全文获取类型
收费全文 | 63063篇 |
免费 | 2857篇 |
国内免费 | 214篇 |
专业分类
电工技术 | 971篇 |
综合类 | 102篇 |
化学工业 | 12291篇 |
金属工艺 | 2279篇 |
机械仪表 | 3396篇 |
建筑科学 | 1352篇 |
矿业工程 | 54篇 |
能源动力 | 2430篇 |
轻工业 | 4635篇 |
水利工程 | 282篇 |
石油天然气 | 216篇 |
武器工业 | 2篇 |
无线电 | 11038篇 |
一般工业技术 | 12514篇 |
冶金工业 | 6347篇 |
原子能技术 | 689篇 |
自动化技术 | 7536篇 |
出版年
2023年 | 600篇 |
2022年 | 964篇 |
2021年 | 1595篇 |
2020年 | 1135篇 |
2019年 | 1156篇 |
2018年 | 1527篇 |
2017年 | 1533篇 |
2016年 | 1908篇 |
2015年 | 1511篇 |
2014年 | 2324篇 |
2013年 | 3915篇 |
2012年 | 3630篇 |
2011年 | 4425篇 |
2010年 | 3363篇 |
2009年 | 3532篇 |
2008年 | 3199篇 |
2007年 | 2742篇 |
2006年 | 2478篇 |
2005年 | 2138篇 |
2004年 | 2062篇 |
2003年 | 1883篇 |
2002年 | 1774篇 |
2001年 | 1409篇 |
2000年 | 1315篇 |
1999年 | 1286篇 |
1998年 | 2383篇 |
1997年 | 1543篇 |
1996年 | 1303篇 |
1995年 | 1019篇 |
1994年 | 782篇 |
1993年 | 730篇 |
1992年 | 534篇 |
1991年 | 520篇 |
1990年 | 442篇 |
1989年 | 429篇 |
1988年 | 337篇 |
1987年 | 287篇 |
1986年 | 270篇 |
1985年 | 239篇 |
1984年 | 210篇 |
1983年 | 162篇 |
1982年 | 156篇 |
1981年 | 136篇 |
1980年 | 136篇 |
1979年 | 109篇 |
1978年 | 97篇 |
1977年 | 130篇 |
1976年 | 167篇 |
1975年 | 82篇 |
1974年 | 81篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
W. Lee 《Journal of power sources》1985,16(2):131-140
The structure of sintered nickel composite plaque is characterized by an irregular pore structure with a wide distribution of pore sizes as well as a l 相似文献
82.
Lee C.K. Hui S.Y.R. Shu-HungChung H. Shrivastava Y. 《Power Electronics, IEEE Transactions on》2002,17(1):94-100
In this paper, a feasibility study of a randomized space vector switching scheme for three-level inverters is reported. Based on the traditional space vector concept for pulse width modulation (PWM) inverters, the sequence of the space vector is randomized in this scheme. The overall vector, resulting from the randomization, is mathematically identical to that of the traditional space vector. It has been found that the randomized scheme can effectively spread the switching noise over a wide frequency range and at the same time keep the steady-state link capacitor voltage balanced. The proposed scheme has been implemented in real time in a digital controller and its features have been experimentally confirmed 相似文献
83.
Biing-Lin Lee 《Polymer Engineering and Science》1985,25(12):729-740
The physical properties of finished polymer blend composites are, in general, strongly influenced by the heterogeneity of the blend and the distribution of ingredients (especially reinforcement fillers) in each of the polymer phases. In this article, we review and update a processing technology specifically for the processing of multiphase rubber blend compounds in order to produce blend compounds with more desirable properties for practical applications. The basic concept is centered on the controlled-ingredient-distribution mixing (CIDM) process. The improvements in the following properties of rubber blend compounds are discussed: crack growth resistance, heat buildup, oil swelling, covulcanization, green strength, and permeability. 相似文献
84.
Michael C. H. Lee 《Polymer Engineering and Science》1985,25(14):909-920
Based on the concept of entropy of mixing, a new method for determining the degree of mixing of the filler in a polymer matrix has been established. The measurement used in this method is based on a new variable, the effective volume fraction of the filler, ?′, which is a function of the mixing index, A, and the volume fraction of the filler, ?. The mixing index can be determined from the tensile modulus data of filled elastomers. Excellent agreement is obtained between the mixing index and the dispersion of the filler as determined by a morphological study of cryogenically fractured surfaces of filled elastomers. Using the new variable, the effective volume fraction of the filler, useful relationships for the tensile modulus and the ultimate stretch ratio of filled elastomer have been established. Experimental data confirm that these relationships can well describe the effects of concentration and degree of mixing on the two tensile properties of filled elastomers. 相似文献
85.
For batchwise radical chain solution multicomponent copolymerization, the minimum end time problem for the predetermined monomer conversion and number average molecular weight has been studied by considering the initiator concentration (or feed rate) and temperature as the two control variables. Applying the maximum principle and “unit segment treatment” (by which the co-polymerization can be treated as homo-polymerization in the kinetic analysis), it is found that for initiator addition processes the optimal initiator addition policy is to make the rate of initiation constant for the optimal temperature variation case, and the initiator concentration constant for the isothermal case as in homo-polymerization. For single charge of initiator processes, the optimal initial initiator concentration is such that it should be maintained at the lowest possible value (by which the polymerization is strongly dead-end) for the optimal temperature variation case without chain transfer steps, and at some optimal value (by which the polymerization is near dead-end) for the best isothermal case. 相似文献
86.
87.
Prentky Robert A.; Knight Raymond A.; Lee Austin F. S. 《Canadian Metallurgical Quarterly》1997,65(1):141
This study examined the predictive efficacy of 10 rationally derived, archivally coded variables for assessing reoffense risk among extrafamilial child molesters. Follow-up data on 111 child molesters who were discharged from the Massachusetts Treatment Center between 1960 and 1984 were used. Degree of sexual preoccupation with children, paraphilias, and number of prior sexual offenses predicted sexual recidivism. Juvenile and adult antisocial behavior, paraphilias, and low amount of contact with children predicted nonsexual victim-involved and violent recidivism. Area under the receiver-operating characteristic curves in all three analyses indicated discrimination that was substantially better than chance, ranging from .73 to .79. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
88.
Lee Kiang Quah 《Building Research & Information》1992,20(4):229-232
The widening of interest and scope of property management and maintenance has attracted a greater diversity of professional disciplines into facilities management. Dr Quah, coordinator of CIB W70 on Management, Maintenance and Modernization of Building facilities, expresses her personal views on the current fascination with the subject. 相似文献
89.
A thermodynamic evaluation of the Fe-Cr-V-C system 总被引:2,自引:0,他引:2
90.
Centralized and distributed automated guided vehicle system (AGVS) models for materials handling, and the model for part processing are integrated into a single coherent model. This formulation can be used to collectively schedule and control the entire flexible manufacturing system (FMS) as opposed to the traditional separate scheduling of part processing and material handling. The two AGVS models are based on Petri nets and can be directly used in the scheduling method that uses Petri nets for formulation and heuristic search for solution. This method employs a global search to seek the optimal operation of an entire FMS. Scheduling examples are presented and the method compares favorably with the results simulated using heuristic dispatch rules 相似文献