全文获取类型
收费全文 | 30225篇 |
免费 | 2821篇 |
国内免费 | 1626篇 |
专业分类
电工技术 | 1874篇 |
技术理论 | 2篇 |
综合类 | 2641篇 |
化学工业 | 4836篇 |
金属工艺 | 1316篇 |
机械仪表 | 1705篇 |
建筑科学 | 2261篇 |
矿业工程 | 672篇 |
能源动力 | 699篇 |
轻工业 | 3496篇 |
水利工程 | 677篇 |
石油天然气 | 1277篇 |
武器工业 | 250篇 |
无线电 | 3291篇 |
一般工业技术 | 3089篇 |
冶金工业 | 1222篇 |
原子能技术 | 357篇 |
自动化技术 | 5007篇 |
出版年
2024年 | 114篇 |
2023年 | 409篇 |
2022年 | 818篇 |
2021年 | 1109篇 |
2020年 | 868篇 |
2019年 | 667篇 |
2018年 | 807篇 |
2017年 | 874篇 |
2016年 | 791篇 |
2015年 | 1145篇 |
2014年 | 1585篇 |
2013年 | 1886篇 |
2012年 | 2195篇 |
2011年 | 2324篇 |
2010年 | 2256篇 |
2009年 | 2117篇 |
2008年 | 2168篇 |
2007年 | 2112篇 |
2006年 | 1809篇 |
2005年 | 1575篇 |
2004年 | 1180篇 |
2003年 | 925篇 |
2002年 | 947篇 |
2001年 | 763篇 |
2000年 | 649篇 |
1999年 | 495篇 |
1998年 | 420篇 |
1997年 | 312篇 |
1996年 | 253篇 |
1995年 | 220篇 |
1994年 | 170篇 |
1993年 | 146篇 |
1992年 | 102篇 |
1991年 | 91篇 |
1990年 | 71篇 |
1989年 | 61篇 |
1988年 | 32篇 |
1987年 | 24篇 |
1986年 | 16篇 |
1985年 | 12篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1980年 | 10篇 |
1978年 | 7篇 |
1977年 | 8篇 |
1976年 | 11篇 |
1974年 | 6篇 |
1973年 | 6篇 |
1931年 | 6篇 |
1908年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 593 毫秒
81.
82.
H Tatar S Ci?ek U Demirkili? E Ozal H Süer O Oztürk H I?iklar 《Canadian Metallurgical Quarterly》1993,55(3):659-661
Among various pharmacological agents used to reduce bleeding after open-heart operations, high-dose aprotinin therapy seems most promising. However, its long-term effects are still obscure; there is almost always possibility of bypass graft occlusions produced by the hypercoagulable state induced by aprotinin in coronary bypass operations. Topical application of aprotinin into the pericardial cavity could prevent the adverse effects. Fifty patients were prospectively studied to evaluate the effects of topical aprotinin. One million KIU of aprotinin was poured into the pericardial cavity before closure of the sternotomy in group 1 (n = 25). Patients in group 2 (n = 25) served as controls. Total postoperative bleeding was significantly reduced in group 1 when compared with that of group 2 (722.7 +/- 230.8 versus 1,282.6 +/- 225.7 mL; p < 0.01). The use of banked donor blood products was significantly less in group 1 than in group 2 (0.33 +/- 0.67 versus 1.36 +/- 0.86 units; p < 0.01). These results show that topical use of aprotinin reduces post-operative blood loss and need for transfusion. It seems promising and warrants further studies to be done. 相似文献
83.
84.
85.
Urban radiowave propagation: a 3-D path-integral wave analysis 总被引:1,自引:0,他引:1
A discussion concerning the need for three-dimensional (3-D) urban radiowave propagation models is presented and followed by a review of previously published work on this topic using the asymptotic path-integral technique. The limitations and advantages of this technique are explained and it is applied to study diffraction by a small number of canonical geometries. The validity of this technique is verified by comparison with controlled laboratory measurements taken at millimetric wave frequencies. Finally, its ability to classify field components according to their distribution in space is employed in order to analyze the observed field strength distributions in the model environments 相似文献
86.
We have examined the applicability of this simple and effective test to polymer systems widely used in the medical industry. First, it was found that not every polymer examined exhibited a distinct onset of autocatalytic oxidation detectable by DSC. However, for cases where distinct onsets are found, powerful insights can be obtained. These included activation energy of the degradation, thermal oxidative shelf life prediction, and correlation, with product performances. Actual examples are presented to illustrate the utility of the test. 相似文献
87.
88.
黄坛口水电站溢洪道弧形闸门的安全检测与更新改造设计 总被引:4,自引:1,他引:3
黄坛口水电站建于50年代,设计和施工时在总体布置上没有考虑弧形闸门的检修条件,使闸门一直处于挡水状态,存在相当多的隐患。通过对弧形闸门和启闭机的安全检测,分析了弧形闸门和启闭机存在的缺陷,提出了更新改造设计方案。 相似文献
89.
EFFECTS OF COLD EXPANSION OF A HOLE ON FATIGUE CRACK INITIATION LOCATION AND LIFE OF AN LY12CZ ALLOY
Ling Chao Zheng Xiulin† 《Fatigue & Fracture of Engineering Materials & Structures》1992,15(3):241-247
Abstract— In the present study the effects of cold expansion of a hole on the location of fatigue crack initiation and life of LY12CZ alloy sheets are experimentally investigated and a quantitative expression of fatigue crack initiation life presented. Test results and analysis show that there may exist an optimum amount of cold expansion, for which both the coefficient of the resistance to fatigue crack initiation and the threshold are increased, and that the direction of cold expansion has no appreciable effect on fatigue crack initiation life. Observations show that, after cold expansion the fatigue crack nearly always initiates on the final entry face from which the mandrel is introduced into the hole during the final cold expansion process. Therefore it may be thought that the entry face is less resistant to fatigue crack initiation. In addition, the assumption of equivalence of residual stresses and also the strain hardening conditions on both the entry and exit faces may be questionable. 相似文献
90.
Ling Tong 《Journal of Infrared, Millimeter and Terahertz Waves》1997,18(2):431-436
This paper introduce the experiment about a new type of quasi-optic cavity Making a experimental model, measuring all parameters of the cavity, giving experiment results. It shows that theoritical research in reference[1] is correct Its results coincide with theory. At same time, it also indicates the cavity is hopeful device in MMW. 相似文献