全文获取类型
收费全文 | 470573篇 |
免费 | 6182篇 |
国内免费 | 1737篇 |
专业分类
电工技术 | 8559篇 |
综合类 | 378篇 |
化学工业 | 68612篇 |
金属工艺 | 16472篇 |
机械仪表 | 13664篇 |
建筑科学 | 11989篇 |
矿业工程 | 1382篇 |
能源动力 | 13370篇 |
轻工业 | 45738篇 |
水利工程 | 4016篇 |
石油天然气 | 4991篇 |
武器工业 | 20篇 |
无线电 | 61863篇 |
一般工业技术 | 88753篇 |
冶金工业 | 90505篇 |
原子能技术 | 7867篇 |
自动化技术 | 40313篇 |
出版年
2021年 | 3733篇 |
2020年 | 2768篇 |
2019年 | 3353篇 |
2018年 | 5495篇 |
2017年 | 5549篇 |
2016年 | 5902篇 |
2015年 | 4120篇 |
2014年 | 7085篇 |
2013年 | 21907篇 |
2012年 | 12013篇 |
2011年 | 16827篇 |
2010年 | 13301篇 |
2009年 | 15069篇 |
2008年 | 15937篇 |
2007年 | 15786篇 |
2006年 | 14297篇 |
2005年 | 12821篇 |
2004年 | 12409篇 |
2003年 | 12530篇 |
2002年 | 11538篇 |
2001年 | 12326篇 |
2000年 | 11279篇 |
1999年 | 12204篇 |
1998年 | 30890篇 |
1997年 | 21394篇 |
1996年 | 16212篇 |
1995年 | 12255篇 |
1994年 | 10791篇 |
1993年 | 10676篇 |
1992年 | 7524篇 |
1991年 | 7187篇 |
1990年 | 6902篇 |
1989年 | 6547篇 |
1988年 | 6391篇 |
1987年 | 5275篇 |
1986年 | 5126篇 |
1985年 | 5978篇 |
1984年 | 5373篇 |
1983年 | 5108篇 |
1982年 | 4682篇 |
1981年 | 4680篇 |
1980年 | 4436篇 |
1979年 | 4104篇 |
1978年 | 3795篇 |
1977年 | 4555篇 |
1976年 | 6079篇 |
1975年 | 3178篇 |
1974年 | 3060篇 |
1973年 | 3074篇 |
1972年 | 2501篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
An analysis of a wide rectangular radiating slot excited by a microstrip line is described. Coupled integral equations are formulated to find the electric current distribution on the feed line and the electric field in the aperture. The solution is based on the method of moments and using the space domain Sommerfeld-type Green's function. The information about the input impedance or reflection coefficient is extracted from the electric current distribution on the microstrip line utilizing the matrix pencil technique. The theoretical analysis is described and data are presented and compared with other theoretical and experimental results 相似文献
972.
Hulfachor R.B. Ellis-Monaghan J.J. Kim K.W. Littlejohn M.A. 《Electron Devices, IEEE Transactions on》1996,43(4):661-663
A comprehensive Monte Carlo simulator is employed to investigate nonlocal carrier transport in 0.1 μm n-MOSFET's under low-voltage stress. Specifically, the role of electron-electron (e-e) interactions on hot electron injection is explored for two emerging device designs biased at a drain voltage Vd considerably less than the Si/SiO2 injection barrier height φb. Simulation of both devices reveal that 1) although qVd<φb, carriers can obtain energies greater than φb, and 2) the peak for electron injection is displaced approximately 20 nm beyond the peak in the parallel channel electric field. These phenomena constitute a spatial retardation of carrier heating that is strongly influenced by e-e interactions near the drain edge. (Virtually no injection is observed in our simulations when e-e scattering is not considered.) Simulations also show that an aggressive design based on larger dopant atoms, steeper doping gradients, and a self-aligned junction counter-doping process produces a higher peak in the channel electric field, a hotter carrier energy distribution, and a greater total electron injection rate into the oxide when compared to a more conventionally-doped design. The impact of spatially retarded carrier heating on hot-electron-induced device degradation is further examined by coupling an interface state distribution obtained from Monte Carlo simulations with a drift-diffusion simulator. Because of retarded carrier heating, the interface states are mainly generated further over the drain region where interface charge produces minimal degradation. Thus, surprisingly, both 0.1 μm n-MOSFET designs exhibit comparable drain current degradation rates 相似文献
973.
Ashok K. Vijh 《Drying Technology》1995,13(1):215-224
An attempt is made to elucidate the electrochemical aspects of the electroosmotic dewatering (EOD) of clays as reported in some recent work, especially that on interrupted DC power electroosmotic dewatering published by Rabie, Mujumdar and Weber (2). These authors showed that the dewatering by EOD stops after the DC power has been on for several minutes or hours; on interruption of their power and on short-circuiting of the electrodes, conditions can be created again for some further dewatering by DC power EOD. This discovery, of Rabie et al. is interpreted as a fuel cell effect and it is shown that it affords clues to several other electrochemical strategies for the possible enhancement of the efficiency of the EOD by DC power.
Further, the open circuit potentials observed by Rabie et al. (2) on the interruption of DC power are given an electrochemical interpretation which leads to quantitative estimates in agreement with the experimental values. 相似文献
Further, the open circuit potentials observed by Rabie et al. (2) on the interruption of DC power are given an electrochemical interpretation which leads to quantitative estimates in agreement with the experimental values. 相似文献
974.
J Lorenz K Wilhelm M Kessler C Peschel U Schwulera R Lissner WG Struff E Huland C Huber WE Aulitzky 《Canadian Metallurgical Quarterly》1996,2(7):1115-1122
Safety, local and systemic immunomodulation, and tumor response to treatment with aerosolized natural interleukin 2 (nIL-2) applied five times a day were studied in a Phase I trial in 16 patients with pulmonary malignancies refractory to conventional therapy. The toxicity of inhaled nIL-2 was different from that observed after systemic administration. Reversible airway irritation causing a nonproductive cough represented the dose-limiting toxicity. Mild to moderate reduction of the vital capacity and forced expiratory volume (FEV1) with minor effects on relative FEV1, peak expiratory flow, airway resistance, and PaO2 was experienced by individual patients. In 14 patients suffering from pulmonary metastases due to renal cell cancer, one durable complete response, one partial response, and one mixed response were observed. Inhalation of nIL-2 aerosol resulted in a dose-dependent expansion of pulmonary immunocompetent cells in bronchoalveolar lavage fluid. Posttreatment bronchoalveolar lavage showed an activated lymphocyte phenotype with increased HLA-DR expression. The only systemic biological effect detectable in peripheral blood was a marked increase of soluble interleukin 2 receptor serum levels. We conclude that treatment with aerosolized nIL-2 is an effective means for site-specific immunomodulation and deserves further investigation for the treatment of malignant and inflammatory lung disease. 相似文献
975.
976.
The mechanism of “475°C embrittlement” of a duplex stainless steel was investigated using finite element modelling of the stress distribution at brittle fracture initiation. Brittle fracture initiated at a critical shear stress, which increased with ferrite hardness. The fracture stress was affected by the duplex microstructure. Fracture was nucleated by deformation twins, which were identified using electron back-scatter diffraction. The ductile-to-brittle fracture transition was sensitive to age-hardening and could be described simply by the effect of age-hardening and test temperature on the yield stress. 相似文献
977.
Zinc sulphide thin film electroluminescent devices doped with Mn or Tb have been produced on p-type Si substrates using a process in which doped zinc oxide films are deposited by a sol-gel drain coating method from a solution of zinc acetate containing a manganese or terbium dopant. The films are then converted to ZnS by heating them in an atmosphere containing hydrogen sulphide which replaces the oxygyn with sulphur. The composition, crystalline structure and optical properties of films have shown that complete conversion from the oxide to the sulphide takes place. The luminescent characteristics of the devices so produced have been measured as a function of the doping concentrations, film thickness, insulator thickness and driving voltage and frequency. It has been found that yellow or green luminescence can be obtained using Mn or Tb doping respectively. 相似文献
978.
Kepko E.L. Khurana K.K. Kivelson M.G. Elphic R.C. Russell C.T. 《IEEE transactions on magnetics》1996,32(2):377-385
Cluster introduces a new generation of spacecraft that will measure the spatial gradients of the magnetic field in the Earth's magnetosphere. As gradients require knowledge of differences, small errors resulting from an inadequate knowledge of the orientations, zero levels and the scale factors of the magnetometer sensors affect the calculation of field gradients disproportionately and must be removed with high accuracy. We show that twelve calibration parameters are required for each of the spacecraft (for a total of 48 for the four spacecraft) to correctly infer the measured magnetic fields at each of the spacecraft. By application of a Fourier transform technique, some of the parameters can be recovered. We show that errors in eight of the twelve calibration parameters generate coherent monochromatic signals at the first and the second harmonics of the spin frequency in the despun data. We relate the real and the imaginary parts of the monochromatic signals to the eight calibration parameters. We then present a least squares scheme that improves the eight calibration parameters by iteration until the power of the coherent signal superimposed above the broad-band background is minimized 相似文献
979.
J. H. Edgar C. A. Carosella C. R. Eddy Jr D. T. Smith 《Journal of Materials Science: Materials in Electronics》1996,7(4):247-253
The effects of nitrogen-beam voltage on the structure, stress, energy band gap and hardness of AIN thin films deposited on Si (111), Si (100) and sapphire (0001) by ion beam assisted deposition (IBAD) are reported. As the nitrogen-beam voltage was increased from 50 to 200 V, the stress and disorder in the AIN films increased as determined by X-ray diffraction, FTIR and Raman spectroscopy. The preferred orientation of the film's c-axis changed from completely normal to the film at 100 V, to a mixture of normal and in the plane of the film at 200 V. For AIN films deposited under the same conditions, the films were more highly oriented on sapphire (0001) than in Si (111). The hardness of the films increased from 18.2 to 23.7 GPa with the nitrogen-beam voltage, and possible reasons for this change in hardness are considered. 相似文献
980.