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   288459篇
  免费   3369篇
  国内免费   816篇
电工技术   5043篇
综合类   162篇
化学工业   45638篇
金属工艺   11920篇
机械仪表   8634篇
建筑科学   6895篇
矿业工程   1835篇
能源动力   6752篇
轻工业   26049篇
水利工程   3209篇
石油天然气   7101篇
武器工业   16篇
无线电   31516篇
一般工业技术   57112篇
冶金工业   51591篇
原子能技术   7534篇
自动化技术   21637篇
  2021年   2125篇
  2018年   3706篇
  2017年   3646篇
  2016年   3946篇
  2015年   2492篇
  2014年   4278篇
  2013年   12085篇
  2012年   6891篇
  2011年   9288篇
  2010年   7620篇
  2009年   8693篇
  2008年   8989篇
  2007年   8871篇
  2006年   7867篇
  2005年   7342篇
  2004年   6836篇
  2003年   6582篇
  2002年   6642篇
  2001年   6512篇
  2000年   6188篇
  1999年   6246篇
  1998年   14815篇
  1997年   11061篇
  1996年   8586篇
  1995年   6544篇
  1994年   5931篇
  1993年   5798篇
  1992年   4485篇
  1991年   4448篇
  1990年   4287篇
  1989年   4308篇
  1988年   4260篇
  1987年   3605篇
  1986年   3598篇
  1985年   4167篇
  1984年   3972篇
  1983年   3625篇
  1982年   3427篇
  1981年   3567篇
  1980年   3427篇
  1979年   3369篇
  1978年   3450篇
  1977年   3927篇
  1976年   5047篇
  1975年   3161篇
  1974年   3009篇
  1973年   3031篇
  1972年   2654篇
  1971年   2474篇
  1970年   2106篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Russian Microelectronics - The recently developed nanomaterials and their production technologies as intellectual property objects (IPOs) are considered. The role of the informational-analytical...  相似文献   
32.
Journal of Communications Technology and Electronics - Approximate formulas for calculating the coefficient of reflection from an artificial magnetic conductor (AMC) based on a capacitive lattice...  相似文献   
33.
We deal with the mathematical model of the incremental degradation of the internal coating (e.g. a polymeric material) of a metallic pipe in which a fluid flows relatively fast. The fluid drags solid impurities so that longitudinal scratches, inaccessible to any direct inspection procedure, are produced on the coating. Time evolution of this kind of defects can be reconstructed from the knowledge of a sequence of temperature maps of the external surface. The time-varying orthogonal section of this damaged interface is determined as a function of time and polar angle through the identification of a suitable effective heat transfer coefficient by means of Thin Plate Approximation.  相似文献   
34.
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   
35.
Potentiometric sensors with plasticized poly(vinyl chloride) membranes based on β-lactam–tetraalkylammonium ion associates sensitive to penicillin antibiotics are proposed. The physicochemical characteristics (solubility product constants and dissociation constants) of active membrane components and the electrode, transport, and selective properties of the membranes of liquidand solid-contact sensors have been studied. The quantitative characteristics of membrane transport (penetrability, ion flux, and transport rate) have been evaluated. The main charge carriers in the membranes and at the membrane/solution interface have been determined from the membrane transport characteristics. The potentiometric sensors are shown to be applicable to the determination of penicillin antibiotics in biological fluids (blood serum and oral fluid) from patients with urinary tract infection.  相似文献   
36.
37.
This work presents simulation of microstructure evolution in the nugget zone (NZ) of a AZ31-Mg-alloy friction stir weld. The process parameters (tool geometrical characteristics, rotational speed, travel speed, applied load) have been correlated with the resulting microstructural features in the NZ of the weld (grain size and population) with the aid of the MICRESS software, which provides the ability to simulate both nucleation and grain growth during dynamic recrystallization phenomena evolving in the NZ during the weld thermal cycle. The input parameters of the developed model include the tool geometry, the welding conditions as well as the recrystallization energy, the grain boundary mobility and specific material properties. NZ microstructure obtained by simulation shows good agreement with experimental measurements for both grain population and size.  相似文献   
38.
This study presents a back-analysis of geotechnical parameters on prefabricated vertical drain improved ground at a site in the Mekong Delta. Various time?settlement behaviors that reflected different clay thicknesses and loading patterns were observed. The total surface settlement behavior at several monitoring locations was simulated using an updated exponential method that considered staged construction. The analyzed results were validated by substituting the values into a theoretical solution for radial consolidation. The estimated theoretical behaviors were comparable with the monitored behaviors. The geotechnical parameters were back-analyzed by applying the previously analyzed results to various theoretical and empirical formulas. However, the use of extensometer data that were installed at large intervals produced different values of the geotechnical properties. Furthermore, finite element analysis supported the back-analyzed total settlement behaviors and nearly disregarded the application of the geotechnical properties that were obtained using either surface or subsurface settlement data. However, settlements and excess pore pressures in the sublayers were not successfully predicted even when the geotechnical properties were adjusted. Thus, subsurface instruments that can be installed closely in thick clay deposits are required to reliably reevaluate the variations in geotechnical properties along a certain depth.  相似文献   
39.
40.
Water Resources Management - A number of models have been developed to simulate seawater intrusion in coastal aquifers, which differ in the accuracy level and computational demands, based on the...  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