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   1051537篇
  免费   13331篇
  国内免费   2817篇
电工技术   18852篇
综合类   970篇
化学工业   159930篇
金属工艺   39788篇
机械仪表   31444篇
建筑科学   25888篇
矿业工程   5935篇
能源动力   27881篇
轻工业   88974篇
水利工程   11209篇
石油天然气   20537篇
武器工业   68篇
无线电   117058篇
一般工业技术   202990篇
冶金工业   201563篇
原子能技术   21627篇
自动化技术   92971篇
  2021年   9323篇
  2020年   6991篇
  2019年   8792篇
  2018年   14858篇
  2017年   14843篇
  2016年   15822篇
  2015年   10610篇
  2014年   17573篇
  2013年   48510篇
  2012年   27747篇
  2011年   38523篇
  2010年   30625篇
  2009年   34231篇
  2008年   35146篇
  2007年   34659篇
  2006年   30439篇
  2005年   27729篇
  2004年   26568篇
  2003年   26161篇
  2002年   25030篇
  2001年   24697篇
  2000年   23283篇
  1999年   24293篇
  1998年   60614篇
  1997年   43017篇
  1996年   33092篇
  1995年   25025篇
  1994年   22200篇
  1993年   21807篇
  1992年   15953篇
  1991年   15073篇
  1990年   14920篇
  1989年   14438篇
  1988年   13777篇
  1987年   12151篇
  1986年   11866篇
  1985年   13582篇
  1984年   12398篇
  1983年   11474篇
  1982年   10586篇
  1981年   10806篇
  1980年   10175篇
  1979年   10054篇
  1978年   9753篇
  1977年   11369篇
  1976年   14734篇
  1975年   8602篇
  1974年   8163篇
  1973年   8395篇
  1972年   6923篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
This paper considers several aspects of the sequential prediction problem for unbounded, nonstationary processes under pth power loss /spl lscr//sub p/(u,v)=|u-v|/sup p/, 1相似文献   
42.
Nucleation and growth mechanisms and kinetics of crystals of an amino acid salt were investigated in a methanol‐water system by measuring and evaluating the induction time as a function of the supersaturation ratio and temperature in batch salting out crystallization experiments. Discrimination between the possible crystallization mechanisms, and estimation of the kinetic parameters were carried out using nonlinear parameter identification. The results concerning the growth mechanism obtained were checked additionally by measuring the induction time as a function of number density of seed crystals.  相似文献   
43.
44.
A series of small–capacity units has recently been constructed in regions of oil field development and crude oil and gas condensate production to satisfy the requirements for such petroleum products as naphtha, diesel fuel, kerosene, and boiler fuel and to reduce costs for delivery of these products. There are almost no data in the technical literature, particularly in periodicals, on the construction and operation of small–capacity units. We attempt to generalize the experience of Orgeneftekhimzavody Trust in this area. We hope that this experience will be useful to specialists in the development and management of small–capacity plants.  相似文献   
45.
伊朗卡尔黑多目标水利枢纽,首台机组于2002年9月投运。介绍了工程历史,并从导流系统遂洪道、渗漏控制和惟幕灌浆等方面介绍了工程的技术要求。  相似文献   
46.
Advances in the fabrication of solid-solution single crystal relaxor ferroelectrics have made it possible to produce highly efficient piezoelectric crystals, and have attracted renewed interest in the use of these crystals for a new generation of piezoelectric transducers, actuators and sensors. Of particular interest is their incorporation into micro-electromechanical systems (MEMS). In this paper we report on the laser-induced wet chemical etching of lead zinc niobate-lead titanate (PZN-PT) in hydrochloric acid (HCl). Argon-ion laser radiation at power levels up to 4 W is focused to a spot diameter of about 15μm and results in the chemical etching of grooves at patterning speeds up to 5μm/sec. Crystal ion slicing, an ion-implant-based film separation technique, is used in combination with laser etching to form 5 to 10μm-thick patterned and freestanding films for incorporation into micro-electromechanical devices.  相似文献   
47.
Non‐isothermal processing of lignocellulosic materials in aqueous media (autohydrolysis reaction) under mild conditions leads to solutions containing valuable chemicals (oligosaccharides, sugars and acetic acid) and other, undesired, compounds (belonging to the extractive and acid‐soluble lignin fractions) which have to be removed in further purification treatments. Liquors obtained by non‐isothermal autohydrolysis of Eucalyptus globulus wood and corncobs under a variety of operational conditions were extracted with ethyl acetate in order to remove non‐saccharide components, and the suitability of the fraction dissolved in the organic phase was assayed for possible utilisation as an antioxidant. The yield and antioxidant activity of ethyl acetate extracts (measured by the α,α‐diphenyl‐β‐picrylhydrazyl (DPPH) radical scavenging capacity) showed a strong dependence on the autohydrolysis conditions. The antioxidant activity of extracts obtained under selected operational conditions compared well with synthetic antioxidants. © 2003 Society of Chemical Industry  相似文献   
48.
The magneto-optical Kerr effect for red (628 nm) and green (532 nm) light is used to study magnetization processes in 2D magnonic crystals obtained by etching pits with the diameter D ≈ 32 μm to a depth of t ≤ 2 μm in a 16.1-μm-thick film of yttrium iron garnet (YIG). Hysteresis loops obtained in the case of the inplane crystal magnetization at 628 nm are characterized by lower saturation fields H s and higher remanent magnetizations than those obtained at 532 nm, a result that is attributed to different absorption coefficients of the YIG film at these wavelengths. This difference between the magnetization curves reflects the fact that the magnonic-crystal surface probed with the green light makes a greater contribution to the magneto-optical Kerr effect. Therefore, the green light is more sensitive to the demagnetizing fields, which govern magnetization processes in the magnonic crystals.  相似文献   
49.
50.
This article, the first of three articles on the synthesis of rice processing plants, focuses on the development of simplified mathematical models necessary for use in optimizing rice processing plants. The second concentrates on the optimal synthesis of a rice plant and the third on the sensitivity of the optimization to uncertainty in model parameters. Existing models for rice processing unit operations are not suitable for flowsheet optimization and new models need to be developed to overcome numerical difficulties that occur in optimization applications, specifically in mixed integer nonlinear programming (MINLP) applications. Simplified models of the drying, cooling, and tempering units are developed. In addition head rice yield models, used as a quality indicator, energy consumption, and economic models were also developed. Naturally, the new models exhibit some mismatch with respect to the existing models from which they were developed. However, a sensitivity analysis, presented in Part III, has shown that the optimal flowsheet structure was not sensitive to a lack of fit between the simplified and complex models. The simplified models were found adequate to be appropriate for use at the synthesis stage.  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