全文获取类型
收费全文 | 436034篇 |
免费 | 6352篇 |
国内免费 | 1542篇 |
专业分类
电工技术 | 7434篇 |
综合类 | 337篇 |
化学工业 | 65764篇 |
金属工艺 | 17764篇 |
机械仪表 | 13636篇 |
建筑科学 | 10284篇 |
矿业工程 | 2675篇 |
能源动力 | 11229篇 |
轻工业 | 38920篇 |
水利工程 | 4839篇 |
石油天然气 | 9480篇 |
武器工业 | 27篇 |
无线电 | 51643篇 |
一般工业技术 | 86847篇 |
冶金工业 | 77661篇 |
原子能技术 | 9578篇 |
自动化技术 | 35810篇 |
出版年
2021年 | 3691篇 |
2020年 | 2782篇 |
2019年 | 3493篇 |
2018年 | 5997篇 |
2017年 | 6038篇 |
2016年 | 6608篇 |
2015年 | 4172篇 |
2014年 | 7056篇 |
2013年 | 19680篇 |
2012年 | 11722篇 |
2011年 | 15914篇 |
2010年 | 12608篇 |
2009年 | 14081篇 |
2008年 | 14620篇 |
2007年 | 14553篇 |
2006年 | 13053篇 |
2005年 | 11893篇 |
2004年 | 11195篇 |
2003年 | 10992篇 |
2002年 | 10423篇 |
2001年 | 10857篇 |
2000年 | 9913篇 |
1999年 | 10416篇 |
1998年 | 25155篇 |
1997年 | 17612篇 |
1996年 | 13381篇 |
1995年 | 10182篇 |
1994年 | 8875篇 |
1993年 | 8990篇 |
1992年 | 6654篇 |
1991年 | 6386篇 |
1990年 | 6154篇 |
1989年 | 5976篇 |
1988年 | 5882篇 |
1987年 | 4904篇 |
1986年 | 4885篇 |
1985年 | 5771篇 |
1984年 | 5282篇 |
1983年 | 4910篇 |
1982年 | 4484篇 |
1981年 | 4504篇 |
1980年 | 4375篇 |
1979年 | 4267篇 |
1978年 | 4127篇 |
1977年 | 4526篇 |
1976年 | 5485篇 |
1975年 | 3679篇 |
1974年 | 3452篇 |
1973年 | 3622篇 |
1972年 | 2999篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
981.
A simple weak avalanche model valid in a wide range of voltages and currents, is presented. The proposed model is derived by using the base-collector depletion capacitance for predicting the avalanche current. The model needs only one additional transistor parameter; the extraction method and temperature dependence of this parameter are discussed. The decrease in avalanche current for high collector current densities may originate from internal device heating, a voltage drop in the epilayer, or mobile carriers in the depleted part. From experimental results it is concluded that, below a critical hot-carrier current, the decrease in avalanche current due to mobile carriers is negligible 相似文献
982.
P. Papet N. Le Bars J. F. Baumard A. Lecomte A. Dauger 《Journal of Materials Science》1989,24(11):3850-3854
Transparent yttria-stabilized zirconia monolithic gels were synthesized under controlled conditions for hydrolysis and chemical polymerization. The influence of acetylacetone on the previous chemical reactions was explored, and a plausible explanation was proposed concerning the outstanding role of this additive during the gelation process. Small-angle X-ray scattering was used to estimate the size of the polymeric species and to investigate the influence of acetylacetone on the structure of the gels prepared. 相似文献
983.
984.
985.
Translated from Izmeritel'naya Tekhnika, No. 6, pp. 19–20, June, 1989. 相似文献
986.
The change in polystyrene (PS) layer thickness, which has been simultaneously determined during post-yield deformation, shows
that crazing is the basic mechanism of toughening in all laminated films, and that shear deformation supplements the contribution
of crazing especially for samples with high polyethylene (PE) volume fractions. Crazes formed in PS layers in the laminated
films are slender and regular compared with the short and lenticular crazes formed in bulk PS film. When PE volume fraction
increased, craze advance speed decreased because of the reduction of the stress concentration effect at craze tips. The life-time
of the first mature craze to be formed at a given strain rate increased with PE volume fraction because the PE supporting
the mature crazes could effectively inhibit craze rupture and blunt out the propagating crack by absorbing the stored elastic
energy in the PS layer that would have been dissipated as fracture surface energy. 相似文献
987.
988.
A voltage-controlled oscillator (VCO) with sine wave output has been built using a tunable inductor along with a tunable capacitor to operate at frequencies ranging from 100 kHz to over 20 MHz. The method of tuning the inductor by changing the permeability of its ferrite core and the ability to extend the frequency response of the core are discussed. Dynamic characteristics of the VCO are explained with examples of a parallel and series tank implementation 相似文献
989.
J. M. Richards M. I. Darby R. Baggott G. H. Wosteim Holm B. Yates G. Dorey L. N. Phillips 《Journal of Materials Science》1989,24(2):584-589
The effects of defects on the mechanical properties of carbon fibre reinforced polyethersulphone laminates have been measured. The defects studied were cut fibre plies, omission of polymer films and local delamination produced by the inclusion of foreign matter. Of these it was found that only cut plies had a significant detrimental effect on the strength of a laminate. For specimens with two cut plies, the failure stress, tensile, flexural and compressive in the remaining continuous plies was the same as in the defect-free material, provided that the cut plies were widely separated. However the failure stresses were 15–18% lower in the continuous plies in the specimens containing two cut plies which were more closely spaced and in specimens containing four cut plies. 相似文献
990.
F. J. C. M. Toolenaar 《Journal of Materials Science》1989,24(3):1089-1094
The formation of zinc ferrite from zinc oxide and iron oxide is evaluated with high temperature X-ray diffraction experiments. Despite the problem of accurately determining the temperature of the part of the sample actually investigated, a kinetic analysis of the isothermal formation is shown to be possible. From these data the energy and entropy of activation are derived. It is further shown that neither corrections for grain growth during formation nor the presence of impurities have any influence on these results. On the other hand, the size of the reactant iron oxide particles is found to have a strong influence on both the energy and entropy of activation. 相似文献