全文获取类型
收费全文 | 9284篇 |
免费 | 932篇 |
出版年
2023年 | 55篇 |
2022年 | 134篇 |
2021年 | 258篇 |
2020年 | 156篇 |
2019年 | 196篇 |
2018年 | 240篇 |
2017年 | 172篇 |
2016年 | 286篇 |
2015年 | 454篇 |
2014年 | 551篇 |
2013年 | 545篇 |
2012年 | 747篇 |
2011年 | 733篇 |
2010年 | 437篇 |
2009年 | 354篇 |
2008年 | 510篇 |
2007年 | 450篇 |
2006年 | 430篇 |
2005年 | 337篇 |
2004年 | 321篇 |
2003年 | 306篇 |
2002年 | 251篇 |
2001年 | 160篇 |
2000年 | 152篇 |
1999年 | 126篇 |
1998年 | 75篇 |
1997年 | 52篇 |
1996年 | 42篇 |
1995年 | 42篇 |
1994年 | 48篇 |
1993年 | 48篇 |
1992年 | 99篇 |
1991年 | 81篇 |
1990年 | 72篇 |
1989年 | 99篇 |
1988年 | 57篇 |
1987年 | 87篇 |
1986年 | 85篇 |
1985年 | 87篇 |
1984年 | 59篇 |
1983年 | 65篇 |
1982年 | 45篇 |
1981年 | 44篇 |
1980年 | 55篇 |
1979年 | 90篇 |
1978年 | 39篇 |
1976年 | 48篇 |
1975年 | 45篇 |
1974年 | 49篇 |
1973年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
23.
24.
25.
M Ryan 《BMJ (Clinical research ed.)》1980,281(6238):501-502
26.
Suppressor T cell growth and differentiation: production of suppressor T cell differentiation factor by the murine thymoma BW5147 总被引:1,自引:0,他引:1
Previous studies have identified a lymphokine, termed Ts differentiation factor (TsDF), in primary MLR supernatants that induces effector function of alloantigen-primed MLR-Ts. The present report describes constitutive production of TsDF by the murine thymoma BW5147, and its use to analyze alloantigen and TsDF requirements for MLR-Ts activation to TsF production. Serum-free supernatants of BW5147 restored the capacity of MLR-TsF production to alloantigen-primed MLR-Ts cultured with glutaraldehyde-fixed allogeneic stimulator cells, and were not themselves directly suppressive in the MLR assay. BW5147 supernatant induced MLR-TsF production from primed L3T4-Ly2+ MLR-Ts in the absence of concomitant proliferation, suggesting that the function of BW5147 supernatant, like that of MLR-derived TsDF, is a differentiative rather than a proliferative one, and is required for the synthesis or release of TsF. The differentiative activity of BW5147 supernatant was associated with a molecular species of approximately 14,500 m.w. by HPLC fractionation and was expressed independently of detectable IL 2, IL 3, IFN-gamma, and IL 1. The functional activity of BW5147 supernatant has therefore been provisionally designated BW5147-derived Ts differentiative factor, or BW-TsDF. By using BW-TsDF, it was demonstrated that MLR-Ts fail to respond to TsDF in the absence of, or preceding, reexposure to priming alloantigen. Instead, alloantigen binding by primed MLR-Ts appears to create a transient state of TsDF responsiveness. Primed MLR-Ts were fully sensitive to delayed addition of TsDF for approximately 12 hr after reexposure to alloantigen, but became TsDF-unresponsive within 24 to 36 hr. MLR-Ts cultured alone for 36 hr were fully responsive to the combined addition of TsDF and alloantigen. Thus, MLR-Ts activation to TsF release requires the sequential events of specific alloantigen binding, which induces a TsDF-responsive state, followed by interaction with TsDF. The transience of induced TsDF responsiveness suggests a precise mechanism for control of antigen-initiated Ts activation to effector function. 相似文献
27.
Ryan K. Cheu Andrew T. Gustin Christina Lee Luca Schifanella Charlene J. Miller Avie Ha Casey Kim Violeta J. Rodriguez Margaret Fischl Adam D. Burgener Kelly B. Arnold Maria L. Alcaide Nichole R. Klatt 《PLoS pathogens》2020,16(12)
Despite the efficacy of antiretroviral-based pre-exposure prophylactics (PrEP) in men who have sex with men, studies in women have produced widely varying outcomes. Recent evidence demonstrates that vaginal microbial communities are associated with increased HIV acquisition risk and may impact PrEP efficacy. Here, we investigate the mechanisms underlying how vaginal bacteria alter PrEP drug levels and impact HIV infection rates ex vivo. Using cervicovaginal lavages (CVLs) from women with or without bacterial vaginosis (BV), we identified microbial metabolism of PrEP drugs in BV samples through LC-MS/MS analysis of soluble drug levels and metabolite formation in dual T-cell cultures. CVL samples were assessed for microbiome analysis using sequencing of bacterial 16S rRNA genes. We also observed non-Lactobacillus bacteria that are associated with BV may potentially impact PrEP efficacy through increased HIV infection rates in co-cultures containing Lactobacillus or BV bacteria, PrEP drugs, CEM-GFP cells, and HIV-1LAI virus. Finally, we used these data to develop a novel predictive mathematical simulation modeling system to predict these drug interactions for future trials. These studies demonstrate how dysbiotic vaginal microbiota may impact PrEP drugs and provides evidence linking vaginal bacteria to PrEP efficacy in women. 相似文献
28.
29.
Deon. C. Nel Peter G. Ryan Jeanne L. Nel Norbert T. W. Klages Rory P. Wilson Graham Robertson & Geoff N. Tuck 《Ibis》2002,144(3):E141-E154
Wandering Albatrosses Diomedea exulans are frequently killed when they attempt to scavenge baited hooks deployed by long-line fishing vessels. We studied the foraging ecology of Wandering Albatrosses breeding on Marion Island in order to assess the scale of interactions with known long-line fishing fleets. During incubation and late chick-rearing, birds foraged further away from the island, in warmer waters, and showed high spatial overlap with areas of intense tuna Thunnus spp. long-line fishing. During early chick-rearing, birds made shorter foraging trips and showed higher spatial overlap with the local Patagonian Toothfish Dissostichus eleginoides long-line fishery. Tracks of birds returning with offal from the Toothfish fishery showed a strong association with positions at which Toothfish long-lines were set and most diet samples taken during this stage contained fishery-related items. Independent of these seasonal differences, females foraged further from the islands and in warmer waters than males. Consequently, female distribution overlapped more with tuna long-line fisheries, whereas males interacted more with the Toothfish long-line fishery. These factors could lead to differences in the survival probabilities of males and females. Non-breeding birds foraged in warmer waters and showed the highest spatial overlap with tuna long-line fishing areas. The foraging distribution of Marion Island birds showed most spatial overlap with birds from the neighbouring Crozet Islands during the late chick-rearing and non-breeding periods. These areas of foraging overlap also coincided with areas of intense tuna long-line fishing south of Africa. As the population trends of Wandering Albatrosses at these two localities are very similar, it is possible that incidental mortality during the periods when these two populations show the highest spatial overlap could be driving these trends. 相似文献
30.
Grant Jewell Rich 《American anthropologist》2001,103(1):266-267
Varieties of Anomalous Experience: Examining the Scientific Evidence. Etzel Cardeña. Steven Jay Lynn. and Stanley Krippner. eds. Washington, DC: American Psychological Association, 2000. 476 pp. 相似文献