全文获取类型
收费全文 | 2179篇 |
免费 | 26篇 |
国内免费 | 6篇 |
专业分类
化学 | 1274篇 |
晶体学 | 9篇 |
力学 | 90篇 |
数学 | 299篇 |
物理学 | 539篇 |
出版年
2022年 | 27篇 |
2021年 | 44篇 |
2020年 | 35篇 |
2019年 | 18篇 |
2018年 | 30篇 |
2017年 | 17篇 |
2016年 | 47篇 |
2015年 | 27篇 |
2014年 | 34篇 |
2013年 | 110篇 |
2012年 | 104篇 |
2011年 | 115篇 |
2010年 | 68篇 |
2009年 | 53篇 |
2008年 | 137篇 |
2007年 | 117篇 |
2006年 | 110篇 |
2005年 | 105篇 |
2004年 | 78篇 |
2003年 | 63篇 |
2002年 | 64篇 |
2001年 | 44篇 |
2000年 | 35篇 |
1999年 | 30篇 |
1998年 | 32篇 |
1997年 | 40篇 |
1996年 | 36篇 |
1995年 | 35篇 |
1994年 | 39篇 |
1993年 | 30篇 |
1992年 | 38篇 |
1991年 | 22篇 |
1990年 | 21篇 |
1989年 | 11篇 |
1988年 | 14篇 |
1987年 | 15篇 |
1986年 | 15篇 |
1985年 | 29篇 |
1984年 | 29篇 |
1983年 | 19篇 |
1982年 | 25篇 |
1981年 | 28篇 |
1980年 | 22篇 |
1979年 | 21篇 |
1978年 | 16篇 |
1977年 | 19篇 |
1976年 | 17篇 |
1975年 | 20篇 |
1974年 | 11篇 |
1973年 | 13篇 |
排序方式: 共有2211条查询结果,搜索用时 15 毫秒
1.
Daniel L. Feldheim Del R. Lawson Charles R. Martin 《Journal of Polymer Science.Polymer Physics》1993,31(8):953-957
We report a strong dependence of the thermal stability of Nafion® perfluorosulfonate ionomer on the nature of the counterion associated with the fixed sulfonate site. These results were obtained using thermal gravimetric analysis on a series of alkali metal and alkyl ammonium cation-exchanged Nafion films. We have found that the temperature of decomposition of Nafion is inversely dependent on the size of the exchanged cation; i.e., Nafion films show improved thermal stability as the size of the counter cation decreases. We attribute this inverse relationship of thermal stability with counterion size to an initial decomposition reaction which is strongly influenced by the strength of the sulfonate-coun-terion interaction. © 1993 John Wiley & Sons, Inc. 相似文献
2.
This paper describes the performance and simulation of a compact integrated optical processor for the real-time reconstruction of two-dimensional images in airborne stripmap synthetic aperture radar applications. The functional behavior of the processor is explained in some detail. The design criteria are briefly given. The simulation step allowed the main processor characteristics and properties to be identified. A number of comparisons were obtained in airborne SAR mission scenarios between the predictions of the optical device and those achieved by the modern electronic digital approach, based on the wavefront reconstruction method by matched filtering. 相似文献
3.
Summary We study the integration theory for general integral metrics when restricted to upper integrals q, finding improvements in the relation between the classes of the q-integrable and the ql-integrable functions. We give new results and notions which lead to the desirable characterizations of q-integrable functions as ql-integrable f with q(|f|) < ∞, and of ql-integrable functions via the integrability of their upper truncations, under natural conditions which are fulfilled in most
finitely additive integration theories. 相似文献
4.
Flow injection methodology based on sample insertion between two different standard solutions used as carrier streams is described. This approach provides a simple system for continuous recalibration in process control; spectrophotometric and ion-selective electrode procedures are outlined. 相似文献
5.
L. Cianchi F. Del Giallo F. Pieralli M. Mancini S. Sciortino G. Spina 《Hyperfine Interactions》1991,66(1-4):387-391
Mössbauer parameters of151Eu in Eu1+x Ba2?x Cu3O7+δ have been studied as a function of temperature, forx=0.15 andx=0.25. The areas of the absorption spectra for the two samples are almost equal. This could mean that thef-Mössbauer factor for151Eu at the barium sites is much smaller than that for151Eu at the rare earth sites, i.e. we only observe the spectra of the latter sites. According to this, the fits of the spectra with a single quadrupolar pattern and with two quadrupolar patterns have given equivalent χ2 values. 相似文献
6.
7.
8.
Vincenzo Piazza Vittorio PellegriniFabio Beltram Werner Wegscheider 《Solid State Communications》2003,127(2):163-168
Time-dependent capacitance measurements reveal an unstable phase of electrons in gallium arsenide quantum well that occurs when two Landau levels with opposite-spin are brought close to degeneracy by applying a gate voltage. This phase emerges below a critical temperature and displays a peculiar non-equilibrium dynamical evolution. The relaxation dynamics is found to follow a stretched-exponential behaviour and correlates with hysteresis loops observed by sweeping the magnetic field. These experiments indicate that metastable randomly distributed magnetic domains with peculiar excitations are involved in the relaxation process in a way that is equivalently tunable by a change in gate voltage or temperature. 相似文献
9.
P. N. Burrows V. Del Duca P. Hoyer 《Zeitschrift fur Physik C Particles and Fields》1992,53(1):149-155
In heavy quark jets the quark mass acts as a regulator of collinear singularities, making the quark momentum an infra-red safe variable in perturbative QCD. This allows a direct comparison of measured heavy hadron momentum spectra with perturbative calculations. We exploit the factorisation of heavy quark fragmentation to derive QCD predictions for momentum correlations between heavy hadrons produced ine + e ? annihilations. We study the practical feasibility and model sensitivity of our approach using Monte Carlo simulations. Higher order perturbative corrections and contributions from non-perturbative effects are found to be at the level of 10%. 相似文献
10.
Vittorio Cantoni 《International Journal of Theoretical Physics》1996,35(10):2121-2124
It is shown that the Kähler equation in a four-dimensional pseudo-Riemannian manifold with Lorentzian signature decomposes uniquely into four uncoupled equations of Duffin type. 相似文献