全文获取类型
收费全文 | 577666篇 |
免费 | 63224篇 |
国内免费 | 420篇 |
专业分类
641310篇 |
出版年
2018年 | 4832篇 |
2016年 | 6575篇 |
2015年 | 9142篇 |
2014年 | 10501篇 |
2013年 | 15391篇 |
2012年 | 17052篇 |
2011年 | 17268篇 |
2010年 | 11631篇 |
2009年 | 10650篇 |
2008年 | 15472篇 |
2007年 | 15996篇 |
2006年 | 15006篇 |
2005年 | 14432篇 |
2004年 | 14090篇 |
2003年 | 13669篇 |
2002年 | 13543篇 |
2001年 | 27807篇 |
2000年 | 28109篇 |
1999年 | 21892篇 |
1998年 | 7254篇 |
1997年 | 7663篇 |
1996年 | 7350篇 |
1995年 | 6716篇 |
1994年 | 6654篇 |
1993年 | 6497篇 |
1992年 | 18124篇 |
1991年 | 17760篇 |
1990年 | 17058篇 |
1989年 | 16626篇 |
1988年 | 15373篇 |
1987年 | 14531篇 |
1986年 | 13316篇 |
1985年 | 13400篇 |
1984年 | 10917篇 |
1983年 | 9439篇 |
1982年 | 7093篇 |
1981年 | 6423篇 |
1980年 | 6021篇 |
1979年 | 10472篇 |
1978年 | 7973篇 |
1977年 | 7458篇 |
1976年 | 6838篇 |
1975年 | 7734篇 |
1974年 | 8269篇 |
1973年 | 8092篇 |
1972年 | 7454篇 |
1971年 | 6623篇 |
1970年 | 5978篇 |
1969年 | 5687篇 |
1968年 | 5197篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
121.
122.
—A resolution of the enhancement of protein synthesis in the visual cortex of rats during first exposure to light (Richardson and Rose , 1972) was achieved by polyacrylamide gel electrophoresis using a double-labelling technique. Differential incorporation of lysine was established between exposed and control animals in two fractions of the soluble proteins and seven fractions of the insoluble proteins. This suggests that exposure to a new experience of this type involves a specific effect on protein synthesis, rather than a general stimulation across all fractions. 相似文献
123.
124.
125.
E Giannazzo F Licata G Li Volsi G Mio F Santangelo M Scivoli 《Bollettino della Società italiana di biologia sperimentale》1992,68(11):677-683
A computer-assisted analysis of the spatial distribution of neurons having homogeneous characteristics is described in this paper. The camera lucida drawings of sections of a brain nucleus and the points representing the neurons labeled on the basis of a specific behavior of discharge rates were digitized on a personal computer Amiga 2000 or IBM compatible. Our software provided: a) the computerized, stereotaxically oriented reconstruction of the stored sections and of the plotted neurons; b) the identification within each section of the mass center (MC) of the units sharing a given behavior and of the area where the density of such neurons was maximal (MDA). The routine was tested on the spatial distribution of neuronal responses to serotonin in the lateral vestibular nucleus. 相似文献
126.
F. Kato T. Hino A. Nakaji M. Tanaka Y. Koyama 《Molecular & general genetics : MGG》1995,247(3):387-390
In many species of actinomycetes, carotenogenesis can be photoinduced. The capacity to respond to photoinduction is, however unstable and, in various strains of Streptomyces, is lost at a relatively high frequency. In Streptomyces setonii ISP5395, which normally produces no carotenoids, carotenoid-producing mutants can be obtained following protoplast regeneration. We report here the characterization of a gene, crtS, which was isolated from one such mutant and can confer on wild-type S. setonii ISP5395 cells the capacity to synthesize carotenoids. Sequence analysis of crtS reveals an open reading frame, which shows homology to genes that encode alternative sigma factors in Bacillus subtilis. We propose that crtS encodes a sigma factor which is necessary for the expression of a cryptic gene(s) for carotenoid biosynthesis in S. setonii ISP5395. 相似文献
127.
128.
129.
Convenient extraction and radioimmunoassay methods for measurement of leukotrienes C4 and D4 (LTC4 and LTD4) in biological fluids are described. LTC4 or LTD4 in plasma was extracted with acetonitrile, and the extract was washed with dichloromethane then adjusted to pH 3.5 or 6.0, respectively. Each leukotriene was partially purified by using a C18-bonded silica cartridge and quantitated by radioimmunoassay. Amounts of LTC4 and LTD4 in the range of 0.025-1.6 ng could be assayed in plasma. This procedure was employed to examine the increase in plasma LTC4 (0.249 +/- 0.036 ng/ml) and LTD4 (1.399 +/- 0.235 ng/ml) of guinea pigs during intravenous challenge-induced anaphylactic bronchoconstriction, and the suppression of the increase of bronchoconstriction and leukotrienes by the administration of 5-lipoxygenase inhibitors such as E6080 (6-hydroxy-2-(4-sulfamoylbenzyl-amino)- 4,5,7-trimethylbenzothiazole hydrochloride), AA861 (2,3,5-trimethyl-6-(12-hydroxy-5,10-dodecadiynyl)-1,4-benzoquinone ) and phenidone. On the other hand, LTC4 and LTD4 were not detected in plasma after an inhaled challenge, though significant bronchoconstriction was provoked. It was concluded that the present study validates a new technique for quantitating plasma leukotrienes on the basis of pH and a suitable method for evaluating the pharmacological efficacy of 5-lipoxygenase inhibitors. 相似文献
130.
1L-myo-Inositol-1-phosphatase, an enzyme purified from brain tissues, catalyzes the dephosphorylation of 1L-myo-inositol 1-phosphate. This enzyme has become the subject of intense research interest, since myo-inositol is needed for the resynthesis of phosphatidylinositol. We have developed a sensitive fluorometric assay for detecting the activity of 1L-myo-inositol-1-phosphatase. The assay is based on o-aminobenzoyl beta-glycerophosphate fluorescence, according to the following principles: (I) The fluorescence yield of o-aminobenzoyl beta-glycerophosphate is increased by 2.75-fold in the presence of saturating concentrations of bovine serum albumin. (II) o-Aminobenzoyl beta-glycerophosphate has the same fluorescence yield as o-aminobenzoyl glycerol, but the latter does not bind to bovine serum albumin. (III) Dephosphorylation of the substrate, catalyzed by the monophosphatase, makes less o-aminobenzoyl beta-glycerophosphate available for binding to bovine serum albumin, thereby producing a decrease in the fluorescence intensity. 相似文献