全文获取类型
收费全文 | 28682篇 |
免费 | 1738篇 |
国内免费 | 859篇 |
专业分类
化学 | 6983篇 |
晶体学 | 332篇 |
力学 | 1749篇 |
综合类 | 216篇 |
数学 | 11046篇 |
物理学 | 10953篇 |
出版年
2023年 | 164篇 |
2022年 | 314篇 |
2021年 | 299篇 |
2020年 | 321篇 |
2019年 | 618篇 |
2018年 | 462篇 |
2017年 | 482篇 |
2016年 | 406篇 |
2015年 | 344篇 |
2014年 | 514篇 |
2013年 | 1410篇 |
2012年 | 793篇 |
2011年 | 1305篇 |
2010年 | 778篇 |
2009年 | 1147篇 |
2008年 | 1296篇 |
2007年 | 1311篇 |
2006年 | 1231篇 |
2005年 | 909篇 |
2004年 | 1264篇 |
2003年 | 1427篇 |
2002年 | 1962篇 |
2001年 | 1948篇 |
2000年 | 1775篇 |
1999年 | 1951篇 |
1998年 | 1659篇 |
1997年 | 1053篇 |
1996年 | 557篇 |
1995年 | 324篇 |
1994年 | 280篇 |
1993年 | 131篇 |
1992年 | 152篇 |
1991年 | 114篇 |
1990年 | 193篇 |
1989年 | 166篇 |
1988年 | 123篇 |
1987年 | 94篇 |
1986年 | 136篇 |
1985年 | 209篇 |
1984年 | 189篇 |
1983年 | 87篇 |
1982年 | 145篇 |
1981年 | 241篇 |
1980年 | 238篇 |
1979年 | 115篇 |
1978年 | 175篇 |
1977年 | 105篇 |
1976年 | 77篇 |
1975年 | 82篇 |
1974年 | 78篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
J. Kudrna I. Pelant J. Štěpánek F. Trojánek P. Malý 《Applied Physics A: Materials Science & Processing》2002,74(2):253-256
We have studied ultra-fast carrier dynamics of photo-excited carriers in hydrogenated microcrystalline silicon prepared by
a very high frequency glow-discharge technique. We report on direct observation of two types of dynamics using selective photo-excitation
in picosecond pump and probe measurements. One type of the observed dynamics has been found to be independent of the sample
preparation, while the other reflects the relative weights of crystalline and amorphous fractions. We propose a simple rate-equation
model that describes the carrier dynamics in microcrystalline silicon in terms of the composition of those in Si microcrystallites
and in the a-Si:H tissue which surrounds the microcrystallites. The model without any fitting parameters reproduces the experimental
data very well when the dynamics are scaled with relative volume fractions as obtained from Raman spectra.
Received: 23 November 2000 / Accepted: 17 March 2001 / Published online: 23 May 2001 相似文献
32.
F. Chen L. Liu Z. Shen G.Q. Xu T.S.A. Hor 《Applied Physics A: Materials Science & Processing》2002,74(2):317-319
Free-standing and supported hydrogenated amorphous carbon films (a:C–H) were prepared upon pyrolysis of the polymer formed
by ethanolamine (EA) and citric acid (CA), under an ambient atmosphere at 300 °C. EA facilitates the formation of the macroscopic
films, while CA is essential for obtaining the a:C–H microstructure, which comprises a mixture of sp2 and sp3 carbon.
Received: 29 May 2001 / Accepted: 17 August 2001 / Published online: 20 December 2001 相似文献
33.
Q. Sun Q. Wang X.G. Gong V. Kumar Y. Kawazoe 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(1):77-81
We report results of the atomic and electronic structures of Al7C cluster using ab initio molecular dynamics with ultrasoft pseudopotentials and generalized gradient approximation. The lowest energy structure is
found to be the one in which carbon atom occupies an interstitial position in Al7 cluster. The electronic structure shows that the recent observation [Chem. Phys. Lett. 316, 31 (2000)] of magic behavior of Al7C- cluster is due to a large highest occupied and lowest unoccupied molecular orbital (HOMO-LUMO) gap which makes Al7C- chemically inert. These results have further led us to the finding of a new neutral magic cluster Al7N which has the same number of valence electrons as in Al7C- and a large HOMO-LUMO gap of 1.99 eV. Further, calculations have been carried out on (Al7N)2 to study interaction between magic clusters.
Received 28 July 2001 相似文献
34.
Nikolaos V. Tsekos Michael Garwood Kmil Ugurbil 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2002,156(2):187
A new technique is presented for generating myocardial tagging using the signal intensity minima of the transition zones between the bands of 0° and 360° rotations, induced by a tandem of two adiabatic delays alternating with nutations for tailored excitation (DANTE) inversion sequences. With this approach, the underlying matrix corresponds to magnetization that has experienced 0° or 360° rotations. The DANTE sequences were implemented from adiabatic parent pulses for insensitivity of the underlying matrix to B1 inhomogeneity. The performance of the proposed tagging technique is demonstrated theoretically with computer simulations and experimentally on phantom and on the canine heart, using a surface coil for both RF transmission and signal reception. The simulations and the experimental data demonstrated uniform grid contrast and sharp tagging profiles over a twofold variation of the B1 field magnitude. 相似文献
35.
Dual fractional cutting plane algorithms, in which cutting planes are used to iteratively tighten a linear relaxation of an integer program,
are well-known and form the basis of the highly successful branch-and-cut method. It is rather less well-known that various primal cutting plane algorithms were developed in the 1960s, for example by Young. In a primal algorithm, the main role of the cutting
planes is to enable a feasible solution to the original problem to be improved. Research on these algorithms has been almost
non-existent.
In this paper we argue for a re-examination of these primal methods. We describe a new primal algorithm for pure 0-1 problems based on strong valid inequalities and give some encouraging computational results. Possible extensions to the case of general
mixed-integer programs are also discussed. 相似文献
36.
37.
38.
Kasper K. Berthelsen Jesper Møller 《Bulletin of the Brazilian Mathematical Society》2002,33(3):351-367
This primer provides a self-contained exposition of the case where spatial birth-and-death processes are used for perfect
simulation of locally stable point processes. Particularly, a simple dominating coupling from the past (CFTP) algorithm and
the CFTP algorithms introduced in [13], [14], and [5] are studied. Some empirical results for the algorithms are discussed.
Received: 30 June 2002 相似文献
39.
40.
We consider immersions: and construct a subspace of which corresponds to a set of embedded manifolds which are either parallel to f, tubes around f or, in general, partial tubes around f. This space is invariant under the action of the normal holonomy group, We investigate the case where is non-trivial and obtain some results on the number of connected components of .
Received 24 March 2000. 相似文献