全文获取类型
收费全文 | 142043篇 |
免费 | 404篇 |
国内免费 | 159篇 |
专业分类
化学 | 53870篇 |
晶体学 | 2128篇 |
力学 | 8983篇 |
综合类 | 2篇 |
数学 | 29015篇 |
物理学 | 48608篇 |
出版年
2021年 | 331篇 |
2019年 | 314篇 |
2018年 | 9987篇 |
2017年 | 10908篇 |
2016年 | 5051篇 |
2015年 | 1348篇 |
2014年 | 841篇 |
2013年 | 1708篇 |
2012年 | 6091篇 |
2011年 | 15195篇 |
2010年 | 9022篇 |
2009年 | 9131篇 |
2008年 | 12931篇 |
2007年 | 16715篇 |
2006年 | 1594篇 |
2005年 | 8577篇 |
2004年 | 4856篇 |
2003年 | 4688篇 |
2002年 | 2481篇 |
2001年 | 1523篇 |
2000年 | 1312篇 |
1999年 | 848篇 |
1998年 | 663篇 |
1997年 | 596篇 |
1996年 | 666篇 |
1995年 | 569篇 |
1994年 | 534篇 |
1993年 | 470篇 |
1992年 | 537篇 |
1991年 | 547篇 |
1990年 | 528篇 |
1989年 | 500篇 |
1988年 | 533篇 |
1987年 | 515篇 |
1986年 | 453篇 |
1985年 | 525篇 |
1984年 | 573篇 |
1983年 | 437篇 |
1982年 | 479篇 |
1981年 | 469篇 |
1980年 | 408篇 |
1979年 | 509篇 |
1978年 | 496篇 |
1977年 | 427篇 |
1976年 | 462篇 |
1975年 | 396篇 |
1974年 | 371篇 |
1973年 | 430篇 |
1972年 | 315篇 |
1968年 | 371篇 |
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
991.
O. V. Shestakov 《Moscow University Computational Mathematics and Cybernetics》2007,31(3):104-108
Multivariate random functions belonging to a certain class are considered. A method of reconstruction of distributions of such functions from the distributions of their projections is described and the stability of the method is discussed. 相似文献
992.
I. Bretos J. Ricote R.J. Jiménez-Riobóo L. Pardo M.L. Calzada 《Applied Physics A: Materials Science & Processing》2007,89(4):967-973
A novel method to investigate the early formation stages of polycrystalline (Pb1-xCax)TiO3 (PCT) perovskite films by means of traditional Brillouin and micro-Brillouin spectroscopy (BS, mBS) is described in the present
work. The films were prepared by chemical solution deposition (CSD) onto oxidized (100)Si substrates and treated at temperatures
between 350–650 °C by rapid thermal processing (RTP). The elastic instability observed by Brillouin spectroscopy at the nano-structured
state of the PCT films was used here to determine their crystallization temperatures. Coexistence of different nanocrystalline
phases (e.g., pyrochlore, perovskite) in the films could also be detected by this technique. The reliability of these results
is demonstrated by complementary information obtained by X-ray diffraction (XRD) and scanning force microscopy (SFM). The
effects of the annealing temperature and of the Ca2+ content on the crystallization process of these films are also discussed.
PACS 78.35.+c; 77.84.-s; 61.82.Rx 相似文献
993.
One-foil targets emit most transition radiation (TR) power in storage ring synchrotrons. Such one-foil TR emitting targets (OFTRTs) are optimized, with respect to the foil material and the foil thickness, for use as X-ray lithography (XRL) sources. The best possible elemental material and the foil thickness of OFTRTs for XRL are determined for our storage ring synchrotrons MIRROIRCLE-20SX and MIRRORCLE-6X, which operate with electrons accelerated to 20 MeV and 6 MeV, respectively. It is shown that the XRL efficiency of a OFTRT, with an optimum thickness, increases when the elemental foil material has a lower atomic number Z. The best elemental OFTRT, for performing XRL by MIRRORCLE-20SX, should contain one Be foil with a thickness of d≅240 nm, while the second best OFTRT should be made of one C foil with d≅220 nm. The best elemental OFTRT, for performing XRL by MIRRORCLE-6X, should contain one C foil with d≅35 nm, while the second best OFTRT should be made of one Be foil with d≅100 nm, because there are no thinner Be foils. The XRL efficiency of a C-foil OFTRT increases when a higher-density foil is used. A OFTRT containing one foil of a given material with optimum thickness, in MIRRORCLE-20SX, has approximately 100 times larger XRL efficiency in comparison with such a target in MIRRORCLE-6X. PACS 41.50.+h; 29.25.-t; 81.16.Nd; 41.60.Ap; 29.20.Dh 相似文献
994.
Yu. N. Zakharov S. I. Raevskaya V. Z. Borodin V. G. Kuznetsov I. P. Raevskiĭ 《Physics of the Solid State》2006,48(6):1077-1078
The magnitudes of the temperature hysteresis and diffuse dielectric anomaly corresponding to the transition from the antiferroelectric phase to the ferroelectric phase in PbZr1 ? x TixO3 (0.03 ≤ x ≤ 0.05) ceramics can be reversibly changed by varying the temperatures of heating and cooling in the course of thermocycling. The results obtained indicate that the antiferroelectric-ferroelectric transition in the PbZr1 ? x TixO3 ceramics materials is a smeared first-order phase transition. 相似文献
995.
Z. Ercan 《Proceedings of the American Mathematical Society》2006,134(3):917-920
We give a characterization of realcompact spaces in terms of nets. By using the technique of this characterization we give easy proofs of the Tychonoff Theorem and the Alaoglu Theorem.
996.
The role played by electronically excited oxygen in exoemission and heterogeneous catalysis is considered. The results obtained in a study of thermally stimulated exoemission from the surface of Al2O3 and SiO2 are compared with data of temperature-programmed desorption of singlet oxygen O2(1Δg) from the surface of Al2O3 and HZSM-5 zeolites with different SiO2/Al2O3 ratios. The role played by electronically excited oxygen states in heterogeneous catalysis is discussed on the basis of our own and literature data. Thermally stimulated exoemission after the action of an electron flow is considered taking into account electron-stimulated desorption and the available data on electron bombardment in catalysis. 相似文献
997.
We study applications of the theory of quadratic differentials to the solution of new extremal problems of nonoverlapping
domains with free poles on rays and generalize known results to a certain class of open sets.
__________
Translated from Neliniini Kolyvannya, Vol. 10, No. 4, pp. 435–442, October–December, 2007. 相似文献
998.
We introduce some relative versions of star selection principles first considered in [5], [11]. Some of the work extends results
from [4], [5] and gives some examples.
相似文献
999.
The 57Fe Mössbauer effect study at 5.0 K and in an external magnetic field of 9.0 T on a high-quality stable decagonal quasicrystal Al65Co15Cu19.9Fe0.1 is presented. It is shown that the iron atoms are located in two distinct classes of sites. The values of the principal component of the electric field gradient tensor and the asymmetry parameter at these sites are, respectively, ?1.90(10)?×?1021 V/m2, 0.97(15) and ?3.95(12)?×?1021 V/m2, 0.00(17). 相似文献
1000.
The paper addresses bivariate surface fitting problems, where data points lie on the vertices of a rectangular grid. Efficient
and stable algorithms can be found in the literature to solve such problems. If data values are missing at some grid points,
there exists a computational method for finding a least squares spline by fixing appropriate values for the missing data.
We extended this technique to arbitrary least squares problems as well as to linear least squares problems with linear equality
constraints. Numerical examples are given to show the effectiveness of the technique presented.
AMS subject classification (2000) 65D05, 65D07, 65D10, 65F05, 65F20 相似文献