全文获取类型
收费全文 | 27645篇 |
免费 | 3103篇 |
国内免费 | 1464篇 |
专业分类
电工技术 | 1978篇 |
技术理论 | 6篇 |
综合类 | 2469篇 |
化学工业 | 2438篇 |
金属工艺 | 1459篇 |
机械仪表 | 1470篇 |
建筑科学 | 3665篇 |
矿业工程 | 1277篇 |
能源动力 | 1357篇 |
轻工业 | 1884篇 |
水利工程 | 2157篇 |
石油天然气 | 1062篇 |
武器工业 | 843篇 |
无线电 | 1209篇 |
一般工业技术 | 3541篇 |
冶金工业 | 1783篇 |
原子能技术 | 458篇 |
自动化技术 | 3156篇 |
出版年
2024年 | 179篇 |
2023年 | 510篇 |
2022年 | 892篇 |
2021年 | 1127篇 |
2020年 | 1155篇 |
2019年 | 908篇 |
2018年 | 982篇 |
2017年 | 1045篇 |
2016年 | 1367篇 |
2015年 | 1270篇 |
2014年 | 1955篇 |
2013年 | 2310篇 |
2012年 | 2004篇 |
2011年 | 2312篇 |
2010年 | 1731篇 |
2009年 | 1581篇 |
2008年 | 1479篇 |
2007年 | 1613篇 |
2006年 | 1482篇 |
2005年 | 1166篇 |
2004年 | 914篇 |
2003年 | 747篇 |
2002年 | 634篇 |
2001年 | 533篇 |
2000年 | 415篇 |
1999年 | 339篇 |
1998年 | 287篇 |
1997年 | 202篇 |
1996年 | 207篇 |
1995年 | 154篇 |
1994年 | 160篇 |
1993年 | 95篇 |
1992年 | 65篇 |
1991年 | 58篇 |
1990年 | 64篇 |
1989年 | 43篇 |
1988年 | 44篇 |
1987年 | 27篇 |
1986年 | 21篇 |
1985年 | 16篇 |
1984年 | 19篇 |
1983年 | 14篇 |
1982年 | 12篇 |
1981年 | 6篇 |
1980年 | 12篇 |
1979年 | 6篇 |
1971年 | 3篇 |
1965年 | 14篇 |
1961年 | 3篇 |
1959年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Barry D. Solomon 《Energy Policy》1985,13(1):97-101
The prospects for rapid near-term development of a synfuel industry in the USA have decreased, due to depressed world oil prices, synfuel project cost overruns, and the lukewarm support of the Reagan administration. Nonetheless, socioeconomic and environmental impact analysis studies can provide valuable information for determining the regional welfare effects of proposed projects. The author discusses the results of a regional econometric analysis of the synfuel projects planned for Western Kentucky, which focuses on environmental impacts, and reveals the inevitable trade-offs that would accompany synfuel development. Some policy issues are briefly reviewed, especially that of efficient energy pricing. 相似文献
32.
该文研究了T300碳纤维单向增强的环氧复合材料,在应变率从10~(-3)/s到10~3/s范围内的冲击拉伸行为.通过对实验数据进行拟合,得出该范围内材料对应变率具有弱的敏感性,表现在破坏强度及破坏应变随应变率增加不显著变化,平均模量几乎不受应变率的影响.分析了试件的几何尺寸效应,讨论了应力波作用对破坏形态的影响以及实验中观察到的拔出现象.从应变率在10~2~10~3/s附近材料行为某些非确定性,指出在更宽范围内了解其性能的必要性. 相似文献
33.
34.
《Displays》2021
As the demand for high-quality stereo images has grown in recent years, stereoscopic image quality assessment (SIQA) has become an important research area in modern image processing technology.In this paper, we propose a no-reference stereoscopic image quality assessment (NR-SIQA) model using heterogeneous ensemble learning ‘quality-aware’ features from luminance image, chrominance image, disparity and cyclopean images via quaternion wavelet transform (QWT). Firstly, luminance image and chrominance image are generated by CIELAB color space as monocular perception, and the novel disparity and cyclopean images are utilized to complement with monocular information. Then, a number of ‘quality-aware’ features in the quaternion wavelet domain are discovered, including entropy, texture features, energy features, energy differences features and MSCN coefficients of high frequency sub-band. Finally, a heterogeneous ensemble model via support vector regression (SVR) & extreme learning machine (ELM) & random forest (RF) is proposed to predict quality score, and bootstrap sampling and rotated feature space are used to increase the diversity of data distribution. Comparing with the state-of-the-art NR-SIQA models, experimental results on four public databases prove the accuracy and robustness of the proposed model. 相似文献
35.
Valerie Shute Seyedahmad Rahimi Ginny Smith Fengfeng Ke Russell Almond Chih-Pu Dai Renata Kuba Zhichun Liu Xiaotong Yang Chen Sun 《Journal of Computer Assisted Learning》2021,37(1):127-141
In this study, we investigated the validity of a stealth assessment of physics understanding in an educational game, as well as the effectiveness of different game-level delivery methods and various in-game supports on learning. Using a game called Physics Playground, we randomly assigned 263 ninth- to eleventh-grade students into four groups: adaptive, linear, free choice and no-treatment control. Each condition had access to the same in-game learning supports during gameplay. Results showed that: (a) the stealth assessment estimates of physics understanding were valid—significantly correlating with the external physics test scores; (b) there was no significant effect of game-level delivery method on students' learning; and (c) physics animations were the most effective (among eight supports tested) in predicting both learning outcome and in-game performance (e.g. number of game levels solved). We included student enjoyment, gender and ethnicity in our analyses as moderators to further investigate the research questions. 相似文献
36.
37.
38.
39.
Weige Lu Haisong Xu M. Ronnier Luo 《Journal of the Society for Information Display》2012,20(5):259-265
Abstract— A psychophysical experiment was carried out to assess the perceptual contrast on a large‐sized liquid‐crystal display (LCD) under nine phases of viewing conditions. Based on the results, six contrast models employing different color attributes or the index of just‐noticeable difference (JND) were developed. Their performances were also tested by the visual data of the nine phases, which indicated that the model CQ employing CIECAM02 brightness gives the best performance in predicting visual data under different viewing conditions among those models. A preprocessing step was also proposed to utilize the contrast model CQ conveniently in the practical contrast evaluation of LCDs. 相似文献
40.
Discusses retouching of the Kallikak family photographs in H. H. Goddard's (1912) study of mental retardation and heredity, with reference to analyses by R. E. Fancher (see record 1987-31600-001) and S. J. Gould (1981), and concurs with Fancher that the retouching was probably not done for deceitful purposes. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献