全文获取类型
收费全文 | 798篇 |
免费 | 59篇 |
国内免费 | 15篇 |
专业分类
化学 | 65篇 |
晶体学 | 4篇 |
力学 | 275篇 |
综合类 | 7篇 |
数学 | 161篇 |
物理学 | 360篇 |
出版年
2024年 | 1篇 |
2023年 | 7篇 |
2022年 | 10篇 |
2021年 | 14篇 |
2020年 | 15篇 |
2019年 | 11篇 |
2018年 | 17篇 |
2017年 | 19篇 |
2016年 | 18篇 |
2015年 | 20篇 |
2014年 | 29篇 |
2013年 | 48篇 |
2012年 | 32篇 |
2011年 | 34篇 |
2010年 | 24篇 |
2009年 | 34篇 |
2008年 | 35篇 |
2007年 | 74篇 |
2006年 | 54篇 |
2005年 | 47篇 |
2004年 | 36篇 |
2003年 | 34篇 |
2002年 | 32篇 |
2001年 | 24篇 |
2000年 | 32篇 |
1999年 | 27篇 |
1998年 | 28篇 |
1997年 | 13篇 |
1996年 | 20篇 |
1995年 | 10篇 |
1994年 | 15篇 |
1993年 | 6篇 |
1992年 | 6篇 |
1991年 | 8篇 |
1990年 | 8篇 |
1989年 | 3篇 |
1988年 | 6篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 1篇 |
1979年 | 4篇 |
1978年 | 1篇 |
排序方式: 共有872条查询结果,搜索用时 921 毫秒
1.
When dealing with simple phenols such as caffeic acid (CA) and ferulic acid (FA), found in a variety of plants, it is very important to have control over the most important factors that accelerate their degradation reactions. This is the first report in which the stabilities of these two compounds have been systematically tested by exposure to various different factors. Forced degradation studies were performed on pure standards (trans-CA and trans-FA), dissolved in different solvents and exposed to different oxidative, photolytic and thermal stress conditions. Additionally, a rapid, sensitive, and selective stability-indicating gas chromatographic-mass spectrometric method was developed and validated for determination of trans-CA and trans-FA in the presence of their degradation products. Cis-CA and cis-FA were confirmed as the only degradation products in all the experiments performed. All the compounds were perfectly separated by gas chromatography (GC) and identified using mass spectrometry (MS), a method that additionally elucidated their structures. In general, more protic solvents, higher temperatures, UV radiation and longer storage times led to more significant degradation (isomerization) of both trans-isomers. The most progressive isomerization of both compounds (up to 43%) was observed when the polar solutions were exposed to daylight at room temperature for 1 month. The method was validated for linearity, precision as repeatability, limit of detection (LOD) and limit of quantitation (LOQ). The method was confirmed as linear over tested concentration ranges from 1−100 mg L−1 (r2s were above 0.999). The LOD and LOQ for trans-FA were 0.15 mg L−1 and 0.50 mg L−1, respectively. The LOD and LOQ for trans-CA were 0.23 mg L−1 and 0.77 mg L−1, respectively. 相似文献
2.
3.
乐毅 《宁波大学学报(理工版)》2004,17(4):437-440
从正交各向异性三维弹性动力学的控制方程出发,在求得四边简支矩形板自由振动频率和位移振型的基础上,构造了受迫振动的位移函数;利用自由振动位移振型的正交性,将控制方程的空间变量和时间变量分离,得到了广义质量、广义力和频率表示的关于时间的2阶常微分方程,从而得到了正交各向异性弹性矩形板在受迫振动下的位移场和应力场.给出了本文方法与薄板理论的算例. 相似文献
4.
5.
Subodh R Shenoy 《Pramana》2002,58(2):385-397
We obtain the dynamics in number and phase difference, for Bose condensates that tunnel between two wells of a double-well
atomic trap, using the (nonlinear) Gross-Pitaevskii equation. The dynamical equations are of the canonical form for the two
conjugate variables, and the Hamiltonian corresponds to that of a momentum-shortened pendulum, supporting a richer set of tunneling oscillation modes than for a superconductor Josephson junction, that has a
fixed-length pendulum as a mechanical model. Novel modes include ‘inverted pendulum’ oscillations with an average angle of
π; and oscillations about a self-maintained population imbalance that we term ‘macroscopic quantum self-trapping’. Other systems
with this phase-number nonlinear dynamics include two-component (interconverting) condensates in a single harmonic trap, and
He3B superfluids in two containers connected by micropores. 相似文献
6.
8.
S G Kamath 《Pramana》1992,38(1):11-20
The Hamiltonian formulation of the BRST method for quantizing constrained systems developed recently by Nemeschanskyet al is applied to the well-known problem of the conical pendulum in classical mechanics. The similarity of the system to a gauge
theory wherein the two constraints serve as generators of local Abelian gauge transformations is also pointed out. The definition
of the physical states of the system as a gauge theory and also as a BRST invariant theory is then discussed in some detail. 相似文献
9.
用线性插值法求单摆运动周期的近似解 总被引:6,自引:1,他引:5
利用线性插值的方法,提出了一个任意摆角条件下的单摆运动周期的近似公式.并利用Mathematica软件将该公式与精确解进行了比较,还与其他近似公式进行了对比.结果表明,该公式的近似程度相当好. 相似文献
10.