全文获取类型
收费全文 | 613071篇 |
免费 | 8642篇 |
国内免费 | 2982篇 |
专业分类
电工技术 | 12101篇 |
技术理论 | 5篇 |
综合类 | 1544篇 |
化学工业 | 94079篇 |
金属工艺 | 24772篇 |
机械仪表 | 19433篇 |
建筑科学 | 14087篇 |
矿业工程 | 3551篇 |
能源动力 | 16085篇 |
轻工业 | 49072篇 |
水利工程 | 6549篇 |
石油天然气 | 12326篇 |
武器工业 | 261篇 |
无线电 | 71368篇 |
一般工业技术 | 120838篇 |
冶金工业 | 114279篇 |
原子能技术 | 13106篇 |
自动化技术 | 51239篇 |
出版年
2022年 | 3870篇 |
2021年 | 5978篇 |
2020年 | 4374篇 |
2019年 | 5482篇 |
2018年 | 9076篇 |
2017年 | 9037篇 |
2016年 | 9733篇 |
2015年 | 6688篇 |
2014年 | 10843篇 |
2013年 | 29295篇 |
2012年 | 17624篇 |
2011年 | 23414篇 |
2010年 | 18806篇 |
2009年 | 20762篇 |
2008年 | 21627篇 |
2007年 | 21537篇 |
2006年 | 19196篇 |
2005年 | 16950篇 |
2004年 | 15705篇 |
2003年 | 15239篇 |
2002年 | 14699篇 |
2001年 | 14634篇 |
2000年 | 13768篇 |
1999年 | 14180篇 |
1998年 | 34719篇 |
1997年 | 24411篇 |
1996年 | 18736篇 |
1995年 | 13971篇 |
1994年 | 12458篇 |
1993年 | 12420篇 |
1992年 | 9154篇 |
1991年 | 8612篇 |
1990年 | 8667篇 |
1989年 | 8368篇 |
1988年 | 7860篇 |
1987年 | 6875篇 |
1986年 | 6819篇 |
1985年 | 7580篇 |
1984年 | 7087篇 |
1983年 | 6467篇 |
1982年 | 5840篇 |
1981年 | 6116篇 |
1980年 | 5604篇 |
1979年 | 5679篇 |
1978年 | 5535篇 |
1977年 | 6103篇 |
1976年 | 7950篇 |
1975年 | 4834篇 |
1974年 | 4518篇 |
1973年 | 4596篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
This study tested a partial version of R. W. Lent, S. D. Brown, and G. Hackett's (1994) social-cognitive career theory model. Among 204 high school girls who attended science, math, and engineering (SME) career conferences, the authors used a 4-year longitudinal design to predict the choice of an SME college major and SME self-efficacy and outcome expectations in college. In addition, among students who had declared SME majors, variables assessed in high school and college were used to predict aspirations to become leaders in SME fields. The results generally provided empirical validation of the model. Regression analyses revealed that college SME outcome expectations were associated with plans to become a leader in an SME field. Implications for research and interventions are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
952.
953.
The results of a comparative numerical investigation of three types of resonator systems of a cyclotron for acceleration of negative hydrogen and deuterium ions up to maximum energy 30 and 15 MeV, respectively, are presented. It is shown that a vertical system with two half-wave resonators excited in-phase has the smallest active losses and the smallest differential of the amplitude of the accelerating voltage along the edge of the dees and is effective for accelerating particles at dual working frequencies. 相似文献
954.
M.Y. Shen Z.B. ZhangX.L. Niu 《Computer Methods in Applied Mechanics and Engineering》2003,192(25):2703-2725
The generalized compact (GC) schemes and some of their important properties are presented. And a new way for constructing high order accuracy and high-resolution GC schemes is presented. The schemes constructed by using this way could satisfy some principles and demands prescribed in advance to ensure some desired properties to the schemes, such as the principle about suppression of the oscillations, the principle of stability, the order of accuracy and number of scheme points, etc. As two examples, a three-point third-order compact scheme and a three-point fifth-order GC scheme satisfying the principle about suppression of the oscillations and the principle of stability are described in this paper. Numerical results show that these schemes are shock-capturing. The time-dependent boundary conditions proposed by Thompson are well employed when the algorithm is applied to the Euler equations of gas dynamics. Fourier analysis shows that the resolution characteristics are spectral-like. 相似文献
955.
956.
An increasing number of connectionist models have been proposed to explain behavioral deficits in developmental disorders. These simulations motivate serious consideration of the theoretical implications of the claim that a developmental disorder fits within the parameter space of a particular computational model of normal development. The authors examine these issues in depth with respect to a series of new simulations investigating past-tense formation in Williams syndrome. This syndrome and the past-tense domain are highly relevant because both have been used to make strong theoretical claims about the processes underlying normal language acquisition. The authors conclude that computational models have great potential to advance psychologists' understanding of developmental deficits because they focus on the developmental process itself as a pivotal causal factor in producing atypical phenotypic outcomes. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
957.
958.
Materials with inherent microstructures like granular media, foams or spongy bones often show a complex constitutive behaviour
on the macroscale while the microscopic constitutive equations may be formulated in a simple fashion. Applying homogenization
procedures allows to transfer the information from the microlevel to the macrolevel.
In the present contribution the porous structure of hard biological tissues, i.e. of spongy bones, is investigated. On the
macroscale the approach is embedded into an extended continuum mechanical setting in order to capture size effects. The constitutive
equations are formulated on the microscopic level taking into account growth and reorientation of the microstructural elements.
By application of a strain-driven numerical homogenization procedure the macroscopic stress response is obtained. 相似文献
959.
960.
Titanium Dioxide, TiO2, is a photocatalyst with a unique characteristic. A surface coated with TiO2 exhibits an extremely high affinity for water when exposed to UV light and the contact angle decreases nearly to zero. Inversely, the contact angle increases when the surface is shielded from UV. This superhydrophilic nature gives a self-cleaning effect to the coated surface and has already been applied to some construction materials, car coatings and so on. We applied this property to the enhancement of boiling heat transfer. An experiment involving the pool boiling of pure water has been performed to make clear the effect of high wettability on heat transfer characteristics. The heat transfer surface is a vertical copper cylinder of 17 mm in diameter and the measurement has been done at saturated temperature and in a steady state. Both TiO2-coated and non-coated surfaces were used for comparison. In the case of the TiO2-coated surface, it is exposed to UV light for a few hours before experiment and it is found that the maximum heat flux (CHF) is about two times larger than that of the uncoated surface. The temperature at minimum heat flux (MHF) for the superhydrophilic surface is higher by 100 K than that for the normal one. The superhydrophilic surface can be an ideal heat transfer surface. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献