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   9745篇
  免费   627篇
  国内免费   493篇
电工技术   322篇
综合类   920篇
化学工业   513篇
金属工艺   143篇
机械仪表   478篇
建筑科学   413篇
矿业工程   79篇
能源动力   235篇
轻工业   384篇
水利工程   105篇
石油天然气   107篇
武器工业   42篇
无线电   1437篇
一般工业技术   1121篇
冶金工业   225篇
原子能技术   99篇
自动化技术   4242篇
  2024年   28篇
  2023年   115篇
  2022年   146篇
  2021年   175篇
  2020年   230篇
  2019年   239篇
  2018年   219篇
  2017年   254篇
  2016年   294篇
  2015年   320篇
  2014年   532篇
  2013年   719篇
  2012年   587篇
  2011年   759篇
  2010年   521篇
  2009年   577篇
  2008年   574篇
  2007年   622篇
  2006年   561篇
  2005年   460篇
  2004年   390篇
  2003年   344篇
  2002年   328篇
  2001年   218篇
  2000年   214篇
  1999年   220篇
  1998年   191篇
  1997年   162篇
  1996年   137篇
  1995年   116篇
  1994年   89篇
  1993年   85篇
  1992年   58篇
  1991年   51篇
  1990年   47篇
  1989年   46篇
  1988年   35篇
  1987年   26篇
  1986年   20篇
  1985年   15篇
  1984年   27篇
  1983年   23篇
  1982年   12篇
  1981年   11篇
  1980年   8篇
  1979年   8篇
  1978年   8篇
  1976年   11篇
  1965年   5篇
  1963年   4篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
In this paper we introduce and describe a new scheme for the numerical integration of smooth functions. The scheme is based on the modified Taylor expansion and is suitable for functions that exhibit near-sinusoidal or repetitive behaviour. We discuss the method and its rate of convergence, then implement it for the approximation of certain integrals. Examples include integrands involving Airy wave, Bessel, Gamma, and elliptic functions. The results, from the data in the tables, demonstrate that the method converges rapidly and approximates the integral as well as some well-known numerical integration methods used with sufficiently small step sizes.  相似文献   
42.
针对ESO参数不易整定的问题,研究了扩张状态观测器(ESO)参数优化的李雅普诺夫函数法.首先建立关于误差的线性定常状态方程和误差指标函数J,在误差指标函数J中综合考虑了跟踪误差的权重和系统的稳定性以及实际运行时的饱和值限制等因素.仿真结果表明,此方法具有概念清晰,实用简便,计算量小的优点.所提ESO参数整定方法是有效的.  相似文献   
43.
本文给出边际函数的绝对连续性性质.  相似文献   
44.
Yozo Takeda  Hamido Fujita 《Knowledge》2004,17(7-8):283-302
Based on the comparative review of several approaches to legacy system conversion and revitalization, the Lyee methodology application for the issue is presented to clarify its idea, the associated procedure, and the implemented tools. It could be said that with the tools and manual developed by ICBSM&T, the mechanical transformation of the conventional program to a Lyee-structured one becomes possible as long as the programs are made in a procedure-oriented language. In addition to the program structure conversion, the Lyee methodology permits people to choose any application language in the transformed program. At the same time, quite a new approach related to the system conversion is introduced, in which the chunk of data extracted from an old program is edited to make a new conventional structure program that has a logical sequence instead of a Lyee type of declarative program. These features can be realized through the concept of LyeeBELT, which is a set of word-information about the attributes, formulae, and conditions for an independent data item.

The overall workflow of the legacy program transformation is shown in the following.

A critical part in its implementation is the feasibility study (pre-analysis) stage where necessary information is supposed to be secured, and an appropriate plan and policy about the system to be revitalized in the new system environment should be clarified so as to customize the tools accordingly. If the initial process is completed, the mechanical legacy system conversion will be realized by registering the parameters in the tool, and the reestablishment of business knowledge in the LyeeBELT will be enabled. With the regulated business logic on the LyeeBELT, the program maintenance afterwards becomes drastically simplified and stable without the ‘spaghetti’ problem, so that software evolution can be possible.  相似文献   

45.
In this paper we investigate the use of the multi-layer perceptron (MLP) for system modelling. A new sigmoidal activation function is introduced and the study is focused at the utilization of this function on a MLP that performs modelling of dynamic, discrete time systems. The role of the activation function in the training process is investigated analytically, and it is proven that the shape of the activation function and it's derivative can affect the training outcome. The method is simulated at a well known benchmark, namely the three tank system, and is incorporated in a Fault Detection and Identification (FDI) method, also applied and simulated at the three tank system. Finally, a comparison is made with an approach that utilizes local model neural networks for system modeling.  相似文献   
46.
Models in economics and other fields often require a restricted Brownian motion because frequently implicit or explicit barriers restrict the domain. This paper contributes to the literature on reflected Brownian motion by deriving its conditional density function as a closed-form expression that consists of infinite sums of Gaussian densities. This solution is compared with an alternative, trigonometric expression derived earlier. Numerical analyses reveal that convergence properties of the expression derived in this paper are superior to those of the alternative representation for most practically relevant set-ups. Despite the complex appearance of the density formula, its use only requires fractions of a second on simple desktop computers such that, next to the theoretical appeal, also practicability is guaranteed.  相似文献   
47.
The properties of matrix-convex functions, which may take values from an expanded numerical axis, are analyzed. Matrix convexity is specified by a pair of matrices, a final set of matrices, or an infinite family of matrices. The results obtained are used in the theory of differential games.  相似文献   
48.
以UC3842电流型控制芯片为核心,以MOSFET IRFPG40作为功率开关器件,设计及研制了一种单端反激式、双闭环电流控制、5路稳定电压输出的40W开关稳压电源,用作于变频器逆变侧IPM模块的专用驱动电源以及其他外围电路工作电源,实验证明所设计的开关电源具有高稳定性。  相似文献   
49.
目的 基于分子生物学技术,研究建立多重实时荧光定量聚合酶链式反应(Polymerase Chain Reaction,PCR)技术检测芝麻酱中的植物源性成分,实现芝麻酱的快速掺假鉴别,突破单标准单物种检测的局限性。方法 该研究以芝麻2S albumim mRNA基因、花生Ara b2基因、大豆Lectin基因、玉米adh1基因设计特异性引物和探针,优化反应体系,建立多重实时荧光定量PCR技术检测芝麻酱中的芝麻源性成分、花生源性成分、大豆源性成分、玉米源性成分,并应用于市售的芝麻酱样本检测分析。结果 该方法高效低成本,特异性好,对小米、绿豆等10种非目标源性成分无特异性扩增;对芝麻源性成分、花生源性成分、大豆源性成分、玉米源性成分的最低检出限为100 pg/μL,具有较高的灵敏度;应用建立的方法,对市售21份芝麻酱样本进行检测分析,检测结果与标签标注不符合的有4份,标签标注符合率80.95%,与参比方法检测结果一致。结论 建立的多重实时荧光定量PCR技术对加工成品的检测具有较好的适用性,为芝麻酱的掺假鉴别提供了一种新的分子生物学方法。  相似文献   
50.
Examines the nature of and importance of creativity in scientists and relates these to the training functions in the university. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  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