全文获取类型
收费全文 | 12715篇 |
免费 | 191篇 |
国内免费 | 142篇 |
专业分类
电工技术 | 162篇 |
综合类 | 3篇 |
化学工业 | 949篇 |
金属工艺 | 470篇 |
机械仪表 | 117篇 |
建筑科学 | 157篇 |
矿业工程 | 1篇 |
能源动力 | 123篇 |
轻工业 | 277篇 |
水利工程 | 36篇 |
石油天然气 | 11篇 |
无线电 | 537篇 |
一般工业技术 | 504篇 |
冶金工业 | 212篇 |
原子能技术 | 108篇 |
自动化技术 | 9381篇 |
出版年
2024年 | 4篇 |
2023年 | 43篇 |
2022年 | 145篇 |
2021年 | 177篇 |
2020年 | 81篇 |
2019年 | 91篇 |
2018年 | 122篇 |
2017年 | 70篇 |
2016年 | 134篇 |
2015年 | 89篇 |
2014年 | 335篇 |
2013年 | 372篇 |
2012年 | 937篇 |
2011年 | 3280篇 |
2010年 | 1266篇 |
2009年 | 1142篇 |
2008年 | 810篇 |
2007年 | 696篇 |
2006年 | 546篇 |
2005年 | 645篇 |
2004年 | 581篇 |
2003年 | 628篇 |
2002年 | 310篇 |
2001年 | 26篇 |
2000年 | 30篇 |
1999年 | 50篇 |
1998年 | 130篇 |
1997年 | 58篇 |
1996年 | 47篇 |
1995年 | 18篇 |
1994年 | 22篇 |
1993年 | 10篇 |
1992年 | 17篇 |
1991年 | 5篇 |
1990年 | 11篇 |
1989年 | 12篇 |
1988年 | 11篇 |
1987年 | 6篇 |
1986年 | 11篇 |
1985年 | 8篇 |
1984年 | 24篇 |
1983年 | 14篇 |
1982年 | 9篇 |
1981年 | 8篇 |
1980年 | 5篇 |
1979年 | 4篇 |
1976年 | 3篇 |
1972年 | 1篇 |
1969年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
71.
Xi-Ren CaoAuthor Vitae Zhiyuan RenAuthor Vitae Shalabh BhatnagarAuthor Vitae Michael FuAuthor Vitae Steven MarcusAuthor Vitae 《Automatica》2002,38(6):929-943
We propose a time aggregation approach for the solution of infinite horizon average cost Markov decision processes via policy iteration. In this approach, policy update is only carried out when the process visits a subset of the state space. As in state aggregation, this approach leads to a reduced state space, which may lead to a substantial reduction in computational and storage requirements, especially for problems with certain structural properties. However, in contrast to state aggregation, which generally results in an approximate model due to the loss of Markov property, time aggregation suffers no loss of accuracy, because the Markov property is preserved. Single sample path-based estimation algorithms are developed that allow the time aggregation approach to be implemented on-line for practical systems. Some numerical and simulation examples are presented to illustrate the ideas and potential computational savings. 相似文献
72.
73.
A very simple algorithm for computing all k nearest neighbors in 2-D is presented. The method does not rely on complicated forms of tessellation, it only requires simple data binning for fast range searching. Its applications range from scattered data interpolation to reverse engineering. 相似文献
74.
P Casolo D Mosca C Amorotti B Drei A Raspadori P Di Blasio E Ganz G De Luca G Colli R De Maria D Amuso 《Canadian Metallurgical Quarterly》1997,68(2):207-11; discussion 212
Primary and sole breast lymphoma is a very rare disease. With the review of our series of 616 cases operated on for breast cancer, only 3 cases (0.48%) of primary breast non-Hodgkin lymphoma (LNH) have been observed. The authors outline the problems concerning diagnosis and therapy of this rare disease: pathological and immunohistochemical aspects are discussed. They stress the importance of staging in order to plan a correct multidisciplinary approach. 相似文献
75.
Using the batch method, the retention of Ga(III) from HCl solutions by two gel‐type pyridine strong‐base anion exchangers containing 1‐methyl‐ or 1‐butyl‐4‐vinylpyridinium chloride structural units, called S1 and S2 resins, respectively, was studied. The influence of the HCl and Ga(III) concentrations as well as of the contact time between the resin and the liquid phase was investigated. The parameters, which characterize the retention process, were estimated using Langmuir and Freundlich isotherms. Both resins exhibited a higher affinity for gallium ions from a 6M HCl solution. According to Langmuir isotherms, maximum retention capacities of 44.44 and 60 mg Ga(III)/g dry resin for the S1 and S2 resins, respectively, were obtained. Freundlich isotherms provide additional proof for a higher affinity of the S2 resin for Ga(III) from HCl solutions. It is clear that the substituent length increase on N+ atoms led to an increasing affinity of the pyridine strong base anion exchangers toward Ga(III). © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3440–3444, 2002 相似文献
76.
This paper describes how SWoRD (scaffolded writing and rewriting in the discipline), a web-based reciprocal peer review system, supports writing practice, particularly for large content courses in which writing is considered critical but not feasibly included. To help students gain content knowledge as well as writing and reviewing skills, SWoRD supports the whole cycle of writing, reviews, back-reviews, and rewriting by scaffolding the journal publication process as its authentic practice model. In addition, SWoRD includes algorithms that compute individual reviewer’s review accuracy, which is in turn used to support the various drawbacks of reciprocal peer reviews (e.g., variation in motivation or ability of reviewers). Finally, this paper describes an empirical evaluation showing that the SWoRD approach is effective in improving writing quality in content classes. 相似文献
77.
A. Palmeri F. Ricciardelli G. Muscolino A. De Luca 《Canadian Metallurgical Quarterly》2004,130(9):1052-1061
The equation of motion of linear dynamic systems with viscoelastic memory is usually expressed in a integrodifferential form, and its numerical solution is computationally heavy. In two recent papers, the writers suggested that the system memory be accounted for through the introduction of a number of additional internal variables. Following this approach, the motion of the system is governed by a set of first-order, linear differential equations, whose solution is quite easy. In this paper, the approach is extended to single-degree-of-freedom systems subjected to random, nonstationary excitation. The equations governing the time variation of the second-order statistics are derived, and an effective step-by-step solution procedure is proposed. Numerical example shows the accuracy of the procedure for white and nonwhite excitations. 相似文献
78.
Jonathan Alexander Author Vitae William P. Banks Author Vitae 《Computers and Composition》2004,21(3):273-293
In this introduction to a special issue of Computers and Composition, the authors critically review current literature on computer-assisted writing pedagogies that grapple with issues of sexuality. Although this body of work is small, it points to provocative ways to develop our students’ critical and rhetorical sensibilities about the constructions of sexuality in our culture. Further, such work innovatively addresses the place of networked communication technologies in the interrogation of such constructions. The authors conclude with both an introduction of the work in this special issue that addresses the intersection of sexuality studies and computer-assisted writing studies and with a call for additional work in this field. 相似文献
79.
80.
A parametric interpolator with confined chord errors, acceleration and deceleration for NC machining 总被引:6,自引:0,他引:6
Tsehaw Yong Author Vitae Author Vitae 《Computer aided design》2003,35(13):1249-1259
Parametric interpolation has many advantages over linear interpolation in machining curves. Real time parametric interpolation research so far has addressed achieving a uniform feed rate, confined chord errors and jerk limited trajectory planning. However, simultaneous consideration of confined chord errors that respect the acceleration and deceleration capabilities of the machine has not been attempted. In this paper, the offline detection of feed rate sensitive corners is proposed. The velocity profile in these zones is planned so that chord errors are satisfied while simultaneously accommodating the machine's acceleration and deceleration limits. Outside the zone of the feed rate sensitive corners, the feed rate is planned using the Taylor approximation. Simulation results indicate that the offline detection of feed rate sensitive corners improves parametric interpolation. For real time interpolation, the parametric curve information can be augmented with the detected feed rate sensitive corners that are stored in 2×2 matrices. 相似文献