全文获取类型
收费全文 | 365篇 |
免费 | 11篇 |
国内免费 | 44篇 |
专业分类
化学 | 253篇 |
晶体学 | 8篇 |
力学 | 1篇 |
物理学 | 158篇 |
出版年
2024年 | 1篇 |
2023年 | 2篇 |
2022年 | 6篇 |
2021年 | 7篇 |
2020年 | 11篇 |
2019年 | 5篇 |
2018年 | 8篇 |
2017年 | 3篇 |
2016年 | 7篇 |
2015年 | 9篇 |
2014年 | 5篇 |
2013年 | 20篇 |
2012年 | 23篇 |
2011年 | 29篇 |
2010年 | 22篇 |
2009年 | 34篇 |
2008年 | 30篇 |
2007年 | 26篇 |
2006年 | 28篇 |
2005年 | 22篇 |
2004年 | 24篇 |
2003年 | 15篇 |
2002年 | 4篇 |
2001年 | 12篇 |
2000年 | 4篇 |
1999年 | 12篇 |
1998年 | 12篇 |
1997年 | 5篇 |
1996年 | 3篇 |
1995年 | 5篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1982年 | 2篇 |
1981年 | 1篇 |
排序方式: 共有420条查询结果,搜索用时 328 毫秒
91.
Theresa Komm 《Journal of solid state chemistry》2005,178(2):454-463
The two non-isotypical rubidium rare-earth(III) thiophosphates Rb3M3[PS4]4 of praseodymium and erbium can easily be obtained by the stoichiometric reaction of the respective rare-earth metal, red phosphorus and sulfur with an excess of rubidium bromide (RbBr) as flux and rubidium source at 950°C for 14 days in evacuated silica tubes. The pale green platelet-shaped single crystals of Rb3Pr3[PS4]4 as well as the pink rods of Rb3Er3[PS4]4 are moisture sensitive. Rb3Pr3[PS4]4 crystallizes triclinically in the space group (, , , α=84.329(4)°, β=88.008(4)°, γ=80.704(4)°; Z=2), Rb3Er3[PS4]4 monoclinically in the space group P21/n (, , , β=95.601(6)°; Z=4). In both structures, there are three crystallographically different rare-earth cations present. (M1)3+ is eightfold coordinated in the shape of a square antiprism, (M2)3+ and (M3)3+ are both surrounded by eight sulfur atoms as bicapped trigonal prisms each with a coordination number of eight as well as for the praseodymium, but better described as CN=7+1 in the case of the erbium compound. These [MS8]13− polyhedra form a layer according to by sharing edges with the isolated [PS4]3− tetrahedra (d(P-S)=200-209 pm, ?(S-P-S)=102-116°). These layers are stacked with a repetition period of three in the case of the praseodymium compound, but of only two for the erbium analog. The rubidium cation (Rb1)+ is located in cavities of these layers and tenfold coordinated in the shape of a tetracapped trigonal antiprism. The also tenfold but more irregularly coordinated rubidium cations (Rb2)+ and (Rb3)+ reside between the layers. 相似文献
92.
在金属氢化物一镍电池(MH/Ni)负极材料中,ABS型贮氢合金是非常具有吸引力的一种,以AB。型贮氢合金作为负极材料的MH/Ni电池目前已大批量进入市场.其中A代表混合稀土RE(主要成分为La,Ce,Pr,Nd);B代表Ni和Co,Mll,AI等取代元素.B侧取代元素已被广泛研究D,习,A侧混合稀土的成分也已引起人们的广泛重视*‘,’],*血1c等【阿针对儿一N13。5C00.75Mll。。A10.3,详细研究了L31。CI。BS系列合金,得出在。=0.2处合金具有较好的综合性能.本文针对B侧Ni。。。Coo,。Mno、。Alo二。(记为民)成分,在研… 相似文献
93.
Single crystals of CsHo3Te5 and Cs3Tm11Te18 have been grown as byproducts in the synthesis of CsLnZnTe3 (Ln=Ho or Tm) through the reaction of Ln, Zn, and Te with a CsCl flux at 850 °C. The crystal structures have been determined from single-crystal X-ray diffraction data. CsHo3Te5 crystallizes in space group Pnma of the orthorhombic system whereas Cs3Tm11Te18 crystallizes in the space group C2/m of the monoclinic system. Each of the compounds adopts a three-dimensional structure; each possesses tunnels built from LnTe6 octahedra that are filled with Cs atoms. The pseudo-rectangular tunnel in CsHo3Te5 is large enough in cross-section to accommodate two symmetrically equivalent Cs atoms. In the Cs3Tm11Te18 structure there are two different sized tunnels: the smaller one is only large enough to host one Cs atom per unit cell whereas the larger one can accommodate two Cs atoms. The electronic structure of CsHo3Te5 was calculated. The band gap is estimated to be about 1.2 eV, consistent with the black color of the crystals. 相似文献
94.
Svilen Bobev Eric D. Bauer John L. Sarrao Bernhard Eck 《Journal of solid state chemistry》2004,177(10):3545-3552
The Zintl compound EuGe2 crystallizes in the trigonal space group (No. 164) with the CeCd2-structure type. Its structure can be formally derived from the hexagonal AlB2-structure type by a strong puckering of the hexagonal layers. The chemical bonding in EuGe2 can be rationalized according to the Zintl concept as (Eu2+)(Ge1−)2, since the europium atoms are divalent and each germanium atom receives one additional valence electron. In that sense, EuGe2 is expected to be a closed-shell compound with semiconducting behavior. However, temperature dependent resistivity measurements show EuGe2 to be metallic. Subsequently, detailed crystallographic studies revealed the structure and the composition of EuGe2 to be free of defects and impurities, which, along with the confirmed divalent oxidation state of the europium atoms by means of magnetic measurements, make EuGe2 another example of a metallic Zintl phase. These results are in good agreement with the results of electronic structure calculations such as TB-LMTO-ASA (LDA) and FLAPW (GGA), which reveal non-zero DOS at the Fermi level. 相似文献
95.
Stephen Caddick Duncan B JuddAlexandra K.de K Lewis Melanie T ReichMeredith R.V Williams 《Tetrahedron》2003,59(29):5417-5423
The scope of nickel boride mediated reduction of nitriles has been extended further to allow the preparation of Boc protected amines via a mild catalytic process. It is noteworthy that the toxicity of this procedure is greatly reduced due to its catalytic nature in nickel(II) chloride used in combination with excess sodium borohydride. The protocol is marked by its resilience towards air and moisture and hence an easy and general practical protocol. 相似文献
96.
《Current Applied Physics》2018,18(11):1205-1211
The frustrated magnet has been regarded as a system that could be a promising host material for the quantum spin liquid (QSL). However, it is difficult to determine the spin configuration and the corresponding mechanism in this system, because of its geometrical frustration (i.e., crystal structure and symmetry). Herein, we systematically investigate one of the geometrically frustrated magnets, the TbB4 compound. Using resonant soft x-ray scattering (RSXS), we explored its spin configuration, as well as Tb's quadrupole. Comprehensive evaluations of the temperature and photon energy/polarization dependences of the RSXS signals reveal the mechanism of spin reorientation upon cooling down, which is the sophisticated interplay between the Tb spin and the crystal symmetry rather than its orbit (quadrupole). Our results and their implications would further shed a light on the search for possible realization of QSL. 相似文献
97.
98.
《Current Applied Physics》2015,15(12):1576-1579
Er3+/Yb3+-codoped SrMoO4 phosphors were prepared by a high-temperature solid-state reaction method. At room temperature, all the as-prepared samples exhibited strong upconversion properties and the emission intensity increased dramatically with the increase of Yb3+ ion concentration, reaching its maximum value when the concentration was 5 mol%. The dependence of emission intensity on the pump power suggested that the upconversion emission was a two-photon process. Furthermore, the optical temperature sensing properties based on green upconversion emissions of the SrMoO4:0.01Er3+/0.05Yb3+ phosphor were studied. It is found that the SrMoO4:0.01Er3+/0.05Yb3+ phosphor can be operated over a very wide temperature range of 93–773 K with a maximum sensitivity of ∼0.0128 K−1, indicating that low- and high-temperature thermometry can be simultaneously realized in this phosphor. 相似文献
99.
Rare-earth ammonium sulfate octahydrates of R2(SO4)3·(NH4)2SO4·8H2O (R=Pr, Nd, Sm, and Eu) were synthesized by a wet process, and the stable temperature region for the anhydrous R2(SO4)3·(NH4)2SO4 form was clarified by thermogravimetry/differential thermal analysis, infrared, Raman, and electrical conductivity measurements. Detailed characterization of these double salts demonstrated that the thermal stability of anhydrous R2(SO4)3·(NH4)2SO4 is different between the Pr, Nd salts and the Sm, Eu salts, and the thermal decomposition behavior of these salts was quite different from the previous reports. 相似文献
100.
R.K. Murakami H.R. Rechenberg A.C. Neiva F.P. Missell V. Villas-Boas 《Journal of magnetism and magnetic materials》2008,320(14):e65-e68
Effects of titanium carbide (TiC) addition on structural and magnetic properties of isotropic (Pr,Nd)–Fe-B nanocrystalline magnetic materials have been investigated. In this work, we investigate the effect of TiC addition on a (Pr,Nd)-poor and B-rich composition, as well as on a B-poor and (Nd,Pr)-rich composition. Rapidly solidified (Pr,Nd)–Fe–B alloys were prepared by melt-spinning. The compositions studied were (Pr1−xNdx)4Fe78B18 (x=0, 0.5, and 1) with addition of 3 at% TiC. Unlike the (PrxNd1−x)9.5Fe84.5B6 materials that present excellent values for coercive field and energy product, the (Pr,Nd)-poor and B-rich composition alloys with TiC addition present lower values. Rietveld analysis of X-ray data and Mössbauer spectroscopy revealed that samples are predominantly composed of Fe3B and -Fe. For the RE-rich compositions (PrxNd1−x)9.5Fe84.5B6 (x=0.1, 0.25, 0.5, 0.75, and 1) with the addition of 3 at% TiC, the highest coercive field and energy product (8.4 kOe and 14.4 MGOe, respectively) were obtained for the composition Pr9.5Fe84.5B6. 相似文献