全文获取类型
收费全文 | 460981篇 |
免费 | 19730篇 |
国内免费 | 1373篇 |
专业分类
电工技术 | 8413篇 |
综合类 | 322篇 |
化学工业 | 79127篇 |
金属工艺 | 17169篇 |
机械仪表 | 14577篇 |
建筑科学 | 10599篇 |
矿业工程 | 2214篇 |
能源动力 | 12774篇 |
轻工业 | 38542篇 |
水利工程 | 4736篇 |
石油天然气 | 8043篇 |
武器工业 | 22篇 |
无线电 | 56324篇 |
一般工业技术 | 97377篇 |
冶金工业 | 81650篇 |
原子能技术 | 9296篇 |
自动化技术 | 40899篇 |
出版年
2021年 | 4749篇 |
2020年 | 4858篇 |
2019年 | 7437篇 |
2018年 | 10237篇 |
2017年 | 10404篇 |
2016年 | 11424篇 |
2015年 | 8569篇 |
2014年 | 11519篇 |
2013年 | 26530篇 |
2012年 | 15328篇 |
2011年 | 18724篇 |
2010年 | 15641篇 |
2009年 | 16990篇 |
2008年 | 16878篇 |
2007年 | 16284篇 |
2006年 | 14465篇 |
2005年 | 12819篇 |
2004年 | 12236篇 |
2003年 | 12016篇 |
2002年 | 11371篇 |
2001年 | 11033篇 |
2000年 | 10398篇 |
1999年 | 10279篇 |
1998年 | 26124篇 |
1997年 | 17985篇 |
1996年 | 13605篇 |
1995年 | 10010篇 |
1994年 | 8767篇 |
1993年 | 8854篇 |
1992年 | 6232篇 |
1991年 | 5827篇 |
1990年 | 5769篇 |
1989年 | 5389篇 |
1988年 | 5117篇 |
1987年 | 4493篇 |
1986年 | 4358篇 |
1985年 | 4888篇 |
1984年 | 4485篇 |
1983年 | 4034篇 |
1982年 | 3719篇 |
1981年 | 3809篇 |
1980年 | 3532篇 |
1979年 | 3371篇 |
1978年 | 3373篇 |
1977年 | 3969篇 |
1976年 | 5377篇 |
1975年 | 2880篇 |
1974年 | 2684篇 |
1973年 | 2764篇 |
1972年 | 2286篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
Results of a numerical investigation of heat and mass transfer at the initial stage of fire within a building in combustion of kerosene, carried out with the use of a three-dimensional mathematical field model, are presented. A comparison of the distribution of the averaged temperatures and velocities along the vertical axis of the convective column and of the mass rates of gas flows through an open opening with the experimental data has been made. Substantial three-dimensional inhomogeneities of the velocities and the temperatures in the near-ceiling layer have been revealed. It has been established that near the opening there is a critical separation zone which influences significantly the parameters of natural gas transfer. 相似文献
962.
The behavior of two series of concrete slabs exposed to sulfate-bearing soils was investigated by a numerical model called
STADIUM. In addition to the diffusion of ions and moisture, the model also accounts for the effects of dissolution/precipitation
reactions on the transport mechanisms. The simulations yielded by the model were compared to the actual degradation of the
slabs after 8 years of exposure. The microstructural alterations of concrete resulting from the penetration of magnesium,
chloride and sulfate ions were studied by backscatter mode scanning electron microscope observations and energy-dispersive
X-ray analyses. The comparison of both series of data indicates that the model can reliably predict the various features of
the microstructural alterations of concrete.
Editorial Note Laval University (Canada) is a RILEM Titular Member. Prof. J. Marchand was awarded the 2000 Robert L'Hermite Medal. He is Editor in Chief for Concrete Science and Engineering and Associate Editor for Materials and Structures. He participates in RILEM TC 186-ISA ‘Internal Sulfate attack’. 相似文献
Résumé Le comportement de deux séries de dalles sur sol en béton exposées à des sols chimiquement agressifs a été étudié à l'aide d'un code de calcul numérique appelé STADIUM. Ce modèle permet de décrire le transport couplé de l'eau et des ions dans des matériaux poreux non-saturés en prenant en considération l'influence des réactions chimiques. Les résultats des simultations de la dégradation du béton après huit ans d'exposition à des ions chlore, sulfate et magnésium. Les observations ont été réalisées par microscopie électronique à balayage. Des analyses par dispersion des rayons X ont également été effectuées. Les données démontrent clairement que le modèle perment de prédire avec précision le comportement du béton soumis à différents types d'agression chimique.
Editorial Note Laval University (Canada) is a RILEM Titular Member. Prof. J. Marchand was awarded the 2000 Robert L'Hermite Medal. He is Editor in Chief for Concrete Science and Engineering and Associate Editor for Materials and Structures. He participates in RILEM TC 186-ISA ‘Internal Sulfate attack’. 相似文献
963.
S. M. Usherenko L. G. Korshunov O. I. Koval' 《Journal of Engineering Physics and Thermophysics》2002,75(6):1249-1253
Consideration is given to the possibility of controlling the efficiency of the process of superdeep penetration of a high-velocity microstriker flux into metal obstacles due to the employment of ballast elements in the jet and to additional supply of energy in compression by an explosive charge along the external perimeter. 相似文献
964.
O. P. Mikheeva A. I. Sidorov A. S. Khaiikina E. V. Chuguevets 《Technical Physics Letters》2002,28(1):48-49
Experimental data on the pulsed laser radiation confinement in compensated GaAs and ZnSe with deep impurity levels are reported for the laser wavelength λ=1.55 μm and a pulse repetition frequency of up to 100 kHz. It is demonstrated that an increase in the pulse repetition rate is accompanied by a decrease in the energy confinement threshold and by an increase in the radiation attenuation coefficient. These effects are explained by the accumulation of nonequilibrium charge carriers related to a dependence of the recombination time constant on the concentration of free impurity centers. 相似文献
965.
Fusing computing and biology expertise, bioinformatics software provides a powerful tool for organizing and mining the vast amounts of data genetics researchers are accumulating. As life scientists and computational scientists interact to create useful bioinformatics software systems, several themes or lessons recur. We identify seven themes: the nature of biological data; data storage, analysis and retrieval; computational modeling and simulation; biologically meaningful information integration; data mining; image processing and visualization; and closing the loop 相似文献
966.
Adaptive motion control using neural network approximations 总被引:1,自引:0,他引:1
In this paper, we present a new adaptive technique for tracking control of mechanical systems in the presence of friction and periodic disturbances. Radial Basis Functions (RBFs) are used to compensate for the effects of nonlinearly occurring parameters in the friction and periodic disturbance model. Theoretical analysis, such as stability and transient performance, is provided. Furthermore, the performance of the adaptive RBF controller and its non-adaptive counterpart are compared. 相似文献
967.
Consideration was given to the decision making procedures based on the fuzzy messages of experts whose preferences on the set of collective decisions can also be fuzzy. 相似文献
968.
Effect of misalignment on electrical characteristics of ACF joints for flip chip on flex applications 总被引:1,自引:0,他引:1
The effect of misalignment on the electrical properties of anisotropic conductive film (ACF) joints is investigated in this work. It is found that along with the increase of misalignment, the connection resistance of ACF joints increases. When the misalignment in x-direction is less than 5 μm, the increase rate of connection resistance is quite large. Then, along with the severity of misalignment, the increase rate becomes smaller. Finally, when the misalignment is close to 20 μm, the increase rate rises again. The Holm's electric contact theory is used for understanding the connection resistance variation. On the other hand, with the increase of misalignment in x-direction, the insulation resistance between ACF joints decreases. If the misalignment exceeded 10 μm, the decrease is prominent for the Ni particle ACF joints. This phenomenon can be explained by the effect of dielectric damage of the epoxy.Computer programs are also developed to calculate the variation of the probability of open and shorting after misalignment and predicate the maximum misalignment tolerance. The results show that the open and shorting probability increase abruptly after misalignment. On the view of pad parameters, the open probability is mainly related to the pad area, while the pads gap is critical to the shorting probability. Large pads gap (small pad width) can reduce the shorting probability obviously. On the other hand, enlarging the pad area by increasing pad length decreases the open probability significantly. So comparing to square shape pad, rectangle shape pad can reduce the failure probability greatly. 相似文献
969.
970.