全文获取类型
收费全文 | 1272篇 |
免费 | 422篇 |
国内免费 | 400篇 |
专业分类
化学 | 267篇 |
晶体学 | 2篇 |
力学 | 194篇 |
综合类 | 42篇 |
数学 | 335篇 |
物理学 | 1254篇 |
出版年
2024年 | 3篇 |
2023年 | 14篇 |
2022年 | 33篇 |
2021年 | 27篇 |
2020年 | 33篇 |
2019年 | 21篇 |
2018年 | 33篇 |
2017年 | 55篇 |
2016年 | 56篇 |
2015年 | 56篇 |
2014年 | 74篇 |
2013年 | 134篇 |
2012年 | 99篇 |
2011年 | 115篇 |
2010年 | 87篇 |
2009年 | 114篇 |
2008年 | 141篇 |
2007年 | 98篇 |
2006年 | 105篇 |
2005年 | 94篇 |
2004年 | 91篇 |
2003年 | 76篇 |
2002年 | 89篇 |
2001年 | 75篇 |
2000年 | 74篇 |
1999年 | 38篇 |
1998年 | 42篇 |
1997年 | 40篇 |
1996年 | 43篇 |
1995年 | 36篇 |
1994年 | 19篇 |
1993年 | 20篇 |
1992年 | 10篇 |
1991年 | 8篇 |
1990年 | 11篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有2094条查询结果,搜索用时 5 毫秒
1.
《Wave Motion》2018
Large cable net structures have been widely applied in aerospace engineering due to the feature of light-weight, high packaging efficiency, and high thermal stability. Structural vibrations induced by a variety of disturbances are inevitable in the space environment, resulting in the requirement of effective vibration control strategies for large cable net structures. Since the large cable net structures have many closely spaced vibrational modes in the range of low frequencies, traditional modal based control may cause modal truncation and spillover problems. In this paper, a wave-based boundary control strategy is adopted and its effectiveness to control the vibration of cable net structures is investigated, by transfer function analysis and numerical methods. It is found that the structural vibration can be absolutely resisted by applying the wave-based boundary controllers onto all the exterior nodes, when disturbances come from the external boundaries of the cable net. Our results in this paper can provide a theoretical basis for the vibration control of large cable net structures. 相似文献
2.
3.
Meng Wen Zu‐Ping Xiao Chun‐Ya Wang Xi‐He Huang 《Acta Crystallographica. Section C, Structural Chemistry》2015,71(2):136-139
The title compound, {[Zn4(C8H4O4)3(OH)2(C12H6N2O2)2]·2H2O}n, has been prepared hydrothermally by the reaction of Zn(NO3)2·6H2O with benzene‐1,4‐dicarboxylic acid (H2bdc) and 1,10‐phenanthroline‐5,6‐dione (pdon) in H2O. In the crystal structure, a tetranuclear Zn4(OH)2 fragment is located on a crystallographic inversion centre which relates two subunits, each containing a [ZnN2O4] octahedron and a [ZnO4] tetrahedron bridged by a μ3‐OH group. The pdon ligand chelates to zinc through its two N atoms to form part of the [ZnN2O4] octahedron. The two crystallographically independent bdc2− ligands are fully deprotonated and adopt μ3‐κO:κO′:κO′′ and μ4‐κO:κO′:κO′′:κO′′′ coordination modes, bridging three or four ZnII cations, respectively, from two Zn4(OH)2 units. The Zn4(OH)2 fragment connects six neighbouring tetranuclear units through four μ3‐bdc2− and two μ4‐bdc2− ligands, forming a three‐dimensional framework with uninodal 6‐connected α‐Po topology, in which the tetranuclear Zn4(OH)2 units are considered as 6‐connected nodes and the bdc2− ligands act as linkers. The uncoordinated water molecules are located on opposite sides of the Zn4(OH)2 unit and are connected to it through hydrogen‐bonding interactions involving hydroxide and carboxylate groups. The structure is further stabilized by extensive π–π interactions between the pdon and μ4‐bdc2− ligands. 相似文献
4.
5.
B. Mukeru 《中国物理C(英文版)》2023,47(2):024104-024104-5
An analysis of the breakup of the \begin{document}$ ^{31}{\rm Ne} $\end{document} ![]()
![]()
weakly-bound neutron-halo system on a lead target is presented, considering the \begin{document}$ 2p_{3/2} $\end{document} ![]()
![]()
and \begin{document}$ 1f_{7/2} $\end{document} ![]()
![]()
ground-state configurations. It is shown that a high centrifugal barrier almost wipes out the breakup channel, thus assimilating the breakup of a weakly-bound system to that of a tightly-bound system, and also reduces the range of the monopole nuclear potential. Consequently, a high centrifugal barrier prevents the suppression of the Coulomb-nuclear interference (CNI) peak by weakening couplings to the breakup channel and reducing the range of the monopole nuclear potential, two main factors that would otherwise suppress such a peak. The present study also identifies couplings to the breakup channel and a long-ranged monopole nuclear potential as the main factors that lead to the suppression of the CNI peak. A low centrifugal barrier together with a Coulomb barrier would also effectively prevent the suppression of the CNI peak in proton-halos as reported in the case of the \begin{document}$ ^8{\rm B} $\end{document} ![]()
![]()
proton-halo. 相似文献
6.
Quantum reaction dynamics of C(1D) + HD → CH(CD) + D(H) on the ground state potential energy surface 下载免费PDF全文
We present accurate quantum dynamic calculations of the reaction C(1D) + HD on the latest version of the potential energy surface [Zhang et al., J. Chem. Phys. 140, 234301 (2014)]. Using a Chebyshev real wave packet method with full Coriolis coupling, we obtain the initial state‐specified ( ) reaction probabilities, integral cross sections, and rate constants. The resulting probabilities display oscillatory structures due to numerous long‐lived resonances supported by the deep potential well. The calculated rate constants and CD/CH product branching ratio at room temperature are in reasonably good agreement with the experimental measurements. 相似文献
7.
Global X2A′ potential energy surface of Li2H and quantum dynamics of H + Li2 (X1Σg+) → Li + LiH (X1Σ+) reaction 下载免费PDF全文
A global potential energy surface (PES) for the electronic ground state of Li2H system is constructed over a large configuration space. About 30 000 ab initio energy points have been calculated by MRCI‐F12 method with aug‐cc‐pVTZ basis set. The neural network method is applied to fit the PES and the root mean square error of the current PES is only 1.296 meV. The reaction dynamics of the title reaction has been carried out by employing time‐dependent wave packet approach with second order split operator on the new PES. The reaction probability, integral cross section and thermal rate constant are obtained from the dynamics calculation. In most of the collision energy regions, the integral cross sections are in well agreement with the results reported by Gao et al. The rate constant calculated from the new PES increases in the temperature range of present investigation. 相似文献
8.
Currently, feature annotation remains one of the main challenges in untargeted metabolomics. In this context, the information provided by high-resolution mass spectrometry (HRMS) in addition to accurate mass can improve the quality of metabolite annotation, and MS/MS fragmentation patterns are widely used. Accurate mass and a separation index, such as retention time or effective mobility (μeff), in chromatographic and electrophoretic approaches, respectively, must be used for unequivocal metabolite identification. The possibility of measuring collision cross-section (CCS) values by using ion mobility (IM) is becoming increasingly popular in metabolomic studies thanks to the new generation of IM mass spectrometers. Based on their similar separation mechanisms involving electric field and the size of the compounds, the complementarity of DTCCSN2 and μeff needs to be evaluated. In this study, a comparison of DTCCSN2 and μeff was achieved in the context of feature identification ability in untargeted metabolomics by capillary zone electrophoresis (CZE) coupled with HRMS. This study confirms the high correlation of DTCCSN2 with the mass of the studied metabolites as well as the orthogonality between accurate mass and μeff, making this combination particularly interesting for the identification of several endogenous metabolites. The use of IM-MS remains of great interest for facilitating the annotation of neutral metabolites present in the electroosmotic flow (EOF) that are poorly or not separated by CZE. 相似文献
9.
V. I. Gulyaev P. Z. Lugovoi M. A. Belova I. L. Solov’ev 《International Applied Mechanics》2006,42(6):692-698
The quasistatic stability of a rotating drillstring under longitudinal force and torque is analyzed. Constitutive equations
are derived, and a technique to solve them is proposed. It is shown that the buckling mode of the drillstring is helical within
a section subjected to compressive forces
__________
Translated from Prikladnaya Mekhanika, Vol. 42, No. 6, pp. 101–109, June 2006. 相似文献
10.
湍流的诱导及其对瓦斯爆炸过程中火焰和爆炸波的作用 总被引:4,自引:3,他引:4
在实验的基础上,研究了管内瓦斯爆炸过程中湍流的诱导及其对瓦斯爆炸过程中火焰和爆炸波的影响作用.研究结果表明,管道面积突变对瓦斯爆炸过程中湍流的产生具有重要影响.管道面积突变(变大、变小)时,产生附加湍流,并使下游火焰气流的湍流度增加,瓦斯爆炸过程中火焰的传播速度迅速提高,并可诱导激波的产生.在80×80mm等截面直管中(瓦斯浓度为理论上最猛烈的爆炸浓度9.5%),瓦斯爆炸最大火焰传播速度为40.8m/s,管内各点均为压力波信号,当管道加装一Φ300mm圆管形成面积突扩11倍和突缩11倍两断面后,面积突扩处(L/D=22)火焰速度增大5.05倍,达到64.4m/s,面积突缩处(L/D=28)火焰速度为156.0m/s, 增大4.55倍,并在L/D=48倍处形成激波(超压1.6976atm、波速416.7m/s),在L/D=98倍处,激波强度最大.在面积突变管内加装加速环可使瓦斯爆炸过程中湍流度加剧,火焰的传播速度更高,激波生成的位置(L/D=28)、最强点位置(L/D=70)均前移,激波强度增大.研究结果对指导现场如何防治瓦斯爆炸,减轻瓦斯爆炸的威力具有一定的指导意义. 相似文献