全文获取类型
收费全文 | 1754篇 |
免费 | 227篇 |
国内免费 | 161篇 |
专业分类
化学 | 139篇 |
力学 | 168篇 |
综合类 | 10篇 |
数学 | 356篇 |
物理学 | 456篇 |
综合类 | 1013篇 |
出版年
2024年 | 23篇 |
2023年 | 39篇 |
2022年 | 42篇 |
2021年 | 67篇 |
2020年 | 64篇 |
2019年 | 54篇 |
2018年 | 54篇 |
2017年 | 69篇 |
2016年 | 77篇 |
2015年 | 69篇 |
2014年 | 96篇 |
2013年 | 115篇 |
2012年 | 104篇 |
2011年 | 108篇 |
2010年 | 108篇 |
2009年 | 108篇 |
2008年 | 88篇 |
2007年 | 68篇 |
2006年 | 99篇 |
2005年 | 80篇 |
2004年 | 66篇 |
2003年 | 63篇 |
2002年 | 70篇 |
2001年 | 63篇 |
2000年 | 50篇 |
1999年 | 49篇 |
1998年 | 45篇 |
1997年 | 31篇 |
1996年 | 14篇 |
1995年 | 22篇 |
1994年 | 32篇 |
1993年 | 20篇 |
1992年 | 12篇 |
1991年 | 14篇 |
1990年 | 16篇 |
1989年 | 6篇 |
1988年 | 11篇 |
1987年 | 7篇 |
1986年 | 6篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1957年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有2142条查询结果,搜索用时 9 毫秒
51.
Laser Doppler anemometry is used for the measurements of the plasma and particle velocity profiles in the coil region of an inductively coupled r.f. plasma. Results are reported for a 50 mm i.d. induction plasma torch operated at atmospheric pressure with argon as the plasma gas. The oscillator frequency is 3 MHz and the plate power is varied between 4.6 and 10.5 kW. Plasma velocity measurements are obtained using a fine carbon powder as a tracer. Measurements are also given for larger silicon particles (
) centrally injected into the discharge under different operating conditions.Nomenclature
d
p
particle diameter
-
P
0
plasma power
-
Q
1
powder carrier gas flow rate
-
Q
2
plasma gas flow rate
-
Q
3
sheath gas flow rate
-
r
distance in the radial direction
-
V
axial plasma velocity
-
V
p
axial particle velocity
-
Z
distance in the axial direction
-
standard deviation 相似文献
52.
颗粒流体两相流模型研究进展 总被引:28,自引:0,他引:28
本文介绍了颗粒流体两相流动的特征及其模拟方法, 重点论述了拟流体模型的研究现状及发展, 并对两相流动模拟中的各种方法进行了展望。 相似文献
53.
54.
The hydrogen molecule ion is a two‐center force system expressed under the prolate spheroidal coordinates, whose quantum motions and quantum trajectories have never been addressed in the literature before. The momentum operators in this coordinate system are derived for the first time from the Hamilton equations of motion and used to construct the Hamiltonian operator. The resulting Hamiltonian comprises a kinetic energy T and a total potential VTotal consisting of the Coulomb potential and a quantum potential. It is shown that the participation of the quantum potential and the accompanied quantum forces in the force interaction within H2+ is essential to develop an electronic motion consistent with the prediction of the probability density function |Ψ|2. The motion of the electron in H2+ can be either described by the Hamilton equations derived from the Hamiltonian H = TK + VTotal or by the Lagrange equations derived from the Lagrangian H = TK ? VTotal. Solving the equations of motion with different initial positions, we show that the solutions yield an assembly of electronic quantum trajectories whose distribution and concentration reconstruct the σ and π molecular orbitals in H2+. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 相似文献
55.
运用Monte-Carlo轨迹法研究了Kr(1Sg)+HF(X1Σ+;ν=1,2,3;J=4)→Kr(1Sg)+HF(X1Σ+,ν',J')的碰撞过程,从而分析Kr原子对HF基频和泛频的影响。研究表明:在初始相对平动能Et≤251.0kJ/mol时,Kr原子能够减少产生基频的粒子数反转,增加产生泛频特别是ν'=2能级的粒子数反转,并且,Kr原子有较强的弛豫高转动态(J'≥4)的能力,因此,Kr原子对HF泛频激光在提高光强和增强大气传输能力方面均有 较大的改善。 相似文献
56.
A quasi-classical trajectory method (QCT) running on the 1A′ and 1A″ potential energy surfaces (PESs) given by Dobbyn and Knowles [A.J. Dobbyn, P.J. Knowles, Mol. Phys. 91 (1997) 1107] has been employed to study the dynamical stereochemistry of the chemical reaction O(1D) + D2 → OD + D, especially the vector correlations between products and reagents. The results indicate that product rotational angular momentum j′ is not only aligned, but also oriented along the direction perpendicular to the scattering plane on both PESs, with different rotational polarization behaviors of product OD for the two PESs and for different collision energies. Calculations show that the alignment effect of products become weaker with an increase of the collision energy on the 1A′ PES but is not sensitive to the collision energy on the 1A″ PES. When the collision energy increases, the product OD mainly tends to the forward scattering on the 1A′ PES and displays a switch from the backward scattering to the forward one on the 1A″ PES. These differences are probably attributed to the different characteristics of the two PESs. 相似文献
57.
Quapp W 《Journal of computational chemistry》2007,28(11):1834-1847
We report a new, high-dimensional application of a method for finding a transition state (TS) between a reactant and a product on the potential energy surface: the search of a growing string along a reaction path defined by any Newton trajectory in combination with the Berny method (Quapp, J Chem Phys (2005), 122, 174106; we have provided this algorithm on a web page). Two given minima are connected by a one-dimensional, but usually curvilinear reaction coordinate. It leads to the TS region. The application of the method to alanine dipeptide finds the TS of the isomerisation C(7 ax) --> C(5), some TSs of the enantiomerisation of C(7 ax) from L-form to quasi-D-form, and it finds the TS region of a transition of a partly unfolded, bent structure which turns back into a mainly alpha-helix in the Ac(Ala)(15)NHMe polyalanine (all at the quantum mechanical level B3LYP/6-31G: the growing string calculation is interfaced with the Gaussian03 package). The formation or dissolvation of some alpha- or 3(10)-hydrogen bonds of the helix are discussed along the TS pathway, as well as the case of an enantiomer at the central residue of the helix. 相似文献
58.
H+CN体系中平行络合反应的动力学 总被引:1,自引:0,他引:1
利用分子反应动力学的经典轨迹法研究化学反应体系已经开展了很多工作,但是,研究长寿命络合物的几何异构体就显得有些困难,主要表现在该方法对几何异构体不容易判别.由于这些原因和计算机时大增,Davis[1]利用经典轨迹法和统计方法相结合,研究了H+CN和H+NC体系在固定方位时的长寿命络合物动力学行为,并且采用Murrel等[2]拟合光谱数据的势能函数,该势能函数在HCN和HNC平衡点的频率与实验值相差较大.本文利用经典轨迹法研究了H+CN产生HCN和HNC平行络合物异构体的分子反应动力学行为,揭示了平行络合反应产生几何异构体的… 相似文献
59.
Feng Xu Lei Zhang Liyun Jiang Lifu Bao Hao Meng 《International journal of quantum chemistry》2016,116(1):7-12
Quantum tunneling effect in entanglement dynamics between two coupled particles with separable Gaussian initial state is investigated using entangled trajectory molecular dynamics method in terms of the reduced‐density linear entropy. It has been presented through showing distinguish contribution of single trajectory to linear entropy between classical trajectory and entangled trajectory with same initial state. We find that quantum tunneling effect makes single trajectory's contribution remarkably decrease under quantum dynamics compared to classical dynamics. The nonlocality of quantum entanglement is presented, and the energy transfer between two coupled particles through quantum correlations and classical ones is also discussed in the end. © 2015 Wiley Periodicals, Inc. 相似文献
60.
We investigate quantum evolution speed in the driven double-well system using the entangled trajectory molecular dynamics method. We emphasize not only the evolution speed of the quantum state but also its limit according to different definitions. The Wasserstein 1-distance is used to quantify the distance between distinguishable quantum states in the phase space, the quantum speed limit based on the geometry has been shown to be the strictest one. The single trajectory's contribution to the quantum speed limit is discussed, which is related to both the time evolution of the trajectory and its position in the total Wigner function. The resonance and chaos strongly enhance the evolution speed and its limit in the driven double-well system. The resonance effect makes a large proportion of representative points pass through the well as a whole, nevertheless, the chaos makes the Wigner function disperse in the phase space. 相似文献