全文获取类型
收费全文 | 114835篇 |
免费 | 2270篇 |
国内免费 | 817篇 |
出版年
2022年 | 176篇 |
2021年 | 342篇 |
2020年 | 156篇 |
2019年 | 278篇 |
2018年 | 12034篇 |
2017年 | 10886篇 |
2016年 | 7893篇 |
2015年 | 1369篇 |
2014年 | 1202篇 |
2013年 | 1404篇 |
2012年 | 5712篇 |
2011年 | 14280篇 |
2010年 | 12930篇 |
2009年 | 9035篇 |
2008年 | 11037篇 |
2007年 | 12625篇 |
2006年 | 1414篇 |
2005年 | 1674篇 |
2004年 | 2072篇 |
2003年 | 2153篇 |
2002年 | 1825篇 |
2001年 | 608篇 |
2000年 | 443篇 |
1999年 | 356篇 |
1998年 | 309篇 |
1997年 | 246篇 |
1996年 | 194篇 |
1995年 | 189篇 |
1994年 | 175篇 |
1993年 | 216篇 |
1992年 | 275篇 |
1991年 | 254篇 |
1990年 | 197篇 |
1989年 | 200篇 |
1988年 | 198篇 |
1987年 | 174篇 |
1986年 | 168篇 |
1985年 | 182篇 |
1984年 | 172篇 |
1983年 | 175篇 |
1982年 | 151篇 |
1981年 | 153篇 |
1980年 | 154篇 |
1979年 | 116篇 |
1978年 | 106篇 |
1977年 | 112篇 |
1975年 | 100篇 |
1974年 | 94篇 |
1972年 | 339篇 |
1971年 | 325篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
151.
Theoretical models for cooperative steady-state ATPase activity of myosin subfragment-1 on regulated actin 总被引:3,自引:0,他引:3 下载免费PDF全文
Recent theoretical work on the cooperative equilibrium binding of myosin subfragment-1-ADP to regulated actin, as influenced by Ca2+, is extended here to the cooperative steady-state ATPase activity of myosin subfragment-1 on regulated actin. Exact solution of the general steady-state problem will require Monte Carlo calculations. Three interrelated special cases are discussed in some detail and sample computer (not Monte Carlo) solutions are given. The eventual objective is to apply these considerations to in vitro experimental data and to in vivo muscle models. 相似文献
152.
Willoughby de Broke Rudyard Kipling Hugh Elliot E. Ray Lankester Leonard Hill Laurence R. Philipps Wm. Arbuthnot Lane James Crichton-Browne H. Bryan Donkin Francis Lloyd R. A. Lyster John MacAlister F. W. Mott William Osler C. W. Saleeby J. H. Sequeira Humphry Rolleston Hugh Wansey Bayly 《BMJ (Clinical research ed.)》1919,2(3074):725
153.
154.
155.
Background
Arsenic contamination is widespread throughout the world and this toxic metalloid is known to cause cancers of organs such as liver, kidney, skin, and lung in human. In spite of a recent surge in arsenic related studies, we are still far from a comprehensive understanding of arsenic uptake, detoxification, and sequestration in plants. Crambe abyssinica, commonly known as 'abyssinian mustard', is a non-food, high biomass oil seed crop that is naturally tolerant to heavy metals. Moreover, it accumulates significantly higher levels of arsenic as compared to other species of the Brassicaceae family. Thus, C. abyssinica has great potential to be utilized as an ideal inedible crop for phytoremediation of heavy metals and metalloids. However, the mechanism of arsenic metabolism in higher plants, including C. abyssinica, remains elusive. 相似文献156.
Transnational Migration in Rural Oaxaca, Mexico: Dependency, Development, and the Household 总被引:1,自引:0,他引:1
Contradictory models of dependency and development have dominated the discussion of migration between Mexico and the United States. Transnational models of migration resolve these contradictions by defining a series of interdependencies (economy and society, for example). Using data collected in a rural Zapotec community in Oaxaca, Mexico, this article focuses on three areas: the stage-specific development of transnational movement; the domestic cycle, household decision making, and migration/remittance outcomes; and the changing nature of community participation. Rooting the discussion in household decision making captures the important role local social variability and economic dynamism play in understanding transnational processes and advancing migration studies. [ households, migration, transnationalism, dependency and development, Oaxaca, Mexico ] 相似文献
157.
Meal prepared from unheated rapeseed (Brassica napus cv. Zephyr) showed the presence of t,iocyanate ion, while meal from heated seed of the same cultivar did not show detectable amounts. Unheated seed meal on autolysis, and heated seed meal on incubation with thioglucosidase, yielded increased amounts of thiocyanate ion. Various commercial rapeseed meals showed the presence of t,iocyanate ion only after enzyme incubation. Low glucosinolate, cv. Bronowski, and higher glucosinolate, cv. Zephyr on enzymic incubation yielded comparable amounts of thiocyanate ion, suggesting that the precursor responsible in the two varieties was the same and present in similar quantities. No formation of thiocyanate ion was observed on incubation of sinigrin with thioglucosidase. Rats dosed with heated meal, containing intact glucosinolate, showed a slight increase of thiocyanate ion in the urine as compared with control rats dosed with water, while a relatively large increase followed dosing with sinigrin. Rats dosed with meal containing free thiocyanate ion excreted the ingested thiocyanate ion almost quantitatively. 相似文献
158.
Background
Meiotic prophase is a critical stage in sexual reproduction. Aberrant chromosome recombination during this stage is a leading cause of human miscarriages and birth defects. However, due to the experimental intractability of mammalian gonads, only a very limited number of meiotic genes have been characterized. Here we aim to identify novel meiotic genes important in human reproduction through computational mining of cross-species and cross-sex time-series expression data from budding yeast, mouse postnatal testis, mouse embryonic ovary, and human fetal ovary. 相似文献159.
Kasper Stovgaard Christian Andreetta Jesper Ferkinghoff-Borg Thomas Hamelryck 《BMC bioinformatics》2010,11(1):429
Background
Genome sequencing projects have expanded the gap between the amount of known protein sequences and structures. The limitations of current high resolution structure determination methods make it unlikely that this gap will disappear in the near future. Small angle X-ray scattering (SAXS) is an established low resolution method for routinely determining the structure of proteins in solution. The purpose of this study is to develop a method for the efficient calculation of accurate SAXS curves from coarse-grained protein models. Such a method can for example be used to construct a likelihood function, which is paramount for structure determination based on statistical inference. 相似文献160.
Food sharing: a model of manipulation by harassment 总被引:3,自引:1,他引:2
Most analyses of food-sharing behavior invoke complex explanationssuch as indirect and delayed benefits for sharing via kin selectionand reciprocal altruism. However, food sharing can be a moregeneral phenomenon accounted for by more parsimonious, mutualisticexplanations. We propose a game theoretical model of a generalsharing situation in which food owners share because it is
in their own self-interestthey avoid high costs associatedwith beggar harassment. When beggars harass, owners may benefitfrom sharing part of the food if their consumption rate islow relative to the rate of cost accrual. Our model predictsthat harassment can be a profitable strategy for beggars if
they reap some direct benefits from harassing other than sharedfood (such as picking up scraps). Therefore, beggars may manipulatethe owner's fitness payoffs in such a way as to make sharingmutualistic. 相似文献