全文获取类型
收费全文 | 249565篇 |
免费 | 4766篇 |
国内免费 | 2552篇 |
专业分类
化学 | 128574篇 |
晶体学 | 4023篇 |
力学 | 11837篇 |
综合类 | 71篇 |
数学 | 27374篇 |
物理学 | 85004篇 |
出版年
2021年 | 2527篇 |
2020年 | 2679篇 |
2019年 | 2856篇 |
2018年 | 3673篇 |
2017年 | 3471篇 |
2016年 | 5181篇 |
2015年 | 3373篇 |
2014年 | 5122篇 |
2013年 | 11530篇 |
2012年 | 9858篇 |
2011年 | 11573篇 |
2010年 | 8040篇 |
2009年 | 7851篇 |
2008年 | 10142篇 |
2007年 | 10190篇 |
2006年 | 9608篇 |
2005年 | 8540篇 |
2004年 | 7779篇 |
2003年 | 6862篇 |
2002年 | 6662篇 |
2001年 | 7805篇 |
2000年 | 5983篇 |
1999年 | 4765篇 |
1998年 | 3803篇 |
1997年 | 3744篇 |
1996年 | 3472篇 |
1995年 | 3287篇 |
1994年 | 3005篇 |
1993年 | 2807篇 |
1992年 | 3230篇 |
1991年 | 3199篇 |
1990年 | 3092篇 |
1989年 | 2850篇 |
1988年 | 2916篇 |
1987年 | 2879篇 |
1986年 | 2649篇 |
1985年 | 3386篇 |
1984年 | 3632篇 |
1983年 | 2946篇 |
1982年 | 3127篇 |
1981年 | 3115篇 |
1980年 | 2916篇 |
1979年 | 3068篇 |
1978年 | 3146篇 |
1977年 | 3163篇 |
1976年 | 3221篇 |
1975年 | 2972篇 |
1974年 | 2916篇 |
1973年 | 3078篇 |
1972年 | 2018篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
The problem considered is that of determining the shape of aplane acoustically sound-soft obstacle from the knowledge ofthe far-field pattern for one time-harmonic incident field.An iterative procedure is proposed based on two boundary integralsrepresenting the incident field and the far-field pattern, respectively.Numerical examples are included which show that the proceduregives accurate numerical approximations in relatively few iterations. 相似文献
993.
I. Kandarakis D. Cavouras P. Prassopoulos E. Kanellopoulos C.D. Nomicos G.S. Panayiotakis 《Applied Physics A: Materials Science & Processing》1998,66(5):521-525
2 SiO4:Mn phosphor was evaluated for use in radiation detectors of medical imaging systems. Zn2SiO4:Mn was used in the form of laboratory-prepared fluorescent layers (screens) with coating weights from 18 to 150 mg/cm2. The phosphor was excited to luminescence by low-energy X-raysusing X-raytube voltages ranging from 15 to 50 kVp. The number
of emitted optical photons per incident X-rayquantum was thus determined for various X-rayenergies and phosphor coating weights.
The optical emission spectrum was also measured and it was used to evaluate the spectral compatibility of Zn2SiO4:Mn with radiographic films, photocathodes and the Si photodiode. Finally, phosphor optical properties were estimated by fitting
a theoretical model to experimental data. Results showed that Zn2SiO4:Mn is more efficient for low-energy X-rays. Its intrinsic conversion efficiency was found equal to 0.08, which is comparable
to that of actually used phosphors. Zn2SiO4:Mn was also adequately compatible with orthochromatic films and the ES-20 photocathode, thus being appropriate for low-voltage
radiography and fluoroscopy.
Received: 31 July 1998/Accepted: 3 August 1998 相似文献
994.
D. Abbaneo P. Antilogus T. Behnke S.C. Blyth M. Elsing R. Faccini R.W.L. Jones K. Mönig S. Petzold R. Tenchini 《The European Physical Journal C - Particles and Fields》1998,4(2):185-191
Measurements of the forward-backward production asymmetry of heavy quarks in Z decays provide a precise determination of
. The asymmetries are sensitive to QCD effects, in particular hard gluon radiation. In this paper QCD corrections for and are discussed. The interplay between the experimental techniques used to measure the asymmetries and the QCD effects is
investigated using simulated events. A procedure to estimate the correction needed for experimental measurements is proposed,
and some specific examples are given.
Received: 26 February 1998 / Published online: 2 June 1998 相似文献
995.
A single-change covering designSC (v, k, b) on av-setV is a sequence ofb k-sets (blocks) onV which together cover every pair of elements ofV at least once, such that two successive blocks havek–1 elements in common. It is desirable to minimizeb. Some constructions and lower bounds forb are given. 相似文献
996.
Mixed block elimination for linear systems with wider borders 总被引:1,自引:0,他引:1
The paper is about the stable solution of possibly ill-conditionedbordered linear systems. Given stable solvers for matrix A andfor AT, we prove that the Govaerts Mixed Block Elimination (BEM)method constitutes a stable solver for the matrix consistingof A or AT with a border of width 1, and hence by recursionfor a border of any width. We express the algorithm in an efficient,iterative, form. We analyse its operation count, and verifythe theory by extensive numerical experiments.
*Senior Research Associate of the Belgian National Fund of ScientificResearch NFWO. 相似文献
997.
Orbital magnetism in an integrable model of a multichannel ring with long-ranged electron-electron interactions is investigated. In a noninteracting multichannel system, the response to an external magnetic flux is the sum of many diamagnetic and paramagnetic contributions, but we find that for sufficiently strong correlations, the contributions of all channels add constructively, leading to a parity (diamagnetic or paramagnetic) which depends only on the total number of electrons. Numerical results confirm that this parity-locking effect is robust with respect to subband mixing due to disorder. 相似文献
998.
The character of the localization of the wave functions of an icosahedral quasicrystal is investigated in the tight-binding
approximation. It is found that the wave functions exhibit “critical behavior”: they are neither localized, as in the case
of Anderson localization, nor delocalized, as in the case of Bloch states.
Pis’ma Zh. éksp. Teor. Fiz. 64, No. 8, 559–563 (25 October 1996) 相似文献
999.
Solid conversion has been of much interest to research workers and the Cumulative Gas Concentration Method (CGCM) has been developed to provide bounds for the reactant solid in irreversible systems having power-law type kinetics. This CGCM is used in conjunction with the Pseudo-Steady-State (PSS) assumption and these bounds appear to be good under certain conditions and for long times.
In this work, the PSS condition is not assumed when deriving the bounds on the cumulative gas concentration and the effect of the inclusion of the transient part is analysed. A technique, based on an iterative scheme incorporating the CGCM, is developed to provide improved estimates for the reactant solid. 相似文献
1000.
N. A. Borisevich D. A. Kazberuk S. V. Mel'nichuk S. A. Tikhomirov G. B. Tolstorozhev 《Journal of Applied Spectroscopy》1995,62(3):441-446
Institute of Molecular and Atomic Physics, Academy of Sciences of Belarus, 70 F. Skaryna Ave, Minsk 220072, Belarus. Translated
from Zhurnal Prikladnoi Spektroskopii, Vol. 62, No. 3, pp. 49–55, May–June, 1995. 相似文献