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   80456篇
  免费   5200篇
  国内免费   31篇
  85687篇
  2023年   577篇
  2022年   534篇
  2021年   1100篇
  2020年   1014篇
  2019年   1023篇
  2018年   2436篇
  2017年   2271篇
  2016年   2987篇
  2015年   4034篇
  2014年   4059篇
  2013年   5403篇
  2012年   6392篇
  2011年   5779篇
  2010年   3625篇
  2009年   2789篇
  2008年   4550篇
  2007年   4297篇
  2006年   3984篇
  2005年   3463篇
  2004年   3364篇
  2003年   3016篇
  2002年   2742篇
  2001年   1740篇
  2000年   1670篇
  1999年   1304篇
  1998年   592篇
  1997年   433篇
  1996年   433篇
  1995年   422篇
  1994年   324篇
  1993年   308篇
  1992年   678篇
  1991年   564篇
  1990年   527篇
  1989年   495篇
  1988年   487篇
  1987年   436篇
  1986年   409篇
  1985年   436篇
  1984年   422篇
  1983年   291篇
  1982年   277篇
  1981年   228篇
  1980年   222篇
  1979年   284篇
  1978年   277篇
  1975年   242篇
  1974年   265篇
  1973年   258篇
  1972年   215篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Following the programme started at Janssen Research Foundation searching for 5-HT(2A/2C) antagonists, we now report on the synthesis of a series of substituted 2-(Dimethylaminomethyl)-2,3,3a,8-tetrahydrodibenzo[c,f]isoxazolo[2,3-a]azepine derivatives. The 5-HT(2A), 5-HT(2C) and H(1) receptor affinities as well as the mCPP antagonistic activity of the compounds synthesised is described.  相似文献   
72.
73.
A major haemophiliac A, 27 years old, has been treated during 30 months, with high dosage of imported Factor VIII, in order to reduce the titer of a F VIII antibody. A good clinical result has been obtained. No sign of immunodeficiency has been observed. Normal values were obtained for T4/T8, ratio B2 microglobulin and no antibody was detected against the LAV virus isolated from cases of AIDS.  相似文献   
74.
The influence of auto-oxidized phospholipids on the reduction of the tetrazolium salt MTT coupled to the NAD+-dependent lactate dehydrogenase reaction was studied. The following results were obtained: (1) peroxidized phosphatidylcholine interfered in the time-course of the lactate dehydrogenase-mediated MTT reduction; (2) there was a time-dependent decrease in the hydroperoxide content of phosphatidylcholine vesicles during the incubation; (3) the diminution of phosphatidylcholine hydroperoxides required the presence of all the components of the system except MTT; (4) hydroperoxide diminution and MTT reduction were mediated by the superoxide radical O2-, since both processes were inhibited by superoxide dismutase; (5) EDTA inhibited the hydroperoxide decrease and abolished the interference of peroxidized phosphatidylcholine with MTT reduction. It was concluded that hydroperoxides compete with MTT for the electrons coming from substrate oxidation. The superoxide radical O2- and traces of some contaminating metal ion are involved in the process. This is a potential complication in the study of the effect of lipids on enzymatic activities assayed by the tetrazolium salt method.  相似文献   
75.
Preincubation of resting cells of Saccharomyces cerevisiae double mutant can1 gap1 (with a single transport system for L-lysine) with metabolic substrates stimulated subsequent uptake of lysine. While in the wild type the stimulation is connected primarily with carrier protein synthesis (delayed, cycloheximide-inhibitable effect) in the mutant an immediate tapping of an energy source (antimycin-inhibited) is practically solely involved.  相似文献   
76.
77.
78.
Frequency of infection by Cryptosporidium sp. in 1,039 faecal smears stained by Ziehl-Neelsen, obtained from undernourished patients of a Nutritional Recovery Center and an ambulatory undernourished center from the Fifth Region, Chile, were studied. All underwent a coproparasitological examination by the modified Telemann method. Thirty eight (3.7%) patients infected by the parasite were detected, with an overall frequency of 8.5% among patients of the Nutritional Recovery Center and 1.9% among the ambulatory patients; this difference was statistically significant. The highest percentage of positive results were detected among the younger milk feeding infants. Also the percentage of difference among these and the older milk feeding infants (3.7%) was statistically significant. Association of Cryptosporidium sp. and Giardia lamblia was observed in 6 ambulatory patients (2.3%).  相似文献   
79.
80.
The pmr spectra of fully acetylated 2S: 3R-2 amino-trans-4 octadecene-1, 3 diol (sphingosine) (lb), 2S : 3R-2 aminooctadecane-1, 3 diol (dihydrosphingosine) (2b), 1-O-β-D-galactopyranosyl-2S : 3R-2 tetracosanoylamido-trans-4 octadecene-1, 3 diol (cerasine) (3b), and 1-O-β-D-galactopyranosyl-2S : 3R-2 (2′ hydroxy) tetracosanoylamido-trans-4 octadecene-1, 3 diol (phrenosine) (4b), were determined in chloroform-d, acetone-d6, and benzene-d6 at 220 MHz. The relative chemical shifts of the various protons in the three solvents were different enough as to permit configurational and conformational information to be derived by partial first order analysis.  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