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   515831篇
  免费   8729篇
  国内免费   2614篇
电工技术   10925篇
综合类   2349篇
化学工业   76685篇
金属工艺   21705篇
机械仪表   19541篇
建筑科学   15931篇
矿业工程   2250篇
能源动力   12763篇
轻工业   46793篇
水利工程   4862篇
石油天然气   5179篇
武器工业   223篇
无线电   65915篇
一般工业技术   99285篇
冶金工业   82066篇
原子能技术   7097篇
自动化技术   53605篇
  2021年   3773篇
  2020年   2646篇
  2019年   3150篇
  2018年   12989篇
  2017年   13871篇
  2016年   9533篇
  2015年   5042篇
  2014年   7227篇
  2013年   21124篇
  2012年   14641篇
  2011年   24916篇
  2010年   20791篇
  2009年   21352篇
  2008年   21900篇
  2007年   24159篇
  2006年   14558篇
  2005年   17097篇
  2004年   14454篇
  2003年   13692篇
  2002年   12419篇
  2001年   11970篇
  2000年   11279篇
  1999年   11738篇
  1998年   24901篇
  1997年   18332篇
  1996年   14646篇
  1995年   11601篇
  1994年   10274篇
  1993年   9814篇
  1992年   7439篇
  1991年   7031篇
  1990年   6624篇
  1989年   6258篇
  1988年   5999篇
  1987年   4976篇
  1986年   4909篇
  1985年   6025篇
  1984年   5641篇
  1983年   4863篇
  1982年   4527篇
  1981年   4465篇
  1980年   4226篇
  1979年   4090篇
  1978年   3776篇
  1977年   4557篇
  1976年   6108篇
  1975年   3119篇
  1974年   3013篇
  1973年   2896篇
  1972年   2320篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
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   
43.
44.
45.
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   
46.
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   
47.
48.
49.
The environmental performance of 316L grade stainless steel, in the form of tensile specimens containing a single corrosion pit with various aspect ratios, under cyclic loading in aerated chloride solutions is investigated in this study. Results from environmental tests were compared and contrasted with those obtained using finite element analysis (FEA). Fractography of the failed specimens obtained from experiments revealed that fatigue crack initiation took place at the base of the shallow pit. The crack initiation shifted towards the shoulder and the mouth of the pit for pits of increasing depth. This process is well predicted by FEA, as the strain contour maps show that strain is the highest around the centric strip of the pit. However, for shallow pits, local strain is uniformly distributed around that strip but begins to concentrate more towards the shoulder and the mouth region for increasingly deep pits.  相似文献   
50.
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