全文获取类型
收费全文 | 4113篇 |
免费 | 343篇 |
国内免费 | 215篇 |
出版年
2024年 | 3篇 |
2023年 | 93篇 |
2022年 | 85篇 |
2021年 | 131篇 |
2020年 | 154篇 |
2019年 | 158篇 |
2018年 | 141篇 |
2017年 | 172篇 |
2016年 | 155篇 |
2015年 | 157篇 |
2014年 | 201篇 |
2013年 | 308篇 |
2012年 | 137篇 |
2011年 | 165篇 |
2010年 | 160篇 |
2009年 | 237篇 |
2008年 | 228篇 |
2007年 | 230篇 |
2006年 | 191篇 |
2005年 | 182篇 |
2004年 | 160篇 |
2003年 | 112篇 |
2002年 | 118篇 |
2001年 | 97篇 |
2000年 | 84篇 |
1999年 | 83篇 |
1998年 | 67篇 |
1997年 | 52篇 |
1996年 | 72篇 |
1995年 | 59篇 |
1994年 | 57篇 |
1993年 | 48篇 |
1992年 | 52篇 |
1991年 | 39篇 |
1990年 | 38篇 |
1989年 | 27篇 |
1988年 | 18篇 |
1987年 | 32篇 |
1986年 | 13篇 |
1985年 | 25篇 |
1984年 | 27篇 |
1983年 | 13篇 |
1982年 | 21篇 |
1981年 | 21篇 |
1980年 | 11篇 |
1979年 | 11篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1976年 | 5篇 |
1974年 | 3篇 |
排序方式: 共有4671条查询结果,搜索用时 15 毫秒
1.
P. G. LADD S. W. CONNELL 《Botanical journal of the Linnean Society. Linnean Society of London》1994,116(1):77-88
It has been suggested by some authors that the low fruit to flower ratio in some Proteaceae is due to andromonoecy, while others, looking particularly at Banksia , have not been able to find evidence for male flowers in the inflorescences. Stirlingia latifolia, Xylomelum occidentals and X. angustifolium are clearly andromonoecous, while no evidence for this condition could be found in Brabejum stellatifoliutn. Production of fertile fruit is related to andromonoecy in Xylomelum and S. latifolia but not in Brabejum. It is unlikely that all-encompassing solutions will be found to what initially seem to be widespread traits in the family, especially in regard to pollination biology, as the genera in the family occupy widely different environments and have very diverse ecological ranges. 相似文献
2.
3.
Benjamin C. Blum Weiwei Lin Matthew L. Lawton Qian Liu Julian Kwan Isabella Turcinovic Ryan Hekman Pingzhao Hu Andrew Emili 《Molecular & cellular proteomics : MCP》2022,21(1):100189
Metabolism is recognized as an important driver of cancer progression and other complex diseases, but global metabolite profiling remains a challenge. Protein expression profiling is often a poor proxy since existing pathway enrichment models provide an incomplete mapping between the proteome and metabolism. To overcome these gaps, we introduce multiomic metabolic enrichment network analysis (MOMENTA), an integrative multiomic data analysis framework for more accurately deducing metabolic pathway changes from proteomics data alone in a gene set analysis context by leveraging protein interaction networks to extend annotated metabolic models. We apply MOMENTA to proteomic data from diverse cancer cell lines and human tumors to demonstrate its utility at revealing variation in metabolic pathway activity across cancer types, which we verify using independent metabolomics measurements. The novel metabolic networks we uncover in breast cancer and other tumors are linked to clinical outcomes, underscoring the pathophysiological relevance of the findings. 相似文献
4.
Lucas Henriques Viscardi Danilo Oliveira Imparato Maria Ctira Bortolini Rodrigo Juliani Siqueira Dalmolin 《Molecular biology and evolution》2021,38(3):735
The origin of nervous systems is a main theme in biology and its mechanisms are largely underlied by synaptic neurotransmission. One problem to explain synapse establishment is that synaptic orthologs are present in multiple aneural organisms. We questioned how the interactions among these elements evolved and to what extent it relates to our understanding of the nervous systems complexity. We identified the human neurotransmission gene network based on genes present in GABAergic, glutamatergic, serotonergic, dopaminergic, and cholinergic systems. The network comprises 321 human genes, 83 of which act exclusively in the nervous system. We reconstructed the evolutionary scenario of synapse emergence by looking for synaptic orthologs in 476 eukaryotes. The Human–Cnidaria common ancestor displayed a massive emergence of neuroexclusive genes, mainly ionotropic receptors, which might have been crucial to the evolution of synapses. Very few synaptic genes had their origin after the Human–Cnidaria common ancestor. We also identified a higher abundance of synaptic proteins in vertebrates, which suggests an increase in the synaptic network complexity of those organisms. 相似文献
5.
Charles L. Nunn Peter H. Thrall Kelly Stewart Alexander H. Harcourt 《Evolutionary ecology》2008,22(4):519-543
Emerging infectious diseases threaten a wide diversity of animals, and important questions remain concerning disease emergence
in socially structured populations. We developed a spatially explicit simulation model to investigate whether—and under what
conditions—disease-related mortality can impact rates of pathogen spread in populations of polygynous groups. Specifically,
we investigated whether pathogen-mediated dispersal (PMD) can occur when females disperse after the resident male dies from
disease, thus carrying infections to new groups. We also examined the effects of incubation period and virulence, host mortality
and rates of background dispersal, and we used the model to investigate the spread of the virus responsible for Ebola hemorrhagic
fever, which currently is devastating African ape populations. Output was analyzed using regression trees, which enable exploration
of hierarchical and non-linear relationships. Analyses revealed that the incidence of disease in single-male (polygynous)
groups was significantly greater for those groups containing an average of more than six females, while the total number of
infected hosts in the population was most sensitive to the number of females per group. Thus, as expected, PMD occurs in polygynous
groups and its effects increase as harem size (the number of females) increases. Simulation output further indicated that
population-level effects of Ebola are likely to differ among multi-male–multi-female chimpanzees and polygynous gorillas,
with larger overall numbers of chimpanzees infected, but more gorilla groups becoming infected due to increased dispersal
when the resident male dies. Collectively, our results highlight the importance of social system on the spread of disease
in wild mammals. 相似文献
6.
7.
8.
Biomass production and plant species diversity in grassland in southern England was monitored before and after a change from conventional to organic farming. Our 18-year study, part of the UK's Environmental Change Network long-term monitoring programme, showed that the cessation of artificial fertiliser use on grassland after conversion to organic farming resulted in a decrease in biomass production and an increase in plant species richness. Grassland productivity decreased immediately after fertiliser application ceased, and after two years the annual total biomass production had fallen by over 50%. In the subsequent decade, total annual grassland productivity did not change significantly, and yields reached 31–66% of the levels recorded pre-management change. Plant species richness that had remained stable during the first 5 years of our study under conventional farming, increased by 300% over the following 13 years under organic farm management. We suggest that the change in productivity is due to the altered composition of species within the plots. In the first few years after the change in farming practice, high yielding, nitrogen-loving plants were outcompeted by lower yielding grasses and forbs, and these species remained in the plots in the following years. This study shows that grassland can be converted from an environment lacking in plant species diversity to a relatively species-rich pasture within 10–15 years, simply by stopping or suspending nitrogen additions. We demonstrate that the trade-off for increasing species richness is a decrease in productivity. Grassland in the UK is often not only managed from a conservation perspective, but to also produce a profitable yield. By considering the species composition and encouraging specific beneficial species such as legumes, it may be possible to improve biomass productivity and reduce the trade-off. 相似文献
9.
《Current biology : CB》2022,32(3):645-653.e8
Download : Download video (10MB) 相似文献
10.
The critical weed-free period in organically-grown winter wheat 总被引:1,自引:0,他引:1
J P WELSH H A J BULSON C E STOPES R J FROUD-WILLIAMS A J MURDOCH 《The Annals of applied biology》1999,134(3):315-320
Two experiments were conducted in central southern England between September 1994 and August 1996 to identify the critical weed-free period in organically grown winter wheat (Triticum aestivum, cv. Mercia). In competition with a mixed weed infestation of predominately Alopecurus myosuroides and Tripleurospermum inodorum it was found that wheat yield decreased as the duration of the weed-infested period increased and that the crop needed to be kept free of weeds from sowing in order to completely avoid any yield loss. Also, weeds emerging in the wheat crop (predominately T. inodorum) during the growing season had a significant and detrimental effect on yield. The existence of the critical period, therefore, depends on the imposition of an acceptable yield loss. If a 5% yield loss gives a marginal benefit compared with the cost of weed control, the critical period will begin at 506°C days after sowing (November) and end at 1023°C days after sowing (February). This information could be used by farmers to target mechanical weeding operations to control weeds at a time that will have maximum benefit to the crop. 相似文献