全文获取类型
收费全文 | 48383篇 |
免费 | 4984篇 |
国内免费 | 3166篇 |
专业分类
电工技术 | 1291篇 |
综合类 | 5474篇 |
化学工业 | 7855篇 |
金属工艺 | 5271篇 |
机械仪表 | 2508篇 |
建筑科学 | 9817篇 |
矿业工程 | 2069篇 |
能源动力 | 1236篇 |
轻工业 | 2172篇 |
水利工程 | 1998篇 |
石油天然气 | 1729篇 |
武器工业 | 380篇 |
无线电 | 1570篇 |
一般工业技术 | 7449篇 |
冶金工业 | 3104篇 |
原子能技术 | 307篇 |
自动化技术 | 2303篇 |
出版年
2024年 | 211篇 |
2023年 | 722篇 |
2022年 | 1230篇 |
2021年 | 1626篇 |
2020年 | 1607篇 |
2019年 | 1431篇 |
2018年 | 1430篇 |
2017年 | 1850篇 |
2016年 | 1876篇 |
2015年 | 1879篇 |
2014年 | 2725篇 |
2013年 | 3223篇 |
2012年 | 3398篇 |
2011年 | 3470篇 |
2010年 | 2573篇 |
2009年 | 2676篇 |
2008年 | 2522篇 |
2007年 | 2938篇 |
2006年 | 2780篇 |
2005年 | 2399篇 |
2004年 | 2055篇 |
2003年 | 1777篇 |
2002年 | 1519篇 |
2001年 | 1331篇 |
2000年 | 1207篇 |
1999年 | 1075篇 |
1998年 | 869篇 |
1997年 | 747篇 |
1996年 | 654篇 |
1995年 | 543篇 |
1994年 | 447篇 |
1993年 | 377篇 |
1992年 | 320篇 |
1991年 | 234篇 |
1990年 | 217篇 |
1989年 | 196篇 |
1988年 | 113篇 |
1987年 | 78篇 |
1986年 | 31篇 |
1985年 | 26篇 |
1984年 | 30篇 |
1983年 | 21篇 |
1982年 | 24篇 |
1981年 | 15篇 |
1980年 | 19篇 |
1979年 | 20篇 |
1964年 | 4篇 |
1961年 | 2篇 |
1959年 | 3篇 |
1954年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Within the framework of the effective-mass approximation and the dipole approximation, considering the three-dimensional confinement of the electron and hole and the strong built-in electric field(BEF) in strained wurtzite Zn O/Mg0:25Zn0:75O quantum dots(QDs), the optical properties of ionized donor-bound excitons(D+, X)are investigated theoretically using a variational method. The computations are performed in the case of finite band offset. Numerical results indicate that the optical properties of(D+, X) complexes sensitively depend on the donor position, the QD size and the BEF. The binding energy of(D+, X) complexes is larger when the donor is located in the vicinity of the left interface of the QDs, and it decreases with increasing QD size. The oscillator strength reduces with an increase in the dot height and increases with an increase in the dot radius. Furthermore, when the QD size decreases, the absorption peak intensity shows a marked increment, and the absorption coefficient peak has a blueshift. The strong BEF causes a redshift of the absorption coefficient peak and causes the absorption peak intensity to decrease remarkably. The physical reasons for these relationships have been analyzed in depth. 相似文献
2.
3.
The micromechanics models for composites usually underpredict the tensile strength of polymer nanocomposites. This paper establishes a simple model based on Kelly–Tyson theory for tensile strength of polymer/CNT nanocomposites assuming the effect of interphase between polymer and CNT. In addition, Pukanszky model is joined with the suggested model to calculate the interfacial shear strength (τ), interphase strength (σi) and critical length of CNT (Lc).The proposed approach is applied to calculate τ, σi and Lc for various samples from recent literature. It is revealed that the experimental data are well fitted to calculations by new model which confirm the important effect of interphase on the properties of nanocomposites. Moreover, the derived equations demonstrate that dissimilar correlations are found between τ and B (from Pukanszky model) as well as Lc and B. It is shown that a large B value obtained by strong interfacial adhesion between polymer and CNT is adequate to reduce Lc in polymer/CNT nanocomposites. 相似文献
4.
Seyed Ali Maghami 《热应力杂志》2015,38(2):250-270
Thermal bending analysis of doubly curved laminated shell panels with general boundary conditions and laminations is presented. The equations of equilibrium are derived in the form of two coupled sets of ordinary differential equations based on a general shell theory and solved through the state-space approach in a repeated manner. It is depicted that the results of the present method are in great agreement with analytical solutions. Cylindrical shell panels with general boundary conditions and laminations, where no analytical solution is available, are solved. It is found that the present method exhibits a high convergence rate as well as presenting accurate results in all cases. 相似文献
5.
Barbara M. Johnston Peter R. Johnston 《International journal for numerical methods in engineering》2003,56(4):589-607
Accurate numerical evaluation of integrals arising in the boundary element method is fundamental to achieving useful results via this solution technique. In this paper, a number of techniques are considered to evaluate the weakly singular integrals which arise in the solution of Laplace's equation in three dimensions and Poisson's equation in two dimensions. Both are two‐dimensional weakly singular integrals and are evaluated using (in a product fashion) methods which have recently been used for evaluating one‐dimensional weakly singular integrals arising in the boundary element method. The methods used are based on various polynomial transformations of conventional Gaussian quadrature points where the transformation polynomial has zero Jacobian at the singular point. Methods which split the region of integration into sub‐regions are considered as well as non‐splitting methods. In particular, the newly introduced and highly accurate generalized composite subtraction of singularity and non‐linear transformation approach (GSSNT) is applied to various two‐dimensional weakly singular integrals. A study of the different methods reveals complex relationships between transformation orders, position of the singular point, integration kernel and basis function. It is concluded that the GSSNT method gives the best overall results for the two‐dimensional weakly singular integrals studied. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
6.
Mohammed Farid 《Chemical engineering science》2003,58(13):2985-2993
A model was developed to predict the change in droplet mass and temperature when it is exposed to hot air, as in spray drying of droplets containing solids. The droplet was assumed first to undergo sensible rapid heating with no mass change. Then the droplet experiences some shrinkage, with no temperature change but rapid mass losses, followed by a period of crust formation with a significant change in droplet mass and temperature and finally a short period of sensible heating of the dried particle. The model, unlike previous models, accounts for shrinkage and for the temperature distribution in the droplet. It provided a good prediction for the change in droplet temperature and mass for some of the experimental measurements available in the literatures. 相似文献
7.
根据石油开采业对石油机械产品的需求 ,利用机械理论基础知识 ,通过实践设计 ,提出了对几何尺寸长的金属管类进行调质处理后的均匀冷却方法 ,以满足其性能要求。 相似文献
8.
9.
Wenlin HE Qishan ZANG+ Zhongguang WANG State Key Laboratory for Fatigue Fracture of Materials 《材料科学技术学报》1993,9(2):107-110
The distributions of plastic strain near grain boundaries induced by fatigue loading were investigatedby the fiducial grid method in pure aluminum specimens, and the resulted grain boundary sliding(GBS) was systematically analysed. The results show that the strain field near a grain boundary isnonuniform. GBS is restricted by the junction of grain boundaries and causes discontinuities of bothdisplacement and strain. A peak value of shear strain was created in short-range area across the grainboundary. GBS plays an important role in cyclic softening and secondary hardening. The control fac-tor of GBS is the relative orientation between two grains and the macro orientation of the grainboundary rather than the ∑ value of the boundary. 相似文献
10.
介绍了日本川崎制铁公司技术研究所开发出的电焊钢管采用热张力减径工艺的特性 ,及这种钢管的高强度、高延性等基本特性。用这种钢管制造的汽车零部件 ,经弯曲、冲击和疲劳特性等实验 ,证明具有良好的机械加工性能 ,是制造汽车用零部件的优良材料。 相似文献