全文获取类型
收费全文 | 54109篇 |
免费 | 5425篇 |
国内免费 | 12篇 |
出版年
2022年 | 350篇 |
2021年 | 693篇 |
2020年 | 462篇 |
2019年 | 571篇 |
2018年 | 760篇 |
2017年 | 674篇 |
2016年 | 1213篇 |
2015年 | 2148篇 |
2014年 | 2098篇 |
2013年 | 2873篇 |
2012年 | 3314篇 |
2011年 | 2995篇 |
2010年 | 2074篇 |
2009年 | 1818篇 |
2008年 | 2573篇 |
2007年 | 2626篇 |
2006年 | 2430篇 |
2005年 | 2364篇 |
2004年 | 2258篇 |
2003年 | 1984篇 |
2002年 | 1994篇 |
2001年 | 1387篇 |
2000年 | 1340篇 |
1999年 | 1270篇 |
1998年 | 822篇 |
1997年 | 711篇 |
1996年 | 685篇 |
1995年 | 676篇 |
1994年 | 608篇 |
1993年 | 630篇 |
1992年 | 1145篇 |
1991年 | 847篇 |
1990年 | 853篇 |
1989年 | 848篇 |
1988年 | 739篇 |
1987年 | 674篇 |
1986年 | 694篇 |
1985年 | 808篇 |
1984年 | 661篇 |
1983年 | 518篇 |
1982年 | 455篇 |
1981年 | 422篇 |
1980年 | 352篇 |
1979年 | 445篇 |
1978年 | 410篇 |
1977年 | 304篇 |
1976年 | 285篇 |
1975年 | 248篇 |
1974年 | 347篇 |
1973年 | 294篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
151.
Sorbose and 2-deoxy-D-galactose are taken up in Saccharomyces fragilis by an active transport mechanism, as indicated by the energy requirement of the process and the accumulation of free sugar against the concentration gradient. There are no indications for transport-associated phosphorylation as mechanism of energy coupling with these two sugars. The measured sugar-proton cotransport and the influx inhibition by uncouplers suggest a chemiosmotic coupling mechanism. Thus there are at least two different active transport mechanisms operative in Saccharomyces fragilis: transport-associated phosphorylation in the case of 2-deoxy-D-glucose and chemiosmotic coupling in the case of sorbose and 2-deoxy-D-galactose. The differences between the two mechanisms are discussed. Uncouplers do not stimulate downhill sorbose transport in energy-depleted cells and evoke an almost complete inhibition of efflux and of exchange transport. The differences between this sugar-proton cotransport system and similar systems in bacteria and Chlorella are discussed. 相似文献
152.
Numerous functional ergatoid replacement reproductives were found in one colony of Nasutitermes columbicus in Panama. Their morphology was mainly workerlike, although several imaginal characters such as the compound eyes and variable wing buds were more or less developed. The sex organs were fully mature and the fat body of the females, not of the males, was of the “royal” type. The development of the eyes was not accompanied by the differentiation of the optic lobes of the brain, nor was the presence of wing buds correlated with a development of the wing muscles. 相似文献
153.
Egg shell membrane protein contains significant quantities of the lysine-derived aldehyde, allysine, and its aldol condensation product. NaB3H4 reduction followed by alkaline hydrolysis of purified protein revealed that there were six residues/1000 of both allysine and the reduced aldol while only traces of desmosine and isodesmosine were detected. The amino acid composition of the membrane protein did not resemble that of mammalian elastin. 相似文献
154.
155.
156.
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
157.
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
158.
159.
Barbara Tillmann Pierre Jolic?ur Masami Ishihara Nathalie Gosselin Olivier Bertrand Yves Rossetti Isabelle Peretz 《PloS one》2010,5(4)
Congenital amusia is a neurogenetic disorder of music processing that is currently ascribed to a deficit in pitch processing. A recent study challenges this view and claims the disorder might arise as a consequence of a general spatial-processing deficit. Here, we assessed spatial processing abilities in two independent samples of individuals with congenital amusia by using line bisection tasks (Experiment 1) and a mental rotation task (Experiment 2). Both amusics and controls showed the classical spatial effects on bisection performance and on mental rotation performance, and amusics and controls did not differ from each other. These results indicate that the neurocognitive impairment of congenital amusia does not affect the processing of space. 相似文献
160.
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