全文获取类型
收费全文 | 4814篇 |
免费 | 541篇 |
国内免费 | 424篇 |
专业分类
化学 | 2661篇 |
晶体学 | 101篇 |
力学 | 1262篇 |
综合类 | 54篇 |
数学 | 263篇 |
物理学 | 1438篇 |
出版年
2024年 | 25篇 |
2023年 | 54篇 |
2022年 | 122篇 |
2021年 | 129篇 |
2020年 | 196篇 |
2019年 | 170篇 |
2018年 | 150篇 |
2017年 | 223篇 |
2016年 | 269篇 |
2015年 | 187篇 |
2014年 | 237篇 |
2013年 | 579篇 |
2012年 | 204篇 |
2011年 | 225篇 |
2010年 | 208篇 |
2009年 | 221篇 |
2008年 | 217篇 |
2007年 | 245篇 |
2006年 | 252篇 |
2005年 | 227篇 |
2004年 | 222篇 |
2003年 | 201篇 |
2002年 | 160篇 |
2001年 | 131篇 |
2000年 | 123篇 |
1999年 | 126篇 |
1998年 | 99篇 |
1997年 | 82篇 |
1996年 | 63篇 |
1995年 | 89篇 |
1994年 | 66篇 |
1993年 | 40篇 |
1992年 | 51篇 |
1991年 | 36篇 |
1990年 | 35篇 |
1989年 | 20篇 |
1988年 | 15篇 |
1987年 | 11篇 |
1986年 | 4篇 |
1985年 | 10篇 |
1984年 | 10篇 |
1983年 | 2篇 |
1982年 | 7篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 11篇 |
1978年 | 3篇 |
1976年 | 2篇 |
1973年 | 2篇 |
1971年 | 7篇 |
排序方式: 共有5779条查询结果,搜索用时 62 毫秒
71.
In this paper, we study the Noether-form invariance of nonholonomic mechanical controllable systems in phase space. Equations of motion of the controllable mechanical systems in phase space are presented. The definition and the criterion for this system are presented. A new conserved quantity and the Noether conserved quantity deduced from the Noether-form invariance are obtained. An example is given to illustrate the application of the results. 相似文献
72.
Mechanical,elastic, anisotropy,and electronic properties of monoclinic phase of m-Si_xGe_(3-x)N_4 下载免费PDF全文
The structural,mechanical,elastic anisotropic,and electronic properties of the monoclinic phase of m-Si_3N_4,mSi_2GeN_4,m-SiGe_2N_4,and m-Ge_3N_4are systematically investigated in this work.The calculated results of lattice parameters,elastic constants and elastic moduli of m-Si_3N_4and m-Ge_3N_4are in good agreement with previous theoretical results.Using the Voigt–Reuss–Hill method,elastic properties such as bulk modulus B and shear modulus G are investigated.The calculated ratio of B/G and Poisson’s ratio v show that only m-SiGe_2N_4should belong to a ductile material in nature.In addition,m-SiGe_2N_4possesses the largest anisotropic shear modulus,Young’s modulus,Poisson’s ratio,and percentage of elastic anisotropies for bulk modulus ABand shear modulus AG,and universal anisotropic index AUamong m-Si_xGe_(3-x)N_4(x=0,1,2,3.)The results of electronic band gap reveal that m-Si_3N_4,m-Si_2GeN_4,m-SiGe_2N_4,and m-Ge_3N_4 are all direct and wide band gap semiconducting materials. 相似文献
73.
利用射频磁控溅射系统在不同N2分压的条件下,制备了一系列ZrN/WN纳米多层膜.借助慢正电子湮没技术分析了样品的缺陷性质,采用纳米压痕仪研究了多层膜的力学性能.结果发现:N2分压为0.4Pa的多层膜具有最小的空位型缺陷浓度,其中心层和膜基结合层的平均S参数分别为0.4402和0.4641,而较低或较高的N2分压都可能导致空位型缺陷浓度的增加.随着空位型缺陷浓度的减小,多层膜的硬度和临界载荷增大.对于空位型缺陷浓度最小的多层膜,其硬度和临界载荷达到最大值,分别为34.8GPa和100mN,说明较低的缺陷浓度有利于提高多层膜的力学性能.
关键词:
ZrN/WN纳米多层膜
缺陷性质
力学性能
慢正电子湮没 相似文献
74.
利用X射线吸收精细结构(XAFS)方法研究机械合金化制备的Fe100-xCux(x=0,10,20,40,60,70,80,100,x为原子百分比)合金中Fe和Cu原子的局域环境结构.对于Fe100-xCux(x≥40)二元混合物,球磨160h后,Fe原子的近邻配位结构从bcc转变为fcc,但Cu原子的近邻结构保持其fcc不变.与之相反,在Fe80Cu20和Fe90Cu10(x≤20)合金中,Fe原子的近邻配位保持其bcc结构而Cu原子的近邻配位结构从fcc转变为bcc结构.XAFS结果还表明,fcc结构的Fe100-xCux样品中Fe的无序因子σ(0.0099nm)比bcc结构的Fe100-xCux中的σ(0.0081nm)大得多;并且在机械合金化Fe100-xCux(x≥40)样品中Fe原子的σ(0.0099nm)比其Cu原子的σ(0.0089nm)大.这表明机械合金化Fe100-xCux样品中Fe和Cu原子可以有相同的局域结构环境但不是均匀的过饱和固溶体,而是由Fe富集区和Cu富集区组成的合金.我们提出互扩散和诱导相变机理来解释在球磨过程中Fe100-xCux合金产生从bcc到fcc和从fcc到bcc变化的结构相变
关键词:
XAFS
100-xCux合金')" href="#">Fe100-xCux合金
机械合金化 相似文献
75.
Andrew J. Majda 《Journal of statistical physics》1993,73(3-4):515-542
The inertial range for a statistical turbulent velocity field consists of those scales that are larger than the dissipation scale but smaller than the integral scale. Here the complete scale-invariant explicit inertial range renormalization theory for all the higher-order statistics of a diffusing passive scalar is developed in a model which, despite its simplicity, involves turbulent diffusion by statistical velocity fields with arbitrarily many scales, infrared divergence, long-range spatial correlations, and rapid fluctuations in time-such velocity fields retain several characteristic features of those in fully developed turbulence. The main tool in the development of this explicit renormalization theory for the model is an exact quantum mechanical analogy which relates higher-order statistics of the diffusing scalar to the properties of solutions of a family ofN- body parabolic quantum problems. The canonical inertial range renormalized statistical fixed point is developed explicitly here as a function of the velocity spectral parameter, which measures the strength of the infrared divergence: for<2, mean-field behavior in the inertial range occurs with Gaussian statistical behavior for the scalar and standard diffusive scaling laws; for>2 a phase transition occurs to a fixed point with anomalous inertial range scaling laws and a non-Gaussian renormalized statistical fixed point. Several explicit connections between the renormalization theory in the model and intermediate asymptotics are developed explicitly as well as links between anomalous turbulent decay and explicit spectral properties of Schrödinger operators. The differences between this inertial range renormalization theory and the earlier theories for large-scale eddy diffusivity developed by Avellaneda and the author in such models are also discussed here. 相似文献
76.
77.
Residual stresses are found in the majority of multilayer thin film structures used in modem technology. The measurement and modeling of such stress fields and the elucidation of their effects on structural reliability and device operation have been a “growth area” in the literature, with contributions from authors in various scientific and engineering disciplines.
In this article the measurement of the residual stresses in thin film structures with X-ray diffraction techniques is reviewed and the interpretation of such data and their relationship to mechanical reliability concerns are discussed. 相似文献
78.
79.
80.
Perturbation to Mei symmetry and Mei adiabatic invariants for mechanical systems in phase space 下载免费PDF全文
For a perturbed mechanical system in phase space, considering d/dt in the structure equation and process of proof including infinitesimal parameter ε obviously, this paper studies the perturbation to Mei symmetry and adiabatic invariants. Firstly, the exact invariant induced directly from the Mei symmetry of the system without perturbation is given. Secondly, based on the concept of high-order adiabatic invariant, the determining equations of the perturbation to Mei symmetry are established, the condition of existence of the Mei adiabatic invariant led by the perturbation to Mei symmetry is obtained, and its form is presented. Lastly, an example is given to illustrate the application of the results. 相似文献