全文获取类型
收费全文 | 7206篇 |
免费 | 758篇 |
国内免费 | 1篇 |
专业分类
7965篇 |
出版年
2021年 | 91篇 |
2018年 | 70篇 |
2017年 | 54篇 |
2016年 | 107篇 |
2015年 | 194篇 |
2014年 | 202篇 |
2013年 | 285篇 |
2012年 | 323篇 |
2011年 | 325篇 |
2010年 | 204篇 |
2009年 | 192篇 |
2008年 | 261篇 |
2007年 | 284篇 |
2006年 | 284篇 |
2005年 | 252篇 |
2004年 | 259篇 |
2003年 | 218篇 |
2002年 | 255篇 |
2001年 | 200篇 |
2000年 | 204篇 |
1999年 | 187篇 |
1998年 | 106篇 |
1997年 | 99篇 |
1996年 | 57篇 |
1995年 | 84篇 |
1994年 | 75篇 |
1993年 | 95篇 |
1992年 | 165篇 |
1991年 | 135篇 |
1990年 | 150篇 |
1989年 | 125篇 |
1988年 | 114篇 |
1987年 | 114篇 |
1986年 | 101篇 |
1985年 | 116篇 |
1984年 | 122篇 |
1983年 | 93篇 |
1982年 | 100篇 |
1981年 | 90篇 |
1980年 | 102篇 |
1979年 | 134篇 |
1978年 | 96篇 |
1977年 | 106篇 |
1976年 | 74篇 |
1975年 | 73篇 |
1974年 | 82篇 |
1973年 | 91篇 |
1972年 | 62篇 |
1971年 | 58篇 |
1970年 | 59篇 |
排序方式: 共有7965条查询结果,搜索用时 15 毫秒
41.
42.
A strain of Clostridium sporogenes, an anaerobic bacterium, isolated from sewage in New York City synthesizes two constitutive enzymes with action on steroid molecules: (i) an enzyme capable of selectively acetylating the 21-hydroxyl function of certain steroids and (ii) the corresponding esterase. Under our experimental conditions the enzymes have a strict structural requirement for 3-keto-4-ene and C-20-keto or 20 alpha-hydroxyl group and convert their respective substrates to a mixture of free and acetylated products. 相似文献
43.
Robert W. Lovitt Robert P. Walter J. Gareth Morris Douglas B. Kell 《Applied microbiology and biotechnology》1986,23(3-4):168-173
Summary The problem of obtaining a rapid estimate of the microbial content of an immobilised cell suspension is addressed. The low-frequency conductivity of free-living cell suspensions of Clostridium pasteurianum is lower than that of the medium in which they are suspended, by an amount conforming to the Bruggeman relation. The conductivity of the cell wall makes a negligible contribution to the measured conductivity under the conditions used. Calcium alginate beads (lacking microbial cells) lower the conductivity of a solution with which they have been equilibrated by an extent which is a function of the concentration of alginate gel used in forming the beads. When this is taken into account, the ratio of the conductivity of a suspension of gel-immobilised cells to that of the suspending medium can be used to give a rapid and convenient assessment of the amount of microbial biomass present. 相似文献
44.
Chicken lens delta-crystallin gene expression and methylation in several non-lens tissues. 总被引:5,自引:2,他引:3 下载免费PDF全文
D J Bower L H Errington D N Cooper S Morris R M Clayton 《Nucleic acids research》1983,11(9):2513-2527
RNA sequences coding for the most abundant chicken lens proteins, delta-crystallin, were detected at very low levels in day old post hatch chick lung, heart, kidney and liver, and in 6 day embryo headless bodies. The pattern of cytosine methylation within the CCGG sequences of the delta-crystallin genes was also examined and shown to vary in several non-lens tissues, from several stages of development. Embryonic neural retina, which expresses a higher level of delta-crystallin RNA than the above tissues, is no less methylated in the sites studied than the tissues which have no association with the eye, and is actually more heavily methylated than the kidney. Thus no obvious correlation was found between undermethylation and gene expression. 相似文献
45.
46.
47.
48.
Metabolism of Glutamic Acid and N-Acetylglutamic Acid in Leaf Discs and Cell-free Extracts of Higher Plants 总被引:9,自引:9,他引:0 下载免费PDF全文
Radioactive glutamic acid and N-acetylglutamic acid have been incubated with normal and wilted leaf discs and radioactivity recovered in uncombined proline. The discs which had been placed under moisture stress incorporated considerably more label in uncombined proline than did normal discs. 相似文献
49.
1. The relative concentrations of the inactive ribosomal components were compared in normal and regenerating rat liver and in two transplantable rat hepatomas (hepatomas 7800 and 5123D). 2. The size of the ribosomal-subunit pools in normal liver was not significantly affected by partial hepatectomy or neoplasia although, as shown previously, significant changes do occur in the monomer pool. 3. Further, the subunit pools in both liver and hepatoma were not significantly influenced by several treatments that caused dramatic changes in the size of the ribosomal monomer (and dimer) pools. 4. The high concentration of inactive monomers and dimers in the hepatomas appears to arise from limitations at the translational level, since they can be incorporated into pre-existing polyribosomes under the influence of cycloheximide. 相似文献
50.