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   74606篇
  免费   6378篇
  国内免费   2624篇
电工技术   4013篇
技术理论   6篇
综合类   4446篇
化学工业   12814篇
金属工艺   4046篇
机械仪表   5042篇
建筑科学   5214篇
矿业工程   2411篇
能源动力   2353篇
轻工业   4923篇
水利工程   1006篇
石油天然气   5313篇
武器工业   460篇
无线电   8033篇
一般工业技术   9746篇
冶金工业   3952篇
原子能技术   872篇
自动化技术   8958篇
  2024年   930篇
  2023年   1526篇
  2022年   2213篇
  2021年   3096篇
  2020年   2407篇
  2019年   2008篇
  2018年   2396篇
  2017年   2578篇
  2016年   2172篇
  2015年   2759篇
  2014年   3497篇
  2013年   4266篇
  2012年   4350篇
  2011年   4858篇
  2010年   4177篇
  2009年   3957篇
  2008年   3853篇
  2007年   3714篇
  2006年   3796篇
  2005年   3431篇
  2004年   2283篇
  2003年   2084篇
  2002年   1870篇
  2001年   1636篇
  2000年   1799篇
  1999年   2050篇
  1998年   1769篇
  1997年   1426篇
  1996年   1408篇
  1995年   1191篇
  1994年   959篇
  1993年   719篇
  1992年   546篇
  1991年   430篇
  1990年   328篇
  1989年   257篇
  1988年   231篇
  1987年   143篇
  1986年   122篇
  1985年   98篇
  1984年   68篇
  1983年   42篇
  1982年   42篇
  1981年   30篇
  1980年   25篇
  1979年   13篇
  1977年   7篇
  1976年   8篇
  1975年   5篇
  1945年   4篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Zan  Wu  Zhang  Qiaochu  Xu  Hu  Liao  Fuyou  Guo  Zhongxun  Deng  Jianan  Wan  Jing  Zhu  Hao  Chen  Lin  Sun  Qingqing  Ding  Shijin  Zhou  Peng  Bao  Wenzhong  Zhang  David Wei 《Nano Research》2018,11(7):3739-3745
Nano Research - A spin-coating method was applied to obtain thinner and smoother PEO/LiClO4 polymer electrolyte films (EFs) with a lower level of crystallization than those obtained using a...  相似文献   
102.
Zhang  Ye  Guo  Jiangna  Xu  Dan  Sun  Yi  Yan  Feng 《Nano Research》2018,11(7):3899-3910
Nano Research - Copper nanowires (CuNWs) are becoming an indispensable item for next-generation transparent optical devices due to their excellent conductivity and transparency. In this work,...  相似文献   
103.
Defense frontier analysis of quantum cryptographic systems   总被引:1,自引:0,他引:1  
Slutsky B  Rao R  Sun PC  Tancevski L  Fainman S 《Applied optics》1998,37(14):2869-2878
When a quantum cryptographic system operates in the presence of background noise, security of the key can be recovered by a procedure called key distillation. A key-distillation scheme effective against so-called individual (bitwise-independent) eavesdropping attacks involves sacrifice of some of the data through privacy amplification. We derive the amount of data sacrifice sufficient to defend against individual eavesdropping attacks in both BB84 and B92 protocols and show in what sense the communication becomes secure as a result. We also compare the secrecy capacity of various quantum cryptosystems, taking into account data sacrifice during key distillation, and conclude that the BB84 protocol may offer better performance characteristics than the B92.  相似文献   
104.
Yu Q  Liu X  Sun X 《Applied optics》1998,37(20):4504-4509
Generalized spin filters, including several directional filters such as the directional median filter and the directional binary filter, are proposed for removal of the noise of fringe patterns and the extraction of fringe skeletons with the help of fringe-orientation maps (FOM's). The generalized spin filters can filter off noise on fringe patterns and binary fringe patterns efficiently, without distortion of fringe features. A quadrantal angle filter is developed to filter off the FOM. With these new filters, the derivative-sign binary image (DSBI) method for extraction of fringe skeletons is improved considerably. The improved DSBI method can extract high-density skeletons as well as common density skeletons.  相似文献   
105.
Summary Catechin binds strongly to both poly(vinylpyrrolidone) and poly(L-proline) in dilute aqueous solution, inducing a collapse of the more flexible poly(vinylpyrrolidone) chains, but forming a microgel with the more extended poly(L-proline) chains. Low concentrations of poly(L-proline) inhibit the discoloration of aqueous solutions of catechin, thereby implicating the ortho hydroxyyl groups in the catechol moiety in the binding process. Modeling shows that the likely binding sites on poly(L-proline) arise from two minor local conformations. These minor conformations are less frequent in poly(-hydroxy-L-proline) than in poly(L-proline), which may explain why catechin interacts more strongly with poly(L-proline) than with poly(-hydroxy-L-proline).  相似文献   
106.
This paper analyses the design sensitivity of a suspension system with material and geometric nonlinearities for a motorcycle structure. The main procedures include nonlinear structural analysis, formulation of the problem with nonlinear dynamic response, design sensitivity analysis, and optimization. The incremental finite element method is used in structural analysis. The stiffness and damping parameters of the suspension system are considered as design variables. The maximum amplitude of nonlinear transient response at the seat is taken as the objective function during the optimization simulation. A more realistic finite element model for the motorcycle structure with elasto-damping elements of different material models is presented. A comparison is made of the optimum designs with and without geometric nonlinear response and is discussed.Nomenclature A amplitude of the excitation function - a 0,a 1 time integration constants for the Newmark method - t+t C s secant viscous damping matrix at timet+t - t C T tangent viscous damping matrix at timet - C linear part of t C T - D i 0 initial value of thei-th design variable - D i instanenous value of thei-th design variables - t+t F(t–1) total internal force vector at the end of iteration (i–1) and timet+t - t+t F (NL) (i–1) nonlinear part of t+t F(i–1) - f frequency of the excitation function - t+t K s secant stiffness matrix at timet+t - t K T tangent stiffness matrix at timet - K linear part of t K T - effective stiffness matrix at timet - L distance between the wheel centres - M constant mass matrix - m T number of solution time steps - NC number of constraint equations - Q nonlinear dynamic equilibrium equation of the structural system - t+t R external applied load vector at timet+t - t e active time interval for the excitation function - t U displacement vector of the finite element assemblage at timet - velocity of the finite element assemblage at timet - t Ü acceleration vector of the finite element assemblage at timet - t+t U (i) displacement vector of the finite element assemblage at the end of iterationi and timet+t - velocity vector of the finite element assemblage at the end of iterationi and timet+t - t+t Ü(i) acceleration vector of the finite element assemblage at the end of iterationi and timet+t - U (i) vector of displacement increments from the end of iteration (i–1) to the end of iterationi at timet+t - V driving speed of motorcycle - x vector of design variable - () quantities of variation - 0 objective function - i i-th constraint equation  相似文献   
107.
FacetAtlas: multifaceted visualization for rich text corpora   总被引:1,自引:0,他引:1  
Documents in rich text corpora usually contain multiple facets of information. For example, an article about a specific disease often consists of different facets such as symptom, treatment, cause, diagnosis, prognosis, and prevention. Thus, documents may have different relations based on different facets. Powerful search tools have been developed to help users locate lists of individual documents that are most related to specific keywords. However, there is a lack of effective analysis tools that reveal the multifaceted relations of documents within or cross the document clusters. In this paper, we present FacetAtlas, a multifaceted visualization technique for visually analyzing rich text corpora. FacetAtlas combines search technology with advanced visual analytical tools to convey both global and local patterns simultaneously. We describe several unique aspects of FacetAtlas, including (1) node cliques and multifaceted edges, (2) an optimized density map, and (3) automated opacity pattern enhancement for highlighting visual patterns, (4) interactive context switch between facets. In addition, we demonstrate the power of FacetAtlas through a case study that targets patient education in the health care domain. Our evaluation shows the benefits of this work, especially in support of complex multifaceted data analysis.  相似文献   
108.
109.
With the rapid development of network technologies and deteriorating of network environment, traditional single-net security system cannot satisfy the security requirement. The excellent security performance of biological systems impels the bio-inspired network security theory to be a hot research area currently. Based on Bio-inspired Multidimensional Network Security Model we have put forward, we have advanced Bio-inspired Multi-Net Security system by implementing the functional distribution of different subnets of different transient states in Multi-Net Paralleling structure. Firstly, parameter estimation and modified algorithms of Hidden Markov Model are introduced to construct the mathematical mode of B-MNS; secondly, the integrated performance of our modified B-MNS has been tested and its simulation has been carried out. So the feasibility, validity and high efficiency of our model have been demonstrated theoretically, and practically.  相似文献   
110.
CAD软件与基于多边形的3D软件之间数据转换需求不断增加,但是CAD模型复杂度和精细度却越来越高,数据转换的难度变大.为了解决这一难题,结合PolyTrans,分析如何解决一般3D软件难以导入大型的IGES(Initial Graphics Exchange Specifi-cation)文件的问题.从PolyTrans模型简化模块的理论依据着手,研究如何控制多边形的数量、降低文件的复杂性和减少文件的数量,使大型CAD装配模型能顺利地以单个实体形式导入Lightwave、3DS MAX以及Maya类的3D软件.并结合具体科研项目,给出了模型优化前后各指标参数对比情况.  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