全文获取类型
收费全文 | 243539篇 |
免费 | 3704篇 |
国内免费 | 678篇 |
专业分类
化学 | 133335篇 |
晶体学 | 3888篇 |
力学 | 9184篇 |
综合类 | 16篇 |
数学 | 27084篇 |
物理学 | 74414篇 |
出版年
2020年 | 2289篇 |
2019年 | 2372篇 |
2018年 | 2905篇 |
2017年 | 3043篇 |
2016年 | 4752篇 |
2015年 | 3162篇 |
2014年 | 4669篇 |
2013年 | 11392篇 |
2012年 | 8595篇 |
2011年 | 10228篇 |
2010年 | 7246篇 |
2009年 | 6947篇 |
2008年 | 9186篇 |
2007年 | 8988篇 |
2006年 | 8490篇 |
2005年 | 7707篇 |
2004年 | 6975篇 |
2003年 | 6211篇 |
2002年 | 5839篇 |
2001年 | 6913篇 |
2000年 | 5297篇 |
1999年 | 3995篇 |
1998年 | 3199篇 |
1997年 | 3103篇 |
1996年 | 3108篇 |
1995年 | 2872篇 |
1994年 | 2775篇 |
1993年 | 2654篇 |
1992年 | 3329篇 |
1991年 | 3081篇 |
1990年 | 3026篇 |
1989年 | 3042篇 |
1988年 | 3030篇 |
1987年 | 3052篇 |
1986年 | 2882篇 |
1985年 | 3752篇 |
1984年 | 3739篇 |
1983年 | 2954篇 |
1982年 | 3087篇 |
1981年 | 3163篇 |
1980年 | 2890篇 |
1979年 | 3222篇 |
1978年 | 3184篇 |
1977年 | 3320篇 |
1976年 | 3155篇 |
1975年 | 2854篇 |
1974年 | 2816篇 |
1973年 | 2725篇 |
1972年 | 1846篇 |
1968年 | 1886篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
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
992.
UV–visible upconversion emission from terbium in a Tb–Yb codoped tellurite glass has been observed on 980-nm excitation. The
ultraviolet and violet upconversion emissions involve three photons and the blue, green, yellow, and red emissions arise due
to two incident photons. The mechanism involved in these emissions is discussed. The effects of doping concentration and of
the sample temperature on the upconversion emissions have also been studied.
PACS 74.25.Gz; 42.70.Hj; 73.61.Jc; 76.30.Kg; 42.70.Ce 相似文献
993.
E. S. Filatov S. V. Sysoev Ludmila N. Zelenina Tamara P. Chusova V. A. Logvinenko P. P. Semyannikov I. K. Igumenov 《Journal of Thermal Analysis and Calorimetry》2006,86(2):537-539
Thermal behaviour
of a series of lithium β-diketonates: Li(dpm) (dpm=dipivaloylmethanate
(2,2,6,6-tetramethylheptane-3,5- dionate)), Li(pta) (pta=pivaloyltrifluoracetonate
(2,2-dimethyl-6,6,6-trifluoro-3,5-hexanedionate)), Li(tfa) (tfa=trifluoracetylacetonate
(1,1,1-trifluoro-2,4-pentandionate)), Li(hfa) (hfa=hexafluoracetylacetonate
(1,1,1,5,5,5-hexafluoro-2,4-pentandionate)) has been investigated. Gas phase
composition of these complexes has been established. Temperature dependences
of vapor pressure of lithium compounds were obtained by static and dynamic
methods, and thermodynamic parameters were calculated. Dependence of compound
volatility on ligand structure is shown. For Li(dpm) detailed investigation
has been done by differential scanning calorimetry (DSC). 相似文献
994.
I. P. Dobrovol’skaya M. K. Mokeev Yu. N. Sazanov A. V. Gribanov T. E. Sukhanova 《Russian Journal of Applied Chemistry》2006,79(7):1178-1180
Changes in the supramolecular structure of heat-resistant fibers based on polyimide PM were studied by X-ray diffraction analysis and NMR spectroscopy. 相似文献
995.
The FRS-ESR facility at GSI provides one of the most efficient methods for direct mass measurements. In the present experiment,
exotic nuclei were produced via fragmentation of 152Sm projectiles in a thick beryllium target at 500-600 MeV/u, separated in-flight with the fragment separator FRS, and injected
into the storage-cooler ring ESR. Time-resolved Schottky Mass Spectrometry was applied for mass measurements of stored and
electron-cooled bare and few-electron ions. 373 different nuclides were identified by means of the spectra of their revolution
frequencies. Masses for 18 nuclides (84Zr, 92Ru, 94Rh, 107,108,110Sb, 111,112,114I, 118Ba, 122,123La, 124Ce, 127Pr, 129Nd, 132Pm, 134Sm, 137Eu) have been determined for the first time. Masses for 111,112I and 113Xe have been obtained via known α-decay energies. The experiment and first results will be presented. 相似文献
996.
997.
Praveen K. Tandon Gayatri Sumita Sahgal Manish Srivastava Santosh B. Singh 《应用有机金属化学》2007,21(3):135-138
Catalytic activities of three transition metals, as iridium (III) chloride, rhodium (III) chloride and palladium (II) chloride, were compared in the oxidation of six aromatic aldehydes (benzaldehyde, p‐chloro benzaldehyde, p‐nitro benzaldehyde, m‐nitro benzaldehyde, p‐methoxy benzaldehyde and cinnamaldehyde), two hydrocarbons (viz. (anthracene and phenanthrene)) and one aromatic and one cyclic alcohol (cyclohexanol and benzyl alcohol) by 50% H2O2. The presence of traces (substrate: catalyst ratio equal to 1:62500 to 1:1961) of the chlorides of iridium(III), rhodium(III) and palladium(II) catalyze these oxidations, resulting in good to excellent yields. It was observed that in most of the cases palladium(II) chloride is the most efficient catalyst. Conditions for the highest and most economical yields were obtained. Deviation from the optimum conditions decreases the yields. Oxidation in aromatic aldehydes is selective at the aldehydeic group only and other groups remain unaffected. This new, simple and economical method, which is environmentally safe, also requires less time. Reactive species of catalysts, existing in the reaction mixture are also discussed. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
998.
We continue the studies on the so–called genuine Bernstein–Durrmeyer operators U
n
by establishing a recurrence formula for the moments and by investigating the semigroup T(t) approximated by U
n
. Moreover, for sufficiently smooth functions the degree of this convergence is estimated. We also determine the eigenstructure
of U
n
, compute the moments of T(t) and establish asymptotic formulas.
Received: January 26, 2007. 相似文献
999.
G. K. Shenoy 《Hyperfine Interactions》2006,170(1-3):5-13
Stanley L. Ruby (1924–2004) made major contributions to Mössbauer spectroscopy and was the first to suggest the feasibility of observing the Mössbauer effect using synchrotron radiation. In this article we recall his scientific legacy that have inspired his scientific colleagues. 相似文献
1000.
Magnetism of Fe/Cr/Sn/Cr multilayers have been studied by the first-principles density-functional theory. Calculations by the full-potential linearized augmented plane waves (FP LAPW) and screened Korringa–Kohn–Rostoker (SKKR) methods have shown that two types of solutions may be found in these systems: a high-spin (HS) and a low-spin (LS) ones in accordance with the Cr magnetic moment magnitudes. In this work, we have concentrated our attention on the LS solution. The calculation has shown that the LS solution has a phase slip of antiferromagnetic ordering in Cr and is classified as an incommensurate spin density wave (ISDW). The dependence of the ISDW solution on the thickness of Cr, lattice parameter and boundary conditions has been investigated. 相似文献