全文获取类型
收费全文 | 10713篇 |
免费 | 2455篇 |
国内免费 | 1709篇 |
专业分类
化学 | 730篇 |
晶体学 | 57篇 |
力学 | 1118篇 |
综合类 | 488篇 |
数学 | 8782篇 |
物理学 | 3702篇 |
出版年
2024年 | 38篇 |
2023年 | 147篇 |
2022年 | 176篇 |
2021年 | 176篇 |
2020年 | 163篇 |
2019年 | 198篇 |
2018年 | 152篇 |
2017年 | 240篇 |
2016年 | 247篇 |
2015年 | 305篇 |
2014年 | 656篇 |
2013年 | 517篇 |
2012年 | 637篇 |
2011年 | 709篇 |
2010年 | 736篇 |
2009年 | 872篇 |
2008年 | 808篇 |
2007年 | 773篇 |
2006年 | 741篇 |
2005年 | 727篇 |
2004年 | 682篇 |
2003年 | 658篇 |
2002年 | 542篇 |
2001年 | 542篇 |
2000年 | 471篇 |
1999年 | 401篇 |
1998年 | 363篇 |
1997年 | 343篇 |
1996年 | 341篇 |
1995年 | 330篇 |
1994年 | 281篇 |
1993年 | 210篇 |
1992年 | 183篇 |
1991年 | 187篇 |
1990年 | 139篇 |
1989年 | 125篇 |
1988年 | 19篇 |
1987年 | 15篇 |
1986年 | 6篇 |
1985年 | 7篇 |
1984年 | 5篇 |
1983年 | 1篇 |
1980年 | 1篇 |
1959年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
We numerically investigate the thermal entanglements of spins (1/2, 1) and spins (1/2, 1/2) in the three-mixed (1/2, 1, 1/2) anisotropic Heisenberg XXZ spin system on a simple triangular cell under an inhomogeneous magnetic field. We show that the external magnetic field induces strong plateau formation in the pairwise thermal entanglement for fixed parame-ters of the Hamiltonian in the cases of ferromagnetic and antiferromagnetic interactions. We also .observe an unexpected critical point at finite temperature in the thermal entanglement of spins (1/2, 1) for the antiferromagnetic case, while the entanglement of spins (1/2, 1) in the ferromagnetic case and the entanglement of spins (1/2, 1/2) in both ferromagnetic and antiferromagnetic cases almost decay exponentially to zero with increasing temperature. The critical point in the en-tanglement of spins (1/2, 1) in the antiferromagnetic case may be a signature of the quantum phase transition at finite temperature. 相似文献
992.
A new manganese-based single-molecule magnet with a record-high antiferromagnetic phase transition temperature 下载免费PDF全文
We perform both dc and ac magnetic measurements on the single crystal of Mn30(Et-sao)3(C104)(MeOH)3 single- molecule magnet (SMM) when the sample is preserved in air for different durations. We find that, during the oxidation process, the sample develops into another SMM with a smaller anisotropy energy barrier and a stronger antiferromagnetic intermolecular exchange interaction. The antiferromagnetic transition temperature observed at 6.65 K in the new SMM is record-high for the antiferromagnetic phase transition in all the known SMMs. Compared to the original SMM, the only apparent change for the new SMM is that each molecule has lost three methyl groups as revealed by four-circle x-ray diffraction (XRD), which is thought to be the origin of the stronger antiferromagnetic intermolecular exchange interaction. 相似文献
993.
Large coercivity and unconventional exchange coupling in manganese-oxide-coated manganese gallium nanoparticles 下载免费PDF全文
The microstructures and magnetic properties of nanoparticles, each composed of an antiferromagnetic (AFM) manganese-oxide shell and a ferromagnetic-like core of manganese-gallium (MnGa) compounds, are studied. The coreshell structure is confirmed by transmission electron microscope (TEM). The ferromagnetic-like core contains three kinds of MnGa binary compounds, i.e., ferrimagnetic (FI) DO22-type MnaGa, ferromagnetic (FM) Mn8Gas, and AFM DO19-type Mn3Ga, of which the first two correspond respectively to a hard magnetic phase and to a soft one. Decoupling effect between these two phases is found at low temperature, which weakens gradually with increasing temperature and disappears above 200 K. The exchange bias (EB) effect is observed simultaneously, which is caused by the exchange coupling between the AFM shell and FM-like core. A large coercivity of 6.96 kOe (1Oe = 79.5775 A·m^-1) and a maximum EB value of 0.45 kOe are achieved at 300 K and 200 K respectively. 相似文献
994.
Analysis of detection limit to time-resolved coherent anti-Stokes Raman scattering nanoscopy 下载免费PDF全文
In the implementation of CARS nanoscopy, signal strength decreases with focal volume size decreasing. A crucial problem that remains to be solved is whether the reduced signal generated in the suppressed focal volume can be detected. Here reported is a theoretical analysis of detection limit (DL) to time-resolved CARS (T-CARS) nanoscopy based on our proposed additional probe-beam-induced phonon depletion (APIPD) method for the low concentration samples. In order to acquire a detailed shot-noise limited signal-to-noise (SNR) and the involved parameters to evaluate DL, the T-CARS process is described with full quantum theory to estimate the extreme power density levels of the pump and Stokes beams determined by saturation behavior of coherent phonons, which are both actually on the order of ~ 109 W/cm2. When the pump and Stokes intensities reach such values and the total intensity of the excitation beams arrives at a maximum tolerable by most biological samples in a certain suppressed focal volume (40-nm suppressed focal scale in APIPD method), the DL correspondingly varies with exposure time, for example, DL values are 103 and 102 when exposure times are 20 ms and 200 ms respectively. 相似文献
995.
A new sol-foam-gel method was developed to fabricate La-doped BiFeO3 muttiferroic materials. It was demonstrated that a gradual increase in the content of La-doped into BiFeO3 results in its structure changing from rhombohedral to orthorhombic. A study of other property changes indicates that La-doping in BiFeO3 enhances its ferromagnetism and ferroelectricity. A temperature-dependent magnetization study suggests that the magnetic property of La-doped BiFeO3 samples varied from antiferromagnetic to ferromagnetic as the content of La-doped into BiFeO3 increased from 0 to 20%. Unique temperature-dependent zero field cooling (ZFC) and field cooling (FC) magnetization behaviors were observed in 15% La-doped BiFeO3 -- its ZFC temperature-dependent magnetization being ferromagnetic and its FC temperature- dependent magnetization being antiferromagnetic. A possible mechanism of such an interesting M-T behavior is discussed. 相似文献
996.
A generalized Padé approximation method of solving homoclinic and heteroclinic orbits of strongly nonlinear autonomous oscillators 下载免费PDF全文
An intrinsic extension of Pad′e approximation method, called the generalized Pad′e approximation method, is proposed based on the classic Pad′e approximation theorem. According to the proposed method, the numerator and denominator of Pad′e approximant are extended from polynomial functions to a series composed of any kind of function, which means that the generalized Pad′e approximant is not limited to some forms, but can be constructed in different forms in solving different problems. Thus, many existing modifications of Pad′e approximation method can be considered to be the special cases of the proposed method. For solving homoclinic and heteroclinic orbits of strongly nonlinear autonomous oscillators, two novel kinds of generalized Pad′e approximants are constructed. Then, some examples are given to show the validity of the present method. To show the accuracy of the method, all solutions obtained in this paper are compared with those of the Runge–Kutta method. 相似文献
997.
Fusion,fission, and annihilation of complex waves for the (2+l)-dimensional generalized Calogero-Bogoyavlenskii-Schiff system 下载免费PDF全文
With the help of the symbolic computation system, Maple and Riccati equation (ξ' = ao + a1ξ+ a2ξ2), expansion method, and a linear variable separation approach, a new family of exact solutions with q = lx + my + nt + Г(x,y, t) for the (2+1)-dimensional generalized Calogero-Bogoyavlenskii-Schiff system (GCBS) are derived. Based on the derived solitary wave solution, some novel localized excitations such as fusion, fission, and annihilation of complex waves are investigated. 相似文献
998.
999.
Raúl Machado 《Frontiers of Physics》2014,9(4):490-510
The influence of the use of the generalized Hermite polynomial on the Hermite-based lattice Bofiz- mann (LB) construction approach, lattice sets, the thermal weights, moments and the equilibrium distribution function (EDF) are addressed. A new moment system is proposed. The theoretical possibility to obtain a unique high-order Hermite-based singel relaxation time LB model capable to exactly inatch some first hydrodynamic inoments thermally i) on-Cartesian lattice, ii) with thermal weights in the EDF, iii) whilst the highest possible hydrodynamic moments that are exactly reatched are obtained with the shortest on-Cartesian lattiee sets with some fixed real-valued temperatures, is also analyzed. 相似文献
1000.
本文研究偏微方程δ/δt(a(t)δ/δu(x,t)+m(t)δu(x,t)/δt+c1(x,t,u(x,t)+c2(x,t,u,t-τ))=∫^ta∑^tj=1(t,ζ)△u(x,hj(t,ζ)dσ(ζ)+f(x,t)的振动性,给出了方程(1)振动的一些充分条件。 相似文献