全文获取类型
收费全文 | 10786篇 |
免费 | 1884篇 |
国内免费 | 1548篇 |
专业分类
化学 | 8127篇 |
晶体学 | 180篇 |
力学 | 603篇 |
综合类 | 66篇 |
数学 | 1495篇 |
物理学 | 3747篇 |
出版年
2024年 | 31篇 |
2023年 | 215篇 |
2022年 | 354篇 |
2021年 | 368篇 |
2020年 | 447篇 |
2019年 | 427篇 |
2018年 | 357篇 |
2017年 | 349篇 |
2016年 | 560篇 |
2015年 | 554篇 |
2014年 | 672篇 |
2013年 | 812篇 |
2012年 | 966篇 |
2011年 | 1011篇 |
2010年 | 718篇 |
2009年 | 694篇 |
2008年 | 754篇 |
2007年 | 629篇 |
2006年 | 582篇 |
2005年 | 549篇 |
2004年 | 453篇 |
2003年 | 362篇 |
2002年 | 370篇 |
2001年 | 317篇 |
2000年 | 185篇 |
1999年 | 248篇 |
1998年 | 163篇 |
1997年 | 109篇 |
1996年 | 134篇 |
1995年 | 140篇 |
1994年 | 114篇 |
1993年 | 80篇 |
1992年 | 79篇 |
1991年 | 82篇 |
1990年 | 85篇 |
1989年 | 55篇 |
1988年 | 32篇 |
1987年 | 30篇 |
1986年 | 33篇 |
1985年 | 20篇 |
1984年 | 14篇 |
1983年 | 14篇 |
1982年 | 9篇 |
1981年 | 10篇 |
1979年 | 6篇 |
1977年 | 5篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1973年 | 2篇 |
1928年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
161.
Dr. Dingfeng Yang Junzhu Yang Xuejun Quan Bin Zhang Guoyu Wang Xu Lu Xiaoyuan Zhou 《Chemphyschem》2021,22(24):2579-2584
Understanding the correlation between crystal structure and thermal conductivity in semiconductors is very important for designing heat-transport-related devices, such as high-performance thermoelectric materials and heat dissipation in micro-nano-scale devices. In this work, the lattice thermal conductivity ( ) of the cage-like compounds Cu3VSe4 and Cu3NbSe4 was investigated by experimental measurements and first-principles calculations. The experimental of Cu3NbSe4 is approximately 25 % lower than that of Cu3VSe4 at 300 K. The relevant important physical parameters, including the sound velocity, heat capacity, weighted phonon phase space (W), and third-order force constants along with atomic mass were theoretically analyzed. It is found that W is the dominant parameter in determining the , and the other factors only play a minor role. The physical origin is the relatively “soft” lattice of Cu3NbSe4 with heavier atomic mass. This research provides deep insight into the correlation between the thermal conductivity and crystal structure and paves the way for discovering high-performance thermal management device and thermoelectric materials with intrinsically low . 相似文献
162.
LI Quan College of Chemistry Sichuan Normal University Chengdu China 《中国科学B辑(英文版)》2006,49(3):209-213
The study of the intermolecular interactions that drive the solvation of six-membered nitrogenated aromatic rings is of particular importance since they are known to constitute key building blocks of pro- teins and nucleotides[1―5]. The investigation of the 1:1 adduct of these molecules with water will be the first step in the understanding of such interactions. These molecules possess two different proton-acceptor sites: the ring π cloud and the lone pairs of electrons on the nitrogen atoms… 相似文献
163.
Eu1—xTbxBa2Cu3O7—δ中Tb离子价态的研究 总被引:1,自引:0,他引:1
研究了BaTbO_3、Tb_4O_7、TbFeO_3的Tb_(4d)XPS谱,找到了表征Tb~(3+)、Tb~(4+)的特征峰,得出的高、低结合能峰强之比与Tb~(4+)/Tb含量间的依赖关系,可用于确定Eu_(1-x)Tb_xBa_2Cu_3O_(7-δ)中“123”相的Tb离子混合价态,用常压高温烧结法,未能获得纯“123”单相,也不易获得纯利Tb~(3+)价态样品.在Eu_(1-x)Tb_xBa_2Cu_3O_(7-δ)中的Tb以Tb~(3+)、Tb~(4+)混合价态存在;当x=0.3时,Tb~(4+)/Tb=0.61.引入Tb~(4+)后“123”主相Cu(2)-O(2)平面上的O_(2p)空穴数降低,这是Tb~(4+)破坏超导电性的一种可能原因。 相似文献
164.
含间苯基聚芳醚酮的合成与性能研究 总被引:3,自引:0,他引:3
含间苯基聚芳醚酮的合成与性能研究林权,张万金,吴忠文,尹玖梅(吉林大学化学系,长春,130021)(中国科学院长春应用化学研究所)关键词聚芳醚酮,间苯基,熔点,结晶度聚芳醚酮作为一类耐高温特种工程塑料,由于具有优异的热、电、机械性能,已被广泛应用于电... 相似文献
165.
166.
Guo Jin-xin Sun Si-xiu Zhu Rong-xiu Yin Zhi-lei Yu Hai-yun Li Da-zhi Zhang Wei-min Xu Xian-gang Sun Xuan Shao Hua 《Journal of Radioanalytical and Nuclear Chemistry》2004,261(1):221-224
The 222Rn emanation fraction (EF) released from the technically enhanced naturally occurring radioactive material (TE-NORM) wastes
at certain sites of petroleum and gas production was determined. The samples were analyzed by γ-ray spectrometry to determine
the activity concentration of the 226Ra content, of which the 222Rn emanation fraction was calculated. The results showed that the 222Rn emanation fraction differs in the oil and gas production sites and it is independent of the activity concentration of 226Ra.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
167.
The refolding of the reduced-denatured insulin from bovine pancreas was investigated with the size exclusion chromatography (SEC). It was shown that the reduced-denatured insulin originally denatured with 7.0 mol L?1 guanidine hydrochloride (GuHCI) or 8.0 mol L?1 urea could not be refolded with a non-oxidized mobile phase. Although the oxidized and reduced glutathione (GSSG and GSH) were employed in the oxidized mobile phase, the reduced-denatured insulin still could not be renatured. However, in the presence of 2.0 mol Lt-1 urea in the oxidized mobile phase employed, the reduced-denatured insulin can be refolded with SEC, and the aggregation of denatured insulin can be diminished by urea. In addition, the disulfide exchange of reduced-denatured insulin also can be accelerated with GSSG/GSH in the oxidized mobile phase. The three disulfide bridges of insulin were formed correctly and the reduced-unfolded insulin can be renatured completely. The results were further tested with reversed-phase liquid chromatography (RPLC) and hydrophobic interaction chromatography (HIC). 相似文献
168.
A procedure for the Raman spectra calculation of vitreous and molten silicates was presented in this paper. It includes molecular dynamics MD simulation for the generation of equilibrium configurations, Wilson's GF matrix method for the calculations of eigenfrequencies and corresponding vectors, electro-optical parameters method (EOPM) for the Raman intensity calculations, and the bond polarizability model (BPM) for the determination of polarizability and polarizability derivative. One of the most important characteristics of this procedure is the achievement of the partial Raman spectra of five tetrahedral units, as well as the total spectral envelope. In this paper, the calculation was carried out for the vitreous and molten calcium silicates with different compositions and at various temperatures. It is worthwhile to note that the calculation is based on statistical configurations distribution in the space and so it is not needed to artificially adjust the full width at half maximum (FWHM) of spectra. It was also tested through the good agreement of the calculated spectra with the experimental, including some regularity of spectral properties. According to the calculation, the symmetrical stretching of whole tetrahedral units, to which the stretching of Si-O(nb) bond gives the main contribution to intensity, is proven to be the dominance in the high-frequency range (800-1200 cm(-1)) and the symmetrical bending of Si-O(b)-Si, to which the stretching of Si-O(b) bond exhibits the main contribution, is the dominance in the medium-frequency range (400-700 cm(-1)). As the first theoretical results, the Raman scattering coefficient of each Q(i) was found little change along with the variation of composition and temperature. 相似文献
169.
The styrene-butadiene rubber (SBR) cured by dicumyl peroxide was reinforced by magnesium methacrylate [Mg(MAA)2], which was added into SBR directly or prepared in situ in SBR through the neutralization of magnesium oxide (MgO) and methacrylic acid (MAA). The experimental results show that the SBR vulcanizates reinforced by Mg(MAA)2 prepared in situ have better mechanical properties than those reinforced by Mg(MAA)2 added directly. The SBR vulcanizates with Mg(MAA)2 prepared in situ are semi-transparent, but those with Mg(MAA)2 added directly are opaque. The Fourier transform infrared analysis shows that the polymerization conversion of Mg(MAA)2 in the SBR vulcanizates with Mg(MAA)2 prepared in situ is much higher than that in the SBR vulcanizates with Mg(MAA)2 added directly. The scan probe microscopy photographs show that the particles in the SBR vulcanizates with Mg(MAA)2 prepared in situ are much finer and disperse more evenly than that in the SBR vulcanizates with Mg(MAA)2 added directly. 相似文献
170.
The liquid chromatographic enantiomer separation of N-fluorenylmethoxycarbonyl (FMOC) protected alpha-amino acids and their ethyl ester derivatives was performed on polysaccharide-derived chiral stationary phases, Chiralcel OD, Chiralpak AD, and Chiralpak AS. In general, Chiralcel OD and Chiralpak AD showed good performance for resolution of N-FMOC alpha-amino acids and their ethyl esters, respectively. All investigated N-FMOC alpha-amino acid enantiomers were baseline separated on Chiralcel OD or Chiralpak AD, whereas N-FMOC alpha-amino acid ethyl ester enantiomers were baseline resolved (alpha = 1.15-3.03) on Chiralpak AD, except for two analytes. The L-enantiomers of all examined FMOC alpha-amino acid ethyl ester derivatives are preferentially retained on Chiralpak AD, while the elution orders of the other enantiomer separations are not consistent. 相似文献