全文获取类型
收费全文 | 24199篇 |
免费 | 313篇 |
国内免费 | 37篇 |
专业分类
教育 | 17581篇 |
科学研究 | 2087篇 |
各国文化 | 170篇 |
体育 | 2123篇 |
综合类 | 17篇 |
文化理论 | 234篇 |
信息传播 | 2337篇 |
出版年
2022年 | 187篇 |
2021年 | 282篇 |
2020年 | 453篇 |
2019年 | 700篇 |
2018年 | 916篇 |
2017年 | 953篇 |
2016年 | 811篇 |
2015年 | 538篇 |
2014年 | 664篇 |
2013年 | 4498篇 |
2012年 | 633篇 |
2011年 | 638篇 |
2010年 | 463篇 |
2009年 | 445篇 |
2008年 | 549篇 |
2007年 | 480篇 |
2006年 | 499篇 |
2005年 | 358篇 |
2004年 | 391篇 |
2003年 | 360篇 |
2002年 | 459篇 |
2001年 | 465篇 |
2000年 | 445篇 |
1999年 | 374篇 |
1998年 | 231篇 |
1997年 | 237篇 |
1996年 | 275篇 |
1995年 | 246篇 |
1994年 | 211篇 |
1993年 | 217篇 |
1992年 | 313篇 |
1991年 | 302篇 |
1990年 | 282篇 |
1989年 | 321篇 |
1988年 | 325篇 |
1987年 | 271篇 |
1986年 | 281篇 |
1985年 | 282篇 |
1984年 | 250篇 |
1983年 | 294篇 |
1982年 | 225篇 |
1981年 | 202篇 |
1980年 | 188篇 |
1979年 | 287篇 |
1978年 | 237篇 |
1977年 | 206篇 |
1976年 | 199篇 |
1975年 | 165篇 |
1974年 | 154篇 |
1973年 | 160篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
Knight DM 《Endeavour》2000,24(4):165-169
Humphry Davy (1778–1829) was one of the first professional scientists, earning his living and rising spectacularly from an impoverished upbringing in Cornwall to be President of the Royal Society and a baronet. He owed his rise to patronage as well as to his range of abilities: as a lecturer, as a chemical theorist and as a very early applied scientist. But his exalted position brought him little happiness, for he could not satisfy all the hopes put upon him as the successor to Sir Joseph Banks. Admired rather than loved, he became unpopular and was seen as haughty. In his last two years, spent wandering lonely and sickly in Italy and the Alps, he sought to make sense of his life, writing dialogues as his bequest to the new generation. 相似文献
102.
Soma Gupta K. K. Singh V. J. Vyas V. N. Chaturvedi M. V. R. Reddy B. C. Harinath 《Indian journal of clinical biochemistry : IJCB》2000,15(1):52-55
Oxidative stress was studied by estimating plasma levels of malondialdehyde (MDA), beta carotene, vitamin E and erythrocytic
superoxide dismutase(E-SOD) activity in 50 cases of carcinoma of upper digestive tract which included carcinoma of oral cavity,
pharynx and oesophagus. While plasma MDA level was found to be increased (3.5±1.0 nmole/ml), a significant decrease in beta
carotene (81.2±14.5mg%), vitamin E (8.5±1.1 mg/L) level and E-SOD activity (657.0±80.6 U/G Hb) were observed in carcinoma
of upper digestive tract. Patients were treated with radiotherapy which itself was toxic enough and produced its deleterious
effects by generation of reactive oxygen species (ROS). As antioxdiants can detoxify ROS, beneficial effect if any, of antioxidant
administration during radiotherapy was studied in two groups of patients, group A (n=5, supplemented with antioxidants) and
group B (n=5, without antioxidant supplementation). Plasma MDA level was found to be elevated in both the groups but the increase
in group B was significant, compared to pretreatment level. Further, body weight was found to be significantly decreased in
group B patients, which was maintained in group A patients. Moreover, group A patients showed significant elevation in beta
carotene concentration, thus showing beneficial effect of administration of antioxidants during radiotherapy without disturbing
the desirable therapeutic effect of radiotherapy. 相似文献
103.
While there is no universal logic of induction, the probabilitycalculus succeeds as a logic of induction in many contexts throughits use of several notions concerning inductive inference. Theyinclude Addition, through which low probabilities representdisbelief as opposed to ignorance; and Bayes property, whichcommits the calculus to a refute and rescale dynamicsfor incorporating new evidence. These notions are independentand it is urged that they be employed selectively accordingto needs of the problem at hand. It is shown that neither isadapted to inductive inference concerning some indeterministicsystems.
- 1 Introduction
- 2 Failure of demonstrations of universality
- 2.1 Working backwards
- 2.2 The surface logic
- 3 Framework
- 3.1 The properties
- 3.2 Boundaries
- 3.2.1 Universalcomparability
- 3.2.2 Transitivity
- 3.2.3 Monotonicity
- 3.2.2 Transitivity
- 3.2 Boundaries
- 4 Addition
- 4.1 The property: disbelief versus ignorance
- 4.2Boundaries
- 5 Bayes property
- 5.1 The property
- 5.2 Bayes' theorem
- 5.3Boundaries
- 5.3.1 Dogmatism of the priors
- 5.3.2 Impossibilityof prior ignorance
- 5.3.3 Accommodation of virtues
- 5.3.2 Impossibilityof prior ignorance
- 5.2 Bayes' theorem
- 6Real values
- 7 Sufficiency and independence
- 8 Illustrations
- 8.1 All properties retained
- 8.2 Bayes propertyonly retained
- 8.3 Induction without additivity and Bayes property
- 8.2 Bayes propertyonly retained
- 9Conclusion
- 2 Failure of demonstrations of universality
104.
We present a new paradigm for the automatic creation of document headlines that is based on direct transformation of relevant textual information into well-formed textual output. Starting from an input document, we automatically create compact representations of weighted finite sets of strings, called WIDL-expressions, which encode the most important topics in the document. A generic natural language generation engine performs the headline generation task, driven by both statistical knowledge encapsulated in WIDL-expressions (representing topic biases induced by the input document) and statistical knowledge encapsulated in language models (representing biases induced by the target language). Our evaluation shows similar performance in quality with a state-of-the-art, extractive approach to headline generation, and significant improvements in quality over previously proposed solutions to abstractive headline generation. 相似文献
105.
106.
In this paper,we prove that the Veronese surface can be determined by the 1-spectrum of the Laplace operator. 相似文献
107.
Incoherent English Immersion and California Proposition 227 总被引:1,自引:0,他引:1
Although during the 1997–98 academic school year, only 25% of the English Language Learners (ELLs) in elementary schools throughout California were receiving some form of bilingual education, the ramifications of the passage of Proposition 227 in June of 1998 were multiple for the teachers, interns, and children involved. The legislative language of Proposition 227 was sufficiently vague and thus created other problems. The proposition was challenged in the California state court system as soon as the ballots were counted. This constitutional challenge further clouded an already murky situation. Districts were receiving little if any clarification from the California State Department of Education in regard to the time lines for implementation of the new law. The law, itself, spoke to specific changes and curriculum, but there was no money to create the new curricular approach, time to in-service teachers in the new methodology to be utilized, or a framework and time line for implementation of the mandated changes.Because of the wording that attempted to hold teachers and administrators personally liable to civil suit for noncompliance, many districts interpreted the new law as conservatively as possible to avoid such litigation. In other districts changes were made site by site as a response of the particular administrator. This type of erratic policy implementation across large district was very demoralizing for most bilingual teachers. It also confused the parent communities. It made no sense to the average person that if a child was at School A s/he could be receiving primary language instruction while a child at School B only a mile away and in the same school district could not even ask the teacher questions in his/her home language without being told, Only speak English at school. 相似文献
108.
The present research examined the role of maladaptive self-regulatory beliefs as vulnerability factors for academic and emotional difficulties during the transition to middle school. A short-term longitudinal design was employed to follow two groups of early adolescents: 187 adolescents who experienced a school transition between the fifth and sixth grades, and 142 adolescents who did not experience a school transition between the fifth and sixth grades. Adolescents completed measures of perceptions of academic control and importance of academic success, experience of chronic academic strain, daily school hassles, and depressive symptoms. Teachers reported on students' academic engagement, including levels of helpless behavior, effort, and academic performance. Consistent with the proposed model of self-regulation, maladaptive self-regulatory beliefs (i.e., decreased perceptions of academic control and importance) predicted individual differences in perceived school-related stress and depressive symptoms over the course of the middle school transition, but were not associated with academic and emotional difficulties in adolescents who remained in a stable school environment. Moreover, a self-regulatory sequence was identified proceeding from maladaptive self-regulatory beliefs, to academic disengagement, to enhanced perceptions of school-related stress, to depressive symptoms. This study bridges prior theory and research concerning the psychological impact of normative developmental transitions, the developmental context of depression, and the associations among self-regulatory beliefs, achievement-related behavior, and emotional experience. 相似文献
109.
OBJECTIVE: A model was examined in which the association between a parent's history of abuse and the parent's own abusive behavior toward his or her children was hypothesized to be mediated by parental psychopathology, early childbearing, and consistency of discipline. Additionally, the effect of severity of abuse on the likelihood of becoming abusive was examined. METHOD: Participants were 109 parents (G1) and their male children (G2) who were involved in a longitudinal study. The G1 parents reported on their own experiences of abuse when they were children. Ten years later, the G2 youths reported on the G1 parents' abusive behavior toward them. A number of other factors, including parental socioeconomic status (SES), antisocial behavior, depression and Post-traumatic Stress Disorder (PTSD), consistency of discipline, and the perceived early difficulty of the G2 children were measured. RESULTS: As reported by their own children, parents who reported having been abused in childhood were significantly more likely to engage in abusive behaviors toward the next generation. Findings indicated that abuse experienced by the parents, as well as consistency of discipline and depression plus PTSD, were predictive of parental abuse of the child. Contrary to hypotheses, the effects were not fully mediated. However, there were significant interactions between parental history of abuse and consistency of discipline, as well as abuse history and depression and PTSD. Parents who had experienced multiple acts of abuse and at least one physical impact were more likely to become abusive than were the other parents. CONCLUSIONS: The implications of these findings for preventive interventions are discussed. 相似文献
110.