全文获取类型
收费全文 | 82077篇 |
免费 | 8779篇 |
国内免费 | 4612篇 |
专业分类
电工技术 | 12916篇 |
技术理论 | 13篇 |
综合类 | 5841篇 |
化学工业 | 10503篇 |
金属工艺 | 2970篇 |
机械仪表 | 3441篇 |
建筑科学 | 10325篇 |
矿业工程 | 2357篇 |
能源动力 | 13306篇 |
轻工业 | 2343篇 |
水利工程 | 1487篇 |
石油天然气 | 2656篇 |
武器工业 | 684篇 |
无线电 | 7077篇 |
一般工业技术 | 8291篇 |
冶金工业 | 3837篇 |
原子能技术 | 1394篇 |
自动化技术 | 6027篇 |
出版年
2024年 | 534篇 |
2023年 | 1835篇 |
2022年 | 2891篇 |
2021年 | 3210篇 |
2020年 | 3425篇 |
2019年 | 3034篇 |
2018年 | 2569篇 |
2017年 | 3075篇 |
2016年 | 3410篇 |
2015年 | 3351篇 |
2014年 | 5633篇 |
2013年 | 5358篇 |
2012年 | 5973篇 |
2011年 | 6674篇 |
2010年 | 5104篇 |
2009年 | 5142篇 |
2008年 | 4685篇 |
2007年 | 5129篇 |
2006年 | 4153篇 |
2005年 | 3222篇 |
2004年 | 2722篇 |
2003年 | 2360篇 |
2002年 | 2069篇 |
2001年 | 1789篇 |
2000年 | 1512篇 |
1999年 | 1191篇 |
1998年 | 939篇 |
1997年 | 746篇 |
1996年 | 691篇 |
1995年 | 513篇 |
1994年 | 460篇 |
1993年 | 359篇 |
1992年 | 295篇 |
1991年 | 247篇 |
1990年 | 205篇 |
1989年 | 164篇 |
1988年 | 133篇 |
1987年 | 101篇 |
1986年 | 70篇 |
1985年 | 108篇 |
1984年 | 88篇 |
1983年 | 56篇 |
1982年 | 72篇 |
1981年 | 39篇 |
1980年 | 44篇 |
1979年 | 26篇 |
1978年 | 13篇 |
1977年 | 12篇 |
1959年 | 5篇 |
1951年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
53.
54.
非零偏移距垂直地震剖面(VSP)模型的制作是非零偏移距VSP资料处理的关键环节之一,是VSP-CDP转换的基础。本文试用旅行时反演修正非零偏移距VSP的模型,以加速模型的制作过程,提高非零偏移距VSP的处理速度。用合成VSP资料试算表明:旅行时的随机误差对模型的制作影响不大;只要能较准确地确定界面位置,用旅行时反演修改制作非零偏移VSP模型是可行的。本文还探讨了初始模型的不同选择方法,并将旅行时反演用于实际VSP资料的处理。结果表明,大大地节省了非零偏移距VSP资料的处理时间。 相似文献
55.
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
56.
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
57.
泡沫铝的动态压缩性能和吸能性研究 总被引:9,自引:0,他引:9
通过测量泡沫铝在动态和准静态压缩条件下的应力 -应变曲线 ,研究了泡沫铝的准静态和动态压缩行为以及不同应变条件下的吸能性 ,并对其应变率效应进行了分析。结果表明 ,在高应变速率和准静态压缩下 ,泡沫铝的σ -ε曲线均表现出弹性变形段、平缓段和密实段三阶段特征 ;泡沫铝的压缩性能具有明显的应变速率敏感性 ,随应变速率的提高 ,流动应力上升 ,吸能性升高 相似文献
58.
In this study forecast of Turkey's net electricity energy consumption on sectoral basis until 2020 is explored. Artificial neural networks (ANN) is preferred as forecasting tool. The reasons behind choosing ANN are the ability of ANN to forecast future values of more than one variable at the same time and to model the nonlinear relation in the data structure. Founded forecast results by ANN are compared with official forecasts. 相似文献
59.
Multilayer calculations by conventional matrix methods for dielectricum/noble metal/dielectricum systems on glass have been performed. The aim has been to maximize the integrated parameters for solar transmission, Tsol, and transmission of visible light, Teye We have found that Ag is superior for maximizing the transmittance over the narrow visible wavelength range owing to the low internal absorptance. When solar energy transmission is considered multilayers based on Au are the best choice for metal film thicknesses above 15 nm. For thinner films, Ag is still to be preferred. 相似文献
60.
Analyses of the practical adhesion strengths of the metal/polymer interfaces in electronic packaging
There is a plethora of techniques to measure the adhesion strength of metal/polymer interfaces. However, the practical adhesion
strength, which is the work done in separating the film from the substrate (or one film from another), is very sensitive to
the test methods and the mechanical effects, such as the residual stress, thickness and mechanical properties of the layers,
strain rate, and phase angle. Deriving intrinsic-adhesion properties of the interfaces, which are independent of such parameters,
from the practical adhesion-strength measurements is a formidable task. In the present work, data from the three commonly
used adhesion tests; pull-out, 90°-peel, and T-peel tests are compared with the intrinsic-adhesion properties of the interface,
such as the interface-fracture toughness or the interface-fracture energy, and their implications are discussed. Material
systems analyzed were Cu-based lead frame/epoxy-molding compound (EMC) and Cu/Cr/polyimide. 相似文献