全文获取类型
收费全文 | 32877篇 |
免费 | 4219篇 |
国内免费 | 2226篇 |
专业分类
化学 | 2034篇 |
晶体学 | 23篇 |
力学 | 3792篇 |
综合类 | 454篇 |
数学 | 22965篇 |
物理学 | 10054篇 |
出版年
2024年 | 71篇 |
2023年 | 315篇 |
2022年 | 385篇 |
2021年 | 512篇 |
2020年 | 968篇 |
2019年 | 940篇 |
2018年 | 903篇 |
2017年 | 864篇 |
2016年 | 1009篇 |
2015年 | 787篇 |
2014年 | 1441篇 |
2013年 | 2808篇 |
2012年 | 1594篇 |
2011年 | 1991篇 |
2010年 | 1931篇 |
2009年 | 2087篇 |
2008年 | 2228篇 |
2007年 | 2173篇 |
2006年 | 1895篇 |
2005年 | 1864篇 |
2004年 | 1574篇 |
2003年 | 1471篇 |
2002年 | 1339篇 |
2001年 | 1028篇 |
2000年 | 995篇 |
1999年 | 910篇 |
1998年 | 843篇 |
1997年 | 714篇 |
1996年 | 538篇 |
1995年 | 489篇 |
1994年 | 387篇 |
1993年 | 276篇 |
1992年 | 251篇 |
1991年 | 239篇 |
1990年 | 223篇 |
1989年 | 130篇 |
1988年 | 124篇 |
1987年 | 120篇 |
1986年 | 121篇 |
1985年 | 109篇 |
1984年 | 102篇 |
1983年 | 54篇 |
1982年 | 98篇 |
1981年 | 81篇 |
1980年 | 57篇 |
1979年 | 65篇 |
1978年 | 49篇 |
1977年 | 42篇 |
1976年 | 27篇 |
1973年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
研究了一个三阶半线性微分方程的奇摄动非线性混合边值问题.利用边界层函数法构造了该问题的形式渐近解,并采用微分不等式理论证明了解的存在性,给出了渐近解的误差估计,最后得出了边界层函数指数型衰减的结论. 相似文献
982.
983.
Zhiber-Shabat方程,描述许多重要的物理现象,是一类重要的非线性方程,有着许多广泛的应用前景.本文给出Zhiber-Shabat方程的多辛几何结构和多辛Fourier拟谱方法.数值算例结果表明多辛离散格式具有较好的长时间的数值稳定性. 相似文献
984.
The main purpose of this paper is using estimates for trigonometric sums and properties of congruence to study the computation of one kind of fourth power mean of a generalized three-term exponential sum, and give an interesting identity for it. 相似文献
985.
986.
Han Joong Koh Suk Jin Kang Dennis N. Kevill 《Phosphorus, sulfur, and silicon and the related elements》2013,188(7):1404-1415
Kinetic and product studies of the solvolyses of acyclic phosphorochloridates are extended to two cyclic diesters, 2-chloro-1,3,2-dioxaphospholane-2-oxide (1) and 2-chloro-5,5-dimethyl-1,3,2-dioxaphosphorinane-2-oxide (2). Slightly faster solvolyses are observed for 1 than for the acyclic dimethyl phosphorochloridate (3), and 2 solvolyzes somewhat slower than 3. An extended Grunwald–Winstein equation treatment shows similar sensitivities to changes in solvent nucleophilicity and solvent ionizing power for 1, 2, and 3, and a concerted SN2 attack is proposed in each case. Product studies for the solvolyses of 2 in aqueous alcohols are presented. 相似文献
987.
In condensed phases, a highly symmetric gas‐phase molecule lowers its symmetry under perturbation of the solvent, which is vital to a variety of structural chemistry related processes. However, the dynamical aspects of solvent‐mediated symmetry‐breaking events remain largely unknown. Herein, direct evidence for two types of solvent‐mediated symmetry‐breaking events that coexist on the picosecond timescale in a highly symmetric anion, namely, hexacyanocobaltate, is presented: 1) an equilibrium symmetry‐breaking event in which a solvent‐bound species having lowered symmetry undergoes a population exchange reaction with the symmetry‐retaining species; 2) a dynamic symmetry‐breaking event that is composed of many dynamic population‐exchange reactions under fluctuating solvent interactions. Ultrafast two‐dimensional infrared spectroscopy is used to simultaneously observe and dynamically characterize these two events. This work opens a new window into molecular symmetry and structural dynamics under equilibrium and non‐equilibrium conditions. 相似文献
988.
Ren-Geng Xiong 《中国化学快报》2013,24(8):681-684
The temperature-dependent,second-order,nonlinear,optical coefficient(x(2)).piezoelectric coefficient (d33),pyroelectric coefficient(Ps) and domains on triglycine sulfate(TGS) reported herein provide a clue for us to investigate these as a typical second-order phase transition.The symmetry breaking occurrence is definitely confirmed by the temperature-dependent x(2) in which x(2) displays a limited value at the ferroelectric phase,indicating the space group(P21) chosen is correct,and when x(2) basically maintains a zero value at the paraelectric phase,indicating the space group should be centric.Interestingly,after normalization of x(2),d33 or Ps,the change trend with temperature is basically overlapped,probably abiding by Landau theory.Moreover,temperature-dependent domains directly show the symmetry breaking occurrence. 相似文献
989.
Densities and speeds of sound of the (2,2,4-trimethylpentane + methylbenzene + butan-1-ol) ternary system as well as all its binary sub-systems were measured at four temperatures, namely 298.15 K, 308.15 K, 318.15 K, and 328.15 K at atmospheric pressure by a vibrating-tube densimeter DSA 5000. The binary (isooctane + toluene) system was studied previously. Excess quantities (molar volume, adiabatic compressibility, and isobaric thermal expansivity) of the mixtures studied were calculated from the experimental densities and speed of sounds. The excess molar volume data were correlated using the Redlich–Kister equation. Both the positive and S-shaped excess molar volume curves were found for the systems studied. The excess molar volumes versus concentration of binary systems differed in the shape and temperature dependence. The experimental binary data were compared with literature data. The experimental excess molar volumes were analyzed by means of the Extended Real Associated Solution (ERAS) model. The experimental data and the ERAS model can help to estimate real behaviour of the systems studied. 相似文献
990.
Chuan Li Marharyta Petukh Lin Li Emil Alexov 《Journal of computational chemistry》2013,34(22):1949-1960
Due to the enormous importance of electrostatics in molecular biology, calculating the electrostatic potential and corresponding energies has become a standard computational approach for the study of biomolecules and nano‐objects immersed in water and salt phase or other media. However, the electrostatics of large macromolecules and macromolecular complexes, including nano‐objects, may not be obtainable via explicit methods and even the standard continuum electrostatics methods may not be applicable due to high computational time and memory requirements. Here, we report further development of the parallelization scheme reported in our previous work (Li, et al., J. Comput. Chem. 2012, 33, 1960) to include parallelization of the molecular surface and energy calculations components of the algorithm. The parallelization scheme utilizes different approaches such as space domain parallelization, algorithmic parallelization, multithreading, and task scheduling, depending on the quantity being calculated. This allows for efficient use of the computing resources of the corresponding computer cluster. The parallelization scheme is implemented in the popular software DelPhi and results in speedup of several folds. As a demonstration of the efficiency and capability of this methodology, the electrostatic potential, and electric field distributions are calculated for the bovine mitochondrial supercomplex illustrating their complex topology, which cannot be obtained by modeling the supercomplex components alone. © 2013 Wiley Periodicals, Inc. 相似文献