全文获取类型
收费全文 | 3699篇 |
免费 | 289篇 |
国内免费 | 166篇 |
出版年
2023年 | 79篇 |
2022年 | 69篇 |
2021年 | 121篇 |
2020年 | 131篇 |
2019年 | 133篇 |
2018年 | 122篇 |
2017年 | 144篇 |
2016年 | 128篇 |
2015年 | 134篇 |
2014年 | 179篇 |
2013年 | 273篇 |
2012年 | 118篇 |
2011年 | 146篇 |
2010年 | 139篇 |
2009年 | 206篇 |
2008年 | 209篇 |
2007年 | 205篇 |
2006年 | 173篇 |
2005年 | 163篇 |
2004年 | 140篇 |
2003年 | 107篇 |
2002年 | 112篇 |
2001年 | 89篇 |
2000年 | 77篇 |
1999年 | 71篇 |
1998年 | 63篇 |
1997年 | 47篇 |
1996年 | 65篇 |
1995年 | 51篇 |
1994年 | 57篇 |
1993年 | 42篇 |
1992年 | 51篇 |
1991年 | 39篇 |
1990年 | 34篇 |
1989年 | 26篇 |
1988年 | 16篇 |
1987年 | 25篇 |
1986年 | 13篇 |
1985年 | 25篇 |
1984年 | 26篇 |
1983年 | 13篇 |
1982年 | 20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 |
1971年 | 3篇 |
排序方式: 共有4154条查询结果,搜索用时 31 毫秒
991.
Hua Wu Xiang-Jiang Zhan Ze-Jun Zhang Li-Feng Zhu Li Yan Ming Li Fu-Wen Wei 《Conservation Genetics》2009,10(3):649-652
Limited microsatellite markers useable in noninvasive genetic methods have hampered the studies of dispersal patterns and
mating systems of giant pandas. Therefore, we describe in this paper the characterization of 15 novel microsatellite loci
from genomic DNA-enriched libraries and 18 redesigned microsatellite loci from published papers on the giant panda. The number
of alleles per locus in 60 individuals ranged from 2 to 13, the average observed heterozygosity per locus from 0.168 to 0.800,
and the average expected heterozygosity per locus from 0.152 to 0.882. All loci followed Hardy-Weinberg expectations. Four
pairs of significant linkage association were found among all these loci. Moreover, the 33 microsatellite loci showed high
amplification successes rate in noninvasive samples, which indicated that these loci will be of use in studying dispersal
patterns and mating systems of giant pandas using noninvasive genetic methods. 相似文献
992.
Hua Wu Xiang-Jiang Zhan Yu Guo Zejun Zhang Lifeng Zhu Li Yan Ming Li Fu-Wen Wei 《Conservation Genetics》2009,10(3):523-525
The information on dispersal patterns and mating systems of red pandas is quite important for the understanding of the genetic
diversity and divergence of this species. And microsatellite marker is an ideal tool to analyze dispersal patterns and mating
systems. Thus, we describe in this paper the isolation and characterization of 12 microsatellite loci in the red panda from
genomic DNA-enriched libraries. These loci were highly polymorphic with numbers of alleles per locus in 24 individuals ranging
from 2 to 14, observed heterozygosity from 0.143 to 0.864 and expected heterozygosity from 0.297 to 0.872. All loci except
for RP6 locus followed Hardy–Weinberg expectations. No significant linkage association was found among all these loci. The
12 novel polymorphic microsatellite loci will be of use in studying dispersal patterns and mating systems of red pandas. 相似文献
993.
Rothert K Strecher VJ Doyle LA Caplan WM Joyce JS Jimison HB Karm LM Mims AD Roth MA 《Obesity (Silver Spring, Md.)》2006,14(2):266-272
Objective: To assess the efficacy of a Web‐based tailored behavioral weight management program compared with Web‐based information‐only weight management materials. Research Methods and Procedures: Participants, 2862 eligible overweight and obese (BMI = 27 to 40 kg/m2) members from four regions of Kaiser Permanente's integrated health care delivery system, were randomized to receive either a tailored expert system or information‐only Web‐based weight management materials. Weight change and program satisfaction were assessed by self‐report through an Internet‐based survey at 3‐ and 6‐month follow‐up periods. Results: Significantly greater weight loss at follow‐up was found among participants assigned to the tailored expert system than among those assigned to the information‐only condition. Subjects in the tailored expert system lost a mean of 3 ± 0.3% of their baseline weight, whereas subjects in the information‐only condition lost a mean of 1.2 ± 0.4% (p < 0.0004). Participants were also more likely to report that the tailored expert system was personally relevant, helpful, and easy to understand. Notably, 36% of enrollees were African‐American, with enrollment rates higher than the general proportion of African Americans in any of the study regions. Discussion: The results of this large, randomized control trial show the potential benefit of the Web‐based tailored expert system for weight management compared with a Web‐based information‐only weight management program. 相似文献
994.
There are a growing number of globally approved products and clinical trials utilizing autologous and allogeneic therapeutic cells for applications in regenerative medicine and immunotherapies. However, there is a need to develop rapid and cost-effective methods for manufacturing therapeutically effective cells. Furthermore, the resulting manufactured cells may exhibit heterogeneities that result in mixed therapeutic outcomes. Engineering approaches that can provide distinct microenvironmental cues to these cells may be able to enhance the growth and characterization of these cell products. This mini-review describes strategies to potentially enhance the expansion of therapeutic cells with biomaterials and bioreactors, as well as to characterize the cell products with microphysiological systems. These systems can provide distinct cues to maintain the quality attributes of the cells and evaluate their function in physiologically relevant conditions. 相似文献
995.
摘要:【目的】假单胞菌株M18(Pseudomonas sp. M18)是从甜瓜根际土壤中分离获得的一株对多种植物病原菌具有显著拮抗作用的菌株,在菌群传感(quorum sensing)系统的调控下,能分泌吩嗪-1-羧酸(PCA)以及多种吩嗪(phz)类衍生物的抗真菌物质。全局性因子GacA是M18菌株吩嗪类物质的合成与菌群传感系统的重要调控因子,本文将就GacA对上述两者的调控做进一步研究。【方法】PCR基因扩增和测序研究M18菌株中PCA合成基因簇,运用RT-PCR及构建phzA-lacZ转录融合手段 相似文献
996.
SCOTT T. LARNED THIBAULT DATRY DAVID B. ARSCOTT KLEMENT TOCKNER 《Freshwater Biology》2010,55(4):717-738
1. Temporary rivers and streams are among the most common and most hydrologically dynamic freshwater ecosystems. The number of temporary rivers and the severity of flow intermittence may be increasing in regions affected by climatic drying trends or water abstraction. Despite their abundance, temporary rivers have been historically neglected by ecologists. A recent increase in temporary‐river research needs to be supported by new models that generate hypotheses and stimulate further research. In this article, we present three conceptual models that address spatial and temporal patterns in temporary‐river biodiversity and biogeochemistry. 2. Temporary rivers are characterised by the repeated onset and cessation of flow, and by complex hydrological dynamics in the longitudinal dimension. Longitudinal dynamics, such as advancing and retreating wetted fronts, hydrological connections and disconnections, and gradients in flow permanence, influence biotic communities and nutrient and organic matter processing. 3. The first conceptual model concerns connectivity between habitat patches. Variable connectivity suggests that the metacommunity and metapopulation concepts are applicable in temporary rivers. We predict that aggregations of local communities in the isolated water bodies of temporary rivers function as metacommunities. These metacommunities may become longitudinally nested due to interspecific differences in dispersal and mortality. The metapopulation concept applies to some temporary river species, but not all. In stable metapopulations, rates of local extinction are balanced by recolonisation. However, extinction and recolonisation in many temporary‐river species are decoupled by frequent disturbances, and populations of these species are usually expanding or contracting. 4. The second conceptual model predicts that large‐scale biodiversity varies as a function of aquatic and terrestrial patch dynamics and water‐level fluctuations. Habitat mosaics in temporary rivers change in composition and configuration in response to inundation and drying, and these changes elicit a range of biotic responses. In the model, aquatic biodiversity initially increases directly with water level due to increasing abundance of aquatic patches. When most of the channel is inundated and most aquatic patches are connected, further increases in aquatic habitat and connectivity cause aquatic biodiversity to decline due to community homogenisation and reduced habitat diversity. The predicted responses of terrestrial biodiversity to changes in water level are the inverse of aquatic biodiversity responses. 5. The third conceptual model represents temporary rivers as longitudinal, punctuated biogeochemical reactors. Advancing fronts carry water, solutes and particulate organic matter downstream; subsequent flow recessions and drying result in deposition of transported material in reserves such as pools and bar tops. Material processing is rapid during inundated periods and slower during dry periods. The efficiency of material processing is predicted to increase with the number of cycles of transport, deposition and processing that occur down the length of a temporary river. 6. We end with a call for conservation and resource management that addresses the unique properties of temporary rivers. Primary objectives for effective temporary river management are preservation or restoration of aquatic‐terrestrial habitat mosaics, preservation or restoration of natural flow intermittence, and identification of flow requirements for highly valued species and processes. 相似文献
997.
Tuan On Xuejian Xiong Shuye Pu Andrei Turinsky Yunchen Gong Andrew Emili Zhaolei Zhang Jack Greenblatt Shoshana J. Wodak John Parkinson 《Proteins》2010,78(9):2075-2089
Model organisms such as yeast, fly, and worm have played a defining role in the study of many biological systems. A significant challenge remains in translating this information to humans. Of critical importance is the ability to differentiate those components where knowledge of function and interactions may be reliably inferred from those that represent lineage‐specific innovations. To address this challenge, we use chromatin modification (CM) as a model system for exploring the evolutionary properties of their components in the context of their known functions and interactions. Collating previously identified components of CM from yeast, worm, fly, and human, we identified a “core” set of 50 CM genes displaying consistent orthologous relationships that likely retain their interactions and functions across taxa. In addition, we catalog many components that demonstrate lineage specific expansions and losses, highlighting much duplication within vertebrates that may reflect an expanded repertoire of regulatory mechanisms. Placed in the context of a high‐quality protein–protein interaction network, we find, contrary to existing views of evolutionary modularity, that CM complex components display a mosaic of evolutionary histories: a core set of highly conserved genes, together with sets displaying lineage specific innovations. Although focused on CM, this study provides a template for differentiating those genes which are likely to retain their functions and interactions across species. As such, in addition to informing on the evolution of CM as a system, this study provides a set of comparative genomic approaches that can be generally applied to any biological systems. Proteins 2010. © 2010 Wiley‐Liss, Inc. 相似文献
998.
The growth of biological systems described by the Gompertz and West–Brown–Enquist functions is considered in the framework of the space-like supersymmetric quantum mechanics. It has been shown that the supersymmetric effect of a fermion-boson conversion has a biological analogue in the phenomenon of a growth-regression transformation under the influence of a cycle-non-specific drug of a constant concentration. The results obtained reveal that the biological growth can be viewed as the macroscopic quantum phenomenon endowed with the space-like supersymmetric properties not established so far in the domain of biology and medicine. 相似文献
999.
We studied female preferences for familiar and unfamiliar males. The subjects were laboratory-born house mice: (1) non-commensal Mus musculus domesticus from the eastern part of Syria along the Euphrates River; and (2) commensal M. m. musculus from the Czech Republic. Pair-choice preference tests have revealed that oestrous females of both populations sniffed towards unfamiliar males more than familiar males. In the case of females exhibiting postpartum oestrus, this preference was less pronounced and statistically not significant. Thus, our mice clearly exhibited the behavioural pattern known from commensal populations of polygynous and/or promiscuous M. m. domesticus. We found no inverse tendency to seek proximity to the familiar male that has been previously reported from closely related and presumably monogamous aboriginal mouse Mus spicilegus. We conclude that neither commensal M. m. musculus, nor non-commensal M. m. domesticus, are likely to share a monogamous mating system with mound-building mice. 相似文献
1000.
Rubén TORICES 《植物分类学报》2010,48(4)
New inference techniques,such as supertrees,have improved the construction of large phylogenies,helping to reveal the tree of life.In addition,these large phylogenies have enhanced the study of other evolutionary questions,such as whether traits have evolved in a neutral or adaptive way,or what factors have influenced diversification.However,supertrees usually lack branch lengths,which are necessary for all these issues to be investigated.Here,divergence times within the largest family of flowering plants,namely the Asteraceae,are reviewed to estimate time-calibrated branch lengths in the supertree of this lineage.An inconsistency between estimated dates of basal branching events and the earliest asteraceous fossil pollen record was detected.In addition,the impact of different methods of branch length assignment on the total number of transitions between states in the reconstruction of sexual system evolution in Asteraceae was investigated.At least for this dataset,different branch length assignation approaches influenced maximum likelihood(ML)reconstructions only and not Bayesian ones.Therefore,the selection of different branch length information is not arbitrary and should be carefully assessed,at least when ML approaches are being used.The reviewed divergence times and the estimated time-calibrated branch lengths provide a useful tool for future phylogenetic comparative and macroevolutionary studies of Asteraceae. 相似文献