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   30023篇
  免费   3491篇
  国内免费   2420篇
电工技术   3943篇
综合类   3697篇
化学工业   2016篇
金属工艺   989篇
机械仪表   1811篇
建筑科学   3902篇
矿业工程   1116篇
能源动力   1368篇
轻工业   374篇
水利工程   1576篇
石油天然气   1732篇
武器工业   452篇
无线电   2612篇
一般工业技术   2618篇
冶金工业   899篇
原子能技术   753篇
自动化技术   6076篇
  2024年   111篇
  2023年   366篇
  2022年   641篇
  2021年   783篇
  2020年   915篇
  2019年   758篇
  2018年   733篇
  2017年   940篇
  2016年   1078篇
  2015年   1123篇
  2014年   1999篇
  2013年   2011篇
  2012年   2255篇
  2011年   2355篇
  2010年   1777篇
  2009年   1830篇
  2008年   1709篇
  2007年   1990篇
  2006年   1777篇
  2005年   1624篇
  2004年   1369篇
  2003年   1156篇
  2002年   971篇
  2001年   925篇
  2000年   816篇
  1999年   651篇
  1998年   525篇
  1997年   496篇
  1996年   376篇
  1995年   354篇
  1994年   315篇
  1993年   253篇
  1992年   219篇
  1991年   144篇
  1990年   133篇
  1989年   118篇
  1988年   74篇
  1987年   41篇
  1986年   26篇
  1985年   36篇
  1984年   28篇
  1983年   24篇
  1982年   16篇
  1981年   15篇
  1980年   15篇
  1979年   14篇
  1978年   10篇
  1977年   13篇
  1976年   5篇
  1959年   12篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
研究了热传导方程的通解,进而提出激光热源形成的微观机理和热源形成过程的三个理论计算式。对激光热效应的应用具有指导意义。  相似文献   
82.
本文应用常规的守恒方程及湍流模型,对二维池内热分层流动建立了数学模型,并在Patankar的压力校正法基础上对该数学模型进行了数值计算,计算中的差分格式为乘方格式、一阶迎风、二阶迎风和QUICK。通过与实验的比较分析,建议计算应采用QUICK格式,并在进行风格独立性试验的基础上使用加密网络。  相似文献   
83.
1 IntroductionSince 1 990 ,chaoticsynchronization[1~ 4] andchaoticcontrolling[5~6] havereceivedagreatdealofattention[7~1 1 ] ,andchaoticsynchronizationisaphenomenonofinterestinfieldsfromelectronicstocommunication[1 2 ] ,andfrombiophysicstoneuro science[1 3] .Ifchaoticsync…  相似文献   
84.
85.
Let us consider n data measurements of a univariate process that have been altered by random errors. We assume that an underlying model function has a substantially smaller number of turning points than the observed ones. We propose algorithms that make least the sum of the moduli of the errors by requiring k monotonic sections, alternately increasing and decreasing, in the sequence of the smoothed values. The main difficulty in this calculation is that the optimal positions of the joins of the monotonic sections have to be found automatically among so many combinations that it is impossible to test each one separately. Moreover, the calculation seems to be very intractable to general optimization techniques because O(nk) local minima can occur. It is shown that dynamic programming can be used for separating the data into optimal disjoint sections of adjacent data, where each section requires a single L1 monotonic calculation. This procedure is highly efficient, requiring at most O(kn2) computer operations and O(n) best L1 monotonic calculations to subranges of data for a global minimum.  相似文献   
86.
本文介绍红外热象技术在工程热物理研究中某些应用的探索。作为实例,通过热象技术,实验研究了具有水平凸台离散热源的倾斜板的散热,在研究它的自然对流换热部份结合利用激光全息干涉技术。此间着重于分析倾斜角对散热的影响。  相似文献   
87.
填料萃取塔液泛速度的计算   总被引:1,自引:0,他引:1  
介绍了三种有代表性的填料萃取塔的液泛速度计算公式,并通过它们用于三种典型的液-液实验体系和两种不同填料的计算结果的比较,对这些公式的适用范围进行了讨论。  相似文献   
88.
An equation of state for 1,1-difluoroethane (HFC 152a, CH3CHF2) has been developed on the basis of reliable experimental data including PVT, liquid Cp, and saturated-liquid-density data measured by our group. It is a non-dimensionalized virial equation whose functional form is the same as that originally developed for 1,1,1,2-tetrafluoroethane (HFC 134a) in our group. The effective range is for pressures up to 15 MPa, temperatures from 230 to 450 K, and densities to 1000 kg m−3. The equation represents reliable PVT measurements within ± 1% in pressure for the superheated vapour and supercritical fluid, while within ±0.5% in density for the compressed liquid. In addition, it should be noted that the equation represents the other essential thermodynamic properties including vapour pressures, saturated-liquid/ vapour densities, isobaric/isochoric specific heats and sound velocity in both the liquid and gaseous phase of HFC 152a.  相似文献   
89.
This paper presents an efficient method which provides the optimal generation mix and the optimal generation construction process. The approximation method in which the dynamic programming technique and gradient method are combined is applied to determine the optimal generation mix with hydropower generation technologies. The successive approximations dynamic programming (SADP) technique, which is very suitable for high-dimensional multistage decision process problems, is used for obtaining the optimal generation construction process. The effectiveness and feasibility of the developed technique are demonstrated on a practical power system model which has five types of generation technologies including a hydropower generation technology.  相似文献   
90.
With the growing size and complexity of power systems, system analysis—such as transients calculation—takes much time. Hence, fast calculation methods are required. Although parallel processing is a hopeful method, there have been difficulties in the parallel solution of linear equations which appear in power-flow calculations by the Newton-Raphson method. This paper aims at the fast calculation of the power-flow problem by means of parallel processing. In order to improve the suitability to the parallel solution of the differential equation in transients calculation, we assume the use of a direct-mapping parallel processing machine to map directly the network of a power system onto a network of processors. Under this assumption, we propose a new parallel-processing-oriented method in which the linear equation is solved by linear iterations between nodes with Aitken acceleration. We simulate the method on three model power systems and compare this Parallel Iterative Method (PIN) with a Parallel Direct Method (PDM) which uses the banded matrix according to the number of operations required. As a result, we can expect that PIM may solve linear equations faster than PDM with m processors, although the PIM might be inferior to the PDM with m × m processors, where m denotes the half-band width of the banded matrix.  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