首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1424篇
  免费   99篇
  国内免费   1篇
  1524篇
  2024年   1篇
  2023年   22篇
  2022年   40篇
  2021年   52篇
  2020年   32篇
  2019年   27篇
  2018年   41篇
  2017年   42篇
  2016年   60篇
  2015年   71篇
  2014年   65篇
  2013年   106篇
  2012年   138篇
  2011年   122篇
  2010年   84篇
  2009年   50篇
  2008年   70篇
  2007年   49篇
  2006年   55篇
  2005年   48篇
  2004年   64篇
  2003年   39篇
  2002年   36篇
  2001年   35篇
  2000年   27篇
  1999年   22篇
  1998年   5篇
  1997年   7篇
  1996年   6篇
  1995年   6篇
  1994年   6篇
  1993年   8篇
  1992年   5篇
  1991年   12篇
  1990年   7篇
  1989年   8篇
  1988年   5篇
  1987年   8篇
  1986年   3篇
  1985年   7篇
  1984年   3篇
  1983年   5篇
  1982年   3篇
  1981年   4篇
  1980年   3篇
  1979年   7篇
  1978年   2篇
  1977年   3篇
  1972年   2篇
  1970年   1篇
排序方式: 共有1524条查询结果,搜索用时 19 毫秒
981.

Introduction

Little is known about the state of HIV transmission among married couples in Vietnam. This study aims to clarify HIV serostatus in this group and elucidate risk factors for intra-marital HIV transmission.

Methods

In 2012, we enrolled a group of HIV-positive married men registered at the HIV outpatient clinic of a referral hospital in northern Vietnam, along with their wives. Sociodemographic, behavioural and clinical data were collected from men and wives. HIV serodiscordant couples were followed until March 2014 to determine seroconversion rate. A phylogenetic analysis was performed based on env V3 sequence to detail cluster formation among men.

Results

Of the 163 HIV-positive men enrolled in the study, 101 (62.0%) had wives testing HIV-negative. Half of men reported injecting drug use (IDU) as a likely transmission route. Couples reported a high incidence of unprotected sexual intercourse prior to diagnosis; the median (inter quartile range) was 4 (4–8) times per month. Only 17 couples (10.4%) reported using condoms during at least half these instances. Multivariable analysis revealed IDU history among men was independently associated with HIV-negative wives (adjusted OR 0.31; 95% CI 0.10–0.95, p=0.041). Phylogenetic analysis of 80 samples indicated CRF01_AE. Of these, 69 (86.3%) clustered with IDU-associated viruses from Vietnam. No HIV seroconversion was identified during a follow-up of 61 serodiscordant couples, with 126.5 person-years of observation during which HIV-infected men were on antiretroviral drug therapy (ART).

Conclusion

High HIV serodiscordance was observed among HIV-affected married couples in northern Vietnam. A large number of at-risk wives therefore remain HIV-negative and can be protected with measures including proper use of ART if couples are made aware of the serodiscordance through screening.  相似文献   
982.
In Vitro Cellular & Developmental Biology - Plant - Micropropagation has proven to be an effective method for large-scale plant production in a short time and a useful tool for plant breeding....  相似文献   
983.
The β-selection checkpoint of T cell development tests whether the cell has recombined its genomic DNA to produce a functional T cell receptor β (TCRβ). Passage through the β-selection checkpoint requires the nascent TCRβ protein to mediate signaling through a pre-TCR complex. In this study, we show that developing T cells at the β-selection checkpoint establish an immunological synapse in in vitro and in situ, resembling that of the mature T cell. The immunological synapse is dependent on two key signaling pathways known to be critical for the transition beyond the β-selection checkpoint, Notch and CXCR4 signaling. In vitro and in situ analyses indicate that the immunological synapse promotes passage through the β-selection checkpoint. Collectively, these data indicate that developing T cells regulate pre-TCR signaling through the formation of an immunological synapse. This signaling platform integrates cues from Notch, CXCR4, and MHC on the thymic stromal cell to allow transition beyond the β-selection checkpoint.  相似文献   
984.
Supraphysiological mechanical stretching in smooth muscle results in decreased contractile activity. However, the mechanism is unclear. Previous studies indicated that intestinal motility dysfunction after edema development is associated with increased smooth muscle stress and decreased myosin light chain (MLC) phosphorylation in vivo, providing an ideal model for studying mechanical stress-mediated decrease in smooth muscle contraction. Primary human intestinal smooth muscle cells (hISMCs) were subjected to either control cyclical stretch (CCS) or edema (increasing) cyclical stretch (ECS), mimicking the biophysical forces in non-edematous and edematous intestinal smooth muscle in vivo. ECS induced significant decreases in phosphorylation of MLC and MLC phosphatase targeting subunit (MYPT1) and a significant increase in p21-activated kinase (PAK) activity compared with CCS. PAK regulated MLC phosphorylation in an activity-dependent biphasic manner. PAK activation increased MLC and MYPT1 phosphorylation in CCS but decreased MLC and MYPT1 phosphorylation in hISMCs subjected to ECS. PAK inhibition had the opposite results. siRNA studies showed that PAK1 plays a critical role in regulating MLC phosphorylation in hISMCs. PAK1 enhanced MLC phosphorylation via phosphorylating MYPT1 on Thr-696, whereas PAK1 inhibited MLC phosphorylation via decreasing MYPT1 on both Thr-696 and Thr-853. Importantly, in vivo data indicated that PAK activity increased in edematous tissue, and inhibition of PAK in edematous intestine improved intestinal motility. We conclude that PAK1 positively regulates MLC phosphorylation in intestinal smooth muscle through increasing inhibitory phosphorylation of MYPT1 under physiologic conditions, whereas PAK1 negatively regulates MLC phosphorylation via inhibiting MYPT1 phosphorylation when PAK activity is increased under pathologic conditions.  相似文献   
985.
Men who spend a greater proportion of time apart from their female partner since the couple’s last copulation are at greater “objective” sperm competition risk. We propose a novel cue to sperm competition risk: the time she spends with her male friends. Four hundred and twenty men in a committed, heterosexual, sexual relationship completed a questionnaire. The results indicate that men at greater objective sperm competition risk report less time desired until the couple’s next copulation, greater interest in copulating with their partner, and greater anger, frustration, and upset in response to their partner’s sexual rejection, but only among men whose partner spends more time with her male friends. These results remain after controlling statistically for the participant’s age and their partner’s age. We discuss limitations of the current research, and discuss how research in human sperm competition can inform social issues, including men’s partner-directed sexual coercion.  相似文献   
986.
Chemical investigation of the soft coral Sinularia maxima resulted in the isolation of seven norditerpenoids, including two new compounds, 12-hydroxy-scabrolide A (2) and 13-epi-scabrolide C (6). The structures of the isolated compounds were elucidated based on extensive spectroscopic evidence including Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) and both one- and two-dimensional nuclear magnetic resonance (1D and 2D NMR, respectively), in comparison with reported data. Compound 6 potently inhibited IL-12 and IL-6 production in LPS-stimulated bone marrow derived dendritic (BMDCs) with IC50 values of 5.30 ± 0.21 and 13.12 ± 0.64 μM, respectively. Compound 1 exhibited moderate inhibitory activity against IL-12 and IL-6 production with IC50 values of 23.52 ± 1.37 and 69.85 ± 4.11 μM, respectively.  相似文献   
987.
GPR119 agonist has emerged as a promising target for the treatment of type 2 diabetes. A series of novel 2,4-disubstituted quinazoline analogues was prepared and evaluated their agonistic activity against human GPR119. The analogues bearing azabicyclic amine substituents (12a, 12c and 12g) exhibited better EC50 values than that of OEA though they appeared to be partial agonists.  相似文献   
988.
Although chemical volatiles emitted from host and non-host trees have been suggested as important cues for bark and ambrosia beetles, their responses to leaf volatiles is poorly understood. The oak ambrosia beetle, Platypus quercivorus (Murayama) (Coleoptera: Curculionidae), is a vector for the fungus that causes Japanese oak wilt. Using a Y-tube olfactometer, we tested the behavioral response of P. quercivorus to leaf volatiles emitted from four host trees – Quercus crispula Blume, Quercus serrata Murray, Quercus salicina Blume, and Castanea crenata Sieb. & Zucc. (all Fagaceae) – and two non-host trees, Fagus crenata Blume (Fagaceae) and Cryptomeria japonica D. Don (Cupressaceae). A flight mill was used to evaluate the effect of flight on the behavioral response to leaf volatiles. The bioassays were repeated 10× before and 10× after flight in the flight mill for each of the 54 individual beetles. Leaf volatile components were analyzed using gas chromatography–mass spectrometry. The bioassay results supported our hypothesis: P. quercivorus was attracted by the leaf volatiles of hosts and was deterred by the leaf volatiles of non-hosts. The behavioral response of P. quercivorus to the leaf volatiles was stronger after flight. Males had a stronger behavioral response than females to leaf volatiles. The leaf volatile chemical profile of the non-host C. japonica differed from the profile of the host plants. However, the chemical profile of the non-host F. crenata was similar to the profile of the hosts. Our findings provide insight into the functions of leaf chemical volatiles in the interaction of P. quercivorus with its hosts and non-hosts and may help improve the control of P. quercivorus and Japanese oak wilt.  相似文献   
989.
In this experiment, golden rabbitfish (Siganus guttatus) were allocated between three treatment groups. The fish were injected with saline, human chorionic gonadotropin (hCG) and D-Ala6, Pro9-Net-mGnRH. After injection, in 6 hr intervals, blood plasma samples were collected for steroid hormone (testosterone [T] in males and estradiol-17β [E2] in females) using enzyme immune assay (EIA). In male fish, T levels significantly increased and reached 170 and 650 pg/ml for hCG and D-Ala6, Pro9-Net-mGnRH treatments, respectively. Then T levels slightly decreased until 24 hr post injection. There were no significant changes of T levels in saline treatment. In female fish, we found significant changes in E2 levels at 2,567 and 524 pg/ml at 12 hr post injection in hCG and D-Ala6, Pro9-Net-mGnRH treatments, respectively. No significant differences of E2 levels were observed in saline group. In the second experiment, we injected 100 golden rabbitfish with both hCG and D-Ala6, Pro9-Net-mGnRH. Fish spawned successfully when hCG and D-Ala6, Pro9-Net-mGnRH were given individually and in combination. Latency periods were between 46–64 hr with an average fertilization rate of 70%–90% and hatching rate of 56%–74%. The embryonic duration was 16–20 hr. The saline-injected group produced no spawning. Our findings contribute to further understanding of exogenous hormones impact on golden rabbitfish reproductive endocrinology, refining breeding protocol and implications for fish propagation.  相似文献   
990.
Idiopathic pulmonary fibrosis (IPF) is a progressive disease thought to result from impaired lung repair following injury and is strongly associated with aging. While vascular alterations have been associated with IPF previously, the contribution of lung vasculature during injury resolution and fibrosis is not well understood. To compare the role of endothelial cells (ECs) in resolving and non‐resolving models of lung fibrosis, we applied bleomycin intratracheally to young and aged mice. We found that injury in aged mice elicited capillary rarefaction, while injury in young mice resulted in increased capillary density. ECs from the lungs of injured aged mice relative to young mice demonstrated elevated pro‐fibrotic and reduced vascular homeostasis gene expression. Among the latter, Nos3 (encoding the enzyme endothelial nitric oxide synthase, eNOS) was transiently upregulated in lung ECs from young but not aged mice following injury. Young mice deficient in eNOS recapitulated the non‐resolving lung fibrosis observed in aged animals following injury, suggesting that eNOS directly participates in lung fibrosis resolution. Activation of the NO receptor soluble guanylate cyclase in human lung fibroblasts reduced TGFβ‐induced pro‐fibrotic gene and protein expression. Additionally, loss of eNOS in human lung ECs reduced the suppression of TGFβ‐induced lung fibroblast activation in 2D and 3D co‐cultures. Altogether, our results demonstrate that persistent lung fibrosis in aged mice is accompanied by capillary rarefaction, loss of EC identity, and impaired eNOS expression. Targeting vascular function may thus be critical to promote lung repair and fibrosis resolution in aging and IPF.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号