全文获取类型
收费全文 | 7038篇 |
免费 | 308篇 |
国内免费 | 56篇 |
专业分类
化学 | 4547篇 |
晶体学 | 76篇 |
力学 | 210篇 |
数学 | 874篇 |
物理学 | 1695篇 |
出版年
2023年 | 41篇 |
2022年 | 60篇 |
2021年 | 200篇 |
2020年 | 157篇 |
2019年 | 171篇 |
2018年 | 151篇 |
2017年 | 150篇 |
2016年 | 221篇 |
2015年 | 212篇 |
2014年 | 275篇 |
2013年 | 472篇 |
2012年 | 506篇 |
2011年 | 550篇 |
2010年 | 367篇 |
2009年 | 296篇 |
2008年 | 500篇 |
2007年 | 424篇 |
2006年 | 426篇 |
2005年 | 342篇 |
2004年 | 331篇 |
2003年 | 273篇 |
2002年 | 262篇 |
2001年 | 186篇 |
2000年 | 125篇 |
1999年 | 101篇 |
1998年 | 60篇 |
1997年 | 32篇 |
1996年 | 42篇 |
1995年 | 57篇 |
1994年 | 43篇 |
1993年 | 41篇 |
1992年 | 30篇 |
1991年 | 22篇 |
1990年 | 32篇 |
1989年 | 34篇 |
1988年 | 21篇 |
1987年 | 20篇 |
1985年 | 30篇 |
1984年 | 12篇 |
1983年 | 12篇 |
1982年 | 17篇 |
1981年 | 14篇 |
1980年 | 12篇 |
1978年 | 8篇 |
1977年 | 10篇 |
1976年 | 8篇 |
1975年 | 6篇 |
1974年 | 7篇 |
1973年 | 10篇 |
1970年 | 5篇 |
排序方式: 共有7402条查询结果,搜索用时 15 毫秒
41.
J.-S. Kang G. Kim S.S. Lee S. Choi S. Cho S.W. Han H.J. Shin B.I. Min 《Journal of magnetism and magnetic materials》2006
The spatial concentration distribution and local electronic structure of ferromagnetic Ge1−xTx (T=Cr, Mn, Fe) DMS single crystals have been investigated by using scanning photoelectron microscopy (SPEM), X-ray absorption spectroscopy (XAS), and photoemission spectroscopy (PES). It is found that doped T ions in Ge1−xTx crystals are chemically phase-separated, suggesting that the observed ferromagnetism arises from the phase-separated T-rich phases in Ge1−xTx. 相似文献
42.
A. Subramanian T.-Y. Choi L.X. Dong J. Tharian U. Sennhauser D. Poulikakos B.J. Nelson 《Applied Physics A: Materials Science & Processing》2007,89(1):133-139
We report on a novel method for local control of shell engineering in multiwalled carbon nanotubes (MWNTs) using Joule-heating
induced electric breakdown. By modulating the heat dissipation along a nanotube, we can confine its thinning and shell breakdown
to occur within localized regions of peak temperatures, which are distributed over one-half of the NT length. The modulation
is achieved by using suitably designed nanomachined heat sinks with different degrees of thermal coupling at different parts
of a current-carrying nanotube. The location of electric breakdown occurs precisely at the regions of high temperatures predicted
by the classical finite-element model of Joule heating in the MWNT. The experiments herein provide new insight into the electric
breakdown mechanism and prove unambiguously that shell removal occurs due to thermal stress, underpinning the diffusive nature
of MWNTs. The method demonstrated here has the potential to be a powerful tool in realizing MWNT bearings with complex architectures
for use in integrated nanoelectromechanical systems (NEMS). In addition, the breakdown current and power in the nanotubes
are significantly higher than those observed in nanotubes without heat removal via additional heat sinks. This indicates future
avenues for enhancing the performance of MWNTs in electrical interconnect and nanoelectronic applications.
PACS 73.63.Fg; 65.80.+n 相似文献
43.
In this paper we prove the semialgebraic version of Palais' covering homotopy theorem, and use this to prove Bredon's covering mapping cylinder conjecture positively in the semialgebraic category. Bredon's conjecture was originally stated in the topological category, and a topological version of our semialgebraic proof of the conjecture answers the original topological conjecture for topological G-spaces over “simplicial” mapping cylinders. 相似文献
44.
Alexopoulos T Allen C Anderson EW Areti H Banerjee S Beery PD Biswas NN Bujak A Carmony DD Carter T Cole P Choi Y De Bonte RJ Erwin AR Findeisen C Goshaw AT Gutay LJ Hirsch AS Hojvat C Kenney VP Lindsey CS LoSecco JM McMahon T McManus AP Morgan N Nelson KS Oh SH Piekarz J Porile NT Reeves D Scharenberg RP Stampke SR Stringfellow BC Thompson MA Turkot F Walker WD Wang CH Wesson DK 《Physical review letters》1990,64(9):991-994
45.
46.
47.
We interpret the recently observedU(3.1) mesons with the \(\Lambda \bar p\) + pions decays as the bound state of \(\Lambda ,\bar p\) andX 0(1480). TheX 0(1480) is a mesonium with \(Q^2 \bar Q^2 \) structures observed in γγ reactions and \(\bar pn\) annihilations. With this interpretation, we can understand its decay modes. Furthermore, we predict the ratio of \(\sigma (\Lambda \bar p\pi ^ + \pi ^ - )/\sigma (\Lambda \bar p\pi ^ + \pi ^ + )\) to be ?3.1 for centrally produced events and that the width of \(U^ - (\Lambda \bar p\pi ^ + \pi ^ - )\) to be greater than that of \(U^ + (\Lambda \bar p\pi ^ + \pi ^ + )\) . Both predictions seem to be in reasonable accord with the available data. We call for the detection of the \(\Lambda \bar p\pi ^ - \pi ^ - \) mode to verify the present interpretation. 相似文献
48.
49.
An optical fiber-chromatographic sensor, aiming at simultaneous and selective response to multiple components following a chromatographic separation, is described. We report an improved approach for immobilization of octadecyl (C(18)) and methyl (C(1)) moieties as stationary phase on an optical fiber suitable as a sensing phase for organic solutes. By this approach, the stability and lifetime of the sensing layer as well as the detectability and retention behavior of the chromatographic sensor could be improved. Infrared spectroscopy was employed to confirm the presence of C(18) and C(1) moieties on the modified surface of the optical fiber. The chromatographic sensor was applied, with good sensitivity and chemical selectivity, to the simultaneous separation and detection of bromobenzene and toluene, using water as the mobile phase. 相似文献
50.
A new caffeoyl quinic acid from aster scaber and its inhibitory activity against human immunodeficiency virus-1 (HIV-1) integrase 总被引:1,自引:0,他引:1
Kwon HC Jung CM Shin CG Lee JK Choi SU Kim SY Lee KR 《Chemical & pharmaceutical bulletin》2000,48(11):1796-1798
The phytochemical study of the aerial parts of Aster scaber Thunb. (Asteraceae) yielded a new caffeoyl quinic acid, (-) 3,5-dicaffeoyl-muco-quinic acid (2) and three known compounds, (-) 3,5-dicaffeoyl quinic acid (1), (-) 4,5-dicaffeoyl quinic acid (3), (-) 5-caffeoyl quinic acid (4). The structures were established by high resolution spectroscopic methods. The antiviral effects against HIV-1 integrase of the compounds was evaluated. (-) 3,5-Dicaffeoyl-muco-quinic acid (2) exhibited potent antiviral activity with an IC50 value of 7.0 +/- 1.3 microg/ml. 相似文献