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   431671篇
  免费   7225篇
  国内免费   1383篇
电工技术   7786篇
综合类   332篇
化学工业   65519篇
金属工艺   16978篇
机械仪表   14108篇
建筑科学   9168篇
矿业工程   2221篇
能源动力   12056篇
轻工业   33361篇
水利工程   4556篇
石油天然气   8023篇
武器工业   22篇
无线电   50326篇
一般工业技术   87828篇
冶金工业   81469篇
原子能技术   9290篇
自动化技术   37236篇
  2022年   2644篇
  2021年   4670篇
  2020年   3593篇
  2019年   4549篇
  2018年   7709篇
  2017年   7648篇
  2016年   8150篇
  2015年   5215篇
  2014年   8224篇
  2013年   22284篇
  2012年   13084篇
  2011年   16826篇
  2010年   13444篇
  2009年   14879篇
  2008年   15176篇
  2007年   14826篇
  2006年   13093篇
  2005年   11700篇
  2004年   11075篇
  2003年   10918篇
  2002年   10292篇
  2001年   10085篇
  2000年   9478篇
  1999年   9889篇
  1998年   26178篇
  1997年   18007篇
  1996年   13639篇
  1995年   10035篇
  1994年   8775篇
  1993年   8861篇
  1992年   6238篇
  1991年   5876篇
  1990年   5814篇
  1989年   5472篇
  1988年   5186篇
  1987年   4544篇
  1986年   4410篇
  1985年   4936篇
  1984年   4534篇
  1983年   4079篇
  1982年   3767篇
  1981年   3859篇
  1980年   3561篇
  1979年   3393篇
  1978年   3404篇
  1977年   4002篇
  1976年   5404篇
  1975年   2895篇
  1974年   2712篇
  1973年   2790篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.
172.
Any knowledge extraction relies (possibly implicitly) on a hypothesis about the modelled-data dependence. The extracted knowledge ultimately serves to a decision-making (DM). DM always faces uncertainty and this makes probabilistic modelling adequate. The inspected black-box modeling deals with “universal” approximators of the relevant probabilistic model. Finite mixtures with components in the exponential family are often exploited. Their attractiveness stems from their flexibility, the cluster interpretability of components and the existence of algorithms for processing high-dimensional data streams. They are even used in dynamic cases with mutually dependent data records while regression and auto-regression mixture components serve to the dependence modeling. These dynamic models, however, mostly assume data-independent component weights, that is, memoryless transitions between dynamic mixture components. Such mixtures are not universal approximators of dynamic probabilistic models. Formally, this follows from the fact that the set of finite probabilistic mixtures is not closed with respect to the conditioning, which is the key estimation and predictive operation. The paper overcomes this drawback by using ratios of finite mixtures as universally approximating dynamic parametric models. The paper motivates them, elaborates their approximate Bayesian recursive estimation and reveals their application potential.  相似文献   
173.
Journal of Communications Technology and Electronics - Microstrip band-pass filters (BPFs) containing quarter-wavelength resonators and a Π-shaped half-wavelength resonator placed next to each...  相似文献   
174.
Water Resources Management - Public awareness of water quality concerns has increased since the Flint, MI crisis, but knowledge about water resources management remains low. Consequently,...  相似文献   
175.
The ‐centroid problem or leader–follower problem is generalized considering different customer choice rules where a customer may use facilities belonging to different firms, if the difference in travel distance (or time) is small enough. Assuming essential goods, some particular customer choice rules are analyzed. Linear programming formulations for the generalized ‐medianoid and ‐centroid problems are presented and an exact solution approach is applied. Some computational examples are included.  相似文献   
176.
Breast and prostate cancers are frequently treated with chemotherapy. Several novel chemicals are being reported for this purpose, particularly synthetic and natural benzophenones. This work reports the synthesis of substituted 2-hydroxybenzophenones through 1,4-conjugate addition/intramolecular cycloaddition/dehydration of nitromethane on key intermediate chromones. Structures were extensively studied by means of 2D NMR spectroscopy and single-crystal XRD. Their cytotoxicity was evaluated in vitro in two breast cancer cell lines (MDA-MB-231 and T47-D) and one prostate cancer cell line (PC3). The most potent compound exhibited good cytotoxic effects against the three cancer cell lines (IC50 values ranging from 12.09 to 26.49 μm ) and induced cell-cycle retardation only on prostate cancer cells, which suggested that it might exert cell-type-specific effects.  相似文献   
177.
Strength of Materials - The paper addresses the investigation of high-strain rate compressive behavior of Al foams subjected to impact at the intermediate striking velocity ranged from 40 to...  相似文献   
178.
A series of 2-phenyloxazoles bearing an amide group at position 4 were designed and synthesized for evaluation as potential inhibitors of human recombinant monoamine oxidases (hrMAOs). Results of kinetics experiments demonstrated that all compounds behave as competitive MAO inhibitors, with good selectivity toward the MAO-B isoform. The most potent and selective derivatives are characterized by inhibition constant (Ki) values in the sub-micromolar range and a good selectivity index (Ki MAO-A/Ki MAO-B>50). Some derivatives were also found to be able to inhibit MAO activity in nerve growth factor (NGF)-differentiated PC12 cells, taken as a model of neuronal cells. In particular, 2-(2-hydroxyphenyl)-N-phenyloxazole-4-carboxamide (compound 4 a ) may be a promising new scaffold, exerting the highest selectivity and inhibitory effect toward MAOs in NGF-differentiated PC12 cell lysates, without compromising cell viability. Molecular docking analysis allowed a rationalization of the experimentally observed binding affinity and selectivity.  相似文献   
179.
Theoretical Foundations of Chemical Engineering - Using chemical and XRD phase analysis, along with electron microscopy, the hydrolytic processing of metallic bismuth into high-purity citrate has...  相似文献   
180.
The potential energy profile of the reaction between dimethyl disulfide and OH? radicals is explored by utilizing ab initio and hybrid meta density functional theory methods. Having the energies and structural data of the stationary points, statistical rate theories, such as transition state theory and variable reaction coordinate-transition state theory, are employed to compute the overall rate constants, and discuss the mechanism and product channels. On the basis of the calculations, the overall rate coefficient is predicted to be 2.49?×?10?10?cm3?molecule?1?s?1 at 298?K. It is found that in the most favorable pathway, the reaction proceeds via formation of the relatively unstable intermediate CH3S?(OH)SCH3 decomposing rapidly to yield CH3S?+CH3SOH.  相似文献   
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