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   160714篇
  免费   24270篇
  国内免费   6428篇
电工技术   8701篇
技术理论   6篇
综合类   8787篇
化学工业   35364篇
金属工艺   7266篇
机械仪表   8467篇
建筑科学   10818篇
矿业工程   3656篇
能源动力   4715篇
轻工业   15153篇
水利工程   2636篇
石油天然气   6598篇
武器工业   1248篇
无线电   20885篇
一般工业技术   24849篇
冶金工业   8954篇
原子能技术   1560篇
自动化技术   21749篇
  2024年   353篇
  2023年   1588篇
  2022年   2808篇
  2021年   4745篇
  2020年   4717篇
  2019年   5898篇
  2018年   6150篇
  2017年   6863篇
  2016年   7014篇
  2015年   8327篇
  2014年   9515篇
  2013年   12011篇
  2012年   10256篇
  2011年   10696篇
  2010年   10283篇
  2009年   9756篇
  2008年   9205篇
  2007年   8885篇
  2006年   8344篇
  2005年   7053篇
  2004年   5808篇
  2003年   5892篇
  2002年   6525篇
  2001年   5609篇
  2000年   4295篇
  1999年   3376篇
  1998年   3039篇
  1997年   2297篇
  1996年   2059篇
  1995年   1528篇
  1994年   1151篇
  1993年   1006篇
  1992年   710篇
  1991年   519篇
  1990年   443篇
  1989年   355篇
  1988年   329篇
  1987年   221篇
  1986年   215篇
  1985年   210篇
  1984年   122篇
  1983年   124篇
  1982年   119篇
  1981年   126篇
  1980年   124篇
  1979年   69篇
  1978年   53篇
  1977年   102篇
  1976年   193篇
  1973年   54篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
In this paper, the material constant sensitivity boundary integral equation is presented, and its numerical solution proposed, based on boundary element techniques. The formulation deals with plane problems with general rectilinear anisotropy. Expressions for the computation of sensitivities for displacements, tractions, strains and stresses are derived, both for boundary and interior points. The sensitivities can be computed with respect to the bulk material properties or to the properties of part of the domain (inclusions, coatings, etc.). To assess the accuracy of the proposed approach, the computed results are compared to analytical ones derived from exact solutions obtained by complex potential theory, when possible, or finite difference derivatives otherwise. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   
992.
993.
994.
影响喷气燃料与橡胶相容性的因素   总被引:5,自引:0,他引:5  
采用几种具有不同初始物理性能及不同丙烯腈含量、不同硫化剂和硫化程度的丁腈橡胶,考察了其配方和物理性能对采用不同工艺条件生产的喷气燃料的相容性。结果表明,喷气燃料与橡胶的相容性不仅与喷气燃料的加工工艺有关,而且与橡胶的组成及其制备工艺有关。采用非加氢工艺生产的喷气燃料与橡胶的相容性好于采用加氢工艺(特别是加氢裂化工艺)生产的喷气燃料。橡胶材料的初始力学性能的好坏并不完全决定其与喷气燃料相容性的好坏,橡胶材料的耐过氧化物侵蚀能力才是影响相容性好坏的主要因素。橡胶的组成和其制备工艺决定了橡胶在喷气燃料中萃取物的数量和组成,不同萃取物的综合作用给相容性带来不同程度的影响。用硫作硫化剂的橡胶虽然原始强度低于用过氧化物作硫化剂的橡胶,但前者与喷气燃料的相容性却远好于后者。  相似文献   
995.
996.
A series of new o‐phenylenediamine (OPD)/o‐phenetidine (PHT) copolymers with partly phenazine‐like structures has been successfully synthesized at three polymerization temperatures by chemically oxidative polymerization in four different polymerization media. The molecular structures and properties of the resulting OPD/PHT polymers were investigated by IR, UV–vis and high‐resolution 1H NMR spectroscopies, and DSC, in order to ascertain the effect of reaction temperature, comonomer ratio and acid medium. The copolymerization mechanism of OPD with PHT monomers has been proposed. It is found that the statistical OPD/PHT copolymer obtained at a temperature of 118 °C has a higher degree of polymerization than that obtained at 12–17 °C. The OPD content in the copolymers calculated from NMR spectroscopic analysis is higher than that in the feed OPD content, whereas the OPD content calculated from element analysis is slightly lower than the feed OPD content. It can be predicted that denitrogenation takes place in the OPD units during the polymerization process at OPD/PHT molar ratios of 90/10 and 100/0. These OPD/PHT copolymers exhibit a much better solubility than the OPD homopolymer, hence suggesting an incorporation of PHT units into the phenazine structure of the homopolymer. The thermal behavior of the copolymers was also studied. Copyright © 2004 Society of Chemical Industry  相似文献   
997.
Three sorbents were compared in order to determine their potential for oil spill cleanup. Polypropylene nonwoven web, rice hull, and bagasse with two different particle sizes were evaluated in terms of oil sorption capacities and oil recovery efficiencies. Polypropylene can sorb almost 7 to 9 times its weight from different oils. Bagasse, 18 to 45 mesh size, follows polypropylene as the second sorbent in oil spill cleanup. Bagasse, 14 to 18 mesh size, and rice hull have comparable oil sorption capacities, which are lower than those of the two former sorbents. It was found that oil viscosity plays an important role in oil sorption by sorbents. All adsorbents used in this work could remove the oil from the surface of the water preferentially.  相似文献   
998.
Different NMR techniques were combined to obtain the structure and velocity information for a systematic investigation of fixed beds with low aspect ratio (tube diameter to particle diamter, dt/dp) in the range 1.4 to 32. The structure of the void space was determined for a variety of packed beds of glass beads or regular and irregular porous pellets by magnetic resonance imaging (MRI). Based on the images the radial distribution of the voids within the bed was obtained. Ordering effects were found even for non‐spherical and polydisperse particles, and a maximum of the fluid density near the tube wall was confirmed for all pellet geometries and sizes. By combining MRI with velocity encoding, velocity profiles and distributions of flow velocity components of a single fluid phase through packed beds have been acquired. The radial velocity distribution follows an oscillatory pattern which largely reflects the ordering of the particles, which can be accessed from the density distribution of the interparticle fluid. Maximum velocities of up to four times the average value were found to occur near the tube wall. This wall effect was observed for all but the smallest particles, where the aspect ratio was dt/dp = 32. Moreover, a visualisation of flow pattern in the presence of packed particles was achieved by using a tagging technique, and the stationary flow field could be identified for an experimental time of several hours.  相似文献   
999.
糯扎渡工程在可行性研究阶段,比较了直心墙堆石坝和斜心墙堆石坝两种方案,分析表明,直心墙堆石坝在坝坡稳定性、坝体应力及抗震性方面均满足设计要求,且在地形地质条件、基础处理、抗震性能、施工方便性、工程造价等方面不同程度地优于斜心墙堆石坝,因此,设计最终选择直心墙堆石坝方案。  相似文献   
1000.
射流泵流场数值模拟的罚有限元法   总被引:1,自引:1,他引:0  
本文采用罚函数有限元法,在标准k-ε双方程紊流模型下,对射流泵内部轴对称流场进行了数值模拟,得到了较全面的参数分布,特别是全场的压力分布,为射流泵的理论研究和优化设计提供了可靠的依据。给出的算例说明了与文献提供的实验结果基本一致。计算方法简捷,有较大的实用价值。  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