全文获取类型
收费全文 | 1422篇 |
免费 | 192篇 |
出版年
2021年 | 20篇 |
2020年 | 12篇 |
2018年 | 16篇 |
2016年 | 22篇 |
2015年 | 42篇 |
2014年 | 54篇 |
2013年 | 63篇 |
2012年 | 76篇 |
2011年 | 80篇 |
2010年 | 49篇 |
2009年 | 46篇 |
2008年 | 61篇 |
2007年 | 60篇 |
2006年 | 53篇 |
2005年 | 59篇 |
2004年 | 60篇 |
2003年 | 51篇 |
2002年 | 60篇 |
2001年 | 18篇 |
2000年 | 14篇 |
1999年 | 16篇 |
1998年 | 27篇 |
1997年 | 18篇 |
1996年 | 12篇 |
1995年 | 12篇 |
1994年 | 17篇 |
1992年 | 14篇 |
1991年 | 20篇 |
1990年 | 12篇 |
1989年 | 14篇 |
1988年 | 16篇 |
1987年 | 16篇 |
1986年 | 13篇 |
1984年 | 12篇 |
1983年 | 16篇 |
1982年 | 17篇 |
1981年 | 25篇 |
1980年 | 18篇 |
1978年 | 12篇 |
1977年 | 14篇 |
1976年 | 17篇 |
1974年 | 14篇 |
1973年 | 16篇 |
1971年 | 14篇 |
1970年 | 13篇 |
1969年 | 15篇 |
1968年 | 18篇 |
1967年 | 12篇 |
1964年 | 16篇 |
1963年 | 15篇 |
排序方式: 共有1614条查询结果,搜索用时 31 毫秒
111.
Hilary K. Hsu Todd T. Brown Xiuhong Li Stephen Young Ross D. Cranston Gypsyamber D’Souza Lisa P. Jacobson Otoniel Martínez-Maza Eric C. Seaberg Joseph B. Margolick Frank J. Jenkins Matthew G. Moran Kristofer Chua Robert K. Bolan Roger Detels Dorothy J. Wiley 《PloS one》2015,10(3)
Background
Human papillomavirus (HPV) types 16 and 18 cause invasive cervical cancer and most invasive anal cancers (IACs). Overall, IAC rates are highest among men who have sex with men (MSM), especially MSM with HIV infection. Testosterone is prescribed for men showing hypogonadism and HIV-related wasting. While there are direct and indirect physiological effects of testosterone in males, its role in anal HPV16/18 infections in men is unknown.Methods
Free testosterone (FT) was measured in serum from 340 Multicenter AIDS Cohort Study (MACS) participants who were tested for anal HPV16/18-DNA approximately 36 months later. The effect of log10-transformed current FT level on anal HPV16/18 prevalence was modeled using Poisson regression with robust error variance. Multivariate models controlled for other HPV types, cumulative years of exogenous testosterone use, race, age, lifetime number of receptive anal intercourse partnerships, body mass index, tobacco smoking, HIV-infection and CD4+ T-cell counts among HIV-infected, and blood draw timing.Results
Participants were, on average, 60 (+5.4) years of age, White (86%), and HIV-uninfected (56%); Twenty-four percent tested positive for anal HPV16 and/or 18-DNA (HPV16 prevalence=17.1%, HPV18=9.1%). In adjusted analysis, each half-log10 increase of FT was associated with a 1.9-fold (95% Confidence Interval: 1.11, 3.24) higher HPV16/18 prevalence. Additionally, other Group 1 high-risk HPVs were associated with a 1.56-fold (1.03, 2.37) higher HPV16/18 prevalence. Traditional risk factors for HPV16/18 infection (age, tobacco smoking; lifetime number of sexual partners, including the number of receptive anal intercourse partnerships within 24 months preceding HPV testing) were poorly correlated with one another and not statistically significantly associated with higher prevalence of HPV16/18 infection in unadjusted and adjusted analyses.Conclusions
Higher free testosterone was associated with increased HPV16/18 prevalence measured approximately three years later, independent of sexual behavior and other potential confounders. The mechanisms underlying this association remain unclear and warrant further study. 相似文献112.
113.
Effective vision for action and effective management of concurrent spatial relations underlie skillful manipulation of objects, including hand tools, in humans. Children’s performance in object insertion tasks (fitting tasks) provides one index of the striking changes in the development of vision for action in early life. Fitting tasks also tap children’s ability to work with more than one feature of an object concurrently. We examine young children’s performance on fitting tasks in two and three dimensions and compare their performance with the previously reported performance of adult individuals of two species of nonhuman primates on similar tasks. Two, three, and four year-old children routinely aligned a bar-shaped stick and a cross-shaped stick but had difficulty aligning a tomahawk-shaped stick to a matching cut-out. Two year-olds were especially challenged by the tomahawk. Three and four year-olds occasionally held the stick several inches above the surface, comparing the stick to the surface visually, while trying to align it. The findings suggest asynchronous development in the ability to use vision to achieve alignment and to work with two and three spatial features concurrently. Using vision to align objects precisely to other objects and managing more than one spatial relation between an object and a surface are already more elaborated in two year-old humans than in other primates. The human advantage in using hand tools derives in part from this fundamental difference in the relation between vision and action between humans and other primates. 相似文献
114.
115.
Hye-Kyeong Kim Mary Anne Della-Fera Dorothy B. Hausman Clifton A. Baile 《Journal of physiology and biochemistry》2010,66(3):197-203
Clenbuterol, a beta2-adrenergic receptor (β2-AR) selective agonist, has been shown to decrease body fat in animals and can induce apoptosis in adipose tissue in mice.
We hypothesized that direct actions of a β-adrenergic receptor agonist on adipocytes could trigger the observed apoptotic
effect. The hypothesis was inspected by investigating the direct effect of clenbuterol on apoptosis, adipogenesis, and lipolysis
in vitro using the 3T3-L1 cell line and rat primary adipocytes. Cells were treated with 10−9 to 10−5 M clenbuterol depending on the experiments. There was no apoptotic effect of clenbuterol both in 3T3-L1 cells and rat primary
adipocytes. Adipogenesis monitored by Oil Red O staining and AdipoRed™ assay was modestly decreased by clenbuterol treatment
(p < 0.05). In fully differentiated primary adipocytes, clenbuterol increased basal lipolysis compared with the control (p < 0.01). In summary, direct stimulation of β2-AR by clenbuterol does not cause apoptosis in adipocytes, despite a direct lipolytic stimulation and attenuation of adipogenesis. 相似文献
116.
Tanis SP Plewe MB Johnson TW Butler SL Dalvie D DeLisle D Dress KR Hu Q Huang B Kuehler JE Kuki A Liu W Peng Q Smith GL Solowiej J Tran KT Wang H Yang A Yin C Yu X Zhang J Zhu H 《Bioorganic & medicinal chemistry letters》2010,20(24):7429-7434
HIV-1 integrase is one of three enzymes encoded by the HIV genome and is essential for viral replication, and HIV-1 IN inhibitors have emerged as a new promising class of therapeutics. Recently, we reported the discovery of azaindole hydroxamic acids that were potent inhibitors of the HIV-1 IN enzyme. N-Methyl hydroxamic acids were stable against oxidative metabolism, however were cleared rapidly through phase 2 glucuronidation pathways. We were able to introduce polar groups at the β-position of the azaindole core thereby altering physical properties by lowering calculated log D values (c Log D) which resulted in attenuated clearance rates in human hepatocytes. Pharmacokinetic data in dog for representative compounds demonstrated moderate oral bioavailability and reasonable half-lives. These ends were accomplished without a large negative impact on enzymatic and antiviral activity, thus suggesting opportunities to alter clearance parameters in future series. 相似文献
117.
Haifeng Tang Yan Yan Zhe Feng Reynalda K. de Jesus Lihu Yang Dorothy A. Levorse Karen A. Owens Taro E. Akiyama Raynald Bergeron Gino A. Castriota Thomas W. Doebber Kenneth P. Ellsworth Michael E. Lassman Cai Li Margaret S. Wu Bei B. Zhang Kevin T. Chapman Sander G. Mills Joel P. Berger Alexander Pasternak 《Bioorganic & medicinal chemistry letters》2010,20(20):6088-6092
A new series of thiazole-substituted 1,1,1,3,3,3-hexafluoro-2-propanols were prepared and evaluated as malonyl-CoA decarboxylase (MCD) inhibitors. Key analogs caused dose-dependent decreases in food intake and body weight in obese mice. Acute treatment with these compounds also led to a drop in elevated blood glucose in a murine model of type II diabetes. 相似文献
118.
119.
Markus Herrmann Tim Harwood Olivia Gaston-Parry Dorothy Kouzios Tang Wong Anna Lih Mark Jimenez Margaret Janu Markus J. Seibel 《Steroids》2010,75(13-14):1106-1112
BackgroundThe accurate measurement of 25-hydoxy vitamin D (25OH-D) in serum has been a challenge for many years. We developed a liquid chromatography tandem mass spectrometry (LC Tandem MS) assay for the quantitative determination of 25OH-D2 and 25OH-D3 in serum. The new method was compared with two widely used commercially available immunoassays.MethodsSample preparation involved protein precipitation with acetonitrile containing deuterated forms of the target species as internal standards. An API 5000 mass spectrometer coupled with a photoionization source was used for quantitation. The performance of the new LC Tandem MS assay was compared with a radioimmunoassay (RIA, Diasorin) and a chemiluminescence immunoassay (ECLIA, Roche Diagnostics), analysing serum obtained from 152 individuals.ResultsUsing 100 μl of serum, the LC Tandem MS assay had a limit of quantitation of 1.3 nmol/L for both 25OH-D2 and 25OH-D3 with a linear response between 1.3 and 625 nmol/L and accuracy of between 95 and 124%. Intra- and inter-assay precision were ≤7% and ≤4%, respectively. Measurement of 25OH-D levels in 152 serum samples gave run averages of 71, 56 and 62 nmol/L for LC Tandem MS, ECLIA and RIA, respectively. Correlations between the various methods were: LC Tandem MS vs. RIA: r = 0.931; LC Tandem MS vs. ECLIA: r = 0.784; RIA vs. ECLIA: r = 0.787. The LC Tandem MS method had a positive proportional bias of 26% over the RIA, whereas the ECLIA showed variable differences.ConclusionThe new LC Tandem MS assay is accurate and precise at physiologically relevant 25OH-D concentrations, and compares favourably with the RIA. In contrast, the ECLIA shows variable bias with the other assays tested. 相似文献
120.
Polymerization of actin filaments powers many dynamic cellular events and is directed by a small group of actin nucleators. In this issue, Ahuja et al. (2007) identify and characterize a new actin nucleator called cordon-bleu (Cobl) that may drive morphogenesis of the central nervous system during development. 相似文献