全文获取类型
收费全文 | 357244篇 |
免费 | 5591篇 |
国内免费 | 2237篇 |
专业分类
电工技术 | 6365篇 |
技术理论 | 5篇 |
综合类 | 3460篇 |
化学工业 | 55922篇 |
金属工艺 | 15876篇 |
机械仪表 | 10981篇 |
建筑科学 | 9621篇 |
矿业工程 | 2304篇 |
能源动力 | 7139篇 |
轻工业 | 30401篇 |
水利工程 | 4243篇 |
石油天然气 | 6525篇 |
武器工业 | 244篇 |
无线电 | 37710篇 |
一般工业技术 | 67232篇 |
冶金工业 | 53299篇 |
原子能技术 | 5989篇 |
自动化技术 | 47756篇 |
出版年
2021年 | 2663篇 |
2019年 | 2326篇 |
2018年 | 17718篇 |
2017年 | 16575篇 |
2016年 | 13672篇 |
2015年 | 3595篇 |
2014年 | 5115篇 |
2013年 | 12523篇 |
2012年 | 11287篇 |
2011年 | 19970篇 |
2010年 | 16668篇 |
2009年 | 14572篇 |
2008年 | 16687篇 |
2007年 | 17761篇 |
2006年 | 9133篇 |
2005年 | 9152篇 |
2004年 | 8209篇 |
2003年 | 7804篇 |
2002年 | 7162篇 |
2001年 | 6693篇 |
2000年 | 6335篇 |
1999年 | 6191篇 |
1998年 | 13173篇 |
1997年 | 9829篇 |
1996年 | 7585篇 |
1995年 | 5815篇 |
1994年 | 5326篇 |
1993年 | 5219篇 |
1992年 | 4193篇 |
1991年 | 3920篇 |
1990年 | 4042篇 |
1989年 | 4022篇 |
1988年 | 3721篇 |
1987年 | 3215篇 |
1986年 | 3233篇 |
1985年 | 3647篇 |
1984年 | 3539篇 |
1983年 | 3273篇 |
1982年 | 2890篇 |
1981年 | 3086篇 |
1980年 | 2792篇 |
1979年 | 2992篇 |
1978年 | 2889篇 |
1977年 | 2984篇 |
1976年 | 3817篇 |
1975年 | 2608篇 |
1974年 | 2439篇 |
1973年 | 2430篇 |
1972年 | 2075篇 |
1971年 | 1835篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Accelerated reliability tests on thin oxide capacitors can be affected by series resistance effects at high stress conditions. The purpose of this work is to point out such problems both with measurements and simulations. It is shown that breakdown electric field is overestimated. Due to the resulting nonuniform stress, charge to breakdown density is underestimated if the test structure layout is not accurately designed. In any case the series resistance effects can have an undesirable impact on the reliability evaluation of thin dielectrics. 相似文献
992.
Moment-method oriented singular integral equation techniques are used for the exact analysis of parallel plate-fed slot antennas loaded by a dielectric semicylinder. Both for TM and for TE incident-mode excitations, high-order acceleration techniques are developed that help recast all matrix elements into rapidly converging series. This, in conjunction with the small matrix sizes required, enables one to obtain extremely accurate results with low computational cost 相似文献
993.
Films of electroactive polymers, such as polyaniline (PAN) in its emeraldine base form, and poly(3-alkylthiophene), poly(3-hexylthiophene) (P6TH), poly(3-octylthiophene) (P8TH), and poly(3-dodecylthiophene) (P12TH) can be readily functionalized via thermal or near ultraviolet-light-induced surface graft copolymerization with monomers of polyelectrolyte, polyampholyte and polymeric acids. The monomers used in the present work include dimethyl sulphate quaternized dimethylamino-ethylmethacrylate (DMAEM·C2H6SO4), 3-dimethyl(methacryloyloxyethyl)ammonium propane sulphonate (DMAPS), acrylic acid (AAc) and a sodium salt of styrene sulphonic acid (NaSS). The surface structures and compositions of the electroactive polymer films after functionalization via graft copolymerization were characterized by angle-resolved X-ray photoelectron spectroscopy. Graft copolymerization of poly(3-alkylthiophene) films, but not PAN films, with the hydrophilic monomers readily results in a stratified surface microstructure arising from the migration of the hydrophilic graft chains beneath a thin surface layer which is much richer in the substrate chains. On the other hand, graft copolymerization of PAN films with AAc and NaSS readily gives rise to a self-protonated (and thus conductive) surface structure. 相似文献
994.
Dispersion-strengthened Al-8.5% Fe-1.2% V-1.7% Si alloy was produced by inert gas atomization and atomized melt deposition processes. Differential scanning calorimetry was used to estimate the extent of undercooling in the alloy powders as a function of powder size and in the atomized melt-deposited alloy as a function of process parameters. The estimated undercooling was found to be a strong function of powder size and processing conditions and varied from 380–200 °C. Alloy powders of diameter greater than 180 jam did not experience any undercooling during solidification. X-ray diffraction analysis was performed to study the dependence of supersaturation of alloying elements and metastable phase formation on the extent of undercooling. When the undercooled alloy was heated to about 400 dgC, formation of Al12(Fe, V)3Si phase with b c c crystal structure from the supersaturated matrix was observed. 相似文献
995.
996.
997.
The Warehouse Scheduling Problem is a deterministic multi-item inventory problem with a restriction on warehouse floor space available. We formulate a mixed integer nonlinear programming problem for the objective of minimizing long run inventory holding and order costs per unit of time. We integrate algorithms for staggering orders, described in companion papers, with a heuristic to choose the order sequences. The result is called Sequenced Staggering. We describe a new algorithm to generate order frequencies, called the powers-of-two-factor-of-three technique, as a generalization of Roundy's roundoff technique for powers-of-two policies. We report on a computational study of four hybrid algorithms for solving the warehouse scheduling problem, including the competing algorithm of Gallego, Queyranne, and Simchi-Levi. Based on these results, we recommend the combination of powers-of-two frequencies with Sequenced Staggering. 相似文献
998.
Lourtioz J.-M. Chusseau L. Brun E. Hamaide J.-P. Lesterlin D. Leblond F. 《Electronics letters》1992,28(16):1499-1500
Fourier-transform-limited pulses ( Delta tau . Delta nu approximately=0.35) have been obtained from a microwave-modulated DBR laser at 1.56 mu m. The chirp of the gain-switched pulse is compensated for by applying a fraction of the microwave signal to the phase section, thereby creating an instantaneous frequency shift of opposite sign. The generation of short coherent pulses from such a monolithic source can be of great interest for long haul soliton transmission.<> 相似文献
999.
Memory reallocation is used to construct a run-time data structure for fast/efficient storage of information during collection and analysis. The data structure presented uses dynamic memory but does not require the use of pointers to link nodes of information together. It allows for simple and efficient access to data via array indexing rather than through the use of lists or tree structures and it provides flexibility for competing storage requirements that are determined dynamically. The data structure is developed in the C programming language and a suite of ANSI standard C subroutines that make up a run-time data structure management system is provided. 相似文献
1000.
Accurate quantitative determinations are often difficult to obtain from fluorescence analysis of complex samples due to sample matrix effects and intermolecular interactions between solutes. Organized media can be used to minimize these unwanted processes without physical separation or extraction of the analytes from the sample matrix by isolating the analyte molecules in a uniform microenvironment within the sample. The advantages of bile salt micellar media over conventional detergent micelles are demonstrated for analysis of coal liquids. The bile salt media is shown to increase the sensitivity and dynamic range of fluorescence measurements relative to simple ethanolic solutions, without promoting gound-state and excited-state interactions that occur in the detergent micellar media. 相似文献