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   416641篇
  免费   6771篇
  国内免费   1404篇
电工技术   7743篇
综合类   370篇
化学工业   62869篇
金属工艺   14360篇
机械仪表   11977篇
建筑科学   11907篇
矿业工程   877篇
能源动力   11300篇
轻工业   44078篇
水利工程   3353篇
石油天然气   1866篇
武器工业   13篇
无线电   55773篇
一般工业技术   77521篇
冶金工业   75583篇
原子能技术   5605篇
自动化技术   39621篇
  2021年   2822篇
  2019年   2591篇
  2018年   4024篇
  2017年   4017篇
  2016年   4284篇
  2015年   3540篇
  2014年   5871篇
  2013年   19572篇
  2012年   10451篇
  2011年   14945篇
  2010年   11500篇
  2009年   13094篇
  2008年   14140篇
  2007年   14502篇
  2006年   12941篇
  2005年   12122篇
  2004年   11705篇
  2003年   11405篇
  2002年   11026篇
  2001年   11195篇
  2000年   10343篇
  1999年   10826篇
  1998年   24193篇
  1997年   17702篇
  1996年   13975篇
  1995年   11060篇
  1994年   9831篇
  1993年   9409篇
  1992年   7162篇
  1991年   6824篇
  1990年   6421篇
  1989年   6125篇
  1988年   5889篇
  1987年   4907篇
  1986年   4848篇
  1985年   6001篇
  1984年   5615篇
  1983年   4845篇
  1982年   4518篇
  1981年   4473篇
  1980年   4225篇
  1979年   4100篇
  1978年   3787篇
  1977年   4572篇
  1976年   6137篇
  1975年   3126篇
  1974年   3015篇
  1973年   2897篇
  1972年   2329篇
  1971年   2005篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
43.
44.
The diagnosis and treatment of prostate cancer (PCa) is a major health-care concern worldwide. This cancer can manifest itself in many distinct forms and the transition from clinically indolent PCa to the more invasive aggressive form remains poorly understood. It is now universally accepted that glycan expression patterns change with the cellular modifications that accompany the onset of tumorigenesis. The aim of this study was to investigate if differential glycosylation patterns could distinguish between indolent, significant, and aggressive PCa. Whole serum N-glycan profiling was carried out on 117 prostate cancer patients’ serum using our automated, high-throughput analysis platform for glycan-profiling which utilizes ultra-performance liquid chromatography (UPLC) to obtain high resolution separation of N-linked glycans released from the serum glycoproteins. We observed increases in hybrid, oligomannose, and biantennary digalactosylated monosialylated glycans (M5A1G1S1, M8, and A2G2S1), bisecting glycans (A2B, A2(6)BG1) and monoantennary glycans (A1), and decreases in triantennary trigalactosylated trisialylated glycans with and without core fucose (A3G3S3 and FA3G3S3) with PCa progression from indolent through significant and aggressive disease. These changes give us an insight into the disease pathogenesis and identify potential biomarkers for monitoring the PCa progression, however these need further confirmation studies.  相似文献   
45.
46.
47.
48.
49.
Combined photochemical arylation, “nuisance effect” (SNAr) reaction sequences have been employed in the design of small arrays for immediate deployment in medium-throughput X-ray protein–ligand structure determination. Reactions were deliberately allowed to run “out of control” in terms of selectivity; for example the ortho-arylation of 2-phenylpyridine gave five products resulting from mono- and bisarylations combined with SNAr processes. As a result, a number of crystallographic hits against NUDT7, a key peroxisomal CoA ester hydrolase, have been identified.  相似文献   
50.
A tensile properties testing study was conducted to understand the influence of thickness, cross-head speed (speed of testing), gauge length (GL; specimen test length), and sample shape on important tensile properties of polyvinyl alcohol (PVA) nanofiber webs. The effects of each testing parameter on load at break, extension at break, Young's modulus, and tensile stress–strain curve of PVA nanofiber webs are analyzed. The Welch two sample t-tests show the significant difference among tested data. Using interaction plots, two-way analysis of variance, and margin mean plots, the interaction effects among testing parameters have been analyzed. Of all the factors, cross-head speed, the interaction among GL, and sample thickness (GL: Thickness) and the interaction among GL, testing speed and sample thickness (GL: Speed: Thickness) have significant influence on the tensile properties of PVA nanofiber webs. Moreover, the hypothesized model of mechanism of tensile strain–stress curve of PVA nanofiber webs has been proposed. Based on the model, the tensile strain–stress curve can be split into three stages: linear elastic, partial break up, and complete breakage. This study will provide a better understanding of tensile testing parameters' effects and their interaction effects on the tensile properties of nanowebs.  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