全文获取类型
收费全文 | 25380篇 |
免费 | 1509篇 |
国内免费 | 995篇 |
专业分类
电工技术 | 1430篇 |
综合类 | 1480篇 |
化学工业 | 1755篇 |
金属工艺 | 3031篇 |
机械仪表 | 2053篇 |
建筑科学 | 1903篇 |
矿业工程 | 582篇 |
能源动力 | 492篇 |
轻工业 | 1384篇 |
水利工程 | 244篇 |
石油天然气 | 1891篇 |
武器工业 | 269篇 |
无线电 | 2172篇 |
一般工业技术 | 3138篇 |
冶金工业 | 1215篇 |
原子能技术 | 184篇 |
自动化技术 | 4661篇 |
出版年
2024年 | 74篇 |
2023年 | 223篇 |
2022年 | 351篇 |
2021年 | 490篇 |
2020年 | 498篇 |
2019年 | 446篇 |
2018年 | 458篇 |
2017年 | 655篇 |
2016年 | 740篇 |
2015年 | 973篇 |
2014年 | 1444篇 |
2013年 | 1441篇 |
2012年 | 1651篇 |
2011年 | 1862篇 |
2010年 | 1522篇 |
2009年 | 1498篇 |
2008年 | 1493篇 |
2007年 | 1726篇 |
2006年 | 1533篇 |
2005年 | 1349篇 |
2004年 | 1098篇 |
2003年 | 1009篇 |
2002年 | 859篇 |
2001年 | 769篇 |
2000年 | 623篇 |
1999年 | 547篇 |
1998年 | 463篇 |
1997年 | 362篇 |
1996年 | 349篇 |
1995年 | 269篇 |
1994年 | 229篇 |
1993年 | 163篇 |
1992年 | 141篇 |
1991年 | 107篇 |
1990年 | 85篇 |
1989年 | 58篇 |
1988年 | 48篇 |
1987年 | 30篇 |
1986年 | 17篇 |
1985年 | 31篇 |
1984年 | 25篇 |
1983年 | 33篇 |
1982年 | 30篇 |
1981年 | 7篇 |
1980年 | 6篇 |
1978年 | 10篇 |
1965年 | 17篇 |
1962年 | 7篇 |
1957年 | 5篇 |
1955年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
振动采油工艺在稠油区的实验研究与应用 总被引:5,自引:2,他引:3
在天然地震的影响下,油井产量发生波动,使人们受到启示,从而引进了振动采油工艺技术。本文对振动增产的机理进行了探讨,指出振动增油机理在于加快地层中流体的流速;改变储集层内油、气、水的重新分布;改变岩石表面润湿性,有利于清除油层堵塞,提高渗透率。通过分析两个试验区的振动采油效果,总结出在不同扰动力、不同激振频率、不同振动周期下的增产效果和规律,对振动采油的实施具有一定的指导意义。 相似文献
42.
Seven hundred three members of the Society for Industrial and Organizational Psychology indicated agreement or disagreement with 49 propositions regarding cognitive ability tests in organizations. There was consensus that cognitive ability tests are valid and fair, that they provide good but incomplete measures, that different abilities are necessary for different jobs, and that diversity is valuable. Items dealing with the unique status of cognitive ability were most likely to generate polarized opinions. A 2-factor model, classifying items as those reflecting societal concerns over the consequences of ability testing and those reflecting an emphasis on the unique status of "g," fit the data well, and these factors proved especially important for predicting responses to the more controversial items. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
43.
利用双种群遗传算法进行数值试井自动拟合 总被引:7,自引:0,他引:7
遗传算法以随机化技术为指导,通过对整个解空间的高效搜索而得到全局最优解,当解空间较大时,常规遗传算法难以同时保证搜索速度和最优解的精度。针对这种缺陷提出了应用双种群遗传算法,即利用具有不同搜索策略的2个种群进行联合搜索,既保证了最优解的精度,又提高了搜索速度,将其应用于数值试井自动拟合解释,比常规遗传算法能节省50%以上的计算时间。 相似文献
44.
Power devices with high capability have been developed. 8‐kV/3.5‐kA‐class light‐triggered thyristors have the highest capability among power devices. These devices are used in the Kii Channel HVDC transmission system in Japan. In this paper, we report the extracted problems of conventional testing methods of 8‐kV/3.5‐kA‐class light‐triggered thyristors among manufacturers, and the proposed unified testing methods on the basis of element characteristics and operating conditions in the Kii Channel HVDC system. Furthermore, we propose a figure of merit for power devices for the practical use, and try to extract elements used at the Kii Channel HVDC system with small margins and low withstand capabilities. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 140(3): 61–70, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10024 相似文献
45.
小型密闭压力容器测试(MCPVT)法是安全工程领域中近几年发展起来的、评价有机过氧化物及自反应物质受热分解反应激烈程度的新方法。pmax是MCPVT方法中用来表征自反应物质受热分解反应激烈程度的物理量之一。文中通过大量实验,研究了样品容器容积V、升温速率R及样品质量M对pmax重复性误差的影响,研究了一系列典型的有机过氧化物和自反应物质在标准实验条件下pmax重复性误差。结果表明,小型密闭压力容器测试系统重复性好,测试结果可靠,从而为MCPVT法最终成为国际上评价自反应物质受热分解反应激烈程度标准方法奠定了基础。 相似文献
46.
47.
48.
When a circuit is tested using random or pseudorandom patterns, it is essential to determine the amount of time (test length) required to test it adequately. We present a methodology for predicting different statistics of random pattern test length. While earlier methods allowed estimation only of upper bounds of test length and only for exhaustive fault coverage, the technique presented here is capable of providing estimates of all statistics of interest (including expected value and variance) for all coverage specifications.Our methodology is based on sampling models developed for fault coverage estimation [1]. Test length is viewed as awaiting time on fault coverage. Based on this relation we derive the distribution of test length as a function of fault coverage. Methods of approximating expected value and variance of test length are presented. Accuracy of these approximations can be controlled by the user. A practical technique for predicting expected test length is developed. This technique is based on clustering faults into equal detectability subsets. A simple and effective algorithm for fault clustering is also presented. The sampling model is applied to each cluster independently and the results are then aggregated to yield test lengths for the whole circuit. Results of experiments with several circuits (both ISCAS '85 benchmarks and other practical circuits) are also provided.This work was done while the author was with the Department of Electrical Engineering, Southern Illinois University, Carbondale, IL 62901. 相似文献
49.
Energy minimization and design for testability 总被引:6,自引:0,他引:6
Srimat T. Chakradhar Vishwani D. Agrawal Michael L. Bushnell 《Journal of Electronic Testing》1994,5(1):57-66
The problem of fault detection in general combinational circuits is NP-complete. The only previous result on identifying easily testable circuits is due to Fujiwara who gave a polynomial time algorithm for detecting any single stuck fault inK-bounded circuits. Such circuits may only contain logic blocks with no more thanK input lines and the blocks are so connected that there is no reconvergent fanout among them. We introduce a new class of combinational circuits called the (k, K)-circuits and present a polynomial time algorithm to detect any single or multiple stuck fault in such circuits. We represent the circuit as an undirected graphG with a vertex for each gate and an edge between a pair of vertices whenever the corresponding gates have a connection. For a (k, K)-circuit,G is a subgraph of ak-tree, which, by definition, cannot have a clique of size greater thank+1. Basically, this is a restriction on gate interconnections rather than on the function of gates comprising the circuit. The (k, K)-circuits are a generalization of Fujiwara'sK-bounded circuits. Using the bidirectional neural network model of the circuit and the energy function minimization formulation of the fault detection problem, we present a test generation algorithm for single and multiple faults in (k, K)-circuits. This polynomial time aggorithm minimizes the energy function by recursively eliminating the variables. 相似文献
50.
本文介绍了弧形小方坯连铸机几种类型的引锭杆和与不同引锭杆相适应的铸坯导向及二冷装置,并讨论了有关设备的结构特性及其优缺点。 相似文献