全文获取类型
收费全文 | 1288742篇 |
免费 | 114702篇 |
国内免费 | 1447篇 |
出版年
2021年 | 17883篇 |
2020年 | 12647篇 |
2019年 | 16229篇 |
2018年 | 17186篇 |
2017年 | 15941篇 |
2016年 | 27810篇 |
2015年 | 42435篇 |
2014年 | 50547篇 |
2013年 | 76925篇 |
2012年 | 35277篇 |
2011年 | 22893篇 |
2010年 | 42845篇 |
2009年 | 44491篇 |
2008年 | 22130篇 |
2007年 | 19747篇 |
2006年 | 25694篇 |
2005年 | 26715篇 |
2004年 | 25991篇 |
2003年 | 23776篇 |
2002年 | 21757篇 |
2001年 | 28500篇 |
2000年 | 25660篇 |
1999年 | 27251篇 |
1998年 | 24949篇 |
1997年 | 24765篇 |
1996年 | 24508篇 |
1995年 | 22544篇 |
1994年 | 22426篇 |
1993年 | 21491篇 |
1992年 | 24417篇 |
1991年 | 22834篇 |
1990年 | 21454篇 |
1989年 | 22494篇 |
1988年 | 20689篇 |
1987年 | 19903篇 |
1986年 | 18882篇 |
1985年 | 20863篇 |
1984年 | 21185篇 |
1983年 | 18911篇 |
1982年 | 19951篇 |
1981年 | 19331篇 |
1980年 | 18001篇 |
1979年 | 17718篇 |
1978年 | 16943篇 |
1977年 | 16308篇 |
1976年 | 15701篇 |
1975年 | 14981篇 |
1974年 | 15529篇 |
1973年 | 15797篇 |
1972年 | 13446篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
991.
992.
993.
994.
M E Pell W C Duckworth D E Peavy 《Biochemical and biophysical research communications》1986,137(3):1034-1040
In the present study, we have examined whether insulin degradation products are present on the surface of isolated rat hepatocytes and can be removed by an acid dissociation technique. Hepatocytes were incubated with [125I]insulin for 30 minutes, rapidly washed to remove unbound insulin, and then briefly exposed to acidic conditions (pH 5.0) to remove bound hormone from the cell surface. The radioactive material removed from the cell by acid dissociation and that remaining with the cells were separately analyzed by high performance liquid chromatography. The two primary degradation products of insulin present in control cell extracts were found only with the cell-associated material after acid dissociation. The insulin-sized radioactive material in the extract of acid-dissociable material consisted of only intact [125I]insulin. These results show that the two primary degradation products of insulin in rat hepatocytes are found only intracellularly and suggest that the degradation of the hormone begins after it is internalized. 相似文献
995.
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
996.
W. B. Chodirker 《CMAJ》1984,130(4):343-344
997.
998.
Methanobacterium thermoautotrophicum, an archaebacterium, possesses the first and last enzymes of the diaminopimelic acid pathway for lysine biosynthesis, dihydrodipicolinate synthase, and diaminopimelate decarboxylase. It does not have saccharopine dehydrogenase, the last enzyme of the aminoadipate pathway for lysine biosynthesis. The dihydrodipicolinate synthase is inhibited but not repressed by lysine. We conclude that this microbe uses the diaminopimelate pathway for synthesis of lysine.Deceased. 相似文献
999.
1000.
Additive reagents have been investigated to improve the stability of methanolic Wright's stain. The addition of ammonium halides, monoalkyiamine hydrochlorides, dialkylamine hydrochlorides or trialkylamine hydrochlorides to methanolic Wright's stain was found to enhance the stability of stain components in methanol. No change in performance is observed with these additives present. Random precipitation in the stain solution was still observed with the addition of ammonium halides and monoalkyiamine hydrochlorides. No precipitation was found in stain solutions containing hydrochlorides of most dialkylamines and trialkylamines. Of the compounds evaluated, 0.6% diethylamine hydrochloride added to methanolic stain solutions produced the most desirable overall results. Mechanisms of stabilization and precipitation in these stain solutions are proposed, Essentially, separation of the thiazine-eosinate ion pair through interaction with an appropriate additive increases stain stability. The solubilities of thiazine-eosinate or additive cation-eosinate ion pairs in methanol determine the formation of precipitate in such stain solutions. 相似文献