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   1266716篇
  免费   105010篇
  国内免费   1563篇
  1373289篇
  2021年   17715篇
  2020年   12608篇
  2019年   16158篇
  2018年   17792篇
  2017年   16613篇
  2016年   28110篇
  2015年   42175篇
  2014年   50140篇
  2013年   76488篇
  2012年   33553篇
  2011年   21832篇
  2010年   43129篇
  2009年   44731篇
  2008年   20937篇
  2007年   18710篇
  2006年   24180篇
  2005年   25705篇
  2004年   24605篇
  2003年   22292篇
  2002年   20459篇
  2001年   29087篇
  2000年   26370篇
  1999年   27787篇
  1998年   24752篇
  1997年   24490篇
  1996年   24108篇
  1995年   22284篇
  1994年   22096篇
  1993年   21137篇
  1992年   24088篇
  1991年   22467篇
  1990年   21460篇
  1989年   22337篇
  1988年   20461篇
  1987年   19399篇
  1986年   18360篇
  1985年   20537篇
  1984年   20811篇
  1983年   18464篇
  1982年   19406篇
  1981年   18877篇
  1980年   17639篇
  1979年   16651篇
  1978年   16239篇
  1977年   15726篇
  1976年   15106篇
  1975年   14446篇
  1974年   14727篇
  1973年   15203篇
  1972年   12644篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Abstract. Degeneration of the archenteron in middle gastrulae occurred in the presence of α,α'-dipyridyl or Zn2+, inhibitors of prolyl hydroxylase. In the presence of these substances the archenteron degenerated and was eventually destroyed. Adding Fe2+ to the embryo culture containing α,α'-dipyridyl protected the archenteron from further degeneration, but the collapsed archenteron was not restored to the upright position. At the late gastrula stage, α,α'-dipyridyl did not cause the degeneration of the archenteron. Treatment of the embryos by α,α'-dipyridyl, starting at the swimming blastula stage, resulted in the production of many mesenchyme-like cells but archenteron was not produced in the embryos. Addition of Fe2+ to α,α'-dipyridyl culture, just before the beginning of gastrulation of normal embryos, resulted in the formation of normal archenteron. α,α'-Dipyridyl inhibited hydroxylation of proline residues of collagen in sea urchin embryos and Fe2+ prevented the inhibition by α,α'-dipyridyl. Respiration was not inhibited by α,α'-dipyridyl.  相似文献   
992.
993.
A group of captive chimpanzees, consisting of one adult male and three mother/infant pairs, was systematically observed over a 15-month period. Over 200 hr of data were collected, using both sequential and time sampling techniques, and compared to the available data on wild chimps. Unlike many captive groups, most behavior patterns were remarkably similar, both qualitatively and quantitatively, to that of wild chimpanzees including: play, grooming, infant sexual development, tool use, food sharing, prosocial partner preferences, and aggressive displays.  相似文献   
994.
The method of extraction of ciliated epithelium from biopsy samples of human bronchial mucosa with glycerol is suggested. Permeabilized cilia of glycerol-extracted cells can be easily reactivated by exogenous ATP. This method was used for the study of ciliary dyskinesia in patients with chronic lung diseases. It was shown that in patients with Kartagener's syndrome neither freshly-isolated, nor glycerol-extracted ATP-treated cilia were motile. On the other hand, in some patients with bronchial asthma ATP reactivated glycerol-extracted cilia, while cilia of freshly-isolated cells remained immotile. The study shows that glycerol permeabilization and reactivation by ATP can be used for the analysis of cilial contractile apparatus in patients with chronic lung disease.  相似文献   
995.
The production of L-lysine fromDL-α-amino-ε-caprolactam (DL-ACL) by new strains producingL-α-amino-ε-caprolactamase and aminocaprolactam racemase is described. Optimal conditions for hydrolysis ofL-ACL byCryptococcus sp. and for racemization of ACL by cells of a strain isolated in nature and identified asPseudomonas sp. were determined. Synthesis ofL-α-amino-ε-caprolactamase is induced byDL-ACL orL-lysine with the same effectivity. A positive effect of phosphates (potassium salts) on reduction of the induction lag was detected, the synthesis of this enzyme was found to be repressed by glucose and some possibilities of the reversion of this repressive effect were demonstrated. Under conditions optimal for the production of both enzymes a quantitative theoretical conversion of 10 % aqueousDL-ACL toL-lysine by a mixture of native cells in a mass ratio of 1: 2 (producer of ACL-hydrolase to producer of ACL-racemase) occurred in 8 h at 40 °C and pH 8.0  相似文献   
996.
Inflammatory reaction to ocular trauma is known to be related to prostaglandins. To further evaluate this phenomenon in human, PGE1 and E2 were measured by R.I.A. after silicic acid chromatography in aqueous humour of 26 patients before and 3 days after surgery for unilateral senile cataract (posterior chamber implant after extracapsular surgery). 13 out of these patients were treated with indomethacin by enteral route and 13 were not treated.PGE2 levels increased in all non-treated patients from : m < 214 pg/ml before surgery, to 2666 ± 869 pg/ml (range : 257 - 8728) p < 0.001 after surgery. PGE2 levels did not increase in indomethacin-treated patients. PGE1 levels did not increase significantly in non-treated as in treated patients.1) Intra-ocular surgery is followed in human by a constant increase of the only PGE2 in the aqueous humour. 2) Indomethacin inhibits this increase. 3) The post-surgical increase in the permeability of blood-aqueous barrier appears to be related to a release of PGE2.  相似文献   
997.
998.
A protein isolated from maize scutella which inhibits catalase in vitro has been shown to contain 12% carbohydrate in the form of galactose. This corresponds to four galactose molecules per inhibitor subunit. Removal of the carbohydrate with β-galactosidase or blockage with a galactose-specific lectin abolished activity of the inhibitor.  相似文献   
999.
Several short-term mammalian test systems were used for mutagenicity testing of the organic solvent dichloromethane. The compound was negative in the forward mutation test on the HGPRT locus in Chinese hamster cells and the unscheduled DNA synthesis test in both human and hamster cells. In the test on DNA synthesis inhibition, dichloromethane caused an aspecific inhibition in both human and hamster cells, but in this test the effect did not indicate a DNA-damaging action. A weak positive effect was found in the test on sister-chromatid exchanges in hamster cells.  相似文献   
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