全文获取类型
收费全文 | 9967篇 |
免费 | 2186篇 |
国内免费 | 1699篇 |
专业分类
化学 | 5022篇 |
晶体学 | 99篇 |
力学 | 592篇 |
综合类 | 119篇 |
数学 | 1170篇 |
物理学 | 6850篇 |
出版年
2024年 | 13篇 |
2023年 | 94篇 |
2022年 | 155篇 |
2021年 | 232篇 |
2020年 | 293篇 |
2019年 | 212篇 |
2018年 | 224篇 |
2017年 | 261篇 |
2016年 | 333篇 |
2015年 | 396篇 |
2014年 | 541篇 |
2013年 | 788篇 |
2012年 | 602篇 |
2011年 | 737篇 |
2010年 | 665篇 |
2009年 | 754篇 |
2008年 | 821篇 |
2007年 | 845篇 |
2006年 | 734篇 |
2005年 | 676篇 |
2004年 | 500篇 |
2003年 | 555篇 |
2002年 | 502篇 |
2001年 | 402篇 |
2000年 | 378篇 |
1999年 | 360篇 |
1998年 | 278篇 |
1997年 | 235篇 |
1996年 | 206篇 |
1995年 | 153篇 |
1994年 | 155篇 |
1993年 | 112篇 |
1992年 | 111篇 |
1991年 | 95篇 |
1990年 | 50篇 |
1989年 | 71篇 |
1988年 | 43篇 |
1987年 | 39篇 |
1986年 | 20篇 |
1985年 | 48篇 |
1984年 | 26篇 |
1983年 | 15篇 |
1982年 | 34篇 |
1981年 | 17篇 |
1980年 | 10篇 |
1979年 | 14篇 |
1977年 | 7篇 |
1976年 | 10篇 |
1974年 | 4篇 |
1973年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
We employ an isospin dependent version of the QMD transport model to study the influence of the isospin dependent part of the nuclear matter equation of state and in-medium nucleon–nucleon cross-sections on the dynamics of heavy-ion collisions at intermediate energies. We find that the extraction of useful information on the isospin-dependent part of the equation of state of nuclear matter from proton or neutron elliptic flows is obstructed by their sensitivity to model parameters and in-medium values of nucleon–nucleon cross-sections. Opposite to that, neutron–proton elliptic flow difference shows little dependence on those variables while its dependence on the isospin asymmetric EoS is enhanced, making it more suitable for a model independent constraining of the high-density behaviour of asy-EoS. Comparison with existing experimental FOPI-LAND neutron–hydrogen data can be used to set an upper limit to the softness of asy-EoS. Successful constraining of the asy-EoS via neutron–proton elliptic flow difference will require experimental data of higher accuracy than presently available. 相似文献
992.
G.Y. Gao K.L. Yao M.H. SongZ.L. Liu 《Journal of magnetism and magnetic materials》2011,323(21):2652-2657
First-principles full-potential linearized augmented plane-wave method is used to investigate the electronic structure and magnetic properties of hypothetical zinc-blende and rocksalt LiS, NaS and KS. We find that all the compounds except rocksalt LiS exhibit half-metallic ferromagnetism with an integer magnetic moment of 1.00 μB per formula unit. The ferromagnetism results from the spin-polarization of p states of anion S. Total energies calculations indicate the rocksalt phase is lower in energy than the zinc-blende one. The total energy differences are about 0.38, 0.36 and 0.32 eV per formula unit for LiS, NaS and KS, respectively. Meanwhile, it is shown that rocksalt NaS and KS have the half-metallic gaps of 0.22 and 0.41 eV, respectively, and the half-metallic gaps are 0.03, 0.46 and 0.65 eV for zinc-blende LiS, NaS and KS, respectively. We also find the half-metallicity is robust against the lattice contraction up to 7% and 13% for rocksalt NaS and KS, respectively. Although rocksalt LiS is nonmagnetic and metallic at the equilibrium lattice constant, it shows half-metallic ferromagnetism when the lattice constant is larger than 5.40 Å. 相似文献
993.
We calculate the strange star properties in the framework of the Field Correlator Method. We find that for gluon condensate values G2 in the range 0.006–0.007 GeV4, which give a critical temperature Tc∼170 MeV at μc=0, the sequences of strange stars are compatible with some of the semi-empirical mass–radius relations and data obtained from astrophysical observations. 相似文献
994.
A scheme is proposed for generating maximally entangled Dicke states among four modes. The scheme only uses Kerr medium and homodyne measurements on coherent light fields, which can be efficiently made in quantum optical laboratories. The scheme can be generalized to produce maximally entangled 2k-qubit states. 相似文献
995.
We investigate the effect of geometry on the ground-state ordering of artificially frustrated magnetic rectangular and triangular lattices by Monte Carlo method. By varying the vertical lattice spacing while keeping the horizontal one fixed, we show that when the ratio of vertical to horizontal lattice spacing, labeled by η, is less than 1.82, the ground state of the rectangular lattice presents long-range antiferromagnetic order and for η?1.82 the ground state changes to long-range mixed ferromagnetic and antiferromagnetic order. For the frustrated triangular lattice, the short-range ordered state as well as two long-range ordered ground states occurs transiently at η=0.87 and 2, where the energies of the two ground states with long-range order are approximately equal. In addition, the level of frustration of both frustrated lattices is found to be largely relevant to the ratio η. 相似文献
996.
A scheme is proposed for the generation of a W state for three atoms trapped in spatially separated cavities connected by optical fibers via quantum Zeno dynamics. Our scheme is based on the resulting effective dynamics induced by continuous coupling between the atoms and cavities. The effects of decoherence such as atomic spontaneous emission and the fiber and cavity losses are considered. Numerical results show that the scheme is very robust against the cavity decay due to a tiny excitation probability of the cavity fields during the operation. 相似文献
997.
We present an approach to faithfully teleport an unknown quantum state of entangled particles in a multi-particle system involving multi spatially remote agents via probabilistic channels. In our scheme, the integrity of an entangled multi-particle state can be maintained even when the construction of a faithful channel fails. Furthermore, in a quantum teleportation network, there are generally multi spatially remote agents which play the role of relay nodes between a sender and a distant receiver. Hence, we propose two schemes for directly and indirectly constructing a faithful channel between the sender and the distant receiver with the assistance of relay agents, respectively. Our results show that the required auxiliary particle resources, local operations and classical communications are considerably reduced for the present purpose. 相似文献
998.
Sridhar S. KannurpattiMichael A. Motes Bart RypmaBharat B. Biswal 《Magnetic resonance imaging》2011,29(1):140-146
Block and event-related stimulus designs are typically used in fMRI studies depending on the importance of detection power or estimation efficiency. The extent of vascular contribution to variability in block and event-related fMRI-BOLD response is not known. With scaling, the extent of vascular variability in the fMRI-BOLD response during block and event-related design tasks was investigated. Blood oxygen level-dependent (BOLD) contrast data from healthy volunteers performing a block design motor task and an event-related memory task requiring performance of a motor response were analyzed from the regions of interest (ROIs) surrounding the primary and supplementary motor cortices. Average BOLD signal change was significantly larger during the block design compared to the event-related design. In each subject, BOLD signal change across voxels in the ROIs had higher variation during the block design task compared to the event-related design task. Scaling using the resting state fluctuation of amplitude (RSFA) and breath-hold (BH), which minimizes BOLD variation due to vascular origins, reduced the within-subject BOLD variability in every subject during both tasks but significantly reduced BOLD variability across subjects only during the block design task. The strong non-neural source of intra- and intersubject variability of BOLD response during the block design compared to event-related task indicates that study designs optimizing for statistical power through enhancement of the BOLD contrast (for, e.g., block design) can be affected by enhancement of non-neural sources of BOLD variability. 相似文献
999.
将基态氦原子的波函数取作1s2和1s2s两个组态函数的叠加,利用组态相互作用方法解析计算了氦原子基态的非相对论能量.计算结果表明,考虑激发态1s2s与基态的相互作用,可以获得0.029 38Hartree的基态能量修正.本文的解析组态相互作用方法可作为量子力学教学的有益补充. 相似文献
1000.
基于改造的弱相干态光源,提出了一种非正交编码被动诱骗态量子密钥分配方案.该方案不主动制备诱骗态,而是根据发送端探测器是否响应,将接收端的探测结果分为响应集合和未响应集合,以此分别作为信号态和诱骗态,并利用这两个集合来估计参量和生成密钥.数值仿真表明,非正交编码被动诱骗态方案的密钥生成效率和安全传输距离都优于现有的被动诱骗态方案,且性能非常接近主动无穷诱骗态方案的理论极限值;未响应集合对密钥生成的参与使方案性能免受发送端探测效率的影响,弥补了实际探测器探测效率低下的缺陷;由于不需要主动制备诱骗态,该方案实现非常简单,适用于高速量子密钥分配的场合.
关键词:
量子光学
量子密钥分配
被动诱骗态
密钥生成效率 相似文献