全文获取类型
收费全文 | 204908篇 |
免费 | 20427篇 |
国内免费 | 13241篇 |
专业分类
化学 | 110454篇 |
晶体学 | 1915篇 |
力学 | 14846篇 |
综合类 | 805篇 |
数学 | 46684篇 |
物理学 | 63872篇 |
出版年
2024年 | 448篇 |
2023年 | 2620篇 |
2022年 | 4411篇 |
2021年 | 4773篇 |
2020年 | 4969篇 |
2019年 | 4781篇 |
2018年 | 13612篇 |
2017年 | 13085篇 |
2016年 | 11370篇 |
2015年 | 6664篇 |
2014年 | 7358篇 |
2013年 | 9635篇 |
2012年 | 15004篇 |
2011年 | 21401篇 |
2010年 | 13103篇 |
2009年 | 13142篇 |
2008年 | 14249篇 |
2007年 | 15570篇 |
2006年 | 7039篇 |
2005年 | 7038篇 |
2004年 | 6027篇 |
2003年 | 5440篇 |
2002年 | 4178篇 |
2001年 | 3026篇 |
2000年 | 2904篇 |
1999年 | 3053篇 |
1998年 | 2664篇 |
1997年 | 2474篇 |
1996年 | 2589篇 |
1995年 | 2140篇 |
1994年 | 1926篇 |
1993年 | 1655篇 |
1992年 | 1446篇 |
1991年 | 1260篇 |
1990年 | 1051篇 |
1989年 | 885篇 |
1988年 | 731篇 |
1987年 | 662篇 |
1986年 | 581篇 |
1985年 | 527篇 |
1984年 | 375篇 |
1983年 | 306篇 |
1982年 | 257篇 |
1981年 | 213篇 |
1980年 | 188篇 |
1979年 | 125篇 |
1978年 | 119篇 |
1977年 | 108篇 |
1975年 | 96篇 |
1973年 | 108篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
In this article, we construct and analyze a residual-based a posteriori error estimator for a quadratic finite volume method (FVM) for solving nonlinear elliptic partial differential equations with homogeneous Dirichlet boundary conditions. We shall prove that the a posteriori error estimator yields the global upper and local lower bounds for the norm error of the FVM. So that the a posteriori error estimator is equivalent to the true error in a certain sense. Numerical experiments are performed to illustrate the theoretical results. 相似文献
4.
The structure, chemical composition, and magnetic properties of electrochemically deposited nanocrystalline Co-Ni-Fe films
were investigated using a number of techniques. A high saturation magnetic induction up to B
s
= 21 kG was attained. An enhancement of the saturation magnetization compared to the ideal anticipated one was revealed,
which correlated with the nonlinear behavior of the structural phase composition and lattice parameters with the change of
the composition.
The text was submitted by the authors in English. 相似文献
5.
在氢化丁苯共聚物13C-NMR谱脂肪碳部分谱带归属的基础上,根据各谱带的主要来源,推导出六个二单元浓度的计算公式。计算出二单元、一单元的相对含量,各结构单元的数均序列长度、嵌段含量和其它结构参数。加氢前后的1H-和13C-NMR谱的组成计算结果基本一致。初步探讨了作为粘度指数改进剂的氢化丁苯共聚物微观结构与性能的关系,为合成提供了依据。 相似文献
6.
玻璃陶瓷材料中Tm3+离子红外到蓝色上转换发光 总被引:4,自引:0,他引:4
系统研究了PbF2+GeO2+WO3ⅩⅣTmF3玻璃陶瓷材料中,在近红外光(1.06μm)激发下,Tm3+离子的发光特性.实验中观测到Tm3+离子的两组峰值位置分别在20920cm-1和22173cm-1的蓝色上转换发光,并证实这两组上转换发光分别与吸收三个和四个光子有关,同时建立了上转换发光的模型.为了选择最佳掺杂浓度,详细地测量了Tm3+离子峰值为20920cm-1的蓝色上转换发光强度与TmF3浓度的关系. 相似文献
7.
A new secoiridoid, multiflorin (1) has been isolated from the EtOAc-soluble fraction of Jasminum multiflorum (Oleaceace). The structure of I was determined by application of spectral methods. 相似文献
8.
A forecasting model is developed for the number of daily applications for loans at a financial services telephone call centre. The purpose of the forecasts and the associated prediction intervals is to provide effective staffing policies within the call centre. The model building process is constrained by the availability of only 2 years and 7 months of data. The distinctive feature of the data is that demand is driven in the main by advertising. The analysis given focuses on applications stimulated by press advertising. Unlike previous analyses of broadly similar data, where ARIMA models were used, a model with a dynamic level, multiplicative calendar effects and a multiplicative advertising response is developed and shown to be effective. 相似文献
9.
In this paper, the authors studied certain properties of the estimate of Liang and Krishnaiah (1985, J. Multivariate Anal. 16, 162–172) for multivariate binary density. An alternative shrinkage estimate is also obtained. The above results are generalized to general orthonormal systems. 相似文献
10.
In this paper, a two-dimensional finite volume unstructured mesh method (FVUM) based on a triangular background interpolation mesh is developed for analysing the evolution of the saltwater intrusion into single and multiple coastal aquifer systems. The model formulation consists of a ground-water flow equation and a salt transport equation. These coupled and non-linear partial differential equations are transformed by FVUM into a system of differential/algebraic equations, which is solved using backward differentiation formulas of order one through five. Simulation results are compared with previously published solutions where good agreement is observed. 相似文献