全文获取类型
收费全文 | 4840篇 |
免费 | 778篇 |
国内免费 | 334篇 |
专业分类
化学 | 1601篇 |
晶体学 | 45篇 |
力学 | 1478篇 |
综合类 | 60篇 |
数学 | 727篇 |
物理学 | 2041篇 |
出版年
2024年 | 15篇 |
2023年 | 56篇 |
2022年 | 196篇 |
2021年 | 205篇 |
2020年 | 230篇 |
2019年 | 156篇 |
2018年 | 167篇 |
2017年 | 183篇 |
2016年 | 245篇 |
2015年 | 163篇 |
2014年 | 265篇 |
2013年 | 367篇 |
2012年 | 270篇 |
2011年 | 313篇 |
2010年 | 253篇 |
2009年 | 274篇 |
2008年 | 224篇 |
2007年 | 235篇 |
2006年 | 226篇 |
2005年 | 222篇 |
2004年 | 172篇 |
2003年 | 185篇 |
2002年 | 138篇 |
2001年 | 110篇 |
2000年 | 148篇 |
1999年 | 108篇 |
1998年 | 118篇 |
1997年 | 102篇 |
1996年 | 77篇 |
1995年 | 72篇 |
1994年 | 76篇 |
1993年 | 73篇 |
1992年 | 52篇 |
1991年 | 47篇 |
1990年 | 43篇 |
1989年 | 25篇 |
1988年 | 26篇 |
1987年 | 18篇 |
1986年 | 14篇 |
1985年 | 21篇 |
1984年 | 8篇 |
1983年 | 7篇 |
1982年 | 13篇 |
1981年 | 3篇 |
1980年 | 4篇 |
1979年 | 6篇 |
1978年 | 4篇 |
1976年 | 2篇 |
1971年 | 4篇 |
1957年 | 6篇 |
排序方式: 共有5952条查询结果,搜索用时 15 毫秒
11.
E.V. Jansson 《Applied Acoustics》2004,65(12):1197-1205
Good violins have a broad hill in the 2-3 kHz range of their frequency response. This hill has previously been attributed to the first in-plane resonance of the violin bridge. Experiments prove, however, that the hill is the result of two forces acting in opposite directions at the bridge feet. The experiments reported here show that the hill can be “tuned” by altering the distance between the bridge feet. It can be tuned both in terms of frequency and level but the properties of the violin cannot be neglected. 相似文献
12.
本文用准平衡模型分析讨论了线性电压扫描下MIS器件的I/V瞬态.文中除了给出一般的处理方法以外,还给出了几种不同电压扫描率下I/Y特性的计算结果,并与已往的模型作了比较. 相似文献
13.
The article concerns heterojunction resonant cavity-enhanced (RCE) Schottky photodiodes with GaAs in the absorption layer. The quantum efficiency and linear pulse response have thoroughly been analysed. For the first time, the response of a heterojunction photodiode has been modelled by the phenomenological model for a two-valley semiconductor. The results obtained have shown that the satellite valleys, as well as the parasitic time constant, significantly influence the response and, accordingly, have to be taken into account when analysing and optimizing RCE photodetectors. 相似文献
14.
15.
An intact auditory system at birth is requisite for the successful accomplishment of many developmental skills. Evoked responses to auditory stimuli have been used as a sensitive test to determine the functional status of the adult and neonatal brain. It has been established that fetuses can hear in utero and respond to external acoustic stimuli. We present an overview of the transmission of sound through the maternal abdomen to the fetal ear and the recordings of an auditory evoked response obtained from the fetus using a non-invasive magnetoencephalography technique. The investigation of cortical activity of the fetus in response to auditory stimulation can help understand and track the neurological development of the fetus. 相似文献
16.
[1]中提出了具有功能反应的三种群捕食者——食饵系统的两种模型(Ⅰ)、(Ⅱ),并给出了局部渐近稳定的条件。本文研究了另外两种模型(Ⅲ)和(Ⅳ)的局部渐近稳定的条件。 相似文献
17.
It is shown that the condition υ > υp (ω), which is necessary in order to trigger the Vavilov-Cherenkov effect, determines the interval of radiated frequencies
and it alone cannot establish a strong restriction to the velocity of the particle. It is exhibited that it is possible to
define a general lower bound for the velocity of the particle, which does not depend on the frequency when both, a specific
response of the medium is taken into account and the mentioned condition is considered. The minimum value of the phase velocity
of light in the medium determines the existence of such general lower bound. 相似文献
18.
偶氮苯衍生物三阶非线性的四波混频研究 总被引:7,自引:0,他引:7
用皮秒Nd:YAG激光器的倍频光(532nm)对具有离域π-共轭电子云结构的偶氮苯类样品材料作简并四波混频补给,测得三阶非线性电极化率x^(3)和它们的时间响应分别为10^-9esu和20ps,并对影响x^(3)的瞬时光栅作用和x^(3)的响应时间人了讨论。 相似文献
19.
Hu Haiyan 《Acta Mechanica Solida Sinica》1994,7(2):137-150
This paper deals with the numerical solution of high dimensional dynamic systems with nonsmooth characteristics, such as structural elastoplasticity, mechanical clearance and dry friction. As a stable periodic response of the system attracts its transient response, it may be extracted from the transient response somehow. The paper suggests a novel iteration scheme to extrapolate the periodic response from a short time history of its transient response by curve fitting. Compared with the current schemes such as shooting and incremental harmonic balancing, the present scheme makes full use of the information within the transient response and the system characters, then its computation efficiency has increased by an order and the numerical convergence depending on the initial iteration has greatly improved.The subject supported by the Chinese Foundation of Aeronautical Science 相似文献
20.
Stochastic mechanism of relaxation, in which a dipole waits until a favourable condition for reorientation exists, is discussed. Assuming that an imposed direction of a dipole moment may be changed when a migrating defect reaches the dipole, we present a mathematically rigorous scheme relating the local random characteristics of a macroscopic system to its effective relaxation behaviour. We derive a relaxation function (the Burr survival probability) that is characterized by the stretched exponential or the power-law behaviour. 相似文献