全文获取类型
收费全文 | 786199篇 |
免费 | 8570篇 |
国内免费 | 1717篇 |
专业分类
电工技术 | 14267篇 |
综合类 | 655篇 |
化学工业 | 122343篇 |
金属工艺 | 34464篇 |
机械仪表 | 25545篇 |
建筑科学 | 18262篇 |
矿业工程 | 5539篇 |
能源动力 | 19525篇 |
轻工业 | 63198篇 |
水利工程 | 9272篇 |
石油天然气 | 18485篇 |
武器工业 | 48篇 |
无线电 | 83933篇 |
一般工业技术 | 160631篇 |
冶金工业 | 133185篇 |
原子能技术 | 18493篇 |
自动化技术 | 68641篇 |
出版年
2021年 | 6697篇 |
2019年 | 6359篇 |
2018年 | 15169篇 |
2017年 | 15373篇 |
2016年 | 14383篇 |
2015年 | 7767篇 |
2014年 | 12762篇 |
2013年 | 34181篇 |
2012年 | 21032篇 |
2011年 | 30687篇 |
2010年 | 25426篇 |
2009年 | 27216篇 |
2008年 | 27919篇 |
2007年 | 28625篇 |
2006年 | 21066篇 |
2005年 | 20952篇 |
2004年 | 19352篇 |
2003年 | 18829篇 |
2002年 | 17863篇 |
2001年 | 17014篇 |
2000年 | 16326篇 |
1999年 | 16118篇 |
1998年 | 37779篇 |
1997年 | 27596篇 |
1996年 | 21491篇 |
1995年 | 16501篇 |
1994年 | 14944篇 |
1993年 | 14571篇 |
1992年 | 11258篇 |
1991年 | 10987篇 |
1990年 | 10780篇 |
1989年 | 10577篇 |
1988年 | 10173篇 |
1987年 | 9071篇 |
1986年 | 8850篇 |
1985年 | 10132篇 |
1984年 | 9355篇 |
1983年 | 8897篇 |
1982年 | 8031篇 |
1981年 | 8277篇 |
1980年 | 7866篇 |
1979年 | 7925篇 |
1978年 | 7816篇 |
1977年 | 8866篇 |
1976年 | 11241篇 |
1975年 | 7080篇 |
1974年 | 6789篇 |
1973年 | 6876篇 |
1972年 | 5902篇 |
1971年 | 5523篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
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
92.
G. Pfaff 《Inorganic Materials》2003,39(2):123-126
A new class of special effect pigments based on synthetically manufactured silica flakes coated with metal oxides was developed and introduced into the market. Silica flake pigments show extraordinary color effects such as improved interference and strong angle-dependent behavior. They can be used in automotive paints, industrial paints, plastics, and printing inks. 相似文献
93.
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
94.
95.
Removal of gold from basic solutions containing [Au(CN)2]? has been demonstrated using the inherently conducting polymer polypyrrole. Polymers containing sulfonated aromatic dopants have been found to display a significant ability to remove gold from such solutions. Experiments performed in solutions containing both gold and copper cyanide complexes indicate that the recovery process is not highly selective. However, the polypyrroles used display significantly faster rates of gold recovery than activated carbon. © 2003 Society of Chemical Industry 相似文献
96.
Dogandzic A. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2003,49(5):1327-1336
We derive Chernoff bounds on pairwise error probabilities of coherent and noncoherent space-time signaling schemes. First, general Chernoff bound expressions are derived for a correlated Ricean fading channel and correlated additive Gaussian noise. Then, we specialize the obtained results to the cases of space-time-separable noise, white noise, and uncorrelated fading. We derive approximate Chernoff bounds for high and low signal-to-noise ratios (SNRs) and propose optimal signaling schemes. We also compute the optimal number of transmitter antennas for noncoherent signaling with unitary mutually orthogonal space-time codes. 相似文献
97.
G Garrote J
M Cruz H Domínguez J
C Paraj 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2003,78(4):392-398
Non‐isothermal processing of lignocellulosic materials in aqueous media (autohydrolysis reaction) under mild conditions leads to solutions containing valuable chemicals (oligosaccharides, sugars and acetic acid) and other, undesired, compounds (belonging to the extractive and acid‐soluble lignin fractions) which have to be removed in further purification treatments. Liquors obtained by non‐isothermal autohydrolysis of Eucalyptus globulus wood and corncobs under a variety of operational conditions were extracted with ethyl acetate in order to remove non‐saccharide components, and the suitability of the fraction dissolved in the organic phase was assayed for possible utilisation as an antioxidant. The yield and antioxidant activity of ethyl acetate extracts (measured by the α,α‐diphenyl‐β‐picrylhydrazyl (DPPH) radical scavenging capacity) showed a strong dependence on the autohydrolysis conditions. The antioxidant activity of extracts obtained under selected operational conditions compared well with synthetic antioxidants. © 2003 Society of Chemical Industry 相似文献
98.
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
99.
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
100.
R. Murgan F. Razak D. R. Tilley T. Y. Tan J. Osman M. N. A. Halif 《Computational Materials Science》2004,30(3-4):468-473
We derive an expression for transmittivity (TSHG) of second harmonic generation (SHG) signals from a ferroelectric (FE) film. Intensities of up and down fields in the medium are investigated in relation to TSHG. The derivations are made based on undepletion of input fields and nonlinear wave equation derived from the Maxwell equations. We present two cases: film without mirrors and with partial mirrors. Expressions for the newly derived nonlinear susceptibility coefficients of SHG for real crystal symmetry [J. Opt. Soc. Am. B 19 (2002) 2007] are used to get more realistic results. Variations in TSHG with respect to film thickness are illustrated. 相似文献