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   422777篇
  免费   7490篇
  国内免费   1389篇
电工技术   7820篇
综合类   357篇
化学工业   64734篇
金属工艺   14451篇
机械仪表   12208篇
建筑科学   12061篇
矿业工程   902篇
能源动力   11545篇
轻工业   45901篇
水利工程   3413篇
石油天然气   1900篇
武器工业   13篇
无线电   55944篇
一般工业技术   78222篇
冶金工业   75776篇
原子能技术   5634篇
自动化技术   40775篇
  2021年   3162篇
  2020年   2189篇
  2019年   2861篇
  2018年   4374篇
  2017年   4444篇
  2016年   4689篇
  2015年   3824篇
  2014年   6251篇
  2013年   20295篇
  2012年   10977篇
  2011年   15507篇
  2010年   11889篇
  2009年   13540篇
  2008年   14446篇
  2007年   14802篇
  2006年   13154篇
  2005年   12250篇
  2004年   11795篇
  2003年   11522篇
  2002年   11099篇
  2001年   11249篇
  2000年   10384篇
  1999年   10870篇
  1998年   24214篇
  1997年   17738篇
  1996年   14033篇
  1995年   11072篇
  1994年   9844篇
  1993年   9414篇
  1992年   7154篇
  1991年   6831篇
  1990年   6418篇
  1989年   6148篇
  1988年   5884篇
  1987年   4906篇
  1986年   4848篇
  1985年   6000篇
  1984年   5614篇
  1983年   4840篇
  1982年   4511篇
  1981年   4456篇
  1980年   4219篇
  1979年   4089篇
  1978年   3785篇
  1977年   4556篇
  1976年   6121篇
  1975年   3124篇
  1974年   3013篇
  1973年   2895篇
  1972年   2321篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
53.
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   
54.
55.
56.
57.
58.
59.
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   
60.
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