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   1632462篇
  免费   152930篇
  国内免费   1741篇
  2021年   18655篇
  2019年   16538篇
  2018年   19557篇
  2017年   18389篇
  2016年   29686篇
  2015年   43664篇
  2014年   51908篇
  2013年   78298篇
  2012年   47918篇
  2011年   38819篇
  2010年   47459篇
  2009年   47604篇
  2008年   35237篇
  2007年   33878篇
  2006年   36993篇
  2005年   38023篇
  2004年   37063篇
  2003年   34290篇
  2002年   32092篇
  2001年   51926篇
  2000年   49744篇
  1999年   44981篇
  1998年   27580篇
  1997年   27399篇
  1996年   26552篇
  1995年   24727篇
  1994年   24336篇
  1993年   23562篇
  1992年   37852篇
  1991年   35931篇
  1990年   34523篇
  1989年   34960篇
  1988年   32232篇
  1987年   30241篇
  1986年   28605篇
  1985年   30009篇
  1984年   28157篇
  1983年   24359篇
  1982年   23112篇
  1981年   21984篇
  1980年   20474篇
  1979年   23783篇
  1978年   21265篇
  1977年   20132篇
  1976年   18854篇
  1975年   18924篇
  1974年   19697篇
  1973年   19966篇
  1972年   17127篇
  1971年   15630篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
921.
D. L. Tyrrell 《CMAJ》1984,130(9):1109-1110
  相似文献   
922.
923.
Four antimicrobial peptides, protegrin-1, RTD-1, cryptdin-4, and indolicidin, were tested for their ability to inhibit the in vitro growth of Chlamydia trachomatis serovars E, L2, and mouse pneumonitis (MoPn). In general, protegrin-1 was found to have the strongest anti-chlamydial activity. Overall, of the three serovars tested, L2 was the most susceptible while MoPn was the most resistant to these peptides.  相似文献   
924.
925.
The activity of cAMP-dependent protein kinases, cAMP binding and the spectrum of cAMP-binding proteins in renal papillary cytosol of intact rats and of rats kept on a water-deprived diet for 24 hours were investigated. It was found that the stimulation of protein kinases by 10(-6) M cAMP in the experimental group was significantly higher than in the control one. On DEAE-cellulose chromatography, the position of peaks of the specific cAMP binding corresponded to those of the regulatory cAMP-dependent protein kinases type I and II. Under these conditions, more than 80% of the binding activity in intact animals was localized in peak II, whereas in rats kept on a water-deprived diet over 60% of the binding activity was localized in peak I. The total binding activity of cytosol in experimental animals remained unchanged is compared to intact rats. It is suggested that in renal papilla dehydration is accompanied by the induction of synthesis of regulatory subunits of cAMP-dependent protein kinase type I.  相似文献   
926.
927.
The eggs, larvae and pelagic juveniles ofOstracion meleagris, Lactoria fornasini andLactoria diaphana were identified from reared and field collected specimens from Hawaii, Japan, Australia and the eastern Pacific. Eggs are large and pelagic with limited chorion ornamentation and a cluster of oil droplets. At hatching, larvae are well developed, rotund, and enclosed in a dermal sac. The sac disappears and dermal plates form prior to notochord flexion. Larvae of the three species can be distinguished by their pigment patterns and development of the carapace of ossified dermal plates. Eggs of the three species could not be distinguished. The larval stage ends at a small size (< 6 mm) but the juveniles may grow to a substantial size while remaining pelagic.L. diaphana matures and spawns while pelagic in the eastern Pacific.  相似文献   
928.
Four peptides possessing both natriuretic activity and smooth muscle relaxant activity were isolated from rat atrium and their amino acid sequences determined. The four peptides designated ANF-I, ANF-II, ANF-III and ANF-IV containing 35, 31, 30 and 25 amino acid residues, respectively, were obtained in a molar ratio of 4:60:20:16. The predominant species ANF-II, which may represent the native form of ANF, has the following sequence: (H2N)-G-P-R-S-L-R-R-S-S-C-F-G-G-R-I-D-R-I-G-A-Q-S-G-L-G-C-N-S-F-R-Y-(COOH) in which Cys-10 and Cys-26 are disulfide linked. Cleavage of the aspartyl linkage at position 16 by staphylococcal protease caused complete inactivation, indicating that the ring conformation is essential. The dose-response relationships determined for the four pepdides in relaxing norepinephrine-induced contraction of rabbit thoracic aorta showed half-maximum relaxation at concentrations ranging from 1.5 × 10?9 to 2.5 × 10?9 M. Comparable dose-response relationships were observed in relaxation of carbacol-induced contraction of chick rectum strips as tested with ANF-II and ANF-IV.  相似文献   
929.
A. T. Lloyd 《Genetica》1982,58(3):223-228
Surveys of gene frequencies in domestic cat (Felis catus) populations were carried out in four cities in the Netherlands. The principal variants recorded included seven mutant alleles affecting coat colour and hair length. Significant differences in frequencies were found between cities at some of the loci considered. The results of these surveys help to clarify certain trends in the distribution of mutant alleles in cat populations across Europe. Some insight is offered into the importance of trade routes in determining these patterns of distribution. In addition, comparisons between owned pets and unwanted cats indicate that human preferences have little effect on mutant allele frequencies.  相似文献   
930.
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