全文获取类型
收费全文 | 60701篇 |
免费 | 4050篇 |
国内免费 | 5548篇 |
专业分类
70299篇 |
出版年
2023年 | 931篇 |
2022年 | 1268篇 |
2021年 | 1503篇 |
2020年 | 1475篇 |
2019年 | 2154篇 |
2018年 | 2013篇 |
2017年 | 1617篇 |
2016年 | 1508篇 |
2015年 | 1555篇 |
2014年 | 2871篇 |
2013年 | 3757篇 |
2012年 | 2240篇 |
2011年 | 2727篇 |
2010年 | 2123篇 |
2009年 | 2750篇 |
2008年 | 2911篇 |
2007年 | 3124篇 |
2006年 | 2904篇 |
2005年 | 2375篇 |
2004年 | 2083篇 |
2003年 | 2026篇 |
2002年 | 1827篇 |
2001年 | 1509篇 |
2000年 | 1277篇 |
1999年 | 1151篇 |
1998年 | 1109篇 |
1997年 | 1044篇 |
1996年 | 1008篇 |
1995年 | 1000篇 |
1994年 | 978篇 |
1993年 | 880篇 |
1992年 | 845篇 |
1991年 | 824篇 |
1990年 | 691篇 |
1989年 | 659篇 |
1988年 | 590篇 |
1987年 | 574篇 |
1986年 | 514篇 |
1985年 | 768篇 |
1984年 | 1036篇 |
1983年 | 805篇 |
1982年 | 836篇 |
1981年 | 686篇 |
1980年 | 678篇 |
1979年 | 600篇 |
1978年 | 478篇 |
1977年 | 435篇 |
1976年 | 395篇 |
1974年 | 253篇 |
1973年 | 270篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
Elizabeth Holt 《Dialectical Anthropology》2005,29(3-4):387-396
In this paper, I read Leïla Sebbar’s staging in her novel Shérazade: 17 ans, brune, frisée, les yeux verts of the resistance by children of North African and other immigrants in the early 1980s to the French state’s cartographic modes and documents of control. The paper will consider the many uses to which the map was put by the French state in its colonization of North Africa and particularly Algeria, and later in its attempts to control the banlieues its policies of citizenship and cartographic control yielded on the margins of Paris. In this context, I will explore the ways in which the novel’s characters, living clandestinely in a squatt, simultaneously resist, put to use, and even supercede state documents of control as they disrupt everyday life and conduct heists across the city of Paris. The paper will explore unofficial cartographies of Paris, from those afforded by the radios libres and alternative publications such as Libération and Sans Frontièrez, to oral and almost proverbial networks of knowledge criss-crossing the city of Paris, while also tracing the uses to which supplemental cartographic sketches and counterfeit identity cards are put in the pages of the novel. The paper will be in dialogue with theoretical and critical formulations of space, cartography, and state control put forward by Michel de Certeau, Henri Lefebvre, Michel Foucault, and Tom Conley. The paper will conclude with a consideration of the means and limits of resistance by the novel’s characters in the context of this body of theory and criticism. 相似文献
72.
Abstract: The enzymatic hydrolysis of UDP-galactose in rat and calf brain was studied. The hydrolysis occurs in two steps: The first is the conversion of UDP-galactose to galactose-1-phosphate catalyzed by nucleotide pyrophosphatase (EC 3.6.1.9), and the second is the conversion of the latter to free galactose by alkaline phosphatase (EC 3.1.3.1). The overall conversion has a pH optimum of 9.0, but there is considerable activity at pH 7.4, which is the optimum for UDP-galactose:ceramide galactosyltransferase in the synthesis of cerebrosides. Preparations from cytosol from calf brain cerebellum or stem that were enriched in UDP-galactose hydrolytic activity inhibit cerebroside synthesis under conditions optimal for the synthesis. Microsome-rich and nuclear debris fractions contain the highest apparent specific activity among the subcellular fractions studied. Hydrolysis of UDP-galactose occurs in all areas of brain, brainstem having the highest activity. The apparent specific activity in jimpy mouse brain homogenate is nearly twice as high as in the control brain homogenate. 相似文献
73.
G. Karrer 《Plant Ecology》1985,59(1-3):199-209
Five plant communities contrasting in successional status and human impact from the southern part of the ‘Wienerwald’ (Austria) are analyzed using vegetation relevés, spectra of area types and a newly proposed disjunction quotient. A climax community (Asperulo-Fagetum), a subclimax community (Querco-Carpinetum s.l.), an anthropogenous substitute community (Mesobromion) and two natural, non-climax permanent communities (Euphorbio saxatilis-Pinetum nigrae and Fumano-Stipetum eriocaulis) are recognized. The disjunction quotient is defined as the number of partial (discontinous) areas divided by the size of the total area of distribution of a species. In particular, the average disjunction quotients of the species in the first two communities reflect relatively table environments only slightly influenced by man, with many ancient, stable taxa. These communities are characterized by species with well-delimited, stable distribution areas. The species in the Mesobromion community have very low average disjunction quotients as its component species are widely and continuously distributed and are often promoted by man. In contrast to these communities, the species linked to the natural permanent, non-climax communities of extreme habitats, have high distribution quotients i.e. small, disconinuous areas; this illustrates the relic character of these plant communities and of the eastern edge of the Alps is a whole. Using the highly variable disjunction quotient of all species and communities examined, the concepts of climax and permanent communities (of different origin) are discussed with regard to European conditions. 相似文献
74.
75.
《Journal of biological dynamics》2013,7(4):318-334
In this paper, we study a two-species competitive system where both the species produce toxin against each other at some cost to their growth rates. A much wider set of outcomes is possible for our system. These outcomes are important contrasts to competitive exclusion or bistable attractors that are often the outcomes for competitive systems. We show that toxin helps to gain an advantage in competition for toxic species whenever the cost of toxin production remains within some moderate value; otherwise it may result in the extinction of the species itself. 相似文献
76.
DefattedMadhuca butyraceae seeds contain 24% of crude protein and 10.4% of saponins. The solubility ofMadhuca seed proteins was determined in water and NaCl as a function of pH and minimum solubility occurred at pH 4.0. The proteins
consist of three components with S20,w values of 2.2, 9.8 and 15.4. On gel filtration the proteins gave three peaks and on diethylaminoethyl cellulose chromatography
they resolved into two components. Thein vitro digestibility ofMadhuca seed protein was found to be 69% when assayed with a pepsin-pancreatin system. 相似文献
77.
78.
Abstract: Slices cut from five frozen human brains were dissected into 2-mm cubes and assayed for choline acetyltransferase (ChAT) activity and protein content. A pattern of enrichment of ChAT activity was found ventral to the anterior commissure; this finding is consistent with the location of the enzyme in the cells of the nucleus basalis of Meynert. The region beneath the anterior commissure was the only place a discrete enrichment of activity could be found, and the precise topography of the enrichment was somewhat variable from brain to brain. The results are discussed in the light of recent knowledge concerning the source of the cortical cholinergic innervation. 相似文献
79.
Felix Roosen-Runge Marcus Hennig Tilo Seydel Fajun Zhang Maximilian W.A. Skoda Stefan Zorn Robert M.J. Jacobs Marco Maccarini Peter Fouquet Frank Schreiber 《Biochimica et Biophysica Acta - Proteins and Proteomics》2010,1804(1):68-75
We report on a combined cold neutron backscattering and spin-echo study of the short-range and long-range nanosecond diffusion of the model globular protein bovine serum albumin (BSA) in aqueous solution as a function of protein concentration and NaCl salt concentration. Complementary small angle X-ray scattering data are used to obtain information on the correlations of the proteins in solution. Particular emphasis is put on the effect of crowding, i.e. conditions under which the proteins cannot be considered as objects independent of each other. We thus address the question at which concentration this crowding starts to influence the static and in particular also the dynamical behaviour. We also briefly discuss qualitatively which charge effects, i.e. effects due to the interplay of charged molecules in an electrolyte solution, may be anticipated. Both the issue of crowding as well as that of charge effects are particularly relevant for proteins and their function under physiological conditions, where the protein volume fraction can be up to approximately 40% and salt ions are ubiquitous. The interpretation of the data is put in the context of existing studies on related systems and of existing theoretical models. 相似文献
80.
Abstract Both the intracellular and the extracellular concentration of cyclic AMP increases logarithmically in synchronously growing cultures of Escherichia coli . Thus, cyclic AMP by itself cannot regulate growth and division of the bacterium during the cell cycle. 相似文献