全文获取类型
收费全文 | 959篇 |
免费 | 185篇 |
国内免费 | 100篇 |
专业分类
化学 | 173篇 |
晶体学 | 4篇 |
力学 | 252篇 |
综合类 | 20篇 |
数学 | 372篇 |
物理学 | 423篇 |
出版年
2024年 | 3篇 |
2023年 | 12篇 |
2022年 | 24篇 |
2021年 | 19篇 |
2020年 | 35篇 |
2019年 | 23篇 |
2018年 | 23篇 |
2017年 | 35篇 |
2016年 | 44篇 |
2015年 | 38篇 |
2014年 | 58篇 |
2013年 | 82篇 |
2012年 | 66篇 |
2011年 | 62篇 |
2010年 | 57篇 |
2009年 | 61篇 |
2008年 | 57篇 |
2007年 | 62篇 |
2006年 | 50篇 |
2005年 | 65篇 |
2004年 | 51篇 |
2003年 | 57篇 |
2002年 | 44篇 |
2001年 | 36篇 |
2000年 | 40篇 |
1999年 | 21篇 |
1998年 | 28篇 |
1997年 | 20篇 |
1996年 | 13篇 |
1995年 | 9篇 |
1994年 | 2篇 |
1993年 | 8篇 |
1992年 | 2篇 |
1991年 | 8篇 |
1990年 | 2篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 4篇 |
1985年 | 1篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1936年 | 1篇 |
排序方式: 共有1244条查询结果,搜索用时 15 毫秒
991.
992.
R. Sheikhpour M. A. Sarram M. Rezaeian E. Sheikhpour 《SAR and QSAR in environmental research》2018,29(4):257-276
The aim of this study was to propose a QSAR modelling approach based on the combination of simple competitive learning (SCL) networks with radial basis function (RBF) neural networks for predicting the biological activity of chemical compounds. The proposed QSAR method consisted of two phases. In the first phase, an SCL network was applied to determine the centres of an RBF neural network. In the second phase, the RBF neural network was used to predict the biological activity of various phenols and Rho kinase (ROCK) inhibitors. The predictive ability of the proposed QSAR models was evaluated and compared with other QSAR models using external validation. The results of this study showed that the proposed QSAR modelling approach leads to better performances than other models in predicting the biological activity of chemical compounds. This indicated the efficiency of simple competitive learning networks in determining the centres of RBF neural networks. 相似文献
993.
The paper proposes a simple and portable approach for the surface enhanced Raman scattering (SERS) spectroscopy in situ determination of carboxylated single walled carbon nanotubes (SWNTs) in river water samples. The method is based on the subsequent microfiltration of a bare gold nanoparticles solution and the water sample containing soluble carbon nanotubes by using a home-made filtration device with a small filtration diameter. An acetate cellulose membrane with a pore size of 0.2 μm first traps gold nanoparticles to form the SERS-active substrate and then concentrates the carbon nanotubes. The measured SERS intensity data were closely fit with a Langmuir isotherm. A portable Raman spectrometer was employed to measure SERS spectra, which enables in situ determination of SWNTs in river waters. The limit of detection was 10 μg L−1. The precision, for a 10 mg L−1 concentration of carbon nanotubes, is 1.19% intra-membrane and 10.5% inter-membrane. 相似文献
994.
Zbigniew Romanowski 《International journal of quantum chemistry》2010,110(10):1793-1802
The approximation properties of Lobatto polynomials are analyzed and then applied to approximate the atomic Kohn–Sham eigenfunction. In the first part of this article the approximation algorithm based on the Galerkin finite element method is derived. To obtain the approximation of the function, based on the presented algorithm, the linear set of equations must be solved. The matrix of the equation set is very sparse and its elements can be evaluated analytically. In the second part of this article, the algorithm is applied to evaluate adaptive polynomial approximation of selected Kohn–Sham eigenstates of indium (In) atom. The proposed r‐adaptive algorithm evaluates the minimum number of subintervals needed to represent the eigenfunction with required accuracy. Based on the r‐adaptive algorithm, the approximations of 4d, 5s 5p In eigenfunctions were calculated. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 相似文献
995.
We extended prior studies on the influence of impeller type on fermentation performance to include a novel low-power-number,
high-efficiency radial flow impeller, the CD-6, possessing six curved blades on a disk turbine. Dual impeller combinations
of CD-6/CD-6, CD-6/Maxflo T, and CD-6/HE-3 were compared with Rushton/Rushton and Maxflo T/Maxflo T base cases. Qualitative
comparisons of unaerated and aerated power draw in both water and glycerol were conducted. These suggested minimal power drops
with aeration for dual CD-6 impellers and hybrids containing the CD-6 impeller design. We also examined fermentation performance
for Streptomyces and Glarea secondary metabolite fermentations. A qualitative comparison of the data suggested that dual CD-6 impellers and hybrids containing
the CD-6 impeller design resulted in reasonable power draws, improved mass transfer rates with airflow increases, and acceptable
peak titers. These arrangements may warrant further study under a wider range of production conditions. 相似文献
996.
997.
Voltz K Trylska J Tozzini V Kurkal-Siebert V Langowski J Smith J 《Journal of computational chemistry》2008,29(9):1429-1439
A coarse-grained simulation model for the nucleosome is developed, using a methodology modified from previous work on the ribosome. Protein residues and DNA nucleotides are represented as beads, interacting through harmonic (for neighboring) or Morse (for nonbonded) potentials. Force-field parameters were estimated by Boltzmann inversion of the corresponding radial distribution functions obtained from a 5-ns all-atom molecular dynamics (MD) simulation, and were refined to produce agreement with the all-atom MD simulation. This self-consistent multiscale approach yields a coarse-grained model that is capable of reproducing equilibrium structural properties calculated from a 50-ns all-atom MD simulation. This coarse-grained model speeds up nucleosome simulations by a factor of 10(3) and is expected to be useful in examining biologically relevant dynamical nucleosome phenomena on the microsecond timescale and beyond. 相似文献
998.
Triflic acid is a functional group of perflourosulfonated polymer electrolyte membranes where the sulfonate group is responsible for proton conduction. However, even at extremely low hydration, triflic acid exists as a triflate ion. In this work, we have developed a force-field for triflic acid and triflate ion by deriving force-field parameters using ab initio calculations and incorporated these parameters with the Optimized Potentials for Liquid Simulations - All Atom (OPLS-AA) force-field. We have employed classical molecular dynamics (MD) simulations with the developed force field to characterize structural and dynamical properties of triflic acid (270-450 K) and triflate ion/water mixtures (300 K). The radial distribution functions (RDFs) show the hydrophobic nature of CF(3) group and presence of strong hydrogen bonding in triflic acid and temperature has an insignificant effect. Results from our MD simulations show that the diffusion of triflic acid increases with temperature. The RDFs from triflate ion/water mixtures shows that increasing hydration causes water molecules to orient around the SO(3)(-) group of triflate ions, solvate the hydronium ions, and other water molecules. The diffusion of triflate ions, hydronium ion, and water molecules shows an increase with hydration. At λ = 1, the diffusion of triflate ion is 30 times lower than the diffusion of triflic acid due to the formation of stable triflate ion-hydronium ion complex. With increasing hydration, water molecules break the stability of triflate ion-hydronium ion complex leading to enhanced diffusion. The RDFs and diffusion coefficients of triflate ions, hydronium ions and water molecules resemble qualitatively the previous findings using per-fluorosulfonated membranes. 相似文献
999.
通过微分求积建立求解变系数空间分数阶扩散方程的一种有效直接数值方法。基于Reciprocal Multiquadric和Thin-Plate Spline径向基函数推导两种逼近分数阶导数的微分求积公式,将所考虑的模型问题转化成易求解的常微分方程组,并采用Crank-Nicolson格式进行离散。给出5个数值算例,计算结果表明,只要径向基函数的形状参数选择恰当,本文方法在精度和效率上均优于一些现有算法。 相似文献
1000.
采用X射线衍射对称反射法,对半结晶聚酯PET2试样收集粉末X射线衍射全图(XDWP)数据,用Rietveld方法和Fourier过滤技术,对XDWP拟合并分离成结晶衍射峰之和CR2和非晶散射峰之和AM2两部分,与此同时获得PET2试样的结晶相CR2的三斜晶系晶胞参数:a=0.445,b=0.592,c=1.072nm,α=99.6,β=116.9,γ=111.9(°),结晶密度dc关键词:
聚对苯二甲酸乙二醇酯
二相共存结构
径向分布函数
Rietveld方法
Fourier过滤技术 相似文献