全文获取类型
收费全文 | 287959篇 |
免费 | 5790篇 |
国内免费 | 3061篇 |
专业分类
电工技术 | 6594篇 |
技术理论 | 1篇 |
综合类 | 1837篇 |
化学工业 | 39818篇 |
金属工艺 | 13392篇 |
机械仪表 | 9002篇 |
建筑科学 | 7838篇 |
矿业工程 | 1484篇 |
能源动力 | 7856篇 |
轻工业 | 23377篇 |
水利工程 | 2795篇 |
石油天然气 | 4578篇 |
武器工业 | 253篇 |
无线电 | 36623篇 |
一般工业技术 | 54869篇 |
冶金工业 | 57196篇 |
原子能技术 | 5753篇 |
自动化技术 | 23544篇 |
出版年
2022年 | 2006篇 |
2021年 | 2879篇 |
2020年 | 2140篇 |
2019年 | 2461篇 |
2018年 | 3734篇 |
2017年 | 3745篇 |
2016年 | 3896篇 |
2015年 | 3262篇 |
2014年 | 5028篇 |
2013年 | 13103篇 |
2012年 | 8077篇 |
2011年 | 10992篇 |
2010年 | 8978篇 |
2009年 | 10290篇 |
2008年 | 10303篇 |
2007年 | 10415篇 |
2006年 | 9300篇 |
2005年 | 8353篇 |
2004年 | 7819篇 |
2003年 | 7405篇 |
2002年 | 7209篇 |
2001年 | 7446篇 |
2000年 | 6745篇 |
1999年 | 7184篇 |
1998年 | 19323篇 |
1997年 | 13223篇 |
1996年 | 10201篇 |
1995年 | 7308篇 |
1994年 | 6273篇 |
1993年 | 6193篇 |
1992年 | 4208篇 |
1991年 | 4048篇 |
1990年 | 3841篇 |
1989年 | 3672篇 |
1988年 | 3476篇 |
1987年 | 2949篇 |
1986年 | 2909篇 |
1985年 | 3240篇 |
1984年 | 2931篇 |
1983年 | 2669篇 |
1982年 | 2521篇 |
1981年 | 2580篇 |
1980年 | 2318篇 |
1979年 | 2251篇 |
1978年 | 2154篇 |
1977年 | 2607篇 |
1976年 | 3604篇 |
1975年 | 1835篇 |
1974年 | 1812篇 |
1973年 | 1850篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
In order to ascertain the metastable phase relation in the Cr2O3-Fe2O3 system, the existing phases were investigated by X-ray analysis using samples obtained by heating the coprecipitated powders for 1 h at 600–1000°C. There was a metastable two-phase region of Cr2O3-rich (CC) and Fe2O3-rich (FC) phases below about 940°C. Equilibrium state of 1:1 composition at 600–900°C was considered to be a single phase of the corundum solid solution. The metastable two-phase CC + FC region was suggested to appear probably due to the compositional inhomogeneity in the coprecipitated powders. 相似文献
52.
Dispersion-relation-preserving FDTD algorithms for large-scale three-dimensional problems 总被引:1,自引:0,他引:1
We introduce dispersion-relation-preserving (DRP) algorithms to minimize the numerical dispersion error in large-scale three-dimensional (3D) finite-difference time-domain (FDTD) simulations. The dispersion error is first expanded in spherical harmonics in terms of the propagation angle and the leading order terms of the series are made equal to zero. Frequency-dependent FDTD coefficients are then obtained and subsequently expanded in a polynomial (Taylor) series in the frequency variable. An inverse Fourier transformation is used to allow for the incorporation of the new coefficients into the FDTD updates. Butterworth or Chebyshev filters are subsequently employed to fine-tune the FDTD coefficients for a given narrowband or broadband range of frequencies of interest. Numerical results are used to compare the proposed 3D DRP-FDTD schemes against traditional high-order FDTD schemes. 相似文献
53.
54.
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
55.
Martin F. Falcone F. Bonache J. Marques R. Sorolla M. 《Microwave and Wireless Components Letters, IEEE》2003,13(12):511-513
A novel compact stop band filter consisting of a 50 /spl Omega/ coplanar waveguide (CPW) with split ring resonators (SRRs) etched in the back side of the substrate is presented. By aligning SRRs with the slots, a high inductive coupling between line and rings is achieved, with the result of a sharp and narrow rejection band in the vicinity of the resonant frequency of the rings. In order to widen the stop band of the filter, several ring pairs tuned at equally spaced frequencies within the desired gap are cascaded. The frequency response measured in the fabricated prototype device exhibits pronounced slopes at either side of the stop band and near 0 dBs insertion loss outside that band. Since SRR dimensions are much smaller than signal wavelength, the proposed filters are extremely compact and can be used to reject frequency parasitics in CPW structures by simply patterning properly tuned SRRs in the back side metal. Additional advantages are easy fabrication and compatibility with MMIC or PCB technology. 相似文献
56.
A.L. Pan H.G. ZhengZ.P. Yang F.X. Liu Z.J. Ding Y.T. Qian 《Materials Research Bulletin》2003,38(5):789-796
Small Ag particles or clusters dispersed mesoporous SiO2 composite films were prepared by a new method: First the matrix SiO2 films were prepared by sol-gel process combined with the dip-coating technique, then they were soaked in AgNO3 solutions followed by irradiation of γ-ray at room temperature and in ambient pressure. The structures of these films were examined by X-ray diffraction (XRD), high-resolution transmission electron microscope (HRTEM), and optical absorption spectroscopy. It has been shown that the Ag particles grown within the porous SiO2 films are very small, and they are isolated and dispersed from each other with very narrow size distributions. With increasing the soaking concentration and an additional annealing, an opposite peakshift effect of the surface plasmon resonance (SPR) was observed in the optical absorption measurements. 相似文献
57.
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
58.
This paper addresses the problem of power control in a multihop wireless network supporting multicast traffic. We face the problem of forwarding packet traffic to multicast group members while meeting constraints on the signal-to-interference-plus-noise ratio (SINR) at the intended receivers. First, we present a distributed algorithm which, given the set of multicast senders and their corresponding receivers, provides an optimal solution when it exists, which minimizes the total transmit power. When no optimal solution can be found for the given set of multicast senders and receivers, we introduce a distributed, joint scheduling and power control algorithm which eliminates the weak connections and tries to maximize the number of successful multicast transmissions. The algorithm allows the other senders to solve the power control problem and minimize the total transmit power. We show that our distributed algorithm converges to the optimal solution when it exists, and performs close to centralized, heuristic algorithms that have been proposed to address the joint scheduling and power control problem. 相似文献
59.
60.
Albul V. I. Bychkov V. B. Gusev K. E. Demidov V. S. Demidova E. V. Kurchanov A. F. Luk'yashin V. E. Sokolov A. Yu. 《Measurement Techniques》2003,46(8):810-814
A monitor is proposed based on ultrasonic production when ionizing radiation passes through a medium. The recording element is a 0.2 mm aluminum plate mounted in a ceramic acoustic converter AC in the form of a wedge of thickness 2 mm. The low plate thickness minimizes the beam parameter distortion, while special technology used in the AC provides high sensitivity. The device has been calibrated in the proton beam from the ITEP accelerator at 200 MeV with 2·109–6·1010 particles in a pulse and a pulse length of 70 nsec. 相似文献