全文获取类型
收费全文 | 2635篇 |
免费 | 72篇 |
国内免费 | 10篇 |
专业分类
化学 | 1620篇 |
晶体学 | 19篇 |
力学 | 49篇 |
数学 | 231篇 |
物理学 | 798篇 |
出版年
2021年 | 24篇 |
2020年 | 39篇 |
2019年 | 24篇 |
2018年 | 23篇 |
2017年 | 25篇 |
2016年 | 41篇 |
2015年 | 39篇 |
2014年 | 33篇 |
2013年 | 126篇 |
2012年 | 81篇 |
2011年 | 103篇 |
2010年 | 54篇 |
2009年 | 45篇 |
2008年 | 91篇 |
2007年 | 104篇 |
2006年 | 118篇 |
2005年 | 85篇 |
2004年 | 93篇 |
2003年 | 89篇 |
2002年 | 84篇 |
2001年 | 63篇 |
2000年 | 83篇 |
1999年 | 41篇 |
1998年 | 37篇 |
1997年 | 31篇 |
1996年 | 47篇 |
1995年 | 53篇 |
1994年 | 39篇 |
1993年 | 50篇 |
1992年 | 45篇 |
1991年 | 42篇 |
1990年 | 42篇 |
1989年 | 24篇 |
1988年 | 26篇 |
1987年 | 38篇 |
1986年 | 40篇 |
1985年 | 48篇 |
1984年 | 52篇 |
1983年 | 29篇 |
1982年 | 33篇 |
1981年 | 44篇 |
1980年 | 46篇 |
1979年 | 46篇 |
1978年 | 38篇 |
1977年 | 44篇 |
1976年 | 48篇 |
1975年 | 31篇 |
1974年 | 32篇 |
1973年 | 44篇 |
1972年 | 17篇 |
排序方式: 共有2717条查询结果,搜索用时 15 毫秒
1.
2.
3.
A comparison of steady-state evoked potentials to modulated tones in awake and sleeping humans. 总被引:12,自引:0,他引:12
L T Cohen F W Rickards G M Clark 《The Journal of the Acoustical Society of America》1991,90(5):2467-2479
Steady-state evoked potential responses were measured to binaural amplitude-modulated (AM) and combined amplitude- and frequency-modulated (AM/FM) tones. For awake subjects, AM/FM tones produced larger amplitude responses than did AM tones. Awake and sleeping responses to 30-dB HL AM/FM tones were compared. Response amplitudes were lower during sleep and the extent to which they differed from awake amplitudes was dependent on both carrier and modulation frequencies. Background EEG noise at the stimulus modulation frequency was also reduced during sleep and varied with modulation frequency. A detection efficiency function was used to indicate the modulation frequencies likely to be most suitable for electrical estimation of behavioral threshold. In awake subjects, for all carrier frequencies tested, detection efficiency was highest at a modulation frequency of 45 Hz. In sleeping subjects, the modulation frequency regions of highest efficiency varied with carrier frequency. For carrier frequencies of 250 Hz, 500 Hz, and 1 kHz, the highest efficiencies were found in two modulation frequency regions centered on 45 and 90 Hz. For 2 and 4 kHz, the highest efficiencies were at modulation frequencies above 70 Hz. Sleep stage affected both response amplitude and background EEG noise in a manner that depended on modulation frequency. The results of this study suggest that, for sleeping subjects, modulation frequencies above 70 Hz may be best when using steady-state potentials for hearing threshold estimation. 相似文献
4.
This paper examines the non-linear dynamic behaviour of a flexible shaft. The shaft is mounted on two journal bearings and the axial load is supported by a defective hydrodynamic thrust bearing at one end. The defect is a levelness defect of the rotor. The thrust bearing behaviour must be considered to be non-linear because of the effects of the defect. The shaft is modelled with typical beam finite elements including effects such as the gyroscopic effects. A modal technique is used to reduce the number of degrees of freedom. Results show that the thrust bearing defects introduce supplementary critical speeds. The linear approach is unable to show the supplementary critical speeds which are obtained only by using non-linear analysis. 相似文献
5.
E. P. Clark 《Fresenius' Journal of Analytical Chemistry》1940,120(3-4):124-125
Ohne Zusammenfassung 相似文献
6.
Processing-induced residual strains in solid cylinders of Nickel 200 were investigated using phase shifting moiré interferometry. Two different experimental approaches were used to study the strains produced during Tungsten-inert gas spot welding. A comparison of results for a ‘hot/fast’ and a ‘cool/slow’ weld demonstrate the capabilities of the general approach. Both experimental methods revealed distinct differences in the residual displacement and strain fields between the two types of welds. 相似文献
7.
JOSEF MÁLEK JINDŘICH NEČAS K. R. RAJAGOPAL 《Archive for Rational Mechanics and Analysis》2002,165(3):243-269
To describe the flows of fluids over a wide range of pressures, it is necessary to take into account the fact that the viscosity
of the fluid depends on the pressure. That the viscosity depends on the pressure has been verified by numerous careful experiments.
While the existence of solutions local-in-time to the equations governing the flows of such fluids are available for small,
special data and rather unrealistic dependence of the viscosity on the pressure, no global existence results are in place.
Our interest here is to establish the existence of weak solutions for spatially periodic three-dimensional flows that are
global in time, for a large class of physically meaningful viscosity-pressure relationships.
(Accepted May 1, 2002) Published online November 15, 2002
Communicated by S. S. ANTMAN 相似文献
8.
Background
The aim of the present study was to characterize the activation profiles of 15 opioid ligands in transfected human embryonic kidney cells expressing only δ opioid receptors. Activation profiles of most of these ligands at δ opioid receptors had not been previously characterized in vitro. Receptor activation was assessed by measuring the inhibition of forskolin-stimulated cAMP production. 相似文献9.
10.
Andrew D. Abell Bruce M. Clark Kathryn B. Morris Jane M. Taylor 《Journal of mass spectrometry : JMS》1993,28(1):27-29
Positive-ion fast atom bombardment mass spectra of 13 keto acid and keto ester phosphoranes were examined. All compounds gave a protonated molecular ion and characteristic peaks at m/z 303, 279, 262 and 201. 相似文献