全文获取类型
收费全文 | 127676篇 |
免费 | 10445篇 |
国内免费 | 6116篇 |
专业分类
电工技术 | 3978篇 |
技术理论 | 4篇 |
综合类 | 15169篇 |
化学工业 | 14729篇 |
金属工艺 | 6878篇 |
机械仪表 | 5504篇 |
建筑科学 | 42028篇 |
矿业工程 | 4261篇 |
能源动力 | 2722篇 |
轻工业 | 5052篇 |
水利工程 | 6850篇 |
石油天然气 | 4480篇 |
武器工业 | 1021篇 |
无线电 | 5484篇 |
一般工业技术 | 12609篇 |
冶金工业 | 4231篇 |
原子能技术 | 600篇 |
自动化技术 | 8637篇 |
出版年
2024年 | 453篇 |
2023年 | 1525篇 |
2022年 | 3096篇 |
2021年 | 3452篇 |
2020年 | 3485篇 |
2019年 | 2700篇 |
2018年 | 2755篇 |
2017年 | 3502篇 |
2016年 | 3721篇 |
2015年 | 4234篇 |
2014年 | 7960篇 |
2013年 | 6207篇 |
2012年 | 8694篇 |
2011年 | 9628篇 |
2010年 | 7505篇 |
2009年 | 8560篇 |
2008年 | 7934篇 |
2007年 | 9413篇 |
2006年 | 8230篇 |
2005年 | 7179篇 |
2004年 | 5748篇 |
2003年 | 5144篇 |
2002年 | 4403篇 |
2001年 | 3592篇 |
2000年 | 3061篇 |
1999年 | 2461篇 |
1998年 | 1871篇 |
1997年 | 1575篇 |
1996年 | 1198篇 |
1995年 | 990篇 |
1994年 | 920篇 |
1993年 | 612篇 |
1992年 | 546篇 |
1991年 | 417篇 |
1990年 | 335篇 |
1989年 | 245篇 |
1988年 | 185篇 |
1987年 | 104篇 |
1986年 | 66篇 |
1985年 | 77篇 |
1984年 | 58篇 |
1983年 | 65篇 |
1982年 | 80篇 |
1981年 | 21篇 |
1980年 | 83篇 |
1979年 | 16篇 |
1978年 | 11篇 |
1976年 | 9篇 |
1975年 | 13篇 |
1959年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
厚膜导体Pd-Ag/Au、Pt-Pd-Au/Au平面复合结构,Pd-Ag/Au立体复合结构可使多种组装技术相互兼容。立体复合结构还可有效地降低导体线电阻,减少线损耗。而且,其超声键合性尤佳 相似文献
102.
103.
104.
随着计算机技术的发展和水平的提高,图像,声音,图形等多媒体信息逐步应用于管理信息系统之中。文章中提出了图文数据库系统设计中存在的三个基本问题。讨论了介绍了图文数据库系统的设计方法和实现技术。 相似文献
105.
106.
The energies of various steps on the As-terminated GaAs(001)-2 × 4 surface are evaluated using a novel, approximate method of “linear combination of structural motifs”. It is based on the observation that previous total energy minimizations of semiconductor surfaces produced invariably equilibrium structures made of the same recurring local structural motifs, e.g. tetrahedral fourfold Ga, pyramidal threefold As, etc. Furthermore, such surface structures were found to obey consistently the octet rules as applied to the local motifs. We thus express the total energy of a given semiconductor surface as a sum of (i) the energies M of the local structural motifs appearing in the surface under consideration and (ii) an electrostatic term representing the Madelung energy of point charges resulting from application of the octet rule. The motif energies are derived from a set of pseudopotential total energy calculations for flat GaAs(001) surfaces and for point defects in bulk GaAs. This set of parameters suffices to reproduce the energies of other (001) surfaces, calculated using the same pseudopotential total energy approach. Application to GaAs(001)-2 × 4 surfaces with steps reveals the following. (i) “Primitive steps”, defined solely according to their geometries (i.e. step heights, widths and orientations) are often unstable. (ii) Additional, non-geometric factors beyond step geometries such as addition of surface adatoms, creation of vacancies and atomic rebonding at step edges are important to lower step energies. So is step-step interaction. (iii) The formation of steps is generally endothermic. (iv) The formation of steps with edges parallel to the direction of surface As dimers (A steps) is energetically favored over the formation of steps whose edges are perpendicular to the As dimers (B steps). 相似文献
107.
Wrinkling is a well known phenomenon experimented by tension membranes in Civil Engineering applications. This paper will
present an efficient numerical technique for the computational simulation of such wrinkles in a prestressed membrane. In particular,
the relaxed energy approach (Pipkin in IMA J Appl Math 36:85–99, 1986) is particularized for prestressed membranes (Gil in
Textile composites and inflatable structures, CIMNE, 2003) undergoing moderate strains. Wrinkling conditions in terms of the
Euler-Lagrange finite deformation tensor along principal directions will be obtained. This will provide a framework to describe
properly the initial instant when wrinkles start to be encountered in a prestressed Saint Venant–Kirchhoff hyperelastic membrane.
Subsequently, a modified Helmholtz’s free energy functional will be introduced with the purpose of describing the modified
constitutive behaviour of the continuum after the onset of wrinkling. Consistent derivations of the stress tensor as well
as the constitutive tensor will de depicted. The results will be particularized for membranes and cables in a Finite Element
discretization basis. Some numerical examples will prove the accuracy and robustness of the described algorithm. 相似文献
108.
就用双辊铸轧机(TRC)生产薄、宽铸轧带技术进行研究并优化铸轧工艺。研究结果表明:3mm厚的铸轧带不仅表面变形.而且整个厚度内部层都发生变形,表面层的铝基中具有较高的合金元素饱和度。 相似文献
109.
In this paper, the detectivity is calculated and analyzed with the front-or backside illuminated case for both N-GaSb/p2-Ga0.8In0.2As0.19Sb0.81/p1-Ga0.9In0.1As0.09Sb0.91 and N1-GaSb/n2-Ga0.9In0.1As0.09Sb0.91/p-Ga0.8In0.2As0.19Sb0.81 infrared photovoltaic detectors, respectively. The analysis results show that the main absorption appears in the p-type Ga0.8In0.2As0.19Sb0.81 material with either front- or backside illuminated case for above two structures. In each structure, the carrier concentration obviously affects the detectivity. The carrier concentration in the wide-bandgap material for the isotype heterojunction should be reduced as low as possible to reduce the tunneling rate at the isotype heterointerface. Moreover, the change of the detectivity with the p-side surface recombination velocity for the N1-n2-p structure is more sensitive than that with the p1-side surface recombination velocity for the N-p2-p1 structure. In the N-p2-p1 structure with the incident light from the p1-side surface, two-color detection is achieved. 相似文献
110.
简要介绍了湘潭新大粉末冶金设备制造有限公司研制的一体化真空烧结炉的炉子结构、脱蜡系统、工艺气体的引入系统、设备的控制系统以及炉子性能的鉴定结果。 相似文献