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   352446篇
  免费   5522篇
  国内免费   896篇
电工技术   6798篇
综合类   1188篇
化学工业   52568篇
金属工艺   10950篇
机械仪表   9853篇
建筑科学   8954篇
矿业工程   1261篇
能源动力   9252篇
轻工业   33985篇
水利工程   3138篇
石油天然气   3752篇
武器工业   14篇
无线电   41722篇
一般工业技术   62339篇
冶金工业   74353篇
原子能技术   5668篇
自动化技术   33069篇
  2021年   2696篇
  2019年   2391篇
  2018年   4296篇
  2017年   4365篇
  2016年   4832篇
  2015年   3466篇
  2014年   5090篇
  2013年   15166篇
  2012年   9656篇
  2011年   12836篇
  2010年   8815篇
  2009年   10168篇
  2008年   10448篇
  2007年   10374篇
  2006年   9238篇
  2005年   11165篇
  2004年   10319篇
  2003年   9562篇
  2002年   8244篇
  2001年   8315篇
  2000年   7534篇
  1999年   8101篇
  1998年   22688篇
  1997年   15919篇
  1996年   12181篇
  1995年   9104篇
  1994年   8091篇
  1993年   7830篇
  1992年   5493篇
  1991年   5309篇
  1990年   5183篇
  1989年   5024篇
  1988年   4928篇
  1987年   4068篇
  1986年   4184篇
  1985年   4871篇
  1984年   4350篇
  1983年   4100篇
  1982年   3710篇
  1981年   3920篇
  1980年   3643篇
  1979年   3470篇
  1978年   3315篇
  1977年   4361篇
  1976年   6002篇
  1975年   2874篇
  1974年   2694篇
  1973年   2716篇
  1972年   2252篇
  1971年   2009篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
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   
92.
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   
93.
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   
94.
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   
95.
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   
96.
97.
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   
98.
99.
100.
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