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   35112篇
  免费   3194篇
  国内免费   3907篇
  42213篇
  2024年   131篇
  2023年   546篇
  2022年   1090篇
  2021年   1751篇
  2020年   1268篇
  2019年   1566篇
  2018年   1569篇
  2017年   1098篇
  2016年   1498篇
  2015年   2307篇
  2014年   2648篇
  2013年   2758篇
  2012年   3385篇
  2011年   3018篇
  2010年   1989篇
  2009年   1683篇
  2008年   2006篇
  2007年   1695篇
  2006年   1530篇
  2005年   1300篇
  2004年   1131篇
  2003年   1054篇
  2002年   886篇
  2001年   568篇
  2000年   486篇
  1999年   506篇
  1998年   312篇
  1997年   237篇
  1996年   209篇
  1995年   212篇
  1994年   219篇
  1993年   139篇
  1992年   188篇
  1991年   150篇
  1990年   122篇
  1989年   92篇
  1988年   99篇
  1987年   78篇
  1986年   78篇
  1985年   87篇
  1984年   58篇
  1983年   42篇
  1982年   41篇
  1981年   32篇
  1979年   28篇
  1978年   24篇
  1977年   19篇
  1974年   24篇
  1973年   26篇
  1972年   21篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
Polo-like kinase 1 is a serine/threonine kinase which plays an essential role in mitosis and malignant transformation. The aim of this study was to investigate the prognostic significance of polo-like kinase 1 expression and determine its possibility as a therapeutic target in non-small cell lung cancer. Semi-quantitative RT-PCR assay was performed to detect polo-like kinase 1 mRNA expression in non-small cell lung cancer cells or tissues. Immunohistochemistry was performed to detect polo-like kinase 1 protein expression in 100 non-small cell lung cancer tissue samples, and the associations of polo-like kinase 1 expression with clinicopathological factors or prognosis of non-small cell lung cancer patients were evaluated. RNA interference was employed to inhibit endogenous polo-like kinase 1 expression and analyzed the effects of polo-like kinase 1 inhibition on the malignant phenotypes of non-small cell lung cancer cells including growth, apoptosis, radio- or chemoresistance. Also, the possible molecular mechanisms were also investigated. The levels of polo-like kinase 1 mRNA expression in non-small cell lung cancer cell lines or tissues were significantly higher than those in normal human bronchial epithelial cell line or corresponding non-tumor tissues. High polo-like kinase 1 expression was significantly correlated with advanced clinical stage, higher tumor classification and lymph node metastasis of non-small cell lung cancer patients (P = 0.001, 0.004 and 0.001, respectively). Meanwhile, high polo-like kinase 1 protein expression was also an independent prognostic molecular marker for non-small cell lung cancer patients (hazard ratio: 2.113; 95% confidence interval: 1.326-3.557; P = 0.017). Polo-like kinase 1 inhibition could significantly inhibit in vitro and in vivo proliferation, induce cell arrest of G2/M phase and apoptosis enhancement in non-small cell lung cancer cells, which might be activation of the p53 pathway and the Cdc25C/cdc2/cyclin B1 feedback loop. Further, inhibition of polo-like kinase 1 could enhance the sensitivity of non-small cell lung cancer cells to taxanes or irradiation. Thus, polo-like kinase 1 might be a prognostic marker and a chemo- or radiotherapeutic target for non-small cell lung cancer.  相似文献   
92.
93.
Glycogen storage disease type Ib (GSD-Ib) is caused by a deficiency in the glucose-6-phosphate transporter (G6PT). Sequence alignments identify a signature motif shared by G6PT and a family of transporters of phosphorylated metabolites. Two null signature motif mutations have been identified in the G6PT gene of GSD-Ib patients. In this study, we characterize the activity of seven additional mutants within the motif. Five mutants lack microsomal G6P uptake activity and one retains residual activity, suggesting that in G6PT the signature motif is a functional element required for microsomal glucose-6-phosphate transport.  相似文献   
94.
大鼠实验性脾虚证胰腺组织化学研究   总被引:6,自引:0,他引:6  
用成年雄性Wistar大鼠30只,分为(1)正常对照组,喂饲自来水。(2)脾虚组,用苦降破气中药和饮食失节法致成脾虚模型。(3)自然恢复组,动物致虚后,喂饲自来水。(4)中药治疗组。取四组动物胰腺进行RNA,琥珀酸脱氢酶(SDH),乳酸脱氢酶(LDH),三磷酸腺苷酶(ATPase),葡萄糖-6-磷酸酶(G-6-Pase)和硫胺素焦磷酸酶(TPPase)组织化学反应和观察,并对SDH,LDH,RNA进行了显微分光光度计定量测定。本研究结果表明,脾虚组胰腺泡细胞的RNA,SDH,ATPase,G-6-Pase,TPPase含量和活性都低于对照组,而LDH活性高于对照组。治疗组与自然恢复组相比,治疗组胰腺泡细胞以上指标接近对照组。定量测定与定性的结果一致。本研究表明,脾虚证时胰腺泡细胞上述几种酶活性和RNA明显下降,可能在脾虚证发病中起主要作用,中药治疗有显著改善  相似文献   
95.
Alien species are brought into countries world wide on a massive scale for agricultural production, ex situ conservation, landscape aesthetics, gardens, and ecosystem restoration. Unfortunately, some of these species have escaped and adversely impacted on regional as well as global biodiversity conservation and agricultural production. To reduce such risks, it is necessary to implement specific and effective measures. Since various government departments and institutions are involved in the management of alien species, it is difficult to prevent native and agroecosystems from being invaded by invited species. We propose the establishment of a supervision and inspection continuum over intentional species introduction, similar to that which exists in some countries over unintentional species introductions. Namely, a justification of the necessity to import, a risk assessment, assurances as to provision of an adequate containment facility assessment, and a damage-limitation protocol should that need to be invoked. These requirements should be satisfied before an alien species is knowingly imported, and the necessary follow-up supervision is important post- importation.  相似文献   
96.
Summary A second species of the hitherto monotypic genusKymatocalyx Herz. is described and figured in detail. The new combinationKymatocalyx dominicensis (Spruce) comb. nova is proposed.  相似文献   
97.
几种常用杀虫剂对蚜虫天敌——瓢虫的影响   总被引:1,自引:0,他引:1  
作者等就11种常用杀虫剂对蚜虫的重要天敌——瓢虫进行了毒性测定,观察了它们对瓢虫的各个虫态的影响。 供试药剂 20%乐果乳剂、50%敌敌畏乳剂、50%对硫磷乳剂、50%内吸磷乳剂、25%三硫磷乳剂、50%杀螟硫磷乳剂、50%磷胺液剂、20%酚开普敦乳剂、6%丙体六六六乳剂、6%丙体六六六可湿性粉(W、P)、2.5%鱼籐精乳剂。 供试瓢虫 异色瓢虫Leis axyridis,室内饲养;龟纹瓢虫Propylaea japonica,田间采回。  相似文献   
98.
本文通过从污水处理厂活性污泥中分离得到一株高效降解轻油(煤油)细菌5092-2,通过形态学、16S rRNA鉴定该菌为Mangroveibacter sp.。进一步对其生长条件进行了研究,发现该菌在23℃到38℃、pH为5.0到9.0范围内生长无明显差异。在温度为35℃,pH 7.2~7.4,160 r/min培养7 d,菌株降解煤油的能力达到52.3%,具有进一步研究的价值。  相似文献   
99.
In this study, we characterized the intratumoral expression of IL-17 and CD8(+) TILs in gastric adenocarcinoma patients after resection and determined the correlation between the survival probability of gastric adenocarcinoma patients and the expression of IL-17 in tumor. Expression of IL-17 and CD8 was assessed by immunohistochemistry, and the prognostic effects of intratumoral IL-17 expression and CD8(+) TILs were evaluated by Cox regression and Kaplan-Meier analysis. Immunohistochemical detection revealed the presence of IL-17 and CD8(+) cells in gastric adenocarcinoma tissue samples (90.6%, 174 out of 192 patients and 96.9%, 186 out of 192 patients, respectively). We have also found that intratumoral IL-17 expression was significantly correlated with age (p=0.004) and that the number of CD8(+)TILs was significantly correlated with UICC staging (p=0.012) and the depth of tumor invasion (p=0.022). The five-year overall survival probability among patients intratumorally expressing higher levels of IL-17 was significantly better than those expressing lower levels of IL-17 (p=0.036). Multivariate Cox proportional hazard analyses revealed that intratumoral IL-17 expression (HR: 0.521; 95% CI: 0.329-0.823; p=0.005) was an independent factor affecting the five-year overall survival probability. We conclude that low levels of intratumoral IL-17 expression may indicate poor prognosis in gastric adenocarcinoma patients.  相似文献   
100.
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