全文获取类型
收费全文 | 465篇 |
免费 | 23篇 |
国内免费 | 1篇 |
出版年
2022年 | 2篇 |
2021年 | 14篇 |
2020年 | 6篇 |
2019年 | 8篇 |
2018年 | 9篇 |
2017年 | 10篇 |
2016年 | 7篇 |
2015年 | 9篇 |
2014年 | 17篇 |
2013年 | 19篇 |
2012年 | 24篇 |
2011年 | 39篇 |
2010年 | 19篇 |
2009年 | 22篇 |
2008年 | 27篇 |
2007年 | 22篇 |
2006年 | 20篇 |
2005年 | 14篇 |
2004年 | 23篇 |
2003年 | 18篇 |
2002年 | 15篇 |
2001年 | 17篇 |
2000年 | 24篇 |
1999年 | 10篇 |
1998年 | 12篇 |
1997年 | 9篇 |
1996年 | 10篇 |
1995年 | 5篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1977年 | 2篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1973年 | 5篇 |
1972年 | 2篇 |
1971年 | 3篇 |
1959年 | 1篇 |
1952年 | 1篇 |
1920年 | 1篇 |
排序方式: 共有489条查询结果,搜索用时 15 毫秒
481.
482.
P. S. Gill J. Blangero G. S. Manis J. Scheffler M. E. Keeling W. H. Stone 《American journal of primatology》1992,27(2):85-92
One of the prime concerns at zoos and at primate breeding facilities is to maintain genetic variability. This can be accomplished by avoiding inbreeding. It is relatively easy to assess genetic variability and the level of inbreeding by using pedigree information and genetic markers. In this study we used genetic markers controlled by 6 independent polymorphic loci (GPI, PGD, CA2, MPI, DIA1, Tf) to ascertain genetic variation in two captive and one wild population of rhesus monkeys. Two other loci ADA and NP were also examined and found to be monomorphic in the three populations. F-statistics and contingency chi-square analyses indicated that there was significant genetic differentiation among the populations. We also found that the mean heterozygosities were very similar in the three populations, in spite of the diverse breeding strategies. These data are important because rhesus monkeys are frequently used for biomedical research; and the genetic markers provide useful information for genetic management of captive colonies of nonhuman primates. © 1992 Wiley-Liss, Inc. 相似文献
483.
484.
Edward M. Hill Benjamin D. Atkins Matt J. Keeling Louise Dyson Michael J. Tildesley 《PLoS computational biology》2021,17(6)
As part of a concerted pandemic response to protect public health, businesses can enact non-pharmaceutical controls to minimise exposure to pathogens in workplaces and premises open to the public. Amendments to working practices can lead to the amount, duration and/or proximity of interactions being changed, ultimately altering the dynamics of disease spread. These modifications could be specific to the type of business being operated. We use a data-driven approach to parameterise an individual-based network model for transmission of SARS-CoV-2 amongst the working population, stratified into work sectors. The network is comprised of layered contacts to consider the risk of spread in multiple encounter settings (workplaces, households, social and other). We analyse several interventions targeted towards working practices: mandating a fraction of the population to work from home; using temporally asynchronous work patterns; and introducing measures to create ‘COVID-secure’ workplaces. We also assess the general role of adherence to (or effectiveness of) isolation and test and trace measures and demonstrate the impact of all these interventions across a variety of relevant metrics. The progress of the epidemic can be significantly hindered by instructing a significant proportion of the workforce to work from home. Furthermore, if required to be present at the workplace, asynchronous work patterns can help to reduce infections when compared with scenarios where all workers work on the same days, particularly for longer working weeks. When assessing COVID-secure workplace measures, we found that smaller work teams and a greater reduction in transmission risk reduced the probability of large, prolonged outbreaks. Finally, following isolation guidance and engaging with contact tracing without other measures is an effective tool to curb transmission, but is highly sensitive to adherence levels. In the absence of sufficient adherence to non-pharmaceutical interventions, our results indicate a high likelihood of SARS-CoV-2 spreading widely throughout a worker population. Given the heterogeneity of demographic attributes across worker roles, in addition to the individual nature of controls such as contact tracing, we demonstrate the utility of a network model approach to investigate workplace-targeted intervention strategies and the role of test, trace and isolation in tackling disease spread. 相似文献
485.
486.
P J Keeling J A Deane C Hink-Schauer S E Douglas U G Maier G I McFadden 《Molecular biology and evolution》1999,16(9):1308-1313
Cryptomonads have acquired photosynthesis through secondary endosymbiosis: they have engulfed and retained a photosynthetic eukaryote. The remnants of this autotrophic symbiont are severely reduced, but a small volume of cytoplasm surrounding the plastid persists, along with a residual nucleus (the nucleomorph) that encodes only a few hundred genes. We characterized tubulin genes from the cryptomonad Guillardia theta. Despite the apparent absence of microtubules in the endosymbiont, we recovered genes encoding alpha-, beta-, and gamma-tubulins from the nucleomorph genome of G. theta. The presence of tubulin genes in the nucleomorph indicates that some component of the cytoskeleton is still present in the cryptomonad symbiont despite the fact that very little cytoplasm remains, no mitosis is known in the nucleomorph, and microtubules have never been observed anywhere in the symbiont. Phylogenetic analyses with nucleomorph alpha- and beta-tubulins support the origin of the cryptomonad nucleomorph from a red alga. We also characterized alpha and beta-tubulins from the host nucleus of G. theta and compared these with tubulins we isolated from two flagellates, Goniomonas truncata and Cyanophora paradoxa, previously proposed to be related to the cryptomonad host. Phylogenetic analyses support a relationship between the cryptomonad host and Goniomonas but do not support any relationship between cryptomonads and Cyanophora. 相似文献
487.
488.
Carbohydrates have a range of effects on soil, dependent on the frequency and concentration of the application. Small quantities of glucose have the effect of accelerating the removal of available N (NH4
+, NO3
–) through incorporation into the bodies of microorganisms. This reduces plant growth (Jenkinson, 1985), the rate of which depends largely on the presence of available N (Addiscott et al., 1991). However, in theory, if appropriate soil glucose concentrations are maintained, asymbiotic N2-fixation will occur, supplying extra nitrogen nutrition to plants over an extended period. Here, it is demonstrated that the use of 0.028 M glucose and an appropriate source of N2-fixing bacteria (green waste-derived compost) can result in increased grass dry matter yields of over 50% in a glasshouse experiment. 相似文献
489.
J R DeLoach K Andrews W Satterfield M Keeling 《Biotechnology and applied biochemistry》1990,12(3):331-335
Carrier erythrocytes were prepared to encapsulate L-asparaginase by a hypotonic dialysis process. Dogs received either intravenous or intraperitoneal injections of cells containing both L-asparaginase and the marker [3H]inulin. The route of administration had no effect on the circulating survival of carrier erythrocytes. For enzyme therapy, intraperitoneal injection of a large volume of cells is technically feasible. Cells circulate with a maximum of 30% of the cells reaching circulation 24 h after injection. Those cells reaching circulation have a 7-day half-life for the encapsulated enzyme L-asparaginase. 相似文献