全文获取类型
收费全文 | 213806篇 |
免费 | 4554篇 |
国内免费 | 227篇 |
学科分类
工业技术 | 218587篇 |
出版年
2021年 | 2655篇 |
2020年 | 2254篇 |
2019年 | 2679篇 |
2018年 | 5045篇 |
2017年 | 5088篇 |
2016年 | 5430篇 |
2015年 | 3237篇 |
2014年 | 4793篇 |
2013年 | 10193篇 |
2012年 | 7138篇 |
2011年 | 7953篇 |
2010年 | 6584篇 |
2009年 | 6785篇 |
2008年 | 6820篇 |
2007年 | 6616篇 |
2006年 | 5316篇 |
2005年 | 4826篇 |
2004年 | 4542篇 |
2003年 | 4369篇 |
2002年 | 4237篇 |
2001年 | 4036篇 |
2000年 | 3870篇 |
1999年 | 3766篇 |
1998年 | 10054篇 |
1997年 | 7142篇 |
1996年 | 5124篇 |
1995年 | 3686篇 |
1994年 | 3190篇 |
1993年 | 3335篇 |
1992年 | 2469篇 |
1991年 | 2527篇 |
1990年 | 2575篇 |
1989年 | 2483篇 |
1988年 | 2498篇 |
1987年 | 2334篇 |
1986年 | 2386篇 |
1985年 | 2445篇 |
1984年 | 2348篇 |
1983年 | 2233篇 |
1982年 | 2108篇 |
1981年 | 2342篇 |
1980年 | 2231篇 |
1979年 | 2345篇 |
1978年 | 2520篇 |
1977年 | 2723篇 |
1976年 | 3753篇 |
1975年 | 2311篇 |
1974年 | 2359篇 |
1973年 | 2421篇 |
1972年 | 2182篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The film-forming capacity of binary systems containing Sb2O3, SnO2, CeO2, Y2O3, Nd2O3, Bi2O3, V2O5, ZnO, CuO, CdO, and Al2O3 are investigated. The best film-formers are Sb2O3 and SnO2, whereas ZnO, CuO, CdO, and Al2O3 cannot produce films of optical quality. The rest of considered oxides do not impair the clarity of coatings when their molding content is 20 – 50%. A proportional dependence is established between the refractive index and the reflection coefficient of a film and the refractive indexes of oxides making parts of this film, as well as between the concentration of deposited FFS, the film-forming capacity of oxides, and the film thickness. 相似文献
992.
A novel active parametric frequency divider configuration using coupled microstrip transmission lines and two balanced pseudomorphic HEMTs (pHEMTs) is presented. The analysis of the divide-by-2 circuit presented applies the principles of subharmonic generation using a nonlinear reactance to an active semiconductor device such as a pHEMT. A 2-1-GHz active analog frequency divider is designed and fabricated, with measurements showing a 20% bandwidth, 13.5-dB conversion gain, and harmonic rejection levels of more than 22 dBc. A maximum conversion gain of 18 dB is also achieved. These higher conversion efficiencies and the ability to cascade dividers allow for higher order division ratios to be achieved with the same topology. 相似文献
993.
I. Zh. Bus'ko V. V. Golubkov M. I. Vasil'ev V. V. Pshenitsina V. A. Tsekhomskii 《Glass Physics and Chemistry》2002,28(3):124-134
The halide phase in copper halide photochromic glasses is studied by the small-angle X-ray scattering (SAXS) technique. The dependences of the volume and composition of the halide phase on the temperature of primary heat treatment are determined. The temperature of the formation of a vacuum pore upon cooling from the temperature of primary heat treatment and the temperature of pore disappearance upon heating are investigated as functions of the size of the halide phase regions. The influence of the size of the halide phase regions and the temperature of secondary heat treatment on the crystallization temperature of the halide phase is elucidated. It is shown that the previously observed increase in the crystallization temperature of the halide phase with an increase in the size of the phase regions is associated with the change-over from homogeneous to heterogeneous crystallization. In turn, the mechanism of crystallization depends on the region where the vacuum pore is formed. In the case when the effective radii of drops are less than 130–140 Å, the vacuum pore is formed in the bulk of a liquid drop and the homogeneous crystallization occurs. The nuclei of heterogeneous crystallization arise when the formation of the vacuum pore is accompanied by the destruction of the vitreous matrix. This takes place when the radii of liquid drops are larger than 165–170 Å. The nuclei of heterogeneous crystallization disappear upon heat treatment of glasses at temperatures above 600°C. As a result, upon cooling from these temperatures, the homogeneous crystallization is observed in all cases and the crystallization temperature does not depend on the size of the halide phase regions. 相似文献
994.
In previous work, it has been found that a hydrogen-covered Pt(110) surface is acidic, but quantification of the acidity has not yet been done. In this paper a spectroscopic method is developed to measure the acidity of a metal surface for the first time. The technique involves measuring the intensity of the N–H stretch from the C5H4XNH+ that forms when hydrogen coadsorbs with pyridine, 2-fluoropyridine and 3-fluoropyridine. The Bethe approximation is then used to estimate the metal surface acidity/electronegativity (MSAEL). The proton affinity/MSAEL of Pt(110) has been determined to be 907 ± 4 kJ/mol at high coverage. This is the first time the MSAEL has been measured on a metal surface. Implications for fuel cell catalysis are discussed. 相似文献
995.
Metal Science and Heat Treatment - 相似文献
996.
997.
A. Kh. Abduev A. Sh. Asvarov A. K. Akhmedov V. G. Baryshnikov E. I. Terukov 《Technical Physics Letters》2002,28(11):952-954
We observed zinc oxide structures formed in an oxygen-containing atmosphere as a result of oxidation of the surface of zinc droplets. The gas-phase oxidation leads to the formation of hollow ZnO whiskers on the metal surface, which grow due to the transport of zinc vapor through their channels. It was found that high partial pressures of zinc and atomic oxygen give rise to fractal structures, which appear in a cascade process involving the sequential formation of zinc oxide vapor, ZnO clusters, and cluster aggregates as a result of the cluster-cluster interaction. A deposit of ZnO synthesized on the cathode surface exhibits a columnar structure. 相似文献
998.
B L Sergeev S P Bogovski? T I Ve?debaum R Kh Tanner I N Shevchuk 《Eksperimental?nai?a onkologii?a》1985,7(5):27-30
The UV irradiation (lambda = 362 nm) of aflatoxin B1 (AfB1) dissolved in water resulted in the formation of an oxidized product. The process was not inhibited by ionol, a routine inhibitor of the radical processes. The oxidized product was not found in the system where AfB1 was metabolized by the 3-methylcholanthrene-activated rat liver microsomes. It is suggested that the product is identical with 2,3-dihydrodiol of AfB1. 相似文献
999.
Translated from Atomnaya Énergiya, Vol. 66, No. 5, pp. 321–324, May, 1989. 相似文献
1000.
L. I. Sokolik 《Measurement Techniques》1989,32(10):956-957
Translated from Izmeritel'naya Tekhnika, No. 10, pp. 16–17, October, 1989. 相似文献