全文获取类型
收费全文 | 4711篇 |
免费 | 215篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 67篇 |
综合类 | 2篇 |
化学工业 | 1306篇 |
金属工艺 | 157篇 |
机械仪表 | 92篇 |
建筑科学 | 120篇 |
矿业工程 | 11篇 |
能源动力 | 162篇 |
轻工业 | 583篇 |
水利工程 | 11篇 |
石油天然气 | 10篇 |
无线电 | 149篇 |
一般工业技术 | 719篇 |
冶金工业 | 1079篇 |
原子能技术 | 23篇 |
自动化技术 | 439篇 |
出版年
2023年 | 32篇 |
2022年 | 154篇 |
2021年 | 218篇 |
2020年 | 105篇 |
2019年 | 93篇 |
2018年 | 156篇 |
2017年 | 162篇 |
2016年 | 175篇 |
2015年 | 133篇 |
2014年 | 167篇 |
2013年 | 279篇 |
2012年 | 189篇 |
2011年 | 254篇 |
2010年 | 157篇 |
2009年 | 153篇 |
2008年 | 150篇 |
2007年 | 145篇 |
2006年 | 99篇 |
2005年 | 81篇 |
2004年 | 80篇 |
2003年 | 66篇 |
2002年 | 63篇 |
2001年 | 36篇 |
2000年 | 32篇 |
1999年 | 34篇 |
1998年 | 191篇 |
1997年 | 213篇 |
1996年 | 147篇 |
1995年 | 112篇 |
1994年 | 57篇 |
1993年 | 72篇 |
1992年 | 20篇 |
1991年 | 15篇 |
1990年 | 21篇 |
1989年 | 19篇 |
1988年 | 23篇 |
1987年 | 30篇 |
1986年 | 20篇 |
1985年 | 32篇 |
1984年 | 37篇 |
1983年 | 29篇 |
1982年 | 50篇 |
1981年 | 54篇 |
1980年 | 61篇 |
1979年 | 32篇 |
1978年 | 39篇 |
1977年 | 122篇 |
1976年 | 238篇 |
1975年 | 17篇 |
1973年 | 13篇 |
排序方式: 共有4930条查询结果,搜索用时 15 毫秒
51.
Maciej Paszyński David Pardo Carlos Torres-Verdín Leszek Demkowicz Victor Calo 《Journal of Parallel and Distributed Computing》2010
In this paper we present a new parallel multi-frontal direct solver, dedicated for the hp Finite Element Method (hp-FEM). The self-adaptive hp-FEM generates in a fully automatic mode, a sequence of hp-meshes delivering exponential convergence of the error with respect to the number of degrees of freedom (d.o.f.) as well as the CPU time, by performing a sequence of hp refinements starting from an arbitrary initial mesh. The solver constructs an initial elimination tree for an arbitrary initial mesh, and expands the elimination tree each time the mesh is refined. This allows us to keep track of the order of elimination for the solver. The solver also minimizes the memory usage, by de-allocating partial LU factorizations computed during the elimination stage of the solver, and recomputes them for the backward substitution stage, by utilizing only about 10% of the computational time necessary for the original computations. The solver has been tested on 3D Direct Current (DC) borehole resistivity measurement simulations problems. We measure the execution time and memory usage of the solver over a large regular mesh with 1.5 million degrees of freedom as well as on the highly non-regular mesh, generated by the self-adaptive hp-FEM, with finite elements of various sizes and polynomial orders of approximation varying from p=1 to p=9. From the presented experiments it follows that the parallel solver scales well up to the maximum number of utilized processors. The limit for the solver scalability is the maximum sequential part of the algorithm: the computations of the partial LU factorizations over the longest path, coming from the root of the elimination tree down to the deepest leaf. 相似文献
52.
Cezary Graczykowski Tomasz Lewiński 《Structural and Multidisciplinary Optimization》2010,42(6):869-877
The paper delivers the benchmark results for the Michell cantilevers constructed within a half strip, for selected values
of the σ
T
/σ
C
ratio, σ
T
, σ
C
being the admissible stresses in tension and compression, respectively. 相似文献
53.
Krzysztof Ciepliński 《Computers & Mathematics with Applications》2011,62(9):3418-3426
A mapping f:Vn?W, where V is a commutative group, W is a linear space, and n≥2 is an integer, is called multi-quadratic if it is quadratic in each variable. In this paper, we prove the generalized Hyers-Ulam stability of multi-quadratic mappings in Banach spaces and complete non-Archimedean spaces. 相似文献
54.
We consider deterministic distributed broadcasting on multiple access channels in the framework of adversarial queuing. Packets
are injected dynamically by an adversary that is constrained by the injection rate and the number of packets that may be injected
simultaneously; the latter we call burstiness. A protocol is stable when the number of packets in queues at the stations stays
bounded. The maximum injection rate that a protocol can handle in a stable manner is called the throughput of the protocol.
We consider adversaries of injection rate 1, that is, of one packet per round, to address the question if the maximum throughput
1 can be achieved, and if so then with what quality of service. We develop a protocol that achieves throughput 1 for any number
of stations against leaky-bucket adversaries. The protocol has
O(n2+\textburstiness){\mathcal{O}(n^2+\text{burstiness})} packets queued simultaneously at any time, where n is the number of stations; this upper bound is proved to be best possible. A protocol is called fair when each packet is
eventually broadcast. We show that no protocol can be both stable and fair for a system of at least two stations against leaky-bucket adversaries. We study in detail small systems of exactly
two and three stations against window adversaries to exhibit differences in quality of broadcast among classes of protocols.
A protocol is said to have fair latency if the waiting time of packets is
O(\textburstiness){\mathcal{O}(\text{burstiness})}. For two stations, we show that fair latency can be achieved by a full sensing protocol, while there is no stable acknowledgment
based protocol. For three stations, we show that fair latency can be achieved by a general protocol, while no full sensing
protocol can be stable. Finally, we show that protocols that either are fair or do not have the queue sizes affect the order
of transmissions cannot be stable in systems of at least four stations against window adversaries. 相似文献
55.
Immune-based algorithms for dynamic optimization 总被引:4,自引:0,他引:4
The main problem with biologically inspired algorithms (like evolutionary algorithms or particle swarm optimization) when applied to dynamic optimization is to force their readiness for continuous search for new optima occurring in changing locations. Immune-based algorithm, being an instance of an algorithm that adapt by innovation seem to be a perfect candidate for continuous exploration of a search space. In this paper we describe various implementations of the immune principles and we compare these instantiations on complex environments. 相似文献
56.
It is shown in the paper that Developmental Genetic Programming is an efficient tool for evolutionary development of intelligent supervisors that solve an extension of Resource-Constrained Project Scheduling Problem. The extension assumes that resources are only partially available. It also assumes that renewable resources affect the project cost. The cost should be as low as possible and a deadline of the project must be met. This is apparent with regard to software houses and building enterprises. Computational experiments showed that supervisors find solutions of the problem much faster than other genetic approaches. A specific property of the supervisor is that it has various strategies of allocating the resources to the tasks. The supervisor uses the strategies in order to develop a procedure for producing the best schedule for the whole project. The analysis of the evolutionary process was performed and experimental results were compared with the optimal ones obtained by means of the exhaustive search method. 相似文献
57.
Dorota Leszczyńska-Jasion Paweł Łupkowski 《Journal of Logic, Language and Information》2016,25(1):51-76
Our aim is to model the behaviour of a cognitive agent trying to solve a complex problem by dividing it into sub-problems, but failing to solve some of these sub-problems. We use the powerful framework of erotetic search scenarios (ESS) combined with Kleene’s strong three-valued logic. ESS, defined on the grounds of Inferential Erotetic Logic, has appeared to be a useful logical tool for modelling cognitive goal-directed processes. Using the logical tools of ESS and the three-valued logic, we will show how an agent could solve the initial problem despite the fact that the sub-problems remain unsolved. Thus our model not only indicates missing information but also specifies the contexts in which the problem-solving process may end in success despite the lack of information. We will also show that this model of problem solving may find use in an analysis of natural language dialogues. 相似文献
58.
We discuss a family of states describing three-qubit systems in a context of quantum steering phenomena. We show that symmetric steering cannot appear between two qubits—only asymmetric steering can appear in such systems. The main aim of this paper is to discuss the possible relations between the entanglement measures and steering parameter for two-mode mixed state corresponding to the qubit–qubit subsystem. We have derived the conditions determining boundary values of the negativity parametrized by concurrence. We show that two-qubit mixed state cannot be steerable when the negativity of such state is smaller than, or equal to, its boundary value. Finally, we have found ranges of the values of the mixedness measure, parametrized by concurrence and negativity for steerable and unsteerable two-qubit mixed states. 相似文献
59.
Michell’s problem of optimizing truss topology for stress or compliance constraints under a single load condition is solved
analytically for plane trusses having a square-shaped line support. Geometrical characteristics of the Hencky nets giving
the truss layout are expressed in terms of Lommel functions. Analytically derived truss volumes for the above problem are
compared with those of trusses supported along circles of equivalent area. Some general implications of the results are also
discussed. 相似文献
60.
The precipitation process in alloys containing 4% Ti and 5 to 16% Ni was investigated using transmission electron microscopy, hardness and electrical conductivity measurements. After ageing, spherical -Ni3Ti precipitates with ordered DO22 superlattice were observed in alloys CuTiNi5 to 10 and the L12 superlattice in the CuTi4Ni16 alloy. With increasing nickel content the size of precipitates decreases; this has only a minor influence on the age hardening. The CuTiNi10 alloy has the best electrical conductivity approaching 18m–1mm–2. 相似文献