全文获取类型
收费全文 | 409547篇 |
免费 | 5015篇 |
国内免费 | 1411篇 |
专业分类
电工技术 | 7898篇 |
综合类 | 426篇 |
化学工业 | 61186篇 |
金属工艺 | 16860篇 |
机械仪表 | 12630篇 |
建筑科学 | 9940篇 |
矿业工程 | 1872篇 |
能源动力 | 10500篇 |
轻工业 | 36263篇 |
水利工程 | 4032篇 |
石油天然气 | 6595篇 |
武器工业 | 70篇 |
无线电 | 50707篇 |
一般工业技术 | 77815篇 |
冶金工业 | 75249篇 |
原子能技术 | 8869篇 |
自动化技术 | 35061篇 |
出版年
2021年 | 3153篇 |
2019年 | 3063篇 |
2018年 | 5181篇 |
2017年 | 5222篇 |
2016年 | 5542篇 |
2015年 | 3656篇 |
2014年 | 6305篇 |
2013年 | 18006篇 |
2012年 | 10352篇 |
2011年 | 14196篇 |
2010年 | 11237篇 |
2009年 | 12812篇 |
2008年 | 13579篇 |
2007年 | 13460篇 |
2006年 | 11929篇 |
2005年 | 11001篇 |
2004年 | 10607篇 |
2003年 | 10169篇 |
2002年 | 9833篇 |
2001年 | 9880篇 |
2000年 | 9393篇 |
1999年 | 9678篇 |
1998年 | 23042篇 |
1997年 | 16530篇 |
1996年 | 12927篇 |
1995年 | 10034篇 |
1994年 | 8747篇 |
1993年 | 8650篇 |
1992年 | 6714篇 |
1991年 | 6317篇 |
1990年 | 6051篇 |
1989年 | 5836篇 |
1988年 | 5631篇 |
1987年 | 4955篇 |
1986年 | 4821篇 |
1985年 | 5608篇 |
1984年 | 5242篇 |
1983年 | 4794篇 |
1982年 | 4416篇 |
1981年 | 4601篇 |
1980年 | 4280篇 |
1979年 | 4229篇 |
1978年 | 4005篇 |
1977年 | 4759篇 |
1976年 | 5929篇 |
1975年 | 3657篇 |
1974年 | 3622篇 |
1973年 | 3685篇 |
1972年 | 3019篇 |
1971年 | 2808篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
991.
992.
Measurements of frequencies and spatial correlations of coherent structures in rod bundle flows 总被引:2,自引:2,他引:0
Cross-wire anemometry was used to identify and characterize coherent flow pulsations in isothermal air flow near the gap regions of a five-rod bundle with a design pitch-to-diameter ratio of 1.149 and contained in a quasi-trapezoidal duct. It was confirmed that such pulsations are quasi-periodic and contribute significantly to the velocity fluctuations across the gap. The frequency of pulsations was found to decrease with diminishing rod–wall gap size in the range between 0.015D and 0.250D, where D is the rod diameter. The pulsations in a rod–wall gap and an adjacent rod–rod gap were strongly coupled and occurred at the same frequency as one rod was displaced towards the duct wall. 相似文献
993.
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
994.
995.
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
996.
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
997.
998.
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
999.
G. F. Molokanov 《Journal of Computer and Systems Sciences International》2006,45(2):331-335
The year 2006 marks the ninetieth anniversary of the air navigation (later called navigation) service of the Air Forces of this country. The history of air navigation is investigated, and an opinion about its modern state and directions of further development is presented. 相似文献
1000.
An adaption is presented to an earlier method for the prediction of time-eigenvalues of the neutron transport equation. Instead of using the full-parity first-order equation, the algorithm uses the even-parity formalism in the most expensive part of the computations resulting in a more economic method. 相似文献