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   808558篇
  免费   88979篇
  国内免费   557篇
  898094篇
  2018年   7646篇
  2017年   7166篇
  2016年   10379篇
  2015年   14308篇
  2014年   16700篇
  2013年   23717篇
  2012年   26545篇
  2011年   26921篇
  2010年   18280篇
  2009年   16639篇
  2008年   23792篇
  2007年   24372篇
  2006年   22985篇
  2005年   22163篇
  2004年   22052篇
  2003年   21165篇
  2002年   20395篇
  2001年   38369篇
  2000年   38583篇
  1999年   30639篇
  1998年   10711篇
  1997年   11208篇
  1996年   10514篇
  1995年   9825篇
  1994年   9555篇
  1993年   9339篇
  1992年   24779篇
  1991年   24039篇
  1990年   23431篇
  1989年   22803篇
  1988年   21165篇
  1987年   19765篇
  1986年   18315篇
  1985年   18144篇
  1984年   15057篇
  1983年   12553篇
  1982年   9518篇
  1981年   8495篇
  1980年   7949篇
  1979年   13489篇
  1978年   10498篇
  1977年   9436篇
  1976年   8539篇
  1975年   9500篇
  1974年   10130篇
  1973年   10030篇
  1972年   8958篇
  1971年   8167篇
  1970年   6975篇
  1969年   6733篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
962.
Nine pairs of polymerase chain reaction (PCR) primers that amplify polymorphic microsatellite loci in the desert locust, Schistocerca gregaria (Forskal), were developed using a magnetic bead‐based enrichment protocol. A sample of 48 locusts collected during the 1993 and 1995 upsurge periods in Eritrea, East Africa, were genotyped. The number of alleles per locus ranged from six to 20; the average was 12.67. Allelic distributions were significantly different between samples from different localities.  相似文献   
963.
964.
In order to develop direct methods for determining the extent of metabolic incorporation of isotopically labeled amino acids into a protein, the determination of deuterated tryptophan in [2H5]tryptophan-bacteriorhodopsin was investigated. The isotopically modified protein was subjected to alkaline hydrolysis. After phenyl isothiocyanate derivatization of the hydrolysate, the mixture was separated by reversed-phase liquid chromatography. Field desorption mass spectrometry and thermospray mass spectrometry were investigated for their ability to determine the ratio between [2H5]tryptophan and total tryptophan in the collected fractions. In order to check the procedure a set of known tryptophan/[2H5]tryptophan mixtures were passed through the same derivatization, HPLC separation, and lyophilization procedure as used for the biological samples.  相似文献   
965.
966.
Fourteen fresh run salmon Satmo salar L. with early extant lesions of ulcerative dermal necrosis (UDN) were kept in separate tanks and treated with zinc free malachite green. Ten of the fish were held at 10° C and 4 at 2° C. The treatment precluded infection with Saprolegnia fungus and allowed natural resolution of the lesions. There was a marked difference in rate of healing between warm and cold water conditions.
Histological examination of healing lesions at different stages showed that there was a primary invasion of cuboidal epithelium over the collagen scar followed by a phase of disorganized proliferation which eventually organized itself into normal epithelium. Melanocytes were very obvious in the dermis of healing lesions.  相似文献   
967.
968.
The 1701-base nucleotide sequence (not including the poly(A) tail) of a cDNA for the gamma subunit of the ATP synthase from Chlamydomonas reinhardtii was determined. A start translation sequence, 23 bases in from the 5' end, initiates an 1074-base-long open reading frame. The sequence of the first 21 amino acids at the amino-terminal end of the mature gamma subunit from C. reinhardtii was determined and compared to the deduced amino acid sequence of the open reading frame. From this it was determined that the mature protein contains 323 amino acids, with the first 35 amino acids probably being part of the transit peptide. The length of the mature protein is the same as that for the mature gamma subunit from spinach, for which only a few of the amino acids of the transit peptide are known. The similarity of the two mature proteins at the nucleotide level is 56% while at the amino acid level it is 77%. In addition, the 3 cysteines, which in spinach are involved in the energy-linked catalytic functions of the ATP synthase, are conserved in the predicted amino acid sequence for the gamma subunit from C. reinhardtii. In contrast, the mature C. reinhardtii gamma subunit contains 3 additional cysteine residues not found in the spinach gamma subunit.  相似文献   
969.
Confluent rabbit corneal endothelial cells incubated in the absence of serum do not produce fibrinogen. When exogenous fibronectin is added to these cultures, fibrinogen production is observed. Fibronectin concentrations stimulate fibrinogen synthesis by endothelial cells in a dose-response fashion. This direct interaction of fibronectin and fibrinogen may be important in both wound healing processes and pathological states.  相似文献   
970.
Gradually altered synthetic entities were employed as molecular probes, and arachidonic acid, ADP, human alpha-thrombin and the Ca2+ ionophore A23187 as aggregation-inducing agents, in a comprehensive study on the response profile of human blood platelets with an emphasis on the effects of exogenous and increased intracellular Ca2+. Corroborating further previous conclusions, some representative carbamoylpiperidine derivatives, at concentrations effecting substantial inhibition of ADP-induced aggregation, failed to retain that effect when 5.0 mM Ca2+ was introduced into the otherwise identical test medium; reference compounds chlorpromazine and propranolol registered corresponding inhibitory patterns. At increased concentrations the compounds' inhibitory potency was regenerated even in the presence of 5 mM Ca2+. In fact, in sufficiently high concentrations, the compounds were even capable of inhibiting aggregation elicited by 15 microM of the ionophore A23187; so did chlorpromazine and propranolol. Another set of congeners revealed the striking sensitivity of ionophore A23187-induced human blood platelet aggregation to the surface active potencies of inhibitor molecules. The loss in inhibitory potency was directly related to the lesser hydrophobic character of the molecule.  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