全文获取类型
收费全文 | 184383篇 |
免费 | 3879篇 |
国内免费 | 195篇 |
专业分类
电工技术 | 3895篇 |
综合类 | 525篇 |
化学工业 | 34782篇 |
金属工艺 | 9695篇 |
机械仪表 | 6084篇 |
建筑科学 | 3639篇 |
矿业工程 | 2053篇 |
能源动力 | 2851篇 |
轻工业 | 10494篇 |
水利工程 | 2845篇 |
石油天然气 | 8749篇 |
武器工业 | 12篇 |
无线电 | 14831篇 |
一般工业技术 | 41034篇 |
冶金工业 | 27941篇 |
原子能技术 | 6956篇 |
自动化技术 | 12071篇 |
出版年
2021年 | 2191篇 |
2019年 | 2134篇 |
2018年 | 3507篇 |
2017年 | 3465篇 |
2016年 | 3938篇 |
2015年 | 2438篇 |
2014年 | 3746篇 |
2013年 | 7708篇 |
2012年 | 4850篇 |
2011年 | 5809篇 |
2010年 | 5179篇 |
2009年 | 5793篇 |
2008年 | 5353篇 |
2007年 | 5234篇 |
2006年 | 4408篇 |
2005年 | 4079篇 |
2004年 | 3847篇 |
2003年 | 3726篇 |
2002年 | 3557篇 |
2001年 | 3572篇 |
2000年 | 3422篇 |
1999年 | 3297篇 |
1998年 | 7192篇 |
1997年 | 5275篇 |
1996年 | 4011篇 |
1995年 | 3096篇 |
1994年 | 2748篇 |
1993年 | 2937篇 |
1992年 | 2403篇 |
1991年 | 2422篇 |
1990年 | 2552篇 |
1989年 | 2485篇 |
1988年 | 2450篇 |
1987年 | 2348篇 |
1986年 | 2423篇 |
1985年 | 2447篇 |
1984年 | 2370篇 |
1983年 | 2308篇 |
1982年 | 2134篇 |
1981年 | 2390篇 |
1980年 | 2217篇 |
1979年 | 2430篇 |
1978年 | 2548篇 |
1977年 | 2576篇 |
1976年 | 3243篇 |
1975年 | 2445篇 |
1974年 | 2490篇 |
1973年 | 2702篇 |
1972年 | 2363篇 |
1971年 | 2060篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Convergence of simultaneous perturbation stochastic approximation for nondifferentiable optimization 总被引:1,自引:0,他引:1
We consider simultaneous perturbation stochastic approximation for function minimization. The standard assumption for convergence is that the function be three times differentiable, although weaker assumptions have been used for special cases. However, all work that we are aware of at least requires differentiability. We relax the differentiability requirement and prove convergence using convex analysis. 相似文献
992.
Dr Kalathur ‘Sim’ Narasimhan 《Metal Powder Report》2003,58(5):12-21
The 42-volt electrical system is to be introduced in automobiles to provide the extra power needed for various electromagnetic devices. This offers an opportunity for insulated iron powder to replace lamination steel in a variety of motors. Brushless motor design can probably benefit most from insulated iron powder compacts because of the design simplicity of powder metal parts and three-dimensional flux capability that is most beneficial in rotating devices says Sim Narasimhan… 相似文献
993.
The methods of X-ray photoelectron spectroscopy and Auger spectroscopy are used to study surface films formed on zinc and zinc-plated steel in the process of holding in aqueous extracts of mixtures of phosphate and calcium-containing pigments. It is shown that protective films formed mainly of zinc and calcium phosphates of different chemical structure are deposited in inhibited solutions on specimens of pure zinc and zinc-plated steel. The protective properties of these films are much better than the protective properties of the surface layers formed on the metal in the extracts of a single phosphate (or calcium-containing) pigment. The mixture of these pigments may serve as a promising substitution of chromate inhibitors in anticorrosive organic coatings. 相似文献
994.
995.
O'Keefe M.F. Atherton J.S. Bosch W. Burgess P. Cameron N.I. Snowden C.M. 《Semiconductor Manufacturing, IEEE Transactions on》2003,16(3):376-383
The establishment of a 150-mm (6-in) gallium arsenide (GaAs) facility is described together with the development of very high yielding and cost-effective semiconductor device technologies and a manufacturing capacity of over 40000 wafers/annum. The background to the demand for very high volumes of RF products for this market is discussed, together with the prospects for future growth. The paper describes recent process development by the utilization of a data-driven yield management system to support the delivery of high-quality RF products to customers. Finally, "end of line" DC and RF testing of finished 150-mm GaAs pHEMT foundry wafers is described, enabling scalar measurements of power, noise, and intermodulation products as well as vector measurements of S-parameters and noise parameters at frequencies of up to 40 GHz. 相似文献
996.
H. Maurer O. Univ.-Prof. Dr. phil. 《e & i Elektrotechnik und Informationstechnik》2003,120(11):411-413
In this article it is argued that in ten years’ time personal computers as we know them now won’t exist anymore — all their functions will by then be integrated in mobiles which will be our steady companions. As such, mobiles will change our lives to an enormous extent. Technology as well as consequences will be discussed in this paper. 相似文献
997.
Sokolovsky V. Meerovich V. Vajda I. Beilin V. 《Applied Superconductivity, IEEE Transactions on》2004,14(3):1990-2000
Design, parameters, and application areas of a superconducting fault current limiter (FCL) are analyzed on the basis of the requirements of power systems. The comparison of resistive and inductive designs is carried out. An example of the effective application of FCLs in distribution substations is considered and the gain from the FCL installation is discussed. It is shown that an FCL not only limits a fault current but also increases the dynamic stability of the synchronous operation of electric machines. The calculation procedure of the parameters of an inductive FCL for a specific application case is described. 相似文献
998.
Video shot detection and condensed representation. a review 总被引:4,自引:0,他引:4
There is an urgent need to develop techniques that organize video data into more compact forms or extract semantically meaningful information. Such operations can serve as a first step for a number of different data access tasks such as browsing, retrieval, genre classification, and event detection. In this paper, we focus not on the high-level video analysis task themselves but on the common basic techniques that have been developed to facilitate them. These basic tasks are shot boundary detection and condensed video representation 相似文献
999.
This paper presents a robustness analysis of the optimal solution of the step tracking problem in a one-degree of freedom control architecture, for the discrete-time multivariable (MIMO) case. It is shown that the resulting closed loop becomes arbitrarily fragile, i.e. the sensitivity peak becomes arbitrarily large, for certain reference directions. The cause of this problem is that the optimal controller depends on the reference direction. The paper shows that this dependence can be eliminated with an alternative formulation of the optimal problem where the cost is averaged over all reference directions. 相似文献
1000.
Ideally selective diisocyanate building blocks: New perspectives for dendrimers and coating binders 总被引:3,自引:0,他引:3
R. A. T. M. van Benthem A. Hofland H. W. I. Peerlings E. W. Meijer 《Progress in Organic Coatings》2003,48(2-4):164-176
Using zirconium (IV) salts as catalyst, the reaction of a diisocyanate carrying one tertiary and one primary isocyanate group (IMCI, DIMP) with alcohols can be conducted with complete regioselectivity. This unique selectivity enables the use of a diisocyanate building block in unprecedented ways. Incomplete regioselectivity of diisocyanates, as commonly encountered in currently commercial ones like IPDI and TDI, inevitably leads to polydisperse products in reaction with polyols. The ultimate monodisperse polymer architecture, dendrimers, can now be made in a facile, straightforward manner using IMCI as the ideal diisocyanate building block. Coating applications of this unique building block are not restricted to these perfect branching polymers, but also include isocyanate-functional coating resins. Without any increase in polydispersity, a hydroxyl-functional polyester can be end-capped with the IMCI diisocyanate and subsequently serve as a crosslinker in powder coatings. 相似文献