全文获取类型
收费全文 | 13579篇 |
免费 | 1438篇 |
国内免费 | 1040篇 |
专业分类
电工技术 | 546篇 |
技术理论 | 1篇 |
综合类 | 1119篇 |
化学工业 | 2021篇 |
金属工艺 | 396篇 |
机械仪表 | 570篇 |
建筑科学 | 1631篇 |
矿业工程 | 154篇 |
能源动力 | 479篇 |
轻工业 | 824篇 |
水利工程 | 445篇 |
石油天然气 | 249篇 |
武器工业 | 109篇 |
无线电 | 950篇 |
一般工业技术 | 2277篇 |
冶金工业 | 746篇 |
原子能技术 | 245篇 |
自动化技术 | 3295篇 |
出版年
2024年 | 94篇 |
2023年 | 386篇 |
2022年 | 675篇 |
2021年 | 684篇 |
2020年 | 591篇 |
2019年 | 527篇 |
2018年 | 488篇 |
2017年 | 566篇 |
2016年 | 566篇 |
2015年 | 527篇 |
2014年 | 827篇 |
2013年 | 947篇 |
2012年 | 829篇 |
2011年 | 901篇 |
2010年 | 649篇 |
2009年 | 707篇 |
2008年 | 713篇 |
2007年 | 747篇 |
2006年 | 623篇 |
2005年 | 573篇 |
2004年 | 479篇 |
2003年 | 427篇 |
2002年 | 386篇 |
2001年 | 323篇 |
2000年 | 264篇 |
1999年 | 236篇 |
1998年 | 186篇 |
1997年 | 170篇 |
1996年 | 127篇 |
1995年 | 140篇 |
1994年 | 95篇 |
1993年 | 78篇 |
1992年 | 72篇 |
1991年 | 63篇 |
1990年 | 67篇 |
1989年 | 65篇 |
1988年 | 58篇 |
1987年 | 27篇 |
1986年 | 15篇 |
1985年 | 22篇 |
1984年 | 16篇 |
1983年 | 21篇 |
1982年 | 14篇 |
1980年 | 9篇 |
1979年 | 8篇 |
1964年 | 6篇 |
1963年 | 6篇 |
1959年 | 7篇 |
1958年 | 6篇 |
1955年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
In this paper, the microstructure of a 1 wt.% Cu/γ-Al2O3 catalyst that was reduced in a 4% hydrogen/argon atmosphere at temperatures of 523, 773 and 1073 K, is studied by Z-contrast imaging and electron energy-loss spectroscopy (EELS) in a scanning transmission electron microscope (STEM). Results show that the copper species are well dispersed when the catalyst is reduced below 523 K. At 773 K, separated Cu(I) and Cu(0) species are found existing as ring-like and bulk-like particles. This appears to indicate that the copper has not been reduced to its metallic form due to the interaction between the copper oxide and the support. Large spherical particles having core-shell structures with Cu(I) in the shells and Cu(0) in the cores are generated when the catalyst is reduced at 1073 K. The formation of partially oxidized copper species upon reduction at 1073 K is attributed to the metallic copper interaction with the alumina support. This study also demonstrates that high-spatial resolution Z-contrast imaging and EELS performed simultaneously can provide unique information on the morphology and chemistry of metal species in supported metal catalysts. 相似文献
22.
23.
A new interaction integral formulation is developed for evaluating the elastic T-stress for mixed-mode crack problems with
arbitrarily oriented straight or curved cracks in orthotropic nonhomogeneous materials. The development includes both the
Lekhnitskii and Stroh formalisms. The former is physical and relatively simple, and the latter is mathematically elegant.
The gradation of orthotropic material properties is integrated into the element stiffness matrix using a “generalized isoparametric
formulation” and (special) graded elements. The specific types of material gradation considered include exponential and hyperbolic-tangent
functions, but micromechanics models can also be considered within the scope of the present formulation. This paper investigates
several fracture problems to validate the proposed method and also provides numerical solutions, which can be used as benchmark
results (e.g. investigation of fracture specimens). The accuracy of results is verified by comparison with analytical solutions. 相似文献
24.
通过规范冶炼的操作,加强冶炼过程控制,细化分解技术指标,制定奖励方案,提高了钢水质量,解决了铰链梁铸件的气孔问题。 相似文献
25.
An account is given of some principal observations made from a series of experiments in which three-span pipe beams were subjected to central impact by indenters with different nose shapes. These pipes were filled and pre-pressurized with water in order to identify the main effects produced by the fluid–structure interaction. In comparison, the impact experiments of the pipes with no water were also carried out. The perforation failure modes and corresponding critical impact energies were obtained in different test conditions. The experimental results indicated that the critical perforation energy and the deformation of the wall of the pipe were significantly influenced by the presence of the water and the pressure. 相似文献
26.
The hydrodynamic interaction between two hard spheres tangentially translating in a power-law fluid is investigated. By considering the gap between the two spheres being sufficiently small such that the Reynolds’ lubrication theory applies, an analytical equation to the pressure in the gap is obtained using truncated Fourier series. To a good approximation, the pressure equation can be further simplified. The simplified approximate equation over-predicts the pressure for shear thickening fluid (n>1) but under-predicts the pressure for shear-thinning fluid (n<1). However, the errors in the predicted tangential force and moment are relatively small. In particular, for a Newtonian fluid, the accurate solution and the simplified approximate solution degenerate to the asymptotic solution of Goldman et al. [1967. Slow viscous motion of a sphere parallel to a plane wall-motion through a quiescent fluid. Chemical Engineering Science 22, 637-651.] and O’Neill and Stewartson [1967. On the slow motion of a sphere parallel to a nearby plane wall. Journal of Fluid Mechanics 27, 705-724.]. Both solutions predict that for shear thickening fluid (n>1), the hydrodynamic force converged in the inner region of the gap between the two spheres and the contribution from the outer region is sufficiently small. For shear thinning fluid (n<1), the contribution from the outer region is also significant. 相似文献
27.
28.
Higher testosterone levels are related to assertiveness and dominance. Given the relevance of those behavioral correlates to spouses' daily transactions, links between testosterone levels and marital interaction were explored among 92 newlywed couples. Marital problem-solving and social support transactions were assessed, and saliva was collected and assayed for testosterone. Whether marital behavior was related to husbands' and wives' testosterone levels was examined. The link between spouses' testosterone and their behavior was contingent on the partner's testosterone levels. Husbands exhibited more adaptive problem-solving behaviors and social support provision when husbands and wives were concordant for lower testosterone levels. In contrast, wives exhibited more adaptive support provision when spouses had discordant testosterone levels such that wives had higher levels and husbands had lower levels. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
29.
Extended Hyperbolic Model for Sand-to-Concrete Interfaces 总被引:1,自引:0,他引:1
Jesús E. Gómez George M. Filz Robert M. Ebeling 《Canadian Metallurgical Quarterly》2003,129(11):993-1000
A relatively simple, four-parameter extended hyperbolic model for interfaces was developed for use in soil-structure interaction analyses. The model accommodates arbitrary stress path directions and includes three important elements: (1) development of a yield surface during interface shear; (2) a formulation for yield-inducing shear stiffness that is applicable to any stress path orientation; and (3) a formulation for unloading-reloading shear stiffness. The model was evaluated against the results of shear tests performed at the interface between three different types of sand and a concrete surface under a variety of stress paths. Comparisons between measured and calculated interface response indicate that the model provides accurate estimates of the response of sand-to-concrete interfaces. 相似文献
30.
We observed change in distance between two droplets in each step after application of large multi-step shear strains. Experiments were performed using a sliding plate apparatus. Large step shear strains were applied to two polyisobutylene droplets in poly(dimethyl siloxane) matrix in the same plane between the plates. The distance between the two droplets decreases with increasing the total shear strain, which is given by the product of the step strain magnitude and the number of application of the step strains. The two droplets coalesce when the distance becomes less than the diameter of the droplets. The slope for plots of the distance versus the total strain is independent of the step strain magnitude. This indicates that the effect per unit strain on the distance is the same, irrespective of the strain magnitude. It is suggested that a stronger hydrodynamic interaction between the droplets is the main cause for the droplet approach. 相似文献