全文获取类型
收费全文 | 13327篇 |
免费 | 904篇 |
国内免费 | 917篇 |
出版年
2024年 | 46篇 |
2023年 | 211篇 |
2022年 | 279篇 |
2021年 | 334篇 |
2020年 | 444篇 |
2019年 | 462篇 |
2018年 | 514篇 |
2017年 | 360篇 |
2016年 | 384篇 |
2015年 | 464篇 |
2014年 | 610篇 |
2013年 | 923篇 |
2012年 | 468篇 |
2011年 | 737篇 |
2010年 | 555篇 |
2009年 | 792篇 |
2008年 | 698篇 |
2007年 | 736篇 |
2006年 | 665篇 |
2005年 | 670篇 |
2004年 | 539篇 |
2003年 | 464篇 |
2002年 | 429篇 |
2001年 | 309篇 |
2000年 | 245篇 |
1999年 | 269篇 |
1998年 | 240篇 |
1997年 | 218篇 |
1996年 | 157篇 |
1995年 | 187篇 |
1994年 | 188篇 |
1993年 | 148篇 |
1992年 | 137篇 |
1991年 | 107篇 |
1990年 | 109篇 |
1989年 | 118篇 |
1988年 | 78篇 |
1987年 | 77篇 |
1986年 | 60篇 |
1985年 | 69篇 |
1984年 | 132篇 |
1983年 | 102篇 |
1982年 | 101篇 |
1981年 | 73篇 |
1980年 | 64篇 |
1979年 | 46篇 |
1978年 | 29篇 |
1977年 | 29篇 |
1976年 | 21篇 |
1973年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
We have studied in detail the effects of dicyclohexylcarbodiimide (DCCD) on the redox activity of the mitochondrialbc
1 complex, and on the binding of its most specific inhibitor antimycin. An inhibitory action of the reagent has been found only at high concentration of the diimide and/or at prolonged times of incubation. Under these conditions, DCCD also displaced antimycin from its specific binding site in thebc
1 complex, but did not apparently change the antimycin sensitivity of the ubiquinol-cytochromec reductase activity. On the other hand, using lower DCCD concentrations and/or short times of incubation, i.e., conditions which usually lead to the specific inhibition of the proton-translocating activity of thebc
1 complex, no inhibitory effect of DCCD could be detected in the ubiquinol-cytochromec reductase activity. However, a clear stimulation of the rate of cytochromeb reduction in parallel to an inhibition of cytochromeb oxidation has been found under these conditions. On the basis of the present work and of previous reports in the literature about the effects of DCCD on thebc
1 complex, we propose a clarification of the various effects of the reagent depending on the experimental conditions employed. 相似文献
92.
L. K. Steinrauf 《Journal of biosciences》1985,8(1-2):293-306
A total of 19 different crystal forms of complexes of valinomycin or its analogues with monovalent cations have been observed.
The crystal structure determinations of valinomycin potassium tetrachloroaurate and valinomycin rubidium tetrachloroaurate
are given here.Including this work complete structure determinations have now been published on 7 with 2 more soon to appear.
Comparisons of these structural results suggest that the valinomycin complex opens at the D-valyl (lactyl) end and that contacts
are possible between the complexed cation and other molecules. Such contacts may play an important part in membrane transport. 相似文献
93.
94.
L. W. D. van Raamsdonk 《Plant Systematics and Evolution》1985,149(3-4):287-297
The pollen fertility and seed formation of six species of theOrnithogalum umbellatum/angustifolium complex and of seven related species were studied. Four types of pollen grains could be recognized. The pollen fertility varied greatly in this complex and is not related to the ploidy level. The seed formation ofO. umbellatum showed an adaptation to a subcontinental-Mediterranean climate, that ofO. angustifolium to an Atlantic climate. In both cases raindrops seem to be important for pollination, in view of the absence of insect pollinators. After open pollination 113 seedlings were obtained in four species. Their chromosome numbers were determined. Nearly all the cultivated seedlings were aneuploid, which points to a positive selection of euploids in nature, because aneuploid individuals are rare in the wild.Biosystematic Studies on theOrnithogalum umbellatum/angustifolium Complex III.—Previous parts of this series are Part I: Taxonomy. Proceeding Kon. Ned. Acad. Wet. series C,85 (4), 563–574 (1982) andvan Raamsdonk (1984). 相似文献
95.
Christian Leuckert 《Plant biology (Stuttgart, Germany)》1985,98(1):401-408
Die Kombination (Koppelung) der Stoffe im Chemosyndrom kann gegenseitig oder einseitig obligat oder auch fakultativ sein. Dabei ist die Stellung der beteiligten eng verwandten Produkte im Rahmen der Biosynthese von Fall zu Fall verschieden. — Dem Chemotaxonomen kann die Berücksichrigung dieser Aspekte zumindest tendenziell als Anhaltspunkt dienen. Bei Vorkommen der Komponenten in verschiedenen Verwandtschaftskreisen wird man ein Chemosyndrom - also eine Kornbination biogenetisch eng verwandter Verbindungen - urn so eher als ein einziges Merkmal betrachten können, je seltener die Kombination aufgelöst ist. Zweifellos stellen der solitare Stoff als Einzelmerkmal und die ohne Ausnahme auftretende (obligate) Kombination als Einzelmerkmal nur Extreme einer gleitenden Reihe dar. Herrn Prof. Dr. E. KLUG (Berlin) danke ich für die Durchsicht des Manuskripts und für werrvolle Diskussion, Herrn H. LÜNSER für die sorgfältige Ausführung der Zeichnungen, Frau I. EGGERT, Frau C. MÜLLER und Frau 1. POHL für die Hilfen bei der Vorbereitung des Manuskripts. Herrn Dr. M. SEAWARD (Bradford) bin ich für Beratung und Diskussion in Zusammenhang mit der Form der englischen Zusammenfassung sehr zu Dank verpflichter, 相似文献
96.
The involvement of transition metal ions in paraquat toxicity was studied in bacterial model system. We show that the addition of micromolar, or lower, concentrations of copper dramatically enhanced the rate of bacterial inactivation. In contrast, the addition of chelating agents totally eliminated the killing of E. coli. No inactivation was observed under anaerobic exposure to paraquat, both in the absence and presence of copper. However, in the presence of copper, the anaerobic addition of hydrogen peroxide resulted in complete restoration of inactivation as under aerobiosis.
Paraquat either produces superoxide ions or directly reduces bound copper ions in a catalytic mode. The reduced cuprous complexes react with hydrogen peroxide to locally form hydroxyl radicals (OH) which are probably responsible for the deleterious effects.
This study indicates the involvement of a site-specific metal-mediated Haber-Weiss mechanism in paraquat toxicity. It is in agreement with earlier observations that copper unusually enhance biological damage induced by either superoxide or ascorbate. 相似文献
Paraquat either produces superoxide ions or directly reduces bound copper ions in a catalytic mode. The reduced cuprous complexes react with hydrogen peroxide to locally form hydroxyl radicals (OH) which are probably responsible for the deleterious effects.
This study indicates the involvement of a site-specific metal-mediated Haber-Weiss mechanism in paraquat toxicity. It is in agreement with earlier observations that copper unusually enhance biological damage induced by either superoxide or ascorbate. 相似文献
97.
Richard B. Rothman Uwe K. Schumacher Candace B. Pert 《Journal of neurochemistry》1984,43(4):1197-1199
Abstract: (β-FNA, the β -fumaramate methyl ester of naltrexone, has been shown to antagonize irreversibly the actions of morphine on the guinea pig ileum and mouse vas deferens bioassays but does not affect the actions of δ-receptor ligands on the mouse vas deferens bioassay, suggesting that the compound does not irreversibly bind to the S receptor. In this paper we examine the effect of (β -FNA on the binding of the prototypic δ agonists, Leuenkephalin and d -Ala2 - d -Leu5 -enkephalin, its metabolically stable analogue, and show that treatment of membranes with β -FNA does lead to alterations in the in vitro properties of δ receptors. 相似文献
98.
The neuropeptides methionine enkephalin and FMRFamide, when injected into intact fiddler crabs, Uca pugilator, produce dark adaptation of the distal retinal pigment. Furthermore, both neuropeptides stimulate release of distal retinal pigment dark-adapting hormone activity from the isolated eyestalk neuroendocrine complex. It is hypothesized that both neuropeptides, when injected into intact fiddler crabs, act only indirectly on the distal retinal pigment, by stimulating release of this dark-adapting hormone. 相似文献
99.
Charles G. Crispens Philip S. Porter John R. J. Sorenson 《Biological trace element research》1986,10(1):19-24
Plasma copper and zinc levels were measured in SJL/J mice, an inbred strain characterized by a high, spontaneous incidence
of reticulum cell sarcoma (RCS). The changes with age in mean concentrations of these metals were consistent with a physiological
response that is required for remission of neoplasia. Treatment of SJL/J mice with a copper complex, Cu(II)(3,4-diisopropylsalicylate)2 (Cu 3,5-DIPS), dissolved in a 10% Tween 80-saline solution revealed a decrease in survival and decline in the incidence of
RCS at 52 wk of age. The toxic effects of Cu 3,5-DIPS therapy appeared to be related to the intraperitoneal route of administration
and to extracellular deposition of collagen. The inhibitory effect on tumor development was not related to Cu 3,5-DIPS. Rather,
Tween 80 was found to be the factor of importance. 相似文献
100.
The arrangement and function of the redox centers of the mammalianbc
1 complex is described on the basis of structural data derived from amino acid sequence studies and secondary structure predictions and on the basis of functional studies (i.e., EPR data, inhibitor studies, and kinetic experiments). Two ubiquinone reaction centers do exist—a QH2 oxidation center situated at the outer, cytosolic surface of the cristae membrane (Q0 center), and a Q reduction center (Q
i
center) situated more to the inner surface of the cristae membrane. The Q0 center is formed by theb-566 domain of cytochromeb, the FeS protein, and maybe an additional small subunit, whereas the Q
i
center is formed by theb-562 domain of cytochromeb and presumably the 13.4kDa protein (QP-C). The Q binding proteins are proposed to be protein subunits of the Q reaction centers of various multiprotein complexes. The path of electron flow branches at the Q0 center, half of the electrons flowing via the high-potential cytochrome chain to oxygen and half of the electrons cycling back into the Q pool via the cytochromeb path connecting the two Q reaction centers. During oxidation of QH2, 2H+ are released to the cytosolic space and during reduction of Q, 2H+ are taken up from the matrix side, resulting in a net transport across the membrane of 2H+ per e– flown from QH2 to cytochromec, the H+ being transported across the membrane as H (H+ + e–) by the mobile carrier Q. The authors correct their earlier view of cytochromeb functioning as a H+ pump, proposing that the redox-linkedpK changes of the acidic groups of cytochromeb are involved in the protonation/deprotonation processes taking place during the reduction and oxidation of Q. The reviewers stress that cytochromeb is in equilibrium with the Q pool via the Q
i
center, but not via the Q0 center. Their view of the mechanisms taking place at the reductase is a Q cycle linked to a Q-pool where cytochromeb is acting as an electron pump. 相似文献