全文获取类型
收费全文 | 249067篇 |
免费 | 22811篇 |
国内免费 | 233篇 |
出版年
2018年 | 2692篇 |
2017年 | 2636篇 |
2016年 | 3506篇 |
2015年 | 3758篇 |
2014年 | 4699篇 |
2013年 | 6848篇 |
2012年 | 7455篇 |
2011年 | 8084篇 |
2010年 | 5514篇 |
2009年 | 4908篇 |
2008年 | 7092篇 |
2007年 | 7308篇 |
2006年 | 6950篇 |
2005年 | 6611篇 |
2004年 | 6547篇 |
2003年 | 6385篇 |
2002年 | 6246篇 |
2001年 | 12174篇 |
2000年 | 12123篇 |
1999年 | 9254篇 |
1998年 | 2665篇 |
1997年 | 2736篇 |
1996年 | 2656篇 |
1995年 | 2512篇 |
1994年 | 2468篇 |
1993年 | 2362篇 |
1992年 | 7282篇 |
1991年 | 7068篇 |
1990年 | 7171篇 |
1989年 | 6963篇 |
1988年 | 6449篇 |
1987年 | 6091篇 |
1986年 | 5430篇 |
1985年 | 5731篇 |
1984年 | 4531篇 |
1983年 | 3918篇 |
1982年 | 2715篇 |
1981年 | 2532篇 |
1980年 | 2334篇 |
1979年 | 4172篇 |
1978年 | 3183篇 |
1977年 | 2924篇 |
1976年 | 2860篇 |
1975年 | 3307篇 |
1974年 | 3534篇 |
1973年 | 3560篇 |
1972年 | 3098篇 |
1971年 | 2867篇 |
1970年 | 2554篇 |
1969年 | 2324篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
Norma L. Pucheu Norma L. Kerber Emilio A. Rivas Néstor Cortez Augusto F. Garcia 《Current microbiology》1997,34(3):155-161
Membranes from in vivo labeled cells of Rhodobacter
capsulatus U43[pTX35] grown photosynthetically carried 60% of
the [32P]-Pi in the “heavy” fraction (HM) after
sucrose gradient sedimentation. Metal-chelating chromatography of either
“heavy” or “light” (LM) membrane fractions rendered
similar Bchl-protein complex profiles after octyl-glucoside treatment,
including most of the radioactivity in the same corresponding elution
fraction (F II). Similar labeling distribution of pigment-protein complexes
was obtained for membranes of dark-grown cells induced by lowering oxygen
tension. Fractions derived from HM showed highly labeled LHIα, whereas the
same complex from LM was essentially [32P]-Pi-free, as revealed
by SDS-PAGE followed by autoradiography. Phospholipid analysis showed a
similar pattern for membranes isolated from cells photosynthetically or
semiaerobically grown, being the most abundant: phosphatidylglycerol,
phosphatidylethanolamine, cardiolipin, and phosphatidylcholine. Part of the
phospholipids from HM comigrated with LHIα during SDS-PAGE and dissociated
from the complexes only after solvent extraction and hydrophobic
chromatography. However, a small amount remained always attached to LHIα,
indicating an unusual strong interaction. These results suggest the existence
of two operationally defined membrane regions carrying LHIα complexes
differing in phosphorylation status and protein-phospholipid interaction.
Received: 10 August 1996 / Accepted: 10 September 1996 相似文献
23.
24.
A N Mayeno A J Curran R L Roberts C S Foote 《The Journal of biological chemistry》1989,264(10):5660-5668
Human eosinophils preferentially utilize bromide to generate a brominating agent, even at physiological halide concentrations, where chloride (140 mM) is over 1000-fold greater than bromide (20-100 microM). Under the same conditions, neutrophils use chloride to generate a chlorinating agent. The total amount of active halogen trapped by 1,3,5-trimethoxybenzene from eosinophils increases by over 2-fold as the added bromide concentration increases from 0 to 100 microM, with approximately 40 nmol of halogen trapped per million cells at the highest bromide level. At least 25-35% of the oxygen consumed by stimulated eosinophils is directed toward the generation of halogenating species. Since the relative halogenating behavior of eosinophil peroxidase and neutrophil myeloperoxidase in this bromide range is essentially identical to that of the cells, the specificity of eosinophils toward bromide is intrinsic to eosinophil peroxidase and not to any special cellular properties. These results suggest that human eosinophils use bromide in vivo and that a deficiency of bromide may influence their ability to produce halogenating agents. 相似文献
25.
The ability of bovine intermediate lobe secretory vesicle membrane-associated enzyme(s) and purified, soluble paired basic residue-specific, pro-opiomelanocortin converting enzyme (Loh, Y.P., Parish, D. C., and Tuteja, R. (1985) J. Biol. Chem. 260, 7194-7205) to cleave bovine NH2-terminal pro-opiomelanocortin1-77 (N-POMC 1-77) was investigated. Purified pro-opiomelanocortin converting enzyme and an enzyme activity associated with the secretory vesicle membrane were shown to cleave bovine N-POMC1-77 to two major products: N-POMC1-49 and Lys-gamma 3-melanotropin (MSH), and one minor product, gamma 3-MSH. These products were identified by their retention times on high performance liquid chromatography, immunological characteristics, and for Lys-gamma 3-MSH, amino acid composition. The products generated indicate cleavage preferentially between Arg 49-Lys 50 of bN-POMC1-77 (where b indicates bovine), which is identical to the processing pattern found in the bovine intermediate lobe in situ. The membrane converting activity was shown to be stimulated by 5 mM Ca2+ and has a pH optimum of 4-5 and an inhibitor profile characteristic of an aspartic protease. This suggests that the membrane-associated enzyme involved is very similar or identical to the purified, soluble pro-opiomelanocortin converting enzyme, which has previously been reported to be an acidic, aspartic protease responsible for the initial steps of POMC processing. The results of this study lead to the proposal that the lack of processing of the Arg49-Lys50 site in POMC in the anterior lobe versus the intermediate lobe of the pituitary in vivo may be due to other regulatory mechanisms rather than invoking the existence in the intermediate lobe of another enzyme specific for this site, different from pro-opiomelanocortin converting enzyme. 相似文献
26.
M. V. Bazunova L. A. Sharafutdinova R. Yu. Lazdin V. V. Chernova D. N. Mixonov V. P. Zakharov 《Applied Biochemistry and Microbiology》2018,54(5):474-477
The conditions to obtain materials with elastic-viscous properties based on chitosan succinamide have been studied. A decreased polymer content and a transition from visco-elastic liquids to elastic-viscous systems were shown upon the addition of glycerol to an aqueous solution of chitosan succinamide. The systemic response, biological compatibility, and dynamics of bioresorbability of the obtained materials were studied during implantation in laboratory animals. 相似文献
27.
28.
29.
30.
Bacteriomorphic organisms found in fruits of capitate infructescences in Kunduricarpus Kodrul, N. Maslova, Tekleva et Golovneva, Platanaceae, are described. Three types of carpel damage have been detected: (1) evidence of penetration of microorganisms in the walls of the carpel, (2) three-dimensional structures (isolated and in chains) rounded in section, which fill the inner space of the carpel, and (3) imprints of these structures on the inner surface of the carpel wall cuticle. The possible nature of the microorganisms is discussed. 相似文献