全文获取类型
收费全文 | 13904篇 |
免费 | 2427篇 |
国内免费 | 1409篇 |
专业分类
化学 | 5836篇 |
晶体学 | 182篇 |
力学 | 362篇 |
综合类 | 65篇 |
数学 | 217篇 |
物理学 | 6619篇 |
综合类 | 4459篇 |
出版年
2024年 | 34篇 |
2023年 | 137篇 |
2022年 | 369篇 |
2021年 | 395篇 |
2020年 | 520篇 |
2019年 | 503篇 |
2018年 | 485篇 |
2017年 | 540篇 |
2016年 | 624篇 |
2015年 | 550篇 |
2014年 | 691篇 |
2013年 | 981篇 |
2012年 | 970篇 |
2011年 | 981篇 |
2010年 | 821篇 |
2009年 | 820篇 |
2008年 | 753篇 |
2007年 | 844篇 |
2006年 | 818篇 |
2005年 | 708篇 |
2004年 | 644篇 |
2003年 | 611篇 |
2002年 | 630篇 |
2001年 | 483篇 |
2000年 | 425篇 |
1999年 | 339篇 |
1998年 | 311篇 |
1997年 | 234篇 |
1996年 | 232篇 |
1995年 | 215篇 |
1994年 | 165篇 |
1993年 | 132篇 |
1992年 | 125篇 |
1991年 | 114篇 |
1990年 | 110篇 |
1989年 | 99篇 |
1988年 | 70篇 |
1987年 | 47篇 |
1986年 | 40篇 |
1985年 | 39篇 |
1984年 | 28篇 |
1983年 | 14篇 |
1982年 | 20篇 |
1981年 | 9篇 |
1980年 | 8篇 |
1978年 | 13篇 |
1977年 | 4篇 |
1976年 | 9篇 |
1975年 | 6篇 |
1973年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
YANG Guo-Hui ZHOU Ling 《理论物理通讯》2008,49(6):1635-1638
The thermal entanglement of a three-qubit Heisenberg chain under a nonuniform magnetic field is studied. It is very interesting to note that the next nearest neighbor entanglement (NNNE) could be larger than the nearest neighbor entanglement (NNE). We analyze the ground state entanglement, and give the conditions that NNNE is larger than NNE near zero temperature. Our results also show that the nonuniform field could induce the entanglement and improve the threshold temperature at certain parameter region. 相似文献
992.
Forward and inverse problem for cardiac magnetic field and electric potential using two boundary element methods 下载免费PDF全文
This paper discusses the forward and inverse problem for cardiac magnetic fields and electric potentials.A torso-heart model established by boundary element method(BEM) is used for studying the distributions of cardiac magnetic fields and electric potentials.Because node-to-node and triangle-to-triangle BEM can lead to discrepant field distributions,their properties and influences are compared.Then based on constructed torso-heart model and supposed current source functional model-current dipole array,the magnetic and electric imaging by optimal constrained linear inverse method are applied at the same time.Through figure and reconstructing parameter comparison,though the magnetic current dipole array imaging possesses better reconstructing effect,however node-to-node BEM and triangleto-triangle BEM make little difference to magnetic and electric imaging. 相似文献
993.
We study a quantum ring (QR) with four electrons in a perpendicular external magnetic field B by exact diagonalization. The low-lying spectra of the QR as a function orb are obtained. A phase diagram is presented indicating that the angular momentum and the spin of the ground state of the QR may jump when B and/or the radius of the QR vary, and a corresponding analysis is performed. By plotting the density functions of the QR, the ground-state configuration is found to be a regular quadrangle. Furthermore, the features of the ground-state persistent current are revealed. 相似文献
994.
Based on the p-f shell model, the effect of strong magnetic field on neutrino energy loss rates by electron capture is investigated. The calculations show that the magnetic field has only a slight effect on the neutrino energy loss rates in the range of 108—1013G on the surfaces of most neutron stars. But for some magnetars, the range of the magnetic field is 1013—1018G, and the neutrino energy loss rates are greatly reduced, even by more than four orders of magnitude due to the strong magnetic field. 相似文献
995.
Magnetic properties of several potential rocksalt half-metallic ferromagnets based on the first-principles calculations 下载免费PDF全文
Several rocksalt Sr4X3N (X=,O, S, Se, and Te) are predicted to be potential half-metallic ferromagnets free of transition-metal and rare-earth elements by performing the first-principles calculations. Then their magnetic properties, such as the half metallicity and the crystal-cell magnetic moments are investigated. The Sr4X3N possibly have higher Curie temperatures and have more stable half metallicity than the Sr4X3C. Their crystal-cell magnetic moments are all 1.00 μB. The crystal-cell magnetic moments and the half metallicity arise mainly from the N ions. The main mechanism is the strong covalent interaction leading to the sp2 hybridized orbitals in the Sr4X3N. Then two Sr-5s and three N-2p electrons enter into three sp2 hybridized orbitals. Among these five electrons, four electrons are paired and one is unpaired, so there are three spin-up electrons and two spin-down electrons in these sp2 hybridized orbitals. 相似文献
996.
利用实验和能带计算相结合的方法,对介于两种预期的半金属Heusler合金Co2FeSi和Co2MnSi间的四元合金Co50Fe25-xMnxSi25的晶体结构、磁性、能带结构和半金属性进行了研究.采用考虑库仑相互作用的的广义梯度近似方法计算了系列合金的能带结构,通过与实验结果进行对比,揭示了成分变化过程中合金分子磁矩及原子磁矩的变化规律.研究发现,
关键词:
磁性
半金属
Heusler合金 相似文献
997.
Jianwei Zhou Liyun Li Hongbing Hu Baolian Yang Zhaohong Dan Jianqing Qiu Jiugao Guo Feng Chen Chaohui Ye 《Solid state nuclear magnetic resonance》1994,3(6):339-351
The results of a study of two types of natural-diamond crystals by dynamic nuclear polarization (DNP)-enhanced high-resolution solid-state 13C nuclear magnetic resonance (NMR) are reported. The home-built DNP magic-angle spinning (MAS) 13C NMR spectrometer operates at 54 GHz for electrons and 20.2 MHz for carbons. The power of the microwave source was about 30 W and the highest DNP enhancement factor came near to 103. It was shown that in the MAS spectra the 13C NMR linewidths of the Ib-type diamond were broader than those of IaB3-type diamond. From the hyperfine structure of the DNP enhancement as a function of frequency, four kinds of nitrogen-centred and one kind of carbon-centred free radicals could be identified in the Ib-type diamond. The hyperfine structures of the DNP enhancement curve that originated from the anisotropic hyperfine interaction between electron and nuclei could be partially averaged out by MAS. The 13C polarization time of DNP was rather long, i.e. 1500 s, and the spin—lattice relaxation time (without microwave irradiation) was about 300 s, which was somewhat shorter than anticipated. Discussions on these experimental results have been made in this report. 相似文献
998.
The Bi2Sr2CaCu2O8 system is viewed as an archetypal of superconductors modelled as Josephson coupled CuO2 bilayers. The isothermal and temperature dependent DC and AC magnetization measurements forH‖c in a single crystal of Bi2212 have been performed. Qualitative changes are observed to occur over a narrow range of temperature
values before reaching the superconducting-normal transition. The observed behaviour can be ascribed to the rapid variation
in the strength of the coupling between the superconducting CuO2 planes (i.e., bilayers in the case of Bi2212). Strongly coupled planes behave like a 3D superconductor, whereas weakly coupled
planes have a two component response attributable to 2D planes and interplanar couplings. We believe that this paper is a
plethora of new findings. Our observations imply that resistivity across the planes becomes zero earlier than that within
the planes. A new line (designated asH
2D(T)) above which the change in the electromagnetic response is dominated by quasi 2D-planes has been determined for the first
time. This paper also contains the first observation of Differential Diamagnetic Effect (DDE) in the In-phase AC susceptibility
data which signals the onset (atT
2D(H)) of dominance of response from 2D-planes. In addition to a host of interesting thermomagnetic history effects which are
a consequence of interplay between the diamagnetic responses from the two components, a comparison of irreversibility lines
(of the 3D state) determined by different methods on the same specimen of a HTSC is also being presented for the first time.
We have come across Paramagnetic Meissner Effect (PME), first recognized in ceramic samples of Bi2212, in the temperature
region of dimensional crossover in our single crystal sample, whichinter-alia confirms our labelling of the two component behaviour. A schematic phase diagram summarizing the various transformations
that can occur nearT
c in the electromagnetic response of an anisotropic layered system has been drawn. 相似文献
999.
A new model (called the Temperley-Lieb interactions model) is introduced, in two-dimensional lattice statistics, on a square lattice . The Temperley-Lieb equivalence of this model to the six-vertex, self-dual Potts, critical hard-hexagons and critical nonintersecting string models is established. A graphical equivalence of this model to the six-vertex model generalizes this equivalence to noncritical cases of the above models. The order parameters of a specialization of this model are studied. 相似文献
1000.
基于本实验室提出一种新型以势能形式表达的分子距边矢量, 深入地系统研究了核磁共振碳-13谱化学位移和(CSS)规律以及分子拓扑指数矢量在定量结构波谱关系(QSSR)中的应用. 借助多种计量化学方法包括多元线性回归、逐步多元回归、主成分回归、主筛选回归等进行分子拟模和定量相关研究, 发现烷烃13C NMR 化学位移和(CSS)与其分子距边矢量及路径长度指数有良好线性相关性, 回归方程及其统计参数为:CSS=bν+cp3=∑mj=0bjνj+b11p3=b0ν+b1ν1+b2ν2+b3ν3+b4ν4+b5ν5+b6ν6+b7ν7+b8ν8+b9ν9+b10ν10+b11p3=-13.576+22.179ν1+28.407ν2+25 .950ν3+26.690ν4+14.498ν5+5.726ν6-5.379ν7-3.214ν8-15.021ν9 -25.710ν10+12.278p3 n=63, R=0.997, EV=99.68%, RMS=3.7348, SD=4.1 18, F= 773.116, U=144228.844, Q=864.938; CV: R2CV=0.980, EV=98.83%, RMS=7.126 1, SDCV=7.634, FCV=221.720, UCV=142121.891, QCV=2971 .896.结果良好. 相似文献