全文获取类型
收费全文 | 528篇 |
免费 | 43篇 |
国内免费 | 28篇 |
专业分类
化学 | 221篇 |
晶体学 | 2篇 |
力学 | 19篇 |
数学 | 148篇 |
物理学 | 106篇 |
无线电 | 103篇 |
出版年
2023年 | 3篇 |
2022年 | 13篇 |
2021年 | 15篇 |
2020年 | 14篇 |
2019年 | 17篇 |
2018年 | 18篇 |
2017年 | 12篇 |
2016年 | 25篇 |
2015年 | 12篇 |
2014年 | 25篇 |
2013年 | 50篇 |
2012年 | 38篇 |
2011年 | 25篇 |
2010年 | 23篇 |
2009年 | 23篇 |
2008年 | 32篇 |
2007年 | 20篇 |
2006年 | 28篇 |
2005年 | 22篇 |
2004年 | 25篇 |
2003年 | 18篇 |
2002年 | 26篇 |
2001年 | 14篇 |
2000年 | 15篇 |
1999年 | 3篇 |
1998年 | 7篇 |
1997年 | 8篇 |
1996年 | 2篇 |
1995年 | 4篇 |
1993年 | 4篇 |
1992年 | 4篇 |
1991年 | 5篇 |
1990年 | 3篇 |
1989年 | 7篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1973年 | 4篇 |
1885年 | 1篇 |
排序方式: 共有599条查询结果,搜索用时 15 毫秒
191.
192.
GUY BOUCHITTÉ IRENE FONSECA GIOVANNI LEONI LUÍSA MASCARENHAS 《Archive for Rational Mechanics and Analysis》2002,165(3):187-242
An integral representation formula for a class of functionals defined on and in (the space of special functions of bounded variation) is obtained without requiring the regularity conditions usually imposed
in the literature. The approach is based on the general results of [10] and on a Poincaré-Wirtinger type inequality introduced
by DE GIORGI, CARRIERO & LEACI [25]. Applications to relaxation problems and dimension-reduction problems in brittle thin
films are presented.
(Accepted May 8, 2002) Published online October 18, 2002
Communicated by L. Ambrosio 相似文献
193.
We investigate the dynamics of femtosecond solitons in photonic crystal fibers (PCFs) by including high-order dispersion terms until to sixth-order in the generalized nonlinear Schrödinger equation, in addition to the nonlinear effects of the self phase modulation, self steepening and Raman scattering. We calculate theoretically the pulse parameters using the moment method. In the case of the fundamental soliton, our computed equations are coupled and difficult to solve analytically. However, we use the finite difference method to calculate numerically pulse parameters using an initially hyperbolic secant pulse at 1550-nm with different peak powers along 10m-PCF. Our numerical results show that the nonlinear regimes allow obtaining pulse compressions and initial pulse amplitudes. Furthermore, we remark a pulse broadening, and weak shifts of the peak power positions and frequencies in the critical and dispersive regimes. The use of an initial chirp provides a better pulse compressions and especially for low input powers. Also, the initial positive chirp reduces the optimal compression position lengths, while the negative one increases them. Therefore, we conclude that our theoretical calculations and numerical simulation results show that the moment method associated with the finite differences method is effective for the study of femtosecond pulse dynamics in PCFs. 相似文献
194.
195.
用酶促聚合和原子转移自由基聚合相结合的"一锅法"合成了聚甲基丙烯酸正丁酯嵌段聚10-羟基癸酸[PBMA-b-P(10-HD)],通过核磁共振(1H NMR)、傅里叶红外光谱(FTIR)和凝胶渗透色谱(GPC)对其结构以及分子量与其分子量分布进行了表征,并通过动态光散射仪(DLS)和原子力显微镜(AFM)对聚合物在水溶液中的性质进行了研究.所得嵌段聚合物纳米粒子呈球形结构,平均直径为135 nm左右. 相似文献
196.
Salima Atlas Mustapha Raihane Gregory B. Kharas Peter G. Hendrickson Hamid Kaddami Mourad Arous 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(12):997-1010
Copolymerization of fluorine ring-substituted 2-phenyl-1,1-dicyanoethenes, RC6H3CH?C(CN)2 (R is 2,3-F,F, 2,4-F,F, 2,5-F,F, 2,6-F,F, and 4-CF3) with 4-fluorostyrene were prepared in the presence of a radical initiator (ABCN) at 70°C. The composition of the copolymers was calculated from nitrogen analysis, and the copolymers were characterized by IR, 1H and 13C-NMR, GPC, DSC, and TGA. The monomer reactivity ratios for 4-fluorostyrene (M1), r1 = 0.6 and 2-(2,4-difluorophenyl)-1,1-dicyanoethene (M2), r2 = 0 were determined from Fineman-Ross plot. The order of relative reactivity (1/r1) for difluoro-substituted monomers is 2,4-F,F (0.31) > 2,3-F,F (0.25) > 2,5-F,F (0.22) > 2,6-F,F (0.10). DSC curves showed that the copolymers were amorphous with high T g in comparison with that poly(4-fluorostyrene) indicating a substantial decrease in chain mobility of the copolymer due to the high dipolar character of the trisubstituted ethylene monomer units. From the thermogravimetric analysis, the copolymers began to degrade in the range 214–260°C. The copolymer of 4-fluorostyrene and 2-(2,4-difluorophenyl)-1,1-dicyanoethene and poly(4-fluorostyrene) were dielectrically characterized in the range 25–200°C. The dominating relaxation process detected in both materials was the α-relaxation, associated with the dynamic glass transition. The relationship polarity-permittivity was discussed. 相似文献
197.
198.
提出了一种采集高动态范围多光谱反射率的实验方 法,并通过测量5个非均匀混浊介 质样品在全视场照射条件下和500~940nm波长范围内的反射图像数据 证明了本方法的可行性。同时 采用在辐射传输理论框架下建立的并行iMC蒙特卡罗仿真模型,通过使用漫反射标准板准确 记录入射光 束能量分布,输入至iMC仿真程序,获得可与反射率测量数据相比较的反射率仿真图像数据 。本文工 作为求解根据反射率确定非均匀混浊介质样品的光学特征与几何参数的逆问题提供了实验与 理论工具。 相似文献
199.
Rizzi J Weitkamp T Guérineau N Idir M Mercère P Druart G Vincent G da Silva P Primot J 《Optics letters》2011,36(8):1398-1400
We present in this Letter a type of quadriwave lateral shearing interferometer for x-ray phase imaging. This device is based on a phase chessboard, and we take advantage of the large spectrum of the source to produce interferograms with a propagation-invariant contrast. Such a grating has been created for hard x-ray interferometry and experimentally tested on a synchrotron beamline at Soleil. 相似文献
200.
Tunable Trimers: Using Temperature and Pressure to Control Luminescent Emission in Gold(I) Pyrazolate‐Based Trimers
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Christopher H. Woodall Dr. Sara Fuertes Dr. Christine M. Beavers Lauren E. Hatcher Andrew Parlett Dr. Helena J. Shepherd Dr. Jeppe Christensen Dr. Simon J. Teat Mourad Intissar Dr. Alexandre Rodrigue‐Witchel Dr. Yan Suffren Prof. Christian Reber Christopher H. Hendon Dr. Davide Tiana Prof. Aron Walsh Prof. Paul R. Raithby 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(51):16933-16942
A systematic investigation into the relationship between the solid‐state luminescence and the intermolecular Au???Au interactions in a series of pyrazolate‐based gold(I) trimers; tris(μ2‐pyrazolato‐N,N′)‐tri‐gold(I) ( 1 ), tris(μ2‐3,4,5‐ trimethylpyrazolato‐N,N′)‐tri‐gold(I) ( 2 ), tris(μ2‐3‐methyl‐5‐phenylpyrazolato‐N,N′)‐tri‐gold(I) ( 3 ) and tris(μ2‐3,5‐diphenylpyrazolato‐N,N′)‐tri‐gold(I) ( 4 ) has been carried out using variable temperature and high pressure X‐ray crystallography, solid‐state emission spectroscopy, Raman spectroscopy and computational techniques. Single‐crystal X‐ray studies show that there is a significant reduction in the intertrimer Au???Au distances both with decreasing temperature and increasing pressure. In the four complexes, the reduction in temperature from 293 to 100 K is accompanied by a reduction in the shortest intermolecular Au???Au contacts of between 0.04 and 0.08 Å. The solid‐state luminescent emission spectra of 1 and 2 display a red shift with decreasing temperature or increasing pressure. Compound 3 does not emit under ambient conditions but displays increasingly red‐shifted luminescence upon cooling or compression. Compound 4 remains emissionless, consistent with the absence of intermolecular Au???Au interactions. The largest pressure induced shift in emission is observed in 2 with a red shift of approximately 630 cm?1 per GPa between ambient and 3.80 GPa. The shifts in all the complexes can be correlated with changes in Au???Au distance observed by diffraction. 相似文献