全文获取类型
收费全文 | 1473篇 |
免费 | 472篇 |
国内免费 | 75篇 |
专业分类
化学 | 164篇 |
晶体学 | 4篇 |
力学 | 173篇 |
综合类 | 103篇 |
数学 | 357篇 |
物理学 | 1219篇 |
出版年
2024年 | 5篇 |
2023年 | 18篇 |
2022年 | 45篇 |
2021年 | 43篇 |
2020年 | 50篇 |
2019年 | 46篇 |
2018年 | 50篇 |
2017年 | 69篇 |
2016年 | 58篇 |
2015年 | 43篇 |
2014年 | 98篇 |
2013年 | 115篇 |
2012年 | 106篇 |
2011年 | 98篇 |
2010年 | 91篇 |
2009年 | 91篇 |
2008年 | 108篇 |
2007年 | 101篇 |
2006年 | 88篇 |
2005年 | 76篇 |
2004年 | 78篇 |
2003年 | 64篇 |
2002年 | 70篇 |
2001年 | 67篇 |
2000年 | 50篇 |
1999年 | 40篇 |
1998年 | 36篇 |
1997年 | 33篇 |
1996年 | 34篇 |
1995年 | 25篇 |
1994年 | 17篇 |
1993年 | 15篇 |
1992年 | 13篇 |
1991年 | 9篇 |
1990年 | 14篇 |
1989年 | 12篇 |
1988年 | 14篇 |
1987年 | 7篇 |
1986年 | 4篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 5篇 |
1982年 | 4篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1959年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有2020条查询结果,搜索用时 203 毫秒
101.
ABSTRACT. In many spatial systems the interaction between various regions decreases dramatically with distance. This suggests that local trade-offs may be more important than global ones in land use planning and that a decentralized, parallel optimization of the individual regions may be an attractive supplement to more centralized optimization approaches. In this paper, we solve a forest planning problem using a series of decentralized approaches. The approaches can be characterized as self-organizing algorithms and are modeled in the framework of a cellular automaton. We compare our results with those obtained by more centralized approaches, viz. a large sample approach, simulated annealing, and a genetic algorithm. We find that the self-organizing algorithms generally converge much faster to solutions which are at least as good as those obtained by simulated annealing and the genetic algorithm. 相似文献
102.
103.
Construction of a spatial light modulator (SLM) using reverse saturable absorber molecules is suggested. The SLM characteristics
are derived using a recently proposed steady-state kinetic analysis. Results are presented for the rhodamine 6G dye molecules. 相似文献
104.
R. Quintanilla 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》2006,57(4):595-603
In this note we investigate the spatial behavior of several nonlinear parabolic equations with nonlinear boundary conditions.
Under suitable conditions on the nonlinear terms we prove that the solutions either cease to exist for a finite value of the
spatial variable or else they decay algebraically. The main tool used is the weighted energy method. Our results can be applied
to several situations concerning heat conduction.
Received: April 4, 2004; revised: September 20, 2004 相似文献
105.
This research presents a thorough evaluation of the reverberation room at Acoustics Laboratory in National Institute of Standards (NIS) according to the related international standards. The evaluation aims at examining the room performance and exploring its effectiveness in the frequency range from 125 Hz to 10000 Hz according to the international standard requirements. The room, which was designed and built several years ago, is an irregular rectangular shape free from diffusers. Its volume is about 158.84 m3, which meets the requirement of the ISO 354 standard Lmax < 1.9V1/3. Cut-off frequencies of one and one-third octave are 63 Hz and 100 Hz respectively; however Schroder frequency is 400 Hz. Calculations of cut-off frequency and modal density showed adequate modes that give acceptable uniformity starting comfortably from frequency of 125 Hz. The room has a reverberation time that is suitable for its size over the frequency range of interest. The room sound absorption surface area and its sound absorption coefficient satisfy the criteria given in ISO 3741 and ISO 354. There is an accepted diffuse sound field inside the room due to the standard deviation of measured sound level, which is less than 1.5 dB over all the frequency range. The only exception was 125 Hz which may be due to a lack of diffusivity of the sound field at this frequency. The evaluation proves that the NIS reverberation room is in full agreement with the international standards, which in turns qualifies the room to host measurements inside without concerns. 相似文献
106.
相移数字云纹测量系统 总被引:2,自引:0,他引:2
介绍了一种相位移数字云纹变形测量系统.测试系统采用CCD摄像系统记录光栅图像,控制采样的空间频率大约为光栅线密度的整数倍,对试件栅进行采样后用数字信号处理的方法,实现空间相位移及进行实时数字云纹条纹显示,并对相移误差及光栅信号的高阶谐波的影响进行了校正 相似文献
107.
Mixtures of Trifluoroethanol (TFE) and water with different proportions are studied using molecular dynamics simulations. The radial and spatial distribution functions, as well as the size distribution of TFE clusters are obtained from the trajectories. The variation of radial and spatial distribution functions with composition show that the addition of TFE enhances the water structure, but the hydrogen bonds between TFE molecules are broken as TFE is diluted with water. The TFE‐rich solutions have stronger TFE–water hydrogen bonds. The clustering of TFE molecules in low concentration region is attributed to the hydrophobic interactions between CF3 groups. The distribution of cluster sizes in solution supports these conclusions. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010 相似文献
108.
介绍了阿贝-波特空间滤波的实验原理,在Matlab环境下建立了带有图形用户界面(GUI)的计算机仿真平台.不仅可以准确地完成针对不同输入图像、不同滤波要求的滤波过程,还可以通过调整滤波器参数观察滤波效果的差异,形象地展现光学空间滤波过程的物理本质,提高教学效果. 相似文献
109.
110.
Jianchu Liang 《Optics Communications》2011,284(19):4477-4479
Experimental observation of spatial solitons in azobenzene-doped organic polymer is demonstrated in dye-doped polymer bulk material. Solitons cannot only be formed in this material with linearly polarized light, but also with circularly polarized light. An interesting phenomenon is revealed that the soliton is polarization-dependent. The solitons with the same intensity but with different polarizations have different widths. The experimental results are further theoretically explained with the dynamics model based on a photochemical process, namely photoisomerization. 相似文献