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   107424篇
  免费   7331篇
  国内免费   17篇
  114772篇
  2023年   567篇
  2022年   440篇
  2021年   1036篇
  2020年   936篇
  2019年   974篇
  2018年   2600篇
  2017年   2321篇
  2016年   3264篇
  2015年   4847篇
  2014年   4932篇
  2013年   6621篇
  2012年   8091篇
  2011年   7575篇
  2010年   4828篇
  2009年   3542篇
  2008年   6196篇
  2007年   6134篇
  2006年   5618篇
  2005年   5258篇
  2004年   4939篇
  2003年   4537篇
  2002年   4183篇
  2001年   2169篇
  2000年   2134篇
  1999年   1852篇
  1998年   766篇
  1997年   587篇
  1996年   522篇
  1995年   542篇
  1994年   555篇
  1993年   413篇
  1992年   1235篇
  1991年   1150篇
  1990年   1016篇
  1989年   947篇
  1988年   890篇
  1987年   756篇
  1986年   692篇
  1985年   769篇
  1984年   666篇
  1983年   555篇
  1982年   424篇
  1981年   419篇
  1979年   573篇
  1978年   440篇
  1977年   392篇
  1976年   377篇
  1975年   427篇
  1974年   444篇
  1973年   456篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
In this work the human plasma fibronectin was purified by affinity chromatography using a tandem column system. The first affinity column was filled with gelatin-Trisacryl whereas the second one contained heparin-Trisacryl. This double affinity chromatography demonstrated its high efficiency in term of purity and yield. Several analytical methods (electrophoresis, immunoelectrophoresis, F.P.L.C. and adhesion assay on cultured eucaryotic cells) evidenced in fact the high purity of the preparation as well as its biological behaviour in term of cell adhesion and spreading. The performances of the sorbents used facilitate the scaling up when large quantities of FNP are needed.  相似文献   
32.
The thrombopoietic serum activity was examined in rats during thrombocytopenia produced by bleeding or after treatment with antithrombocyte serum (ATS). 6 hours after both treatments the thrombopoietic activity of the serum, i.e. its content of thrombopoietin, is increased. After the ATS treatment of nephrectomized animals a similar increase of thrombopoietic activity as in normal animals could be achieved. In contrast to that, no similar increase of thrombopoietic activity was observed in nephrectomized animals after blood loss. According to the results of the authors the increase of thrombopoietic activity produced by different stimuli can be attributed to different mechanisms.  相似文献   
33.
Arthur Vineberg     
Brian Bérubé 《CMAJ》1981,125(10):1176
  相似文献   
34.
35.
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   
36.
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   
37.
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   
38.
39.
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   
40.
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   
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