全文获取类型
收费全文 | 1631篇 |
免费 | 123篇 |
国内免费 | 459篇 |
专业分类
化学 | 1998篇 |
晶体学 | 41篇 |
力学 | 19篇 |
综合类 | 3篇 |
物理学 | 152篇 |
出版年
2024年 | 1篇 |
2023年 | 24篇 |
2022年 | 44篇 |
2021年 | 57篇 |
2020年 | 66篇 |
2019年 | 69篇 |
2018年 | 58篇 |
2017年 | 66篇 |
2016年 | 78篇 |
2015年 | 61篇 |
2014年 | 72篇 |
2013年 | 164篇 |
2012年 | 93篇 |
2011年 | 111篇 |
2010年 | 76篇 |
2009年 | 111篇 |
2008年 | 105篇 |
2007年 | 97篇 |
2006年 | 96篇 |
2005年 | 87篇 |
2004年 | 103篇 |
2003年 | 93篇 |
2002年 | 72篇 |
2001年 | 38篇 |
2000年 | 38篇 |
1999年 | 49篇 |
1998年 | 42篇 |
1997年 | 40篇 |
1996年 | 47篇 |
1995年 | 43篇 |
1994年 | 20篇 |
1993年 | 15篇 |
1992年 | 16篇 |
1991年 | 12篇 |
1990年 | 7篇 |
1989年 | 6篇 |
1988年 | 6篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1985年 | 7篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有2213条查询结果,搜索用时 171 毫秒
71.
Summary For the quantitative analyses of evolved CO2and H2O during the thermal decomposition of solids, calibration curves, i.e. the amounts of evolved gases vs. the corresponding
peak areas of mass chromatograms measured by TG-MS, were plotted as referenced by the reaction stoichiometry of the thermal
decomposition of sodium hydrogencarbonate NaHCO3. The accuracy and reliability of the quantitative analyses of the evolved CO2and H2O based on the calibration curves were evaluated by applying the calibration curves to the mass chromatograms for the thermal
decompositions of copper(II) and zinc carbonate hydroxides. It was indicated from the observed ratio of evolved CO2and H2O that the compositions of copper(II) and zinc carbonate hydroxides examined in this study correspond to mineral malachite,
Cu2CO3(OH)2, and hydrozincate, Zn5(CO3)2(OH)6, respectively. Reliability of the present analytical procedure was confirmed by the fairly good agreement of the mass fraction
of the evolved gases calculated from the analytical values with the total mass-loss during the thermal decompositions measured
by TG. 相似文献
72.
Rb2I(OH): A Hydroxide Iodide in the System RbOH/RbI The pseudobinary system RbOH/RbI was investigated by X-ray methods. The crystal structure of Rb2I(OH) was solved by single crystal data: Rb2I(OH): Pnma, Z = 4, a = 7.748(1) Å, b = 5.654(2) Å,c = 13.254(2) Å Z(Fo) with (Fo)2 ? 3σ = (Fo)2 = 449, Z (parameter) = 25, R/Rw = 0.021/0.023 Rb2I(OH) crystallizes in a new type of structure, built up by a three dimensional network of [Rb2(OH)+] containing the iodide ions. 相似文献
73.
M. Jayalakshmi P. Radhika K. Phani Raja M. Mohan Rao 《Journal of Solid State Electrochemistry》2007,11(2):165-172
Nanoparticles of α-phase nickel hydroxide were synthesized by a single-step hydrothermal method using urea as the hydrolytic agent. Precipitated powders were of pure turbostratic α-phase as confirmed by x-ray diffraction profile. The ageing of α-Ni(OH)2 in 1.0 M alkali solutions is investigated for pure non-intercalated α-Ni(OH)2 and thiourea intercalated/absorbed α-phase nanomaterials. The α-Ni(OH)2 powder immobilized on the surface of graphite electrodes shows a gradual α→β phase transformation with continuous voltammetric cycling, and the concentration gradient of water that exists in the layered-double-hydroxide-like interlayers of α-phase and the solution was shown to play a crucial role on the high electrochemical activity of this phase nickel hydroxide. To understand the role of water in the ageing process, concomitant entries of non-aqueous solvents like ethanol and acetonitrile along with thiourea were effected. Cyclic voltammetric measurements of thiourea-treated α-Ni(OH)2 samples revealed that hydroxyl ion influx during the anodic oxidation depends on the counter flux of solvent molecules, and if the intercalated the solvent is acetonitrile, then the electrochemical activity of α-Ni(OH)2 reduced drastically; Q
a/Q
c>1 for water as solvent in the interlayers α-Ni(OH)2 and Q
a/Q
c<1 for ethanol and acetonitrile as solvents. The α-phase gets stabilized in the presence of thiourea with water and ethanol as co-intercalates. Transmission electron microscope images of α-Ni(OH)2 and thiourea-treated samples show a change in particle size and morphology. Elemental CHNS analysis confirms the presence of sulphur in the thiourea intercalated samples. 相似文献
74.
本文采用溶胶凝聚方法制备了超细氢氧化亚镍电极材料并通过在其中掺加适量碳纳米管的方法大大提高了电极的比容量并有效改善了电极材料的阻抗特性。掺有20%碳纳米管的氢氧化亚镍复合电极材料的单电极比容量可达到320 F·g-1。本文分别采用氢氧化亚镍/碳纳米管复合电极作为正极,活性炭作为负极,6 mol·L-1 KOH作为电解液制备了复合型电化学电容器。采用上述方法制备的复合型电容器工作电压达到1.6 V,电容器质量比容量达到60 F·g-1。复合型电容器能量密度达到20.11 Wh·kg-1,最大功率密度达到8.6 kW·kg-1,兼具高能量特性和优良的大电流放电特性。 相似文献
75.
76.
77.
Helmut G. Alt 《Russian Chemical Bulletin》1995,44(1):1-8
Ansa metallocene dichloride complexes of titanium, zirconium, and hafnium can be activated by methyl aluminoxane (MAO) to give excellent catalysts for the homogeneous polymerization of ethylene and propylene. The symmetry of the corresponding metaliocene dichloride complexes is essential for the stereospecific polymerization of propylene (isotactic, syndiotactic or atactic). The application of fluorenyl groups instead of cyclopentadienyl groups greatly increases the activity of the catalysts. The first ansa bis(fluorenyl) complexes of zirconium and hafnium, (C13H8-C2H4-C13Hs)MCl2 (M = Zr, Hf), have been prepared. It was found that after the activation by MAO the zirconium derivative demonstrates a very high activity. Several model complexes are presented in order to discuss the mechanism of the polymerization.This paper was presented at the INEOS-94 Workshop The Modern Problems of Organometallic Chemistry (Moscow, May 21–27, 1994).Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 7–14, January, 1995. 相似文献
78.
Addition of one equivalent of LiN(i-Pr)2 or LiN(CH2)5 to carbodiimides, RN=C=NR [R=cyclohexyl (Cy), isopropyl (i-Pr)], generated the corresponding lithium of tetrasubstituted guanidinates {Li[RNC(N R^′2)NR](THF)}2 [R=i-Pr, N R^′2=N(i-Pr)2 (1), N(CH2)5 (2); R=Cy, N R^′2=N(i-Pr)2 (3), N(CH2)5 (4)]. Treatment of ZrCl4 with freshly prepared solutions of their lithium guanidinates provided a series of bis(guanidinate) complexes of Zr with the general formula Zr[RNC(N R^′2)NR]2Cl2 [R=i-Pr, N R^′2=N(i-Pr)2 (5), N(CH2)5 (6); R=Cy, N R^′2=N(i-Pr)2 (7), N(CH2)5 (8)]. Complexes 1, 2, 5-8 were characterized by elemental analysis, IR and ^1H NMR spectra. The molecular structures of complexes 1, 7 and 8 were further determined by X-ray diffraction studies. 相似文献
79.
In order to obtain a catalyst support with a high surface area, ZrO2 and ZrO2-Y2O3 were prepared by the hydrolytic decomposition of the corresponding isopropoxide dissolved in benzene. The hydrolysis was carried out at 80°C using an excess amount of distilled water in flowing dry nitrogen. The precipitates thus obtained were dried at 100°C followed by calcination at 500°C in air or nitrogen for 1 h. The specific surface areas for both of the ZrO2 and ZrO2-Y2O3 increased with increasing amount of water added for hydrolysis, and the surface areas for ZrO2-Y2O3 increased with increasing yttrium content. A ZrO2 having a surface area of 130 m2/g was produced, and a stabilized tetragonal ZrO2 with 15 mol% Y3+ having a surface area of 200 m2/g was produced. Furthermore, despite the difference in the ZrO2 and ZrO2-Y2O3 crystal structures, the lattice-strain of ZrO2 has been unequivocally related to the surface area. 相似文献
80.
Mit"kina T. V. Gerasko O. A. Sokolov M. N. Naumov D. Yu. Fedin V. P. 《Russian Chemical Bulletin》2004,53(1):80-85
Slow evaporation of hydrochloric acid solutions of zirconium(iv) or hafnium(iv) oxochlorides and cucurbituril in air afforded compounds with composition [M4(OH)8(H2O)16]Cl8·(C36H36N24O12)·16H2O, where M = Zr (1) or Hf (2). According to the X-ray diffraction data, complexes 1 and 2 are isostructural. Their crystal structures can be described as packings of polymer chains consisting of alternating cucurbituril molecules and tetranuclear cations [M4(OH)8(H2O)16]8+ linked to each other via an extensive network of hydrogen bonds. Compound 2 is the first structurally characterized tetranuclear hafnium aqua complex. 相似文献