全文获取类型
收费全文 | 6261篇 |
免费 | 204篇 |
国内免费 | 333篇 |
专业分类
化学 | 1277篇 |
晶体学 | 4篇 |
力学 | 381篇 |
综合类 | 28篇 |
数学 | 3906篇 |
物理学 | 1202篇 |
出版年
2023年 | 76篇 |
2022年 | 84篇 |
2021年 | 103篇 |
2020年 | 93篇 |
2019年 | 134篇 |
2018年 | 114篇 |
2017年 | 128篇 |
2016年 | 146篇 |
2015年 | 144篇 |
2014年 | 240篇 |
2013年 | 551篇 |
2012年 | 300篇 |
2011年 | 334篇 |
2010年 | 311篇 |
2009年 | 458篇 |
2008年 | 458篇 |
2007年 | 420篇 |
2006年 | 318篇 |
2005年 | 230篇 |
2004年 | 222篇 |
2003年 | 191篇 |
2002年 | 178篇 |
2001年 | 120篇 |
2000年 | 120篇 |
1999年 | 109篇 |
1998年 | 111篇 |
1997年 | 116篇 |
1996年 | 129篇 |
1995年 | 94篇 |
1994年 | 117篇 |
1993年 | 88篇 |
1992年 | 87篇 |
1991年 | 44篇 |
1990年 | 44篇 |
1989年 | 34篇 |
1988年 | 30篇 |
1987年 | 27篇 |
1986年 | 32篇 |
1985年 | 43篇 |
1984年 | 36篇 |
1983年 | 16篇 |
1982年 | 47篇 |
1981年 | 23篇 |
1980年 | 23篇 |
1979年 | 27篇 |
1978年 | 17篇 |
1977年 | 13篇 |
1976年 | 10篇 |
1973年 | 2篇 |
1969年 | 2篇 |
排序方式: 共有6798条查询结果,搜索用时 46 毫秒
91.
In this work we display a numerical comparison, under statistical and computational point of view, between semi-analytical Eulerian and Lagrangian dispersion models to simulate the ground-level concentration values of a passive pollutant released from a low height source. The Eulerian approach is based on the solution of the advection–diffusion equation by the Laplace transform technique. The Lagrangian approach is based on solution of the Langevin equation through the Picard’s Iterative Method. Turbulence inputs are calculated according to a parameterization capable of generating continuous values in all stability conditions and in all heights of the Planetary Boundary Layer (PBL). Numerical simulations and comparisons show a good agreement between predicted and observed concentrations values. The comparison reveals the main advantages and disadvantages between the models. 相似文献
92.
There is a general interest in ranking schemes applied to complex entities described by multiple attributes. Published rankings
for universities are in great demand but are also highly controversial. We compare two classification and ranking schemes
involving universities; one from a published report, ‘Top American Research Universities’ by the University of Florida's TheCenter and the other using DEA. Both approaches use the same data and model. We compare the two methods and discover important equivalences.
We conclude that the critical aspect in classification and ranking is the model. This suggests that DEA is a suitable tool
for these types of studies. 相似文献
93.
Juray De Wilde Denis Constales Geraldine J. Heynderickx Guy B. Marin 《International Journal of Multiphase Flow》2007
The propagation speeds of linear waves in gas–solid suspensions depend strongly on the solids volume fraction and the wave frequency. The latter is due to gas–solid momentum transfer and allows a simple test on filtered gas–solid momentum transfer models. Such models may predict linear wave propagation speeds different from those obtained with the non-filtered model at wave frequencies higher than the filter frequency, but not at wave frequencies lower than the filter frequency. 相似文献
94.
波罗的海运价指数BD I是综合反应干散货航运市场运价总水平的指标,在众多的运价指数中占有公认的主导地位。本文以BD I运价指数为研究对象,通过协整研究,证明了BD I运价指数与BC I4条样本航线期租价格之间稳定的联动关系,并且给出了它们的误差修正模型。 相似文献
95.
应用改进的量子分子动力学模型,在严格挑选初始核考虑弹靶结构效应的基础上,研究了近垒和垒上融合反应40,48Ca+90,96Zr. 研究表明: 4个反应的理论计算截面与实验值很好符合; 丰中子反应40Ca+96Zr的垒下融合截面比其他3个反应有明显增强的现象.为了理解丰中子反应40Ca+96Zr与40Ca+90Zr相比垒下融合截面增强,而Ca+96Zr垒下融合截面没有明显增强的原因, 进一步分析了484个反应的融合位垒,中子转移与融合位垒的关系、中子转移与Q值的关系,结果表明: 正反应Q值会引起核子(特别是中子)转移的增强,从而导致动力学融合位垒的下降和垒下融合截面增强. 相似文献
96.
Model or variable selection is usually achieved through ranking models according to the increasing order of preference. One of methods is applying Kullback–Leibler distance or relative entropy as a selection criterion. Yet that will raise two questions, why use this criterion and are there any other criteria. Besides, conventional approaches require a reference prior, which is usually difficult to get. Following the logic of inductive inference proposed by Caticha [Relative entropy and inductive inference, in: G. Erickson, Y. Zhai (Eds.), Bayesian Inference and Maximum Entropy Methods in Science and Engineering, AIP Conference Proceedings, vol. 707, 2004 (available from arXiv.org/abs/physics/0311093)], we show relative entropy to be a unique criterion, which requires no prior information and can be applied to different fields. We examine this criterion by considering a physical problem, simple fluids, and results are promising. 相似文献
97.
The convergence of iterative based domain decomposition methods is linked with the absorbing boundary conditions defined on the interface between the sub-domains. For linear elasticity problems, the optimal absorbing boundary conditions are associated with non-local Dirichlet-to-Neumann maps. Most of the methods to approximate these non-local maps are based on a continuous analysis. In this paper, an original algebraic technique based on the computation of local Dirichlet-to-Neumann maps is investigated. Numerical experiments are presented for linear elasticity problems with extreme contrasts in the coefficients. 相似文献
98.
FANG DAOYUAN GONG XIAOQING Department of Applied Mathematics Zhejiang University Hangzhou Department of Applied Mathematics Wuhan University of Hydraulic Electrical Engineering Wuhan 《高校应用数学学报(英文版)》1996,11(1):43-50
In this paper we study the Goursat problem for semilinear hyperbolicequations with zero boundary condition where the boundary is the characteristic conefor hyperbolic operator. Our result shows that the solution is Lipschitz and is smoothaway from the characteristic cone. 相似文献
99.
激光对生物分子的共振激发作用 总被引:7,自引:0,他引:7
在生物分子的“谐”和“非谐”振子势模型的基础上,用量子力学讨论了激光对生物分子的共振激作用;并用之对激光的生物激活、诱变机理的“共振吸收”定性理论作一解析分析。 相似文献
100.
The effect of ultraviolet (UV) light on the thermooxidative stability of Linear Low Density Polyethylene(LLDPE) films was studied. LLDPE was stabilized with phenolic type antioxidant known as Irganox 1010, hindered amine light stabilizer known as Chimmasorb 944 and phenolic type gamma stabilizer. The influence of these additives on the thermooxidative stability of gamma and UV irradiated LLDPE were investigated by isothermal Differential Scanning Calorimeter (DSC). The oxidation induction time (OIT) experiments indicate that antirad free LLDPE films which contains antioxidant and UV stabilizer are more sensitive to gamma and UV radiation. On the other hand, films which contain antirad and irradiated to different doses of γ-radiation demonstrated improved thermooxidative stability. 相似文献