全文获取类型
收费全文 | 11556篇 |
免费 | 677篇 |
国内免费 | 357篇 |
专业分类
电工技术 | 193篇 |
综合类 | 1058篇 |
化学工业 | 1052篇 |
金属工艺 | 1436篇 |
机械仪表 | 3405篇 |
建筑科学 | 566篇 |
矿业工程 | 1182篇 |
能源动力 | 200篇 |
轻工业 | 372篇 |
水利工程 | 95篇 |
石油天然气 | 663篇 |
武器工业 | 102篇 |
无线电 | 311篇 |
一般工业技术 | 1042篇 |
冶金工业 | 385篇 |
原子能技术 | 44篇 |
自动化技术 | 484篇 |
出版年
2024年 | 21篇 |
2023年 | 90篇 |
2022年 | 272篇 |
2021年 | 249篇 |
2020年 | 306篇 |
2019年 | 190篇 |
2018年 | 199篇 |
2017年 | 323篇 |
2016年 | 343篇 |
2015年 | 405篇 |
2014年 | 638篇 |
2013年 | 614篇 |
2012年 | 705篇 |
2011年 | 807篇 |
2010年 | 593篇 |
2009年 | 624篇 |
2008年 | 542篇 |
2007年 | 765篇 |
2006年 | 726篇 |
2005年 | 669篇 |
2004年 | 545篇 |
2003年 | 472篇 |
2002年 | 432篇 |
2001年 | 421篇 |
2000年 | 281篇 |
1999年 | 258篇 |
1998年 | 211篇 |
1997年 | 185篇 |
1996年 | 130篇 |
1995年 | 137篇 |
1994年 | 107篇 |
1993年 | 47篇 |
1992年 | 52篇 |
1991年 | 40篇 |
1990年 | 42篇 |
1989年 | 50篇 |
1988年 | 28篇 |
1987年 | 15篇 |
1986年 | 14篇 |
1985年 | 4篇 |
1984年 | 12篇 |
1983年 | 8篇 |
1982年 | 7篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1966年 | 2篇 |
1965年 | 1篇 |
1963年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
2.
Saw-tooth chip changes from macroscopically continuous ribbon to separated segments with the increase of cutting speed. The aim of this study is to find the correlations between chip morphology and machined surface micro-topography at different chip serration stages encountered in high speed cutting. High strength alloy steel AerMet100 was employed in orthogonal cutting experiments to obtain chips at different serration stages and corresponding machined surfaces. The chips and machined surfaces obtained were then examined with optical microscope (OM), scanning electron microscope (SEM), and white light interferometer (WLI). The result shows that chip serration causes micro-waves on machined surface, which increases machined surface roughness. However, wave amplitudes (surface roughness) at different serration stages are different. The principal factor influencing wave amplitude is the thickness of the sawed segment (tooth) of saw-tooth chip. With cutting parameters in this study, surface roughness contributed by chip serration ranges from 0.39 μm to 1.85 μm. This may bring on serious problems in the case of trying to replace grinding with high-speed cutting in rough machining. Some suggestions have been proposed to control the chip serration-caused surface roughness in high-speed cutting based on the results of the current study. 相似文献
3.
Rheological properties of MR fluids under large step strain shear are presented in this paper. The experiments were carried out using a rheometer with parallel-plate geometry. Under the large step strain shear, MR fluids behave as nonlinear viscoelastic properties, where the stress relaxation modulus, G(t, γ), shows a decreasing trend with step strain. The experimental results indicate that G(t, γ) obeys time-strain separability. Thus, a mathematical form based on finite exponential serials is proposed to predict MR behavior. In this model, G(t, γ) is represented as the product of a linear stress relaxation, G(t), and the damping function, h(γ), i.e. G(t, γ)=G(t) h(γ). G(t) is simply represented as a three-parameter exponential serial and h(γ) has a sigmoidal form with two parameters. The parameters are identified by adopting an efficient optimization method proposed by Stango et al. The comparison between the experimental results and the model-predicted values indicates that this mathematical model can accurately predict MR behavior. 相似文献
4.
Starting from a microscopic Hamiltonian defined on a semi-infinite cubic lattice, and employing a mean-field approximation, the surface parameters relevant for wetting in confined ternary mixtures are derived. These are found in terms of the microscopic coupling constants, and yield a physical interpretation of their origins. In comparison with the standard expression for the surface free-energy density, several new terms arising from the derivation are identified. The influence of the surface parameters on a predicted unbinding transition in a mixture of oil, water, and amphiphile demonstrate that existing results are robust to the addition of the extra surface terms. 相似文献
5.
6.
S.J. Curran R.E. Hayes A. Afacan M.C. Williams P.A. Tanguy 《Journal of food science》2002,67(1):176-180
ABSTRACT: The effect of pH on the non-Newtonian viscosity (η)of aqueous Carbopol 940 solutions is presented with high resolution (pH increments about 0.4) between pH = 2.8 and 12.7. Aqueous NaOH was used to adjust pH of 1.48 wt % Carbopol solutions. A Contraves viscometer was used to measure steady-flow shear stress at known shear rate (γ) over the range γ= 8 to 195 s−1 . Yield stresses and shear-thinning η(γ) were observed. Data were fitted with a Herschel-Bulkley model, whose parameters (including yield stress) were expressed as functions of pH. Comparisons were made of η(γ) to the dynamic viscometric properties η'(ω) and η*(ω) for comparable ranges of γ and frequency (ω): A fairly close match was found between η and η* but η«η'. pH dependence included previously unreported extrema of h(pH) in the range of pH = 6.2 to 6.6. Because of sensitive control of rheological properties with pH, Carbopol solutions can be used to mimic a great range of shear-thinning and yield-stress behavior that should make them useful for model studies directed toward process and equipment design and evaluation. 相似文献
7.
8.
90年代以来,国外钻井液和完井液用聚合物添加剂的发展取得长足进步。本文介绍了国外目前用于钻井液和完井液的聚合物添加剂的类型及作用。 相似文献
9.
晶须取向对SiCw/Al复合材料切削表面质量的影响 总被引:2,自引:0,他引:2
切削与晶须取向方向间的夹角对SiCw/Al复合材料切削表面质量有很大影响。当切削角为45°时,晶须拔出和转动现象均较少,复合材料切削表面粗糙度最低。当切削角为135度时,晶段转动造成的撕裂破坏程度很大,复合材料切削表面粗糙度最大。 相似文献
10.