematopathology at Mayo Medical School has evolved from instructor‐guided direct inspection under the light microscope (laboratory method), to photomicrographs of glass slides with classroom projection (projection method). These methods have not been compared directly to date. Forty‐one second‐year medical students participated in this pilot study, a prospective, randomized, crossover study measuring educational performance during a hematology pathophysiology course. The students were randomized to one of two groups. All students received the same didactic lectures in the classroom and subsequent case‐based review of peripheral blood smears using either laboratory or projection methods, on day one with a crossover to the other method on day two. Pre‐ and post‐test examinations centered on morphology recognition measured educational performance on each day, followed by a questionnaire identifying the student's favored method. There was no significant difference in the pre‐test and post‐test scores between the two teaching methods (rank‐sum P = 0.43). Students overwhelmingly preferred the projection method and perceived it as superior (76%), although post‐test scores were not significantly different. Student's recommended method was split with 50% favoring the projection method, 43% favoring a combined approach, and 23% noting logistical challenges to the laboratory. In this study, the laboratory and projection method were equivalent in terms of educational performance for hematopathology among medicals students. A classroom‐based approach such as the projection method is favored, given the large class sizes in undergraduate medical education, as well as the ergonomic challenges and additional resources required for large group instruction in a laboratory setting. Anat Sci Educ 7: 130–134. © 2013 American Association of Anatomists.  相似文献   
996.
This four‐wave prospective longitudinal study evaluated stability of language in 324 children from early childhood to adolescence. Structural equation modeling supported loadings of multiple age‐appropriate multisource measures of child language on single‐factor core language skills at 20 months and 4, 10, and 14 years. Large stability coefficients (standardized indirect effect = .46) were obtained between language latent variables from early childhood to adolescence even when accounting for child nonverbal intelligence and social competence and maternal verbal intelligence, education, speech, and social desirability. Stability coefficients were similar for girls and boys. Stability of core language skill was stronger from 4 to 10 to 14 years than from 20 months to 4 years, so early intervention to improve lagging language is recommended.  相似文献   
997.
In 2011, according to a National Center for Education Statistics report, part-time instructional staff in all higher education institutions exceeded full-time faculty members for the first time, accounting for 50% of all instructional staff (National Center for Education Statistics [NCES], 2012 National Center for Education Statistics . ( 2012 ). IPEDS, Digest of education statistics, Winter 2011–12, human resources component, fall staff section: Table 286 [data file]. Retrieved from http://nces.ed.gov/programs/digest/d12/tables/dt12_286.asp  [Google Scholar]). The same report indicates part-time faculty in community colleges exceeds 70% of instructional staff. Perhaps more alarming are the numbers of contingent instructional staff—faculty without long-term employment commitments. According to this measure, nearly 70% of faculty members in all areas of higher education have little-to-no job stability (American Association of University Professors [AAUP], 2013 American Association of University Professors (AAUP) . ( 2013 ). Background facts on contingent faculty. Retrieved from http://www.aaup.org/issues/contingency/background-facts  [Google Scholar]; Schuster & Finklestein, 2006 Schuster , J. H. , & Finklestein , M. J. ( 2006 ). The American faculty: The restructuring of academic work and careers . Baltimore , MD : The Johns Hopkins University Press . [Google Scholar]). However, limited research exists on the working experiences of this major subpopulation of United States professors.

The purpose of this qualitative study was to explore the experiences of part-time contingent community college faculty regarding the assessment processes their institutions implemented. Through interviews, researchers gathered data identifying what 20 part-time contingent faculty professors reported regarding teaching conditions and institutional assessment procedures. Participant interviews revealed two major themes centered on a lack of institutional engagement and meaningful assessment policies or procedures.  相似文献   
998.
This paper examines how scientific and technological (S&T) human capital is transformed into financial capital through the creation of firms by scientists. The analysis is based on a database describing the positions held by 132 founders from 62 French biotech SMEs. It shows that star scientists engage in highly risky but also valuable firms. Less famous scientists must develop their human capital rather than valorising a stock. The paper concludes by pointing to three paradoxes concerning the commitment and compensation scheme of star scientists and the managerial position of less known scientists.  相似文献   
999.
Metabolic abnormalities were investigated in 44 stone patients with first time (group 1) and 56 with 2 times stone formation (group 2), and in 25 normal individuals. 24hr urine was analysed spectrophotometrically for oxalate, calcium, magnesium, citrate, uric acid, phosphate and creatinine. Hypocitraturia and hyperoxaluria were the common abnormalities in the stone formers. Stone patients had significantly higher urinary oxalate, calcium and uric acid and lower phosphate than normal individuals. Citrate/calcium and magnesium/calcium ratio were significantly high in normal individuals than stone formers. Patients in group 2 excreted significantly higher urinary calcium and lower citrate that patients in group 1. Citrate/calcium ratio was higher in group 1 than group 2. Hypocitraturia, hyperoxaluria, hypercalciuria and increased citrate/calcium and magnesium/calcium ratio seem to be an essential risk factor for stone formation. Patients with recurrent stone formation could be distinguished from patients with first time stone formation on the basis of urinary calcium and citrate.  相似文献   
1000.
To study the mechanism of action of water soluble compound GII purified from fenugreek (Trigonella foenum graecum) seeds which was shown earlier to have antidiabetic effect in the subdiabetic, moderately and severely diabetic rabbits. In rabbits (1–1.5 kg bw) diabetes was induced by intravenous injection of 80 mg/kg bw of alloxan. They were fed with GII at a dose of 50 mg/kg bw daily once in the morning for 15 days in the subdiabetic and moderately diabetic and 30 days in the severely diabetic rabbits. Serum total cholesterol (TC), triglycerides (TG), LDL + VLDL cholesterol [(LDL + VLDL)C], HDL cholesterol [(HDL)C], total tissue lipids, glycogen and enzymes of carbohydrate metabolism (glycolysis, gluconeogenesis, polyol pathway) hexokinase, glucokinase, pyruvate kinase, malic enzyme, glucose-6-phosphatase, glucose-6-phosphate dehydrogenase, aldose reductase and sorbitol dehydrogenase and antioxidant enzymes glutathione peroxidase, glutathione reductase and superoxide dismutase were estimated. Liver and kidney function parameters were also estimated. Treatment with GII for 15 days in the subdiabetic and moderately diabetic rabbits and for 30 days in the severely diabetic rabbits (i) decreased the elevated lipids TC, TG, (LDL + VLDL)C and increased the decreased (HDL)C, (ii) decreased the elevated liver and heart total lipids, TC and TG, (iii) increased the decreased liver and muscle glycogen, (iv) increased the decreased hexokinase, glucokinase, pyruvate kinase, malic enzyme, glucose-6-phosphate dehydrogenase, superoxide dismutase, glutathione peroxidase, (v) decreased the increased glucose-6-phosphatase, sorbitol dehydrogenase, aldose reductase. Results thus show that treatment with GII compound purified from fenugreek seeds for 15 days in the subdiabetic and moderately diabetic and 30 days in the severely diabetic rabbits corrects the altered serum lipids, tissue lipids, glycogen, enzymes of glycolysis, gluconeogenesis, glycogen metabolism, polyol pathway and antioxidant enzymes. Histopathological abnormalities (fatty infiltration and other cellular changes) seen in the pancreas, liver, heart and kidneys were repaired after treatment with GII. In fact partially damaged pancreas was repaired. Liver and kidney function test results were normal in the GII treated animals indicating that GII treatment is safe and free from any side effects.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号