全文获取类型
收费全文 | 964篇 |
免费 | 130篇 |
国内免费 | 119篇 |
专业分类
化学 | 722篇 |
晶体学 | 11篇 |
力学 | 81篇 |
综合类 | 16篇 |
数学 | 54篇 |
物理学 | 329篇 |
出版年
2024年 | 3篇 |
2023年 | 18篇 |
2022年 | 40篇 |
2021年 | 34篇 |
2020年 | 38篇 |
2019年 | 29篇 |
2018年 | 38篇 |
2017年 | 23篇 |
2016年 | 47篇 |
2015年 | 49篇 |
2014年 | 50篇 |
2013年 | 55篇 |
2012年 | 82篇 |
2011年 | 91篇 |
2010年 | 65篇 |
2009年 | 41篇 |
2008年 | 48篇 |
2007年 | 63篇 |
2006年 | 45篇 |
2005年 | 41篇 |
2004年 | 39篇 |
2003年 | 27篇 |
2002年 | 37篇 |
2001年 | 20篇 |
2000年 | 17篇 |
1999年 | 22篇 |
1998年 | 10篇 |
1997年 | 31篇 |
1996年 | 16篇 |
1995年 | 7篇 |
1994年 | 16篇 |
1993年 | 12篇 |
1992年 | 12篇 |
1991年 | 14篇 |
1990年 | 7篇 |
1989年 | 3篇 |
1988年 | 8篇 |
1987年 | 2篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 3篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1975年 | 1篇 |
1973年 | 3篇 |
1971年 | 1篇 |
排序方式: 共有1213条查询结果,搜索用时 0 毫秒
961.
962.
自适应光学系统的数值模拟:动态控制过程和频率响应特性 总被引:3,自引:0,他引:3
对自适应光学系统的动态控制过程进行了数值模拟。与自动控制理论的解析分析相比,动态控制过程的数值模拟有其优越性。系统的频率响应特性与动态控制性能密切相关,对自适应光学系统的频率响应特性也进行了数值模拟。模拟计算的结果与实验测量结果符合得很好。还实现了多频率成份的同时计算,可以大大提高计算效率。其结果与单频率结果只在低频下有小的差别,可以满足得到带宽和裕量等参数的实用要求。将频率响应特性的模拟计算与长时间曝光斯特列耳(Strehl)比的数值模拟结合,可得到对自适应光学系统性能的有效评估。 相似文献
963.
964.
Scaling is an important measure of multi-scale fluctuation systems. Turbulence as the most remarkable multi-scale system possesses scaling over a wide range of scales. She-Leveque (SL) hierarchical symmetry, since its publication in 1994, has received wide attention. A number of experimental, numerical and theoretical work have been devoted to its verification, extension, and modification. Application to the understanding of magnetohydrodynamic turbulence, motions of cosmic baryon fluids, cosmological supersonic turbulence, natural image, spiral turbulent patterns, DNA anomalous composition, human heart variability are just a few among the most successful examples. A number of modified scaling laws have been derived in the framework of the hierarchical symmetry, and the SL model parameters are found to reveal both the organizational order of the whole system and the properties of the most significant fluctuation structures. A partial set of work related to these studies are reviewed. Particular emphasis is placed on the nature of the hierarchical symmetry. It is suggested that the SL hierarchical symmetry is a new form of the self-organization principle for multi-scale fluctuation systems, and can be employed as a standard analysis tool in the general multi-scale methodology. It is further suggested that the SL hierarchical symmetry implies the existence of a turbulence ensemble. It is speculated that the search for defining the turbulence ensemble might open a new way for deriving statistical closure equations for turbulence and other multi-scale fluctuation systems. 相似文献
965.
The mechanisms for heterogeneous cubic → tetragonal martensite nucleation due to different types of microscopic defects (voids, stress-concentration site, inertial inclusion and pre-existing nucleus) and the temporal evolution of martensite morphology are monitored with finite element simulation of phase filed model. The results demonstrate that the nucleation prefers to occur around void and stress-concentration site initially; high residual stress exists around inertial inclusion; pre-existing nucleus promotes nearby martensite phase to develop on it. The effects of various defects on heterogeneous nucleation are different, and stress relaxation behavior is the dominant factor which characterizes the whole microstructure evolution process. 相似文献
966.
A challenge in the study of turbulent boundary layers (TBLs) is to understand the non-equilibrium relaxation process after sep-aration and reattachment due to shock-wave/boundary-layer interaction. The classical boundary layer theory cannot deal with the strong adverse pressure gradient, and hence, the computational modeling of this process remains inaccurate. Here, we report the direct numerical simulation results of the relaxation TBL behind a compression ramp, which reveal the presence of intense large-scale eddies, with significantly enhanced Reynolds stress and turbulent heat flux. A crucial finding is that the wall-normal profiles of the excess Reynolds stress and turbulent heat flux obey a β-distribution, which is a product of two power laws with respect to the wall-normal distances from the wall and from the boundary layer edge. In addition, the streamwise decays of the excess Reynolds stress and turbulent heat flux also exhibit power laws with respect to the streamwise distance from the corner of the compression ramp. These results suggest that the relaxation TBL obeys the dilation symmetry, which is a specific form of self-organization in this complex non-equilibrium flow. The β-distribution yields important hints for the development of a turbulence model. 相似文献
967.
968.
邻苯基苯酚与浓硫酸、甲醛和高铁离子生成红色化合物。该法可直接用于测定柑桔中的邻苯基苯酚的含量。邻苯基苯酚含量在0~2.5ug/5ml服从比耳定律。对桔皮的平均回收率为95.54%(n=10),标准偏差为±0.39,变异系数为2.43%。对桔肉的平均回收率为97.26%(n=10),标准偏差为±0.51 相似文献
969.
以氧化牛脂、牛肉水解蛋白及含硫化合物为原料,通过Maillard反应,制备一种固体牛肉香料。 相似文献
970.