全文获取类型
收费全文 | 8947篇 |
免费 | 1212篇 |
国内免费 | 1280篇 |
专业分类
化学 | 5514篇 |
晶体学 | 85篇 |
力学 | 1342篇 |
综合类 | 65篇 |
数学 | 539篇 |
物理学 | 3894篇 |
出版年
2024年 | 18篇 |
2023年 | 102篇 |
2022年 | 213篇 |
2021年 | 267篇 |
2020年 | 362篇 |
2019年 | 306篇 |
2018年 | 286篇 |
2017年 | 369篇 |
2016年 | 386篇 |
2015年 | 357篇 |
2014年 | 466篇 |
2013年 | 737篇 |
2012年 | 577篇 |
2011年 | 623篇 |
2010年 | 474篇 |
2009年 | 547篇 |
2008年 | 509篇 |
2007年 | 553篇 |
2006年 | 468篇 |
2005年 | 486篇 |
2004年 | 418篇 |
2003年 | 350篇 |
2002年 | 307篇 |
2001年 | 312篇 |
2000年 | 245篇 |
1999年 | 226篇 |
1998年 | 200篇 |
1997年 | 165篇 |
1996年 | 149篇 |
1995年 | 152篇 |
1994年 | 123篇 |
1993年 | 89篇 |
1992年 | 81篇 |
1991年 | 73篇 |
1990年 | 64篇 |
1989年 | 42篇 |
1988年 | 46篇 |
1987年 | 34篇 |
1986年 | 31篇 |
1985年 | 32篇 |
1984年 | 32篇 |
1983年 | 11篇 |
1982年 | 26篇 |
1981年 | 17篇 |
1980年 | 17篇 |
1979年 | 19篇 |
1978年 | 10篇 |
1977年 | 22篇 |
1976年 | 13篇 |
1973年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 60 毫秒
921.
Anastassia N. Rissanou Spiros H. Anastasiadis Ioannis A. Bitsanis 《Journal of polymer science. Part A, Polymer chemistry》2009,47(24):2462-2476
When a polymer chain in solution interacts with an atomically smooth solid substrate, its conformational properties are strongly modified and deviate substantially from those of chains in bulk. In this work, the interplay of two competing transitions that affect the conformations of polymer chains near an energetically attractive surface is studied by means of Monte Carlo simulations on a cubic lattice. The transition from an extended to a compact conformation of a polymer chain near an attractive wall, as solubility deteriorates, exhibits characteristics akin to the “coil-to-globule” transition in bulk. An effective θ-temperature is determined. Its role as the transition point is confirmed in a variety of ways. The nature of the coil-to-compact transition is not qualitatively different from that in the bulk. Adsorbed polymer chains may assume “globular” or “pancake” configurations depending on the competition among adsorption strength, cohesive energy, and entropy. In a very relevant range of conditions, the dependence of the adsorbate thickness on chain-length is intermediate between that of 3-d (“semidroplets”) and 2-d (“pancake”) objects. The focus of this study is on rather long polymer chains. Several crucial features of the transitions of the adsorbed chains are N-dependent and various aspects of the adsorption and “dissolution” process are manifested clearly only at the “long chain” limit. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2462–2476, 2009 相似文献
922.
Youngeup Jin Minjung Lee Sun Hee Kim Suhee Song Il Kim Han Young Woo Kwanghee Lee Hongsuk Suh 《Journal of polymer science. Part A, Polymer chemistry》2009,47(19):5068-5077
In this study, a novel conjugated polymer, poly(4,4‐bis(2‐ethylhexyl)‐4H‐cyclopenta[def]phenanthrene‐2,6‐vinylene) (PCPPV) has been synthesized and characterized. For the polymerization, Gilch's reaction was applied for the first time with the cyclopenta[def]phenanthrene system. The absorption and emission spectra of PCPPV are red‐shifted about 40–50 nm due to the vinylene units when compared with those of poly(2,6‐(4,4‐bis(2‐ethylhex‐yl)‐4H‐cyclopenta[def]phenanthrene)) (PCPP). The solid‐state fluorescence is significantly broadened, possibly due to π–π interactions introduced by the phenanthrene and vinylene moieties. In solution, as the concentration of polar solvent increased, the photoluminescence (PL) intensity decreased due to quenching and aggregation by the interchain interactions between the conjugated backbones. After annealing the film at 80 °C, the PL and electroluminescence (EL) emission spectra exhibited also the quenching and aggregation effects indicating the interchain interactions of PCPPV. The large number of aromatic rings in a unit and the increased planarity achieved through introduction of vinylene units are able to give interchain interactions stronger than fluorene or phenylene units. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5068–5077, 2009 相似文献
923.
晶体中三阶有效非线性系数的计算方法 总被引:5,自引:2,他引:3
经过对x(3)ijkl的脚标进行简化压缩处理,首次得出了全部晶体点群共11种不同的X(3)im矩阵表达形式及Kleinman对称条件成立下的简化形式,给出了各类晶体中四波相互作用过程中X(3)^eff的计算方法。 相似文献
924.
复合结构与流体耦合运动方程的时域分析方法 总被引:1,自引:0,他引:1
本文就复合结构与流体耦合的时域运动方程,利用核函数矩阵的特点,将二阶微分积分方程变形为Volterra型积分方程,然后引入积分变换,得到一组一阶常微分方程组,该微分方程组的形式与现代控制论中的状态方程类似。 相似文献
925.
In this work we use the vapor-sorption equilibrium data to show the degree of solvent upturn in each solvent-polymer system. For this purpose, 23 isothermal data sets for four polymer + solvent binaries, one block copolymer + solvent binary and for the corresponding polymer pairs have been used in the temperature range of 25-70 °C. Solvents studied are benzene, carbon tetrachloride, chloroform and pentane. Homopolymers studied are polyisobutylene, poly(ε-caprolactone), poly(ethylene oxide), n-heptadecane, polystyrene, poly(vinyl chloride), poly(vinyl methyl ether), and n-tetracosane.According to these data sets, solvent weight fraction in the polymer is plotted against solvent-vapor activity that is calculated assuming an ideal gas phase of pure solvent vapor neglecting the vapor pressure of the polymer. We use the Flory-Huggins theory to obtain dimensionless interaction parameter, χ. Also the Zimm-Lundberg clustering theory and non-ideality thermodynamic factor, Γ are used to interpret the equilibrium data. 相似文献
926.
927.
Jiangang Gao Youyi Sun Jingli Zhou Zhi Zheng Hongwei Chen Wei Su Qijin Zhang 《Journal of polymer science. Part A, Polymer chemistry》2007,45(23):5380-5386
A new synthetic approach to prepare Ag nanoparticles protected side‐chain liquid crystalline (LC) azobenzene polymers was reported. It is based on the reduction of silver ions in presence of a LC polymer polymerized by RAFT. The formation of Ag colloidal nanoparticles was confirmed by TEM and UV analysis. At the same time, according to the results of DSC, XPS, and FTIR spectra, Ag nanoparticles were protected by the side‐chain LC azobenzene polymers through surface attachment interactions between thiol groups and Ag. The out‐plane orientation of side‐chain LC is confirmed by surface‐enhanced Raman spectra analysis and scanning near‐field optical microscope, resulting from the large electromagnetic field arising from the excitation of surface plasmon polariton of Ag nanoparticles. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5380–5386, 2007 相似文献
928.
探讨隐变量交互作用分析的建模方法及其在SA S软件上的实现;首先阐述隐变量交互作用分析建模的原理,通过拟合一个隐变量交互作用分析示例,对加入交互作用项的统计分析结果与无交互作用项的统计分析结果进行对比;示例中交互作用项引起的变异在结果变量的总变异中占到79.20%.在应用结构方程模型分析隐变量产生的效应时,有时候不进行隐变量交互作用的分析可能会产生偏倚. 相似文献
929.
Wataru Sakamoto 《Computational Statistics》2007,22(4):583-597
An empirical Bayes method to select basis functions and knots in multivariate adaptive regression spline (MARS) is proposed,
which takes both advantages of frequentist model selection approaches and Bayesian approaches. A penalized likelihood is maximized
to estimate regression coefficients for selected basis functions, and an approximated marginal likelihood is maximized to
select knots and variables involved in basis functions. Moreover, the Akaike Bayes information criterion (ABIC) is used to
determine the number of basis functions. It is shown that the proposed method gives estimation of regression structure that
is relatively parsimonious and more stable for some example data sets. 相似文献
930.
You Zhi WAN Ying Hua LIU Ping XIE Rong Ben ZHANG* Department of Applied Chemistry School of Science Beijing University of Chemical Technology Beijing State Key Laboratory of Polymer Physics Chemistry Joint Laboratory of Polymer Science Materials Institute of Chemistry Chinese Academy of Sciences Beijing 《中国化学快报》2006,17(10):1361-1364
Ladder polysiloxanes (LPS) including both oxygen-bridged ladder polysilsesquioxanes (LPSQ) and organo-bridged ladder polysiloxanes (OLPS) are very important materials because of their excellent properties1. Adrianov et al. in 1960 attempted to prepare 1, … 相似文献