全文获取类型
收费全文 | 59457篇 |
免费 | 3832篇 |
国内免费 | 2588篇 |
专业分类
电工技术 | 2207篇 |
技术理论 | 1篇 |
综合类 | 3080篇 |
化学工业 | 14098篇 |
金属工艺 | 6468篇 |
机械仪表 | 2876篇 |
建筑科学 | 1404篇 |
矿业工程 | 682篇 |
能源动力 | 1818篇 |
轻工业 | 3126篇 |
水利工程 | 217篇 |
石油天然气 | 2367篇 |
武器工业 | 439篇 |
无线电 | 6660篇 |
一般工业技术 | 7749篇 |
冶金工业 | 2020篇 |
原子能技术 | 1284篇 |
自动化技术 | 9381篇 |
出版年
2024年 | 195篇 |
2023年 | 775篇 |
2022年 | 1658篇 |
2021年 | 1807篇 |
2020年 | 1416篇 |
2019年 | 1173篇 |
2018年 | 1058篇 |
2017年 | 1502篇 |
2016年 | 1825篇 |
2015年 | 2074篇 |
2014年 | 3016篇 |
2013年 | 3095篇 |
2012年 | 3439篇 |
2011年 | 5260篇 |
2010年 | 4106篇 |
2009年 | 4473篇 |
2008年 | 3842篇 |
2007年 | 4078篇 |
2006年 | 3577篇 |
2005年 | 3052篇 |
2004年 | 2564篇 |
2003年 | 2515篇 |
2002年 | 2171篇 |
2001年 | 1436篇 |
2000年 | 1167篇 |
1999年 | 972篇 |
1998年 | 754篇 |
1997年 | 616篇 |
1996年 | 440篇 |
1995年 | 333篇 |
1994年 | 294篇 |
1993年 | 247篇 |
1992年 | 234篇 |
1991年 | 140篇 |
1990年 | 133篇 |
1989年 | 77篇 |
1988年 | 54篇 |
1987年 | 55篇 |
1986年 | 42篇 |
1985年 | 45篇 |
1984年 | 38篇 |
1983年 | 18篇 |
1982年 | 21篇 |
1981年 | 16篇 |
1980年 | 18篇 |
1979年 | 11篇 |
1977年 | 8篇 |
1974年 | 7篇 |
1959年 | 5篇 |
1951年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
文章通过对五口井的现场应用介绍,阐述了快速色谱分析技术在油气层识别和解释方面的准确性,探讨了该技术在薄油气层的发现和评价、快速钻进条件下油气层的发现、对油气层全烃组份变化的统一、水平井的地质导向以及排除钻井液添加荆对油气显示的影响五个方面的优势,从而论证了快速色谱分析技术在油气勘探中的应用价值。 相似文献
92.
本文介绍了HSDPA的发展背景,针对HSDPA的主要技术特点,依据市场发展规划、用户需求等方面对HSDPA部署进行探讨,并对HSDPA的覆盖与容量方面进行规划分析. 相似文献
93.
Finite sample properties of estimators of spatial autoregressive models with autoregressive disturbances 总被引:1,自引:0,他引:1
The article investigates the finite sample properties of estimators for spatial autoregressive models where the disturbance
terms may follow a spatial autoregressive process. In particular we investigate the finite sample behavior of the feasible
generalized spatial two-stage least squares (FGS2SLS) estimator introduced by Kelejian and Prucha (1998), the maximum likelihood
(ML) estimator, as well as that of several other estimators. We find that the FGS2SLS estimator is virtually as efficient
as the ML estimator. This is important because the ML estimator is computationally burdensome, and may even be forbidding
in large samples, while the FGS2SLS estimator remains computationally feasible in large samples.
Received: 20 January 2001 / Accepted: 31 August 2001 相似文献
94.
ZnO-based varistor samples were prepared by the direct mixing of the constituent phases (DMCP) and sintering at 1100 °C for 2 h. The influence of the starting powder mixture's composition – the amounts of the pre-reacted varistor compounds and their composition – and its preparation, either with or without mechano-chemical activation (MCA), on the microstructure, phase composition and electrical characteristics of the varistor samples was studied. It showed that MCA improved the density and microstructural homogeneity of the varistor samples. MCA strongly affected the grain growth: it enhanced the nucleation of inversion boundaries (IBs) in the ZnO grains and the IBs-induced grain-growth mechanism resulted in uniform grain growth and hence a microstructure with smaller ZnO grains and a narrower grain size distribution. The final phase composition of the samples prepared by the DMCP method mainly depended on the presence of varistor dopants that can prevent the formation of the pyrochlore phase, especially Cr2O3, while MCA can affect it mostly by providing a homogeneous distribution of those dopants. The DMCP varistor samples prepared with MCA had much better current–voltage characteristics than the samples of the same composition prepared from unactivated powders. 相似文献
95.
Sun-Jung Kim Pyeong-Seok Cho Jong-Heun Lee Chong-Yun Kang Jin-Sang Kim Seok-Jin Yoon 《Ceramics International》2008,34(4):827-831
Various compositions of gas sensing films were prepared by the combinatorial deposition of SnO2, ZnO, and WO3 sol solutions and their gas sensing behaviors were investigated. The film composition could be manipulated conveniently via the alternate dropping of different oxide sol solutions. From the correlation between film compositions and gas sensitivities, the selective detection of C2H5OH and CH3COCH3 in the presence of CO, C3H8, H2, and NO2 could be attained. In addition, the discrimination between C2H5OH and CH3COCH3, which is a challenging issue due to their similar chemical nature, becomes possible. This research demonstrates the precise design of the sensor-material composition for the selective gas detection via the combinatorial approach. 相似文献
96.
Heidi Bernas Arie J. Plomp Johannes H. Bitter Dmitry Yu. Murzin 《Catalysis Letters》2008,120(1-2):8-13
The density functional theory (DFT/B3LYP) calculations were applied to investigate the interaction of a Pt6 particle with the ZSM-5 zeolite framework. The electronic structure of the metal particle is strongly affected by the interaction with basic framework oxygens and acid sites of the zeolite support. Adsorption on basic sites (Eads = 6 kcal/mol) favors the formation of the electron enriched metal cluster. Interaction of the platinum cluster with the acid site characterized by stabilization energy of 47 kcal/mol results in oxidation of the metal particle and suppression of Brønsted acidity of the support. The hypothesis is put forward that the oxidized platinum particle can function as an active site for the alkane isomerisation on platinum supported high silica zeolites. 相似文献
97.
The purpose of this study is to apply continuum damage mechanics – introduced through the concept of fabric tensors – to composite materials within the framework of the theory of elasticity. A directional data model of damage mechanics for composite materials will be developed using fabric tensors. The introduction of fabric tensors into the analysis of damage of composite materials will allow for an enhanced and better understood physical meaning of damage. The micromechanical approach will be used here to relate the damage effect through fabric tensors to the behavior of composite materials. In this approach, damage mechanics is introduced separately to the constituents of the composite material through different constituents’ damage effect tensors. The damaged properties of the composite system as a whole can then be obtained by proper homogenization of the damaged properties of the constituents.
The derivation of a generalized formulation of damage evolution will be shown here in a mathematically consistent manner that is based on sound thermodynamic principles. Numerical examples will be presented to show applicability. In addition, damage evolution for the one-dimensional tension case is also illustrated. 相似文献
98.
M. Jayasankar 《Materials Letters》2007,61(3):790-793
Formation of aluminium titanate (AT) has been achieved at low temperature through sol-gel process using boehmite and titanium hydroxide as precursors by controlling the particle size at nanoscale followed by in-situ peptisation. The formations of AT phase, particle size distributions, sintering and thermal expansion characteristics, and microstructural features have been reported. DTA and XRD analysis have been performed to confirm the formation of AT. A 94% relative density was obtained for aluminium titanate sintered at 1550 °C with controlled grain size in the range of 2-3 μm. 相似文献
99.
DSP与PC间的数据通讯 总被引:1,自引:0,他引:1
DSP由于具有高性能和灵活可编程的优点而得到广泛的应用。文章给出了用PC机作主机 ,DSP作从机来实现DSP与PC机间有效、可靠通讯的实现方法。同时通过一个数据传输程序的例子来详细阐述如何使用VB6.0专业版作为开发工具 ,并利用DSP中的SCI(SerialCommunicationInter face)模块来实现DSP与微机间的数据传递方法。 相似文献
100.