全文获取类型
收费全文 | 5440篇 |
免费 | 808篇 |
国内免费 | 327篇 |
专业分类
化学 | 2054篇 |
晶体学 | 66篇 |
力学 | 597篇 |
综合类 | 68篇 |
数学 | 800篇 |
物理学 | 2990篇 |
出版年
2024年 | 11篇 |
2023年 | 36篇 |
2022年 | 120篇 |
2021年 | 151篇 |
2020年 | 160篇 |
2019年 | 136篇 |
2018年 | 134篇 |
2017年 | 191篇 |
2016年 | 223篇 |
2015年 | 168篇 |
2014年 | 285篇 |
2013年 | 456篇 |
2012年 | 285篇 |
2011年 | 323篇 |
2010年 | 279篇 |
2009年 | 339篇 |
2008年 | 382篇 |
2007年 | 368篇 |
2006年 | 339篇 |
2005年 | 270篇 |
2004年 | 228篇 |
2003年 | 228篇 |
2002年 | 166篇 |
2001年 | 163篇 |
2000年 | 131篇 |
1999年 | 161篇 |
1998年 | 120篇 |
1997年 | 100篇 |
1996年 | 79篇 |
1995年 | 95篇 |
1994年 | 55篇 |
1993年 | 53篇 |
1992年 | 52篇 |
1991年 | 40篇 |
1990年 | 30篇 |
1989年 | 21篇 |
1988年 | 33篇 |
1987年 | 16篇 |
1986年 | 16篇 |
1985年 | 19篇 |
1984年 | 15篇 |
1983年 | 9篇 |
1982年 | 17篇 |
1981年 | 18篇 |
1980年 | 15篇 |
1979年 | 6篇 |
1978年 | 7篇 |
1977年 | 13篇 |
1974年 | 4篇 |
1973年 | 4篇 |
排序方式: 共有6575条查询结果,搜索用时 31 毫秒
11.
A tomographic reconstruction method based on Monte Carlo random searching guided by the information contained in the projections
of radiographed objects is presented. In order to solve the optimization problem, a multiscale algorithm is proposed to reduce
computation. The reconstruction is performed in a coarse-to-fine multigrid scale that initializes each resolution level with
the reconstruction of the previous coarser level, which substantially improves the performance. The method was applied to
a real case reconstructing the internal structure of a small metallic object with internal components, showing excellent results. 相似文献
12.
A new stochastic method of reconstructing porous media 总被引:1,自引:0,他引:1
We present a new stochastic method of reconstructing porous medium from limited morphological information obtained from two-dimensional
micro- images of real porous medium. The method is similar to simulated annealing method in the capability of reconstructing
both isotropic and anisotropic structures of multi-phase but differs from the latter in that voxels for exchange are not selected
completely randomly as their neighborhood will also be checked and this new method is much simpler to implement and program.
We applied it to reconstruct real sandstone utilizing morphological information contained in porosity, two-point probability
function and linear-path function. Good agreement of those references verifies our developed method’s powerful capability.
The existing isolated regions of both pore phase and matrix phase do quite minor harm to their good connectivity. The lattice
Boltzmann method (LBM) is used to compute the permeability of the reconstructed system and the results show its good isotropy
and conductivity. However, due to the disadvantage of this method that the connectivity of the reconstructed system’s pore
space will decrease when porosity becomes small, we suggest the porosity of the system to be reconstructed be no less than
0.2 to ensure its connectivity and conductivity. 相似文献
13.
双氯芬酸钠与牛血清白蛋白结合反应的特征 总被引:2,自引:0,他引:2
在模拟人体生理条件下,采用荧光光谱和紫外 可见吸收光谱法研究了双氯芬酸钠与牛血清白蛋白的结合反应.实验结果显示,双氯芬酸钠对牛血清白蛋白有较强的荧光猝灭作用,该猝灭过程主要为静态荧光猝灭过程;二者结合常数KLB=2.167×105mol·L-1;二者的结合位置距212位色氨酸2.13nm;同时,由结合反应的热力学参数得出二者作用力主要是氢键或VanderWall's力. 相似文献
14.
15.
数码相机CMOS图像传感器的特性参数与选择 总被引:2,自引:0,他引:2
介绍了数码相机的核心器件———CMOS图像传感器的特性参数和在数码相机设计过程中CMOS图像传感器的选择。选择CMOS图像传感器,不仅需要考虑包括传感器的尺寸、像素总数和有效像素数、最小照度、动态范围、灵敏度、分辨力、光电响应不均匀性以及光谱响应等在内的特性参数,而且还要考虑电源管理和功耗、模数转换位数、开发的简便性以及成本等因素。 相似文献
16.
应用小波变换和非线性动力学方法研究了混沌信号在相空间中的行为,指出混沌时间序 列的小波变换实质上是在重构的相空间中,混沌吸引子向小波滤波器向量所张的空间中的投 影,与Packard等人提出的相空间重构方法本质上是一致的.实验结果表明,混沌信号经过 小波变换后,吸引子轨迹与原有轨迹具有相似的结构,同时,系统的关联维数、Kolmogorov 熵等非线性不变量仍然得到保留.这些结果表明,利用小波变换研究混沌信号是有效的.
关键词:
小波变换
相空间重构
混沌信号
脑电信号 相似文献
17.
18.
Kinetic parameters of amino acid cations in an MK-40 ion-exchange membrane are calculated from the conductivity data. A theoretical quantum-chemical analysis of experimental activation energies for conduction suggests a mechanism of elementary act of transport of amino acid cations in the membrane. 相似文献
19.
Vincent Maurice 《Surface science》2005,581(1):88-104
STM, STS, LEED and XPS data for crystalline θ-Al2O3 and non-crystalline Al2O3 ultra-thin films grown on NiAl(0 0 1) at 1025 K and exposed to water vapour at low pressure (1 × 10−7-1 × 10−5 mbar) and room temperature are reported. Water dissociation is observed at low pressure. This reactivity is assigned to the presence of a high density of coordinatively unsaturated cationic sites at the surface of the oxide film. The hydroxyl/hydroxide groups cannot be directly identify by their XPS binding energy, which is interpreted as resulting from the high BE positions of the oxide anions (O1s signal at 532.5-532.8 eV). However the XPS intensities give evidence of an uptake of oxygen accompanied by an increase of the surface coverage by Al3+ cations, and a decrease of the concentration in metallic Al at the alloy interface. A value of ∼2 for the oxygen to aluminium ions surface concentration ratio indicates the formation of an oxy-hydroxide (AlOxOHy with x + y ∼ 2) hydroxylation product. STM and LEED show the amorphisation and roughening of the oxide film. At P(H2O) = 1 × 10−7 mbar, only the surface of the oxide film is modified, with formation of nodules of ∼2 nm lateral size covering homogeneously the surface. STS shows that essentially the valence band is modified with an increase of the density of states at the band edge. With increasing pressure, hydroxylation is amplified, leading to an increased coverage of the alloy by oxy-hydroxide products and to the formation of larger nodules (∼7 nm) of amorphous oxy-hydroxide. Roughening and loss of the nanostructure indicate a propagation of the reaction that modifies the bulk structure of the oxide film. Amorphisation can be reverted to crystallization by annealing under UHV at 1025 K when the surface of the oxide film has been modified, but not when the bulk structure has been modified. 相似文献
20.