全文获取类型
收费全文 | 191549篇 |
免费 | 3591篇 |
国内免费 | 1926篇 |
专业分类
化学 | 102847篇 |
晶体学 | 2785篇 |
力学 | 8987篇 |
综合类 | 91篇 |
数学 | 19890篇 |
物理学 | 62466篇 |
出版年
2022年 | 1242篇 |
2021年 | 1418篇 |
2020年 | 1494篇 |
2019年 | 1525篇 |
2018年 | 1545篇 |
2017年 | 1541篇 |
2016年 | 2938篇 |
2015年 | 2398篇 |
2014年 | 3257篇 |
2013年 | 8848篇 |
2012年 | 7625篇 |
2011年 | 9492篇 |
2010年 | 6015篇 |
2009年 | 6130篇 |
2008年 | 8554篇 |
2007年 | 8426篇 |
2006年 | 8115篇 |
2005年 | 7496篇 |
2004年 | 6652篇 |
2003年 | 5718篇 |
2002年 | 5619篇 |
2001年 | 6954篇 |
2000年 | 5243篇 |
1999年 | 4060篇 |
1998年 | 3062篇 |
1997年 | 3044篇 |
1996年 | 2924篇 |
1995年 | 2576篇 |
1994年 | 2466篇 |
1993年 | 2253篇 |
1992年 | 2599篇 |
1991年 | 2526篇 |
1990年 | 2210篇 |
1989年 | 2168篇 |
1988年 | 2134篇 |
1987年 | 2049篇 |
1986年 | 1959篇 |
1985年 | 2860篇 |
1984年 | 2801篇 |
1983年 | 2250篇 |
1982年 | 2425篇 |
1981年 | 2301篇 |
1980年 | 2249篇 |
1979年 | 2191篇 |
1978年 | 2267篇 |
1977年 | 2222篇 |
1976年 | 2159篇 |
1975年 | 2145篇 |
1974年 | 2049篇 |
1973年 | 2126篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
In the following we find all of the three-dimensional flat spacetimes which are static and rotationally symmetric. 相似文献
22.
A method using third order moments for estimating the regression coefficients as well as the latent state scores of the reduced-rank regression model when the latent variable(s) are non-normally distributed is presented in this paper. It is shown that the factor analysis type indeterminacy of the regression coefficient matrices is eliminated. A real life example of the proposed method is presented. Differences of this solution with the reduced-rank regression eigen solution are discussed. 相似文献
23.
Using Wagner's polarization technique and EMF method the joinic and silver ionic transport number measurements of various
compositions of the mixed system CdI2-Ag2O-CrO3 have been made. The presence of AgI in these materials has been inferred from the typical β → α phase transition of AgI,
which is characterized by an endothermic peak at around 420 K in the DSC traces of these specimens. While the structural analysis
performed by means of powder X-ray diffraction has revealed the formation of ionic phases involving polycrystalline compounds,
the Fourier transform infrared (FTIR) spectroscopic results have indicated the presence of ionic species thus confirming the
ionic nature of the products. The complex impedance studies carried out in the frequency range 20 Hz - 1 MHz and over the
temperature range 294 – 442 K have revealed that the best conducting composition, namely 55%(CdI2) – 45%(Ag2O·CrO3), would exhibit a silver ionic conductivity of 1.3×10−5Scm−1 at 294 K. 相似文献
24.
A. I. Magunov A. Ya. Faenov I. Yu. Skobelev T. A. Pikuz E. Biémont P. Quinet F. Blasco C. Bonte F. Dorchies T. Caillaud F. Salin C. Stenz 《Journal of Experimental and Theoretical Physics》2002,95(6):998-1005
The satellite structure of 1s2p 1,3 P 1-1s 21 S 0 lines of the He-like argon ion in plasma produced by a 45-fs laser pulse in a gas-jet cluster target is measured with a high spectral resolution. Radiation transitions 2p → 1s from autoionizing states (AISs) are detected for ions ranging from Li-like to F-like. The spectrum observed is theoretically simulated with the use of the spectroscopic data for the AISs of multicharged ions obtained within the multiconfiguration relativistic Hartree-Fock method. Good agreement with experimental data is obtained when the main population channels of these states are taken into account for typical values of cluster-target plasma parameters. 相似文献
25.
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
26.
In intonation research, prominence-lending pitch movements have either been described on a linear or on a logarithmic frequency scale. An experiment has been carried out to check whether pitch movements in speech intonation are perceived on one of these two scales or on a psychoacoustic scale representing the frequency selectivity of the auditory system. This last scale is intermediary between the other two scales. Subjects matched the excursion size of prominence-lending pitch movements in utterances resynthesized in different pitch registers. Their task was to adjust the excursion size in a comparison stimulus in such a way that it lent equal prominence to the corresponding syllable in a fixed test stimulus. The comparison stimulus and the test stimulus had pitches running parallel on either the logarithmic frequency scale, the psychoacoustic scale, or the linear frequency scale. In one-half of the experimental sessions, the test stimulus was presented in the low register, while the comparison stimulus was presented in the high register, and, conversely, for the other half of the sessions. The result is that, in all cases, stimuli are matched in such a way that the average excursion sizes in different registers are equal on the psychoacoustic scale. 相似文献
27.
28.
C. Maurel 《Surface science》2006,600(2):442-447
Light emitted in the tunneling junction of a scanning tunneling microscope has been used to establish the electrical characteristics of nanojunctions made of Au islands deposited on flat MoS2 surfaces. It is shown that these characteristics are those of rectifying contacts when the gold islands are isolated and that they evolve toward those of ohmic contacts when the island density increases. It is observed that the rectifying behavior also evolves over time as on infinite metal/semiconductor contacts. Using the STM tip, single gold islands can be manipulated on the MoS2 surface so that their electrical behavior can be changed depending on their position with regard to the other islands. 相似文献
29.
V. Edon M.C. Hugon B. Agius L. Miotti C. Radtke F. Tatsch J.J. Ganem I. Trimaille I.J.R. Baumvol 《Applied Physics A: Materials Science & Processing》2006,83(2):289-293
The influence of processing parameters on the electrical characteristics of RuO2/LaAlO3/Si metal-oxide-semiconductor structures was investigated. In particular, the sputtering regime during deposition of LaAlO3 on Si and the atmosphere used in the post-deposition annealing step were addressed by determining capacitance-voltage and
gate current-voltage characteristics. These results were correlated with compositional information obtained by Rutherford
backscattering spectrometry and nuclear reaction analysis. A post-deposition annealing step in oxygen at 600 °C resulted in
better electrical characteristics of the final structure as compared to the same treatment performed in nitrogen. This result
is explained by oxygen ability to heal oxygen vacancies in the LaAlO3 film, especially at the dielectric/semiconductor interface region. A thermalized sputtering regime during deposition of LaAlO3 on Si leads to capacitors with electrical characteristics superior to those deposited in ballistic regime.
PACS 77.84.Dy; 81.15.Cd; 81.40.Gh; 73.40.Qv; 82.80.Yc 相似文献
30.
Benjamin J. K. Evans Susan M. Scott Antony C. Searle 《General Relativity and Gravitation》2002,34(10):1675-1684
We have developed a new tool for numerical work in General Relativity: GRworkbench. We discuss how GRworkbench's implementation of a numerically-amenable analogue to Differential Geometry facilitates the development of robust and chart-independent numerical algorithms. We consider, as an example, geodesic tracing on two charts covering the exterior Schwarzschild space-time. 相似文献