全文获取类型
收费全文 | 36784篇 |
免费 | 2437篇 |
国内免费 | 970篇 |
专业分类
电工技术 | 1479篇 |
技术理论 | 4篇 |
综合类 | 1550篇 |
化学工业 | 5974篇 |
金属工艺 | 1528篇 |
机械仪表 | 1673篇 |
建筑科学 | 1680篇 |
矿业工程 | 749篇 |
能源动力 | 1190篇 |
轻工业 | 2206篇 |
水利工程 | 446篇 |
石油天然气 | 999篇 |
武器工业 | 146篇 |
无线电 | 5378篇 |
一般工业技术 | 5052篇 |
冶金工业 | 4784篇 |
原子能技术 | 388篇 |
自动化技术 | 4965篇 |
出版年
2024年 | 78篇 |
2023年 | 420篇 |
2022年 | 770篇 |
2021年 | 1183篇 |
2020年 | 906篇 |
2019年 | 782篇 |
2018年 | 883篇 |
2017年 | 923篇 |
2016年 | 852篇 |
2015年 | 1061篇 |
2014年 | 1407篇 |
2013年 | 2116篇 |
2012年 | 1989篇 |
2011年 | 2308篇 |
2010年 | 1831篇 |
2009年 | 1876篇 |
2008年 | 1929篇 |
2007年 | 1738篇 |
2006年 | 1566篇 |
2005年 | 1255篇 |
2004年 | 1107篇 |
2003年 | 1194篇 |
2002年 | 1397篇 |
2001年 | 1178篇 |
2000年 | 816篇 |
1999年 | 793篇 |
1998年 | 1643篇 |
1997年 | 1040篇 |
1996年 | 822篇 |
1995年 | 603篇 |
1994年 | 504篇 |
1993年 | 471篇 |
1992年 | 259篇 |
1991年 | 242篇 |
1990年 | 251篇 |
1989年 | 219篇 |
1988年 | 194篇 |
1987年 | 161篇 |
1986年 | 141篇 |
1985年 | 140篇 |
1984年 | 109篇 |
1983年 | 80篇 |
1982年 | 78篇 |
1981年 | 66篇 |
1980年 | 97篇 |
1979年 | 50篇 |
1978年 | 66篇 |
1977年 | 101篇 |
1976年 | 185篇 |
1975年 | 44篇 |
排序方式: 共有10000条查询结果,搜索用时 484 毫秒
231.
KI el-Noueam V Giuliano ME Schweitzer BJ O''Hara 《Canadian Metallurgical Quarterly》1997,21(5):796-799
A 62-year-old female who had a complaint of palpitation was diagnosed as bicuspid aortic stenosis and left single coronary artery by the echocardiographic examination, cardiac catheterization study and coronary artery angiography. Aortic valve replacement was performed and the patient was discharged 22 days after surgery with good post-operative course. Preoperative coronary artery angiography was important in the case of aortic valvular disease. 相似文献
232.
233.
Te-Yu Wei Shih-Yuan Lu Yu-Cheng Chang 《Journal of the Chinese Institute of Chemical Engineers》2007,38(5-6):477-481
Tin oxide–silica composite aerogels were successfully prepared with a co-fed precursor sol–gel process. The crystallinity of the tin oxide nanoparticles, embedded in the mesoporous SiO2 network, was improved with increasing the post-reaction thermal treatment temperature. The composite aerogels exhibited a rich photoluminescence (PL) emission contributed by both SnO2 and SiO2. The PL peak of 346 nm was from the near band edge emission of the tin oxide nanoparticles, and the ones located at 310 and 476 nm were attributable to the oxygen deficiencies of the silica network. Three more emission peaks, 387, 432, and 522 nm, were observed, with the 387 nm peak contributed by the oxygen vacancies VO++, the 432 nm peak by the Sn interstitials, and the 522 nm peak by the oxygen vacancies VO+, respectively, of the tin oxide nanoparticles. The intensities of these three defect level emissions were found decreased, as compared to that of the near band edge emission, with increasing the post-reaction thermal treatment temperature as the tin oxide crystallinity improved. 相似文献
234.
235.
Kyu-Hyun Han Kyong-Won Seo Dae-Hyun Hwang Soon Heung Chang 《Nuclear Engineering and Design》2006,236(2):164-178
Gas-cooled reactors have been highlighted as a promising option for next generation reactor technology. A thermal hydraulic analysis code for gas-cooled reactors has been developed with a heat transfer model of a block element, which is solved implicitly with the helium energy equation. Validation was carried out through comparison with both experimental and analytical results. A computation module for annular fuel rods has been coupled to the code for comparative analyses of an annular fuel-based block element. At normal operation, the annular fuel shows 80 °C lower peak temperature than the solid fuel for the same power in Japan's high temperature engineering test reactor (HTTR), even though the pressure drop is higher in the annular fuel. 相似文献
236.
本文讨论了M序列的自相关性,并证明了:当0<|t-2^n-1|≤[n-1/2]时,|CM(t)|≤2^n-1。 相似文献
237.
D. Li A. F. Yee I. -W. Chen S. -C. Chang K. Takahashi 《Journal of Materials Science》1994,29(8):2205-2215
The fracture toughness and uniaxial tensile yield strengths of unmodified and CTBN-rubber-modified epoxies were measured under hydrostatic pressure. The purpose of these experiments was to learn how suppressing cavitation in rubber particles affects the deformation mechanisms and the fracture toughness of rubber-modified epoxy. It was found that the cavitation of CTBN-rubber could be suppressed at a relatively low pressure (between 30 and 38 M Pa). With cavitation suppressed, the rubber particles are unable to induce massive shearyielding in the epoxy matrix, and the fracture toughness of the rubber-modified epoxy is no higher than that of the unmodified epoxy in the pressure range studied. Unmodified epoxy shows a brittle-to-ductile transition in fracture toughness test. The reason for this transition is the postponement of the cracking process by applied pressure.Work performed while on a sabbatical leave at the University of Michigan. 相似文献
238.
A new method to predict the critical heat flux (CHF) is proposed, based on the fuzzy clustering and artificial neural network. The fuzzy clustering classifies the experimental CHF data into a few data clusters (data groups) according to the data characteristics. After classification of the experimental data, the characteristics of the resulting clusters are discussed with emphasis on the distribution of the experimental conditions and physical mechanism. The CHF data in each group are trained in an artificial neural network to predict the CHF. The artificial neural network adjusts the weight so as to minimize the prediction error within the corresponding cluster. Application of the proposed method to the KAIST CHF data bank shows good prediction capability of the CHF, better than other existing methods. 相似文献
239.
Minor Thomas R.; Dess Nancy K.; Ben-David Eli; Chang Wei-Chao 《Canadian Metallurgical Quarterly》1994,20(4):402
The present study determined whether individual differences in neophobia during an open-field pretest predict vulnerability to inescapable electric shock, as measured by 2 tests of learned helplessness in rats. Shuttle-escape latencies and saccharin finickiness increased across groups that had received increasing numbers of inescapable shocks 24 hr earlier. Dispersion in the test measure as well as the percentage of variance explained by pretest neophobia were greater when no or few shocks were delivered in the interpolated stress phase. Pretest neophobia was positively related to stress vulnerability in both tests under these conditions. Further increments in stressor severity overwhelmed even the most stress-resistant rats, thereby decreasing dispersion in the test measure and eliminating the predictive value of pretest neophobia. This pattern of outcomes was more robust for the shuttle-escape measure of helplessness. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
240.
Long-Wen Chang Shui-kung Chuag Shang-shung Yu 《Multidimensional Systems and Signal Processing》1994,5(3):319-330
The compression of Chinese characters is very important for Chinese office automation and desktop publishing. In this paper, various methods are used to compress 13,051 Chinese characters losslessly by coding their skeleton points. The skeleton points are composed of isolated points and curves. To trace every point in a curve once and consecutively is a NP problem. Therefore, we use contour path following and revisiting algorithms to trace skeleton curves with chain codes. The remaining isolated skeleton points are encoded by an Elias code. Our coding method has a better compression rate than that of conventional skeleton coding. 相似文献