全文获取类型
收费全文 | 152626篇 |
免费 | 1323篇 |
国内免费 | 751篇 |
专业分类
电工技术 | 3165篇 |
综合类 | 140篇 |
化学工业 | 21105篇 |
金属工艺 | 10345篇 |
机械仪表 | 8450篇 |
建筑科学 | 3001篇 |
矿业工程 | 1266篇 |
能源动力 | 2648篇 |
轻工业 | 7883篇 |
水利工程 | 1966篇 |
石油天然气 | 3589篇 |
武器工业 | 41篇 |
无线电 | 15096篇 |
一般工业技术 | 36640篇 |
冶金工业 | 18407篇 |
原子能技术 | 3688篇 |
自动化技术 | 17270篇 |
出版年
2022年 | 592篇 |
2021年 | 1034篇 |
2020年 | 795篇 |
2019年 | 890篇 |
2018年 | 10119篇 |
2017年 | 10706篇 |
2016年 | 6664篇 |
2015年 | 1583篇 |
2014年 | 1876篇 |
2013年 | 3910篇 |
2012年 | 5244篇 |
2011年 | 11515篇 |
2010年 | 10647篇 |
2009年 | 9702篇 |
2008年 | 9442篇 |
2007年 | 11464篇 |
2006年 | 2441篇 |
2005年 | 5662篇 |
2004年 | 4035篇 |
2003年 | 3630篇 |
2002年 | 2494篇 |
2001年 | 1841篇 |
2000年 | 1884篇 |
1999年 | 1649篇 |
1998年 | 3798篇 |
1997年 | 2666篇 |
1996年 | 2004篇 |
1995年 | 1572篇 |
1994年 | 1393篇 |
1993年 | 1407篇 |
1992年 | 1033篇 |
1991年 | 1083篇 |
1990年 | 1087篇 |
1989年 | 1063篇 |
1988年 | 955篇 |
1987年 | 887篇 |
1986年 | 889篇 |
1985年 | 938篇 |
1984年 | 788篇 |
1983年 | 770篇 |
1982年 | 676篇 |
1981年 | 691篇 |
1980年 | 663篇 |
1979年 | 648篇 |
1978年 | 622篇 |
1977年 | 774篇 |
1976年 | 931篇 |
1975年 | 581篇 |
1974年 | 552篇 |
1973年 | 545篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
141.
P. G. Muzykov Y. I. Khlebnikov S. V. Regula Y. Gao T. S. Sudarshan 《Journal of Electronic Materials》2003,32(6):505-510
To establish fast, nondestructive, and inexpensive methods for resistivity measurements of SiC wafers, different resistivity-measurement
techniques were tested for characterization of semi-insulating SiC wafers, namely, the four-point probe method with removable
graphite contacts, the van der Pauw method with annealed metal and diffused contacts, the current-voltage (I-V) technique,
and the contactless resistivity-measurement method. Comparison of different techniques is presented. The resistivity values
of the semi-insulating SiC wafer measured using different techniques agree fairly well. As a result, application of removable
graphite contacts is proposed for fast and nondestructive resistivity measurement of SiC wafers using the four-point probe
method. High-temperature van der Pauw and room-temperature Hall characterization for the tested semi-insulating SiC wafer
was also obtained and reported in this work. 相似文献
142.
143.
The main objective of this present study was to evaluate, for a standard mortar, the drying effect on its mechanical behaviour. Numerous uniaxial compression tests were thus performed with loading-unloading cycles. They were carried out on different samples previously preserved under various conditions of conservation: preserved from desiccation, air drying and rapid drying at 60°C. The obtained results showed significant influences of these conditions on the material behaviour (increase in strength, decrease in Young's modulus and Poisson's ratio) and the necessity of taking into account the coupling effects between mechanical—poromechanical behaviours and drying. 相似文献
144.
L. V. Kuzmin V. A. Morozov S. O. Starkov B. A. Khadzhi 《Journal of Communications Technology and Electronics》2006,51(11):1283-1289
The models of indoor multipath propagation of wideband and ultrawideband (UWB) signals are considered. Application of these models is recommended by an IEEE working group. In the framework of one of the models corresponding to the line-of-sight conditions, the algorithms for reception of UWB chaotic signals in the presence of reflection from multiple surfaces (echo signals) are proposed and analyzed. The efficiency of reception techniques is estimated from the viewpoint of the error probabilities. Limitations caused by the specific properties of echo signals are revealed, and the methods for improvement of reception quality are discussed. 相似文献
145.
A multipath structure of a ring resonator is proposed to expand the free spectral range. Simulation work indicates that the multipath ring resonator has 25 GHz-adjacent-channel crosstalk of -41 dB, maximum interchannel crosstalk of -18 dB, and -1 dB bandwidth of 4 GHz for a typical expansion factor of 10. The results show the advantages of characteristics compared with a double-cavity ring resonator and a triple-coupler ring resonator. 相似文献
146.
147.
D. Vignolles D. Smirnov G. Rikken B. Raquet H. Rakoto C. Proust M. Nardone J. Léotin F. Lecouturier M. Goiran O. Drachenko J. M. Broto L. Brossard A. Audouard 《Journal of Low Temperature Physics》2003,133(1-2):97-120
An overview over past and present activities and future developments at the Toulouse pulsed magnetic field facility is given, both as far as technical developments of the infrastructure, as well as low temperature physics performed at the LNCMP are concerned. 相似文献
148.
A mechanism of soldering of an aluminum alloy die casting to a steel die is proposed. A soldering critical temperature is
postulated, at which iron begins to react with aluminum to form an aluminum-rich liquid phase and solid intermetallic compounds.
The liquid joins the die with the casting upon solidification. The critical temperature is determined by the elements in both
the casting alloy and the die material and is equal to the solidus temperature of the resulting alloy. The critical temperature
is used to predict the onset of die soldering, and the local liquid fraction is related to the soldering tendency. Experiments
have been carried out to validate the concept and to determine the critical temperature for die soldering in an iron-aluminum
system. Thermodynamic calculations are used to determine the critical temperature and soldering tendency for the cases of
pure aluminum and a 380 alloy in a steel mold. Factors affecting the soldering tendency are discussed, and methods for reducing
die soldering are suggested. 相似文献
149.
O. A. Lambri J. I. Prez-Landazbal J. A. Cano V. Recarte 《Materials Science and Engineering: A》2004,370(1-2):459-463
Mechanical spectroscopy, neutron diffraction and differential scanning calorimetry (DSC) were performed on commercial Fe–6 wt.% Si alloy after quenching from high temperature. The damping spectrum shows a peak at around 800 K and an associated modulus defect. The modulus shows an increase during the second and subsequent heating runs. In addition, an anomaly in the modulus behavior has been found at around 400 K. Different thermal treatments allows to obtain two different recovery degrees of the quenched-in defects. The influence of the recovery degree on the 800 K internal friction peak and on the anelastic modulus has been evaluated and confirm the validity of the grain boundary mechanism associated to this peak. Experimental results are discussed on the basis of recovery and ordering processes. 相似文献
150.
Valentian A. Thomas O. Vladimirescu A. Amara A. 《Very Large Scale Integration (VLSI) Systems, IEEE Transactions on》2004,12(6):662-669
A simple, yet realistic physics-based model is introduced to describe the subthreshold drain current of a MOSFET taking into account the body- and drain-voltage dependencies, including the short channel effects. This model, verified by SPICE simulations, describes adequately the pseudotriode and pseudosaturation regions of MOS transistors operated below V/sub T/. It can be applied for predicting bulk- or partially depleted (PD) SOI CMOS circuit operation. Analytical expressions derived for the logic switching threshold and delay are applied to predict the performance of CMOS-SOI inverters. 相似文献