全文获取类型
收费全文 | 1998篇 |
免费 | 243篇 |
国内免费 | 1篇 |
出版年
2022年 | 23篇 |
2021年 | 30篇 |
2020年 | 19篇 |
2019年 | 19篇 |
2018年 | 28篇 |
2017年 | 20篇 |
2016年 | 30篇 |
2015年 | 76篇 |
2014年 | 68篇 |
2013年 | 87篇 |
2012年 | 107篇 |
2011年 | 112篇 |
2010年 | 51篇 |
2009年 | 66篇 |
2008年 | 87篇 |
2007年 | 83篇 |
2006年 | 73篇 |
2005年 | 68篇 |
2004年 | 57篇 |
2003年 | 48篇 |
2002年 | 61篇 |
2001年 | 70篇 |
2000年 | 72篇 |
1999年 | 51篇 |
1998年 | 36篇 |
1997年 | 36篇 |
1996年 | 29篇 |
1995年 | 22篇 |
1994年 | 20篇 |
1993年 | 26篇 |
1992年 | 50篇 |
1991年 | 37篇 |
1990年 | 30篇 |
1989年 | 47篇 |
1988年 | 40篇 |
1987年 | 25篇 |
1986年 | 30篇 |
1985年 | 19篇 |
1984年 | 33篇 |
1983年 | 22篇 |
1981年 | 24篇 |
1980年 | 18篇 |
1979年 | 17篇 |
1977年 | 22篇 |
1975年 | 24篇 |
1973年 | 23篇 |
1972年 | 19篇 |
1971年 | 16篇 |
1970年 | 19篇 |
1969年 | 21篇 |
排序方式: 共有2242条查询结果,搜索用时 156 毫秒
1.
2.
Free and polymerized tubulin in cultured bone cells and Chinese hamster ovary cells: the influence of cold and hormones 总被引:1,自引:1,他引:0
A low pH method of liposome-membrane fusion (Schneider et al., 1980, Proc. Natl. Acad. Sci. U. S. A. 77:442) was used to enrich the mitochondrial inner membrane lipid bilayer 30-700% with exogenous phospholipid and cholesterol. By varying the phospholipid-to- cholesterol ratio of the liposomes it was possible to incorporate specific amounts of cholesterol (up to 44 mol %) into the inner membrane bilayer in a controlled fashion. The membrane surface area increased proportionally to the increase in total membrane bilayer lipid. Inner membrane enriched with phospholipid only, or with phospholipid plus cholesterol up to 20 mol %, showed randomly distributed intramembrane particles (integral proteins) in the membrane plane, and the average distance between intramembrane particles increased proportionally to the amount of newly incorporated lipid. Membranes containing between 20 and 27 mol % cholesterol exhibited small clusters of intramembrane particles while cholesterol contents above 27 mol % resulted in larger aggregations of intramembrane particles. In phospholipid-enriched membranes with randomly dispersed intramembrane particles, electron transfer activities from NADH- and succinate-dehydrogenase to cytochrome c decreased proportionally to the increase in distance between the particles. In contrast, these electron- transfer activities increased with decreasing distances between intramembrane particles brought about by cholesterol incorporation. These results indicate that (a) catalytically interacting redox components in the mitochondrial inner membrane such as the dehydrogenase complexes, ubiquinone, and heme proteins are independent, laterally diffusible components; (b) the average distance between these redox components is effected by the available surface area of the membrane lipid bilayer; and (c) the distance over which redox components diffuse before collision and electron transfer mediates the rate of such transfer. 相似文献
3.
4.
5.
Use of Metabolic Inhibitors to Estimate Protozooplankton Grazing and Bacterial Production in a Monomictic Eutrophic Lake with an Anaerobic Hypolimnion 总被引:15,自引:8,他引:7
下载免费PDF全文
![点击此处可从《Applied microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Inhibitors of eucaryotes (cycloheximide and amphotericin B) and procaryotes (penicillin and chloramphenicol) were used to estimate bacterivory and bacterial production in a eutrophic lake. Bacterial production appeared to be slightly greater than protozoan grazing in the aerobic waters of Lake Oglethorpe. Use of penicillin and cycloheximide yielded inconsistent results in anaerobic water and in aerobic water when bacterial production was low. Production measured by inhibiting eucaryotes with cycloheximide did not always agree with [3H]thymidine estimates or differential filtration methods. Laboratory experiments showed that several common freshwater protozoans continued to swim and ingest bacterium-size latex beads in the presence of the eucaryote inhibitor. Penicillin also affected grazing rates of some ciliates. We recommend that caution and a corroborating method be used when estimating ecologically important parameters with specific inhibitors. 相似文献
6.
W.S. Rehm S.S. Sanders R.L. Shoemaker J. OCallaghan J.T. Tarvin E.A. Friday 《Journal of theoretical biology》1973,39(1):131-153
Several workers have suggested that cell membranes have a high proton conductance. Our interest in this concept arose from the possibility that the nutrient (submucosal-facing) membrane of the gastric mucosa may have a high proton or hydroxyl ion conductance which would play a role in the regulation of the acid-base balance of the cell. We found that wide changes in the H+ concentration of the fluid bathing the nutrient side of the in vitro frog gastric mucosa did not result in significant changes in p.d. However, a maintained change of the H+ concentration of the bathing fluid would be expected to produce only a temporary change in p.d. Since a diffusion barrier is present on the nutrient side the temporary change in p.d. might be masked. An analysis of this possibility was made on the basis of a conceptual model and as a result of the analysis it is concluded that the proton (and/or OH?) conductance of the nutrient membrane of the frog gastric mucosa is not a significant fraction of its total conductance. The present status of the proton conductance hypothesis with respect to striated muscle and to the secretory membrane of the gastric mucosa is reviewed. 相似文献
7.
8.
The poly-beta-hydroxybutyrate granule in vivo. A new insight based on NMR spectroscopy of whole cells 总被引:6,自引:0,他引:6
High resolution 13C NMR spectroscopy of live cells has been used to show that poly-beta-hydroxybutyrate (PHB) is predominantly in a mobile state within the storage granules of Alcaligenes eutrophus, Methylobacterium extorquens, and Methylobacterium AM1. Comparison of chemical and NMR analysis of PHB indicates that about 70% of the polymer in A. eutrophus gives sharp observable resonances. Temperature-dependent line widths and relaxation rates together with nuclear Overhauser effect measurements demonstrate that the observed material is effectively a mobile amorphous elastomer that is well above its glass transition temperature. The hydroxyvalerate-hydroxybutyrate copolymer produced by propionate-fed A. eutrophus has virtually the same mobility as the homopolymer. Evidence is presented indicating that water is an integral component of the PHB granule and that this component acts as a plasticizer for the polymer. These observations strongly suggest that the enzyme(s) responsible for PHB biosynthesis and consumption operate only on mobile hydrated material and that the solid granules characteristic of dried cells are partially artifactual. This model is supported by a reinterpretation of previously inexplicable biochemical results. 相似文献
9.
10.
Clive Sanders 《Biochemical and biophysical research communications》1977,78(3):1034-1042
A method is given for the preparation of four non-histone chromosomal proteins, one of which, protein 14, hitherto has not been isolated. The method also enables the preparation of histone H1 in gram quantities. The four non-histone chromosomal proteins so prepared are all polar molecules over 50% of each being composed of acidic and basic amino acids. It is also shown that protein 14 can be prepared from calf thymus without prior isolation of chromatin. 相似文献