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   346431篇
  免费   5063篇
  国内免费   884篇
电工技术   6683篇
综合类   1182篇
化学工业   50723篇
金属工艺   10856篇
机械仪表   9642篇
建筑科学   8695篇
矿业工程   1248篇
能源动力   8951篇
轻工业   32882篇
水利工程   3034篇
石油天然气   3716篇
武器工业   12篇
无线电   41391篇
一般工业技术   61465篇
冶金工业   74241篇
原子能技术   5627篇
自动化技术   32030篇
  2021年   2347篇
  2019年   2178篇
  2018年   4037篇
  2017年   4090篇
  2016年   4544篇
  2015年   3282篇
  2014年   4834篇
  2013年   14646篇
  2012年   9302篇
  2011年   12376篇
  2010年   8504篇
  2009年   9821篇
  2008年   10142篇
  2007年   10128篇
  2006年   9014篇
  2005年   11026篇
  2004年   10201篇
  2003年   9450篇
  2002年   8140篇
  2001年   8238篇
  2000年   7463篇
  1999年   8033篇
  1998年   22629篇
  1997年   15872篇
  1996年   12134篇
  1995年   9067篇
  1994年   8061篇
  1993年   7807篇
  1992年   5478篇
  1991年   5299篇
  1990年   5167篇
  1989年   5008篇
  1988年   4916篇
  1987年   4060篇
  1986年   4175篇
  1985年   4858篇
  1984年   4332篇
  1983年   4083篇
  1982年   3702篇
  1981年   3910篇
  1980年   3631篇
  1979年   3464篇
  1978年   3311篇
  1977年   4352篇
  1976年   5997篇
  1975年   2870篇
  1974年   2692篇
  1973年   2715篇
  1972年   2252篇
  1971年   2006篇
排序方式: 共有10000条查询结果,搜索用时 367 毫秒
81.
Technical Physics Letters - The influence of excitation photons energy on the relaxation times of photoexcited carriers is studied. The involved relaxation mechanisms are evaluated and the...  相似文献   
82.
Technical Physics Letters - Specific features of monitoring the state of a flowing medium by method of nuclear magnetic resonance (NMR) are considered. An approach to studying the state of a...  相似文献   
83.
Technical Physics Letters - We present the results of a comparative investigation of the friction and wear characteristics of MoSx and MoSex coatings in an oxidizing medium (argon–air...  相似文献   
84.
Fusion behavior of poly(vinyl chloride) (PVC) compounds plays an important role in the development of physical properties of processed material. The fusion characteristics in PVC processing are governed by material variables that affect the fusion with some interactions. In this research, the aim was to characterize the effects of formulation ingredients on fusion characteristics of PVC. Four material parameters, including the contents of nanoclay (NC), azodicarbonamide, calcium stearate, and processing aid, are proposed as affecting variables. The fusion time (FT) as well as fusion factor (FF) are considered fusion indicators and are experimentally determined in some different levels of affecting parameters. The multivariable regression analysis (MRA) and the Artificial Neural Network (ANN) modeling are considered as two analytical methods. The regression analysis result for the FT denotes, in part, significant linear and quadratic effects of NC and also its significant interactions with azodicarbonamide and calcium stearate, whereas that of FF indicates only a linear effect of NC. ANN modeling is performed with a three‐layer (input, hidden, and output) neural network. The results of the comparison of the MRA and ANN predictions with experimental values are reported as the correlation coefficient (R2), mean‐square error, and mean absolute percentage error for both FF and FT parameters. The obtained values clearly denote that the ANN results are more precise and especially more general than those of MRA. However, in the case of FT, improvement of the ANN modeling is much greater than that of FF. J. VINYL ADDIT. TECHNOL., 21:147–155, 2015. © 2014 Society of Plastics Engineers  相似文献   
85.
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   
86.
87.
Powder Metallurgy and Metal Ceramics - Multiphase La 2 MgNi 9 alloys are synthesized by induction melting. The crystalline structures of all phases in the alloys are determined with X-ray...  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