全文获取类型
收费全文 | 706818篇 |
免费 | 11417篇 |
国内免费 | 1805篇 |
专业分类
电工技术 | 12627篇 |
综合类 | 760篇 |
化学工业 | 109308篇 |
金属工艺 | 26459篇 |
机械仪表 | 20641篇 |
建筑科学 | 17198篇 |
矿业工程 | 3404篇 |
能源动力 | 18354篇 |
轻工业 | 66827篇 |
水利工程 | 7153篇 |
石油天然气 | 12703篇 |
武器工业 | 69篇 |
无线电 | 76986篇 |
一般工业技术 | 134047篇 |
冶金工业 | 139302篇 |
原子能技术 | 14392篇 |
自动化技术 | 59810篇 |
出版年
2021年 | 6793篇 |
2020年 | 4984篇 |
2019年 | 6347篇 |
2018年 | 10761篇 |
2017年 | 10539篇 |
2016年 | 11163篇 |
2015年 | 7663篇 |
2014年 | 12430篇 |
2013年 | 32760篇 |
2012年 | 19624篇 |
2011年 | 26414篇 |
2010年 | 20870篇 |
2009年 | 23138篇 |
2008年 | 23711篇 |
2007年 | 23478篇 |
2006年 | 20461篇 |
2005年 | 18569篇 |
2004年 | 17820篇 |
2003年 | 17473篇 |
2002年 | 16711篇 |
2001年 | 16575篇 |
2000年 | 15535篇 |
1999年 | 16265篇 |
1998年 | 42247篇 |
1997年 | 29531篇 |
1996年 | 22543篇 |
1995年 | 16957篇 |
1994年 | 14792篇 |
1993年 | 14459篇 |
1992年 | 10496篇 |
1991年 | 9764篇 |
1990年 | 9851篇 |
1989年 | 9518篇 |
1988年 | 8937篇 |
1987年 | 7945篇 |
1986年 | 7859篇 |
1985年 | 8846篇 |
1984年 | 8307篇 |
1983年 | 7385篇 |
1982年 | 6983篇 |
1981年 | 7112篇 |
1980年 | 6800篇 |
1979年 | 6575篇 |
1978年 | 6448篇 |
1977年 | 7638篇 |
1976年 | 10053篇 |
1975年 | 5632篇 |
1974年 | 5286篇 |
1973年 | 5469篇 |
1972年 | 4493篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The capacitive idling converters derived from the Cuk, SEPIC, Zeta, and flyback topologies allow soft commutation of power switches without the need for additional circuitry, making it possible to increase the switching frequency while maintaining high efficiency 相似文献
992.
993.
The robust Schur stability of a polynomial with uncertain coefficients will be investigated. A formula for the stability radius of a Schur polynomial is established. The result is the counterpart of [1] for linear discrete-time systems 相似文献
994.
995.
George V. Eleftheriades Gabriel M. Rebeiz 《Journal of Infrared, Millimeter and Terahertz Waves》1993,14(10):1925-1946
In this paper, an efficient implementation of the spectral domain moment technique is presented for computing the self and mutual coupling between slot antennas on a dielectric half-space. It is demonstrated that by the proper selection of the weighting functions in the method of moments, the analytic evaluation or simplification of the transverse moment integrals is enabled. This results into a significant reduction of the required computational labor. The method is then utilized in order to provide design data for the self and mutual admittances between two slot antennas on a dielectric substrate lens in the case of fused quartz (∈ r =3.80), crystal quartz (∈ r =4.53), silicon (∈ r =11.9) and GaAs (∈ r =12.8). The presented technique and associated results are useful when designing twin slot quasi-optical receivers, imaging arrays, phased arrays or power-combining arrays of slot elements at millimeter-wave frequencies. 相似文献
996.
Cured samples of a nitrogen-containing acetylene-terminated resin, N,N′-(1,3-phenylene-dimethylidene)bis(3-ethynylaniline), have been heated at 10°C/min up to 900°C in a pyroprobe attached to a gas chromatograph/mass spectrometer (GC/MS). Analysis of the volatiles evolved during heating identified both gases and higher boiling compounds. The major higher boiling compounds are benzene, toluene, xylene, aniline, benzonitrile, m-methylaniline, and m-methylbenzonitrile; the gases include ammonia, methane, and traces of carbon dioxide. Correlations between sample temperature and the evolution of each of these compounds have been made. The onset of all volatile formation occurs between 450 and 500°C. The higher boiling volatiles peak, then end by approximately 700°C, while the gases peak then fall off but are still being evolved at 900°C. Average weight loss measurements of 13.6% at 700°C and 15.7% at 900°C agree with previously published thermogravimetric analysis (TGA) data. © 1993 John Wiley & Sons, Inc. 相似文献
997.
998.
Prolog/Rex represents a powerful amalgamation of the latest techniques for knowledge representation and processing, rich in semantic features that ease the difficult task of encoding heterogeneous knowledge of real-world applications. The Prolog/Rex concept mechanism lets a user represent domain entities in terms of their structural and behavioral properties, including multiple inheritance, arbitrary user-defined relations among entities, annotated values (demons), incomplete knowledge, etc. A flexible rule language helps the knowledge engineer capture human expertise and provide flexible control of the reasoning process. Additional Prolog/Rex strength that cannot be found in any other hybrid language made on top of Prolog is language level support for keeping many potentially contradictory solutions to a problem, allowing possible solutions and their implications to be automatically generated and completely explored before they are committed. The same mechanism is used to model time-states, which are useful in planning and scheduling applications of Prolog/Rex 相似文献
999.
Solotorevsky G. Gudes E. Meisels A. 《Knowledge and Data Engineering, IEEE Transactions on》1994,6(5):681-697
A general language for specifying resource allocation and time-tabling problems is presented. The language is based on an expert system paradigm that was developed previously by the authors and that enables the solution of resource allocation problems by using experts' knowledge and heuristics. The language enables the specification of a problem in terms of resources, activities, allocation rules, and constraints, and thus provides a convenient knowledge acquisition tool. The language syntax is powerful and allows the specification of rules and constraints that are very difficult to formulate with traditional approaches, and it also supports the specification of various control and backtracking strategies. We constructed a generalized inference engine that runs compiled resource allocation problem specification language (RAPS) programs and provides all necessary control structures. This engine acts as an expert system shell and is called expert system for resource allocation (ESRA). The performance of RAPS combined with ESRA is demonstrated by analyzing its solution of a typical resource allocation problem 相似文献
1000.
It is well known that the effectiveness of relational database systems is greatly dependent on the efficiency of the data access strategies. For this reason, much work has been devoted to the development of new access techniques, supported by adequate access structures such as the B+trees. The effectiveness of the B +tree also depends on the data distribution characteristics; in particular, poor performance results when the data show strong key value distribution unbalancing. The aim of this paper is to present the partial index: a new access structure that is useful in such cases of unbalancing, as an alternative to the B+tree unclustered indexes. The access structures are built in the physical design phase, and at execution (or compilation) time, the optimizer chooses the most efficient access path. Thus, integration of the partial indexing technique in the design and in the optimization process are also described 相似文献