全文获取类型
收费全文 | 568篇 |
免费 | 32篇 |
国内免费 | 2篇 |
出版年
2023年 | 2篇 |
2022年 | 2篇 |
2021年 | 7篇 |
2020年 | 6篇 |
2019年 | 11篇 |
2018年 | 14篇 |
2017年 | 17篇 |
2016年 | 19篇 |
2015年 | 23篇 |
2014年 | 22篇 |
2013年 | 34篇 |
2012年 | 41篇 |
2011年 | 40篇 |
2010年 | 30篇 |
2009年 | 27篇 |
2008年 | 31篇 |
2007年 | 27篇 |
2006年 | 29篇 |
2005年 | 24篇 |
2004年 | 18篇 |
2003年 | 17篇 |
2002年 | 23篇 |
2001年 | 7篇 |
2000年 | 8篇 |
1999年 | 9篇 |
1998年 | 12篇 |
1997年 | 5篇 |
1996年 | 7篇 |
1994年 | 4篇 |
1993年 | 7篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1988年 | 5篇 |
1987年 | 6篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1979年 | 6篇 |
1977年 | 7篇 |
1976年 | 2篇 |
1975年 | 4篇 |
1973年 | 2篇 |
1970年 | 1篇 |
1969年 | 6篇 |
1968年 | 4篇 |
1967年 | 6篇 |
1966年 | 1篇 |
排序方式: 共有602条查询结果,搜索用时 15 毫秒
1.
The interaction of antigen with specific receptor sites of primed murine spleen lymphocytes has been estimated quantitatively. The antigen-specific receptors are restricted to a small segment of the entire spleen cell population, one which may be enriched by centrifugation of the cells in a discontinuous density gradient. The specificity of the receptors, their variable affinities for the specific ligand, their quantitative fluctuations following immunization, have been investigated. Attempts have also been initiated for their isolation. The possibility that these receptors may represent passively adherent cytophilic immunoglobulins was excluded. The results of these experiments suggest that the union of antigen with a portion of cell membrane receptors initiates a sequence of reaction steps involving DNA production and multiplication, leading to a small net synthesis of immunoglobulins. The continued presence of antigen during this period leads to complex formation with these immunoglobulins. The resulting immune complexes bind to both adherent and nonadherent cells, thereby amplifying the immune response. 相似文献
2.
3.
4.
5.
6.
7.
Removal of Cr(VI) from ground water by Saccharomyces cerevisiae 总被引:1,自引:0,他引:1
Chromium can be removed from ground water by the unicellular yeast, Saccharomyces cerevisiae. Local ground water maintains chromium as CrO4
2- because of bicarbonate buffering and pH and E
h
conditions (8.2 and +343 mV, respectively). In laboratory studies, we used commercially available, nonpathogenic S. cerevisiae to remove hexavalent chromium [Cr(VI)] from ground water. The influence of parameters such as temperature, pH, and glucose concentration on Cr(VI) removal by yeast were also examined. S. cerevisiae removed Cr(VI) under aerobic and anaerobic conditions, with a slightly greater rate occurring under anaerobic conditions. Our kinetic studies reveal a reaction rate (Vmax) of 0.227 mg h-1 (g dry wt biomass)-1 and a Michaelis constant (Km) of 145 mg/l in natural ground water using mature S. cerevisiae cultures. We found a rapid (within 2 minutes) initial removal of Cr(VI) with freshly hydrated cells [55–67 mg h-1 (g dry wt biomass)-1] followed by a much slower uptake [0.6–1.1 mg h-1 (g dry wt biomass)-1] that diminished with time. A materials-balance for a batch reactor over 24 hours resulted in an overall shift in redox potential from +321 to +90 mV, an increase in the bicarbonate concentration (150–3400 mg/l) and a decrease in the Cr(VI) concentration in the effluent (1.9-0 mg/l). 相似文献
8.
L. Martinelli G. Mandolino 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1994,88(6-7):621-628
Isolated somatic embryos from petiole-derived callus cultures ofVitis rupestris Scheele have been employed in experiments on genetic transformation. Co-cultivation of somatic embryos during embryogenesis induction withAgrobacterium tumefaciens strain LBA4404, which contains the plasmid pBI121 carrying the neomycin phosphotranspherase and the-glucuronidase genes, produced transformed cellular lines capable of recurrent somatic embryogenesis. Precocious selection for high levels of kanamycin (100 mgl-1) was an important part of our transformation protocol. Transformed lines still have strong-glucuronidase expression as well as stable insertion of the marker genes after 3 years of in-vitro culture, during which they have maintained their capacity to organize secondary embryos and to regenerate transgenic plants with an agreeable efficiency (13%). 相似文献
9.
The ATP-binding-cassette transmembrane transporters (ABC transporters)
known from vertebrates belong to four major subfamilies: (1) the P-
glycoproteins (Pgp); (2) the cystic fibrosis transmembrane conductance
regulators (CFTR); (3) the Tap proteins encoded with the major
histocompatibility complex of mammals; and (4) the peroxisomal membrane
proteins. Both Pgp and CFTR have a structure suggesting a past internal
gene duplication; a phylogenetic analysis indicated that these duplications
occurred independently, while an independent tandem gene duplication
occurred in the case of the Tap family. Both the Pgp and Tap proteins show
evidence of relationship to bacterial ABC transporters lacking internal
duplication, and both are significantly more closely related to the HlyB
and MsbA families of transporters from purple bacteria than they are to ABC
transporters from nonpurple bacteria. The simplest hypothesis to explain
this observation is that eukaryotic Pgp and Tap genes are descended from a
mitochondrial gene or genes that were subsequently translocated to the
nuclear genome. The Pgp genes of eukaryotes are characterized by a
remarkable degree of convergent evolution between the ATP-binding cassettes
of their N- terminal and C-terminal halves, whereas no such convergence is
seen between the two halves of CFTR genes or between the duplicated Tap
genes. Exon 13 of the CFTR gene, which encodes a putative regulatory domain
not found in other ABC transporters apart from CFTR, showed high levels of
both synonymous and nonsynonymous difference in comparisons among different
mammalian species, suggesting that this region is a mutational hot spot.
相似文献
10.