全文获取类型
收费全文 | 524739篇 |
免费 | 7662篇 |
国内免费 | 1468篇 |
专业分类
电工技术 | 9559篇 |
综合类 | 526篇 |
化学工业 | 78655篇 |
金属工艺 | 19960篇 |
机械仪表 | 15190篇 |
建筑科学 | 12665篇 |
矿业工程 | 2269篇 |
能源动力 | 14516篇 |
轻工业 | 47054篇 |
水利工程 | 5219篇 |
石油天然气 | 9334篇 |
武器工业 | 37篇 |
无线电 | 59910篇 |
一般工业技术 | 101758篇 |
冶金工业 | 103495篇 |
原子能技术 | 10558篇 |
自动化技术 | 43164篇 |
出版年
2022年 | 3159篇 |
2021年 | 4892篇 |
2020年 | 3477篇 |
2019年 | 4554篇 |
2018年 | 7808篇 |
2017年 | 7607篇 |
2016年 | 7932篇 |
2015年 | 5559篇 |
2014年 | 9241篇 |
2013年 | 24065篇 |
2012年 | 14625篇 |
2011年 | 20143篇 |
2010年 | 15798篇 |
2009年 | 17694篇 |
2008年 | 18089篇 |
2007年 | 17775篇 |
2006年 | 15503篇 |
2005年 | 14208篇 |
2004年 | 13599篇 |
2003年 | 13397篇 |
2002年 | 12633篇 |
2001年 | 12830篇 |
2000年 | 11867篇 |
1999年 | 12594篇 |
1998年 | 32811篇 |
1997年 | 22895篇 |
1996年 | 17446篇 |
1995年 | 13033篇 |
1994年 | 11283篇 |
1993年 | 10972篇 |
1992年 | 7913篇 |
1991年 | 7417篇 |
1990年 | 7261篇 |
1989年 | 7013篇 |
1988年 | 6468篇 |
1987年 | 5766篇 |
1986年 | 5655篇 |
1985年 | 6265篇 |
1984年 | 5900篇 |
1983年 | 5170篇 |
1982年 | 4900篇 |
1981年 | 4966篇 |
1980年 | 4705篇 |
1979年 | 4609篇 |
1978年 | 4408篇 |
1977年 | 5334篇 |
1976年 | 6971篇 |
1975年 | 3796篇 |
1974年 | 3550篇 |
1973年 | 3665篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
The work focuses on the synthesis of a red ceramic pigment by inclusion of hematite in a fumed silica matrix with different specific surface areas. Iron(II) sulfate was used as hematite precursor. Mixtures of iron(II) sulfate and fumed silica with different mole ratios were heated at different temperatures from 1000 to 1300 °C for 4 h. 相似文献
942.
We identify the time dependence of temperature of a surface of a long hollow thermosensitive cylinder and its thermal and
thermal stressed states according to the known temperature and strains on the other surface. The posed problem is reduced
to the inverse problem of thermoelasticity. By using the solution of the direct problem of thermoelasticity, we perform the
numerical verification of the proposed procedure of solution of the inverse problem.
__________
Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 43, No. 6, pp. 55–61, November–December, 2007. 相似文献
943.
J. H. Elder S. J. D. Prince Y. Hou M. Sizintsev E. Olevskiy 《International Journal of Computer Vision》2007,72(1):47-66
We address the problem of localizing and obtaining high-resolution footage of the people present in a scene. We propose a
biologically-inspired solution combining pre-attentive, low-resolution sensing for detection with shiftable, high-resolution,
attentive sensing for confirmation and further analysis.
The detection problem is made difficult by the unconstrained nature of realistic environments and human behaviour, and the
low resolution of pre-attentive sensing. Analysis of human peripheral vision suggests a solution based on integration of relatively
simple but complementary cues. We develop a Bayesian approach involving layered probabilistic modeling and spatial integration
using a flexible norm that maximizes the statistical power of both dense and sparse cues. We compare the statistical power
of several cues and demonstrate the advantage of cue integration. We evaluate the Bayesian cue integration method for human
detection on a labelled surveillance database and find that it outperforms several competing methods based on conjunctive
combinations of classifiers (e.g., Adaboost). We have developed a real-time version of our pre-attentive human activity sensor
that generates saccadic targets for an attentive foveated vision system. Output from high-resolution attentive detection algorithms
and gaze state parameters are fed back as statistical priors and combined with pre-attentive cues to determine saccadic behaviour.
The result is a closed-loop system that fixates faces over a 130 deg field of view, allowing high-resolution capture of facial
video over a large dynamic scene. 相似文献
944.
945.
Y. L. Hao R. Yang M. Niinomi D. Kuroda Y. L. Zhou K. Fukunaga A. Suzuki 《Metallurgical and Materials Transactions A》2003,34(4):1007-1012
Alloys for implant devices require improved strength but a reduced Young’s modulus, in order to become mechanically more compatible
with adjacent bone tissues. In this study, a new metastable β-type titanium alloy, Ti-29Nb-13Ta-4.6Zr (wt pct), was subjected to aging treatment to produce different microstructures,
and the resulting mechanical properties, including the Young’s modulus, were measured. The Young’s modulus of this alloy is
found to be sensitive to microstructures generated by various heat treatments. For microstructures varying from (α + β) to (α + β + ω) and (β + ω), the Young’s modulus increases with an accompanying increase in tensile strength and hardness, but decreases in ductility.
The (β + ω) microstructure has a low strength, high modulus, and poor ductility and cannot be used for biomedical applications. For
an (α + β) microstructure, the volume fraction of the phases is shown to be the main factor that determines the mechanical properties. 相似文献
946.
The processes of optical spin orientation and spin relaxation of electrons are treated theoretically for semiconductor quantum wells, in which the spin splitting of the energy spectrum is comparable with the characteristic energy of charge carriers. The density matrix of photoexcited electrons at the instant of optical excitation is obtained in explicit form. A system of kinetic equations describing the behavior of the spin density matrix at an arbitrary relation between the average energy of charge carriers and the spin splitting is derived. It is demonstrated that, upon photoexcitation, a noticeable degree of orientation can be attained only in the pulse mode of operation, when the photoexcitation pulse duration is comparable with the period of spin precession in the field of spin splitting. It is shown that the total spin of the ensemble of electrons exhibits oscillations damping with time; the shape and damping time of the oscillations are sensitive to the parameters of photoexcitation and the spin splitting. 相似文献
947.
M. Mahboubkhah M. J. Nategh S. Esmaeilzade Khadem 《The International Journal of Advanced Manufacturing Technology》2008,38(11-12):1236-1243
Parallel mechanisms have found new applications in machine tool’s as the end effector carrying the spindle or used as the table of the machine. Investigations on the dynamics and especially the vibration behavior of these mechanisms are in the initial stage. The authors developed a vibration model for the hexapod table of milling machines and machining centers and derived the relevant explicit equations. The eigenvalue problem of the upper platform of hexapod was solved to obtain the natural frequencies of the platform. The results have been verified with FEM simulation. The distinguishing features of the hexapod tables from the view point of dynamic behavior have also been concluded. 相似文献
948.
Rajoo R. Lim S.S. Wong E.H. Hnin W.Y. Seah S.K.W. Tay A.A.O. Iyer M. Tummala R.R. 《Advanced Packaging, IEEE Transactions on》2008,31(2):377-385
A wafer level packaging technique has been developed with an inherent advantage of good solder joint co-planarity suitable for wafer level testing. A suitable weak metallization scheme has also been established for the detachment process. During the fabrication process, the compliancy of the solder joint is enhanced through stretching to achieve a small shape factor. Thermal cycling reliability of these hourglass-shaped, stretch solder interconnections has been found to be considerably better than that of the conventional spherical-shaped solder bumps. 相似文献
949.
Effect of Thickness of the p-AlGaN Electron Blocking Layer on the Improvement of ESD Characteristics in GaN-Based LEDs 总被引:1,自引:0,他引:1
Chung-Hsun Jang Sheu J.K. Tsai C.M. Shei S.C. Lai W.C. Chang S.J. 《Photonics Technology Letters, IEEE》2008,20(13):1142-1144
The following letter presents a study regarding GaN-based light-emitting diodes (LEDs) with p-type AlGaN electron blocking layers (EBLs) of different thicknesses. The study revealed that the LEDs could endure higher electrostatic discharge (ESD) levels as the thickness of the AlGaN EBL increased. The observed improvement in the ESD endurance ability could be attributed to the fact that the thickened p-AlGaN EBL may partly fill the dislocation-related pits that occur on the surface of the InGaN-GaN multiple-quantum well (MQW) and that are due to the strain and the low-temperature-growth process. If these dislocation-related pits are not partly suppressed, they will eventually result in numerous surface pits associated with threading dislocations that intersect the InGaN-GaN (MQW), thereby reducing the ESD endurance ability. The results of the experiment show that the ESD endurance voltages could increase from 1500 to 6000 V when the thickness of the p-AlGaN EBL in the GaN LEDs is increased from 32.5 to 130 nm, while the forward voltages and light output powers remained almost the same. 相似文献
950.
Porous carbon nanofibers are synthesized by CVD method from acetylene with use of iron-containing catalysts. Activation of the nanofibers in melted potassium hydroxide results in increasing surface area from initial 300–400 m2 g−1 to 1700 m2 g−1. As follows from XRD data, activated nanofibers do not contain regular packages of graphene layers, but retain high electric conductivity. Deposition of copper improves electrochemical hydrogen storing characteristics of carbon nanofibers. Carbon nanomaterials obtained can be used as hydrogen storing materials in batteries instead of hydride forming metals. 相似文献