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   19266篇
  免费   1340篇
  国内免费   3篇
  2023年   127篇
  2022年   122篇
  2021年   448篇
  2020年   312篇
  2019年   427篇
  2018年   488篇
  2017年   460篇
  2016年   703篇
  2015年   1021篇
  2014年   1090篇
  2013年   1318篇
  2012年   1619篇
  2011年   1500篇
  2010年   982篇
  2009年   868篇
  2008年   1154篇
  2007年   1083篇
  2006年   1068篇
  2005年   867篇
  2004年   805篇
  2003年   801篇
  2002年   695篇
  2001年   176篇
  2000年   125篇
  1999年   163篇
  1998年   166篇
  1997年   144篇
  1996年   146篇
  1995年   114篇
  1994年   114篇
  1993年   108篇
  1992年   104篇
  1991年   100篇
  1990年   69篇
  1989年   65篇
  1988年   59篇
  1987年   52篇
  1986年   47篇
  1985年   68篇
  1984年   68篇
  1983年   61篇
  1982年   60篇
  1981年   64篇
  1980年   49篇
  1979年   38篇
  1978年   42篇
  1977年   39篇
  1975年   30篇
  1974年   31篇
  1973年   34篇
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
111.
We have isolated a cDNA clone carrying a 1560 bp long insert which contains the entire coding and 3' untranslated regions of an H-2K(d) mouse histocompatibility antigen. Its sequence and overal features are described. They point to the existence of unique properties of DNA sequences associated with the H-2K(d) antigen.  相似文献   
112.
113.
114.
Synopsis Four acid hydrolases in the secretory cells and the sebum of the preputial sebaceous gland of the rat were incestigated cytochemically. A strong -glucuronidase activity was found to occur in the matrix of the perinuclear secretion granules, whereas the granule crystalloids were unreactive. The distribution of acid phosphatase at the light microscope level was similar, though the intensity of the reaction was lower and the number of positive granules smaller. By electron microscopy, the final reaction product of acid phosphatase occurred in patches at the periphery of the granule matrix, as well as in the vesicles adjoining the Golgi stacks, from which the perinuclear granules seemed to arise. In the sebum, the two hydrolases occurred in the background material between the unstained crystalloid masses. There was noN-acetyl--glucosaminidase or aryl sulphatase activity in the gland. The perinuclear granules appear to be secretory lysosomes which, after discharge from the disaggregating cell, release their acid hydrolases into the sebum.  相似文献   
115.
1. l-Glutamate decarboxylase (EC 4.1.1.15) from Clostridium perfringens was inactivated by exposure to visible light at pH6.2. 2. Inactivation does not occur at pH4.6 or in the absence of bound pyridoxal phosphate. 3. On prolonged photo-oxidation six histidine residues per molecule of enzyme were destroyed. 4. The loss of six cysteine residues per molecule occurred both in irradiated samples and in controls oxygenated in the dark. 5. This dark-oxidation of cysteine residues is apparently required before the photo-oxidation process. 6. The absorbance, fluorescence and circular-dichroism properties of the enzyme as well as its elution volume during Sephadex gel-filtration were unaffected by prolonged irradiation. 7. However, an apparently homogeneous product of photo-oxidation could be separated from the control enzyme by ion-exchange chromatography. 8. The K(m) for l-glutamate was unchanged in an irradiated sample retaining 22% of control activity. 9. These data and the catalytic role of imidazole residues at the active sites of amino acid decarboxylases are discussed.  相似文献   
116.
117.
A partially purified M protein, extracted from a mouse-virulent strain of type 3, group A streptococcus, was administered subcutaneously in gradually increasing amounts at weekly intervals to 21 children in a Family Program. Seven children with type 3 bactericidal antibody in prevaccination sera showed a secondary response. Of 14 children with no detectable type 3 bactericidal antibody prior to vaccination, 13 developed definite type 3 antibody during or soon after vaccination. This response appeared to be of the primary variety in at least some of the 13 children because (i) the total incidence of antibody response (20 of 21) was greater than can be accounted for by the documented incidence of clinical and subclinical type 3 infections among children of our Family Program during a period of 14 years, (ii) the response in the 13 children with no detectable antibody prior to vaccination was more delayed than in those showing a definite secondary response, and (iii) on the average, the amount of vaccine needed for a response in these 13 children was 15 to 28 times greater than that required for the secondary response. Local skin reactions were variable among the vaccinated children. Systemic reactions were infrequent and not severe. The giving of multiple injections of partially purified M protein did not seem to cause cutaneous hypersensitivity.  相似文献   
118.
119.
120.
The causes and the nature of the psychiatric disorder labeled schizophrenia remain vexingly obscure. Perhaps as an expression of a still extant body-mind controversy, most of the experiments and statements made toward an elucidation of the problem follow one or the other of two opposing postulations: (a) That its origin is genetico-organic; (b) that it is environmental. In a review of the outstanding “facts” for either argument, it is notable that they presuppose not only a difference in theoretical frameworks, but two radically distinct outlooks. This is reflected in therapy, a field in which organicists and environmentalists stand even further apart; the organicist, relying heavily on electroshock and drugs, hopes to counteract a hypothetical body malfunction, and the environmentalist, through psychotherapy, attempts to make it possible for the patient to disentangle his own conflicting feelings and reaction patterns.Between the two an eclectic position seems hardly tenable. For, in spite of voluminous research and speculation, it has not been possible to build a bridge between the two camps and integrate different outlooks which, at times, have brought psychiatry almost to the point of schism.  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