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   25074篇
  免费   2870篇
  国内免费   1895篇
电工技术   2356篇
综合类   2744篇
化学工业   3028篇
金属工艺   1520篇
机械仪表   1740篇
建筑科学   1757篇
矿业工程   981篇
能源动力   739篇
轻工业   2670篇
水利工程   885篇
石油天然气   758篇
武器工业   414篇
无线电   2724篇
一般工业技术   2002篇
冶金工业   1669篇
原子能技术   330篇
自动化技术   3522篇
  2024年   162篇
  2023年   396篇
  2022年   994篇
  2021年   1243篇
  2020年   937篇
  2019年   658篇
  2018年   720篇
  2017年   795篇
  2016年   721篇
  2015年   1135篇
  2014年   1407篇
  2013年   1657篇
  2012年   2010篇
  2011年   2057篇
  2010年   2095篇
  2009年   1875篇
  2008年   1927篇
  2007年   1874篇
  2006年   1588篇
  2005年   1275篇
  2004年   896篇
  2003年   620篇
  2002年   567篇
  2001年   579篇
  2000年   398篇
  1999年   178篇
  1998年   300篇
  1997年   184篇
  1996年   139篇
  1995年   71篇
  1994年   57篇
  1993年   62篇
  1992年   27篇
  1991年   26篇
  1990年   22篇
  1989年   26篇
  1988年   22篇
  1987年   16篇
  1986年   11篇
  1985年   4篇
  1984年   4篇
  1983年   4篇
  1982年   5篇
  1981年   5篇
  1980年   12篇
  1978年   2篇
  1977年   18篇
  1976年   38篇
  1959年   10篇
  1951年   8篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
数字程序控制计算机辅助教学是将计算机技术用于数字程序控制的教学过程,它帮助学生学习并模拟教学实验.本文介绍了数字程序控制中直线插补和圆孤插补的CAI实现方法.  相似文献   
2.
3.
Forty-three rescuers responding to a bus crash that killed 12 children and 4 adults and injured many more answered questionnaires at 1 and 13 months following the crash. This study compared the responses of the voluntary and professional helpers, using the Impact of Event Scale (IES) and the General Health Questionnaire (GHQ). For all helpers taken together, the decline in IES-intrusion and IES-total scores was significant from 1 to 13 months. The voluntary helpers reported significantly more intrusion and avoidance on the IES at 1 month than professional helpers, and for avoidance the voluntary helpers still evidenced a significantly higher score than professional helpers at 13 months. The GHQ scores at 13 months reflected that the long-term negative impact of the event was low.  相似文献   
4.
吉永业  刘百田 《炼铁》1994,13(6):10-12
太钢4号高炉喷煤站从1990年起采用MFD-Ⅲ型脉动反吹式布袋除尘器。这种除尘器采用脉动式反吹清灰设施,合理布置布袋间距,布袋支撑骨架及选用针呢材质的布袋,过滤面积大,反吹清灰效果好,设备运行平稳,除尘效率高达99.8%,排放浓度小于10mg/m^3,故障率低。  相似文献   
5.
目的探讨膝下动脉的球囊成形术在治疗糖尿病缺血性下肢病变中的价值。方法对53例糖尿病合并缺血性下肢病变患者64侧缺血性下肢进行膝下动脉Deep球囊扩张成形术。对比患者手术前后临床症状的改变及足部溃疡的变化。结果53例患者共119支动脉分支接受PTA治疗,50例患者的101个分支成功地开通,技术成功率为84.9%,所有50例患者的临床症状均明显缓解,足部溃疡均变小,无需截肢。结论膝下动脉的球囊成形术是治疗缺血性糖尿病下肢病变安全有效的微创手段  相似文献   
6.
7.
8.
艺术建筑设计的探索   总被引:1,自引:0,他引:1  
通过徐州一中艺术楼的设计实践,寻求优美而独特的艺术形象,并用纯几何形体的组合来达到功能与形式的完美统一。  相似文献   
9.
Phenotypic analysis of antigen-specific T lymphocytes   总被引:4,自引:0,他引:4  
Identification and characterization of antigen-specific T lymphocytes during the course of an immune response is tedious and indirect. To address this problem, the peptide-major histocompatability complex (MHC) ligand for a given population of T cells was multimerized to make soluble peptide-MHC tetramers. Tetramers of human lymphocyte antigen A2 that were complexed with two different human immunodeficiency virus (HIV)-derived peptides or with a peptide derived from influenza A matrix protein bound to peptide-specific cytotoxic T cells in vitro and to T cells from the blood of HIV-infected individuals. In general, tetramer binding correlated well with cytotoxicity assays. This approach should be useful in the analysis of T cells specific for infectious agents, tumors, and autoantigens.  相似文献   
10.
Human immunodeficiency virus type-1 (HIV-1) Rev acts by inducing the specific nucleocytoplasmic transport of a class of incompletely spliced RNAs that encodes the viral structural proteins. The transfection of HeLa cells with a rev-defective HIV-1 expression plasmid, however, resulted in the export of overexpressed, intron-containing species of viral RNAs, possibly through a default process of nuclear retention. Thus, this system enabled us to directly compare Rev+ and Rev+ cells as to the usage of RRE-containing mRNAs by the cellular translational machinery. Biochemical examination of the transfected cells revealed that although significant levels of gag and env mRNAs were detected in both the presence and absence of Rev, efficient production of viral proteins was strictly dependent on the presence of Rev. A fluorescence in situ hybridisation assay confirmed these findings and provided further evidence that even in the presence of Rev, not all of the viral mRNA was equally translated. At the early phase of RNA export in Rev+ cells, gag mRNA was observed throughout both the cytoplasm and nucleoplasm as uniform fine stippling. In addition, the mRNA formed clusters mainly in the perinuclear region, which were not observed in Rev+ cells. In the presence of Rev, expression of the gag protein was limited to these perinuclear sites where the mRNA accumulated. Subsequent staining of the cytoskeletal proteins demonstrated that in Rev+ cells gag mRNA is colocalized with beta-actin in the sites where the RNA formed clusters. In the absence of Rev, in contrast, the gag mRNA failed to associate with the cytoskeletal proteins. These results suggest that in addition to promoting the emergence of intron-containing RNA from the nucleus, Rev plays an important role in the compartmentation of translation by directing RRE-containing mRNAs to the beta-actin to form the perinuclear clusters at which the synthesis of viral structural proteins begins.  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