全文获取类型
收费全文 | 475654篇 |
免费 | 4391篇 |
国内免费 | 1532篇 |
专业分类
电工技术 | 8091篇 |
综合类 | 599篇 |
化学工业 | 72041篇 |
金属工艺 | 23333篇 |
机械仪表 | 16348篇 |
建筑科学 | 9960篇 |
矿业工程 | 4613篇 |
能源动力 | 10071篇 |
轻工业 | 30159篇 |
水利工程 | 6476篇 |
石油天然气 | 16022篇 |
武器工业 | 68篇 |
无线电 | 49110篇 |
一般工业技术 | 105853篇 |
冶金工业 | 76058篇 |
原子能技术 | 15615篇 |
自动化技术 | 37160篇 |
出版年
2021年 | 4367篇 |
2019年 | 4214篇 |
2018年 | 7812篇 |
2017年 | 8148篇 |
2016年 | 8621篇 |
2015年 | 4940篇 |
2014年 | 8495篇 |
2013年 | 20067篇 |
2012年 | 12818篇 |
2011年 | 16858篇 |
2010年 | 13404篇 |
2009年 | 15237篇 |
2008年 | 15603篇 |
2007年 | 15318篇 |
2006年 | 12864篇 |
2005年 | 11676篇 |
2004年 | 11544篇 |
2003年 | 11251篇 |
2002年 | 10877篇 |
2001年 | 10818篇 |
2000年 | 10413篇 |
1999年 | 10161篇 |
1998年 | 22041篇 |
1997年 | 16256篇 |
1996年 | 12452篇 |
1995年 | 9799篇 |
1994年 | 8798篇 |
1993年 | 8955篇 |
1992年 | 6963篇 |
1991年 | 6895篇 |
1990年 | 6807篇 |
1989年 | 6704篇 |
1988年 | 6338篇 |
1987年 | 5916篇 |
1986年 | 5839篇 |
1985年 | 6344篇 |
1984年 | 5961篇 |
1983年 | 5669篇 |
1982年 | 5271篇 |
1981年 | 5423篇 |
1980年 | 5401篇 |
1979年 | 5353篇 |
1978年 | 5555篇 |
1977年 | 5879篇 |
1976年 | 7168篇 |
1975年 | 4912篇 |
1974年 | 4968篇 |
1973年 | 5015篇 |
1972年 | 4351篇 |
1971年 | 3945篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
K.P. Pipe R.J. Ram 《Photonics Technology Letters, IEEE》2003,15(4):504-506
By measuring the total energy flow from an optical device, we can develop new design strategies for thermal stabilization. Here we present a comprehensive model for heat exchange between a semiconductor laser diode and its environment that includes the mechanisms of conduction, convection, and radiation. We perform quantitative measurements of these processes for several devices, deriving parameters such as a laser's heat transfer coefficient, and then demonstrate the feasibility of thermal probing for the nondestructive wafer-scale characterization of optical devices. 相似文献
12.
The basic methods of verifying continuous automatic belt weighers are described. A comparative analysis of these methods on the basis of experimental studies is made and ways of implementing the results in industry are recommended. 相似文献
13.
L. Gao P. Hrter Ch. Linsmeier J. Gstttner R. Emling D. Schmitt-Landsiedel 《Materials Science in Semiconductor Processing》2004,7(4-6):331
Deposition of Ag films by direct liquid injection-metal organic chemical vapor deposition (DLI-MOCVD) was chosen because this preparation method allows precise control of precursor flow and prevents early decomposition of the precursor as compared to the bubbler-delivery. Silver(I)-2,2-dimethyl-6,6,7,7,8,8,8-heptafluoro-3,5-octanedionato-triethylphosphine [Ag(fod)(PEt3)] as the precursor for Ag CVD was studied, which is liquid at 30 °C. Ag films were grown on different substrates of SiO2/Si and TiN/Si. Argon and nitrogen/hydrogen carrier gas was used in a cold wall reactor at a pressure of 50–500 Pa with deposition temperature ranging between 220 °C and 350 °C. Ag films deposited on a TiN/Si diffusion barrier layer have favorable properties over films deposited on SiO2/Si substrate. At lower temperature (220 °C), film growth is essentially reaction-limited on SiO2 substrate. Significant dependence of the surface morphology on the deposition conditions exists in our experiments. According to XPS analysis pure Ag films are deposited by DLI-MOCVD at 250 °C by using argon as carrier gas. 相似文献
14.
Yu. I. Golovin D. V. Lopatin R. K. Nikolaev A. V. Umrikhin 《Technical Physics Letters》2004,30(5):426-428
The effect of crystal orientation on the photogeneration of free charge carriers was studied for C60 single crystals in a weak magnetic field. The photoconductivity sharply depends on the orientation of magnetic field with
respect to the crystallographic directions, showing a 5–8% increase for seven axes of the C60 crystal. 相似文献
15.
We propose a standardization procedure that provides a convenient, quantitative and reproducible laboratory-based method for measuring the state of polarization (SOP) fluctuations produced by polarization varying devices. This method is based on the SOP distributions generated by commercial polarization scramblers. We show that these devices generate distributions of the maximum change of the SOP (in a given sample time) that follow Rayleigh statistics, which scale linearly with scrambling frequency and the sample time. We use this procedure to measure the SOP fluctuations in a short length of coiled fiber subject to mechanical perturbations. 相似文献
16.
V. G. Deibuk 《Semiconductors》2003,37(10):1151-1155
The miscibility gaps and the critical temperatures of spinodal decomposition of ternary semiconducting Ga-In-Sb, Ga-In-P, and In-As-Sb systems are calculated by taking into account the deformation energy and the effect of plastic relaxation caused by the misfit dislocations. It is shown that taking into consideration elastic energy narrows the ranges of spinodal decomposition and lowers its critical temperature. The introduction of the phenomenological parameter into Matthews-Blakeslee formula makes it possible to reach a satisfactory agreement between theoretically calculated values of critical thickness of epitaxial films and the experimental data. 相似文献
17.
Korolev I. A. Alekseenko N. N. Porodnov B. T. Sapunov V. A. Savel'ev D. V. 《Measurement Techniques》2003,46(9):865-871
The design of a sylphon bellows sensor and the basic circuits of an LC-generator and of a microprocessor unit are presented. An analytical pressure–frequency conversion function and a special method of adjusting the sensor ensure an error of less than 0.05%. The dynamic range is up to 105. The instruments developed cover the ranges 103, 104, and 105 Pa. 相似文献
18.
The application of barrier discharges at atmospheric pressure in air expands on the market of plasma technology, because it is an ecological and cost‐effective alternative to other processes of surface treatment. These plasmas usually consist of a multitude of spatially and temporally localized filaments, whose distribution should be as even as possible for homogeneous treatment. This holds especially for the plasma treatment of sensitive goods such as wool or other textiles. In equipment for continuous pass of material the barrier arrangements often consist of a system cylinder – cylinder or cylinder – plane, whereby the gap width changes locally. Space distribution and intensity of filaments has been investigated by means of short‐time photography and spatially resolved measurement of current distribution and energy distribution derived from it. The local dependency found can be explained by means of a capacitive equivalent circuit. 相似文献
19.
20.
B. Pantchev P. Danesh K. Antonova B. Schmidt D. Grambole J. Baran 《Journal of Materials Science: Materials in Electronics》2003,14(10-12):751-752
The hydrogen content, its depth distribution, and its bonding configuration have been studied in hydrogenated amorphous silicon prepared by plasma-enhanced chemical vapor deposition with hydrogen-diluted silane. Nuclear reaction analysis and infrared spectroscopy were used to determine the total amount of hydrogen and its bonded component, respectively. It has been established that the total concentration of hydrogen does not depend on the film thickness, and has a uniform depth profile. The concentration of bonded hydrogen changes with the film thickness within the measurement accuracy. The data obtained suggest the presence of molecular (non-bonded) hydrogen, uniformly distributed in concentration across the film thickness. 相似文献