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   17485篇
  免费   1691篇
  国内免费   731篇
电工技术   1127篇
技术理论   2篇
综合类   1002篇
化学工业   3050篇
金属工艺   1033篇
机械仪表   1130篇
建筑科学   1312篇
矿业工程   606篇
能源动力   508篇
轻工业   1079篇
水利工程   282篇
石油天然气   1343篇
武器工业   119篇
无线电   2004篇
一般工业技术   2121篇
冶金工业   970篇
原子能技术   176篇
自动化技术   2043篇
  2024年   122篇
  2023年   401篇
  2022年   668篇
  2021年   915篇
  2020年   670篇
  2019年   540篇
  2018年   633篇
  2017年   644篇
  2016年   547篇
  2015年   741篇
  2014年   928篇
  2013年   989篇
  2012年   1071篇
  2011年   1184篇
  2010年   990篇
  2009年   960篇
  2008年   954篇
  2007年   823篇
  2006年   857篇
  2005年   696篇
  2004年   567篇
  2003年   476篇
  2002年   465篇
  2001年   393篇
  2000年   373篇
  1999年   434篇
  1998年   322篇
  1997年   308篇
  1996年   259篇
  1995年   236篇
  1994年   183篇
  1993年   129篇
  1992年   109篇
  1991年   66篇
  1990年   67篇
  1989年   49篇
  1988年   32篇
  1987年   26篇
  1986年   16篇
  1985年   13篇
  1984年   14篇
  1983年   6篇
  1982年   5篇
  1981年   9篇
  1980年   5篇
  1979年   3篇
  1977年   1篇
  1970年   1篇
  1959年   1篇
  1951年   5篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
This paper proposes a new approach, named Card-Aided Firewall (CAF) that combines the simplified firewall and the state-oriented smart card technologies to construct a controllable and accountable Internet access framework. The idea suggests that a client computer, protected by a light-weight firewall, could establish diversified authenticated communication channels, controlled and accounted by “legal” states of the smart card.The program of a smart card is state-oriented or a state machine, which defines a chain of events involving various state transitions. The “legal” states of a smart card program are defined to be legal to communicate with surfing targets. A predefined Access Control List (ACL), stored in the same card, is necessary. An ACL is a sequential list of permit or deny statements that apply to addresses or upper-layer protocols. The proposed firewall decides acceptance or rejection messages by matching the current state of the card program and the ACL. In addition, a complete surfing account for tracing back is recorded. It is a by-product of the smart card authentication.The proposed Card-Aided Firewall framework is implemented to demonstrate its effectiveness. The implementation is done at the driver level. It keeps up with the high line speed. The driver takes 39K bytes and works well with other firewalls. The average packet processing time of the CAF driver is 31.74 μs. On the premise of secure authentication within the smart card, the Card-Aided Firewall would facilitate various rapidly growing applications in campus cards, family cards, and employee cards, etc. that require accurate controllability and accountability in the surfing boundary.  相似文献   
42.
In this paper, we consider finite-time control problems for linear multi-agent systems subject to exogenous constant disturbances and impulses. Some sufficient conditions are obtained to ensure the finite-time boundedness of the multi-agent systems, which could be then reduced to a feasibility problem involving linear matrix inequalities. Numerical examples are given to illustrate the results.  相似文献   
43.
44.
Large holes are unavoidably generated in depth image based rendering (DIBR) using a single color image and its associated depth map. Such holes are mainly caused by disocclusion, which occurs around the sharp depth discontinuities in the depth map. We propose a divide-and-conquer hole-filling method which refines the background depth pixels around the sharp depth discontinuities to address the disocclusion problem. Firstly, the disocclusion region is detected according to the degree of depth discontinuity, and the target area is marked as a binary mask. Then, the depth pixels located in the target area are modified by a linear interpolation process, whose pixel values decrease from the foreground depth value to the background depth value. Finally, in order to remove the isolated depth pixels, median filtering is adopted to refine the depth map. In these ways, disocclusion regions in the synthesized view are divided into several small holes after DIBR, and are easily filled by image inpainting. Experimental results demonstrate that the proposed method can effectively improve the quality of the synthesized view subjectively and objectively.  相似文献   
45.
With the rapid development of the vehicle industry, crashworthiness has become a crucial aspect in vehicle body design. In fact, crashworthiness is a multivariable optimization design problem for a vehicle body, regardless of structure or material. However, when crashworthiness involves a large number of design variables, including both material and structure variables, it is more difficult to deal with. In this paper, an integrated design technique for materials and structures of vehicle body under crash safety consideration is suggested. First, a finite element model of the vehicle body is established according to relevant vehicle safety standards. Then, the material parameters of the vehicle body are set as analytical factors for factor screening. Next, significant factors are obtained using a three-level saturated design integrated with multi-index comprehensive balance analysis and the MaxUr (3) method, with an improved evaluation method. These screened material parameters along with the corresponding continuous variables of the structure, are considered as the design variables of the integrated design of the vehicle body. Both the weight and the crashworthiness properties are set as the design objectives. Optimal Latin hypercube sampling and radius basis functions are utilized to construct highly accurate surrogate models. Furthermore, the non-dominated sorting genetic algorithm II is implemented to seek the optimal solutions. Finally, two cases considering the roof module and the frontal module of a vehicle body are analyzed to verify the proposed method.  相似文献   
46.
Semidiscrete (spatially discrete) finite element approximations of the Stokes equations are studied in this paper. Properties of L 2, H 1 and H –1 projections onto discretely divergence-free spaces are discussed and error estimates are derived under minimal regularity assumptions on the solution.  相似文献   
47.
本文提出了一种既便于自动求值,又不致产生歧义的色谱分离优化目标函数。对于反相高效液相色谱RP-HPLC流动相组成优化问题,提出了新的高效迭代方法,并建立了组成优化专家系统。该系统包括优化搜索区域确定、实验谱图辨识、保留特性关系的自适应回归和最优目标预测等功能。经实验验证,该系统具有较高的迭代搜索效率。  相似文献   
48.
工程总承包公司的合同管理研究   总被引:1,自引:0,他引:1  
山东鲁能工程有限责任公司开展电力工程总承包始于上世纪九十年代中期,近五年来总承包事业发展迅速,公司陆续签订了嘉峪关宏晟2×300M W电厂、重庆永川2×125M W电厂、费县2×600M W电厂脱硫、章丘2×300M W电厂脱硫、潍坊2×25M W电厂、单县1×25M W生物发电厂等一批总承包合同,均采用了国际上通行的FID IC合同条款。为规范公司的经营管理,防范合同风险,维护公司合法权益,我们研究摸索了一套适应矩阵管理的总承包公司合同管理体系,在此做简要介绍,与同行交流。一、合同管理中常见问题合同是市场经济下确定不同主体之间经济关系的重…  相似文献   
49.
The atomic configuration of chemical short-range order (CSRO) for the Zr-base metallic glasses was investigated by using nano-diffraction and high resolution transmission electronic microscopy (HRTEM) technology with a beam size of 0.5 rim. It is illustrated that the pattern of atomic configuration of CSRO might have various compound counterparts because of the chemical interaction of bonding atoms. Some atomic configuration of MCSRO is similar to the icosahedral structure with 10-fold symmetry of very weak spots. In deed, the nano-beam technology could clearly detect the evolution of atomic configuration in nanometer scale during the transformation from the metallic melt to the primary crystallization. The local atomic configuration of CSRO is also investigated by molecular dynamics simulation (MD) for the Zr2Ni compound in a wider temperature range. The CSRO in the melt could be pictorially demonstrated as distorted coordination polyhedron of the compound structure and/or the structure similar to cubo-octahedron analogs. The MD simulation illustrates that the atomic packing of long-range order disappears just above the melting point, but the chemical interaction of bonding atoms still exists that leads to form the various CSRO with the atomic configuration similar to stable or metastable unit cell of Zr2Ni compound. The icosahedral polyhedron became more abundance as the overheating temperature was raised.  相似文献   
50.
IPv6的高级套接口规范还在定义之中,不断地增加新的功能。该文根据IPv6接入路由器的实现经验,提供给大家新一代网络层协议IPv6高级套接口主要功能的实现机制和应用示例。通过对实现机制的分析,文章给出了新增高级套接口功能的实现参考。  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