全文获取类型
收费全文 | 1531465篇 |
免费 | 20592篇 |
国内免费 | 5236篇 |
专业分类
电工技术 | 28573篇 |
技术理论 | 5篇 |
综合类 | 3067篇 |
化学工业 | 231043篇 |
金属工艺 | 56271篇 |
机械仪表 | 44268篇 |
建筑科学 | 39831篇 |
矿业工程 | 8414篇 |
能源动力 | 40101篇 |
轻工业 | 125015篇 |
水利工程 | 15525篇 |
石油天然气 | 25392篇 |
武器工业 | 378篇 |
无线电 | 171080篇 |
一般工业技术 | 286388篇 |
冶金工业 | 308507篇 |
原子能技术 | 28624篇 |
自动化技术 | 144811篇 |
出版年
2021年 | 13299篇 |
2020年 | 10135篇 |
2019年 | 12283篇 |
2018年 | 20049篇 |
2017年 | 19913篇 |
2016年 | 21446篇 |
2015年 | 15258篇 |
2014年 | 24370篇 |
2013年 | 71989篇 |
2012年 | 39002篇 |
2011年 | 54078篇 |
2010年 | 43119篇 |
2009年 | 48138篇 |
2008年 | 49704篇 |
2007年 | 49468篇 |
2006年 | 43805篇 |
2005年 | 39521篇 |
2004年 | 37728篇 |
2003年 | 37262篇 |
2002年 | 35832篇 |
2001年 | 34679篇 |
2000年 | 32964篇 |
1999年 | 34859篇 |
1998年 | 88355篇 |
1997年 | 63089篇 |
1996年 | 49196篇 |
1995年 | 37060篇 |
1994年 | 33111篇 |
1993年 | 32809篇 |
1992年 | 23676篇 |
1991年 | 22196篇 |
1990年 | 22157篇 |
1989年 | 21623篇 |
1988年 | 20485篇 |
1987年 | 18523篇 |
1986年 | 18180篇 |
1985年 | 20994篇 |
1984年 | 19178篇 |
1983年 | 17573篇 |
1982年 | 16352篇 |
1981年 | 16666篇 |
1980年 | 15747篇 |
1979年 | 15558篇 |
1978年 | 14964篇 |
1977年 | 18095篇 |
1976年 | 24379篇 |
1975年 | 13265篇 |
1974年 | 12663篇 |
1973年 | 12797篇 |
1972年 | 10585篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Two types of photo heterojunction bipolar transistor (HBT) to directly down-convert optical signals to electronic signals have been reported in the literature: a conventional photo-HBT in which light penetrates through the area of the base-collector junction and an HBT where light shines through the base-collector edge for higher conversion efficiency. Although the performance in relation to bias conditions has been published, the detailed analyses for identifying the parameters and bias conditions that provide optimum direct down-conversion have not been examined. This paper provides a full explanation of the operation of the down-conversion for both HBT configurations based on low-frequency analyses. Such information is useful for both understanding the nonlinear mechanisms involved and designing for maximum efficiency. In addition, a new circuit has been developed from the basic HBT down-conversion circuit that provides improved performance. 相似文献
62.
To enhance the understanding of the behavior and effects of the precipitation of MnO2 particles in the subsurface generated during in situ chemical oxidation (ISCO) using permanganate, laboratory batch experiments were completed to examine the influence that varied reaction matrix conditions have on the generation and properties of manganese oxides. The conditions examined include organic material type and concentration, permanganate concentration, pH, and the presence of calcium (as a representative divalent cation) in solution. Experimental studies included: (1) spectrophotometric examination of permanganate depletion and manganese oxides generation over time during reactions with trichloroethene; (2) scanning electron microscopy analyses of manganese particle morphology; (3) particle size distribution (filtration) characterization studies; and (4) optical particle sizing and numeration studies. Bench-scale, batch experiments were conducted to focus on fundamental chemical properties affecting particle development under varied potential environmental conditions. The amount of manganese oxides particles that develop, grow, and potentially settle as a result of permanganate ISCO of organic contaminants is a function of the particle size and concentration, the time allowed for particle development, and the impact of matrix conditions on the ability of particles to agglomerate. 相似文献
63.
Thomy V. Dubois L. Vanoverschelde C. Sozanski J.P. Pribetich J. 《IEEE sensors journal》2004,4(6):772-778
This paper describes a novel planar antenna sensor created for the purpose of noninvasive temperature measurements using microwave radiometry. In order to improve radiometric measurements in industrial applications, a new generation of sensors is introduced, composed of a metallic sheet. Simulations based upon the method of moments is used both to design and to determine their electromagnetic performances. This paper also describes a radiometric device using these sensors to measure and control the temperature of food products during deep freezing processes. The results and discussions are presented. 相似文献
64.
65.
Gas/liquid mass transfer has been investigated using a stirred vessel gas/liquid contactor using non‐Newtonian media and carbon dioxide as absorbent and gas phase, respectively. The volumetric mass transfer coefficients at different operational variables have been determined. Non‐Newtonian media (liquid phase) were prepared as aqueous solutions of sodium carboxymethyl cellulose salt. The influence of the rheological properties, polymer concentration, stirring rate, and gas flow rate on mass transfer was studied for these liquid phases. Kinematic viscosity and density experimental data were used to calculate the average molecular weight corresponding to the polymer employed. The Ostwald model has been used to fit the rheological behavior of aqueous solutions of the polymer employed as absorbent phase. Reasonably good agreement was found between the predictions of the proposed models and the experimental data of mass transfer coefficients. 相似文献
66.
Eduardo Freire Teodiano Bastos-Filho Mário Sarcinelli-Filho Ricardo Carelli 《IEEE transactions on systems, man, and cybernetics. Part B, Cybernetics》2004,34(1):419-429
This paper proposes an alternative approach to address the problem of coordinating behaviors in mobile robot navigation: fusion of control signals. Such approach is based on a set of two decentralized information filters, which accomplish the data fusion involved. Besides these two fusion engines, control architectures designed according to this approach also embed a set of different controllers that generate reference signals for the robot linear and angular speeds. Such signals are delivered to the two decentralized information filters, which estimate suitable overall reference signals for the robot linear and angular speeds, respectively. Thus, the background for designing such control architectures is provided by the nonlinear systems theory, which makes this approach different from any other yet proposed. This background also allows checking control architectures designed according to the proposed approach for stability. Such analysis is carried out in the paper, and shows that the robot always reaches its final destination, in spite of either obstacles along its path or the environment layout. As an example, a control architecture is designed to guide a mobile robot in an experiment, whose results allows checking the good performance of the control architecture and validating the design approach proposed as well. 相似文献
67.
68.
On the effect of spatial variances in historical rainfall time series to CSO performance evaluation.
Historical, high-resolution rain series are the backbone of modern combined sewer overflow (CSO) structure design. These rain series are the input to the computational estimation of the performance of the measures with respect to CSO pollution abatement. However, those historical precipitation measurements are available at only a few locations. Frequently rain series have to be used from gauging stations at a significant distance. In order to judge and to compensate for this influence an estimate between rain characteristics and combined sewer outflow (CSO) performance indicators would be useful. In this paper such correlations have been sought for a collection of 37 rain series covering large areas of Europe. It was found that the mean annual rain volume can explain most of the variances for the performance indicators Number of overflows and CSO volume. For explaining the spatial differences in the efficiency of the CSO structure another rain characteristic, i.e. the maximum event with a return period of one year, is to be used. 相似文献
69.
H. L. Du S. R. Rose Z. D. Xiang P. K. Datta X. Y. Li 《Materialwissenschaft und Werkstofftechnik》2003,34(4):421-426
The oxidation/sulphidation behaviour of a Ti‐46.7Al‐1.9W‐0.5Si alloy with a TiAl3 diffusion coating was studied in an environment of H2/H2S/H2O at 850oC. The kinetic results demonstrate that the TiAl3 coating significantly increased the high temperature corrosion resistance of Ti‐46.7Al‐1.9W‐0.5Si. The SEM, EDX, XRD and TEM analysis reveals that the formation of an Al2O3 scale on the surface of the TiAl3‐coated sample was responsible for the enhancement of the corroison resistance. The Ti‐46.7Al‐1.9W‐0.5Si alloy was also modified by Nb ion implantation. The Nb ion implanted and as received sampels were subjected to cyclic oxidation in an open air at 800oC. The Nb ion implantation not only increased the oxidation resistance but also substantially improved the adhesion of scale to the substrate. 相似文献
70.
Nobel A.B. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2003,49(1):83-98
This paper considers several aspects of the sequential prediction problem for unbounded, nonstationary processes under pth power loss /spl lscr//sub p/(u,v)=|u-v|/sup p/, 1
相似文献