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   200996篇
  免费   3308篇
  国内免费   2133篇
电工技术   4814篇
综合类   1580篇
化学工业   23987篇
金属工艺   13727篇
机械仪表   10276篇
建筑科学   4952篇
矿业工程   1731篇
能源动力   4117篇
轻工业   8575篇
水利工程   2202篇
石油天然气   3699篇
武器工业   213篇
无线电   25310篇
一般工业技术   44745篇
冶金工业   32414篇
原子能技术   2695篇
自动化技术   21400篇
  2023年   581篇
  2022年   1095篇
  2021年   1574篇
  2020年   1222篇
  2019年   1259篇
  2018年   10723篇
  2017年   11452篇
  2016年   6755篇
  2015年   2349篇
  2014年   2634篇
  2013年   5870篇
  2012年   6610篇
  2011年   14090篇
  2010年   12786篇
  2009年   12124篇
  2008年   11859篇
  2007年   14337篇
  2006年   4875篇
  2005年   8162篇
  2004年   5872篇
  2003年   5259篇
  2002年   3866篇
  2001年   3491篇
  2000年   3307篇
  1999年   3621篇
  1998年   9824篇
  1997年   6504篇
  1996年   5082篇
  1995年   3458篇
  1994年   3057篇
  1993年   2919篇
  1992年   1776篇
  1991年   1696篇
  1990年   1579篇
  1989年   1369篇
  1988年   1231篇
  1987年   892篇
  1986年   908篇
  1985年   927篇
  1984年   815篇
  1983年   710篇
  1982年   709篇
  1981年   686篇
  1980年   568篇
  1979年   476篇
  1978年   414篇
  1977年   533篇
  1976年   958篇
  1975年   299篇
  1974年   276篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
The data on the use of solar photovoltaic plants (PVPs) for providing a reliable and guaranteed power supply to telecommunication systems and cellular communication systems in the conditions prevalent in Uzbekistan are given. The research-based structures developed by OOO MIR SOLAR and the selection of PVP elements ensuring their reliable operation are described. The main influencing factors are discussed, and the use of effective combinations of different types of panels (from monocrystalline and polycrystalline silicon) and a specially developed controller are considered.  相似文献   
52.
This work presents simulation of microstructure evolution in the nugget zone (NZ) of a AZ31-Mg-alloy friction stir weld. The process parameters (tool geometrical characteristics, rotational speed, travel speed, applied load) have been correlated with the resulting microstructural features in the NZ of the weld (grain size and population) with the aid of the MICRESS software, which provides the ability to simulate both nucleation and grain growth during dynamic recrystallization phenomena evolving in the NZ during the weld thermal cycle. The input parameters of the developed model include the tool geometry, the welding conditions as well as the recrystallization energy, the grain boundary mobility and specific material properties. NZ microstructure obtained by simulation shows good agreement with experimental measurements for both grain population and size.  相似文献   
53.
54.
55.
56.
Everninomicins are orthoester oligosaccharide antibiotics with potent activity against multidrug-resistant bacterial pathogens. Everninomicins act by disrupting ribosomal assembly in a distinct region in comparison to clinically prescribed drugs. We employed microporous intergeneric conjugation with Escherichia coli to manipulate Micromonospora for targeted gene-replacement studies of multiple putative methyltransferases across the octasaccharide scaffold of everninomicin effecting the A1, C, F, and H rings. Analyses of gene-replacement and genetic complementation mutants established the mutability of the everninomicin scaffold through the generation of 12 previously unreported analogues and, together with previous results, permitted assignment of the ten methyltransferases required for everninomicin biosynthesis. The in vitro activity of A1- and H-ring-modifying methyltransferases demonstrated the ability to catalyze late-stage modification of the scaffold on an A1-ring phenol and H-ring C-4’ hydroxy moiety. Together these results establish the potential of the everninomicin scaffold for modification through mutagenesis and in vitro modification of advanced biosynthetic intermediates.  相似文献   
57.
58.
59.
Circulating nucleic acids (CNAs) are under investigation as a liquid biopsy in cancer as potential non-invasive biomarkers, as stable structure in circulation nucleosomes could be valuable sources for detection of cancer-specific alterations in histone modifications. Our interest is in histone methylation marks with a focus on colorectal cancer, one of the leading cancers respective the incidence and mortality. Our previous work included the analysis of trimethylations of lysine 9 on histone 3 (H3K9me3) and of lysine 20 on histone 4 (H4K20me3) by chromatin immuno- precipitation-related PCR in circulating nucleosomes. Here we asked whether global immunologic measurement of histone marks in circulation could be a suitable approach to show their potential as biomarkers. In addition to H3K9me3 and H4K20me3 we also measured H3K27me3 in plasma samples from CRC patients (n = 63) and cancer free individuals (n = 40) by ELISA-based methylation assays. Our results show that of three marks, the amounts of H3K27me3 (p = 0.04) and H4K20me3 (p < 0.001) were significantly lower in CRC patients than in healthy controls. For H3K9me3 similar amounts were measured in both groups. Areas under the curve (AUC) in receiver operating characteristic (ROC) curves indicating the power of CRC detection were 0.620 for H3K27me3, 0.715 for H4K20me3 and 0.769 for the combination of both markers. In conclusion, findings of this preliminary study reveal the potential of blood-based detection of CRC by quantification of histone methylation marks and the additive effect of the marker combination.  相似文献   
60.
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