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   4434篇
  免费   383篇
  国内免费   285篇
  5102篇
  2024年   11篇
  2023年   46篇
  2022年   135篇
  2021年   231篇
  2020年   165篇
  2019年   188篇
  2018年   201篇
  2017年   135篇
  2016年   183篇
  2015年   287篇
  2014年   357篇
  2013年   330篇
  2012年   415篇
  2011年   350篇
  2010年   210篇
  2009年   227篇
  2008年   253篇
  2007年   202篇
  2006年   164篇
  2005年   136篇
  2004年   109篇
  2003年   120篇
  2002年   111篇
  2001年   80篇
  2000年   74篇
  1999年   53篇
  1998年   27篇
  1997年   35篇
  1996年   37篇
  1995年   43篇
  1994年   33篇
  1993年   24篇
  1992年   28篇
  1991年   22篇
  1990年   17篇
  1989年   14篇
  1988年   8篇
  1987年   8篇
  1986年   9篇
  1985年   3篇
  1984年   6篇
  1983年   6篇
  1982年   2篇
  1981年   1篇
  1980年   1篇
  1975年   1篇
  1973年   1篇
  1971年   1篇
  1970年   1篇
  1967年   1篇
排序方式: 共有5102条查询结果,搜索用时 0 毫秒
941.
邵胜利  柳振清 《蛇志》1992,4(4):7-9
本文通过对我院101例住院精神分裂症患者做了血液流变学10项指标测定,结果表明:患者的全血粘度、血浆粘度、红细胞压积、血小板粘附、红细胞电泳、纤维蛋白原、还原粘度以及体外血栓三项指标中,除还原粘度一项与正常值无显著差异外,其余9项均明显高于正常值。证实精神分裂症存在着高粘滞血症.  相似文献   
942.
Wang Y  Liu Q  Liu Z  Li B  Sun Z  Zhou H  Zhang X  Gong Y  Shao C 《Mutation research》2012,734(1-2):20-29
Berberine has been shown to possess anti-tumor activity against a wide spectrum of cancer cells. It inhibits cancer cell proliferation by inducing cell cycle arrest, at G1 and/or G2/M, and apoptosis. While it has been documented that berberine induces G1 arrest by activating the p53-p21 cascade, it remains unclear what mechanism underlies the berberine-induced G2/M arrest, which is p53-independent. In this study, we tested the anti-proliferative effect of berberine on murine prostate cancer cell line RM-1 and characterized the underlying mechanisms. Berberine dose-dependently induced DNA double-strand breaks and apoptosis. At low concentrations, berberine was observed to induce G1 arrest, concomitant with the activation of p53-p21 cascade. Upon exposure to berberine at a higher concentration (50μM) for 24h, cells exhibited G2/M arrest. Pharmacological inhibition of ATM by KU55933, or Chk1 by UCN-01, could efficiently abrogate the G2/M arrest in berberine-treated cells. Downregulation of Chk1 by RNA interference also abolished the G2/M arrest caused by berberine, confirming the role of Chk1 in the pathway leading to G2/M arrest. Abrogation of G2/M arrest by ATM inhibition forced more cells to undergo apoptosis in response to berberine treatment. Chk1 inhibition by UCN-01, on the other hand, rendered cells more sensitive to berberine only when p53 was inhibited. Our results suggest that combined administration of berberine and caffeine, or other ATM inhibitor, may accelerate the killing of cancer cells.  相似文献   
943.

Background  

Porcine contagious pleuropneumonia (PCP) is a highly contagious disease that is caused by Actinobacillus pleuropneumoniae (APP) and characterized by severe fibrinous necrotizing hemorrhagic pleuropneumonia, which is a severe threat to the swine industry. In addition to APP RTX-toxins I (ApxI), APP RTX-toxin II (ApxII), APP RTX-toxin III (ApxIII) and Outer membrane protein (OMP), there may be other useful antigens that can contribute to protection. In the development of an efficacious vaccine against APP, the immunogenicities of multicomponent recombinant subunit vaccines were evaluated.  相似文献   
944.
锯缘青蟹精子发生的超微结构   总被引:13,自引:0,他引:13  
王艺磊  张子平 《动物学报》1997,43(3):249-254
采用透射电镜观察锯缘青蟹精子发生过程中超微结构的变化,结果表明:精原细胞椭圆形,染色质分布于核膜周围,胞质中具嵴少的线粒体,内质网小泡等。初级精母细胞染色质呈非浓缩状,胞质中具众 内质网小泡,特殊的膜系及晶格状结构。次级精母细胞核质间出现由内质小泡聚集成的腔。  相似文献   
945.
946.
Jiang Y  Yin W  Zhou L  Yan T  Zhou Q  Du Y  Shen Z  Shao Z  Lu J 《PloS one》2012,7(3):e32474

Background

Capecitabine is effective and indicated for the salvage treatment of metastatic breast cancer. Therefore, it is essential to evaluate the efficacy of capecitabine in the adjuvant setting. There have been two large randomized studies to determine whether patients with high-risk early breast cancer benefit from the addition of capecitabine to standard chemotherapy, but they have yielded inconsistent results. We first undertook a meta-analysis to evaluate the efficacy of the addition of capecitabine over standard treatment.

Methods

PubMed, EBSCO, Web of Science, conference proceedings and key trials were searched from 1998 to 2011. The hazard ratio (HR) was used to evaluate the efficacy of a taxane-anthracycline regimen and a taxane-anthracycline-capecitabine regimen in early breast cancer. All of the data from each study use either fixed-effects or random-effects by Stata.

Findings

We found significant improvement in the additional capecitabine arm versus control in disease-free survival (DFS) (HR = 0.83, 95% CI: 0.71–0.98, P = 0.027), overall survival (OS) (HR = 0.71, 95% CI: 0.57–0.88, P = 0.002), distant recurrence (HR = 0.79, 95% CI: 0.66–0.94, P = 0.008) and the death from breast cancer only (HR = 0.65, 95% CI: 0.51–0.83, P = 0.001). Meanwhile, the subgroup analysis revealed that capecitabine improved the DFS in triple negative (HR = 0.71, 95% CI: 0.53–0.96, P = 0.028), hormone receptor negative (HR = 0.73, CI: 0.56–0.94, P = 0.017) and HER2 negative (HR = 0.81, CI: 0.67–0.98, P = 0.034) patients.

Conclusion

Due to the synergistic effect of taxane and capecitabine, taxane-anthracycline-capecitabine regimen may effectively improve the efficacy in the adjuvant setting and may be a novel generation of adjuvant chemotherapy regimen. The results of the current meta-analysis support this hypothesis and indicate that taxane-based regimen with capecitabine may be an effective, convenient, and well tolerated regimen in patients with early breast cancer.  相似文献   
947.
Mesenchymal stem cells (MSCs) are considered to be one of the most promising therapeutic cell sources as they encompass a plasticity of multiple cell lineages. The challenge in using these cells lies in developing well-defined protocols for directing cellular differentiation to generate a desired lineage. In this study, we investigated the effect of 5-azacytidine, a DNA demethylating agent, on osteogenic differentiation of MSCs. The cells were exposed to 5-azacytidine in culture medium for 24 h prior to osteogenic induction. Osteogenic differentiation was determined by several the appearance of a number of osteogenesis characteristics, including gene expression, ALP activity, and calcium mineralization. Pretreatment of MSCs with 5-azacytidine significantly facilitated osteogenic differentiation and was accompanied by hypomethylation of genomic DNA and increased osteogenic gene expression. Taking dlx5 as a representative, methylation alterations of the “CpG island shore” in the promoter caused by 5-azacytidine appeared to contribute to osteogenic differentiation.  相似文献   
948.
蛋白质组学是后基因组时代兴起的新型学科,是从整体水平对蛋白质的综合分析。阿尔茨海默病、帕金森病、肌萎缩侧索硬化症等是最常见的神经退行性疾病。应用蛋白质组学对它们进行研究,不仅可从蛋白质水平上揭示疾病的本质,还有助于全面探讨其病理机制,建立诊断标准,发现药物治疗靶点。  相似文献   
949.
利用硫酸铵分级沉淀、离子交换层析(DEAE-22)、SephadexG-75凝胶过滤从嗜热脂肪芽孢杆菌胞内提纯得B半乳糖甘酶。研究表明,该酶最适表观反应曙度和最适PH分别为60OCT6.4D50OC该酶具有良好的热稳定性.碱金属和碱土金属盐对酶有激活作用,重金属Zn  相似文献   
950.
The NAD-dependent deacetylase Sirtuin 1 (SIRT1) plays a vital role in leukemogenesis. Nicotinamide (NAM) is the principal NAD+ precursor and a noncompetitive inhibitor of SIRT1. In our study, we showed that NAM enhanced the sensitivity of chronic myeloid leukemia (CML) to doxorubicin (DOX) via SIRT1. We found that SIRT1 high expression in CML patients was associated with disease progression and drug resistance. Exogenous NAM efficiently repressed the deacetylation activity of SIRT1 and induced the apoptosis of DOX-resistant K562 cells (K562R) in a dose-dependent manner. Notably, the combination of NAM and DOX significantly inhibited tumor cell proliferation and induced cell apoptosis. The knockdown of SIRT1 in K562R cells enhanced NAM+DOX-induced apoptosis. SIRT1 rescue in K562R reduced the NAM+DOX-induced apoptosis. Mechanistically, the combinatory treatment significantly increased the cleavage of caspase-3 and PARP in K562R in vitro and in vivo. These results suggest the potential role of NAM in increasing the sensitivity of CML to DOX via the inhibition of SIRT1.  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