全文获取类型
收费全文 | 531456篇 |
免费 | 5367篇 |
国内免费 | 1631篇 |
专业分类
化学 | 286833篇 |
晶体学 | 7846篇 |
力学 | 23314篇 |
综合类 | 16篇 |
数学 | 62844篇 |
物理学 | 157601篇 |
出版年
2020年 | 3816篇 |
2019年 | 4020篇 |
2018年 | 4818篇 |
2017年 | 4723篇 |
2016年 | 7826篇 |
2015年 | 5497篇 |
2014年 | 8121篇 |
2013年 | 22795篇 |
2012年 | 17162篇 |
2011年 | 21156篇 |
2010年 | 14071篇 |
2009年 | 13975篇 |
2008年 | 19681篇 |
2007年 | 20011篇 |
2006年 | 19159篇 |
2005年 | 17361篇 |
2004年 | 15750篇 |
2003年 | 14123篇 |
2002年 | 13929篇 |
2001年 | 15452篇 |
2000年 | 11920篇 |
1999年 | 9408篇 |
1998年 | 7954篇 |
1997年 | 7731篇 |
1996年 | 7594篇 |
1995年 | 6952篇 |
1994年 | 6888篇 |
1993年 | 6458篇 |
1992年 | 7296篇 |
1991年 | 7181篇 |
1990年 | 6912篇 |
1989年 | 6607篇 |
1988年 | 6948篇 |
1987年 | 6592篇 |
1986年 | 6306篇 |
1985年 | 8797篇 |
1984年 | 9087篇 |
1983年 | 7506篇 |
1982年 | 7982篇 |
1981年 | 7933篇 |
1980年 | 7695篇 |
1979年 | 7792篇 |
1978年 | 8092篇 |
1977年 | 8012篇 |
1976年 | 8041篇 |
1975年 | 7660篇 |
1974年 | 7559篇 |
1973年 | 7872篇 |
1972年 | 5063篇 |
1971年 | 3990篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
We demonstrate a method that permits to obtain generalized solutions for some quasilinear equations and systems of hyperbolic
type. The corresponding variational principle is constructed using the theory of equilibrium of a potential in an external
field.
Dedicated to the memory of B. M. Levitan
Supported by RFBR grants Nos. 05-01-00522 and NSh-1551.2003.1, by Program No. 1 of the Branch of Mathematics, Russian Academy
of Sciences, and by INTAS project No. 03-51-6637. 相似文献
42.
T. Kumita Y. Kamiya M. Babzien I. Ben-Zvi K. Kusche I. V. Pavlishin I. V. Pogorelsky D. P. Siddons V. Yakimenko T. Hirose T. Omori J. Urakawa K. Yokoya D. Cline F. Zhou 《Laser Physics》2006,16(2):267-271
Thomson scattering of high-power laser and electron beams is a good test of electrodynamics in the high-field region. We demonstrated production of high-intensity X-rays in the head-on collision of a CO2 laser and 60-MeV electron beams at Brookhaven National Laboratory, Accelerator Test Facility. The energy of an X-ray photon was limited at 6.5 keV in the linear (lowest order) Thomson scattering, but the nonlinear (higher order) process produces higher energy X-rays. We measured the angular distribution of the high-energy X-rays and confirmed that it agrees with theoretical predictions. 相似文献
43.
The tape stripping technique is an experimental method frequently used for reconstruction of the in-depth distribution of various topically administered substances within the horny layer of human skin, e.g., compounds contained in sunscreens. Titanium dioxide (TiO2) nanoparticles (25–200 nm in diameter) are one such compound. Optical techniques which apply blue light are found to be suitable for reconstruction. However, the presence of particles affects the light propagation within the skin and therefore causes incorrect determination of strip thickness, leading to an improper reconstructed distribution of nanoparticle concentration revealed from the experimental data. This study evaluates the errors emerging from the use of blue (400 nm) and NIR (800 nm) radiation and finds the use of longer wavelength light more advantageous. Particles of different diameters are considered, and it is revealed that the application of small particles (25–60 nm) results in the lowest rate of error. 相似文献
44.
45.
de Souza P. A. Garg V. K. Klingelhöfer G. Gellert R. Gütlich P. 《Hyperfine Interactions》2002,139(1-4):705-714
A portable Mössbauer spectrometer, developed for extraterrestrial applications, opens up new industrial applications of MBS. But for industrial applications, an available tool for fast data analysis is also required, and it should be easy to handle. The analysis of Mössbauer spectra and their parameters is a barrier for the popularity of this wide-applicable spectroscopic technique in industry. Based on experience, the analysis of a Mössbauer spectrum is time-consuming and requires the dedication of a specialist. However, the analysis of Mössbauer spectra, from the fitting to the identification of the sample phases, can be faster using by genetic algorithms, fuzzy logic and artificial neural networks. Industrial applications are very specific ones and the data analysis can be performed using these algorithms. In combination with an automatic analysis, the Mössbauer spectrometer can be used as a probe instrument which covers the main industrial needs for an on-line monitoring of its products, processes and case studies. Some of these real industrial applications will be discussed. 相似文献
46.
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
47.
We calculate the leading and next-to-leading logarithmic resummed distribution for the jet broadening in deep inelastic scattering,
as well as the power correction for both the distribution and mean value. A truncation of the answer at NLL accuracy, as is
standard, leads to unphysical divergences. We discuss their origin and show how the problem can be resolved. We then examine
DIS specific procedures for matching to fixed order calculations and compare our results to the data. One of the tools developed
for the comparison is an NLO parton distribution evolution code. When compared to PDF sets from MRST and CTEQ it reveals limited
discrepancies in both.
Received: 16 October 2001 / Published online: 12 April 2002 相似文献
48.
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
49.
G. A. Pel'ts 《Journal of Mathematical Sciences》1991,54(3):930-939
We show that the wave functions of a string with nontrivial topology of the world sheet should be considered as sections of line bundles over the space of conformal classes of Riemann surfaces. We construct a BRST operator for the case of arbitrary topology and give it a geometric interpretation.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova AN SSSR, Vol. 169, pp. 107–121, 1988. 相似文献
50.
We analyze diffusion from a periodic array of hemispherical droplets through a membrane. We find that the multiple sources do not interact strongly, even when the droplets are closely spaced, so that the flux through the membrane appears nearly additive. 相似文献