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   333111篇
  免费   24036篇
  国内免费   12572篇
电工技术   17924篇
技术理论   56篇
综合类   19695篇
化学工业   56556篇
金属工艺   18560篇
机械仪表   21180篇
建筑科学   25727篇
矿业工程   10971篇
能源动力   9765篇
轻工业   18634篇
水利工程   5262篇
石油天然气   23018篇
武器工业   2601篇
无线电   36638篇
一般工业技术   39804篇
冶金工业   18380篇
原子能技术   3216篇
自动化技术   41732篇
  2024年   1291篇
  2023年   5217篇
  2022年   8878篇
  2021年   12561篇
  2020年   9837篇
  2019年   8019篇
  2018年   9204篇
  2017年   10382篇
  2016年   9286篇
  2015年   12229篇
  2014年   15870篇
  2013年   19185篇
  2012年   20174篇
  2011年   22452篇
  2010年   19202篇
  2009年   18337篇
  2008年   17976篇
  2007年   17398篇
  2006年   18278篇
  2005年   16133篇
  2004年   10349篇
  2003年   9136篇
  2002年   8135篇
  2001年   7475篇
  2000年   8004篇
  1999年   9654篇
  1998年   8157篇
  1997年   6769篇
  1996年   6363篇
  1995年   5339篇
  1994年   4378篇
  1993年   3089篇
  1992年   2492篇
  1991年   1961篇
  1990年   1504篇
  1989年   1232篇
  1988年   1019篇
  1987年   681篇
  1986年   535篇
  1985年   342篇
  1984年   243篇
  1983年   204篇
  1982年   196篇
  1981年   129篇
  1980年   130篇
  1979年   67篇
  1978年   33篇
  1977年   38篇
  1976年   55篇
  1975年   20篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
151.
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   
152.
Reports an error in "What is in a word? No versus Yes differentially engage the lateral orbitofrontal cortex" by Nelly Alia-Klein, Rita Z. Goldstein, Dardo Tomasi, Lei Zhang, Stephanie Fagin-Jones, Frank Telang, Gene-Jack Wang, Joanna S. Fowler and Nora D. Volkow (Emotion, 2007[Aug], Vol 7[3], 649-659). The supplemental materials link should appear as follows: http://dx.doi.org/10.1037/1528-3542.7.3.649.supp. (The following abstract of the original article appeared in record 2007-11660-018.) The words "No" and "Yes" are involved in conditioning to prohibit or encourage behavior, respectively. The authors, therefore, hypothesized that these words would be attributed to endogenous valence, activating neuronal circuits involved with valence and emotional control. Functional MRI (fMRI) at 4 Tesla was used to record regional brain activity while participants were exposed to emphatic vocalizations of the words. Results showed that No and Yes were associated with opposite brain-behavior responses; while No was negatively valenced, produced slower response times, and evoked a negative signal in the right lateral orbitofrontal cortex (OFC), Yes was positively valenced, produced faster response times, and evoked a positive signal in a contiguous region of the OFC. Attribution of negative valence to No and trait anger control were associated with increased responsivity of the OFC to No. Inasmuch as sensitivity to the prohibitive command No develops during childhood through interaction with primary caregivers as the first social objects, our findings may implicate the lateral OFC in the neurobiology of emotion regulation and subsequent social development. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
153.
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   
154.
155.
3-D MCM封装技术及其应用   总被引:1,自引:0,他引:1  
介绍了超大规模集成电路(VLSI)用的3-D MCM封装技术的最新发展,重点介绍了3-D MCM封装垂直互连工艺,分析了3-D MCM封装技术的硅效率、复杂程度、热处理、互连密度、系统功率与速度等问题,并对3-D MCM封装的应用作了简要说明。  相似文献   
156.
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   
157.
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   
158.
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   
159.
镁钴铝类水滑石催化合成安息香甲醚   总被引:1,自引:0,他引:1  
采用共沉淀法制备了镁钴铝类水滑石化合物(MgCoAl-HTLcs),并用 X 射线衍射、扫描电子显微镜、NH_3程序升温脱附等方法对 MgCoAl-HTLcs 进行了表征,并以 MgCoAl-HTLcs 为催化剂催化苯甲醛与甲醇反应合成安息香甲醚,研究了n(Mg):n(Co):n(Al)、催化剂用量、原料配比、反应温度、反应时间对合成反应的影响。表征结果显示,MgCoAl-HTLcs 的晶相完整,表面主要为弱酸、弱碱性。催化合成安息香甲醚的适宜条件为:MgCoAl-HTLcs 催化剂用量0.10 g(约为原料总质量的0.23%),n(Mg):n(Co):n(Al)=0.4:1.6:1.0,V(苯甲醛):V(甲醇)=3:50,反应温度50℃,反应时间150 min。在此条件下,苯甲醛的平衡转化率达77.49%,安息香甲醚选择性接近100%。为洁净合成安息香甲醚开辟了一条新的途径。  相似文献   
160.
This paper proposes a new computer algorithm to solve the fuzzy relation equation P/spl ogr/Q=R, where /spl ogr/ denotes max-min composition or max-product composition. This algorithm operates systematically and graphically on a matrix pattern to get all the solutions of P. Furthermore, by using MATLAB software 6.0, the algorithm is implemented in a computer program attached in the appendix of this paper. Two examples are given to illustrate the effectiveness of the proposed algorithm.  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