全文获取类型
收费全文 | 3081篇 |
免费 | 186篇 |
国内免费 | 4篇 |
出版年
2022年 | 18篇 |
2021年 | 36篇 |
2020年 | 36篇 |
2019年 | 31篇 |
2018年 | 55篇 |
2017年 | 43篇 |
2016年 | 59篇 |
2015年 | 107篇 |
2014年 | 108篇 |
2013年 | 154篇 |
2012年 | 188篇 |
2011年 | 168篇 |
2010年 | 138篇 |
2009年 | 115篇 |
2008年 | 150篇 |
2007年 | 172篇 |
2006年 | 150篇 |
2005年 | 139篇 |
2004年 | 147篇 |
2003年 | 138篇 |
2002年 | 117篇 |
2001年 | 32篇 |
2000年 | 32篇 |
1999年 | 37篇 |
1998年 | 37篇 |
1997年 | 23篇 |
1996年 | 28篇 |
1995年 | 38篇 |
1994年 | 23篇 |
1993年 | 27篇 |
1992年 | 11篇 |
1991年 | 15篇 |
1990年 | 19篇 |
1988年 | 19篇 |
1987年 | 19篇 |
1985年 | 18篇 |
1983年 | 24篇 |
1982年 | 27篇 |
1981年 | 15篇 |
1980年 | 18篇 |
1979年 | 19篇 |
1978年 | 14篇 |
1977年 | 14篇 |
1976年 | 14篇 |
1975年 | 11篇 |
1971年 | 12篇 |
1962年 | 11篇 |
1961年 | 10篇 |
1926年 | 10篇 |
1912年 | 18篇 |
排序方式: 共有3271条查询结果,搜索用时 15 毫秒
81.
Control of the Lysine Biosynthesis Sequence in Corynebacterium glutamicum as Analyzed by Overexpression of the Individual Corresponding Genes 总被引:7,自引:2,他引:5 下载免费PDF全文
The gene cluster that codes for feedback-resistant aspartate kinase (lysCα and lysCβ) and aspartate semialdehyde dehydrogenase (asd) was cloned from a mutant strain of Corynebacterium glutamicum. Its functional analysis by subcloning, enzyme assays, and type of aspartate kinase regulation enabled the isolation of a fragment for separate expression of the feedback-resistant kinase without aspartate semialdehyde dehydrogenase expression. This was used together with other clones constructed (J. Cremer, L. Eggeling, and H. Sahm, Mol. Gen. Genet. 220:478-480, 1990) to overexpress individually each of the six genes that convert aspartate to lysine. Analysis of lysine formation revealed that overexpression of the feedback-resistant kinase alone suffices to achieve lysine formation (38 mM). Also, sole overexpression of wild-type dihydrodipicolinate synthase resulted in lysine formation but in a lower amount (11 mM). The other four enzymes had no effect on lysine secretion. With a plasmid overexpressing both relevant enzymes together, a further increase in lysine yield was obtained. This shows that of the six enzymes that convert aspartate to lysine the kinase and the synthase are responsible for flow control in the wild-type background and can be useful for construction of lysine-producing strains. 相似文献
82.
83.
84.
Dagmar Jičínská Eduard Brabec Marcel Rejmánek Jan Jeník Joří Haager Josef Holub Věroslav Samek Hana Rambousková Josef Holub Marie Naděžda Končalová Robert Neuhäusl Josev Kyncl František Krahuleo Jaroslav Dobrý Blanka Úlehlová Jiří Úlehla Eliška Rybníčková Kamil Rybníček 《Folia Geobotanica》1982,17(4):431-448
85.
Subcellular Distribution of 3α-Hydroxysteroid Dehydrogenase and Antiestrogen Action on Androgen-Metabolizing Enzymes in Rat Pituitary Gland 总被引:1,自引:1,他引:0
Rüdiger Ghraf Klaus Schneider Josef Kirchhoff Christoph Hiemke 《Journal of neurochemistry》1982,38(4):876-883
Abstract: Gonadectomy of male rats led to a threefold increase of 3α-hydroxysteroid dehydrogenase (3α-HSDH) activity in pituitary homogenates that could be completely reversed by chronic administration of estradiol or 5α-dihydrotestosterone (DHT). 3α-HSDH was found to be distributed mainly between the 10,000 g and 100,000 g sediments from whole homogenates. The microsomal enzyme activity showed a substantial specificity for NADH whereas the cytosolic enzyme (100,000 g supernatant) demonstrated a slight preference for NADPH. The changes in V max found in homogenates following gonadectomy and gonadal steroid administration reflected changes in NADH- linked activity of the microsomal, but not the cytosolic enzyme. Estradiol-induced suppression of NADH-linked 3α-HSDH activity in pituitary homogenates from gonadectomized rats of either sex was accompanied by a similar suppression of NADPH-linked 5α-reductase activity and a marked decrease of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) release. In the ovariectomized rat chronic administration of nonsteroidal antiestrogens had strong estrogenic effects on 3α-HSDH activity and LH release, but not on 5α-reductase activity and FSH release. In the gonadectomized male rat, which was much less sensitive to intrinsic estrogenicity of the antiestrogens tested, nafoxidine completely blocked estradiol-induced suppression of 5α-reductase activity and FSH release and partially antagonized suppression of LH release. The trans -isomeric, substituted triphenylethylenes, tamoxifen, and enclomiphene, as well as nitromifene (mixture of trans and cis isomers) were able partially to counteract estradiol-induced suppression of 5α-reductase, but not 3α-HSDH activity. It is concluded that estradiol action on pituitary 5α-reductase, but not 3α-HSDH activity, involves an estrogen receptor mechanism. 相似文献
86.
Fritz Schöffl Walter Arnold Alfred Pühler Josef Altenbuchner Rüdiger Schmitt 《Molecular & general genetics : MGG》1981,181(1):87-94
Summary The 10.7 kilobase (kb) tetracycline resistance transposons Tn1721 and Tn1771, isolated from disparate sources, are completely homologous on the basis of heteroduplex analyses. Both transposable elements are capable of forming multiple duplications of a 5.3 kb portion encompassing the resistance genes (tet region). A model accounting for both, recA-independent translocation and recA-dependent amplification, postulates two direct and one inverted repeat as essential constituents of the transposons. DNA sequence analyses of Tn1721 and Tn1771 have substantiated this model. They demonstrated three identical 38 base pair repeats identically in both transposons dividing them into a minor transposon and a tet region. Identical sequences of at least 87 base pairs providing recombination hot spots for gene duplication have been found at the ends of the repetitious tet region. Translocation of Tn1721 and Tn1771 generates five base pair direct repeats at the respective sites of insertion. On the basis of the heteroduplex molecules and sequences analyzed the two transposons are identical.To Professor Wolfram Heumann on the occasion of his 65th birthday 相似文献
87.
When Acetobacterium woodii was co-cultured in continuous or in stationary culture with Methanobacterium strain AZ, fructose instead of being converted to 3 mol of acetate was converted to 2 mol of acetate and 1 mol each of carbon dioxide and methane, showing that interspecies hydrogen transfer occurred. In continous culture the organisms formed a close physical association in clumps; the doubling time for each organism was 6h at 33°C. Methane mainly was derived from carbon positions 3 and 4 of the sugar, but other carbons also yielded methane; this was shown to be due to carbon dioxide-acetate exchange reactions by A. woodii in a manner similar to that carried out by Clostridium thermoaceticum. Four other methanogens, Methanobacterium M.o.H. and M.o.H. G, Methanobacterium formicicum, and Methanosarcina barkeri (not acetate-adapted) also produced similar results, when co-cultured with A. woodii. 相似文献
88.
John J. Just Josef Schwager Rudolf Weber Hans Fey Hedi Pfister 《Development genes and evolution》1980,188(1):75-80
Summary Antisera against larval and adultXenopus hemoglobins as well as adult human hemoglobin showed no cross-reaction when tested by immunodiffusion against each heterologous antigen. In this test hemoglobin of a single animal produced two precipitation lines for larvae, but only one for adult stages. Immunoelectrophoresis also revealed more complex precipitation patterns for larval than for adult hemoglobins. Hemoglobin of the isogenic hybrid cloneXenopus laevis/X. gilli also reacted with antisera against normalXenopus hemoglobin.Quantitation of hemoglobins, analyzed by radial immunodiffusion showed fewer than 1% of adult hemoglobin in red cells of larvae, but 30% at completion of metamorphosis. Two weeks later adult hemoglobin attained over 90%, and in red cells of adultXenopus an average of 1% larval hemoglobin were detected.The relatively short transition period suggests that the loss of larval hemoglobin may be due to the elimination of larval red cells, and that the increase in adult hemoglobin may be indicative of a new cell line. 相似文献
89.
90.
The transposons Tn21, Tn501, and Tn1721 are related to Tn3. Transposition-deficient mutants (tnpA) of these elements were used to test for complementation of transpostion. Transposition of tnpA mutants of Tn501 and Tn1721 was restored by the presence in trans of Tn21, Tn501, and Tn1721, but transposition of a tnpA mutant of Tn21 was restored in trans only by Tn21 itself. Tn3 did not complement transposition of Tn21, Tn501, or Tn1721, and these elements did not complement transposition of Tn3. 相似文献