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   25264篇
  免费   167篇
  国内免费   7篇
教育   18924篇
科学研究   2374篇
各国文化   80篇
体育   1457篇
综合类   7篇
文化理论   464篇
信息传播   2132篇
  2021年   106篇
  2020年   159篇
  2019年   259篇
  2018年   2473篇
  2017年   2409篇
  2016年   1855篇
  2015年   310篇
  2014年   393篇
  2013年   2657篇
  2012年   507篇
  2011年   1023篇
  2010年   1035篇
  2009年   630篇
  2008年   946篇
  2007年   1350篇
  2006年   366篇
  2005年   582篇
  2004年   617篇
  2003年   520篇
  2002年   339篇
  2001年   328篇
  2000年   304篇
  1999年   259篇
  1998年   128篇
  1997年   169篇
  1996年   171篇
  1995年   176篇
  1994年   139篇
  1993年   162篇
  1992年   234篇
  1991年   215篇
  1990年   209篇
  1989年   244篇
  1988年   245篇
  1987年   208篇
  1986年   206篇
  1985年   219篇
  1984年   191篇
  1983年   231篇
  1982年   172篇
  1981年   163篇
  1980年   157篇
  1979年   230篇
  1978年   181篇
  1977年   164篇
  1976年   150篇
  1975年   129篇
  1974年   121篇
  1973年   125篇
  1971年   106篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
901.
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   
902.
Although the importance of intellectual capital has already been highlighted in the management literature, few articles have focused on the importance of its green counterpart, green intellectual capital. Nowadays, when environmental concerns cannot be ignored by firms, it is therefore time to explore the role of green intellectual capital in environmental improvement. For that reason, our research aims to explore the relationships between green intellectual capital components and the environmental performance of the firms. In particular, we try to show the importance of green organizational and social capital in the development of environmental product innovations, which are vital to the development and implementation of environmental strategies since, as scholars have pointed out, they generate some of the greatest environmental impacts. The empirical results show that green organizational capital has an indirect impact on environmental product innovation through green social capital, meaning that the latter is a significant mediator of that relationship, and at the same time emphasizing that informal relationships play a key role in the improvement of the environmental performance of the firm and, more specifically, in the development of environmental product innovations.  相似文献   
903.
This study aims to examine the relationships between managerial learning as a facet of knowledge absorption (KA), firm innovation as a facet of knowledge exploitation (KE), and performance of small firms (i.e., firms with fewer than 50 employees). It builds on the knowledge-based view of the firm and the upper echelons theory to describe the effects of KA on KE, and that of KE on firm performance, in the small-firm context. Using survey data of 1441 small firms in New Zealand, the study applies a partial least squares approach to structural equation modelling to test the main hypotheses of the study. The main findings show the positive and significant effects of three types of managerial learning, namely, practice-based, proximal, and distal learning, on innovation and on innovation in firm performance. However, the curvilinear relationships suggest rather that the effects are finite and, potentially, confounded by factors unaccounted for in the models.  相似文献   
904.
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
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
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
9Conclusion
  相似文献   
905.
906.
This article offers a discussion of the connection between technology and values and, specifically, I take a closer look at ethically sound design. In order to bring the discussion into a concrete context, the theory of Value Sensitive Design (VSD) will be the focus point. To illustrate my argument concerning design ethics, the discussion involves a case study of an augmented window, designed by the VSD Research Lab, which has turned out to be a potentially surveillance-enabling technology. I call attention to a “positivist problem” that has to do with the connection between the design context and the use context, which VSD seems to presuppose, and I argue that it is necessary to clearly distinguish between the two, since the designers’ intentions do not always correspond with the users’ practice; in fact, the relation between design and use is very complex and principally unpredictable. Thus, a design theory must accept that foresight is limited to anticipation rather than prediction. To overcome the positivist problem, I suggest a phenomenological approach to technology inspired by Don Ihde’s concept of multistability. This argument, which is general in nature and thus applies to any theory of design ethics, is intended as a constructive criticism, which can hopefully contribute to the further development of design ethics.  相似文献   
907.
James Tabery 《Metascience》2007,16(1):143-146
  相似文献   
908.
909.
910.
Deficiency or excess of certain trace elements has been considered as risk factor for prostate cancer. This study was aimed to detect differential changes and mutual correlations of selected trace elements in prostate cancer tissue versus benign prostatic hyperplasia tissue. Zinc, copper, iron, calcium and selenium were analysed in histologically proven 15 prostate cancer tissues and 15 benign prostatic hyperplasia tissues using atomic absorption spectrophotometer. Unpaired two tailed t test/Mann–Whitney U test and Pearson correlation coefficient were used to compare the level of trace elements, elemental ratios and their interrelations. As compared to benign prostatic tissue, malignant prostatic tissue had significantly lower selenium (p = 0.038) and zinc (p = 0.043) concentrations, a lower zinc/iron ratio (p = 0.04) and positive correlation of selenium with zinc (r = 0.71, p = 0.02) and iron (r = 0.76, p = 0.009). Considerably divergent interrelationship of elements and elemental ratios in prostate cancer versus benign prostatic hyperplasia was noted. Understanding of differential elemental changes and their interdependence may be useful in defining the complex metabolic alterations in prostate carcinogenesis with potential for development of element based newer diagnostic, preventive and therapeutic strategies. Further studies may be needed to elucidate this complex relationship between trace elements and prostate carcinogenesis.  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