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   13953篇
  免费   183篇
  国内免费   7篇
教育   10195篇
科学研究   1208篇
各国文化   80篇
体育   1113篇
综合类   7篇
文化理论   86篇
信息传播   1454篇
  2021年   103篇
  2020年   154篇
  2019年   253篇
  2018年   350篇
  2017年   359篇
  2016年   328篇
  2015年   201篇
  2014年   279篇
  2013年   2580篇
  2012年   297篇
  2011年   361篇
  2010年   223篇
  2009年   216篇
  2008年   322篇
  2007年   231篇
  2006年   302篇
  2005年   199篇
  2004年   183篇
  2003年   174篇
  2002年   213篇
  2001年   319篇
  2000年   287篇
  1999年   259篇
  1998年   128篇
  1997年   156篇
  1996年   171篇
  1995年   175篇
  1994年   139篇
  1993年   161篇
  1992年   234篇
  1991年   209篇
  1990年   207篇
  1989年   242篇
  1988年   244篇
  1987年   205篇
  1986年   204篇
  1985年   216篇
  1984年   189篇
  1983年   229篇
  1982年   170篇
  1981年   159篇
  1980年   156篇
  1979年   229篇
  1978年   181篇
  1977年   164篇
  1976年   149篇
  1975年   128篇
  1974年   119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 78 毫秒
931.
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   
932.
This year marks the 25th anniversary of the discovery of crown ethers by C. J. Pedersen (see Mary R. Truter and C. J. Pedersen Endeavour, 30, 142, 1971). This article reviews some new developments in this important field. New crown ether and related ligand systems that contain organometallic redoxactive groups can complex and electrochemically detect cations (metals, ammonium) and anions (halide, nitrate) in polar solvents. Thus, they represent prototypes of novel molecular sensory devices of the future.  相似文献   
933.
934.
In the United States the ascendancy of speech protection is due to an expansive and unjustified view of the value or primacy of free expression and access to information. This is perhaps understandable, given that privacy has been understood as a mere interest, whereas speech rights have been seen as more fundamental. I have argued elsewhere that the “mere interest” view of privacy is false. Privacy, properly defined, is a necessary condition for human well-being or flourishing. The opening section of this article will provide an overview of this theory. Next, after a few remarks on speech absolutism, privacy absolutism, and balancing theories, I will sketch several of the dominant argument strands that have been offered in support of presumptively weighty speech rights. While these arguments, taken together, establish that free speech is important, they do not support the view that speech should nearly always trump privacy. In final section I will present and defend a way to balance free speech and privacy claims.  相似文献   
935.
A general input-to-state stability (ISS)-type small-gain result is presented. It specializes to a small-gain theorem for ISS operators, and it also recovers the classical statement for ISS systems in state-space form. In addition, we highlight applications to incrementally stable systems, detectable systems, and to interconnections of stable systems.  相似文献   
936.
In this paper the patenting activity of the international pharmaceutical industry in London between 1900 and 1966 is analysed. Although patent data as a measure of industrial activity is not without defects it can be used both as an adjunct to and as a surrogate for more conventional yardsticks such as concentration ratios, sales statistics and so on. The results indicate that patenting activity can be used as both an absolute and relative indicator of an industry's pace of technological change. They help pinpoint the international distribution of pharmaceutical research and development. If analysed by product or process they can aid in the understanding of why an industry's competitive behaviour is or is not primarily one of price rivalry. Finally, they illustrate the continuing role of the individual inventor.  相似文献   
937.
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   
938.
Many plants have been used for the treatment of diabetes mellitus in Indian system of medicine and in other ancient systems of the world. Out of these only a few have been evaluated as per modern system of medicine. From many such plants only extracts have been prepared and their usefulness evaluated in experimental diabetes in animals. In some plants likeAllium cepa, Allium sativum, Ficus bengalensis, Gymnema sylvestre, Pterocarpus marsupium etc. active hypoglycemic principles have been isolated and their mechanism of action studied. Most of them seem to act directly on pancreas (pancreatic effect) and stimulate insulin level in blood. Some have extra pancreatic effect also by acting directly on tissues like liver, muscle etc. and alter favourably the activities of the regulatory enzymes of glycolysis, gluconeogenesis and other pathways. Since the plant products have less side effects, they have the potential as good hypoglycemic drugs. They may also provide clues for the development of new and better oral drugs for diabetes.  相似文献   
939.
Globalization has contributed to the dismantling of national boundaries, which have enabled firms to compete and conduct business on a wider scale [Held, D., McGrew, A., Goldblatt, D., & Perraton, J. (1999). Global transformations. Politics, economics and culture. Cambridge: Polity Press]. Firms can move freely between different markets using Internet-based technology. While access to such markets can provide firms with greater choice of suppliers and cost efficiencies, they need to be aware of challenges that can influence their business performance. With this in mind, we examine how these factors influenced Alcoa Alumina's drive to a global procurement platform through a global marketplace. The staged adoption process experienced at Alcoa Alumina offers a learning opportunity for other firms considering the transition to global marketplace.  相似文献   
940.
The present study was designed to determine the association between extent of hepatocellular injury and plasma level of thiobarbituric acid reactive substances (TBARS) in pre term infants with cholestasis. Preterm infants (<35 weeks gestation) admitted to the neonatal intensive care unit were enrolled (with their parents informed consent) in either the ‘cholestasis’ group (if their direct bilirubin was >2 mg/dl) (n=25) or in the control group (n=16). Blood samples for measurement of TBARS, direct bilirubin and transaminases were obtained with-in 24 hours of enrollment. The cholestasis and control groups were comparable with respect to gestational age, birth weight and Apgar score. Serum direct bilirubin, SGOT (EC 2.6.1.1) and SGPT (EC 2.6.1.2) levels were significantly high in the cholestasis group. Plasma levels of TBARS in cholestasis group were correlated with SGOT (F=276.92; P<0.0001) and SGPT (F=355.17; P<0.0001) and differed significantly between cholestatic and control infants. Our findings suggest that oxidative stress in preterm infants with cholestasis is associated with hepatocellular injury.  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