全文获取类型
收费全文 | 3182篇 |
免费 | 309篇 |
国内免费 | 160篇 |
出版年
2024年 | 11篇 |
2023年 | 63篇 |
2022年 | 80篇 |
2021年 | 130篇 |
2020年 | 112篇 |
2019年 | 146篇 |
2018年 | 107篇 |
2017年 | 106篇 |
2016年 | 155篇 |
2015年 | 181篇 |
2014年 | 240篇 |
2013年 | 267篇 |
2012年 | 186篇 |
2011年 | 158篇 |
2010年 | 132篇 |
2009年 | 193篇 |
2008年 | 157篇 |
2007年 | 154篇 |
2006年 | 141篇 |
2005年 | 132篇 |
2004年 | 127篇 |
2003年 | 131篇 |
2002年 | 93篇 |
2001年 | 65篇 |
2000年 | 56篇 |
1999年 | 47篇 |
1998年 | 42篇 |
1997年 | 34篇 |
1996年 | 41篇 |
1995年 | 18篇 |
1994年 | 31篇 |
1993年 | 13篇 |
1992年 | 14篇 |
1991年 | 13篇 |
1990年 | 13篇 |
1989年 | 5篇 |
1988年 | 14篇 |
1987年 | 12篇 |
1986年 | 5篇 |
1985年 | 12篇 |
1984年 | 7篇 |
1983年 | 1篇 |
1982年 | 4篇 |
1979年 | 2篇 |
排序方式: 共有3651条查询结果,搜索用时 31 毫秒
1.
H. Ronald Pulliam 《Human ecology: an interdisciplinary journal》1982,10(3):353-363
Patterns of conflict and cooperation both within and between societies may be related to the degree of cultural similarity within and between the same societies. A simple model of social learning is used to predict patterns of conflict and cooperation in hypothetical societies that differ in the roles of relatives and nonrelatives in the enculturation of children. The model is illustrated by comparing its predictions to known differences in the patterns of conflict between males inpatrilocal and matrilocal societies. 相似文献
2.
《Current biology : CB》2022,32(3):645-653.e8
Download : Download video (10MB) 相似文献
3.
4.
5.
Ronald E. Koes Cornelis E. Spelt Jos N. M. Mol Anton G. M. Gerats 《Plant molecular biology》1987,10(2):159-169
Chalcone synthase (CHS) genes in Petunia hybrida comprise a multigene family containing at least 7 complete members in the strain Violet 30 (V30). Based on a high sequence homology in both coding and non-coding sequence, a number of CHS genes can be placed into two subfamilies. By restriction fragment length polymorphism (RFLP) analysis it was shown that both chromosomes II and V carry one of these subfamilies, in addition to the other CHS genes identified so far. Members of a subfamily were found to be closely linked genetically. Analysis of the Petunia species that contributed to the hybrid nature of P. hybrida (P. axillaris, P. parodii, P. inflata and P. violacea) shows that none of the CHS gene clusters is specific for either one of the parents and therefore did not arise as a consequence of the hybridization. The number of CHS genes within a subfamily varies considerably among these Petunia species. From this we infer that the CHS subfamilies arose from very recent gene duplications. 相似文献
6.
Summary A method for isolating high quality DNA from wholeEuglena cells is described. The procedure consists in: the weakening of the cell pellicle in glycerol avoiding the mechanical disruption of cells and shearing damage in DNA molecules; the decondensation ofEuglena compact chromatin directly inside the cells; the complete dissociation of cells and nucleoproteins in sarkosyl detergent; the optional digestion of proteins and RNA with DNase-free enzymes and the final purification of DNA by isopycnic banding in CsCl gradients. Degradation of DNA is prevented all along the extraction procedure by glycerol, antioxydants, EDTA and sarkosyl detergent. Using the enzymatic digestion step, DNA containing few single-stranded nicks is obtained with a yield approaching 100%. DNA with no single-stranded nick could be obtained with a 35% yield when the enzymatic digestion step was omitted. In both cases, the double-stranded DNA has an average molecular weight equal or greater than 6×107. It is free of contaminants and could be easily digested with restriction enzymes. After digestion with Eco RI and size-fractionation in agarose gel this DNA has permitted specific hybridization of the rDNA sequences with a radioactive rRNA probe.Abbreviations Kbp
kilobasepairs
- Kb
kilobases 相似文献
7.
Ronald E. Koes Cornelis E. Spelt Jos N. M. Mol Anton G. M. Gerats 《Plant molecular biology》1988,10(4):375-385
Chalcone synthase (CHS) genes in Petunia hybrida comprise a multigene family containing at least 7 complete members in the strain Violet 30 (V30). Based on a high sequence homology in both coding and non-coding sequence, a number of CHS genes can be placed into two subfamilies. By restriction fragment length polymorphism (RFLP) analysis it was shown that both chromosomes II and V carry one of these subfamilies, in addition to the other CHS genes identified so far. Members of a subfamily were found to be closely linked genetically. Analysis of the Petunia species that contributed to the hybrid nature of P. hybrida (P. axillaris, P. parodii, P. inflata and P. violacea) shows that none of the CHS gene clusters is specific for either one of the parents and therefore did not arise as a consequence of the hybridization. The number of CHS genes within a subfamily varies considerably among these Petunia species. From this we infer that the CHS subfamilies arose from very recent gene duplications. 相似文献
8.
9.
Summary
Dalbergia sissoo, a wind-dispersed tropical tree, shows a positively skewed distribution of seeds per pod. This is attributed to the enhanced dispersal advantage of few-seeded pods due to their reduced wing loading (ratio of weight to pod surface area) and low settling velocity. The proximate mechanisms causing the positively skewed distribution were investigated. The distribution could not be attributed to the distribution pattern of ovule number per ovary, pollen grain limitation, lack of ovule fertilization, or post-fertilization elimination of many-seeded pods. Rather, it was caused by the post-fertilization abortion of seeds within a pod 2 weeks after fertilization. This intra-pod seed abortion (IPSA) is due to a dominance hierarchy of fertilized ovules from the distal (near stigma) to the basal end, generated by the temporal differences in fertilization. The dominant developing seeds at the distal end cause the abortion of others through the production and diffusion of an aborting agent. When the dominance hierarchy of the siblings is not intense, pods are formed with more than one seed. We argue that the positively skewed distribution of seeds per pod is not due to maternal regulation but is a result of sibling rivalry. We propose that this sibling rivalry is generated by genetic differences in pollen grain fitness and disucss the results in the context of parent-offspring conflict. 相似文献
10.
BRUCE GRANT RORY J. HOWLETT 《Biological journal of the Linnean Society. Linnean Society of London》1988,33(3):217-232
The hypothesis that dimorphically coloured, cryptic moths select appropriate rest sites by comparing their body scales to substrate reflectance was tested using typical and melanic morphs of the peppered moth, Biston betularia (L.). Experiments designed to block the individual's inspection of its inherited colour phenotype do not support Kettlewell's contrast/conflict (self-inspection) hypothesis. Instead, tracking of marked moths over successive days revealed individual differences in rest-site selection which were not related to treatments, experience (imprinting), nor closely to a moth's inherited colour pattern. Differences between family broods indicate that some genetic bias in background selection exists. The production of artificially selected lines with consistent but opposing preferences will allow us to investigate the co-evolution of pattern and behaviour. 相似文献