全文获取类型
收费全文 | 469164篇 |
免费 | 4254篇 |
国内免费 | 1082篇 |
专业分类
电工技术 | 8362篇 |
综合类 | 274篇 |
化学工业 | 70873篇 |
金属工艺 | 22909篇 |
机械仪表 | 16193篇 |
建筑科学 | 9756篇 |
矿业工程 | 4288篇 |
能源动力 | 10367篇 |
轻工业 | 29236篇 |
水利工程 | 5865篇 |
石油天然气 | 14751篇 |
武器工业 | 40篇 |
无线电 | 51089篇 |
一般工业技术 | 104391篇 |
冶金工业 | 77040篇 |
原子能技术 | 14597篇 |
自动化技术 | 34469篇 |
出版年
2021年 | 4521篇 |
2019年 | 4272篇 |
2018年 | 7906篇 |
2017年 | 8204篇 |
2016年 | 8616篇 |
2015年 | 4883篇 |
2014年 | 8559篇 |
2013年 | 20065篇 |
2012年 | 12543篇 |
2011年 | 16291篇 |
2010年 | 13204篇 |
2009年 | 14893篇 |
2008年 | 15440篇 |
2007年 | 15060篇 |
2006年 | 12836篇 |
2005年 | 11294篇 |
2004年 | 11022篇 |
2003年 | 11089篇 |
2002年 | 10487篇 |
2001年 | 10785篇 |
2000年 | 10233篇 |
1999年 | 10080篇 |
1998年 | 22896篇 |
1997年 | 16575篇 |
1996年 | 12711篇 |
1995年 | 9794篇 |
1994年 | 8897篇 |
1993年 | 8989篇 |
1992年 | 6932篇 |
1991年 | 6878篇 |
1990年 | 6852篇 |
1989年 | 6533篇 |
1988年 | 6354篇 |
1987年 | 5841篇 |
1986年 | 5697篇 |
1985年 | 6103篇 |
1984年 | 5760篇 |
1983年 | 5537篇 |
1982年 | 5213篇 |
1981年 | 5193篇 |
1980年 | 5139篇 |
1979年 | 5119篇 |
1978年 | 5137篇 |
1977年 | 5635篇 |
1976年 | 7025篇 |
1975年 | 4591篇 |
1974年 | 4637篇 |
1973年 | 4640篇 |
1972年 | 4079篇 |
1971年 | 3625篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
We propose and evaluate a parallel “decomposite best-first” search branch-and-bound algorithm (dbs) for MIN-based multiprocessor systems. We start with a new probabilistic model to estimate the number of evaluated nodes for a serial best-first search branch-and-bound algorithm. This analysis is used in predicting the parallel algorithm speed-up. The proposed algorithm initially decomposes a problem into N subproblems, where N is the number of processors available in a multiprocessor. Afterwards, each processor executes the serial best-first search to find a local feasible solution. Local solutions are broadcasted through the network to compute the final solution. A conflict-free mapping scheme, known as the step-by-step spread, is used for subproblem distribution on the MIN. A speedup expression for the parallel algorithm is then derived using the serial best-first search node evaluation model. Our analysis considers both computation and communication overheads for providing realistic speed-up. Communication modeling is also extended for the parallel global best-first search technique. All the analytical results are validated via simulation. For large systems, when communication overhead is taken into consideration, it is observed that the parallel decomposite best-first search algorithm provides better speed-up compared to other reported schemes 相似文献
102.
Moser L.E. Melliar-Smith P.M. Agrawala V. 《Parallel and Distributed Systems, IEEE Transactions on》1994,5(5):459-473
Presents protocols for determining processor membership in asynchronous distributed systems that are subject to processor and communication faults. These protocols depend on the placement of a total order on broadcast messages. The types of systems for which each of these protocols is applicable are characterized by the properties of the communication mechanisms and by the availability of stable storage. In the absence of stable storage or of a mechanism for distinguishing promptly delivered messages, the authors show that no membership protocol can exist. They also discuss their experience in implementing these membership protocols 相似文献
103.
Considers the applicability of algorithm based fault tolerance (ABET) to massively parallel scientific computation. Existing ABET schemes can provide effective fault tolerance at a low cost For computation on matrices of moderate size; however, the methods do not scale well to floating-point operations on large systems. This short note proposes the use of a partitioned linear encoding scheme to provide scalability. Matrix algorithms employing this scheme are presented and compared to current ABET schemes. It is shown that the partitioned scheme provides scalable linear codes with improved numerical properties with only a small increase in hardware and time overhead 相似文献
104.
Several variations of cache-based checkpointing for rollback error recovery from transient errors in shared-memory multiprocessors have been recently developed. By modifying the cache replacement policy, these techniques use the inherent redundancy in the memory hierarchy to periodically checkpoint the computation state. Three schemes, different in the manner in which they avoid rollback propagation, are evaluated in this paper. By simulation with address traces from parallel applications running on an Encore Multimax shared-memory multiprocessor, we evaluate the performance effect of integrating the recovery schemes in the cache coherence protocol. Our results indicate that the cache-based schemes can provide checkpointing capability with low performance overhead, but with uncontrollable high variability in the checkpoint interval 相似文献
105.
We present new methods for load balancing of unstructured tree computations on large-scale SIMD machines, and analyze the scalability of these and other existing schemes. An efficient formulation of tree search on an SIMD machine consists of two major components: a triggering mechanism, which determines when the search space redistribution must occur to balance the search space over processors, and a scheme to redistribute the search space. We have devised a new redistribution mechanism and a new triggering mechanism. Either of these can be used in conjunction with triggering and redistribution mechanisms developed by other researchers. We analyze the scalability of these mechanisms and verify the results experimentally. The analysis and experiments show that our new load-balancing methods are highly scalable on SIMD architectures. Their scalability is shown to he no worse than that of the best load-balancing schemes on MIMD architectures. We verify our theoretical results by implementing the 15-puzzle problem on a CM-2 SIMD parallel computer 相似文献
106.
McKinley P.K. Xu H. Esfahanian A.-H. Ni L.M. 《Parallel and Distributed Systems, IEEE Transactions on》1994,5(12):1252-1265
Multicast communication, in which the same message is delivered from a source node to an arbitrary number of destination nodes, is being increasingly demanded in parallel computing. System supported multicast services can potentially offer improved performance, increased functionality, and simplified programming, and may in turn be used to support various higher-level operations for data movement and global process control. This paper presents efficient algorithms to implement multicast communication in wormhole-routed direct networks, in the absence of hardware multicast support, by exploiting the properties of the switching technology. Minimum-time multicast algorithms are presented for n-dimensional meshes and hypercubes that use deterministic, dimension-ordered routing of unicast messages. Both algorithms can deliver a multicast message to m-1 destinations in [log 2 m] message passing steps, while avoiding contention among the constituent unicast messages. Performance results of implementations on a 64-node nCUBE-2 hypercube and a 168-node Symult 2010 2-D mesh are given 相似文献
107.
Implementing a neural network on a digital or mixed analog and digital chip yields the quantization of the synaptic weights dynamics. This paper addresses this topic in the case of Kohonen's self-organizing maps. We first study qualitatively how the quantization affects the convergence and the properties, and deduce from this analysis the way to choose the parameters of the network (adaptation gain and neighborhood). We show that a spatially decreasing neighborhood function is far more preferable than the usually rectangular neighborhood function, because of the weight quantization. Based on these results, an analog nonlinear network, integrated in a standard CMOS technology, and implementing this spatially decreasing neighborhood function is then presented. It can be used in a mixed analog and digital circuit implementation. 相似文献
108.
The bounded disorder file organization proposed by W. Litwin and D.B. Lomet (1987) uses a combination of hashing and tree indexing. Lomet provided an approximate analysis with the mention of the difficulty involved in exact modeling of data nodes, which motivated this work. In an earlier paper (M.V. Ramakrishna and P. Mukhopadhyay, 1988) we provided an exact model and analysis of the data nodes, which is based on the solution of a classical sequential occupancy problem. After summarizing the analysis of data nodes, an alternate file growth method based on repeated trials using universal hashing is proposed and analyzed. We conclude that the alternate file growth method provides simplicity and significant improvement in storage utilization 相似文献
109.
We describe a binding environment for the AND and OR parallel execution of logic programs that is suitable for both shared and nonshared memory multiprocessors. The binding environment was designed with a view of rendering a compiler using this binding environment machine independent. The binding environment is similar to closed environments proposed by J. Conery. However, unlike Conery's scheme, it supports OR and independent AND parallelism on both types of machines. The term representation, the algorithms for unification and the join algorithms for parallel AND branches are presented in this paper. We also detail the differences between our scheme and Conery's scheme. A compiler based on this binding environment has been implemented on a platform for machine independent parallel programming called the Chare Kernel 相似文献
110.
Shrivastava S.K. McCue D.L. 《Parallel and Distributed Systems, IEEE Transactions on》1994,5(4):421-432
The object-oriented approach to system structuring has found widespread acceptance among designers and developers of robust computing systems. The authors propose a system structure for distributed programming systems that support persistent objects and describe how properties such as persistence and recoverability can be implemented. The proposed structure is modular, permitting easy exploitation of any distributed computing facilities provided by the underlying system. An existing system constructed according to the principles espoused here is examined to illustrate the practical utility of the proposed approach to system structuring 相似文献