全文获取类型
收费全文 | 21052篇 |
免费 | 2587篇 |
国内免费 | 8篇 |
专业分类
23647篇 |
出版年
2022年 | 147篇 |
2021年 | 275篇 |
2020年 | 157篇 |
2019年 | 197篇 |
2018年 | 258篇 |
2017年 | 237篇 |
2016年 | 394篇 |
2015年 | 693篇 |
2014年 | 762篇 |
2013年 | 949篇 |
2012年 | 1214篇 |
2011年 | 1193篇 |
2010年 | 790篇 |
2009年 | 688篇 |
2008年 | 979篇 |
2007年 | 1081篇 |
2006年 | 988篇 |
2005年 | 968篇 |
2004年 | 921篇 |
2003年 | 896篇 |
2002年 | 925篇 |
2001年 | 410篇 |
2000年 | 385篇 |
1999年 | 371篇 |
1998年 | 313篇 |
1997年 | 258篇 |
1996年 | 225篇 |
1995年 | 241篇 |
1994年 | 243篇 |
1993年 | 233篇 |
1992年 | 309篇 |
1991年 | 279篇 |
1990年 | 309篇 |
1989年 | 322篇 |
1988年 | 424篇 |
1987年 | 296篇 |
1986年 | 229篇 |
1985年 | 247篇 |
1984年 | 241篇 |
1983年 | 238篇 |
1982年 | 228篇 |
1981年 | 201篇 |
1980年 | 193篇 |
1979年 | 173篇 |
1978年 | 191篇 |
1977年 | 187篇 |
1976年 | 149篇 |
1975年 | 139篇 |
1974年 | 162篇 |
1973年 | 142篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
In C4 plants phosphoenolpyruvate (PEP) of the C4 cycle may betransported on a chloroplast transporter which also transports3-phosphoglycerate (3-PGA) and triosephosphates. In C3 plantsPEP is not considered to be effectively transported on the chloroplastphosphate translocator. The influences of certain organic phosphates,having a similar structure to either PEP or triose-phosphates,on 3-PGA dependent O2 evolution by C4 (Digitaria sanquinalisL. Scop.) and C3 (Hordeum vulgare L.) mesophyll chloroplastswere investigated. In the C4 mesophyll chloroplasts phosphoglycolatewas a competitive inhibitor (Ki = 2.1 mM) of 3-PGA dependentO2 evolution, and was as effective as previously reported forPEP. 2-Phosphoglycerate was also a competitive inhibitor (Kt= 8.6 mM) of O2 evolution in the C4 mesophyll chloroplasts with3-PGA as substrate, while phospholactate was a weak inhibitorand glyphosate had no effect. Neither PEP, phosphoglycolatenor 2-phosphoglycerate were effective inhibitors of 3- PGA dependentO2 evolution in the C3 chloroplasts. Phosphohydroxypyruvatewas a competitive inhibitor of 3-PGA dependent O22 evolutionin both chloroplast types. The selectivity in inhibition ofO2 evolution with 3-PGA as substrate suggests that the C4 mesophyllchloroplasts can recognize certain organic phosphates with thephosphate in the C-2 or C-3 position but that the C4 mesophyllchloroplasts can only effectively recognize certain organicphosphates with the phosphate in the C-3 position. The resultsalso support the view that 3-PGA and PEP are transported onthe same phosphate translocator in C4 mesophyll chloroplasts.
1 Current address: Department of Horticulture, 2001 Fyffe Court,The Ohio State University, Columbus, Ohio 43210-1096. (Received March 24, 1987; Accepted April 16, 1987) 相似文献
4.
5.
Raj K. Singh Mary F. Ruh Thomas S. Ruh 《Biochimica et Biophysica Acta (BBA)/General Subjects》1984,800(1):33-40
In the present study we investigated the binding characteristics of estrogen and antiestrogen-receptor complexes to rabbit uterine chromatin. Activated or nonactivated estrogen receptors were partially purified by DEAE-cellulose chromatography using low (1 mM) or high (10 mM) concentrations of sodium molybdate. Activated [3H]estradiol-receptor complexes showed enhanced binding to chromatin acceptor sites unmasked by 1 M, 4 M and 6 M guanidine hydrochloride. We also examined the chromatin-binding characteristics of the estrogen receptors when bound by the high-affinity triphenylethylene antiestrogen, H1285. The acceptor site activity for the [3H]H1285-receptor complexes was markedly decreased at sites unmasked by 4 M and 6 M guanidine hydrochloride. Further, the nonactivated receptor complexes showed very low binding to deproteinized chromatin. The estrogen-receptor chromatin-acceptor sites were tissue specific and saturable. These chromatin acceptor sites differ in their affinity and capacity (number of binding sites per cell) for the estrogen- and antiestrogen-receptor complexes. Thus, we suggest that the differences in the physiological and physicochemical properties of estrogens and antiestrogens may be related to their differential interaction with uterine chromatin subfractions. 相似文献
6.
7.
In order to evaluate the effectiveness and selectivity of various reagents in the solubilization of bacterial membranes, membranes of Micrococcus lysodeikticus were treated with detergents and chaotropic agents. The composition of the extracts so obtained was analyzed by rocket and two-dimensional immunoelectrophoretic techniques. Recovery of succinate-, malate-, and reduced nicotinamide adenine dinucleotide- (NADH) dehydrogenases, ATPase, succinylated lipomannan and cytochromes in the extracts was measured. Treatment with a variety of non-denaturing detergents produced extracts that were generally qualitatively uniform although quantitative differences were observed. The degree of extraction of various components was correlated with the hydrophile-lipophile balance. Several chaotropic agents were also evaluated as reagents for membrane solubilization. These agents were less effective in extraction of bulk protein, but produced extracts enriched in some membrane components. 相似文献
8.
9.
J M Katz W G Laver D O White E M Anders 《Journal of immunology (Baltimore, Md. : 1950)》1985,134(1):616-622
The recognition of influenza virus hemagglutinin (HA) by T lymphocytes was examined by assaying the T cell proliferative response of influenza virus-primed T cells to purified HA of different influenza A subtypes or to isolated heavy (HA1) or light (HA2) polypeptide chains of the HA molecule. The proliferative response to HA was dependent on the activation of an Ly-1+2- subset of T cells and required the presence of nylon wool-adherent, radiation-resistant accessory cells. T cells from mice primed by infection with one strain of type A influenza virus cross-reacted with other purified HA not only of the same subtype as the priming virus but also of serologically distinct subtypes of influenza A (but not B) virus. The response of virus-primed T cells to the homologous HA or to HA of the same subtype was shown to involve recognition of determinants on both the HA1 and the HA2 chains. The recognition of HA of different subtype by cross-reactive T cells appeared to be directed predominantly to determinants on HA2. Because the antibody response to influenza virus HA is not cross-reactive between subtypes and is directed predominantly to determinants on HA1, the present results indicate that at least some of the determinants on HA recognized by T cells are different from those recognized by B cells and that the HA2 chain may be involved primarily in stimulation of T cell rather than B cell immunity. 相似文献
10.
Pollution of freshwater and estuaries 总被引:1,自引:1,他引:0