全文获取类型
收费全文 | 44857篇 |
免费 | 4750篇 |
国内免费 | 12篇 |
专业分类
49619篇 |
出版年
2022年 | 328篇 |
2021年 | 563篇 |
2020年 | 384篇 |
2019年 | 470篇 |
2018年 | 589篇 |
2017年 | 569篇 |
2016年 | 978篇 |
2015年 | 1744篇 |
2014年 | 1717篇 |
2013年 | 2259篇 |
2012年 | 2596篇 |
2011年 | 2309篇 |
2010年 | 1591篇 |
2009年 | 1468篇 |
2008年 | 1997篇 |
2007年 | 1983篇 |
2006年 | 1777篇 |
2005年 | 1721篇 |
2004年 | 1627篇 |
2003年 | 1429篇 |
2002年 | 1423篇 |
2001年 | 1366篇 |
2000年 | 1352篇 |
1999年 | 1206篇 |
1998年 | 665篇 |
1997年 | 624篇 |
1996年 | 605篇 |
1995年 | 585篇 |
1994年 | 541篇 |
1993年 | 573篇 |
1992年 | 1141篇 |
1991年 | 859篇 |
1990年 | 890篇 |
1989年 | 854篇 |
1988年 | 741篇 |
1987年 | 673篇 |
1986年 | 694篇 |
1985年 | 778篇 |
1984年 | 604篇 |
1983年 | 468篇 |
1982年 | 389篇 |
1981年 | 343篇 |
1980年 | 291篇 |
1979年 | 426篇 |
1978年 | 374篇 |
1977年 | 280篇 |
1976年 | 261篇 |
1975年 | 234篇 |
1974年 | 323篇 |
1973年 | 285篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
132.
133.
C. van Leeuwen 《Biotechnology and bioengineering》1979,21(11):2125-2131
The determination of the overall volumetric mass-transfer coefficient with the dynamic measurement technique involves modeling, parameter estimation, and experimental design. The combination and extension of previous efforts lead to some suggestions for improvements. 相似文献
134.
To enable large-scale antibody production, the creation of a stable, high producer cell line is essential. This process often takes longer than 6 months using standard limited dilution techniques and is very labor intensive. The use of a tri-cistronic vector expressing green fluorescent protein (GFP) and both antibody chains, separated by a GT2A peptide sequence, allows expression of all proteins under a single promotor in equimolar ratios. By combining the advantages of 2A peptide cleavage and single cell sorting, a chimeric antibody-antigen fusion protein that contained the variable domains of mouse IgG with a porcine IgA constant domain fused to the FedF antigen could be produced in CHO-K1 cells. After transfection, a strong correlation was found between antibody production and GFP expression (r = 0.69) using image analysis of formed monolayer patches. This enables the rapid selection of GFP-positive clones using automated image analysis for the selection of high producer clones. This vector design allowed the rapid selection of high producer clones within a time-frame of 4 weeks after transfection. The highest producing clone had a specific antibody productivity of 2.32 pg/cell/day. Concentrations of 34 mg/L were obtained using shake-flask batch culture. The produced recombinant antibody showed stable expression, binding and minimal degradation. In the future, this antibody will be assessed for its effectiveness as an oral vaccine antigen. 相似文献
135.
A. Cohen A. M. Breure D. J. M. Schmedding R. J. Zoetemeyer J. G. van Andel 《Applied microbiology and biotechnology》1985,21(6):404-408
Summary The effect of partial pre-acidification of carbohydrate containing wastewaters on anaerobic digester performance was investigated. The influent was a 1% (w/v) glucose solution in a mineral salts medium imposing carbon-limited growth conditions. Up to 13% of the Chemical Oxygen Demand (COD) was added as volatile fatty acids (VFA).In all cases, addition of VFA to the glucose medium resulted in significant increases in the maximum specific COD-conversion rates of the sludge (both with respect to continuous feeding and following a shock loading), as compared with values found on digestion of glucose media alone. 相似文献
136.
Inducible DNA polymerase I synthesis in a UV hyper-resistant mutant of Escherichia coli 总被引:1,自引:0,他引:1
A mutant of Escherichia coli which is more resistant to shortwave UV light than its wild-type parent strain and which can synthesise DNA polymerase I constitutively has been further analysed. It carries two mutational alleles which are located about 1.5 min apart and cotransducible by P1 with the argH locus. The two mutational alleles have been segregated and their analysis shows that one of them is responsible for UV hyper-resistance whereas the other mutation confers UV sensitivity. Recombinant plasmids carrying various sections of the polA regulatory region, linked to a galK gene, were introduced into the mutant strains. Analysis of galactokinase shows that the enzyme activity in the UV hyper-resistant mutant is increased. The results suggest that the synthesis of DNA polymerase I in E. coli is inducible. 相似文献
137.
Iodination of the exposed Tyr-25 in the coat protein decreases the fluorescence intensity of the filamentous phage Pf1 to less than 3% of its original fluorescence. If one assumes that the total residual fluorescence originates from the non-iodinated, buried Tyr-40, one can estimate the distance between Tyr-40 and the DNA bases in Pf1 to be less than 7 A, making use of the Foerster law for fluorescence energy transfer. The result is consistent with the idea that Tyr-40-DNA interaction is responsible for the unusually large axial base separation in Pf1-DNA. 相似文献
138.
139.
J. P. van der Walt 《Antonie van Leeuwenhoek》1967,33(1):97-99
The yeast species previously described asPichia robertsii v. d. Walt has been transferred to the new genusWingea. The diagnosis for the genus is given. 相似文献
140.
Preferential expression of cellular retinoic acid binding protein in a subpopulation of neural cells in the developing mouse embryo 总被引:2,自引:0,他引:2
Marie-Josée Vaessen Erika Kootwijk Dirk Bootsma Ad Geurts van Kessel Christine Mummery John Hilkens 《Differentiation; research in biological diversity》1989,40(2):99-105
The cellular retinoic acid binding protein is thought to be involved in the retinoic-acid-mediated signal transduction pathway. We have isolated the mouse cellular retinoic acid binding protein cDNA from an embryonal-carcinoma-derived cell line by using differential cDNA cloning strategies. In situ hybridization on sections of mouse embryos of various developmental stages indicated that the cellular retinoic acid binding protein gene, which we localized on mouse chromosome 9, is preferentially expressed in a subpopulation of neurectodermal cells. This restricted expression pattern suggests an important role for cellular retinoic acid binding protein in murine neurogenesis. 相似文献