全文获取类型
收费全文 | 45547篇 |
免费 | 5763篇 |
国内免费 | 4495篇 |
专业分类
化学 | 19560篇 |
晶体学 | 620篇 |
力学 | 1571篇 |
综合类 | 301篇 |
数学 | 1911篇 |
物理学 | 16119篇 |
综合类 | 15723篇 |
出版年
2024年 | 130篇 |
2023年 | 370篇 |
2022年 | 834篇 |
2021年 | 921篇 |
2020年 | 1137篇 |
2019年 | 1025篇 |
2018年 | 1018篇 |
2017年 | 1273篇 |
2016年 | 1569篇 |
2015年 | 1638篇 |
2014年 | 2097篇 |
2013年 | 3471篇 |
2012年 | 2577篇 |
2011年 | 2754篇 |
2010年 | 2304篇 |
2009年 | 2546篇 |
2008年 | 2651篇 |
2007年 | 2957篇 |
2006年 | 2667篇 |
2005年 | 2525篇 |
2004年 | 2161篇 |
2003年 | 2062篇 |
2002年 | 2129篇 |
2001年 | 1612篇 |
2000年 | 1605篇 |
1999年 | 1415篇 |
1998年 | 1129篇 |
1997年 | 1004篇 |
1996年 | 909篇 |
1995年 | 828篇 |
1994年 | 741篇 |
1993年 | 616篇 |
1992年 | 572篇 |
1991年 | 477篇 |
1990年 | 379篇 |
1989年 | 351篇 |
1988年 | 320篇 |
1987年 | 231篇 |
1986年 | 159篇 |
1985年 | 148篇 |
1984年 | 108篇 |
1983年 | 50篇 |
1982年 | 88篇 |
1981年 | 46篇 |
1980年 | 41篇 |
1979年 | 53篇 |
1978年 | 16篇 |
1977年 | 14篇 |
1976年 | 16篇 |
1973年 | 24篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
钟凡 《中山大学学报(自然科学版)》1996,(2)
把重正化群理论应用于一受外场驱动而发生一级相变的系统中,结果表明,与有序化过程一样,该系统也由零温不动点所决定,并得到磁化强度及结构函数的新的动力学标度关系.由此可获得滞后回约面积与变场速率的标度关系. 相似文献
72.
Poly (n-butylisocyanate)-benzene solutions prepared by solubilization at 45°C, followed by aging at room temperature were found to be metastable for months, although, eventually, they separated into a birefringent polymer-rich phase and an isotropic solution. These metastable solutions, as well as isothermally phase-separated biphasic samples, flowed and exhibited dynamic moduli indicative of low polymer connectivity. By contrast samples prepared by a freeze-thaw cycle were uniformly and highly birefringent and showed network (gel) behavior at room temperature. The mechanism of gel formation is most likely the exclusion of the polymer from the benzene crystal during crystallization, forcing the polymer to align and exist at grain boundaries. Films formed from solutions have different moduli than those formed from gels, and are consistent with the proposed mechanism. 相似文献
73.
Using the appropriate harmonic oscillator states and reasonable approximations, we construct coherent wavepackets corresponding
to the solutions of the Klein-Gordon equation for the attractive potentialV(r)=−k/r, k>0, in two and three space dimensions. We deduce the corresponding classical limit in two dimension by requiring that the
expectation value 〈r〉 of the radial variable is large. In the case of three dimensions, besides the condition of large 〈r〉, we make the uncertainty Δr=[〈r
2〉 − 〈r〉2]1/2 a minimum with respect to certain parameter of the wavepacket. We then investigate the trajectory traversed by the wavepacket
in the classical limit. We find that the classical limit of this relativistic quantal problem gives, in the leading order,
the same expression for the rate of motion of the perihelion as that given by the solution of the corresponding special relativistic
classical dynamical problem. We also briefly discuss some of the subtle aspects of the classical limit of the relativistic
quantal system, in general. 相似文献
74.
量子退相干理象是由系统与环境的纠缠所引起的系统相干性的消失,是一种纯粹量子力学效应[1]. 相似文献
75.
对PT方程等几个立方型状态方程描述氩的临界等温线的能力作比较研究。在临界压力以下区域.PT方程、HS-SRK方程和SRK方程推算精度较好,AAD<0.4%。在临界压力以上区域,所讨论的五个方程都不能提供具有合理精度的描述。 相似文献
76.
Timur Zharnikov Alexander Yakovlev Semion Kuchanov 《Journal of Polymer Science.Polymer Physics》2003,41(9):892-902
The problem of finding conditions of the loss of thermodynamic stability by the reaction system was solved on the basis of the developed theory of living free‐radical copolymerization. The spinodal's calculations were carried out for a significant number of systems differing in the values of kinetic, stoichiometric, and thermodynamic parameters. Analysis of the results of such calculations revealed some regularities in the spinodal curves' behavior and permitted us to classify their possible topological types. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 892–902, 2003 相似文献
77.
G. N. Merrill 《Journal of Physical Organic Chemistry》2007,20(1):19-29
Ab initio molecular orbital calculations were carried out on epibromohydrin (EBH) and epichlorohydrin (ECH) in an attempt to elucidate their reactivity with respect to a hard nucleophile, hydroxide. These systems were modeled in both the gas phase and a polar solvent under basic conditions. In the gas phase, it was determined that a direct displacement mechanism (nucleophilic attack at the C1 position) was operative for EBH, while an indirect pathway (nucleophilic attack at the C3 position and subsequent intramolecular displacement) was followed for ECH. In an acetone solution, only the indirect displacement mechanism was found to occur. An electrostatic argument is advanced to account for this behavior in polar solution. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
78.
T. K. Melik-Barkhudarov 《Journal of Contemporary Physics (Armenian Academy of Sciences)》2007,42(5):173-177
An approach is discussed which allows one to describe within the framework of the single model the aggregative states of a system of atoms obeying the Fermi statistics. A phase diagram is obtained containing both the critical point where the distinctions between the liquid and vapor vanish and the triple point where the liquid, vapor, and crystal are in equilibrium. 相似文献
79.
We study phase separation in a system of hard-core particles driven by a fluctuating two-dimensional self-affine potential landscape which evolves through Kardar–Parisi–Zhang (KPZ) dynamics. We find that particles tend to cluster together on a length scale which grows in time. The final phase-separated steady state is characterized by an unusual cusp singularity in the scaled correlation function and a broad distribution for the order parameter. Unlike the one-dimensional case studied earlier, the cluster-size distribution is asymmetric between particles and holes, reflecting the broken reflection symmetry of the KPZ dynamics, and has a contribution from an infinite cluster in addition to a power law part. A study of the surface in terms of coarse-grained depth variables helps understand many of these features. 相似文献
80.
Small‐Angle Neutron Scattering has been performed from poly(ethylene oxide) in deuterated water at temperature ranging from 10 to 80 °C. A simple fitting model was used to obtain a correlation length and a Porod exponent. The correlation length L characterizes the average distance between entanglements in the semidilute region and is proportional to the individual coil sizes in the dilute region. L was found to increase with temperature in the semidilute region but it decreases with temperature in the dilute region. This decrease is the precursor to the single‐chain collapse which applies to very dilute polymer solutions. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2196–2200, 2007 相似文献