全文获取类型
收费全文 | 292795篇 |
免费 | 3073篇 |
国内免费 | 1070篇 |
专业分类
电工技术 | 5430篇 |
综合类 | 2511篇 |
化学工业 | 41907篇 |
金属工艺 | 15563篇 |
机械仪表 | 13492篇 |
建筑科学 | 7523篇 |
矿业工程 | 1656篇 |
能源动力 | 5591篇 |
轻工业 | 21237篇 |
水利工程 | 3109篇 |
石油天然气 | 2458篇 |
武器工业 | 5篇 |
无线电 | 34886篇 |
一般工业技术 | 60673篇 |
冶金工业 | 32239篇 |
原子能技术 | 3646篇 |
自动化技术 | 45012篇 |
出版年
2018年 | 21432篇 |
2017年 | 21152篇 |
2016年 | 14095篇 |
2015年 | 2114篇 |
2014年 | 2100篇 |
2013年 | 6875篇 |
2012年 | 8212篇 |
2011年 | 20348篇 |
2010年 | 18004篇 |
2009年 | 15421篇 |
2008年 | 16381篇 |
2007年 | 19295篇 |
2006年 | 4592篇 |
2005年 | 8758篇 |
2004年 | 6837篇 |
2003年 | 6433篇 |
2002年 | 5018篇 |
2001年 | 4159篇 |
2000年 | 4054篇 |
1999年 | 3815篇 |
1998年 | 6909篇 |
1997年 | 5397篇 |
1996年 | 4604篇 |
1995年 | 3792篇 |
1994年 | 3458篇 |
1993年 | 3296篇 |
1992年 | 2833篇 |
1991年 | 2755篇 |
1990年 | 2660篇 |
1989年 | 2643篇 |
1988年 | 2498篇 |
1987年 | 2198篇 |
1986年 | 2141篇 |
1985年 | 2584篇 |
1984年 | 2351篇 |
1983年 | 2230篇 |
1982年 | 2100篇 |
1981年 | 2022篇 |
1980年 | 1876篇 |
1979年 | 1893篇 |
1978年 | 1796篇 |
1977年 | 2112篇 |
1976年 | 2607篇 |
1975年 | 1609篇 |
1974年 | 1447篇 |
1973年 | 1476篇 |
1972年 | 1213篇 |
1971年 | 1123篇 |
1970年 | 949篇 |
1968年 | 890篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
The extended quadratic residue code is the only (48,24,12) self-dual doubly-even code 总被引:3,自引:0,他引:3
Houghten S.K. Lam C.W.H. Thiel L.H. Parker J.A. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2003,49(1):53-59
An extremal self-dual doubly-even binary (n,k,d) code has a minimum weight d=4/spl lfloor/n/24/spl rfloor/+4. Of such codes with length divisible by 24, the Golay code is the only (24,12,8) code, the extended quadratic residue code is the only known (48,24,12) code, and there is no known (72,36,16) code. One may partition the search for a (48,24,12) self-dual doubly-even code into three cases. A previous search assuming one of the cases found only the extended quadratic residue code. We examine the remaining two cases. Separate searches assuming each of the remaining cases found no codes and thus the extended quadratic residue code is the only doubly-even self-dual (48,24,12) code. 相似文献
132.
Several kinds of waveguide components such as curved waveguide bends, arbitrary angle waveguide bends and T-junctions have been analyzed with boundary element method in this paper. A new discretization method for the boundary element method to solve the waveguide discontinuities has been given. The numerical results obtained agree well with the experimental results and numerical results in other literature. Especially, the scattering characteristics of Forded E-, H-plane T-junctions in 3mm band have been analyzed using boundary element method and the calculation results are presented. 相似文献
133.
On the effect of spatial variances in historical rainfall time series to CSO performance evaluation.
Historical, high-resolution rain series are the backbone of modern combined sewer overflow (CSO) structure design. These rain series are the input to the computational estimation of the performance of the measures with respect to CSO pollution abatement. However, those historical precipitation measurements are available at only a few locations. Frequently rain series have to be used from gauging stations at a significant distance. In order to judge and to compensate for this influence an estimate between rain characteristics and combined sewer outflow (CSO) performance indicators would be useful. In this paper such correlations have been sought for a collection of 37 rain series covering large areas of Europe. It was found that the mean annual rain volume can explain most of the variances for the performance indicators Number of overflows and CSO volume. For explaining the spatial differences in the efficiency of the CSO structure another rain characteristic, i.e. the maximum event with a return period of one year, is to be used. 相似文献
134.
Commercial purity aluminum (99.5%) was fabricated by equal channel angular pressing (ECAP) up to total accumulated strains of approx. 10. The annealing behavior of material deformed to total strains of approx. 1 and 10 was investigated, using heat treatments of 2 h at various temperatures from 100 to 500 °C. The microstructure of the annealed materials was characterized using the electron back-scatter pattern technique. A number of parameters were determined including the distribution and average values of both the boundary spacings and misorientations. For samples deformed to a total strain of 1, annealing resulted in discontinuous recrystallization. For samples deformed to a total strain of 10, annealing resulted in microstructures exhibiting characteristics of both uniform coarsening and, in a number of places, of discontinuous recrystallization. An attempt was made, based on the boundary spacing distributions, to separate these two components. The grain size after annealing was still however small, being just 6.4 μm after 2 h at 300 °C. 相似文献
135.
V. N. Petrov V. V. Grebenshikov B. D. Grachev A. S. Kamochkin M. K. Yarmarkin 《Technical Physics Letters》2004,30(2):157-160
A compact electron polarimeter employing the classical Mott scheme has been developed and tested. The device has an efficiency
of about 5.6×10−4, a maximum count rate of 5×105 cps, dimensions 15 cm (diameter) × 25 cm (length), and a working voltage of 40 kV. The polarimeter can operate for a long
time under arbitrary vacuum conditions without maintenance, exhibiting no changes in the main working characteristics, and
obeys all requirements to the electron spin polarization studies on the modern level. 相似文献
136.
W. Wang J. Dai J. Tang D.-T. Jiang Y. Chen J. Fang J. He W. Zhou L. Spinu 《Journal of Superconductivity》2003,16(1):155-157
Ball-milling method was applied to dissolve Fe into titanium dioxide (TiO2). X-ray diffraction indicated the starting anatase changed to a rutile-type structure with oxygen deficiency after ball milling. Transmission electron microscopy and X-ray absorption experiments were conducted to examine the possible existence of magnetic impurities in the ball-milled powders after they were leached in HCl solutions. Temperature dependence of the resistivity shows semiconducting behavior and the magnetic hysteresis loops at 5 and 300 K exhibit ferromagnetic characteristics. Fe-doped TiO2 films were also prepared by pulsed laser deposition. The magnetic properties of the films are discussed. 相似文献
137.
C.-W.Jang J.-C.Juang F.-C.Kung 《战术导弹技术》2003,(1):58-63
给出了一种GPS卡尔曼滤波的自适应方案,该方案能根据GPS导航中变化的动态来估计协方差.当增强卡尔曼滤波器时,方案可得到更精确的定位修正.此外,也可将此估计方法用于完整监测,以增强故障检测的阈值选择.采用模拟数据验证了提出方法的正确性. 相似文献
138.
R. K. Melekhov A. V. Vasylyk E. I. Palashchuk H. M. Krutsan Ya. D. Onyshchak 《Materials Science》2004,40(5):668-675
We study the process of degradation and damage for superheater tubes of the pressure boilers of power plants made of austenitic chromium-nickel steel. The role of sensitization and partial sigmatization of austenitic steel in the embrittlement of the tubes is analyzed.__________Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 40, No. 4, pp. 81–86, July–August, 2004. 相似文献
139.
140.
A coupled finite-element model, CON2D, has been developed to simulate temperature, stress, and shape development during the
continuous casting of steel, both in and below the mold. The model simulates a transverse section of the strand in generalized
plane strain as it moves down at the casting speed. It includes the effects of heat conduction, solidification, nonuniform
superheat dissipation due to turbulent fluid flow, mutual dependence of the heat transfer and shrinkage on the size of the
interfacial gap, the taper of the mold wall, and the thermal distortion of the mold. The stress model features an elastic-viscoplastic
creep constitutive equation that accounts for the different responses of the liquid, semisolid, delta-ferrite, and austenite
phases. Functions depending on temperature and composition are employed for properties such as thermal linear expansion. A
contact algorithm is used to prevent penetration of the shell into the mold wall due to the internal liquid pressure. An efficient
two-step algorithm is used to integrate these highly nonlinear equations. The model is validated with an analytical solution
for both temperature and stress in a solidifying slab. It is applied to simulate continuous casting of a 120 mm billet and
compares favorably with plant measurements of mold wall temperature, total heat removal, and shell thickness, including thinning
of the corner. The model is ready to investigate issues in continuous casting such as mold taper optimization, minimum shell
thickness to avoid breakouts, and maximum casting speed to avoid hot-tear crack formation due to submold bulging. 相似文献