全文获取类型
收费全文 | 264141篇 |
免费 | 3505篇 |
国内免费 | 826篇 |
专业分类
电工技术 | 5164篇 |
综合类 | 336篇 |
化学工业 | 37796篇 |
金属工艺 | 10313篇 |
机械仪表 | 8571篇 |
建筑科学 | 6387篇 |
矿业工程 | 1090篇 |
能源动力 | 6480篇 |
轻工业 | 23151篇 |
水利工程 | 2585篇 |
石油天然气 | 3913篇 |
武器工业 | 69篇 |
无线电 | 35164篇 |
一般工业技术 | 50631篇 |
冶金工业 | 47759篇 |
原子能技术 | 5456篇 |
自动化技术 | 23607篇 |
出版年
2021年 | 2088篇 |
2019年 | 2089篇 |
2018年 | 3518篇 |
2017年 | 3597篇 |
2016年 | 3799篇 |
2015年 | 2365篇 |
2014年 | 4145篇 |
2013年 | 11519篇 |
2012年 | 6689篇 |
2011年 | 9036篇 |
2010年 | 7127篇 |
2009年 | 7994篇 |
2008年 | 8861篇 |
2007年 | 8789篇 |
2006年 | 7973篇 |
2005年 | 7297篇 |
2004年 | 7022篇 |
2003年 | 6851篇 |
2002年 | 6475篇 |
2001年 | 6549篇 |
2000年 | 6252篇 |
1999年 | 6357篇 |
1998年 | 14543篇 |
1997年 | 10473篇 |
1996年 | 8267篇 |
1995年 | 6493篇 |
1994年 | 5806篇 |
1993年 | 5671篇 |
1992年 | 4594篇 |
1991年 | 4245篇 |
1990年 | 4083篇 |
1989年 | 3818篇 |
1988年 | 3669篇 |
1987年 | 3217篇 |
1986年 | 3095篇 |
1985年 | 3646篇 |
1984年 | 3413篇 |
1983年 | 3059篇 |
1982年 | 2884篇 |
1981年 | 2992篇 |
1980年 | 2803篇 |
1979年 | 2674篇 |
1978年 | 2528篇 |
1977年 | 2998篇 |
1976年 | 3626篇 |
1975年 | 2337篇 |
1974年 | 2336篇 |
1973年 | 2332篇 |
1972年 | 1859篇 |
1971年 | 1763篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
An incremental iterative process based on direct energy minimization is presented for a limit analysis of nonlinear elastic lateral displacements and twists of reinforced and prestressed beams. Problems encountered with the constitutive relations are discussed and two possible material models are presented. 相似文献
992.
Replicated W. K. Kirchner and M. D. Dunnette's (see record 1955-03161-001) study on attitudes toward older workers with 71 male and 5 female hourly employees (aged 18–61 yrs) and 22 male supervisors (aged 27–63 yrs) of a nonunion manufacturing plant. Ss completed a questionnaire that was nearly identical to the one administered in the Kirchner and Dunnette study. Results are similar to those obtained in the earlier study: Hourly workers held more positive attitudes toward older employees than did supervisors, and attitude score correlated strongly with the age of hourly workers but not with the age of supervisors. (9 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
993.
Supercritical gases pasteurization of apple juice 总被引:3,自引:0,他引:3
Supercritical CO2 and N2O pasteurization of apple juice, inoculated with Saccharomyces cerevisiae as test microorganism, was performed at 36 °C on a laboratory multi-batch apparatus of a total volume of 150 ml. The pressure values ranged from 100 to 200 bar. Experimental results indicate the effectiveness of the method proposed. A stochastic model of the process was developed on the basis of the experimental evidence: high-pressure inactivation curves were analysed using a stochastic model based on multi-hit model. Furthermore, the samples of the cells subjected to high-pressure treatments were examined by environmental scanning electron microscopy (ESEM) to determine the effect of the process on the cell wall. 相似文献
994.
995.
Wastewater treatment technologies suitable for serving large populations are generally reliable and reasonably cost-effective, yet they are almost always financially inappropriate for small communities (< 2,000 p.e.). Comparative cost data suggests that waste stabilization ponds should be an attractive option for small communities, yet perceptions relating to land costs, climate and effluent quality have limited their application in the UK. This paper details typical UK land costs, climate and winter performance data for a pilot-scale waste stabilization pond with various upgrading technologies: system A, two tertiary maturation ponds in series; B, two tertiary maturation ponds in series followed by a reed bed channel; C, a control rock filter; D, an aerated rock filter; and E, a constructed wetland. System D was found to perform best, closely followed by system B. 相似文献
996.
Results of the studies of nonstationary electromagnetic and electromechanical processes that develop during the start-up (restart) of a frequency-controlled electric drive of a mainline pump as result of perturbation in the electric supply system are presented. 相似文献
997.
D. Greubel 《Holz als Roh- und Werkstoff》1987,45(4):145-149
On the basis of the finite difference method, a computer programme was developed for multidimensionally calculating the transport of heat and moisture in building elements. Apart from water vapor diffusion, capillary conduction of water and sorptional behavior of hygroscopic materials were also considered. Calculations were done iteratively since the material properties were not constants but depend on temperature and moisture contents of the materials. For programme testing purposes, calculations with socalled light weight wall elements were carried out, based on an artificial fast motion climate of the city of Madrid. Calculated and measured moisture contents of the materials in particleboard sheathings were compared with one another. 相似文献
998.
I. E. Gorbatkina L. D. Konoval'chikov B. K. Nefedov B. L. Khusid 《Chemistry and Technology of Fuels and Oils》1989,25(3):127-130
Translated from Khimiya i Tekhnoloyiya Topliv i Masel, No. 3, pp. 3–5, March, 1989. 相似文献
999.
1000.
U. Amato G. Amodeo V. Brandi V. Cuomo D. Ruggi C. Serio V. Silvestrini G. C. Tosato 《国际能源研究杂志》1985,9(1):33-51
In Italy solar thermal energy and energy from biogas are two possible means of reducing dependence on energy imports. Using a multiperiod LP model (MARKAL) the authors assessed the likely potential of both technologies under various circumstances. The study covered the period 1980–2005, in five segments of five years. It focused only on the subsystem of the energy end-uses which can be substituted for by solar thermal and biogas technologies. The overall non-renewable sources which can be saved in 20 years by these technologies total 450 PJ (1 PJ = 101 5 J) if the fuel prices rise at 0 per cent average annual, 1450 PJ if the fuel prices rise at 4.2 per cent average annual, 1860 PJ if the fuel prices rise at 7.2 per cent average annual and 3780 PJ if the fuel prices rise at 15 per cent average annual. However the most competitive technologies appear to be solar water heaters used mainly in the private and commercial sectors and biogas systems used mainly in the agricultural sector. The study was carried out by APRE under ENEA (formerly CNEN) contract and was intended to serve as an analytical basis for establishing an overall development and demonstration strategy for end-use renewable technologies in Italy. 相似文献