全文获取类型
收费全文 | 6330篇 |
免费 | 726篇 |
国内免费 | 1925篇 |
专业分类
化学 | 4334篇 |
晶体学 | 242篇 |
力学 | 2041篇 |
综合类 | 47篇 |
数学 | 329篇 |
物理学 | 1988篇 |
出版年
2024年 | 22篇 |
2023年 | 113篇 |
2022年 | 256篇 |
2021年 | 312篇 |
2020年 | 276篇 |
2019年 | 200篇 |
2018年 | 151篇 |
2017年 | 284篇 |
2016年 | 333篇 |
2015年 | 279篇 |
2014年 | 369篇 |
2013年 | 464篇 |
2012年 | 424篇 |
2011年 | 451篇 |
2010年 | 425篇 |
2009年 | 468篇 |
2008年 | 464篇 |
2007年 | 530篇 |
2006年 | 411篇 |
2005年 | 389篇 |
2004年 | 390篇 |
2003年 | 344篇 |
2002年 | 264篇 |
2001年 | 205篇 |
2000年 | 189篇 |
1999年 | 147篇 |
1998年 | 133篇 |
1997年 | 120篇 |
1996年 | 106篇 |
1995年 | 76篇 |
1994年 | 73篇 |
1993年 | 43篇 |
1992年 | 60篇 |
1991年 | 41篇 |
1990年 | 31篇 |
1989年 | 21篇 |
1988年 | 28篇 |
1987年 | 21篇 |
1986年 | 23篇 |
1985年 | 9篇 |
1984年 | 7篇 |
1983年 | 3篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1979年 | 8篇 |
1978年 | 1篇 |
1974年 | 1篇 |
1971年 | 2篇 |
1957年 | 2篇 |
排序方式: 共有8981条查询结果,搜索用时 46 毫秒
941.
Analytical study for electromagnetothermoelastic behaviors of a hollow cylinder composed of functionally graded piezoelectric material (FGPM), placed in a uniform magnetic field, subjected to electric, thermal and mechanical loads are presented. For the case that the electric, magnetic, thermal and mechanical properties of the material obey an identical power law in the radial direction, exact solutions for electric displacement, stresses, electric potential and perturbation of magnetic field vector in the FGPM hollow cylinder are determined by using the infinitesimal theory of electromagnetothermoelasticity. Some useful discussions and numerical examples are presented to show the significant influence of material inhomogeneity, and adopting a certain value of the inhomogeneity parameter β and applying suitable electric, thermal and mechanical loads can optimize the FGPM hollow cylindrical structures. This will be of particular importance in modern engineering design. 相似文献
942.
The paper is concerned with the eigenvalue problems for piezoelectric bodies with voids in contact with massive rigid plane punches and coved by the system of open-circuited and short-circuited electrodes. The linear theory of piezoelectric materials with voids for porosity change properties according to Cowin–Nunziato model is used. The generalized statements for eigenvalue problem are obtained in the extended and reduced forms. A variational principle is constructed which has the properties of minimality, similar to the well-known variational principle for problems with pure elastic media. The discreteness of the spectrum and completeness of the eigenfunctions are proved. The orthogonality relations for eigenvectors are obtained in different forms. As a consequence of variational principles, the properties of an increase or a decrease in the natural frequencies, when the mechanical, electric and “porous” boundary conditions and the moduli of piezoelectric solid with voids change, are established. 相似文献
943.
C. L. Kester R. O. Rye C. A. Johnson Ch. Schwartz Ch. Holmes 《Isotopes in environmental and health studies》2013,49(1):53-65
Abstract Sulfur isotopes have received little attention in ecology studies because plant and animal materials typically have low sulfur concentrations (< 1 wt.%) necessitating labor-intensive chemical extraction prior to analysis. To address the potential of direct combustion of organic material in an elemental analyzer coupled with a mass spectrometer, we compared results obtained by direct combustion to results obtained by sulfur extraction with Eschka's mixture. Direct combustion of peat and animal tissue gave reproducibility of better than 0.5‰ and on average, values are 0.8‰ higher than values obtained by Eschka extraction. Successful direct combustion of organic material appears to be a function of sample matrix and sulfur concentration. Initial results indicate that direct combustion provides fast, reliable results with minimal preparation. Pilot studies underway include defining bear diets and examining fluctuations between freshwater and brackish water in coastal environments. 相似文献
944.
U. Niese 《Isotopes in environmental and health studies》2013,49(7):260-262
Die Radiogaschromatographie stellt eine ausgezeichnete Methode für die Reinheitskontrolle 14C-markierter Präparate dar. Es werden jedoch in der Literatur kaum Größen zur Charakterisierung der Detektorempfindlichkeit für die radiogaschromatographische Messung angegeben. 相似文献
945.
为了进一步提高深亚微米SOI (Silicon-On-Insulator) MOSFET (Metal-Oxide Semiconductor Field Effect Transistor) 的电流驱动能力, 抑制短沟道效应和漏致势垒降低效应, 提出了非对称Halo异质栅应变Si SOI MOSFET. 在沟道源端一侧引入高掺杂Halo结构, 栅极由不同功函数的两种材料组成. 考虑新器件结构特点和应变的影响, 修正了平带电压和内建电势. 为新结构器件建立了全耗尽条件下的表面势和阈值电压二维解析模型. 模型详细分析了应变对表面势、表面场强、阈值电压的影响, 考虑了金属栅长度及功函数差变化的影响. 研究结果表明,提出的新器件结构能进一步提高电流驱动能力, 抑制短沟道效应和抑制漏致势垒降低效应, 为新器件物理参数设计提供了重要参考.
关键词:
非对称Halo
异质栅
应变Si
短沟道效应 相似文献
946.
Most studies on granular physics have focused on dry granular media, with no liquids between the grains. However, in geology and many real world applications (e.g. food processing, pharmaceuticals, ceramics, civil engineering, construction, and many industrial applications), liquid is present between the grains. This produces inter-grain cohesion and drastically modifies the mechanical properties of the granular media (e.g. the surface angle can be larger than 90 degrees). Here we present a review of the mechanical properties of wet granular media, with particular emphasis on the effect of cohesion. We also list several open problems that might motivate future studies in this exciting but mostly unexplored field.
Table 相似文献
947.
948.
Thermoluminescence (TL) and electron spin resonance studies have been carried out on SrS:Bi phosphor. The TL glow curve is broad and indicates a dominant peak at 120 °C with two additional peaks, not clearly resolved, appearing as shoulders at around 180 and 250 °C. Two defect centres are observed at room temperature. One of them is characterized by an isotropic g-value 2.0034 and is assigned to an F+ centre. Step annealing measurements indicate a possible association between the F+ centre and the three TL peaks. 相似文献
949.
Mustapha El Jarroudi 《Applicable analysis》2013,92(5):693-715
We consider an elastic material in contact with a three-dimensional rigid plate of varying thickness. We suppose that a perfect adhesion occurs along thin zones disposed in a self-similar way on the interface between the two materials. We suppose that the elasticity coefficients in the plate depend on its thickness and tend to infinity as this thickness tends to zero. We derive the effective material properties using Γ-convergence methods. 相似文献
950.
We consider a quasistatic frictional contact problem between a piezoelectric body and a foundation. The contact is modeled with normal compliance and friction is modeled with a general version of Coulomb's law of dry friction; the process is quasistatic and the material's behavior is described by an electro-viscoelastic constitutive law with damage. We derive a variational formulation for the model which is in the form of a system involving the displacement field, the electric potential field, and the damage field. Then we provide the existence of a unique weak solution to the model. The proof is based on arguments of evolutionary variational inequalities and fixed point. 相似文献