全文获取类型
收费全文 | 168518篇 |
免费 | 1173篇 |
国内免费 | 193篇 |
专业分类
电工技术 | 2553篇 |
综合类 | 119篇 |
化学工业 | 26612篇 |
金属工艺 | 9471篇 |
机械仪表 | 5715篇 |
建筑科学 | 3008篇 |
矿业工程 | 1887篇 |
能源动力 | 2703篇 |
轻工业 | 8815篇 |
水利工程 | 2730篇 |
石油天然气 | 8692篇 |
武器工业 | 12篇 |
无线电 | 14492篇 |
一般工业技术 | 38253篇 |
冶金工业 | 27794篇 |
原子能技术 | 6933篇 |
自动化技术 | 10095篇 |
出版年
2018年 | 2977篇 |
2017年 | 3091篇 |
2016年 | 3344篇 |
2015年 | 1672篇 |
2014年 | 2956篇 |
2013年 | 6338篇 |
2012年 | 4311篇 |
2011年 | 5398篇 |
2010年 | 4421篇 |
2009年 | 4894篇 |
2008年 | 4940篇 |
2007年 | 4868篇 |
2006年 | 4141篇 |
2005年 | 3819篇 |
2004年 | 3634篇 |
2003年 | 3520篇 |
2002年 | 3450篇 |
2001年 | 3463篇 |
2000年 | 3361篇 |
1999年 | 3212篇 |
1998年 | 7018篇 |
1997年 | 5148篇 |
1996年 | 3821篇 |
1995年 | 2916篇 |
1994年 | 2593篇 |
1993年 | 2720篇 |
1992年 | 2254篇 |
1991年 | 2304篇 |
1990年 | 2409篇 |
1989年 | 2315篇 |
1988年 | 2313篇 |
1987年 | 2190篇 |
1986年 | 2246篇 |
1985年 | 2292篇 |
1984年 | 2206篇 |
1983年 | 2135篇 |
1982年 | 1980篇 |
1981年 | 2193篇 |
1980年 | 2053篇 |
1979年 | 2269篇 |
1978年 | 2431篇 |
1977年 | 2430篇 |
1976年 | 3095篇 |
1975年 | 2244篇 |
1974年 | 2307篇 |
1973年 | 2342篇 |
1972年 | 2155篇 |
1971年 | 1911篇 |
1970年 | 1701篇 |
1969年 | 1632篇 |
排序方式: 共有10000条查询结果,搜索用时 12 毫秒
831.
Around the world, the electricity industry, which has long been dominated by vertically integrated utilities, is experiencing major changes in the structure of its markets and regulations. Owing to new regulations, it's evolving into a distributed industry in which market forces drive electricity's price. The industry is becoming competitive; a market environment is replacing the traditional centralized-operation approach. This transformation is often called the deregulation of the electricity market. MASCEM, a multiagent simulator system, is a valuable framework for evaluating new rules, new behavior, and new participants in the numerous electricity markets that are moving toward liberalization and competition. 相似文献
832.
I. Lum E. Biro Y. Zhou S. Fukumoto D. R. Boomer 《Metallurgical and Materials Transactions A》2004,35(1):217-226
Electrode pitting was investigated in resistance spot welding of 1.5-mm-thick sheet aluminum alloy 5182 using a medium-frequency
direct-current welder and electrodes with a tip face curvature radius of 50 mm and tip face diameter of 10 mm. Detailed investigation
of the metallurgical interactions between the copper electrode and aluminum alloy sheet was carried out using scanning electron
microscopy/energy-dispersive X-ray spectroscopy (SEM/EDX) and X-ray diffraction (XRD). The results indicated that electrode
degradation, which eventually leads to weld failure, proceeded in four basic steps: aluminum pickup, electrode alloying with
aluminum, electrode tip face pitting, and cavitation. Since pitting and cavitation result from Al pickup and alloying, periodic
electrode cleaning could extend electrode tip life by limiting the buildup of Al on the tip face. This work is part of the
effort to improve electrode tip life in resistance spot welding of aluminum alloys for automotive applications. 相似文献
833.
M. I. El-Kawni H. Okuyucu Z. Aslanoglu Y. Akin Y. S. Hascicek 《Journal of Superconductivity and Novel Magnetism》2003,16(3):533-536
YbBa2Cu3O7?x (YbBCO) thick films were grown on buffered, cube-textured Nickel tapes by sol–gel dip-coating method. Yb-123 films were prepared using solutions of Yb, Ba, and Cu organometallic compounds. A solution-based Gd2O3 buffer layer was deposited by dip-coating process with excellent texture and uniformity. The texture development and surface morphology of the buffer-layer films were examined by X-ray diffraction, pole figures, and ESEM analysis. Microstructure and characterization of Yb-123 films were done by ESEM, EDS, and XRD analysis. T c and J c were conducted by four-wire measurement method 相似文献
834.
We studied the corrosion and corrosion-mechanical resistance of new austenitic high-nitrogen 12Kh18AG18Sh steel for the retaining rings of turbogenerators in aqueous solutions containing chlorides and copper (II) cations. A significant decrease in the corrosion resistance of this steel (P constitutes 0.52–14.50 mm/year) and in its resistance to corrosion cracking and corrosion-fatigue fracture in CuCl2 solutions was established. We also calculated the coefficients of linear parts of the kinetic diagrams of fatigue fracture of the steel under study in air with a humidity of 40% and in 22% NaCl and CuCl2 solutions. 相似文献
835.
A. T. Al-Halhouli M. I. Kilani A. Al-Salaymeh S. Büttgenbach 《Microsystem Technologies》2007,13(7):677-687
This paper investigates the effect of radius ratio, and channel aspect ratio on the flow performance of newly introduced single
and double disk viscous micropumps. A lubrication solution for the flow field, which accounts for both radius and channel
aspect ratios either in single or double disk micropumps was developed and compared with available experimental data and with
an approximate solution which estimates for the flow rate only in single disk pump and neglects channel aspect ratio. Additionally,
a number of 3D numerical models for single and double disk micropumps were built and analyzed using the finite volume method.
Pressure and drag shape factors were introduced to describe the effects of radius and channel aspect ratios on the flow rate.
The values of these factors for the whole range of studied parameters are found analytically and numerically. The error in
estimating the flow rate was found to be less than 10% for r
1 /r
2 > 0.2, and less than 7% for the studied range of h/w. Also, the lubrication solution was found to be in good agreement with the numerical and experimental results. 相似文献
836.
I. A. Lyutarevich 《Journal of Engineering Physics and Thermophysics》2007,80(2):364-369
Results of experimental investigations of the desorption of carbon dioxide from water in a rotor dispersion-film apparatus
are presented. The main factors influencing the volume mass-transfer coefficient in the liquid phase and the efficiency of
mass transfer in this apparatus were determined. A comparative analysis of the apparatus investigated with other analogous
apparatus has been carried out.
__________
Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 80, No. 2, pp. 144–148, March–April, 2007. 相似文献
837.
A. V. Chirkov G. G. Denisov A. N. Kuftin V. E. Zapevalov V. I. Malygin M. A. Moiseev S. Yu. Kornishin 《Technical Physics Letters》2007,33(4):350-352
The results of numerical simulation and experimental investigation of a prototype of a megawatt multifrequency gyrotron for controlled thermonuclear fusion facilities are presented. In experiments, the gyrotron has operated at six frequencies in the range 105–152 GHz with small diffraction losses in the internal quasi-optical system and a high Gaussian mode content in the output beam. 相似文献
838.
This paper presents a comprehensive set of exact stability criteria for Euler columns with an intermediate elastic restraint. A subset of this class of problem is the buckling problem of columns with an intermediate rigid support where the elastic restraint takes on an infinite stiffness. Also, this study reiterates the existence of a critical elastic restraint stiffness in which the buckled mode switches to a higher-buckling mode of the corresponding column without an intermediate support. It is clear that this critical stiffness value exists only when the restraint is placed at the node of the higher-buckling mode and the buckling load associated with this critical stiffness value is the maximum achievable value that can be attained with an intermediate elastic restraint. 相似文献
839.
840.
Carels Robert A.; Cacciapaglia Holly; Pérez-Benítez Carlos I.; Douglass Olivia; Christie Samantha; O'Brien William H. 《Canadian Metallurgical Quarterly》2003,71(4):753
Reports an error in the original article by R. A. Carels et al (Journal of Consulting & Clinical Psychology, 2003[Jun], Vol 71[3], 613-618). On page 615, Lines 18, 20, 22, of Table 1, the data in the rows that read "Tachycardia in min per hr," "Repetitive PVCs per hr," and "PVCs per hr" are incorrectly reported in the n and % columns. They should have been reported in the M and SD columns. The corrected table is provided. (The following abstract of this article originally appeared in record 2003-00756-023.) Ventricular arrhythmia exhibits considerable within-subject variability that cannot be attributed to clinical status alone. This investigation examined the extent to which cardiac arrhythmia was associated with psychological and physical factors assessed during the hour preceding arrhythmic or nonarrhythmic activity. Approximately twice hourly, 46 patients randomly completed a diary assessing mood and physical symptoms during 24-hr electrocardiographic monitoring. Greater negative emotion was associated with increased arrhythmia. Additionally, greater negative emotion was significantly associated with increased arrhythmia among participants in a low left ventricular ejection fraction group (LVEF). However, this relationship between negative emotion and arrhythmia was not... (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献