全文获取类型
收费全文 | 13104篇 |
免费 | 1851篇 |
国内免费 | 1271篇 |
专业分类
电工技术 | 572篇 |
技术理论 | 1篇 |
综合类 | 1838篇 |
化学工业 | 1376篇 |
金属工艺 | 215篇 |
机械仪表 | 496篇 |
建筑科学 | 928篇 |
矿业工程 | 474篇 |
能源动力 | 195篇 |
轻工业 | 428篇 |
水利工程 | 335篇 |
石油天然气 | 506篇 |
武器工业 | 109篇 |
无线电 | 1713篇 |
一般工业技术 | 768篇 |
冶金工业 | 993篇 |
原子能技术 | 112篇 |
自动化技术 | 5167篇 |
出版年
2024年 | 35篇 |
2023年 | 126篇 |
2022年 | 301篇 |
2021年 | 336篇 |
2020年 | 357篇 |
2019年 | 324篇 |
2018年 | 303篇 |
2017年 | 307篇 |
2016年 | 413篇 |
2015年 | 468篇 |
2014年 | 768篇 |
2013年 | 790篇 |
2012年 | 992篇 |
2011年 | 1069篇 |
2010年 | 878篇 |
2009年 | 970篇 |
2008年 | 960篇 |
2007年 | 1095篇 |
2006年 | 975篇 |
2005年 | 833篇 |
2004年 | 705篇 |
2003年 | 567篇 |
2002年 | 493篇 |
2001年 | 419篇 |
2000年 | 306篇 |
1999年 | 223篇 |
1998年 | 171篇 |
1997年 | 136篇 |
1996年 | 127篇 |
1995年 | 113篇 |
1994年 | 90篇 |
1993年 | 79篇 |
1992年 | 68篇 |
1991年 | 46篇 |
1990年 | 27篇 |
1989年 | 27篇 |
1988年 | 26篇 |
1987年 | 13篇 |
1986年 | 11篇 |
1965年 | 14篇 |
1964年 | 16篇 |
1963年 | 18篇 |
1961年 | 17篇 |
1960年 | 19篇 |
1959年 | 23篇 |
1958年 | 16篇 |
1957年 | 19篇 |
1956年 | 21篇 |
1955年 | 27篇 |
1954年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
数字签名通常作为不可反驳的密码学证据用于解决电子交易中的纷争,但是其可信的时间戳和证书撤销服务在实际使用中代价很高。免撤销公钥框架作为一种新的PKI使得终端用户可以控制他自己的公钥证书的有效性,使验证证书不需要折回到CA去获取证书撤销信息.从而降低其使用代价。 相似文献
43.
New mesogenic homologous series having an azo central linkage was synthesized by fixing a rigid 4-methyl phenyl azo group
to resorcinol moiety. The terminal and lateral phenolic -OH groups were esterified, one by one, with 4-n-alkoxybenzoyl and acetyl group, respectively. All the twelve homologues synthesized exhibit mesomorphism. The methoxy ton-decyloxy andn-hexadecyloxy derivatives exhibit monotropic nematic mesophase whereas,n-dodecyloxy andn-tetradecyloxy derivatives exhibit enantiotropic nematic mesophase. The mesogenic properties of the present series was compared
with those of other structurally related mesogenic series.
Paper presented at the 5th National Seminar on Liquid Crystals, University of Jammu, Jammu, December 1997. 相似文献
44.
Gregory S. Ho Chen Huang Emily A. Carter 《Current Opinion in Solid State & Materials Science》2007,11(5-6):57-61
Orbital-free density functional theory (OF-DFT) can be made to scale linearly with sample size, allowing thousands of atoms to be treated explicitly with quantum mechanics. State-of-the-art kinetic energy density functionals and ion–electron pseudopotentials are used to obtain accurate structural property predictions for nanoparticles, nanowires, extended surfaces, and nanoindentation of simple metals. 相似文献
45.
Interventions for a variety of emotional and behavioral problems are commonly delivered in the context of treatment groups, with many using rolling admission to sustain membership (i.e., admission, dropout, and discharge from group are perpetual and ongoing). The authors present an overview of the analytic challenges inherent in rolling group data and outline commonly used (but flawed) analytic and design approaches to addressing (or sidestepping) these issues. Moreover, the authors propose use of latent class pattern mixture models (LCPMMs) as a statistically and conceptually defensible approach for modeling treatment data from rolling groups. The LCPMM approach is illustrated with rolling group data from a group-based alcoholism pilot treatment trial (N = 128). Different inferences were made with regard to treatment efficacy under LCPMM vs. the commonly used standard group-clustered latent growth model (LGM); coupled with other preliminary findings in this area, inferences from LGMs may be overly liberal when applied to data from rolling groups. Continued work on data analytic difficulties in groups with membership turnover is critical for furthering the ecological validity of research on behavioral treatments. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
46.
Hua-Chieh Li 《Applicable Algebra in Engineering, Communication and Computing》2007,18(4):313-348
In this paper, we give a general criterion to determine when a complex space-time block code has a ring structure and then
we provide a complete list of complex space-time block codes which have ring structures up to size 4. 相似文献
47.
The authors investigated the relationship between transformational leadership behavior and group performance in 218 financial services teams that were branches of a bank in Hong Kong and the United States. Transformational leadership influenced team performance through the mediating effect of team potency. The effect of transformational leadership on team potency was moderated by team power distance and team collectivism, such that higher power distance teams and more collectivistic teams exhibited stronger positive effects of transformational leadership on team potency. The model was supported by data in both Hong Kong and the United States, which suggests a convergence in how teams function in the East and West and highlights the importance of team values. (PsycINFO Database Record (c) 2011 APA, all rights reserved) 相似文献
48.
Yoon Carolyn; Feinberg Fred; Hu Ping; Gutchess Angela Hall; Hedden Trey; Chen Hiu-Ying Mary; Jing Qicheng; Cui Yao; Park Denise C. 《Canadian Metallurgical Quarterly》2004,19(3):379
Understanding how aging influences cognition across different cultures has been hindered by a lack of standardized, cross-referenced verbal stimuli. This study introduces a database of such item-level stimuli for both younger and older adults, in China and the United States, and makes 3 distinct contributions. First, the authors specify which item categories generalize across age and/or cultural groups, rigorously quantifying differences among them. Second, they introduce novel, powerful methods to measure between-group differences in freely generated ranked data, the rank-ordered logit model and Hellinger Affinity. Finally, a broad archive of tested, cross-linguistic stimuli is now freely available to researchers: data, similarity measures, and all stimulus materials for 105 categories and 4 culture-by-age groups, comprising over 10,000 fully translated unique item responses. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
49.
50.
Ricardo Garcia-Padron Dan Loyd Stefan Sjökvist 《Subsurface Sensing Technologies and Applications》2002,3(2):125-150
One promising method of locating buried objects, such as land mines, is to use optical systems for detecting contrasts in surface temperature. With enhanced knowledge about the interacting physical processes behind these temperature contrasts, it is possible to improve detection precision. In such a context, moisture movement in the soil and moisture evaporation from the surface have been found to be of particular interest. This study was based on indoor experiments on wet and dry sand exposed to radiation from a solar panel. Simulations of heat and moisture transfer conducted with a one-dimensional model are also presented for the experiments. The calculations were successful in accurately predicting surface temperatures for both wet and dry sand, making it possible to predict surface temperatures under different conditions. These findings will contribute to increasing the probability of successful detection of buried objects under real conditions using optical methods. 相似文献