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   225856篇
  免费   15249篇
  国内免费   45篇
  241150篇
  2021年   1814篇
  2018年   3164篇
  2017年   3070篇
  2016年   3723篇
  2015年   3299篇
  2014年   4544篇
  2013年   6422篇
  2012年   7675篇
  2011年   8166篇
  2010年   5789篇
  2009年   4946篇
  2008年   7300篇
  2007年   7564篇
  2006年   7266篇
  2005年   6776篇
  2004年   6930篇
  2003年   6641篇
  2002年   6601篇
  2001年   9311篇
  2000年   8975篇
  1999年   7020篇
  1998年   2149篇
  1997年   1973篇
  1996年   1847篇
  1992年   5493篇
  1991年   5703篇
  1990年   5676篇
  1989年   5649篇
  1988年   5231篇
  1987年   4881篇
  1986年   4456篇
  1985年   4696篇
  1984年   3713篇
  1983年   3039篇
  1982年   2029篇
  1981年   1729篇
  1980年   1734篇
  1979年   3342篇
  1978年   2584篇
  1977年   2389篇
  1976年   2340篇
  1975年   2833篇
  1974年   3127篇
  1973年   3092篇
  1972年   2752篇
  1971年   2610篇
  1970年   2218篇
  1969年   2162篇
  1968年   2033篇
  1967年   1800篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The results of complementation analysis of nitrosoguanidine-induced mutants of F-like drd-plasmid pAP18-1 (Tc, ColV) testified to the existence of at least 3 tra regions (tra1, tra2, tra3) and regulating locus fin V in the genome of this plasmid. By means of molecular cloning of tra2 region and locus fin V of plasmid pAP18-1drd were located in Sall-fragment f5 (3.9 MD).  相似文献   
992.
993.
The article reports experimental data on new bacteria, the so-called ‘stone nannobacteria’. Recent publications in Russia and abroad show that this bacterial species may cause various human ailments, thus being a serious environmental hazard. According to our findings, one of the natural habitats of nannobacteria is water which aggregates the nannobacteria-related ecological problem.  相似文献   
994.
DdeI polymorphism in the HLA-DRA regulatory region   总被引:1,自引:0,他引:1       下载免费PDF全文
  相似文献   
995.
Varlamova  E. G.  Goltyaev  M. V. 《Biophysics》2018,63(5):700-705
Biophysics - Abstract—Sodium selenite, which is one of the most common selenium compounds, is considered a potential anticancer agent that can decrease cell viability; this compound is...  相似文献   
996.
For 35 of 50 patients with rheumatoid arthritis traditional drug therapy was a minor success for a long time. Without any modifications of the drug therapy every patient went through a course of hyperbaric oxygenation (HBO): 21 sessions under 1.7 ata for 40 min. Good clinical results both immediate and remote have been obtained. The effect of HBO on the immune system of the patients has intensified the suppressive function of T-lymphocytes (especially with systemic symptoms of the disease), normalized cell-bound immunity and decreased the serum concentration in immune complexes.  相似文献   
997.
Recent data and concepts on the structure and functioning of apolipoprotein genes as well as on the role of hereditary factors in pathogenesis of atherosclerosis are reviewed. The most important variants of inherited disorders in the system of apolipoproteins promoting the development of atherosclerosis are considered. Special attention is paid to the RFLP of apolipoprotein genes which serves as a peculiar genetic background, increasing probability of the atherosclerosis development in certain individuals.  相似文献   
998.
Solid (smooth) and porous films of polydimethylsiloxane (PDMS) have been obtained; the effect of their structure on the adhesion of mesenchymal stem cells (MSCs) on their surface was found. It is shown that modification of these films with a (chitosan/pectin)4 multilayer increased the efficiency of viable cell adhesion. A (3-aminopropyl)triethoxysilane–glutaraldehyde system was used to enhance the binding of the polysaccharide layer to the hydrophobic surface of PDMS. It was found that MSCs formed a monolayer culture of the fibroblast-like cells with high viability on porous PDMS modified with (chitosan/pectin)4.  相似文献   
999.
The phytocenotic diversity of the Altai steppe piedmont is described. Plant communities were ordinated along the moisture gradient. The results were used to analyze the structure of vegetation of steppe hill massifs. Distribution of steppe vegetation over an ideal hill was simulated, and the main patterns of distribution were typified.  相似文献   
1000.
The utilization of guanidino and ureido compounds was studied in several Pseudomonas species. Multiple routes of agmatine catabolism were found. All members of the homology group I of Pseudomonas use the initial deamination of agmatine to carbamoylputrescine which is subsequently converted to putrescine. In Pseudomonas indigofera, the catabolism of agmatine can also occur via an initial hydrolysis of the amidino group to putrescine catalyzed by an agmatine amidinohydrolase. A third pathway was found in Pseudomonas cepacia, namely oxidative deamination producing guanidinobutyraldehyde catalyzed by agmatine dehydrogenase, followed by formation of guanidinobutyrate and removal of urea by guanidinobutyrate amidinohydrolase to produce 4-aminobutyrate. Novel amidino-hydrolases were characterized in P. putida for the utilization of arcaine and audouine, and in P. cepacia for arcaine, homoarginine and guanidinovalerate. Guanidinovalerate amidinohydrolase was also detected in P. doudoroffii. Some of these amidinohydrolases accept more than one substrate, e.g., guanidinobutyrate and guanidinovalerate utilization by P. doudoroffii and P. cepacia, the catabolism of arcaine and audouine by P. putida, and the degradation of arcaine and homoarginine by P. cepacia.  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