全文获取类型
收费全文 | 4097篇 |
免费 | 478篇 |
专业分类
4575篇 |
出版年
2021年 | 40篇 |
2019年 | 39篇 |
2018年 | 48篇 |
2016年 | 65篇 |
2015年 | 106篇 |
2014年 | 133篇 |
2013年 | 154篇 |
2012年 | 171篇 |
2011年 | 184篇 |
2010年 | 113篇 |
2009年 | 86篇 |
2008年 | 168篇 |
2007年 | 151篇 |
2006年 | 129篇 |
2005年 | 131篇 |
2004年 | 119篇 |
2003年 | 107篇 |
2002年 | 126篇 |
2001年 | 116篇 |
2000年 | 145篇 |
1999年 | 113篇 |
1998年 | 59篇 |
1997年 | 46篇 |
1996年 | 48篇 |
1995年 | 45篇 |
1994年 | 43篇 |
1993年 | 36篇 |
1992年 | 76篇 |
1991年 | 82篇 |
1990年 | 93篇 |
1989年 | 94篇 |
1988年 | 76篇 |
1987年 | 86篇 |
1986年 | 70篇 |
1985年 | 86篇 |
1984年 | 66篇 |
1983年 | 53篇 |
1982年 | 48篇 |
1981年 | 46篇 |
1979年 | 56篇 |
1978年 | 51篇 |
1977年 | 46篇 |
1976年 | 45篇 |
1975年 | 57篇 |
1974年 | 38篇 |
1973年 | 55篇 |
1972年 | 66篇 |
1971年 | 43篇 |
1970年 | 50篇 |
1969年 | 41篇 |
排序方式: 共有4575条查询结果,搜索用时 0 毫秒
61.
Phosphopeptide analysis of phenylalanine hydroxylase isolated from liver cells exposed to hormonal stimuli. 下载免费PDF全文
Hormonal control of the phosphorylation of phenylalanine hydroxylase was studied by using rat liver cells incubated with [32P]Pi. After immunoprecipitation from cell extracts, the hydroxylase was subjected to proteinase digestion and subsequent sodium dodecyl sulphate/polyacrylamide-gel electrophoresis. V8-proteinase digestion yielded one major 32P-labelled fragment, of approx. 9 kDa. Chymotrypsin digestion gave five 32P-labelled fragments ranging from approx. 39 kDa to approx. 10 kDa. Noradrenaline (10 microM) and glucagon (0.1 microM) enhanced the 32P content of all peptide fragments uniformly. Phorbol ester, in contrast with ionophore A23187, did not stimulate enzyme phosphorylation or enhance phenylalanine metabolism in liver cells. These results are discussed in relation to the nature of the protein kinase(s) that mediate phosphorylation of phenylalanine hydroxylase in liver cells. 相似文献
62.
The subunit structure of membrane-bound mitochondrial transhydrogenase was investigated. Chemical modification of bovine heart submitochondrial particles with the cleavable bifunctional cross-linking reagent, dithiobis(succinimidyl propionate), resulted in the formation of three dimeric "cross-link isomers" of the enzyme, identified by immunoautoradiography, that are characteristic of cross-linked purified transhydrogenase. A limited amount of cross-linking of transhydrogenase monomer to Mr = 25,000 polypeptide was also observed. At high concentration of the cross-linker, a small amount of a higher molecular weight species was formed with both purified and membrane enzyme. Reductive cleavage of the dimeric and higher molecular weight species resulted in the regeneration of transhydrogenase monomer and several other proteolytically derived fragments. It is concluded that transhydrogenase exists in the native membrane primarily as a dimeric species. 相似文献
63.
A complementary DNA oligomer releases a transcription pause complex 总被引:10,自引:0,他引:10
64.
Extracellular release of dissolved organic compounds by the bluegreen algal community of a brackish marsh was studied using 14C techniques. Mannitol and trehalose were identified as the most commonly released compounds. The proportions of these two extracellular compounds varied in response to light intensity and the water potential of the environment. The presence of mannitol, in particular, suggests that excretion of organic compounds in natural situations is a function of osmotic adjustment. 相似文献
65.
66.
67.
J. B. Fisher 《Planta》1971,97(3):257-268
Summary The axillary buds in the leaf crown of Cyperus alternifolius seedlings remain completely inhibited although the shoot is determinate and has no active apex. Buds can be released by detachment of the crown from the plant or by direct application of aqueous enzyladenine (BA), and grow out as inflorescences or vegetative shoots. These arise from activated growth centers of the primordial reproductive branch system which is enclosed within the prophyll of the inhibited bud. Buds are also released by the growth retardant, (2-chloroethyl) trimethylammonium chloride (CCC). Gibberellic acid maintains bud inhibition in detached crowns and inhibits bud release caused by CCC or BA. Naphthaleneacetic acid somewhat reduces BA-induced bud release and causes abnormal root proliferation in CCC-treated crowns. It is suggested that a high level of gibberellin within the crown, possibly in relation to a low level of cytokinin, maintains bud inhibition. 相似文献
68.
Five species of cultured Trebouxia—T. anticipata, T. decolorans, T. erici, T. gelatinosa, and T. impressa—were examined with the electron microscope. A comparative examination of their pyrenoids revealed pyrenoglobuli associated with single pyrenoid thylakoids. The pyrenoids of T. decolorans, T. erici, and T. gelatinosa possess single thylakoids that cross or deeply penetrate the pyrenoid matrix and are often disposed in parallel arrays. T. anticipata possesses both single and double pyrenoid thylakoids within the matrix. T. impressa possesses vesiculate invaginations of thylakoid membranes into the pyrenoid matrix. The phycobiont. T. erici was examined in detail at the light and electron microscopic levels for pyrenoid alterations associated, with varied environmental regimes and with cell division. A greater amount of starch is present in cells grown in organic culture at 215 lux light intensity than in cells of similar size grown at 1075 or 3600 lux. Pyrenoglobuli are present throughout the life cycle and occur both in aplanospores and in zoospores. 相似文献
69.
70.