全文获取类型
收费全文 | 9010篇 |
免费 | 1437篇 |
国内免费 | 846篇 |
专业分类
化学 | 6372篇 |
晶体学 | 91篇 |
力学 | 485篇 |
综合类 | 47篇 |
数学 | 1015篇 |
物理学 | 3283篇 |
出版年
2024年 | 27篇 |
2023年 | 159篇 |
2022年 | 298篇 |
2021年 | 309篇 |
2020年 | 331篇 |
2019年 | 323篇 |
2018年 | 288篇 |
2017年 | 267篇 |
2016年 | 393篇 |
2015年 | 414篇 |
2014年 | 491篇 |
2013年 | 682篇 |
2012年 | 803篇 |
2011年 | 780篇 |
2010年 | 555篇 |
2009年 | 518篇 |
2008年 | 585篇 |
2007年 | 480篇 |
2006年 | 486篇 |
2005年 | 397篇 |
2004年 | 359篇 |
2003年 | 269篇 |
2002年 | 271篇 |
2001年 | 202篇 |
2000年 | 143篇 |
1999年 | 154篇 |
1998年 | 145篇 |
1997年 | 155篇 |
1996年 | 151篇 |
1995年 | 112篇 |
1994年 | 118篇 |
1993年 | 91篇 |
1992年 | 57篇 |
1991年 | 53篇 |
1990年 | 59篇 |
1989年 | 41篇 |
1988年 | 28篇 |
1987年 | 22篇 |
1986年 | 33篇 |
1985年 | 28篇 |
1984年 | 22篇 |
1983年 | 19篇 |
1982年 | 11篇 |
1981年 | 13篇 |
1980年 | 16篇 |
1979年 | 10篇 |
1978年 | 22篇 |
1977年 | 10篇 |
1976年 | 13篇 |
1974年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
The growth of a prolate or oblate elliptic micro-void in a fiber reinforced anisotropic incompressible hyper-elastic rectangular thin plate subjected to uniaxial extensions is studied within the framework of finite elasticity. Coupling effects of void shape and void size on the growth of the void are paid special attention to. The deformation function of the plate with an isolated elliptic void is given, which is expressed by two parameters to solve the differential equation. The solution is approximately obtained from the minimum potential energy principle. Deformation curves for the void with a wide range of void aspect ratios and the stress distributions on the surface of the void have been obtained by numerical computation. The growth behavior of the void and the characteristics of stress distributions on the surface of the void are captured. The combined effects of void size and void shape on the growth of the void in the thin plate are discussed. The maximum stresses for the void with different sizes and different void aspect ratios are compared. 相似文献
102.
Fuzzy identification of cutting acoustic emission with extended subtractive cluster analysis 总被引:1,自引:0,他引:1
This paper presents fuzzy acoustic emission identification in high precision hard turning process based on extended subtractive cluster analysis combined with the least-square estimation method. The fuzzy identification method provides a simple way to arrive at a definite conclusion based upon the information obtained with the difficulty in understanding the exact physics of the machining process. The experimental results prove that the proposed method is efficient and feasible. 相似文献
103.
104.
搭建了一套研究金属和金属氧化物表面的超快激发态电子动力学和光化学动力学的飞秒双光子光电子能谱仪. 该装置将半球形电子能量分析仪和成像技术相结合,同时测量光电子的能量和角度分布.通过Mach-Zehnder干涉仪测量时间分辨的双光子光电子能谱获得超快激发电子态的动力学信息. 这一功能在Cu(111)上得到了证实. 另外还发展了一个通过实时测量双光子光电子能谱来研究表面光化学的方法,并成功应用到CH3CH2OH/TiO2(110)体系. 研究表明,只有将两种方法结合起来才能正确地研究光诱导的表面激发共振的动力学. 相似文献
105.
映射法是一种非常经典、有效和成熟的求解非线性演化方程的方法,其最大的特点是可以有多种不同形式的设解,使得最终求得的解丰富多彩. 利用改进的 Riccati 方程映射法和变量分离法,得到了(2+1)维非对称 Nizhnik-Novikov-Veselov 系统的新显式精确解.根据得到的孤波解,构造出该系统的峰孤子和分形孤子等局域结构,研究了两个孤立波的“追碰”现象.
关键词:
改进的映射法
(2+1)维非对称 Nizhnik-Novikov-Veselov 系统
局域结构
“追碰”现象 相似文献
106.
A linear optical unambiguous discrimination of hyperentangled Bell states is proposed for two‐photon systems entangled in both the polarization and momentum degrees of freedom (DOFs) assisted by time bin. This unambiguous discrimination scheme can completely identify 16 orthogonal hyperentangled Bell states using only linear optical elements, where the function of the auxiliary entangled Bell state is replaced by time bin. Moreover, the possibility of extending this scheme for distinguishing hyperentangled Bell states in n DOFs is discussed, and it shows that hyperentangled Bell states in n ( ) DOFs can be distinguished with k ( ) auxiliary entangled states of additional DOFs by introducing a time delay, which decreases the auxiliary entanglement resource required for unambiguous discrimination of hyperentangled Bell state. Therefore, this scheme provides a new way for distinguishing hyperentangled states with current technology, which will extend the application of discrimination of hyperentangled states via linear optics to other quantum information protocols besides hyperdense coding schemes in the future. 相似文献
107.
Cai and Zhang establish separate perturbation bounds for distances with spectral and Frobenius norms (Cai T, Zhang A. Rate‐optimal perturbation bounds for singular subspaces with applications to high‐dimensional statistics. The Annals of Statistics. 2018; Vol. 46, No. 1: 60?89). We extend their theorem to each unitarily invariant norm. It turns out that our estimation is optimal as well. 相似文献
108.
109.
Pengfei Sun Biao Deng Guohao Du He Li Weidong Sun Jiangbo Ren Tiqiao Xiao 《X射线光谱测定》2015,44(6):442-446
X‐ray fluorescence computed tomography is an emerging imaging modality that allows for the nondestructive reconstruction of the internal distribution of elements within a sample. The common use of X‐ray excitation energy (up to approximately 20 keV) has necessitated the use of l ‐shell fluorescence for heavy elements. In this study, based on high energy X‐ray at BL13W1 of the Shanghai Synchrotron Radiation Facility, we employed high‐energy excitation for tomographic imaging of the heavy metals (rare earth elements) in fish teeth from deep‐sea sediments on the micrometer scale using K‐shell X‐ray fluorescence. The virtual cross‐sectional distribution of La, Ce, Pm, Pr, Nd, and Sm were obtained, thereby providing a feasible approach for analyzing the enrichment mechanism of rare earth elements. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
110.
Wen-Yan Ji Xiao-Li Xia Xiao-Hui Ren Fang Wang Hai-Jun Wang Kai-Sheng Diao 《Structural chemistry》2013,24(1):49-54
Ab initio calculations have been performed on the complexes of CF2Cl2 with NO and SO2, and a set of stable configurations for CF2Cl2–NO and CF2Cl2–SO2 were found with no imaginary frequencies by the MP2 method. In addition, the binding energy and the NBO analysis were used to evaluate the relative stability of the complexes. The calculated results indicate that the weak interactions in the CF2Cl2–NO and CF2Cl2–SO2 systems involved are enhanced with the increase of the number of non-covalent bonds. Further studies predict that the CF2Cl2–SO2 system may play a more important role than the CF2Cl2–NO system in environmental problem because the former offers a stronger interaction than the latter. Furthermore, the non-covalent binding interactions of Cl···N and Cl···O for CF2Cl2–NO system, Cl···O, Cl···S and F···S for CF2Cl2–SO2 system, are the dominant forces, which seem to be very significant as a driving force influencing the arrangement of molecules, especially in CF2Cl2–SO2 system. 相似文献