全文获取类型
收费全文 | 3666篇 |
免费 | 636篇 |
国内免费 | 318篇 |
专业分类
化学 | 1496篇 |
晶体学 | 32篇 |
力学 | 483篇 |
综合类 | 27篇 |
数学 | 367篇 |
物理学 | 2215篇 |
出版年
2024年 | 4篇 |
2023年 | 26篇 |
2022年 | 59篇 |
2021年 | 75篇 |
2020年 | 81篇 |
2019年 | 78篇 |
2018年 | 74篇 |
2017年 | 90篇 |
2016年 | 131篇 |
2015年 | 121篇 |
2014年 | 200篇 |
2013年 | 307篇 |
2012年 | 245篇 |
2011年 | 253篇 |
2010年 | 190篇 |
2009年 | 237篇 |
2008年 | 252篇 |
2007年 | 256篇 |
2006年 | 207篇 |
2005年 | 205篇 |
2004年 | 245篇 |
2003年 | 177篇 |
2002年 | 143篇 |
2001年 | 139篇 |
2000年 | 102篇 |
1999年 | 105篇 |
1998年 | 120篇 |
1997年 | 89篇 |
1996年 | 64篇 |
1995年 | 65篇 |
1994年 | 53篇 |
1993年 | 55篇 |
1992年 | 26篇 |
1991年 | 24篇 |
1990年 | 13篇 |
1989年 | 12篇 |
1988年 | 20篇 |
1987年 | 11篇 |
1986年 | 8篇 |
1985年 | 11篇 |
1984年 | 13篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1978年 | 2篇 |
1977年 | 5篇 |
1976年 | 3篇 |
1968年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有4620条查询结果,搜索用时 0 毫秒
981.
Herein, PEGylated multi-walled carbon nanotube (MWNT) was prepared for the successive fabrication of poly(vinyl alcohol) PVA/MWNT nanocomposite film by solution casting. The surface modified MWNT showed a good colloidal stability in a polar solvent, i.e., water. Also, the PEGylated MWNT had an improved dispersion stability in aqueous PVA solution. The mixture of PEGylated MWNT and PVA dissolved in water was film casted and the dispersion uniformity and corresponding improvement of electrical conductivity were investigated. The electrical conductivity of PVA/modified MWNT composite film was three-fold higher than that of PVA/pristine MWNT composite film due to the much improved distribution uniformity of modified MWNT in PVA matrix. 相似文献
982.
以非线性薛定谔方程为模型,采用分步傅里叶方法对光纤放大器中自相似脉冲的传输特性进行详细的研究,结果表明:抛物型的自相似脉冲可以在不包含高阶色散的光纤放大器系统中稳定传输;当系统的高阶色散(如:三阶色散)不容忽略时,自相似脉冲在光纤放大器中传输时将在脉冲沿出现抖动现象,导致脉冲的抛物线形状产生畸变. 相似文献
983.
984.
反萃分散组合液膜分离提取氨基酸 总被引:1,自引:0,他引:1
建立了分离提取蛋氨酸、亮氨酸、苯丙氨酸和色氨酸的磷酸二(2-乙基己基)酯(D2EHPA) 煤油-HCl反萃分散组合液膜体系,考察了料液相pH值、载体D2EHPA浓度、液膜相与反萃相体积比、反萃相组成、料液相与反萃分散相流速、传输时间以及支撑膜重复使用次数对氨基酸渗透系数和传输效率的影响。 在优化的条件下,建立的反萃分散组合液膜体系对4种氨基酸均可以获得大于35%的传输效率,其中色氨酸和亮氨酸的传输效率超过了79%,且传输效率呈Et,Trp>Et,Leu>Et,Phe>Et,Met的趋势。 支撑膜重复使用25次,对氨基酸的传输效率没有明显改变。建立的液膜体系对考察的氨基酸展示了较高传输效率和优越的传输选择性,是一种简单和环境友好的分离技术。 相似文献
985.
986.
Probing Transient Conformational States of Proteins by Solid‐State R1ρ Relaxation‐Dispersion NMR Spectroscopy 下载免费PDF全文
Dr. Peixiang Ma Jens D. Haller Jérémy Zajakala Dr. Pavel Macek Dr. Astrid C. Sivertsen Prof. Dr. Dieter Willbold Dr. Jérôme Boisbouvier Dr. Paul Schanda 《Angewandte Chemie (International ed. in English)》2014,53(17):4312-4317
The function of proteins depends on their ability to sample a variety of states differing in structure and free energy. Deciphering how the various thermally accessible conformations are connected, and understanding their structures and relative energies is crucial in rationalizing protein function. Many biomolecular reactions take place within microseconds to milliseconds, and this timescale is therefore of central functional importance. Here we show that R1ρ relaxation dispersion experiments in magic‐angle‐spinning solid‐state NMR spectroscopy make it possible to investigate the thermodynamics and kinetics of such exchange process, and gain insight into structural features of short‐lived states. 相似文献
987.
对用分光计测定光栅常数为1/300 mm透射光栅1级角色散的方法进行了改进,给出了引入自组光具组进行测量的方法.改进后的方法充分利用自组光具组基本特性参数在较大范围内连续可调的优点,克服传统的用分光计测量方法中光路的关键参数不可调节的不足,从而提高了测量精度.自组光具组的引入,也起到使光路参数选取具有多样性和丰富光路调... 相似文献
988.
This work addresses the analysis of an isotropic planarly layered waveguide consisting of an inhomogeneous core that is enclosed between two homogeneous layers forming the cladding. The analysis relies on an auxiliary one-dimensional spectral problem that is intimately linked with the scalar wave equation for planarly layered media. We construct the Green function of the waveguide as an expansion involving the eigenfunctions of the continuous and the discrete spectrum of the auxiliary problem. From the eigenvalues of the discrete spectrum, we calculate the allowed propagation constants of the guided modes. The Spectral Parameter Power Series (SPPS) method [Math. Method Appl. Sci. 2010;33: 459–468] leads us to analytic expressions for the eigenfunctions of the auxiliary problem in the form of power series of the spectral parameter. In addition, we obtain an SPPS representation for the dispersion relation without making any kind of approximation or discretisation to the core of the waveguide. The SPPS analysis here presented is well suited for its numerical implementation, since all these series can be truncated due to their uniform convergence. 相似文献
989.
A highly birefringent index-guiding photonic crystal fibers with flattened dispersion and low effective area is proposed by introducing elliptical air holes in the cladding and small holes both in the core area and in the cladding. With the plane wave expansion (PWE) method, the birefringent, dispersion and effective area of the fundamental modes in such photonic crystal fibers are analyzed in detail. The simulation result shows that high birefringence with a magnitude of the order of 10−3, flattened chromatic dispersion from 1100 nm to 1800 nm and low effective area (which mean high nonlinearity) are obtained. Furthermore, the influences on the birefringence and dispersion by geometrical parameters have also been discussed and a modest number of design parameters are given. 相似文献
990.
Francesco Innocenti Alberto Milani Chiara Castiglioni 《Journal of Raman spectroscopy : JRS》2010,41(2):226-236
The molecular and vibrational structures of cumulenic carbon chains are investigated by density functional theory calculations and compared with that of hydrogen‐capped polyynes. The small value of bond length alternation (BLA) along the CC bonds sequence obtained by geometry optimization of uncapped Cn chains and vinyl‐capped carbon chains confirms their cumulenic structure. It is demonstrated that for finite length chains the structural parameters are determined by end effects as far as the Peierls distortion, expected for very long molecules, does not occur. The Raman spectra of such molecules are calculated to verify the possibility of identifying markers of cumulenic chains by means of vibrational spectroscopy. As expected, the longitudinal mode consisting of the BLA oscillation, which is responsible for the strongest Raman transition of polyynes, becomes very weak for cumulenes; this behaviour is rationalized in terms of local polarizability derivatives. However, other longitudinal modes can be observed in the Raman spectra of Cn chains. The wavenumber behaviour and the optical activity of these modes are interpreted on the basis of the phonon dispersion branch of an ideally infinite cumulenic polymer. Raman intensities computed for chains of different lengths allow to conclude that cumulenic molecules could be detected and identified by means of Raman spectroscopy. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献