全文获取类型
收费全文 | 1406篇 |
免费 | 55篇 |
国内免费 | 46篇 |
专业分类
化学 | 1028篇 |
晶体学 | 9篇 |
力学 | 79篇 |
数学 | 119篇 |
物理学 | 272篇 |
出版年
2024年 | 2篇 |
2023年 | 8篇 |
2022年 | 42篇 |
2021年 | 45篇 |
2020年 | 58篇 |
2019年 | 59篇 |
2018年 | 82篇 |
2017年 | 51篇 |
2016年 | 83篇 |
2015年 | 66篇 |
2014年 | 89篇 |
2013年 | 208篇 |
2012年 | 96篇 |
2011年 | 93篇 |
2010年 | 73篇 |
2009年 | 66篇 |
2008年 | 75篇 |
2007年 | 66篇 |
2006年 | 43篇 |
2005年 | 27篇 |
2004年 | 26篇 |
2003年 | 12篇 |
2002年 | 29篇 |
2001年 | 15篇 |
2000年 | 13篇 |
1999年 | 14篇 |
1998年 | 10篇 |
1997年 | 7篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1994年 | 5篇 |
1993年 | 4篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1988年 | 4篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 5篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 1篇 |
1978年 | 3篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1964年 | 1篇 |
排序方式: 共有1507条查询结果,搜索用时 0 毫秒
101.
Hamid?GoudarziafsharEmail author Majid?Rezaeivala Fayezeh?Khosravi Yunes?Abbasityula Somaieh?Yousefi Neslihan??zbek Václav?Eigner Michal?Du?ek 《Journal of the Iranian Chemical Society》2015,12(1):113-119
The ligand 1,2-dimorpholinoethane (DME) was used to prepare Zn(II) and Ni(II) complexes of the general formulation MLX2 (L = DME, X = Cl or NO3). Zinc(II) complex exhibits spectral properties indicative of a distorted tetrahedral geometry, with DME coordinating through two nitrogen atoms and two chlorides completing the tetrahedron. This is in contrast to the six-coordinated, distorted octahedral geometry exhibited by nickel(II) complex of DME when NO3 was used as counter ions. The X-ray diffraction confirms the structures of two complexes and shows that the ligand coordinates through two nitrogen atoms while the two ether linkages are not involved in complexation, which would have been the case if the morpholine rings were in the boat form. The ligand and related complexes have antibacterial activity against the five Gram-positive bacteria: Bacillus subtilis ATCC 6633, Staphylococcus aureus ATCC 6538, Bacillus cereus NRRL-B-3711, Enterococcus faecalis ATCC 29212 and Streptococcus pyogenes and also against the three Gram-negative bacteria: Escherichia coli ATCC 11230, Pseudomonas aeruginosa ATCC 15442 and Klebsiella pneumonia ATCC 70063. The results showed that in some cases the antibacterial activity of the complexes exceeded the one of sulfisoxazole used as a standard. 相似文献
102.
Majid M. Heravi Neda Zamani Ahari Hossein A. Oskooie Mitra Ghassemzadeh 《Phosphorus, sulfur, and silicon and the related elements》2013,188(7):1701-1712
Abstract Mild and efficient S-methylation of thiols and o-methylation of phenols and naphthols occurs with dimethyl sulfate (DMS) supported on basic alumina under microwave irradiation in solventless system. 相似文献
103.
Amorphous and crystalline states of As2Se3, (As2Se3)3 : Tl2Se and As2Se3 : Tl2Se have been studied using X-ray diffraction techniques. Structural changes arise during the process of annealing in the temperature range between their softening and melting points are reported and their rates investigated. The crystallization temperatures were found to be 105 ± 5 °C, 135 ± 5 °C and 180 ± 5 °C respectively. The unit cell parameters are identified for each of the three resulting crystalline phases, that for As2Se3 : Tl2Se being orthorhombic while the other two are monoclinic. 相似文献
104.
Seyyed Majid Jafarian Amiri 《代数通讯》2013,41(6):2055-2059
105.
Relativistic symmetries in the Rosen-Morse potential and tensor interaction using the Nikiforov-Uvarov method 下载免费PDF全文
Approximate analytical bound-state solutions of the Dirac particle in the fields of attractive and repulsive Rosen- Morse (RM) potentials including the Coulomb-like tensor (CLT) potential are obtained for arbitrary spin-orbit quantum number κ. The Pekeris approximation is used to deal with the spin-orbit coupling terms κ(κ± 1)r 2 . In the presence of exact spin and pseudospin (p-spin) symmetries, the energy eigenvalues and the corresponding normalized two-component wave functions are found by using the parametric generalization of the Nikiforov-Uvarov (NU) method. The numerical results show that the CLT interaction removes degeneracies between the spin and p-spin state doublets. 相似文献
106.
New (3+1)‐dimensional nonlinear equations with KdV equation constituting its main part: multiple soliton solutions 下载免费PDF全文
Abdul‐Majid Wazwaz 《Mathematical Methods in the Applied Sciences》2016,39(4):886-891
In thiswork,we present two new(3+1)‐dimensional nonlinear equationswith Korteweg‐de Vries equation constituting its main part. We show that the dispersive relation is distinct for each model, whereas the phase shift remains the same. We determine multiple solitons solutions, with distinct physical structures, for each established equation. The architectures of the simplified Hirota's method is implemented in this paper. The constraint conditions that fall out which must remain valid in order for themultiple solitons to exist are derived.Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
107.
The kinetic theory of plasma has been employed to compute the test-charge potential distributions accounting for quantization effects in magnetized electron-positron-ion (EPI) plasmas. In this regard, the degenerate positrons and electrons are assumed to follow the Fermi-Dirac distribution, while inertial ions are modelled by Maxwellian velocity distribution. By solving the Fourier-transformed Vlasov–Poisson equations, a modified dielectric function and electrostatic potential is obtained. By imposing various constraints on the test-charge speed, the potential profile has been analysed in terms of Debye–Hückel (DH), far-field (FF), and wake-field (WF) potentials. It has been found that the amplitude of DH and FF potentials increases by the inclusion of quantization effects, and it becomes the opposite for the WF potential profile. Furthermore, the variation of positron concentration significantly affects the DH, FF, and WF potentials. The present findings are important to understand the shielding phenomenon in degenerate multi-species plasmas. 相似文献
108.
We study the effect of time-dependent linear and quadratic potentials on the profile and dynamics of rogue waves represented by a Peregrine soliton. The Akhmediev breather, Ma breather, bright soliton, Peregrine soliton, and constant wave (CW) are all obtained by changing the value of one parameter in the general solution corresponding to the amplitude of the input CW. The corresponding solutions for the case with linear and quadratic potentials were derived by the similarity transformation method. While the peak height and width of the rogue wave turn out to be insensitive to the linear potential, the trajectory of its center-of-mass can be manipulated with an arbitrary time-dependent slope of the linear potential. With a quadratic potential, the peak height and width of the rogue wave can be arbitrarily manipulated to result, for a special case, in a very intense pulse. 相似文献
109.
Abdul‐Majid Wazwaz Randolph Rach Jun‐Sheng Duan 《Mathematical Methods in the Applied Sciences》2014,37(1):10-19
In this paper, we introduce systems of Volterra integral forms of the Lane–Emden equations. We use the systematic Adomian decomposition method to handle these systems of integral forms. The Volterra integral forms overcome the singular behavior at the origin x = 0. The Adomian decomposition method gives reliable algorithm for analytic approximate solutions of these systems. Our results are supported by investigating several numerical examples. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
110.
Effective Stress in Unsaturated Soils: A Thermodynamic Approach Based on the Interfacial Energy and Hydromechanical Coupling 总被引:2,自引:0,他引:2
Ehsan Nikooee Ghassem Habibagahi S. Majid Hassanizadeh Arsalan Ghahramani 《Transport in Porous Media》2013,96(2):369-396
In recent years, the effective stress approach has received much attention in the constitutive modeling of unsaturated soils. In this approach, the effective stress parameter is very important. This parameter needs a correct definition and has to be determined properly. In this paper, a thermodynamic approach is used to develop a physically-based formula for the effective stress tensor in unsaturated soils. This approach accounts for the hydro-mechanical coupling, which is quite important when dealing with hydraulic hysteresis in unsaturated soils. The resulting formula takes into account the role of interfacial energy and the contribution of air?Cwater specific interfacial area to the effective stress tensor. Moreover, a bi-quadratic surface is proposed to represent the contribution of the so-called suction stress in the effective stress tensor. It is shown that the proposed relationship for suction stress is in agreement with available experimental data in the full hydraulic cycle (drying, scanning, and wetting). 相似文献