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   133956篇
  免费   9539篇
  国内免费   25篇
  143520篇
  2023年   703篇
  2022年   812篇
  2021年   1672篇
  2020年   1398篇
  2019年   1586篇
  2018年   3222篇
  2017年   2919篇
  2016年   4024篇
  2015年   5837篇
  2014年   6102篇
  2013年   8087篇
  2012年   9755篇
  2011年   9158篇
  2010年   5995篇
  2009年   4740篇
  2008年   7534篇
  2007年   7423篇
  2006年   6812篇
  2005年   6246篇
  2004年   5979篇
  2003年   5427篇
  2002年   5029篇
  2001年   2960篇
  2000年   2798篇
  1999年   2445篇
  1998年   1158篇
  1997年   903篇
  1996年   801篇
  1995年   814篇
  1994年   773篇
  1993年   626篇
  1992年   1548篇
  1991年   1457篇
  1990年   1289篇
  1989年   1212篇
  1988年   1114篇
  1987年   992篇
  1986年   898篇
  1985年   962篇
  1984年   806篇
  1983年   700篇
  1982年   561篇
  1981年   510篇
  1979年   706篇
  1978年   525篇
  1977年   470篇
  1976年   464篇
  1975年   523篇
  1974年   573篇
  1973年   559篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
42.
Proteins are released from the surface of sporozoites of Eimeria falciformis during their in vitro incubation in a detergent solution. Some of these proteins reacted with antibodies from infected mice and specifically stimulated the proliferation of mesenteric lymph node cells of these mice. Oral immunization of mice with liposome encapsulated sporozoite surface antigens protected mice against a challenge infection. Two proteins (M.W. 27 and 180 K) induced an antibody synthesis in these vaccinated mice.  相似文献   
43.
We investigated body-size inheritance in interspecific sterile hybrids by crossing a Drosophila simulans strain with 13 strains of Drosophila melanogaster, which were of various origins and chosen for their broad range of genetic variation. A highly significant parent-offspring correlation was observed, showing that the D. melanogaster genes for size are still expressed in a hybrid background. Superimposed on to this additive inheritance, the size of hybrids was always less than the mid-parent value. This phenomenon, which at first sight might be described as dominance or overdominance, is more precisely interpreted as a consequence of a hybrid breakdown, that is, a dysfunction of the parental genes for size when put to work together. This interpretation is enforced by the fact that phenotypic variability was much more prevalent in hybrids than in parents. We also analysed body pigmentation inheritance in the same crosses and got a very different picture. There was no increase in the phenotypic variance of F(1) hybrids and only a low parent-offspring correlation. Apparent overdominance could be observed but in opposite directions, with no evidence of hybrid breakdown. Our data point to the possibility of analysing a diversity of quantitative traits in interspecific hybrids, and indicate that breakdown might be restricted to some traits only.  相似文献   
44.
Analogs of deamino-oxytocin and deamino-oxypressin containing a CH2-NH group instead of an amide bond between positions 8 and 9 were synthesized. All tested compounds exhibit significantly lowered biological activities.  相似文献   
45.
46.
Liver microsomal concentration of cytochrome P.450 is increased in animals which are fed diets rich in polyunsaturated fatty acids. On the other hand, the effects of phenobarbital are more important when the dietary fat is more unsaturated. The unsaturation index in liver microsomal phosphatidylcholines depends on the unsaturation of the dietary fats. The treatment with phenobarbital constantly results in a decrease of the unsaturation index of fatty acids both in lecithins and cephalins. The importance of the liver microsomal cytochrome P.450 increase and the importance of the unsaturation index decrease in liver microsomal lecithins, both promoted by phenobarbital, are in good agreement.  相似文献   
47.
The author describes the history of the concept of depression in modern psychiatry from the end of the Age of Enlightenment until today in three parts. In the first period (1793–1854), the opposition of general delusion (mania) and partial delusion (melancholia) prevails, without the problem of changes of the affective state being an issue. Only with the work of J. Guislain, and later of W. Griesinger, does the concept of mood disorders become a categorical form in mental pathology with the idea of psychological pain. The second period (1854–1926) is distinguished firstly by the works of J.P. Falret on circular insanity, and then those of V. Magnan, J. Ségnan, J. Séglas et Ph. Chaslin in France and E. Kraepelin in Germany. This period is characterized by the classical construction of periodic manicdepressive psychosis and takes into account the opposition of mania and melancholia. In the third period (1926–1977), the influences of phenomenology, psychoanalysis and structuralism predominate. Gradually melancholia loses its place at the core of this field, in favour of the concept of depression and this change now characterizes contemporary psychiatry.  相似文献   
48.
49.
50.
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