全文获取类型
收费全文 | 54012篇 |
免费 | 4377篇 |
国内免费 | 4093篇 |
专业分类
电工技术 | 2526篇 |
综合类 | 4603篇 |
化学工业 | 9470篇 |
金属工艺 | 4445篇 |
机械仪表 | 3405篇 |
建筑科学 | 4212篇 |
矿业工程 | 1869篇 |
能源动力 | 2014篇 |
轻工业 | 6569篇 |
水利工程 | 1046篇 |
石油天然气 | 1384篇 |
武器工业 | 295篇 |
无线电 | 5614篇 |
一般工业技术 | 8693篇 |
冶金工业 | 1981篇 |
原子能技术 | 630篇 |
自动化技术 | 3726篇 |
出版年
2024年 | 225篇 |
2023年 | 615篇 |
2022年 | 986篇 |
2021年 | 1208篇 |
2020年 | 1250篇 |
2019年 | 1164篇 |
2018年 | 1077篇 |
2017年 | 1441篇 |
2016年 | 1514篇 |
2015年 | 1626篇 |
2014年 | 2637篇 |
2013年 | 2768篇 |
2012年 | 3486篇 |
2011年 | 4212篇 |
2010年 | 3164篇 |
2009年 | 3457篇 |
2008年 | 2989篇 |
2007年 | 3927篇 |
2006年 | 3691篇 |
2005年 | 3199篇 |
2004年 | 2866篇 |
2003年 | 2520篇 |
2002年 | 2067篇 |
2001年 | 1852篇 |
2000年 | 1541篇 |
1999年 | 1306篇 |
1998年 | 1038篇 |
1997年 | 897篇 |
1996年 | 748篇 |
1995年 | 677篇 |
1994年 | 554篇 |
1993年 | 438篇 |
1992年 | 327篇 |
1991年 | 234篇 |
1990年 | 165篇 |
1989年 | 158篇 |
1988年 | 98篇 |
1987年 | 88篇 |
1986年 | 35篇 |
1985年 | 35篇 |
1984年 | 39篇 |
1983年 | 29篇 |
1982年 | 21篇 |
1981年 | 16篇 |
1980年 | 20篇 |
1979年 | 16篇 |
1978年 | 8篇 |
1977年 | 6篇 |
1975年 | 8篇 |
1959年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
91.
本文评价了塑料闪烁片用作软β核素探测器时的计数效率、β谱、本底谱和康普顿电子谱的特征。文中强调:采用胶合光导剂构成的系统是一种新型探测器(软β核素内部样品塑料闪烁探测器)。本文提出内部样品固体探测器、胶合光导剂和胶合闪烁光导剂的新概念。 相似文献
92.
93.
A framework of virtual prototyping environment for the design and analysis of mechanical mechanism with clearance 总被引:7,自引:0,他引:7
Mechanical mechanisms with clearance abound in technological fields such as robotics, machine and steam turbine industry. The dynamic performance of these mechanisms in working condition can be achieved provided that the effects of the different on the mechanisms (such as mechanism dynamics, technological effects and thermal behaviour) are thoroughly understood. Virtual prototyping provides an integration of multi-domain dynamic simulation for the design and analysis process. In the current paper, a framework of virtual prototyping environment for the design and analysis of mechanical mechanism with clearance is presented. A case study with such a simulation strategy is studied for the optimum design and analysis of the technological parameter. 相似文献
94.
Fabrication of multi-walled carbon nanotube reinforced polyelectrolyte hollow nanofibers by electrospinning 总被引:1,自引:0,他引:1
Hybrid hollow multi-walled carbon nanotubes (MWCNTs)/polyelectrolytes (PE) nanofibers were prepared by a combination of the electrospinning method and layer-by-layer (LbL) technique. The mixed polystyrene (PS)/MWCNTs nanofibers were obtained by electrospinning method, which were employed as templates to self-assembly multilayered polyelectrolytes by LbL technique. Hollow MWCNTs/PE nanofibers were obtained by selectively removed part of the template: PS, which is confirmed by Raman spectra, transmission electron microscopy (TEM) and scanning electron microscopy (SEM). 相似文献
95.
A photochromic nanocomposite based on Keggin structure phosphomolybdic acid (PMoA) well dispersed in polyethyleneglycol (PEG) was fabricated. TEM image showed that PMoA nanoparticles with narrow size distribution were finely dispersed in polymer matrix. FT-IR results showed that the Keggin geometry of polyoxometalates was still preserved inside the composites and strong coulombic interaction was built between PMoA and polymer matrix. Under UV irradiation, the film was reduced photochemically to yield a blue species, which was in accordance with a charge-transfer mechanism. 相似文献
96.
用己二酸二酰肼(ADH)对透明质酸(HA)进行化学修饰,制备交联透明质酸(HA-ADH)薄膜。粘度法测试表明HA-ADH是一种可降解的生物材料,并且与HA相比,HA.ADH的降解速率减慢。在此基础上,研究了以疏水性的替硝唑(TDZ)和亲水性的头孢唑啉钠(CEZ)为模拟药物的HA-ADH药物载体薄膜的释药性能。紫外-可见(UV-Vis)吸收光谱检测表明,HA-ADH是一种疏水性药物TDZ的优良缓释制荆,这是由于TDZ的疏水性和HA-ADH薄膜的缓慢溶胀和降解性能的结合而得到的,药物的释放主要受扩散机制控制。 相似文献
97.
A lubrication-flow model for a free film in a corner is presented. The model, written in the hyperbolic coordinate system
ξ = x
2 −y
2, η = 2xy, applies to films that are thin in the η-direction. The lubrication approximation yields two coupled evolution equations
for the film thickness and the velocity field which, to lowest order, describes plug flow in the hyperbolic coordinates. A
free film in a corner evolving under surface tension and gravity is investigated. The rate of thinning of a free film is compared
to that of a film evolving over a solid substrate. Viscous shear and normal stresses are both captured in the model and are
computed for the entire flow domain. It is shown that normal stress dominates over shear stress in the far field, while shear
stress dominates close to the corner.
This revised version was published online in October 2005 with corrected page numbers. 相似文献
98.
This study is concerned with the stability of a two-dimensional incompressible conducting liquid film surrounded by a passive
conducting medium, when an electric field is applied in a direction parallel to the initially flat bounding fluid interfaces.
Currents generate charges at the bounding interfaces which in turn affect the stress balances there. In the absence of an
electric field, the viscous liquid film is stable (instability can be induced by the inclusion of van der Waals forces for
ultra thin films). A complete model is presented, at arbitrary Reynolds number, which accounts for conductivity and permittivity
contrasts between the fluid and surrounding medium, as well as surface tension. The linear stability of the system is considered
for arbitrary Reynolds numbers and it is shown that the stable film can become unstable if, (i) σ
R
ɛ
p
>1, or (ii) σ
R
ɛ
p
<1 and (σ
R
−1)(1−ɛ
p
)<0, where σ
R
is the ratio of outer to inner conductivity and ε
p
is the ratio of inner to outer permittivity. Instability is possible only if the electric field is non-zero and the scalings
near bifurcation points that can be used to construct nonlinear theories are calculated. Several asymptotic limits are also
considered including zero Reynolds numbers and short or long waves. The instability criteria given above are constructed explicitly
in the case of Stokes flow. 相似文献
99.
The dynamics of a thin liquid film falling down a uniformly heated wall is studied. The model introduced by Kalliadasis et al. [J. Fluid Mech. 475 (2003) 377] for the same problem is revisited and its deficiencies, namely the prediction of a critical
Reynolds number with 20% error, cured. For the energy equation a high-order Galerkin projection in terms of polynomial test
functions is developed. It is shown that not only does this more refined formulation correct the critical Reynolds number,
but it also gives, with an appropriate expansion close to criticality, the long-wave theory. Bifurcation diagrams for permanent
solitary waves are constructed and compared with the solution branches obtained from different models. It is shown that, in
all cases, the long-wave theory exhibits limit points and branch multiplicity, while the other models predict the continuing
existence of solitary waves. Time-dependent computations show that the free surface and interfacial temperature approach a
train of coherent structures that resemble the infinite-domain stationary solitary pulses. 相似文献
100.
略论中国传统合院住宅形式的固化与沿用 总被引:1,自引:1,他引:0
合院式住宅是中国人沿用了二千多年的典型形制,除了其能满足采光、通风的要求和建造相对简化外,中国传统社会早期的中霤祭祀和以五行为基本元素的统括万物的宇宙模式对于中国式合院住宅的固化与沿用,也起了不可忽视的作用。 相似文献