全文获取类型
收费全文 | 9262篇 |
免费 | 827篇 |
国内免费 | 412篇 |
专业分类
化学 | 2338篇 |
晶体学 | 72篇 |
力学 | 1305篇 |
综合类 | 41篇 |
数学 | 3409篇 |
物理学 | 3336篇 |
出版年
2024年 | 8篇 |
2023年 | 99篇 |
2022年 | 111篇 |
2021年 | 195篇 |
2020年 | 245篇 |
2019年 | 234篇 |
2018年 | 203篇 |
2017年 | 225篇 |
2016年 | 287篇 |
2015年 | 255篇 |
2014年 | 392篇 |
2013年 | 880篇 |
2012年 | 394篇 |
2011年 | 534篇 |
2010年 | 420篇 |
2009年 | 572篇 |
2008年 | 626篇 |
2007年 | 611篇 |
2006年 | 486篇 |
2005年 | 412篇 |
2004年 | 405篇 |
2003年 | 368篇 |
2002年 | 283篇 |
2001年 | 283篇 |
2000年 | 256篇 |
1999年 | 255篇 |
1998年 | 207篇 |
1997年 | 197篇 |
1996年 | 110篇 |
1995年 | 115篇 |
1994年 | 126篇 |
1993年 | 95篇 |
1992年 | 79篇 |
1991年 | 83篇 |
1990年 | 43篇 |
1989年 | 30篇 |
1988年 | 38篇 |
1987年 | 40篇 |
1986年 | 33篇 |
1985年 | 52篇 |
1984年 | 38篇 |
1983年 | 30篇 |
1982年 | 29篇 |
1981年 | 23篇 |
1980年 | 19篇 |
1979年 | 18篇 |
1978年 | 10篇 |
1977年 | 11篇 |
1976年 | 5篇 |
1973年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
1.
《Mendeleev Communications》2022,32(4):534-536
Correlation times and diffusion coefficients of water molecules were measured for the first time by 1H spin relaxation and pulsed field gradient NMR in Li+, Na+ and Cs+ ionic forms of Nafion 117 membrane. Hydration numbers of Li+, Na+ and Cs+ cations were calculated. It was shown that at high humidity macroscopic transfer is controlled by the local translational motion of water molecules. 相似文献
2.
3.
Atopic dermatitis is characterized by leukocyte migration into the skin dermis and typically driven by excessive chemokine production at the site of inflammation. Conventional topical formulations such as gels, creams, and ointments are insufficient for this treatment because of low penetration of drug molecules into the targeted skin tissues. Herein, using a simple, green, sustainable strategy, we have developed novel primary zein nanoparticles embedded in curcumin (Cur) and coated with silk sericin (ZHSCs) for the topical delivery of Cur to penetrate into the dermis and exercise anti-dermatitis effects on the lesion with minimal side-effects. Transdermal delivery experiments and porcine skin fluorescence imaging indicated that ZHSCs facilitate the penetration of Cur across the epidermis layer of skin to reach deep-seated sites. Notably, ZHSCs = 1:0.25 (zein-to-silk sericin mass ratios of 1:0.25) markedly elevated the skin permeability and cumulative turnover of Cur transferred, which were provided a greater than a 3.8-fold increase relative to free Cur. The special nanoparticles of ZHS = 1:0.25 possessed the deepest localization depth and experience a transition of the particle structure and core-shell separation after penetrating into the dermis of skin. In a cell model of dermatitis induced by tumor necrosis factor α/interferon γ co-stimulation, compared with free Cur, Cur-loaded ZHS nanoparticles down-regulated the generation of inflammatory cytokines and chemokines in keratinocytes through suppression of the nuclear translocation of NF-κBp65 and hence exerted an anti-dermatitis effect. This strategy may provide new avenues and direction for the demanding issues of valid topical delivery systems. 相似文献
4.
5.
针对传统红外图像增强算法中细节模糊及过度增强的问题,提出了一种基于Retinex理论与概率非局部均值相结合的红外图像增强方法.首先通过单尺度Retinex方法调整图像中过暗与过亮部分的灰度级;然后利用概率非局部均值对图像进行分解处理得到基本层与细节层,对基本层采用直方图均衡化拉伸对比度,对细节层采用非线性函数进行增强;最后,将不同层次的结果融合得到对比度与细节增强的红外图像.用该方法对多组不同场景的红外图像进行仿真实验,并将其与多种增强方法进行主、客观对比分析,结果表明所提方法在红外图像的细节及对比度增强方面都获得了更好的效果. 相似文献
6.
Transformation hydrodynamics and the corresponding metamaterials have been proposed as a means to exclude the drag force acting on an object. Here, we report a strategy to deploy the hydrodynamic cloaks in a more practical manner by assembling different-shaped cloaking parts. Our strategy is to first model a square-shaped cloak and a carpet cloak and then combine them to conceal a more complex-shaped space in the three-dimensional hydrodynamic flow. With the derivation of transformation hydrodynamics, the coordinate transformations for each hydrodynamic cloaking are demonstrated with the calculated viscosity tensors. The pressure and velocity fields of the square, triangular (carpet), and exemplary three-dimensional house-shaped cloaks are numerically simulated, thus showing a cloaking effect and reduced drag. This study suggests an efficient way of cloaking complex architectures from fluid-dynamic forces. 相似文献
7.
《Electroanalysis》2006,18(6):595-604
The following two numerical models have been applied to zinc cations electroreduction in 1 M NaClO4 water solution: a classical EE model describing the concentration of involved species in solution (semi infinitive diffusion region), an extended EE model describing both: the concentration of involved species in solution and the concentration of metallic zinc inside mercury drop (in limited area of diffusion). In the latter model the inner part of mercury drop and surrounding solution were treated as dynamic interrelated system. Both models were applied to experimental cyclic voltammetric CV data in 1 M NaClO4, the results compared and discussed. The concentration profiles of all species including metallic zinc inside mercury drop were performed. The presented integrated model is essential for theoretical and analytical aspects of the electrochemistry of mercury soluble metal cations and amalgams. 相似文献
8.
9.
P.A. Ramachandran 《Numerical Methods for Partial Differential Equations》2006,22(4):831-846
Time‐dependent differential equations can be solved using the concept of method of lines (MOL) together with the boundary element (BE) representation for the spatial linear part of the equation. The BE method alleviates the need for spatial discretization and casts the problem in an integral format. Hence errors associated with the numerical approximation of the spatial derivatives are totally eliminated. An element level local cubic approximation is used for the variable at each time step to facilitate the time marching and the nonlinear terms are represented in a semi‐implicit manner by a local linearization at each time step. The accuracy of the method has been illustrated on a number of test problems of engineering significance. © 2005 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 2006 相似文献
10.
We analyze diffusion from a periodic array of hemispherical droplets through a membrane. We find that the multiple sources do not interact strongly, even when the droplets are closely spaced, so that the flux through the membrane appears nearly additive. 相似文献