全文获取类型
收费全文 | 6067篇 |
免费 | 700篇 |
国内免费 | 413篇 |
专业分类
7180篇 |
出版年
2024年 | 37篇 |
2023年 | 107篇 |
2022年 | 162篇 |
2021年 | 250篇 |
2020年 | 366篇 |
2019年 | 452篇 |
2018年 | 322篇 |
2017年 | 245篇 |
2016年 | 248篇 |
2015年 | 269篇 |
2014年 | 322篇 |
2013年 | 506篇 |
2012年 | 268篇 |
2011年 | 260篇 |
2010年 | 238篇 |
2009年 | 282篇 |
2008年 | 305篇 |
2007年 | 269篇 |
2006年 | 256篇 |
2005年 | 217篇 |
2004年 | 208篇 |
2003年 | 161篇 |
2002年 | 165篇 |
2001年 | 134篇 |
2000年 | 100篇 |
1999年 | 125篇 |
1998年 | 104篇 |
1997年 | 93篇 |
1996年 | 62篇 |
1995年 | 80篇 |
1994年 | 67篇 |
1993年 | 49篇 |
1992年 | 53篇 |
1991年 | 53篇 |
1990年 | 39篇 |
1989年 | 31篇 |
1988年 | 34篇 |
1987年 | 34篇 |
1986年 | 31篇 |
1985年 | 35篇 |
1984年 | 23篇 |
1983年 | 11篇 |
1982年 | 25篇 |
1981年 | 12篇 |
1980年 | 15篇 |
1979年 | 12篇 |
1978年 | 7篇 |
1977年 | 7篇 |
1976年 | 9篇 |
1974年 | 6篇 |
排序方式: 共有7180条查询结果,搜索用时 15 毫秒
1.
2.
Few fish species form single, panmictic populations throughout their geographic range, most form subpopulations or 'stocks' with differing levels of interconnectivity. Different patterns of interconnectivity between subpopulations will give rise to different responses to exploitation and management, but they will also have different capacities to generate the genetic and phenotypic differences often used to discriminate between stocks. Consequently, knowledge of ontogenetic and seasonal patterns in the distribution, movement and behaviour of individuals is crucial to identifying population substructure. This paper considers the evidence gathered about movements and behaviour of adult fishes from mark-recapture and electronic tagging studies for a number of fish species in the North Sea and elsewhere in U.K. waters in an attempt to understand population structure and the processes that may give rise to it. 相似文献
3.
4.
Summary The intercellular contacts of the migrating edge of chick and quail blastoderms during gastrulation were studied by transmission electron microscopy of thin sections and of freeze-fracture replicas. Tight junctions and gap junctions as well as desmosomes were found. Tight junctions were organized as single junctional strands or as a complex of numerous junctional strands interposed between the lamellae and the bodies of the cells building up the margin of overgrowth. The function of these intercellular junctions is considered in relation to the locomotion of the margin of overgrowth cells. 相似文献
5.
Several aspects of a diel vertical migration (DVM) of adultEudiaptomus gracilis in Lake Maarsseveen (The Netherlands) are described. The period of DVM lasted from the end of May until the middle of August. On May 21, 1989, the population was found divided into a deep dwelling part and a part in the upper five meter. Large shoals of juvenile perch were observed in the open water for the first time. On June 7, the whole population was down below 10 m and concentrated in a zone of high chlorphyll-a concentrations. One week later, a regular DVM was performed. The amplitude of this migration gradually decreased towards the end of the migration period. The ascent in the evening and the descent in the morning took place after sunset and before sunrise, respectively. The movements coincided with high relative changes in light intensity. Population size increased rapidly during the period of DVM but decreased again before the end of this period. 相似文献
6.
7.
The laminated structure of the optic tectum is formed by radial and tangential cell migration during development. Studies of developing chick optic tectum have revealed two streams of tangential cell migration in the middle and superficial layers, which have distinctive origins, migratory paths, modes of migration, and destinations. We will review the process of the two types of tangential migrations, in order to elucidate their roles in the formation of the optic tectum layers. 相似文献
8.
A. Doisy S. Paillasson P. Tracqui F. Germain F. Leitner M. Robert-Nicoud X. Ronot 《Cell biology and toxicology》1996,12(4-6):363-366
The organization of eukaryotic chromatin is not static but changes as a function of cell status during processes such as proliferation, differentiation, and migration. DNA quantification has not been used extensively to investigate chromatin dynamics in combination with cellular migration. In this context, an optimized DNA-specific, nonperturbant method has been developed for studying chromatin organization, using the fluorescent vital bisbenzimidazole probe Hoechst 33342: this property has been described by Hamori et al. (1980). Computer-assisted image analysis was used to follow migratory activity and chromatin organization of L929 fibroblasts during in vitro wound healing. Cell movements were analyzed using an optical flow technique, which consists in the calculation of the velocity field of cells and nuclear movements in the frame. This system allows the correlation of cell migration and position in the cell cycle. It makes it possible to study chromatin dynamics using a quantitative analysis of nuclear differentiation reorganization (nuclear texture) and to correlate this with migration characteristics. The present system would be of interest for studying cell-extracellular matrix interactions using differing substrates, and also the migratory response to chemotactic factors. Such a model is a prerequisite for gaining better understanding of drug action. 相似文献
9.
10.