全文获取类型
收费全文 | 475647篇 |
免费 | 4391篇 |
国内免费 | 1532篇 |
专业分类
电工技术 | 8090篇 |
综合类 | 599篇 |
化学工业 | 72038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 | 105852篇 |
冶金工业 | 76057篇 |
原子能技术 | 15614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 | 20066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 | 11250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 | 8797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 | 5554篇 |
1977年 | 5879篇 |
1976年 | 7167篇 |
1975年 | 4912篇 |
1974年 | 4968篇 |
1973年 | 5014篇 |
1972年 | 4350篇 |
1971年 | 3945篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
The effects of parameter uncertainty on optimal policy have been a matter of interest for academics, and even for some policymakers,
for a long time. Two lines of literature have developed analytical results on this matter. The first line uses static models
and the second dynamic models. In this dynamic line most of the results are confined to models with a single state and a single
control variable.
In this paper we want to encourage the analysis of more general dynamic cases. To do so, the results in the dynamic line are
extended from one-state and one-control finite horizon models to models with a pair of control variables. We then discuss
some of the hurdles which must be surmounted for the results to be made more general and suggests some lines for further research.
JEL classification: C61; E61 相似文献
52.
A method of measuring and identifying the static parameters of a bipolar transistor is considered. The characteristic of the transistor, from which the parameters of the model are determined, is chosen depending on what group the calculated parameters belong to. The characteristics are measured in such a way that the equations of the model describing them can be reduced to the simplest form. 相似文献
53.
M. N. Levin A. V. Tatarintsev V. A. Makarenko V. R. Gitlin 《Russian Microelectronics》2006,35(5):329-336
A model is formulated that describes how radiation-induced charge accumulates in the gate oxide of a MOS structure and how it decays through tunneling and thermal emission. The model is used in a numerical analysis of the x-ray or UV adjustment of threshold voltage in MOS-circuit manufacture. The limits of this process technique are evaluated. 相似文献
54.
A. V. Butko A. A. Klimov S. A. Nikitov Yu. A. Filimonov 《Journal of Communications Technology and Electronics》2006,51(8):944-947
The magneto-optical Kerr effect for red (628 nm) and green (532 nm) light is used to study magnetization processes in 2D magnonic crystals obtained by etching pits with the diameter D ≈ 32 μm to a depth of t ≤ 2 μm in a 16.1-μm-thick film of yttrium iron garnet (YIG). Hysteresis loops obtained in the case of the inplane crystal magnetization at 628 nm are characterized by lower saturation fields H s and higher remanent magnetizations than those obtained at 532 nm, a result that is attributed to different absorption coefficients of the YIG film at these wavelengths. This difference between the magnetization curves reflects the fact that the magnonic-crystal surface probed with the green light makes a greater contribution to the magneto-optical Kerr effect. Therefore, the green light is more sensitive to the demagnetizing fields, which govern magnetization processes in the magnonic crystals. 相似文献
55.
This article, the first of three articles on the synthesis of rice processing plants, focuses on the development of simplified mathematical models necessary for use in optimizing rice processing plants. The second concentrates on the optimal synthesis of a rice plant and the third on the sensitivity of the optimization to uncertainty in model parameters. Existing models for rice processing unit operations are not suitable for flowsheet optimization and new models need to be developed to overcome numerical difficulties that occur in optimization applications, specifically in mixed integer nonlinear programming (MINLP) applications. Simplified models of the drying, cooling, and tempering units are developed. In addition head rice yield models, used as a quality indicator, energy consumption, and economic models were also developed. Naturally, the new models exhibit some mismatch with respect to the existing models from which they were developed. However, a sensitivity analysis, presented in Part III, has shown that the optimal flowsheet structure was not sensitive to a lack of fit between the simplified and complex models. The simplified models were found adequate to be appropriate for use at the synthesis stage. 相似文献
56.
The electrical properties and microstructure of (Ba,Y)TiO3 PTCR ceramics were studied. The results indicate that the Mn ions increase the intergranular barrier height and produce a high-resistance layer on the grain surface. The temperature-dependent resistances of the grain bulk, surface layer, and grain boundaries, the temperature coefficient of resistance, and the magnitude of the varistor effect were assessed as a function of Mn content. 相似文献
57.
The paper presents an improved statistical analysis of the least mean fourth (LMF) adaptive algorithm behavior for a stationary Gaussian input. The analysis improves previous results in that higher order moments of the weight error vector are not neglected and that it is not restricted to a specific noise distribution. The analysis is based on the independence theory and assumes reasonably slow learning and a large number of adaptive filter coefficients. A new analytical model is derived, which is able to predict the algorithm behavior accurately, both during transient and in steady-state, for small step sizes and long impulse responses. The new model is valid for any zero-mean symmetric noise density function and for any signal-to-noise ratio (SNR). Computer simulations illustrate the accuracy of the new model in predicting the algorithm behavior in several different situations. 相似文献
58.
Hambleton P.J. Ng B.K. Plimmer S.A. David J.P.R. Rees G.J. 《Electron Devices, IEEE Transactions on》2003,50(2):347-351
The nonlocal enhancement in the velocities of charge carriers to ionization is shown to outweigh the opposing effects of dead space, increasing the avalanche speed of short avalanche photodiodes (APDs) over the predictions of a conventional local model which ignores both of these effects. The trends in the measured gain-bandwidth product of two short InAlAs APDs reported in the literature support this result. Relatively large speed benefits are predicted to result from further small reductions in the lengths of short multiplication regions. 相似文献
59.
S. V. Doronin 《Chemical and Petroleum Engineering》2006,42(7-8):461-464
Current features are considered in the calculation of carrying capacities for constructions in engineering plant (EP). Methods
and algorithms are described for EP calculations with comprehensive incorporation of the effects from technological and working
defects on the behavior of structures under standard and emergency conditions.
__________
Translated from Khimicheskoe i Neftegazovoe Mashinostroenie, No. 8, pp. 38–40, August, 2006. 相似文献
60.