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   577756篇
  免费   5923篇
  国内免费   1536篇
电工技术   10389篇
综合类   390篇
化学工业   87656篇
金属工艺   27136篇
机械仪表   19874篇
建筑科学   11605篇
矿业工程   4939篇
能源动力   14287篇
轻工业   35677篇
水利工程   7255篇
石油天然气   16913篇
武器工业   36篇
无线电   62495篇
一般工业技术   126370篇
冶金工业   97983篇
原子能技术   16418篇
自动化技术   45792篇
  2021年   5543篇
  2020年   4275篇
  2019年   5431篇
  2018年   9773篇
  2017年   9968篇
  2016年   10637篇
  2015年   6254篇
  2014年   10575篇
  2013年   26877篇
  2012年   16203篇
  2011年   21261篇
  2010年   17067篇
  2009年   19210篇
  2008年   19652篇
  2007年   19223篇
  2006年   16717篇
  2005年   14881篇
  2004年   14302篇
  2003年   14089篇
  2002年   13389篇
  2001年   13215篇
  2000年   12597篇
  1999年   12582篇
  1998年   29747篇
  1997年   21096篇
  1996年   16109篇
  1995年   12226篇
  1994年   10904篇
  1993年   11031篇
  1992年   8365篇
  1991年   8043篇
  1990年   8128篇
  1989年   7685篇
  1988年   7365篇
  1987年   6729篇
  1986年   6520篇
  1985年   7222篇
  1984年   6781篇
  1983年   6241篇
  1982年   5788篇
  1981年   5906篇
  1980年   5646篇
  1979年   5769篇
  1978年   5878篇
  1977年   6354篇
  1976年   7791篇
  1975年   5205篇
  1974年   5116篇
  1973年   5216篇
  1972年   4546篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
Translated from Kibernetika i Sistemnyi Analiz, No. 2, pp. 95–112, March–April, 1994.  相似文献   
82.
Translated from Kibernetika i Sistemnyi Analiz, No. 3, pp. 172–176, May–June, 1994  相似文献   
83.
An extended logistic model with a varying asymptotic upper bound for long-range peak demand forecasting is described. The model has been applied to a typical fast growing system, the Saudi Consolidated Electric Company. The forecasts are compared with actual demands and with those obtained from classical forecasting methods. The model gave relatively accurate peak demand forecasts compared with other classical methods. The model with a single load observation is capable of producing several peak demand forecasts corresponding to different levels of maximum temperature and various levels of social activity. The forecasts produced by the model were also stable irrespective of the length of the ex-post simulation period  相似文献   
84.
85.
The electrochemical and corrosion behaviour of a nickel base super alloy (C-263) has been investigated in the deaerated binary and ternary solution mixture of concentrated phosphoric acid, acetic acid, sulphuric acid, nitric acid or water using potentiostatic technique at 35°C. The possibilities of electropolishing of this alloy in these solution mixtures have been also explored. The alloy showed distinct active, passive and transpassive behaviour in the experimental solutions. The alloy remained active and turned passive in the negative potential region. Transpassive dissolution of the alloy is observed and electropolishing is achieved in this region. The best electropolishing is obtained in 50% H3PO4 + 40% CH3COOH + 10% H2SO4. Higher content of water in the electrolytic solution is not useful for electropolishing of the alloy The experimental results also suggest that a current plateau in the transpassive potential region is not a sufficient condition to achieve electropolishing.  相似文献   
86.
Several in vivo and in vitro methods for monitoring immunological properties of two allergoids obtained by formaldehyde treatment of ovalbumin (OA) were developed. The calculated molecular weight of allergoids was 80 kD (OA-F1) and 165 kD (OA-F2), respectively. The allergenic activity in vitro of allergoids in mast-cell histamine release assay was 1000 times lower than of OA. Both allergoids showed reduced ability to induce passive cutaneous anaphylaxis in the Sprague-Dawley rats or systemic anaphylaxis in Dunkin-Harley guinea-pigs. The ability of OA and allergoids to bind to the OA-specific IgE antibodies was measured in vivo by the inhibition of passive cutaneous anaphylaxis (PCA-inhibition). Allergoid binding to IgE was 51-66% lower than the native allergen. Moreover, the avidity of OA-specific IgG antibodies, measured by ELISA-inhibition, for allergoids and allergen was of the same order. Allergoids induced a different pattern of humoral immune response from that, induced by the native allergen. Thus, after immunization of BALB/c mouse, both allergoids induced a higher production of IgG and a lower production of IgE than OA, only OA-F2 induced a lower production of IgG1. The differences in the IgA response to the immunogens was not significant. Delayed hypersensitivity studies in the BALB/c mouse showed that allergoids were 5- to 12-times less effective in inducing a cell-mediated immune response than OA. The present study provides a battery of immunological methods for preclinical testing of modified allergens.  相似文献   
87.
The effectiveness of the hybrid system sonication followed by wet oxidation (SONIWO) to treat otherwise refractory waste has been demonstrated. In such a hybrid system homogeneous CuSO4 catalyst was found to be very efficient.  相似文献   
88.
A novel class of narrow-band tunable wavelength filters is proposed and evaluated. Wavelength selectivity of the proposed filters Is derived from the finite time response of an optical nonlinearity. The nonlinearity is gain saturation in semiconductor optical amplifier structures. The filters are shown to have very narrow passbands tunable over the entire semiconductor gain bandwidth. The key to filter implementation is a device configuration in which the wave-mixing products can be isolated from the amplified inputs. Three integrated optics compatible configurations are considered and shown to have high filter throughputs 34 to 180% and subangstrom bandwidths  相似文献   
89.
The technological process of cold forging applied for the first time in the production of the casing of the internal joint with races is described. The process operations of cold forging and the annealing and carburizing regimes for this part me described.  相似文献   
90.
A fiber optic ring network, such as fiber distributed data interface (FDDI), can be operated over multiple wavelengths on its existing fiber plant consisting of point-to-point fiber links. Using wavelength division multiplexing (WDM) technology, FDDI nodes can be partitioned to operate over multiple subnetworks, with each subnetwork operating independently on a different wavelength, and inter-subnetwork traffic forwarding performed by a bridge. For this multiwavelength version of FDDI, which we refer to as wavelength distributed data interface (WDDI), we examine the necessary upgrades to the architecture of a FDDI node, including its possibility to serve as a bridge. The main motivation behind this study is that, as network traffic scales beyond (the single-wavelength) FDDI's information-carrying capacity, its multiwavelength version, WDDI, can gracefully accommodate such traffic growth. A number of design choices exist in constructing a good WDDI network. Specifically, we investigate algorithms using which, based on prevailing traffic conditions, partitioning of nodes into subnetworks can be performed in an optimized fashion. Our algorithms partition the nodes into subrings, such that the total traffic flow in the network and/or the network-wide average packet delay is minimized  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