全文获取类型
收费全文 | 5947篇 |
免费 | 700篇 |
国内免费 | 3篇 |
出版年
2021年 | 85篇 |
2020年 | 46篇 |
2019年 | 57篇 |
2018年 | 74篇 |
2017年 | 81篇 |
2016年 | 105篇 |
2015年 | 153篇 |
2014年 | 200篇 |
2013年 | 289篇 |
2012年 | 292篇 |
2011年 | 298篇 |
2010年 | 202篇 |
2009年 | 166篇 |
2008年 | 236篇 |
2007年 | 267篇 |
2006年 | 244篇 |
2005年 | 219篇 |
2004年 | 215篇 |
2003年 | 204篇 |
2002年 | 199篇 |
2001年 | 139篇 |
2000年 | 162篇 |
1999年 | 131篇 |
1998年 | 96篇 |
1997年 | 71篇 |
1996年 | 78篇 |
1995年 | 67篇 |
1994年 | 59篇 |
1993年 | 59篇 |
1992年 | 109篇 |
1991年 | 102篇 |
1990年 | 83篇 |
1989年 | 87篇 |
1988年 | 105篇 |
1987年 | 104篇 |
1986年 | 81篇 |
1985年 | 83篇 |
1984年 | 97篇 |
1983年 | 85篇 |
1982年 | 54篇 |
1981年 | 67篇 |
1980年 | 58篇 |
1979年 | 78篇 |
1978年 | 50篇 |
1977年 | 45篇 |
1976年 | 55篇 |
1975年 | 41篇 |
1974年 | 55篇 |
1973年 | 43篇 |
1969年 | 44篇 |
排序方式: 共有6650条查询结果,搜索用时 31 毫秒
11.
12.
Draud Matthew; Macias-Ordonez Rogelio; Verga Jack; Itzkowitz Murray 《Behavioral ecology》2004,15(1):102-108
Selection usually acts differently on males and females duringintrasexual competition for resources and/or mates. Nevertheless,agonistic behavior has been examined both theoretically andempirically mostly in males. Our research questions whethermales and females follow the same rules of engagement in intrasexualcontests as predicted by the sequential assessment model (SAM).The SAM predicts negative correlations between contest intensityand duration and the magnitude of asymmetry in resource holdingpower (RHP) between the contestants, such that the most escalatedcontests are those between similarly endowed individuals. Westaged male and female intrasexual contests with varying degreesof body size asymmetry under a round robin design using themonogamous Texas cichlid fish (Herichthys cyanoguttatum) asa study case. We used Mantel's matrix analysis to compare howthe behavioral content, duration, structure, and outcome ofmale and female contests were affected by the relative bodysize of the contestants. In the case of males, relative sizein each contest predicted outcome, duration, and frequency ofconventional and escalated behaviors according to prevailingtheory. Female contest structure and outcome, however, werenot predicted by the relative size of contestants. We discussour results in terms of other asymmetries that might be importantin structuring female contests, and we propose potential approachesto study femalefemale aggression. 相似文献
13.
14.
15.
16.
HCC ligation: rapid and specific DNA construction with blunt ended DNA fragments. 总被引:1,自引:0,他引:1 下载免费PDF全文
J A Murray 《Nucleic acids research》1986,14(24):10118
17.
Neuron differentiation and axon growth in the developing wing of Drosophila melanogaster 总被引:2,自引:0,他引:2
Sensory neurons in the wing of Drosophila originate locally from epithelial cells and send their axons toward the base of the wing in two major bundles, the L1 and L3 nerves. We have estimated the birth times of a number of identified wing sensory neurons using an X-irradiation technique and have followed the appearance of their somata and axons by means of an immunohistochemical stain. These cells become immunoreactive and begin axon growth in a sequence which mirrors the sequence of their birth times. The earliest ones are born before pupariation and begin axonogenesis within 1 to 2 hr after the onset of metamorphosis; the last are born and differentiate some 12 to 14 hr later. The L1 and L3 nerves are formed in sections, with specific neurons pioneering defined stretches of the pathways during the period between 0 and 4 hr after pupariation (AP), and finally joining together around 12 hr AP. By 16 hr AP the adult complement of neurons is present and the adult peripheral nerve pattern has been established. Pathway establishment appears to be specified by multiple cues. In places where neurons differentiate in close proximity to one another, random filopodial exploration followed by axon growth to a neighboring neuron soma might be the major factor leading to pathway construction. In other locations, filopodial contact between neighboring somata does not appear to occur, and axon pathways joining neural neighbors by the most direct route are not established. We propose that in these cases additional factors, including veins which are already present at the time of axonogenesis, influence the growth of axons through non-neural tissues. 相似文献
18.
Andrew W. Saxe Ji-Won Yoon Phillip Gorden Murray F. Brennan 《In vitro cellular & developmental biology. Plant》1982,18(10):884-890
Summary Dispersed cells from both fresh and cryopreserved human insulinoma have been maintained in cell culture. Initial yield of
viable cells was 50% for fresh and 25% for cryopreserved tissue. Viability of cells in culture was documented by increasing
numbers of cells (doubling time approximately 5 d initially and 2 d at the sixth subculture for both fresh and cryopreserved
tissue) and continued release of insulin over time (approximately 100 ng/ml per 105 cells at 10 d and 175 ng/ml per 105 cells at 30 d of culture for both fresh and cryopreserved tissue). Evidence that cells growing in culture were beta cells
was provided by: (a) recovery of intracellular and extracellular immunoreactive insulin (IRI), (b) electron microscopic morphology,
and (c) immunohistochemical staining. Cells from fresh insulinoma incubated with increasing concentrations of extracellular
glucose released increasing amounts of IRI up to approximately 15 mM glucose, which paralleled changes in plasma insulin obtained during a preoperative glucose tolerance test.
Under an Intergovernmental Personnel Act Exchange from the Department of Surgery, University of California, Davis, Sacramento
Medical Center. 相似文献
19.
G Murray Jones 《BMJ (Clinical research ed.)》1981,283(6303):1406-1407
20.
K Murray S Stahl P G Ashton-Rickardt 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》1989,324(1224):461-476
The simplest application of the modern genetic manipulation methods to vaccine development is the expression in microbial cells of genes from pathogens that encode surface antigens capable of inducing neutralizing antibodies in the host of the pathogen involved. This procedure has been exploited successfully for development of a vaccine against hepatitis B virus (HBV) that is now widely used. Similar approaches have been directed towards formulations for immunization against several other animal and human diseases and some of these preparations are now presently in trials. Of no less importance is the impact of biotechnology in providing reagents for fundamental studies of topics such as the determination of virulence, antigenic variation, virus receptors and the immunological response to viral antigens. The core antigen of HBV is a good example of a product of genetic engineering that is a valuable diagnostic reagent, and that is finding important use in immunological studies of particular pertinence to vaccine development. 相似文献