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991.
ASP.NET中几种状态管理技术的分析与比较 总被引:2,自引:0,他引:2
由于Web窗体的无状态性,在开发基于B/S结构的动态Web应用程序时,跟踪特定用户在应用程序中页面的活动情况,并根据用户的请求正确地引导用户,需要解决状态管理的问题。文中通过对ASP.NET的客户端和服务器端状态管理技术的特点进行分析与比较,并在.NET环境下分别对这些状态管理方法进行代码测试,得出了一些实用的使用技巧,即如何在不同的情况使用不同的状态管理方法得到最佳的执行或安全效率。 相似文献
992.
压缩文件可以节省大量的磁盘空间。为此,笔者设计了一种基于动态规划算法的无损文件压缩技术,并编写了程序。通过对不同文件的压缩和解压,发现文件的压缩效率通常在1.3左右,在一定范围内对文件进行多次压缩可以将文件压缩的更小,超过这个范围后,文件反而会变大。得到的结论就是,基于动态规划算法的文件压缩技术可以显著地减少文件的大小,但是由于压缩是无损的,所以经过多次压缩后对文件的平均压缩效率也就在1.4左右,可以通过各种压缩算法的组合使文件的压缩效率得到提高。 相似文献
993.
Cees Duin 《Algorithmica》2004,41(2):131-145
We formulate and study an algorithm for all-pairs
shortest paths in a network with $n $ nodes and $m $ arcs of
positive length. Using the dynamic programming principle of optimality of
subpaths the algorithm avoids redundant updates of distance labels. A shortest $v$--$w$ path, say $\langle v,
r_{1} , r_{2} , \ldots ,
r_{k } = w \rangle$ with $k $ arcs
($k \geq 1$), is only then combined with an arc
$(w,t) \in A$ to update the distance label of pair
$v$--$t$, if $(w,t) $ is present on the shortest
$r_{\ell } $--$ t$ path for each node
$r_{\ell}$ $(\ell=k- 1 , k- 2,
\ldots, 1) $.
The algorithm extracts shortest paths in order of length from a data structure
and builds two shortest path trees per node, an extra effort of
$O(n^{2})$. This way it can execute efficiently only the
aforementioned distance updates, by picking the arcs $(w,t)$ out of
these trees. The time complexity order per distance update and path extraction
is similar as in other algorithms. An implementation with a data structure of
heaps is possible, but a bucket-type data structure may be more appropriate.
The implied number of distance updates does not exceed
$nm_{0}$ ($m_{0}$ being the total number of
shortest path arcs), but is frequently much lower. In extreme cases the new
algorithm applies $O(n^{2})$ distance updates, whereas known
algorithms require $\Omega( n ^{3})$ updates.
The algorithm is especially suited for undirected graphs; here the construction
of one tree per node is sufficient and the computation times halve. 相似文献
994.
The Earth Simulator (ES) is an SMP cluster system. There are two types of parallel programming models available on the ES. One is a flat programming model, in which a parallel program is implemented by MPI interfaces only, both within an SMP node and among nodes. The other is a hybrid programming model, in which a parallel program is written by using thread programming within an SMP node and MPI programming among nodes simultaneously. It is generally known that it is difficult to obtain the same high level of performance using the hybrid programming model as can be achieved with the flat programming model.
In this paper, we have evaluated scalability of the code for direct numerical simulation of the Navier–Stokes equations on the ES. The hybrid programming model achieves the sustained performance of 346.9 Gflop/s, while the flat programming model achieves 296.4 Gflop/s with 16 PNs of the ES for a DNS problem size of 2563. For small scale problems, however, the hybrid programming model is not as efficient because of microtasking overhead. It is shown that there is an advantage for the hybrid programming model on the ES for the larger size problems. 相似文献
995.
Stochastic unit commitment problem 总被引:1,自引:0,他引:1
The electric power industry is undergoing restructuring and deregulation. We need to incorporate the uncertainty of electric power demand or power generators into the unit commitment problem. The unit commitment problem is to determine the schedule of power generating units and the generating level of each unit. The objective is to minimize the operational cost which is given by the sum of the fuel cost and the start‐up cost. In this paper we propose a new algorithm for the stochastic unit commitment problem which is based on column generation approach. The algorithm continues adding schedules from the dual solution of the restricted linear master program until the algorithm cannot generate new schedules. The schedule generation problem is solved by the calculation of dynamic programming on the scenario tree. 相似文献
996.
This paper discusses Extreme Programming (XP), a relatively new and increasingly popular ‘user-centred’ software design approach.
Extreme Programming proposes that collaborative software development should be centred on the practices of programming. That
proposal contrasts strongly with more heavily instrumented, formalised and centrally managed software engineering methodologies.
The paper maps the interactions of an Extreme Programming team involved in building a commercial organisational knowledge
management system. Using ethnographic techniques, it analyses how this particular style of software development developed
in a given locality, and how it uniquely hybridised documents, conversations, software tools and office layout in that locality.
It examines some of the many artifices, devices, techniques and talk that come together as a complicated contemporary software
system is produced. It argues that XP's emphasis on programming as the core activity and governing metaphor can only be understood in relation to competing overtly formal software engineering
approaches and the organisational framing of software development. XP, it suggests, gains traction by re-embodying the habits
of programming as a collective practice.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
997.
Matthias M. Müller 《Empirical Software Engineering》2004,9(4):335-351
From the first presentation of extreme programming on, pair programming has attracted a wide range of programmers to work together in front of one display. The proposed advantages of pair programming are a faster development cycle and code with higher quality. However, the nearly doubled personnel cost when compared to single developers seems to outweigh these advantages. Instead of showing the superiority of pair programming, we seek an alternative. Can a single developer be assisted by an already known technique with which he produces the quality of pairs with only a fraction of the cost? The answer with some restrictions is: yes, he can. Reviews are a reasonable candidate with respect to code quality and cost. 相似文献
998.
This research builds on prior work on developing near optimal solutions to the product line design problems within the conjoint analysis framework. In this research, we investigate and compare different genetic algorithm operators; in particular, we examine systematically the impact of employing alternative population maintenance strategies and mutation techniques within our problem context. Two alternative population maintenance methods, that we term “Emigration” and “Malthusian” strategies, are deployed to govern how individual product lines in one generation are carried over to the next generation. We also allow for two different types of reproduction methods termed “Equal Opportunity” in which the parents to be paired for mating are selected with equal opportunity and a second based on always choosing the best string in the current generation as one of the parents which is referred to as the “Queen bee”, while the other parent is randomly selected from the set of parent strings. We also look at the impact of integrating the artificial intelligence approach with a traditional optimization approach by seeding the GA with solutions obtained from a Dynamic Programming heuristic proposed by others. A detailed statistical analysis is also carried out to determine the impact of various problem and technique aspects on multiple measures of performance through means of a Monte Carlo simulation study. Our results indicate that such proposed procedures are able to provide multiple “good” solutions. This provides more flexibility for the decision makers as they now have the opportunity to select from a number of very good product lines. The results obtained using our approaches are encouraging, with statistically significant improvements averaging 5% or more, when compared to the traditional benchmark of the heuristic dynamic programming technique. 相似文献
999.
This paper presents an extension of the capacitated facility location problem (CFLP), in which the general setup cost functions and multiple facilities in one site are considered. The setup costs consist of a fixed term (site setup cost) plus a second term (facility setup costs). The facility setup cost functions are generally non-linear functions of the size of the facility in the same site. Two equivalent mixed integer linear programming (MIP) models are formulated for the problem and solved by general MIP solver. A Lagrangian heuristic algorithm (LHA) is also developed to find approximate solutions for this NP-hard problem. Extensive computational experiments are taken on randomly generated data and also well-known existing data (with some necessary modifications). The detailed results are provided and the heuristic algorithm is shown to be efficient. 相似文献
1000.
The authors’ work on lobster fishery in Chile is summarized in this paper. The paper presents the formulation and algorithmic resolution of a two-stage stochastic nonlinear programming model with recourse. The proposed model considers a long-term planning horizon and specifically allows an optimal total allowable catch quota to be obtained for the first planning period. This model takes into account biomass dynamics, the conditions guaranteeing sustained species management and uncertain parameters such as growth rate and species carrying capacity. These parameters are explicitly incorporated via a discrete random variable (scenarios). The proposed model is solved by Lagrangian decomposition using the algebraic modeling software AMPL, in combination with the solver MINOS to solve the nonlinear models resulting from the scenario decomposition. The article also presents the results obtained with this methodology and the conclusions drawn from the work. 相似文献