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   777324篇
  免费   84142篇
  国内免费   351篇
  861817篇
  2016年   9051篇
  2015年   12024篇
  2014年   14203篇
  2013年   20514篇
  2012年   22732篇
  2011年   23439篇
  2010年   16037篇
  2009年   14823篇
  2008年   21132篇
  2007年   22223篇
  2006年   20884篇
  2005年   19827篇
  2004年   20022篇
  2003年   19255篇
  2002年   18843篇
  2001年   30988篇
  2000年   31119篇
  1999年   25015篇
  1998年   9271篇
  1997年   9703篇
  1996年   9113篇
  1995年   8606篇
  1994年   8383篇
  1993年   8503篇
  1992年   21599篇
  1991年   21285篇
  1990年   21089篇
  1989年   20569篇
  1988年   19552篇
  1987年   18601篇
  1986年   17401篇
  1985年   17676篇
  1984年   14778篇
  1983年   12737篇
  1982年   9938篇
  1981年   8932篇
  1980年   8565篇
  1979年   14262篇
  1978年   11241篇
  1977年   10485篇
  1976年   10034篇
  1975年   10815篇
  1974年   12016篇
  1973年   11760篇
  1972年   10953篇
  1971年   9977篇
  1970年   8743篇
  1969年   8684篇
  1968年   8217篇
  1967年   6995篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
The peptide nature of the posture asymmetry factor (PAF) produced in the brain after unilateral removal of the motor region of the neocortex was established. The inactivation of PAF activity in the brain toward the end of the third week after the removal is due to PAF inactivation by the endogenous factor absent from the intact brain. The molecular weight of the inactivation factor exceeds 5.0 kD that makes it possible to separate it from the PAF by gel filtration on Sephadex G-25. The correlation was marked between the increasing activity of the PAF inactivation factor and the recovery of the initial symmetric functioning of the spinal centers during three weeks after unilateral damage to the CNS.  相似文献   
994.
Thirteen model alpha-ketocarboxylic acids and alpha-dicarbonyl compounds have been observed to be reduced by titanium(III) chloride. The products of these reactions were shown by melting (boiling) points, mixed melting points, derivatives, refractive indices, infrared, and NMR comparisons with authentic compounds or literature information to be the corresponding alpha-hydroxycarboxylic acids or alpha-hydroxyketones.  相似文献   
995.
Endogenous cyclic adenosine and guanosine monophosphate (cAMP, cGMP) levels were studied in human peripheral blood lymphocytes during mixed leukocyte reactions (MLR). cAMP level was consistently elevated in one-way MLR, with good correlation to 3H-thymidine uptake in these reactions. In contrast, cGMP level was practically unchanged. Irradiation of reacting cell populations resulted in inhibition of cyclic nucleotide phosphodiesterase (PDE) activity. These results suggest that metabolic alterations in cAMP may be associated with immune reactions of cellular recognition.  相似文献   
996.
997.
998.
Effects of noradrenaline (NA) and dopamine (DA) on apoptosis of nonapeptidergic neurons of supraoptic (SON) and paraventricular (PVN) nuclei of hypothalamus of male Wistar rats was studied in experiments in vitro. Incubation of hypothalamic sections in the medium with added NA was shown to induce an increase of the amount of pro-apoptotic protein caspase-9 in the nonapeptidergic neurons of the SON and PVN. A comparison of the level of neuronal NO-synthase with the level of caspase-9 expression in these neurons allows concluding that NA leads to initiation of apoptosis in neurons of the SON with mediation by nitric oxide (NO). In the PVN, the NA-induced initiation of apoptosis does not depend on the NO level. Addition of DA to the incubation medium results in an increase of the caspase-9 amount only in PVN neurons regardless of the NO content. The absence of neuronal death after the NA-induced increase of the caspase-9 level in the cells of SON and PVN seems to be due to increased expression of the anti-apoptotic protein bcl-2. Protection of the PVN neurons from death after addition of DA to the incubation medium is probably independent of the expression level of bcl-2. Thus, in the nonapeptidergic neurons of the SON and PVN, which are related by origin and by performed functions, modulation of the process of apoptosis by elevated concentrations of NA and DA is realized by different mechanisms.  相似文献   
999.
1000.
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