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   17832篇
  免费   1440篇
  国内免费   1107篇
电工技术   1640篇
综合类   2218篇
化学工业   718篇
金属工艺   470篇
机械仪表   1253篇
建筑科学   483篇
矿业工程   283篇
能源动力   445篇
轻工业   165篇
水利工程   379篇
石油天然气   214篇
武器工业   139篇
无线电   1226篇
一般工业技术   1418篇
冶金工业   216篇
原子能技术   54篇
自动化技术   9058篇
  2024年   45篇
  2023年   143篇
  2022年   239篇
  2021年   281篇
  2020年   378篇
  2019年   423篇
  2018年   342篇
  2017年   513篇
  2016年   544篇
  2015年   626篇
  2014年   958篇
  2013年   1346篇
  2012年   1035篇
  2011年   1137篇
  2010年   870篇
  2009年   994篇
  2008年   1088篇
  2007年   1189篇
  2006年   1045篇
  2005年   909篇
  2004年   791篇
  2003年   711篇
  2002年   636篇
  2001年   536篇
  2000年   477篇
  1999年   419篇
  1998年   338篇
  1997年   351篇
  1996年   291篇
  1995年   253篇
  1994年   258篇
  1993年   189篇
  1992年   177篇
  1991年   144篇
  1990年   106篇
  1989年   99篇
  1988年   90篇
  1987年   52篇
  1986年   53篇
  1985年   37篇
  1984年   51篇
  1983年   30篇
  1982年   36篇
  1981年   23篇
  1980年   23篇
  1979年   29篇
  1978年   11篇
  1977年   21篇
  1976年   14篇
  1975年   12篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
在基于单片机的智能化重力加速度测试仪中采用C语言编程简化了程序设计任务,对于汇编语言难于处理的浮点数运算及汉字打印输出可通过C语言编译器的内部库函数调用实现,介绍了一种专为8051系列单片机设计的C语言编译器Frankilin C51,它具有代码优化功能,能产生极高效率的机器码,并且提供了丰富的内部函数库。描述了C51函数库所支持的IEEE标准浮点数的内存格式以及采用sprintf()函数处理包括  相似文献   
62.
Parallel computers have not yet had the expected impact on mainstream computing. Parallelism adds a level of complexity to the programming task that makes it very error-prone. Moreover, a large variety of very different parallel architectures exists. Porting an implementation from one machine to another may require substantial changes. This paper addresses some of these problems by developing a formal basis for the design of parallel programs in the form of a refinement calculus. The calculus allows the stepwise formal derivation of an abstract, low-level implementation from a trusted, high-level specification. The calculus thus helps structuring and documenting the development process. Portability is increased, because the introduction of a machine-dependent feature can be located in the refinement tree. Development efforts above this point in the tree are independent of that feature and are thus reusable. Moreover, the discovery of new, possibly more efficient solutions is facilitated. Last but not least, programs are correct by construction, which obviates the need for difficult debugging. Our programming/specification notation supports fair parallelism, shared-variable and message-passing concurrency, local variables and channels. The calculus rests on a compositional trace semantics that treats shared-variable and message-passing concurrency uniformly. The refinement relation combines a context-sensitive notion of trace inclusion and assumption-commitment reasoning to achieve compositionality. The calculus straddles both concurrency paradigms, that is, a shared-variable program can be refined into a distributed, message-passing program and vice versa. Received July 2001 / Accepted in revised form May 2002  相似文献   
63.
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   
64.
Imperative programs can be inverted directly from their forward-directed program code with the use of logical inference. The relational semantics of imperative computations treats programs as logical relations over the observable state of the environment, which is taken to be the state of the variables in memory. Program relations denote both forward and backward computations, and the direction of the computation depends upon the instantiation pattern of arguments in the relation. This view of inversion has practical applications when the relational semantics is treated as a logic program. Depending on the logic programming inference scheme used, execution of this relational program can compute the inverse of the imperative program. A number of nontrivial imperative computations can be inverted with minimal logic programming tools.  相似文献   
65.
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   
66.
对二阶A型Cooper变换进行增强,放宽可用性条件,并证明了其正确性,最后举例说明其应用。  相似文献   
67.
Reorganisation and evolution of class hierarchies is important for object-oriented system development and has received considerable attention in the literature. The contributions of this paper are: (1) a formal study of a set of extension relations and transformations on class hierarchies; (2) a presentation of a small set of primitive transformations which form a minimal and complete basis for the extension relations; and (3) an analysis of the impact of these transformations at the object level.The study leads to a better understanding of evolution and reuse of object-oriented software and class hierarchies. It also provides a terminology and a means of classification for design reuse. The theory presented in this paper is based on the Demeter data model, which gives a concise mathematical foundation for classes and their inheritance and part-of relationships. Parts of the theory have been implemented in the Demeter System TM C++, a CASE tool for object-oriented design and programming.  相似文献   
68.
The present paper demonstrates the applicability of population based search optimization method, namely, Differential Evolution (DE) to a case study of Mahi Bajaj Sagar Project (MBSP), India. Ten different strategies of DE are employed to assess the ability of DE for solving higher dimensional problems as an alternative methodology for irrigation planning. The parameters considered in DE are population size, crossover constant and weighting factor. Linear Programming (LP) is utilized as a comparative approach to assess the ability of DE. Comparison of results of LP and the 10 DE strategies for the given parameters indicated that both the results are comparable even for high dimensional problems. Extensive sensitivity analysis studies, performed for 3,600 combinations of above parameters for the 10 DE strategies suggested that DE/rand-to-best/1/bin strategy is the best strategy giving maximum benefits taking minimum CPU time. It is concluded that DE can be utilized for efficient planning of any irrigation system with suitable modifications.  相似文献   
69.
中等职业学校一般开设VB、VC及数据库等涉及程序设计的计算机课程。本文拟就程序设计中一题多解的教学方法进行探讨。  相似文献   
70.
模糊规划在炼油厂生产计划优化中的应用   总被引:7,自引:1,他引:6  
生产计划的编制是炼油化工企业生产经营管理中的一个关键环节,然而由于市场变化的不确定性,使得企业的长远规划制定受到限制,笔者将模糊数学应用于炼厂生产计划的编制,通过模糊规划对炼油企业生产计划进行优化,使编得的生产计划在一定程度上反映市场的变化并使企业的生产效益最优,为企业管理决策者进行长期规划给予指导,给出了实例来说明该方法的可行性。  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