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   4219篇
  免费   287篇
  国内免费   8篇
  2023年   25篇
  2022年   77篇
  2021年   150篇
  2020年   62篇
  2019年   75篇
  2018年   104篇
  2017年   77篇
  2016年   129篇
  2015年   173篇
  2014年   199篇
  2013年   282篇
  2012年   311篇
  2011年   342篇
  2010年   197篇
  2009年   134篇
  2008年   202篇
  2007年   191篇
  2006年   165篇
  2005年   145篇
  2004年   144篇
  2003年   133篇
  2002年   105篇
  2001年   87篇
  2000年   68篇
  1999年   76篇
  1998年   30篇
  1997年   24篇
  1995年   31篇
  1994年   25篇
  1993年   29篇
  1992年   44篇
  1991年   57篇
  1990年   36篇
  1989年   42篇
  1988年   31篇
  1987年   36篇
  1986年   31篇
  1985年   26篇
  1984年   26篇
  1983年   27篇
  1982年   24篇
  1980年   19篇
  1979年   39篇
  1978年   20篇
  1977年   24篇
  1974年   23篇
  1973年   25篇
  1972年   20篇
  1971年   17篇
  1970年   17篇
排序方式: 共有4514条查询结果,搜索用时 31 毫秒
71.
72.
H. Y. Mohan Ram  Rina Sett 《Planta》1980,149(4):413-415
Aqueous solutions of silver nitrate (10–100 g/plant) and cobalt chloride (125–500 g/plant), injected into the main stem of plants of the pistillate cv. 240 ofRicinus communis when the vegetative shoot apex was beginning to become reproductive, induced the formation of staminate (male) flowers with viable pollen in the normally strictly pistillate (female) terminal inflorescence, their number increasing with the dose of Ag+ and Co2+. No formation of bisexual flowers was noted. Female flowers pollinated with pollen from the induced male ones produced fruits and viable seeds.  相似文献   
73.
Sera from 517 laboratory-housed nonhuman primates representing five genera and from 13 laboratory workers were examined for the presence of neutralizing antibodies to SA12 virus. The antibody prevalences were as follows: baboons, 66%; patas and vervet monkeys, 24%; macaques, 8%, and chimpanzees, 2%. The serum of one laboratory worker had antibodies. These results suggest that SA12 virus is a common infection of nonhuman primates in laboratory colonies, especially baboons.  相似文献   
74.
Summary Arthrobacter simplex, Serratia marcescens, Fusarium and Mycobacterium were tested for their ability to transform phytosterol to Androsta 1, 4 diene 3, 17 dione (ADD). Arthrobacter simplex ATCC 6946 was found to be more efficient than the other species tested.  相似文献   
75.
Studies were carried out to investigate the influence of adrenalectomy on the 24 hour periodicity in the hypothalamo-pituitary axis in adult male rat. Adrenal gland ablation resulted in the shift in the occurrence of peak content of hypothalamic LHRH and attenuation in the responsiveness of the pituitary to synthetic LHRH. Following adrenalectomy, the circadian serum LH peak was attenuated and serum FSH showed a 24 hour periodicity. In conclusion, the results suggest the possible role of adrenal gland in the maintenance of 24 hour periodicity of hormones in the hypothalamo-hypophyseal axis in male rat.  相似文献   
76.
Hypercholesterolemia was induced in adult male rhesus monkeys with a high-fat diet containing an elevated cholesterol level (0.5%). Plasma lipoproteins were chromatographically separated into four size populations (regions) that were subdivided by density until fractions with single electrophoretic mobilities were obtained. The region III lipoproteins (LDL) contained 80% of plasma cholesterol and were present in the highest concentration of all fractions. Their molecular weight was increased over that of controls so that each particle averaged 1.8 times the number of cholesteryl ester molecules as did control LDL. Region II lipoproteins, a heterogeneous group, were present in next highest concentration. Most were cholesteryl ester-rich, beta-migrating lipoproteins that overlapped the VLDL and LDL density ranges; apoB was the predominant apoprotein. One region II subfraction had pre beta 2 migration and the density range. 1.050 less than d less than 1.10. Another subfraction, cholesteryl ester-rich VLDL including only about 1% of plasma cholesterol, had pre beta 1 migration and apoB and apoC as the predominant apoproteins with no apoprotein E. Region I lipoproteins were larger sized, slow beta-migrating cholesteryl ester-rich VLDL that included 5% of plasma cholesterol. ApoB and apoE were the predominant apoproteins. Region IV lipoproteins (HDL) contained 4% of the plasma cholesterol; their concentration was decreased to about 1/3 of the control level. Atherogenic features of the diet-induced dyslipoproteinemia included the increased plasma concentrations and cholesteryl ester contents of the region I, II, and III lipoproteins in addition to the decreased HDL concentration.  相似文献   
77.
The recently isolated primate papovavirus HD is shown to be indistinguishable from the stump-tailed macaque virus by immunofluorescent reactivity, by restriction endonuclease analysis, and by nucleic acid hybridization assay.  相似文献   
78.
Phage M-1 produced clear plaques with a halo in the lawn of Rhizobium japonicum D211. A one step growth curve of phage M-1 showed a latent period of 3 h, burst size of 55 and rise period of 2 h. The inactivation of phage M-1 was found to be dependent upon the concentraion of d-glucosomanine. The neutralization kinetics of phage M-1 by antiphage serum gave a K value (velocity constant) of 83.1 min–1. Transduction of str and kan was studied in the presence of antiphage serum and d-glucosamine. Cotransduction of different antibiotic resistance markers suggested that the system can be further explored for high resolution mapping in R. japonicum.Abbreviations YM yeast mannitol medium - PFU plaque forming unit - moi multiplicity of infection - EOP efficiency of plating  相似文献   
79.
Complex mitochondrial DNA in Drosophila.   总被引:1,自引:0,他引:1       下载免费PDF全文
The larval mtDNA isolated from D. virilis, D. simulans and D. melanogaster exists in complex molecular forms in addition to the simple monomeric circular form. The frequency of circular dimers and oligomers is highly elevated in apparently normal larval tissues. These complex forms of mtDNA are separable on agarose gels. Hind III restriction endonuclease and electron microscopic analyses used in the present study have revealed that circular dimers are simply the circular concatemers of two monomeric circles which are arranged in a head-to-tail structure with no detectable heterologous regions such as insertions or deletions. The electrophoretic patterns of Hind III digested mtDNAs of D. simulans and D. melanogaster (sibling species) are identical and distinguishable from that of distantly related species, D. virilis.  相似文献   
80.
Summary A new variant malate dehydrogenase is described, designated S-MDHInd to indicate its discovery in the Indian subcontinent pending full comparison with all other variants. It occurred during a survey of the incidence of variant S-MDH phenotypes in 4149 subjects in north-east England and 1494 subjects from several populations in the Indian region. The variants previously thought to be restricted to the New Guinea region and to African populations occurred in three English subjects in northeast England. The incidence of variant S-MDH phenotypes in other populations is summarised.  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