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   346925篇
  免费   5112篇
  国内免费   888篇
电工技术   6701篇
综合类   1183篇
化学工业   50966篇
金属工艺   10875篇
机械仪表   9653篇
建筑科学   8702篇
矿业工程   1248篇
能源动力   8967篇
轻工业   32939篇
水利工程   3054篇
石油天然气   3719篇
武器工业   12篇
无线电   41420篇
一般工业技术   61514篇
冶金工业   74255篇
原子能技术   5628篇
自动化技术   32089篇
  2021年   2380篇
  2019年   2191篇
  2018年   4064篇
  2017年   4099篇
  2016年   4559篇
  2015年   3289篇
  2014年   4840篇
  2013年   14677篇
  2012年   9331篇
  2011年   12394篇
  2010年   8519篇
  2009年   9835篇
  2008年   10154篇
  2007年   10135篇
  2006年   9018篇
  2005年   11028篇
  2004年   10204篇
  2003年   9454篇
  2002年   8145篇
  2001年   8242篇
  2000年   7466篇
  1999年   8037篇
  1998年   22633篇
  1997年   15874篇
  1996年   12135篇
  1995年   9068篇
  1994年   8063篇
  1993年   7811篇
  1992年   5480篇
  1991年   5300篇
  1990年   5167篇
  1989年   5009篇
  1988年   4917篇
  1987年   4063篇
  1986年   4177篇
  1985年   4860篇
  1984年   4332篇
  1983年   4086篇
  1982年   3702篇
  1981年   3910篇
  1980年   3631篇
  1979年   3465篇
  1978年   3311篇
  1977年   4352篇
  1976年   5998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 15 毫秒
81.
The data on the use of solar photovoltaic plants (PVPs) for providing a reliable and guaranteed power supply to telecommunication systems and cellular communication systems in the conditions prevalent in Uzbekistan are given. The research-based structures developed by OOO MIR SOLAR and the selection of PVP elements ensuring their reliable operation are described. The main influencing factors are discussed, and the use of effective combinations of different types of panels (from monocrystalline and polycrystalline silicon) and a specially developed controller are considered.  相似文献   
82.
This work investigates the effect of the addition of small amounts of Ru (0.5‐1 wt%) to carbon supported Co (10 wt%) catalysts towards both NaBH4 and NH3BH3 hydrolysis for H2 production. In the sodium borohydride hydrolysis, the activity of Ru‐Co/carbon catalysts was sensibly higher than the sum of the activities of corresponding monometallic samples, whereas for the ammonia borane hydrolysis, the positive effect of Ru‐Co systems with regard to catalytic activity was less evident. The performances of Ru‐Co bimetallic catalysts correlated with the occurrence of an interaction between Ru and Co species resulting in the formation of smaller ruthenium and cobalt oxide particles with a more homogeneous dispersion on the carbon support. It was proposed that Ru°, formed during the reduction step of the Ru‐Co catalysts, favors the H2 activation, thus enhancing the reduction degree of the cobalt precursor and the number of Co nucleation centers. A subsequent reduction of cobalt and ruthenium species also occurs in the hydride reaction medium, and therefore the state of the catalyst before the catalytic experiment determines the state of the active phase formed in situ. The different relative reactivity of the Ru and Co active species towards the two investigated reactions accounted for the different behavior towards NaBH4 and NH3BH3 hydrolysis.  相似文献   
83.
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   
84.
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   
85.
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   
86.
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   
87.
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   
88.
89.
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   
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