全文获取类型
收费全文 | 15350篇 |
免费 | 1471篇 |
国内免费 | 2篇 |
专业分类
16823篇 |
出版年
2023年 | 50篇 |
2022年 | 148篇 |
2021年 | 297篇 |
2020年 | 150篇 |
2019年 | 223篇 |
2018年 | 283篇 |
2017年 | 238篇 |
2016年 | 500篇 |
2015年 | 783篇 |
2014年 | 829篇 |
2013年 | 1008篇 |
2012年 | 1275篇 |
2011年 | 1135篇 |
2010年 | 740篇 |
2009年 | 723篇 |
2008年 | 911篇 |
2007年 | 936篇 |
2006年 | 863篇 |
2005年 | 849篇 |
2004年 | 795篇 |
2003年 | 790篇 |
2002年 | 744篇 |
2001年 | 146篇 |
2000年 | 89篇 |
1999年 | 161篇 |
1998年 | 195篇 |
1997年 | 142篇 |
1996年 | 118篇 |
1995年 | 126篇 |
1994年 | 115篇 |
1993年 | 111篇 |
1992年 | 103篇 |
1991年 | 85篇 |
1990年 | 81篇 |
1989年 | 69篇 |
1988年 | 70篇 |
1987年 | 54篇 |
1986年 | 67篇 |
1985年 | 71篇 |
1984年 | 83篇 |
1983年 | 49篇 |
1982年 | 77篇 |
1981年 | 61篇 |
1980年 | 63篇 |
1979年 | 47篇 |
1977年 | 37篇 |
1976年 | 27篇 |
1974年 | 33篇 |
1972年 | 28篇 |
1971年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
A protein which specifically binds [3H]benzo[a]pyrene and other polycyclic aromatic hydrocarbons has been purified over 6000-fold from rat hepatic cytosol by using ion-exchange, gel permeation, and hydrophobic interaction chromatography. The binding protein differs from the 9S binding protein characterized in other laboratories. A Stokes radius of 2.75 nm was determined by gel filtration on Sephadex G-100. A sedimentation coefficient of 3.3 S was determined by using sucrose gradient analysis. The ability of this protein to bind total rat liver DNA as well as subclones containing portions of the rat cytochrome P-450c gene was investigated. Under high stringency conditions, this binding protein was found to interact in a specific and saturable manner with several subclones of the rat cytochrome P-450c gene containing 5'-upstream sequences, as well as portions of intron 1. Binding was not observed to the coding portions of the gene. These data implicate the "4S" binding protein in the transregulation of rat cytochrome P-450c expression. 相似文献
72.
Anne B. Clark 《International journal of primatology》1985,6(6):581-600
A 16-month field study of the nocturnal prosimianGalago crassicaudatus umbrosus in the Northern Transvaal, South Africa, revealed extensive homerange overlaps between adults of both sexes, age-graded
male tolerance, and a high rate of direct affiliative contact between individuals of most age-sex classes. These results contrast
with the general characterization of nocturnal lorisid sociality given by Charles-Dominique (1978). Nocturnal prosimians’
dispersion while foraging supports the predation model of group cohesion in diurnal primates. The problem of group size and
cohesion should be divorced from that of social networks and social complexity. There may be benefits to social interactions
which transcend group living. The more subtle differences in nocturnal prosimian sociality need to be reconsidered in the
light of current sociobiological and socioecological theory. 相似文献
73.
Summary A microtechnique for the detection of DNA or RNA in small numbers of plant cells (1–50) has been developed using cauliflower mosaic virus (CaMV) infection of turnip as a model system. Both DNA and RNA extracted from 10 mesophyll protoplasts from CaMV-infected plants can be detected by hybridization using a radioactive probe made from cloned CaMV DNA (pCaMV10). No hybridization above background was detected in extracts of protoplasts from uninfected plants. At least 0.15 pg (11 000 molecules) of purified pCaMV10 DNA can be detected. This method is superior to existing macro techniques for nucleic acid detection as smaller amounts of tissue are required and the detection is approximately 100-fold more sensitive. re]19850326 rv]19850530 ac]19850611 相似文献
74.
Dr. Michel Jangoux Philippe Dubois Anne Lambert Catherine Yourassowsky 《Cell and tissue research》1985,242(3):657-660
Summary A microcanalicular network is demonstrated within the ossicle stroma and the dermal tissue of two asteroid species. Microcanaliculi are presumed to be mesodermal structures. They consist of convoluted tubular ducts lined by epithelial cells associated with scattered basiepithelial nervous processes. Such a microcanalicular system has not been reported previously from any echinoderm species. Its discovery in asteroids entails some conceptual changes, especially considering the physiology of the body wall.Research assistants of the National Fund for Scientific Research (NFSR, Belgium) 相似文献
75.
The major factors thought to control the distribution of associations on the sea cliffs in Britain are discussed in relation to the zonation of cliff vegetation, and some experiments to investigate the effects of these factors are described.The seeds of the maritime cliff species are able to germinate in higher salinities than those of closely related inland species.Relative growth rates of maritime cliff species indicate stimulation at low salinities over non-saline conditions, and less reduction in growth at higher salinities than those of closely related inland species.Increasing salinity reduces both photosynthesis and dark respiration in Lavatera arborea. Mesophyll and stomatal resistances are increased while transpiration is reduced.The distribution of ions within Lavatera arborea grown at different salinities indicates differential accumulation between young leaves, old leaves and roots.Nomenclature follows Clapham, Tutin & Warburg (1962). 相似文献
76.
77.
Two computer controlled experiments in an olfactory cross-modal matching task, using two-component odour mixtures matched against bar diagrams, were designed so that stimulus presentation was contingent upon the recent performance of the subject; stimuli that were relatively poorly (in experiment 1) or well (in experiment 2) matched were more frequently presented. Analysis shows that the autoregressive structure of the performance is modified by such contingent presentation and that there is a weak relationship between transmitted information in matching and the time series structure of the matching errors. It is suggested that the process is nonlinear. 相似文献
78.
79.
The effect of ampicillin and tylosin on the faecal enterococci of healthy young chickens 总被引:2,自引:2,他引:0
Enterococcal isolates from young chickens were differentiated into one of three species, namely Enterococcus faecalis, Ent. faecium and Ent. gallinarum . The proportion of each species among the enterococcal population changed with time in birds not dosed with antibiotics. This pattern of change was modified in birds dosed with either tylosin or ampicillin even though ampicillin did not select for ampicillin resistance among the enterococcal population. A gradual increase in tylosin resistance was recorded with time among the enterococci of the 'undosed' control birds. This was associated with an increase in the proportion of Ent. faecium , a species commonly resistant to tylosin, among the enterococci of the birds as they grew older. 相似文献
80.
Several models have been proposed to interpret the mechanism of proton-pumping associated with the electron transfer reactions in the cytochrome b/f complex. Energetics considerations suggest that the proton pump is coupled to the oxidation of cytochrome b by plastoquinone. Experiments performed in living cells under anaerobic conditions suggest that proton-pumping can occur through two independent mechanisms. When the two b cytochromes are reduced prior to a flash illumination i.e. after a long dark anaerobic incubation (>10 minutes), proton-pumping is very likely associated with the reduction of a semiquinone by cyt b which occurs at a site close to the inner face of the membrane. The electrogenic phase is associated with the tranfer of protons via a transmembrane channel. This process is not inhibited by 2-n-nonyl-4-hydroxyquinoline N-oxide (NQNO). Under repetitive-flash or under aerobic conditions, proton-pumping occurs according to a modified Q-cycle mechanism, which is inhibited by NQNO.Dedicated to Prof. L.N.M. Duysens on the occasion of his retirement 相似文献