全文获取类型
收费全文 | 3901篇 |
免费 | 446篇 |
国内免费 | 312篇 |
专业分类
电工技术 | 64篇 |
技术理论 | 1篇 |
综合类 | 329篇 |
化学工业 | 49篇 |
金属工艺 | 10篇 |
机械仪表 | 79篇 |
建筑科学 | 135篇 |
矿业工程 | 27篇 |
能源动力 | 15篇 |
轻工业 | 19篇 |
水利工程 | 35篇 |
石油天然气 | 26篇 |
武器工业 | 20篇 |
无线电 | 674篇 |
一般工业技术 | 220篇 |
冶金工业 | 125篇 |
原子能技术 | 5篇 |
自动化技术 | 2826篇 |
出版年
2024年 | 17篇 |
2023年 | 27篇 |
2022年 | 52篇 |
2021年 | 66篇 |
2020年 | 72篇 |
2019年 | 86篇 |
2018年 | 88篇 |
2017年 | 113篇 |
2016年 | 124篇 |
2015年 | 118篇 |
2014年 | 200篇 |
2013年 | 275篇 |
2012年 | 238篇 |
2011年 | 310篇 |
2010年 | 211篇 |
2009年 | 262篇 |
2008年 | 274篇 |
2007年 | 287篇 |
2006年 | 227篇 |
2005年 | 210篇 |
2004年 | 186篇 |
2003年 | 160篇 |
2002年 | 123篇 |
2001年 | 109篇 |
2000年 | 84篇 |
1999年 | 82篇 |
1998年 | 72篇 |
1997年 | 42篇 |
1996年 | 60篇 |
1995年 | 46篇 |
1994年 | 50篇 |
1993年 | 34篇 |
1992年 | 36篇 |
1991年 | 28篇 |
1990年 | 21篇 |
1989年 | 16篇 |
1988年 | 15篇 |
1987年 | 7篇 |
1986年 | 6篇 |
1985年 | 21篇 |
1984年 | 23篇 |
1983年 | 25篇 |
1982年 | 26篇 |
1981年 | 21篇 |
1980年 | 25篇 |
1979年 | 29篇 |
1978年 | 10篇 |
1977年 | 6篇 |
1976年 | 12篇 |
1964年 | 5篇 |
排序方式: 共有4659条查询结果,搜索用时 15 毫秒
1.
2.
Private information retrieval(PIR) is an important privacy protection issue of secure multi-party computation, but the PIR protocols based on classical cryptography are vulnerable because of new technologies,such as quantum computing and cloud computing. The quantum private queries(QPQ) protocols available, however, has a high complexity and is inefficient in the face of large database. This paper, based on the QKD technology which is mature now, proposes a novel QPQ protocol utilizing the key dilution and auxiliary parameter. Only N quits are required to be sent in the quantum channel to generate the raw key, then the straight k bits in the raw key are added bitwise to dilute the raw key, and a final key is consequently obtained to encrypt the database. By flexible adjusting of auxiliary parameters θ and k, privacy is secured and the query success ratio is improved. Feasibility and performance analyses indicate that the protocol has a high success ratio in first-trial query and is easy to implement, and that the communication complexity of O(N) is achieved. 相似文献
3.
The pharmacy service requires that some pharmacies are always available and shifts have to be organized: a shift corresponds to a subset of pharmacies that must be open 24 hours a day on a particular week. Under the requirement that each pharmacy belongs to exactly one shift and the assumption that users minimize the distance to the closest open pharmacy during each shift, we want to determine a partition of the pharmacies into a given number of shifts, such that the total distance covered by users is minimized. It may be also required that shift cardinalities are balanced. We discuss different versions and the related computational complexity, showing that the problem is NP-hard in general. A set packing formulation is presented and solved by branch-and-price, together with a fast solution technique based on a tabu search. They have been applied to real and random instances showing that (i) the set packing formulation is very tight and often exhibits no integrality gap; (ii) the branch-and-price solves problems of practical relevance to optimality in a reasonable amount of time (order of minutes); (iii) the tabu search finds optimal or near-optimal solutions in order of seconds. 相似文献
4.
5.
The Label-Cover problem, defined by S. Arora, L. Babai, J. Stern, Z. Sweedyk [Proceedings of 34th IEEE Symposium on Foundations of Computer Science, 1993, pp. 724-733], serves as a starting point for numerous hardness of approximation reductions. It is one of six ‘canonical’ approximation problems in the survey of Arora and Lund [Hardness of Approximations, in: Approximation Algorithms for NP-Hard Problems, PWS Publishing Company, 1996, Chapter 10]. In this paper we present a direct combinatorial reduction from low error-probability PCP [Proceedings of 31st ACM Symposium on Theory of Computing, 1999, pp. 29-40] to Label-Cover showing it NP-hard to approximate to within 2(logn)1−o(1). This improves upon the best previous hardness of approximation results known for this problem.We also consider the Minimum-Monotone-Satisfying-Assignment (MMSA) problem of finding a satisfying assignment to a monotone formula with the least number of 1's, introduced by M. Alekhnovich, S. Buss, S. Moran, T. Pitassi [Minimum propositional proof length is NP-hard to linearly approximate, 1998]. We define a hierarchy of approximation problems obtained by restricting the number of alternations of the monotone formula. This hierarchy turns out to be equivalent to an AND/OR scheduling hierarchy suggested by M.H. Goldwasser, R. Motwani [Lecture Notes in Comput. Sci., Vol. 1272, Springer-Verlag, 1997, pp. 307-320]. We show some hardness results for certain levels in this hierarchy, and place Label-Cover between levels 3 and 4. This partially answers an open problem from M.H. Goldwasser, R. Motwani regarding the precise complexity of each level in the hierarchy, and the place of Label-Cover in it. 相似文献
6.
John Watrous 《Computational Complexity》2003,12(1-2):48-84
This paper studies the space-complexity of predicting the
long-term behavior of a class of stochastic processes based on evolutions
and measurements of quantum mechanical systems. These processes
generalize a wide range of both quantum and classical space-bounded
computations, including unbounded error computations given by machines
having algebraic number transition amplitudes or probabilities.
It is proved that any space s quantum stochastic process from this class
can be simulated probabilistically with unbounded error in space O(s),
and therefore deterministically in space O(s2). 相似文献
7.
Comments on the article "A house divided? The psychology of red and blue America" by D. C. Seyle and M. L. Newman (see record 2006-11202-001). Seyle and Newman concluded that the red and blue metaphor is inaccurate and proposed a purple America strategy to better convey that the majority of people do not align themselves with political extremes. There is interdisciplinary agreement on this. Although not cited by Seyle and Newman, the findings by Professor Fiorina of Stanford University were reported by the APA Monitor on Psychology in its coverage of the 2005 APA State Leadership Conference (Murray Law, 2005). In contrast to their social psychological analysis, Seyle and Newman were incorrect in concluding that "[a]s psychologists, we are not in a position to change either the elements of the American political system that may spur this conflict or even the decisions made by pundits, politicians, and reporters about the terms they choose to use in political discussion" (p. 579). (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
8.
Sándor P. Fekete 《Information Processing Letters》2003,88(5):219-223
We prove NP-completeness of deciding the existence of an economic equilibrium in so-called house allocation markets. House allocation markets are markets with indivisible goods in which every agent holds exactly one copy of some good. 相似文献
9.
Gouvier W. Drew; Sytsma-Jordan Sara; Mayville Stephen 《Canadian Metallurgical Quarterly》2003,48(3):175
Objective: To evaluate the effects of disability type, job complexity, and public contact on hiring decisions. Design and Participants: An Americans With Disabilities Act (ADA; 1990) fact sheet and matched resumes with vocational and medical histories including chronic mental illness, developmental disability, closed head injury, and back injury were provided to 295 undergraduate business-related majors, who rated the applicants' suitability for 2 job positions and work shifts. Results: Findings indicated disparities in ratings of employability as a function of disability type. Paired comparisons yielded complementary findings, with effects of disability type and Disability Type × Job Complexity, but no effects of public contact. Conclusions: Stereotyping and discrimination in employment decisions apparently persist, more than 10 years after the ADA. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
10.
Abstract. In this paper we refer to the Temporal Precedence Problem on Pure Pointer Machines . This problem asks for the design of a data structure, maintaining a set of stored elements and supporting the following
two operations: insert and precedes . The operation insert (a) introduces a new element a in the structure, while the operation precedes (a,b) returns true iff element a was inserted before element b temporally. In [11] a solution was provided to the problem with worst-case time complexity O (log log n ) per operation and O(n log log n) space, where n is the number of elements inserted. It was also demonstrated that the precedes operation has a lower bound of Ω (log log n ) for the Pure Pointer Machine model of computation. In this paper we present two simple solutions with linear space and worst-case constant insertion
time. In addition, we describe two algorithms that can handle the precedes (a,b) operation in O (log log d ) time, where d is the temporal distance between the elements a and b . 相似文献