全文获取类型
收费全文 | 6743篇 |
免费 | 992篇 |
国内免费 | 689篇 |
专业分类
化学 | 3586篇 |
晶体学 | 60篇 |
力学 | 308篇 |
综合类 | 35篇 |
数学 | 582篇 |
物理学 | 1951篇 |
无线电 | 1902篇 |
出版年
2024年 | 19篇 |
2023年 | 171篇 |
2022年 | 140篇 |
2021年 | 223篇 |
2020年 | 244篇 |
2019年 | 178篇 |
2018年 | 182篇 |
2017年 | 176篇 |
2016年 | 268篇 |
2015年 | 274篇 |
2014年 | 361篇 |
2013年 | 426篇 |
2012年 | 509篇 |
2011年 | 555篇 |
2010年 | 412篇 |
2009年 | 426篇 |
2008年 | 394篇 |
2007年 | 410篇 |
2006年 | 372篇 |
2005年 | 334篇 |
2004年 | 256篇 |
2003年 | 193篇 |
2002年 | 223篇 |
2001年 | 179篇 |
2000年 | 149篇 |
1999年 | 163篇 |
1998年 | 161篇 |
1997年 | 155篇 |
1996年 | 144篇 |
1995年 | 110篇 |
1994年 | 128篇 |
1993年 | 84篇 |
1992年 | 77篇 |
1991年 | 72篇 |
1990年 | 44篇 |
1989年 | 58篇 |
1988年 | 45篇 |
1987年 | 40篇 |
1986年 | 14篇 |
1985年 | 18篇 |
1984年 | 9篇 |
1983年 | 9篇 |
1982年 | 5篇 |
1981年 | 9篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1957年 | 2篇 |
排序方式: 共有8424条查询结果,搜索用时 484 毫秒
991.
Guoping Dong Xiudi Xiao Xiaofeng Liu Bin Qian Zhijun Ma Song Ye Danping Chen Jianrong Qiu 《Journal of nanoparticle research》2010,12(4):1319-1329
Poly (vinyl alcohol) (PVA) and poly (vinyl pyrrolidone) (PVP) nanofibers embedding Ag nanoparticles (5–18 nm) have been prepared
successfully by electrospinning at room temperature. Scanning electron microscope (SEM), X-ray diffraction (XRD), high-resolution
transmission electron microscopy (HRTEM), Fourier transform IR spectra (FTIR), and Raman scattering were used to characterize
the structure and properties of Ag nanoparticle-embedded PVA and PVP nanofibers before and after heat treatment at different
temperature. The antibacterial activity of Ag nanoparticle-embedded PVP nanofibers after heat treatment was also tested, which
indicated that the biological activity of yeast cells was effectively inhibited by these Ag nanoparticle-embedded PVP nanofibers. 相似文献
992.
A modified spatially extended Tang-Othmer Ca2+ model is used to study intracellular Ca2+ spiral waves numerically.It is found that,as a local stimulation,the local agonist-binding on the cell membrane,which enhances the local concentration of the messenger molecule inositol 1,4,5-trisphosphate(IP 3),can influence the dynamics of the spiral waves.1) Strong enough stimuli can change the spiral wave from a meandering to a rigidly rotating one.2) On the other hand,strong enough stimuli can suppress the spiral wave from the system.It provides the theoretical clue for controlling the spiral waves by stimulating the cell membrane. 相似文献
993.
Shi-liang Li Dao-xin Yao Yi-ming Qiu Hye Jung Kang E. W. Carlson Jiang-ping Hu Gen-fu Chen Nan-lin Wang Peng-cheng Dai 《Frontiers of Physics in China》2010,5(2):161-165
We use inelastic neutron scattering to study the low-energy spin excitations of polycrystalline samples of nonsuperconducting
CeFeAsO and superconducting CeFeAsO0.84F0.16. Two sharp dispersionless modes are found at 0.85 and 1.16 meV in CeFeAsO below the Ce antiferromagnetic (AF) ordering temperature
of T
N
Ce ˜ 4 K. On warming to above T
N
Ce ˜ 4 K, these two modes become one broad dispersionless mode that disappears just above the Fe ordering temperature T
N
Fe ˜ 140 K. For superconducting CeFeAsO0.84F0.16, where Fe static AF order is suppressed, we find a weakly dispersive mode center at 0.4 meV that may arise from short-range
Ce-Ce exchange interactions. Using a Heisenberg model, we simulate powder-averaged Ce spin wave excitations. Our results show
that we need both Ce spin wave and crystal electric field excitations to account for the whole spectra of low-energy spin
excitations. 相似文献
994.
Qiu W Zhang L Okobiah O Yang Y Wang L Zhong D Zewail AH 《The journal of physical chemistry. B》2006,110(21):10540-10549
Human serum albumin, the most abundant protein found in blood plasma, transports a great variety of ligands in the circulatory system and undergoes reversible conformational transitions over a wide range of pH values. We report here our systematic studies of solvation dynamics and local rigidity in these conformations using a single intrinsic tryptophan (W214) residue as a local molecular probe. With femtosecond resolution, we observed a robust bimodal distribution of time scales for all conformational isomers. The initial solvation occurs in several picoseconds, representing the local librational/rotational motions, followed by the dynamics, in the tens to hundreds of picoseconds, which result from the more bonded water in the tryptophan crevice. Under the physiological condition of neutral pH, we measured approximately 100 ps for the decay of the solvation correlation function and observed a large wobbling motion at the binding site that is deeply buried in a crevice, revealing the softness of the binding pocket and the large plasticity of the native structure. At acidic pH, the albumin molecule transforms to an extended conformation with a large charge distribution at the surface, and a similar temporal behavior was observed. However, at the basic pH, the protein opens the crevice and tightens its globular structure, and we observed significantly faster dynamics, 25-45 ps. These changes in the solvation dynamics are correlated with the conformational transitions and related to their structural integrity. 相似文献
995.
Wang Y Xu H Wang X Zhang X Jia H Zhang L Qiu J 《The journal of physical chemistry. B》2006,110(28):13835-13840
Monodispersed porous crystalline TiO(2), SrTiO(3), and BaTiO(3) spheres were produced through a one-step hydrothermal process from amorphous TiO(2) spheres. The resulting samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and nitrogen sorption measurements. On the basis of the characterization results, we proposed a formation process of these porous spheres according to a mechanism analogous to the Kirkendall effect. This study provides a general way to synthesize porous titania-based spheres. 相似文献
996.
A method combined the self-consistent field theory (SCFT) for the rigid rod with the Helfrich curvature elasticity theory for the vesicle has been developed for studying the shape of vesicles anchored by rigid rod. Both the deformation of the vesicle and the density distribution of rod segments can be obtained. Because of the vesicle's impenetrability for the rod segments and the decrease of the available space for the rod orientational configurations, the anchored rod segments exert the inhomogeneous entropic pressure on the vesicle and induce the change of vesicle shape. The interaction between the rod segments and the vesicle membrane exerts an extra tension to the membrane. Thus the interaction between the vesicle membrane and the rod segments, the rod length, and the bending rigidity of vesicle are investigated as the important factors to the shape transformation of the vesicle and the density distribution of rod segments. This method can be extended to more complicated and real biological systems, such as polymers with different topological architectures/vesicle, multiple chains/vesicle, protein inclusions, etc. 相似文献
997.
Zhijian Qiu 《Integral Equations and Operator Theory》2006,56(3):415-429
For a compact subset K in the complex plane, let A(K) denote the algebra of all functions continuous on K and analytic on K° and let R(K) denote the uniform closure of the rational functions with poles off K. Let G is a bounded open subset whose complement in the plane has a finite number of components. Suppose that
and every function in H∞(G) is the pointwise limit of a bounded sequence of functions in
. The purpose of this paper is to characterize all subnormal operators similar to Mz, the operator of multiplication by the independent variable z on the Hardy space H2(G). We also characterize all bounded linear operators that are unitarily equivalent to Mz in the case when each of the components of G is simply connected. In particular, our similarity result extends a well-known result of W. Clary on the unit disk to multiply
connected domains. 相似文献
998.
物理教学中,经常碰到一些极值问题,学生大都感到十分棘手.物理极值问题,简单说就是求某物理量在某过程中的极大值或极小值.物理极值问题是中学物理教学经常遇到的一个重要内容,涉及的知识面广,综合性强,对学生数理结合、综合分析能力要求较高.物理极值问题已成为中学生学习物理的一大难点,解决这类问题一般有两种途径:一是极值问题的数学解法;二是极值问题的物理解法.笔者主要讨论后者,就如何巧用“矢量图”分析物理极值问题进行一些探讨. 相似文献
999.
Daohai Xie Bensheng Qiu Jiangyang Zhang Xiaoming Yang 《Applied magnetic resonance》2010,39(4):373-380
The aim of this study was to evaluate the capability of using micro-magnetic resonance imaging (MRI) to visualize and characterize
atherosclerotic plaques of mouse models. Twenty five apolipoprotein E-knockout mice were fed atherogenic diet, which enabled
creation of aortic atherosclerotic plaques. Aortic plaques were examined in vivo by 4.7 T MRI and then characterized ex vivo
by 11.7 T three-dimensional MRI. MR images were correlated with subsequent histological confirmation. In vivo 4.7-T MRI demonstrated
unevenly thickened aortic walls due to formation of atherosclerotic plaques. Ex vivo 11.7-T MRI enabled not only to acquire
full volume-rendered images of the entire vessels but also to characterize plaque components (such as lipid cores and fibrous
caps) at any level and any projection, which were confirmed by histological correlation. Micro-MRI provides an excellent imaging
tool for basic science to investigate atherosclerosis in small animal models, which may become a supplement to histopathology
of atherosclerotic cardiovascular disease. 相似文献
1000.
Three B-containing lithium salts, lithium bis(oxalato)borate, lithium (malonatooxalato)borate, and lithium bis(malonato)borate,
are studied by density functional theory. The relationships between the structure of lithium salts and their physical chemistry
characteristics are investigated. A linear correlation is observed between the highest occupied molecular orbital energy of
lithium salts and their oxidation potentials. The correlation between ionic conductivity and binding energy of lithium salt
is also studied. The physical chemistry characteristics of a novel lithium salt, lithium oxalyldifluoroborate, are predicted
according to the rules concluded from other B-containing lithium salts. 相似文献