全文获取类型
收费全文 | 7385篇 |
免费 | 1183篇 |
国内免费 | 752篇 |
专业分类
化学 | 4991篇 |
晶体学 | 74篇 |
力学 | 412篇 |
综合类 | 47篇 |
数学 | 728篇 |
物理学 | 3068篇 |
出版年
2024年 | 15篇 |
2023年 | 150篇 |
2022年 | 122篇 |
2021年 | 178篇 |
2020年 | 266篇 |
2019年 | 235篇 |
2018年 | 220篇 |
2017年 | 194篇 |
2016年 | 314篇 |
2015年 | 315篇 |
2014年 | 378篇 |
2013年 | 522篇 |
2012年 | 563篇 |
2011年 | 629篇 |
2010年 | 420篇 |
2009年 | 423篇 |
2008年 | 460篇 |
2007年 | 397篇 |
2006年 | 380篇 |
2005年 | 359篇 |
2004年 | 304篇 |
2003年 | 220篇 |
2002年 | 254篇 |
2001年 | 191篇 |
2000年 | 180篇 |
1999年 | 184篇 |
1998年 | 130篇 |
1997年 | 136篇 |
1996年 | 157篇 |
1995年 | 110篇 |
1994年 | 117篇 |
1993年 | 115篇 |
1992年 | 101篇 |
1991年 | 83篇 |
1990年 | 64篇 |
1989年 | 75篇 |
1988年 | 56篇 |
1987年 | 47篇 |
1986年 | 40篇 |
1985年 | 39篇 |
1984年 | 25篇 |
1983年 | 22篇 |
1982年 | 15篇 |
1981年 | 13篇 |
1980年 | 11篇 |
1979年 | 8篇 |
1976年 | 7篇 |
1975年 | 5篇 |
1974年 | 5篇 |
1973年 | 6篇 |
排序方式: 共有9320条查询结果,搜索用时 15 毫秒
991.
992.
Liu Q Hong IP Ahn MJ Yoo HS Han SB Hwang BY Lee MK 《Natural product communications》2011,6(12):1839-1841
Inhibition of adipocytes differentiation is suggested to be an important strategy for prevention and/or treatment of obesity. In our present study, Cordyceps militaris showed significant inhibitory activity on adipocyte differentiation in 3T3-L1 preadipocytes as assessed by measuring fat accumulation using Oil Red O staining. Activity-guided fractionation led to the isolation of cordycepin (1), guanosine (2) and tryptophan (3) as active compounds. All the three compounds were more effective in the prevention of early stage of adipogenesis than in lipolysis. In addition, combinational treatment of three compounds significantly increased anti-adipogenic activity. 相似文献
993.
Yan Gu Wen Chen Chuan-Zeng Zhang 《International Journal of Solids and Structures》2011,48(18):2549-2556
This study documents the first attempt to apply the singular boundary method (SBM), a novel boundary only collocation method, to two-dimensional (2D) elasticity problems. Unlike the method of fundamental solutions (MFS), the source points coincide with the collocation points on the physical boundary by using an inverse interpolation technique to regularize the singularity of the fundamental solution of the equation governing the problems of interest. Three benchmark elasticity problems are tested to demonstrate the feasibility and accuracy of the proposed method through detailed comparisons with the MFS, boundary element method (BEM), and finite element method (FEM). 相似文献
994.
995.
For 0≤k≤n, let be the entries in Euler’s difference table and let . Dumont and Randrianarivony showed equals the number of permutations on [n] whose fixed points are contained in {1,2,…,k}. Rakotondrajao found a combinatorial interpretation of the number in terms of k-fixed-points-permutations of [n]. We show that for any n≥1, the sequence is essentially 2-log-concave and reverse ultra log-concave. 相似文献
996.
文章研究了一类函数增量的局部渐近性质,发现这类函数增量的局部渐近性对于一元实函数,二元及多元实函数,向量值函数和复函数在一定条件下都会保持不变,进而提出了两个相关的猜想:此类函数增量的渐近性是关于函数变换的拓扑不变量。 相似文献
997.
Given an isotropic random vector X with log-concave density in Euclidean space
\mathbbRn{\mathbb{R}^n} , we study the concentration properties of |X| on all scales, both above and below its expectation. We show in particular that
l \mathbbP( | |X| - ?n | 3 t?n ) £ C exp ( -cn1/2 min(t3, t) ) "t 3 0, \begin{array}{l} \mathbb{P}\left ( \left | |X| - \sqrt{n} \right | \geq t\sqrt{n} \right ) \leq C \, {\rm exp} \left ( -cn^{1/2} {\rm min}(t^{3}, t) \right) \; \forall t \geq 0, \end{array} 相似文献
998.
We present a partial first-order affine-scaling method for solving smooth optimization with linear inequality constraints. At each iteration, the algorithm considers a subset of the constraints to reduce the complexity. We prove the global convergence of the algorithm for general smooth objective functions, and show it converges at sublinear rate when the objective function is quadratic. Numerical experiments indicate that our algorithm is efficient. 相似文献
999.
Xian-Ming Gu Yong-Liang Zhao Xi-Le Zhao Bruno Carpentieri & Yu-Yun Huang 《高等学校计算数学学报(英文版)》2021,14(4):893-919
The $p$-step backward difference formula (BDF) for solving systems of
ODEs can be formulated as all-at-once linear systems that are solved by parallel-in-time preconditioned Krylov subspace solvers (see McDonald et al. [36] and Lin
and Ng [32]). However, when the BDF$p$ (2 ≤ $p$ ≤ 6) method is used to solve time-dependent PDEs, the generalization of these studies is not straightforward as $p$-step
BDF is not selfstarting for $p$ ≥ 2. In this note, we focus on the 2-step BDF which is
often superior to the trapezoidal rule for solving the Riesz fractional diffusion equations, and show that it results into an all-at-once discretized system that is a low-rank
perturbation of a block triangular Toeplitz system. We first give an estimation of the
condition number of the all-at-once systems and then, capitalizing on previous work,
we propose two block circulant (BC) preconditioners. Both the invertibility of these
two BC preconditioners and the eigenvalue distributions of preconditioned matrices
are discussed in details. An efficient implementation of these BC preconditioners is
also presented, including the fast computation of dense structured Jacobi matrices.
Finally, numerical experiments involving both the one- and two-dimensional Riesz
fractional diffusion equations are reported to support our theoretical findings. 相似文献
1000.
Effective heat dissipation from nano-fluidic devices is sometimes necessary to ensure their performance and lifespan. In the molecular dynamics simulation of nanoscale convective heat transfer, thermostats cannot be directly applied to the fluid because of the non-uniform temperature distribution. Periodic boundary is typically utilised, but unrealistic axial heat conduction exists when there is a temperature difference between the outlet and images of inlet atoms. In this paper, the effect of axial conduction caused by periodic boundary is investigated through the Péclet number (Pe). Taking viscous dissipation into consideration, the magnitude of outlet thermal diffusion is observed to decrease with increasing Pe. The local average temperature of fluid changes in an exponential form except in the region close to the outlet. Results show that the contribution of outlet axial conduction to the local average temperature is less than 2.0% when Pe > 10. The main reason is that the magnitude of fluid velocity and viscous heat dissipation in nanochannels is much larger than that in macro-channels at the same Péclet number. 相似文献
|