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   348031篇
  免费   25517篇
  国内免费   13422篇
电工技术   18939篇
技术理论   59篇
综合类   20904篇
化学工业   58695篇
金属工艺   19353篇
机械仪表   22175篇
建筑科学   27126篇
矿业工程   11370篇
能源动力   10162篇
轻工业   19685篇
水利工程   5544篇
石油天然气   23674篇
武器工业   2745篇
无线电   38449篇
一般工业技术   41450篇
冶金工业   19165篇
原子能技术   3369篇
自动化技术   44106篇
  2024年   1405篇
  2023年   5456篇
  2022年   9403篇
  2021年   13261篇
  2020年   10359篇
  2019年   8440篇
  2018年   9630篇
  2017年   10827篇
  2016年   9731篇
  2015年   12845篇
  2014年   16616篇
  2013年   20009篇
  2012年   21064篇
  2011年   23366篇
  2010年   20077篇
  2009年   19132篇
  2008年   18836篇
  2007年   18194篇
  2006年   19050篇
  2005年   16854篇
  2004年   10949篇
  2003年   9582篇
  2002年   8590篇
  2001年   7872篇
  2000年   8388篇
  1999年   10011篇
  1998年   8461篇
  1997年   7044篇
  1996年   6624篇
  1995年   5550篇
  1994年   4561篇
  1993年   3249篇
  1992年   2599篇
  1991年   2041篇
  1990年   1584篇
  1989年   1303篇
  1988年   1055篇
  1987年   711篇
  1986年   565篇
  1985年   356篇
  1984年   259篇
  1983年   219篇
  1982年   212篇
  1981年   137篇
  1980年   150篇
  1979年   72篇
  1978年   38篇
  1977年   51篇
  1976年   58篇
  1975年   24篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
研究了富氧燃烧技术对梭式窑烧成的影响.研究结果表明,随着氧浓度从21%-30%的逐渐增加,CO总浓度和NO总浓度都先明显下降,后缓慢上升;节能效果在初始段较为明显,而后效果不明显;而实际烟气量与氧浓度成反比,与过剩空气系数成正比.  相似文献   
32.
干凝胶作为一种新型的轻质多孔材料在工业生产和人们的生活中具有广泛的应用,但是其较低的强度和易碎裂的特点却限制了其实际应用.结合干凝胶的制备过程,总结了几种有效的降低结构破坏的途径,并对其机理做了简要分析,最后对干凝胶的应用前景做了展望.  相似文献   
33.
通过对车身漆膜质量问题的分析,采取专业清洁公司整体承包车间保洁、工艺方面改进、更换生产外材料、供应商加强对汽车漆使用的监控等一系列措施,漆膜质量水平得以提高.  相似文献   
34.
Nanofiber bundles of Ag2S, Ag2Se, and Ag have been successfully synthesized by making use of Ag2C2O4 template nanofiber bundles, utilizing both anion‐exchange and redox reactions. The obtained bundles were polycrystalline nanofibers composed of nanoparticles in which the precursor morphology was well‐preserved, indicating that Ag2C2O4 nanofiber bundles acted as a general sacrificial template for the synthesis of silver‐based semiconductor and metal nanofibers. Dispersing media and transforming reactants were found to be key factors influencing the chemical transformation in the system. In particular, separate single‐crystalline Ag nanofibers were obtained via a nontemplate route when ascorbic acid was used as a relatively weak reductant. An electrical transfer and switching device was built with the obtained Ag2S and Ag nanofiber bundles, utilizing the unique ion‐conductor nature of Ag2S and revealing their potential applications in electronics.  相似文献   
35.
By applying a combination of characterisation tools, changes in structural and superconducting properties with nominal Mg non‐stoichiometry in MgxB2 are found. The non‐stoichiometry produces enhanced in‐field critical current densities (Jc's) and upper critical field / irreversibility field (Hc2/Hirr(T)) values. Upper critical fields of ~ 21 T (4.2 K) were obtained in nominal Mg‐deficient samples compared to ~ 17 T (4.2 K) for near‐stoichiometric samples.  相似文献   
36.
This paper presents an investigation on a single-mode-multimode-single-mode fiber structure. A one-way guided-mode propagation analysis for the circular symmetry waveguide is employed to model the light propagation and the approximated formulations are derived and evaluated concerning the accuracy. Phase conjunction of the multimode interference within the fiber structure is revealed. A simple way to predict and analyze the spectral response of the structure is presented through the space to wavelength mapping with the derived approximated formulations. The prediction of spectral response is verified numerically and experimentally.  相似文献   
37.
Hydrate formation rate plays an important role in making hydrates for the storage and transport of natural gas. Micellar surfactant solutions were found to increase gas hydrate formation rate and storage capacity. With the presence of surfactant, hydrate could form quickly in a quiescent system and the energy costs of hydrate formation reduced. Surfactants (an anionic surfactant, a non‐ionic surfactant and their mixtures) and liquid hydrocarbons (cyclopentane and methylcyclohexane) were used to improve hydrate formation. The experiments of hydrate formation were carried out in the pressure range 3.69–6.82 MPa and the temperature range 274.05–277.55 K. The experimental pressures were kept constant during hydrate formation in each experimental run. The effect of anionic surfactant (sodium dodecyl sulphate (SDS)) on natural gas storage in hydrates is more pronounced compared to a non‐ionic surfactant (dodecyl polysaccharide glycoside (DPG)). The induction time of hydrate formation was reduced with the presence of cyclopentane (CP). Cyclopentane and methylcyclohexane (MCH) could increase hydrate formation rate, but reduced hydrate storage capacity The higher methylcyclohexane concentration, the lower the hydrate storage capacity. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   
38.
In this paper, we discuss average consensus problem in undirected networks of dynamic agents with fixed and switching topologies as well as multiple time-varying communication delays. By employing a linear matrix inequality method, we prove that all the nodes in the network achieve average consensus asymptotically for appropriate communication delays if the network topology is connected. Particularly, several feasible linear matrix inequalities are established to determine the maximal allowable upper bound of time-varying communication delays. Numerical examples are given to demonstrate the effectiveness and the sharpness of the theoretical results.  相似文献   
39.
A theoretical construction of one-to-many (OTM) and many-to-one (MTO) chaos synchronization communications using semiconductor lasers is presented. One center laser provides strong injections (strong link) to other side lasers, and the side lasers also provide weak injections (weak link) to the center one. Simulation results show that the side lasers synchronize with the center laser through injection-locking. In addition, messages transmitted via the strong links or the weak links experience strong chaos pass filtering, enabling us to realize OTM and MTO communications.  相似文献   
40.
基于MoCA标准的家庭网络研究   总被引:1,自引:0,他引:1  
本文描述了一种基于MOCA标准的家庭网络,并对该网络及设备进行了基本性能的测试.本文首先介绍了家庭网络的发展现状,对目前的各种家庭网络标准进行了比较.在此基础上详细描述了基于MOCA标准的家庭网络,并对该网络的设计,实现、网络性能进行了详述.然后对该网络进行了测试并得出了相关的测试结论.最后指出该网络的不足及改进之处.  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