全文获取类型
收费全文 | 103848篇 |
免费 | 1363篇 |
国内免费 | 1228篇 |
专业分类
电工技术 | 2019篇 |
综合类 | 140篇 |
化学工业 | 10658篇 |
金属工艺 | 5484篇 |
机械仪表 | 3212篇 |
建筑科学 | 2053篇 |
矿业工程 | 159篇 |
能源动力 | 2986篇 |
轻工业 | 6148篇 |
水利工程 | 705篇 |
石油天然气 | 674篇 |
武器工业 | 15篇 |
无线电 | 16045篇 |
一般工业技术 | 21883篇 |
冶金工业 | 25406篇 |
原子能技术 | 1399篇 |
自动化技术 | 7453篇 |
出版年
2022年 | 459篇 |
2021年 | 714篇 |
2020年 | 527篇 |
2019年 | 683篇 |
2018年 | 1146篇 |
2017年 | 1100篇 |
2016年 | 1190篇 |
2015年 | 932篇 |
2014年 | 1511篇 |
2013年 | 4713篇 |
2012年 | 2608篇 |
2011年 | 3872篇 |
2010年 | 3139篇 |
2009年 | 3750篇 |
2008年 | 3935篇 |
2007年 | 4112篇 |
2006年 | 3721篇 |
2005年 | 3362篇 |
2004年 | 3205篇 |
2003年 | 3050篇 |
2002年 | 2686篇 |
2001年 | 2988篇 |
2000年 | 2742篇 |
1999年 | 3101篇 |
1998年 | 9506篇 |
1997年 | 6203篇 |
1996年 | 4782篇 |
1995年 | 3191篇 |
1994年 | 2807篇 |
1993年 | 2739篇 |
1992年 | 1638篇 |
1991年 | 1603篇 |
1990年 | 1525篇 |
1989年 | 1337篇 |
1988年 | 1184篇 |
1987年 | 867篇 |
1986年 | 898篇 |
1985年 | 926篇 |
1984年 | 814篇 |
1983年 | 713篇 |
1982年 | 710篇 |
1981年 | 690篇 |
1980年 | 581篇 |
1979年 | 484篇 |
1978年 | 421篇 |
1977年 | 540篇 |
1976年 | 969篇 |
1975年 | 303篇 |
1974年 | 280篇 |
1973年 | 259篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
941.
I. Lum E. Biro Y. Zhou S. Fukumoto D. R. Boomer 《Metallurgical and Materials Transactions A》2004,35(1):217-226
Electrode pitting was investigated in resistance spot welding of 1.5-mm-thick sheet aluminum alloy 5182 using a medium-frequency
direct-current welder and electrodes with a tip face curvature radius of 50 mm and tip face diameter of 10 mm. Detailed investigation
of the metallurgical interactions between the copper electrode and aluminum alloy sheet was carried out using scanning electron
microscopy/energy-dispersive X-ray spectroscopy (SEM/EDX) and X-ray diffraction (XRD). The results indicated that electrode
degradation, which eventually leads to weld failure, proceeded in four basic steps: aluminum pickup, electrode alloying with
aluminum, electrode tip face pitting, and cavitation. Since pitting and cavitation result from Al pickup and alloying, periodic
electrode cleaning could extend electrode tip life by limiting the buildup of Al on the tip face. This work is part of the
effort to improve electrode tip life in resistance spot welding of aluminum alloys for automotive applications. 相似文献
942.
M. I. El-Kawni H. Okuyucu Z. Aslanoglu Y. Akin Y. S. Hascicek 《Journal of Superconductivity and Novel Magnetism》2003,16(3):533-536
YbBa2Cu3O7?x (YbBCO) thick films were grown on buffered, cube-textured Nickel tapes by sol–gel dip-coating method. Yb-123 films were prepared using solutions of Yb, Ba, and Cu organometallic compounds. A solution-based Gd2O3 buffer layer was deposited by dip-coating process with excellent texture and uniformity. The texture development and surface morphology of the buffer-layer films were examined by X-ray diffraction, pole figures, and ESEM analysis. Microstructure and characterization of Yb-123 films were done by ESEM, EDS, and XRD analysis. T c and J c were conducted by four-wire measurement method 相似文献
943.
944.
Creep crack growth rates were measured using centrally cracked tension specimens of thin polypropylene film with different
crack lengths at various stresses and temperatures. The creep crack growth rates were correlated with the stress intensity
factor. There was the region of the minimum constant crack growth rate which occupied more than 70% of the total creep failure
life. This constant creep crack growth rate characteristics were analyzed on the basis of the stress-dependent Arrhenius type
thermally activated process. 相似文献
945.
946.
947.
Gueheneuc Y.-G. Antoniol G. 《IEEE transactions on pattern analysis and machine intelligence》2008,34(5):667-684
Design patterns are important in object-oriented programming because they offer design motifs, elegant solutions to recurrent design problems, which improve the quality of software systems. Design motifs facilitate system maintenance by helping to understand design and implementation. However, after implementation, design motifs are spread throughout the source code and are thus not directly available to maintainers. We present DeMIMA, an approach to identify semi-automatically micro-architectures that are similar to design motifs in source code and to ensure the traceability of these micro-architectures between implementation and design. DeMIMA consists of three layers: two layers to recover an abstract model of the source code, including binary class relationships, and a third layer to identify design patterns in the abstract model. We apply DeMIMA to five open-source systems and, on average, we observe 34% precision for the considered 12 design motifs. Through the use of explanation-based constraint programming, DeMIMA ensures 100% recall on the five systems. We also apply DeMIMA on 33 industrial components. 相似文献
948.
D.E. Kvasov D. Menniti A. Pinnarelli Y.D. Sergeyev N. Sorrentino 《Electric Power Systems Research》2008
In this paper, the problem of global tuning of fuzzy power-system stabilizers (FPSSs) present in a multi-machine power system in order to damp the power system oscillations is considered. In particular, it is formulated as a problem of global minimization of a multiextremal black-box function over a multidimensional hyperinterval. A global optimization technique, recently proposed, is used for solving the stated problem: the search hyperinterval is partitioned into smaller hyperintervals and the objective function is evaluated only at two vertices corresponding to the main diagonal of the generated hyperintervals, thus avoiding unnecessary ponderous simulations. Then, the performances of this technique are numerically compared with ones of a genetic algorithm (GA). 相似文献
949.
950.
Teh C. K. Hamada M. Fujita T. Hara H. Ikumi N. Oowaki Y. 《Very Large Scale Integration (VLSI) Systems, IEEE Transactions on》2006,14(12):1379-1383
This paper introduces a new family of low-power and high-performance flip-flops, namely conditional data mapping flip-flops (CDMFFs), which reduce their dynamic power by mapping their inputs to a configuration that eliminates redundant internal transitions. We present two CDMFFs, having differential and single-ended structures, respectively, and compare them to the state-of-the-art flip-flops. The results indicate that both CDMFFs have the best power-delay product in their groups, respectively. In the aspect of power dissipation, the single-ended and differential CDMFFs consume the least power at data activity less than 50%, and are 31% and 26% less power than the conditional capture flip-flops at 25% data activity, respectively. In the aspect of performance, CDMFFs achieve small data-to-output delays, comparable to those of the transmission-gate pulsed latch and the modified-sense-amplifier flip-flop. In the aspect of timing reliability, CDMFFs have the best internal race immunity among pulse-triggered flip-flops. A post-layout case study is demonstrated with comparison to a transmission-gate flip-flop. The results indicate the single-ended CDMFF has 34% less in data-to-output delay and 28% less in power at 25% data activity, in spite of the 34% increase in size 相似文献