全文获取类型
收费全文 | 704988篇 |
免费 | 9195篇 |
国内免费 | 2109篇 |
专业分类
电工技术 | 13000篇 |
综合类 | 671篇 |
化学工业 | 105497篇 |
金属工艺 | 26721篇 |
机械仪表 | 20472篇 |
建筑科学 | 17388篇 |
矿业工程 | 2944篇 |
能源动力 | 19830篇 |
轻工业 | 61444篇 |
水利工程 | 6800篇 |
石油天然气 | 11416篇 |
武器工业 | 45篇 |
无线电 | 83466篇 |
一般工业技术 | 137293篇 |
冶金工业 | 136505篇 |
原子能技术 | 13873篇 |
自动化技术 | 58927篇 |
出版年
2022年 | 4207篇 |
2021年 | 6444篇 |
2020年 | 4705篇 |
2019年 | 5937篇 |
2018年 | 10104篇 |
2017年 | 9907篇 |
2016年 | 10392篇 |
2015年 | 7133篇 |
2014年 | 11952篇 |
2013年 | 32626篇 |
2012年 | 18887篇 |
2011年 | 26108篇 |
2010年 | 20670篇 |
2009年 | 23317篇 |
2008年 | 23950篇 |
2007年 | 23527篇 |
2006年 | 20678篇 |
2005年 | 18579篇 |
2004年 | 17964篇 |
2003年 | 17844篇 |
2002年 | 16895篇 |
2001年 | 17273篇 |
2000年 | 16021篇 |
1999年 | 16974篇 |
1998年 | 43437篇 |
1997年 | 30410篇 |
1996年 | 23342篇 |
1995年 | 17588篇 |
1994年 | 15367篇 |
1993年 | 15151篇 |
1992年 | 10899篇 |
1991年 | 10360篇 |
1990年 | 10107篇 |
1989年 | 9678篇 |
1988年 | 9120篇 |
1987年 | 8027篇 |
1986年 | 7874篇 |
1985年 | 8718篇 |
1984年 | 8138篇 |
1983年 | 7388篇 |
1982年 | 6920篇 |
1981年 | 6893篇 |
1980年 | 6633篇 |
1979年 | 6380篇 |
1978年 | 6050篇 |
1977年 | 7351篇 |
1976年 | 9736篇 |
1975年 | 5149篇 |
1974年 | 4904篇 |
1973年 | 4947篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Kyle A. Crawford
Osama K. Eyada PhD PE
《Computers & Industrial Engineering》1989,17(1-4):298-302The worldwide proliferation of fraudulent materials has brought about the need for a new approach to the control of purchased material quality. Nuclear power, defense, aerospace and many other industries are affected by the supply of poor quality clones that presume to be original replacement parts. Safety considerations abound as these highly defective materials are used in systems that are critical to the preservation of human lives. Commonly utilized quality assurance programs have not effectively stopped the influx of fraudulent materials. These programs fail to concentrate inspection efforts on materials and inspection attributes that would effectively prevent the acceptance of fraudulent materials. herein a solution is presented to this problem in the form of an expert system application. Information commonly available in industry is formulated into a knowledge based system wherein advisories are given to the user regarding key purchased material receipt inspection strategies. 相似文献
993.
This paper considers the integration of alternative technical systems (TS) belonging to a wider class of competing TS, into a supersystem. The paper introduces the notion of alternative TS, shows the peculiarities of their incorporation into a supersystem, reveals the mechanisms used for such incorporation, and shows areas of application for the suggested method. 相似文献
994.
995.
Sehyun Park Okajima Y. Hirokawa J. Ando M. 《Antennas and Propagation, IEEE Transactions on》2005,53(9):2865-2871
This work proposes a dual-polarized planar antenna; two post-wall slotted waveguide arrays with orthogonal 45/spl deg/ linearly-polarized waves interdigitally share the aperture on a single layer substrate. Uniform excitation of the two-dimensional slot array is confirmed by experiment in the 25 GHz band. The isolation between two slot arrays is also investigated in terms of the relative displacement along the radiation waveguide axis in the interdigital structure. The isolation is 33.0 dB when the relative shift of slot position between the two arrays is -0.5/spl lambda//sub g/, while it is only 12.8 dB when there is no shift. The cross-polarization level in the far field is -25.2 dB for a -0.5/spl lambda//sub g/ shift, which is almost equal to that of the isolated single polarization array. It is degraded down to -9.6 dB when there is no shift. 相似文献
996.
997.
The effect of treatment with a zirconyl nitrate aqueous solution on the structure; the hydroxyl-layer constitution; and the adsorptive, acid, and catalytic properties of dealuminated zeolite Y was studied. The zeolite was prepared by boiling NH4Y in an ethylenediaminetetraacetic acid disodium salt solution followed by ion exchange with ammonium chloride and calcination in a 100% steam flow at 750°C. X-ray diffraction, IR spectroscopy, and DTA data show the formation of an ultrastable form of zeolite Y. The incorporation of zirconium in zeolite led to an increase in the proportion of strong acid sites, thus raising the yield of cracking products during n-hexane conversion tested on platinum-containing catalyst samples. 相似文献
998.
E Persson M Ljunggren J la Cour Jansen R Strube L J?nsson 《Water science and technology》2006,53(12):139-147
A Discfilter with 10 and 18 microm filter openings, respectively, was placed in parallel to a flotation plant for separation of biological flocs from a post-denitrifying Kaldnes Moving Bed Process, the last treatment step at the municipal wastewater treatment plant at Sj?unda, Malm?, Sweden. The effluent concentrations from the 10 and 18 microm filter were 2-5 and 2-8 mg SS L(-1), respectively, which is comparable to, or better than, the flotation plant. Comparison with experiences from activated sludge plants shows that the Discfilter works especially well after the Kaldnes process. Particle size distribution (PSD) studies show that particles larger than the filter openings of 10 and 18 microm are separated with approximately 90% efficiency, whereas most of the smaller particles pass the filter. This fact indicates that the major particle separation mechanism is physical blocking. These findings point to the possibility of improving the prediction of the separation efficiency by combining measurements of turbidity and suspended solids with particle size analysis. 相似文献
999.
Friendship affects individual and organizational well-being through direct relations, social positions, and complex network structures. In this study, the authors use longitudinal data from 2 groups of master's of business administration students to increase understanding of how friendship networks develop. The authors propose and test a dynamic model in which attribute similarity facilitates dyadic friendship ties, as well as similar network centrality and social position; early friendship increases later similarity in structural position and centrality; and early structural similarity enhances the likelihood of future friendship. Findings largely supported the model, demonstrating how homophily and early social contacts can jointly shape maturing friendship networks. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
1000.
O. T. Tsyrul’nyk H. M. Nykyforchyn D. Yu. Petryna M. I. Hredil’ I. M. Dz’oba 《Materials Science》2007,43(5):708-717
We study the degradation of the mechanical and corrosion properties of 17G1S steel in gas mains as a result of operation for
28–40 yr. We reveal the simultaneous decrease in its strength and hardness, on the one hand, and impact toughness and crack
resistance, on the other hand. The indicated parameters prove to be most sensitive to the in-service degradation of the metal.
The degradation of steel leads to the increase in the strain-hardening coefficient and the appearance of the yield plateau
in the tensile stress-strain diagram and causes the appearance of sensitivity to hydrogen embrittlement increasing in the
process of operation. We analyze the role of absorbed hydrogen affecting the mechanism of strain aging and responsible for
the appearance of defects. It is shown that the polarization resistance can be used not only for monitoring of the corrosion
state of gas pipelines but also for the prediction of changes in their mechanical properties in the process of operation.
__________
Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 43, No. 5, pp. 97–104, September–October, 2007. 相似文献