全文获取类型
收费全文 | 2802篇 |
免费 | 265篇 |
国内免费 | 1篇 |
出版年
2021年 | 43篇 |
2020年 | 19篇 |
2019年 | 18篇 |
2018年 | 32篇 |
2017年 | 36篇 |
2016年 | 49篇 |
2015年 | 96篇 |
2014年 | 114篇 |
2013年 | 130篇 |
2012年 | 186篇 |
2011年 | 176篇 |
2010年 | 121篇 |
2009年 | 96篇 |
2008年 | 172篇 |
2007年 | 140篇 |
2006年 | 139篇 |
2005年 | 125篇 |
2004年 | 116篇 |
2003年 | 126篇 |
2002年 | 115篇 |
2001年 | 34篇 |
2000年 | 20篇 |
1999年 | 25篇 |
1998年 | 32篇 |
1997年 | 38篇 |
1996年 | 24篇 |
1994年 | 21篇 |
1993年 | 39篇 |
1992年 | 20篇 |
1991年 | 23篇 |
1990年 | 25篇 |
1986年 | 14篇 |
1985年 | 25篇 |
1984年 | 32篇 |
1983年 | 26篇 |
1982年 | 37篇 |
1981年 | 28篇 |
1980年 | 35篇 |
1979年 | 18篇 |
1978年 | 28篇 |
1977年 | 27篇 |
1976年 | 26篇 |
1974年 | 16篇 |
1973年 | 23篇 |
1972年 | 17篇 |
1971年 | 15篇 |
1970年 | 16篇 |
1969年 | 15篇 |
1967年 | 14篇 |
1960年 | 15篇 |
排序方式: 共有3068条查询结果,搜索用时 140 毫秒
21.
Edwin B. Smith 《Brittonia》1983,35(2):164-169
22.
23.
B. Edwin Blaisdell 《Journal of molecular evolution》1983,19(2):122-133
Summary Coding sequences of eucaryotic nuclear DNA were characterized by an excess of short runs and a deficit of long runs of weak
and of strong hydrogen bonding bases; non-coding sequences by a deficit of short runs and an excess of long runs, in the same
of purines and of pyrimidines. The conservation of these attributes across DNA sequences coding for proteins of widely different
function, across widely different eucaryotic species for the same protein and across related genes that diverged a long time
ago and that now show large differences in base and, if coding, amino acid sequence suggested that these attributes have survival
value. It was concluded that these attributes constitute probalistic constraints on th primary structure (base sequence) of
both coding and non-coding DNA. 相似文献
24.
Richard F. Selden Andre Steinmetz Lee McIntosh Lawrence Bogorad Gerard Burkard Mfika Mubumbila Marcel Kuntz Edwin J. Crouse Jacques H. Weil 《Plant molecular biology》1983,2(3):141-153
A minimum of 37 genes corresponding to tRNAs for 17 different amino acids have been localized on the restriction endonuclease cleavage site map of theZea mays chloroplast DNA molecule. Of these, 14 genes corresponding to tRNAs for 11 amino acids are located in the larger of the two single-copy regions which separate the two inverted copies of the repeat region. One tRNA gene is in the smaller single-copy region. Each copy of the large repeated sequence contains, in addition to the ribosomal RNA genes, 11 tRNA genes corresponding to tRNAs for 8 amino acids. The genes for tRNA2 Ile and tRNAAla map in the ribosomal spacer sequence separating the 16S and 23S ribosomal RNA genes. The three isoaccepting species for the tRNAsLeu and the three for tRNAsSer, as well as the two isoaccepting species for tRNAAsn, tRNAGly, tRNAsIle, tRNAsMet, tRNAsThr, are shown to be encoded at different loci. Two independent methods have been used for the localization of tRNA genes on the physical map of the maize chloroplast DNA molecule: (a) cloned chloroplast DNA fragments were hybridized with radioactively-labelled total 4S RNAs, the hybridized RNAs were then eluted, and identified by two-dimensional polyacrylamide gel electrophoresis, and (b) individual tRNAs were32P-labelledin vitro and hybridized to DNA fragments generated by digestion of maize chloroplast DNA with various restriction endonucleases. 相似文献
25.
Mycoplasma, in particular species laidlawii and gallisepticum, are found to have a very small, low frequency conductivity as would be predicted by the dielectric model for bacteria and their apparent lack of cell wall structure. Membrane capacitance values for the two organisms are both about 0.9 μF/cm2, although electron micrographs show that the membrane of M. gallisepticum is 20-40 A thicker than that of M. laidlawii. 相似文献
26.
Edwin B. Smith 《Brittonia》1973,25(2):200-208
On the basis of morphological, hybridization, genetic, and field studies, it is proposed thatCoreopsis saxicola Alex. be reduced to varietal rank asC. grandiflora var. saxicola. 相似文献
27.
Passive Electrical Properties of Microorganisms: V. Low-Frequency Dielectric Dispersion of Bacteria 总被引:2,自引:0,他引:2 下载免费PDF全文
Very high dielectric constants have been observed for bacteria at low frequencies. High dielectric constants such as these can be explained by a theory which has been developed for the low-frequency dielectric dispersion of porous charged particles and which has been tested successfully through measurements with ion exchange resins. The bacterial cell wall is electrically similar to an ion exchange resin. Observations show that the theory provides a quantitative explanation for the low-frequency dielectric dispersion of bacteria. 相似文献
28.
The Relationship between Cell Membrane Potassium Ion Transport and Glycolysis : The effect of ethacrynic acid 总被引:2,自引:0,他引:2 下载免费PDF全文
Cell membrane transport of K+ stimulates the rate of glycolysis in Ehrlich ascites tumor cells. A study of the characteristics of this relationship indicates that the stimulation occurs under anaerobic as well as under aerobic conditions. The data suggest that glycolysis is stimulated by a K+ transport mechanism that is coupled to Na+ transport because the effect is blunted or abolished when the principal intracellular ion is lithium or choline. This stimulus to glycolysis is blocked by ouabain and ethacrynic acid, agents that have been shown to inhibit monovalent cation transport in erythrocytes. In contrast to the action of ouabain, glycolysis is inhibited by ethacrynic acid in Ehrlich ascites tumor cells in the absence of cell membrane K+ transport. In studies with ghost-free hemolysates of human erythrocytes and with cytosol prepared from Ehrlich ascites tumor cells, ethacrynic acid significantly blocks lactate formation from fructose diphosphate demonstrating the direct inhibitory effect of this agent on one or more enzymes of the Embden-Meyerhof pathway. Since ethacrynic acid has no influence on lactate formation in intact erythrocytes utilizing an endogenous substrate, the presumptive site of inhibition is proximal to the 3-phosphoglycerate level. 相似文献
29.
An electrophoretic procedure is described which resulted in the separation of up to four bands with beta-glucuronidase activity in human sera. Initial screening of a small sample of individuals revealed persons with two, three, and four bands.Supported by Special Project Grant Number 414 of the Children's Bureau, U.S. Department of Health, Education and Welfare. 相似文献
30.
Serological Comparison of the Three Morphological Phases of Coccidioides immitis by the Agar Gel Diffusion Method 总被引:6,自引:1,他引:5 下载免费PDF全文
Marshall E. Landay Robert W. Wheat Norman F. Conant Edwin P. Lowe 《Journal of bacteriology》1967,93(1):1-6
Hyperimmune sera against spherules and against arthrospores of Coccidioides immitis were prepared by inoculation of rabbits. The antibody content of these sera was studied by the agar gel diffusion method. It was observed that antispherule pooled sera formed multiple precipitin bands with extracts of spherules and of arthrospores. The antiarthrospore pooled serum, however, failed to precipitate with the spherule extract, and formed a single band in the presence of an arthrospore solution. When the spherule and the arthrospore extracts were tested with a variety of different antisera, it was observed that the spherule preparation formed bands only in combination with anti-purified spherule pooled serum, whereas the arthrospore extract precipitated with anti-purified spherule, antiarthrospore, and anti-Histoplasma capsulatum pooled sera. It was also observed that a spherule culture supernatant solution formed five precipitin bands in combination with anti-spherule pooled sera, formed one band with pooled antiserum from rabbits with coccidioidomycosis, and did not precipitate in the presence of antiarthrospore pooled serum. Coccidioidin, however, formed two bands in the presence of any of these antisera. It was therefore concluded that extracts from the spherule phase of C. immitis differed from solutions obtained from the arthrospore and mycelial phases. 相似文献