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   621843篇
  免费   9257篇
  国内免费   2480篇
电工技术   11191篇
综合类   855篇
化学工业   90784篇
金属工艺   22934篇
机械仪表   18037篇
建筑科学   16271篇
矿业工程   2326篇
能源动力   16167篇
轻工业   57919篇
水利工程   5786篇
石油天然气   7173篇
武器工业   56篇
无线电   78082篇
一般工业技术   119449篇
冶金工业   117663篇
原子能技术   11937篇
自动化技术   56950篇
  2021年   4478篇
  2019年   4208篇
  2018年   6880篇
  2017年   7003篇
  2016年   7498篇
  2015年   5488篇
  2014年   9213篇
  2013年   28574篇
  2012年   15632篇
  2011年   22115篇
  2010年   17080篇
  2009年   19515篇
  2008年   20651篇
  2007年   20981篇
  2006年   18478篇
  2005年   17150篇
  2004年   16850篇
  2003年   16421篇
  2002年   15824篇
  2001年   15829篇
  2000年   14893篇
  1999年   15630篇
  1998年   36787篇
  1997年   26465篇
  1996年   19689篇
  1995年   15919篇
  1994年   14096篇
  1993年   13865篇
  1992年   10150篇
  1991年   9736篇
  1990年   9325篇
  1989年   8990篇
  1988年   8502篇
  1987年   7455篇
  1986年   7449篇
  1985年   8757篇
  1984年   8151篇
  1983年   7234篇
  1982年   6785篇
  1981年   6799篇
  1980年   6504篇
  1979年   6293篇
  1978年   6020篇
  1977年   7079篇
  1976年   9560篇
  1975年   5133篇
  1974年   4939篇
  1973年   4873篇
  1972年   4036篇
  1971年   3511篇
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
81.
82.
83.
84.
85.
Site-specific seismic hazard analysis is crucial for designing earthquake resistance structures, particularly in seismically active regions. Shear wave velocity ( V S) is a key parameter in such analysis, although the economy and other factors restrict its direct field measurement in many cases. Various V S–SPT– N correlations are routinely incorporated in seismic hazard analysis to estimate the value of V S. However, many uncertainties question the reliability of these estimated V S values. This paper comes up with a statistical approach to take care of such uncertainties involved in V S calculations. The measured SPT– N values from all the critical boreholes were converted into statistical parameters and passed through various correlations to estimate V S at different depths. The effect of different soil layers in the boreholes on the Vs estimation was also taken into account. Further, the average shear wave velocity of the top 30 m soil cover ( V S30) is estimated after accounting for various epistemic and aleatoric uncertainties. The scattering nature of the V S values estimated using different V SN correlations was reduced significantly with the application of the methodology. Study results further clearly demonstrated the potential of the approach to eliminate various uncertainties involved in the estimation of V S30 using general and soil-specific correlations.  相似文献   
86.
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   
87.
Interaction of molybdenyl(VI) bis(acetylacetonate) with polyphenylsiloxane in xylene and under mechanochemical activation conditions has been investigated. The interaction in solution proceeds with splitting of the siloxane bond and formation of polymolybdenum(VI) phenylsiloxane with different silicon/metal ratios. The fractions with the silicon/metal ratio < 2 are characterized with high degree of crystallinity and low solubility, whereas those with the ratio > 2 are amorphous. The interaction of the above reagents under mechanical activation conditions proceeds with the formation of soluble polymers similar to those obtained in a solution with the silicon/molybdenum ratio equal to 2.6. The crystal chemistry parameters of the fraction obtained in solution with the ratio Si/Mo equals to 1:2 have been calculated on the basis of the X-ray diffraction analysis data using the Debye–Shearer equation. It has been demonstrated that the chain cross section found using the Miller–Boyer method coincides with that calculated geometrically on the basis of literature data on bond lengths and angles. It is shown that the interaction of molybdenyl(VI) bis(acetylacetonate) with polyphenylsiloxane takes place in solution more deeply than under the conditions of mechanochemical activation and is accompanied by the process of separation siloxanes connection. This leads to the formation of a fraction with smaller ratio of substances than the initial ratio.  相似文献   
88.
89.
90.
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