全文获取类型
收费全文 | 462088篇 |
免费 | 6427篇 |
国内免费 | 2206篇 |
专业分类
电工技术 | 9087篇 |
技术理论 | 5篇 |
综合类 | 1418篇 |
化学工业 | 74539篇 |
金属工艺 | 18769篇 |
机械仪表 | 13917篇 |
建筑科学 | 11252篇 |
矿业工程 | 2886篇 |
能源动力 | 10057篇 |
轻工业 | 45408篇 |
水利工程 | 4974篇 |
石油天然气 | 10020篇 |
武器工业 | 274篇 |
无线电 | 48415篇 |
一般工业技术 | 86243篇 |
冶金工业 | 86231篇 |
原子能技术 | 10336篇 |
自动化技术 | 36890篇 |
出版年
2021年 | 4234篇 |
2019年 | 3775篇 |
2018年 | 6263篇 |
2017年 | 6179篇 |
2016年 | 6666篇 |
2015年 | 4689篇 |
2014年 | 7770篇 |
2013年 | 20078篇 |
2012年 | 12647篇 |
2011年 | 17087篇 |
2010年 | 13542篇 |
2009年 | 14636篇 |
2008年 | 15700篇 |
2007年 | 15904篇 |
2006年 | 14133篇 |
2005年 | 12358篇 |
2004年 | 11398篇 |
2003年 | 10799篇 |
2002年 | 10925篇 |
2001年 | 10857篇 |
2000年 | 10324篇 |
1999年 | 10358篇 |
1998年 | 23577篇 |
1997年 | 17047篇 |
1996年 | 13089篇 |
1995年 | 10054篇 |
1994年 | 9087篇 |
1993年 | 8874篇 |
1992年 | 6973篇 |
1991年 | 6519篇 |
1990年 | 6783篇 |
1989年 | 6595篇 |
1988年 | 6263篇 |
1987年 | 5475篇 |
1986年 | 5478篇 |
1985年 | 6210篇 |
1984年 | 6022篇 |
1983年 | 5466篇 |
1982年 | 5017篇 |
1981年 | 5262篇 |
1980年 | 4930篇 |
1979年 | 5028篇 |
1978年 | 4961篇 |
1977年 | 5361篇 |
1976年 | 6967篇 |
1975年 | 4443篇 |
1974年 | 4171篇 |
1973年 | 4284篇 |
1972年 | 3621篇 |
1971年 | 3327篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
G.D. Wignall R.W. Hendricks W.C. Koehler J.S. Lin M.P. Wai E.L. Thomas R.S. Stein 《Polymer》1981,22(7):886-889
A series of small angle neutron scattering measurements on blends of normal polystyrene (PSH) and labelled (deuterated) polystyrene (PSD) have been made with concentrations of PSD from 5 to 50 mol %. It is shown that the single chain form factor of the polymer in bulk can be obtained from a single concentration measurement for any concentration of labelled molecules, providing the molecular weights of the parent and labelled molecules are the same and the molecular weight distributions are narrow. 相似文献
82.
Rapeseed protein concentrate (RC), prepared with 2% hexameta-phosphate, was tested for its functionality and performance in some foods. The RC had good nitrogen solubility, fat absorption, emulsification, and whipping capacities but poor water absorption and gelling properties. It increased the emulsion stability, and protein but lowered the fat content of wieners. It also increased the cooking yield, reduced the shrinkage and tenderized meat patties. Results were similar to soybean isolate except for the poorer color and flavor. The cooking yield of RC supplemented wieners was less than the all-meat control and soybean-supplemented wieners. A 9% RC dispersion mixed with an equal volume of eggwhite produced a meringue of comparable stability and texture to that of eggwhite alone. 相似文献
83.
A. A. Konstantinov N. V. Kurenkov A. B. Malinin T. E. Sazonova S. V. Sepman 《Atomic Energy》1989,67(3):696-698
Translated from Atomnaya Énergiya, Vol. 67, No. 3, pp. 215–216, September, 1989. 相似文献
84.
Intensive fertilizer use has led to nitrate contamination of groundwater in many areas. This article examines the possibility of removing nitrates through the construction of artificial wetlands. A pilot study conducted in Denmark has found that the method is effective and economical, at least for small waterworks, though further treatment is necessary before an acceptable microbiological water quality is attained. 相似文献
85.
Nagpal R. Zambonelli F. Sirer E.G. Chaouchi H. Smirnov M. 《Intelligent Systems, IEEE》2006,21(2):50-58
No generally accepted principles and guidelines currently exist to help engineers design local interaction mechanisms that result in a desired global behavior. However, several communities have developed ways of approaching this problem in the context of niched application areas. Because the ideas underlying these approaches are often obscured or underemphasized in technical papers, the authors review the role of self-organization in their work. They provide a better picture of the status of the emerging field of self-organizing systems or autonomic computing. 相似文献
86.
L. GbahoueF. Barbeu S. Martemianov 《International Journal of Heat and Mass Transfer》2002,45(18):3865-3873
Electrochemical method is applied to study coherent structures in a complex three-dimensional flow generated by a rotating magnetic rod. In order to detect these structures, the power spectral density (PSD) analysis of the limiting diffusion current fluctuations is provided. This analysis reveals the existence of resonance frequencies when the probe is located in the very vicinity of the stirrer. The main resonance is related to the mechanical excitation frequency. The detailed analysis of the PSD curves points out some mechanisms of development of turbulence as sub-harmonics and non-linear interactions. For different locations of the probe and different angular rates of the stirrer Ω, a similarity of the energy repartition is obtained when the PSD is plotted versus the adimensional frequency f/Ω. Flow visualization by laser tomography is also provided and the local secondary flow past the electrode probe is sketched. The laser Doppler velocimetry (LDV) at a given location in a horizontal z-plane indicates a tornado wise mean flow structure. 相似文献
87.
88.
A method for fabricating single crystal blades that combines the techniques of seed crystals and selection is suggested. The method realizes the advantages of both techniques, i.e., the high structural perfection and the possibility of fabricating single crystals with specified spatial orientation. Metallographic and x-ray diffraction analyses are used to study the processes of nucleation of the single crystal structure of blade castings fabricated from high-temperature nickel alloys by the method of selection and seed crystals. A commercial process for fabricating cast single crystal turbine blades by the new method is suggested. 相似文献
89.
Shamansky H.T. Dominek A.K. Peters L. Jr. 《Antennas and Propagation, IEEE Transactions on》1989,37(8):1019-1025
The traveling-wave energy, which multiply diffracts on a straight thin wire, is represented as a sum of terms, each with a distinct physical meaning, that can be individually examined in the time domain. Expressions for each scattering mechanism on a straight thin wire are cast in the form of four basic electromagnetic wave concepts: diffraction, attachment, launch, and reflection. Using the basic mechanisms from P.Ya. Ufimtsev (1962), each of the scattering mechanisms is included into the total scattered field for the straight thin wire. Scattering as a function of angle and frequency is then compared to the moment-method solution. These analytic expressions are then extended to a lossy wire with a simple approximate modification using the propagation velocity on the wire as derived from the Sommerfeld wave on a straight lossy wire. Both the perfectly conducting and lossy wire solutions are compared to moment-method results, and excellent agreement is found. As is common with asymptotic solutions, when the electrical length of wire is smaller than 0.2 λ the results lose accuracy. The expressions modified to approximate the scattering for the lossy thin wire yield excellent agreement even for lossy wires where the wire radius is on the order of skin depth 相似文献
90.
Buttari D. Chini A. Meneghesso G. Zanoni E. Moran B. Heikman S. Zhang N.Q. Shen L. Coffie R. DenBaars S.P. Mishra U.K. 《Electron Device Letters, IEEE》2002,23(2):76-78
Pre-metal-deposition reactive ion etching (RIE) was performed on an Al0.3Ga0.7N/AlN/GaN heterostructure in order to improve the metal-to-semiconductor contact resistance. An optimum AlGaN thickness for minimizing contact resistance was determined. An initial decrease in contact resistance with etching time was explained in terms of removal of an oxide surface layer and/or by an increase in tunnelling current with the decrease of the AlGaN thickness. The presence of a dissimilar surface layer was confirmed by an initial nonuniform etch depth rate. An increase in contact resistance for deeper etches was experienced. The increase was related to depletion of the two-dimensional (2-D) electron gas (2-DEG) under the ohmics. Etch depths were measured by atomic force microscopy (AFM). The contact resistance decreased from about 0.45 Ωmm for unetched ohmics to a minimum of 0.27 Ωmm for 70 Å etched ohmics. The initial thickness of the AlGaN layer was 250 Å. The decrease in contact resistance, without excessive complications on device processing, supports RIE etching as a viable solution to improve ohmic contact resistance in AlGaN/GaN HEMTs 相似文献