全文获取类型
收费全文 | 512篇 |
免费 | 7篇 |
国内免费 | 2篇 |
专业分类
化学 | 333篇 |
晶体学 | 2篇 |
力学 | 3篇 |
数学 | 78篇 |
物理学 | 105篇 |
出版年
2018年 | 3篇 |
2017年 | 4篇 |
2015年 | 6篇 |
2013年 | 15篇 |
2012年 | 7篇 |
2011年 | 15篇 |
2010年 | 5篇 |
2009年 | 7篇 |
2008年 | 10篇 |
2007年 | 7篇 |
2006年 | 11篇 |
2005年 | 11篇 |
2004年 | 11篇 |
2003年 | 12篇 |
2002年 | 16篇 |
2001年 | 14篇 |
2000年 | 12篇 |
1999年 | 13篇 |
1998年 | 19篇 |
1997年 | 13篇 |
1996年 | 6篇 |
1995年 | 15篇 |
1994年 | 18篇 |
1993年 | 21篇 |
1992年 | 14篇 |
1991年 | 15篇 |
1990年 | 11篇 |
1989年 | 6篇 |
1988年 | 15篇 |
1987年 | 6篇 |
1986年 | 18篇 |
1985年 | 11篇 |
1984年 | 15篇 |
1983年 | 5篇 |
1982年 | 10篇 |
1981年 | 10篇 |
1980年 | 15篇 |
1979年 | 11篇 |
1978年 | 16篇 |
1977年 | 9篇 |
1976年 | 6篇 |
1975年 | 4篇 |
1974年 | 4篇 |
1973年 | 5篇 |
1970年 | 6篇 |
1969年 | 3篇 |
1967年 | 3篇 |
1966年 | 4篇 |
1929年 | 2篇 |
1920年 | 2篇 |
排序方式: 共有521条查询结果,搜索用时 15 毫秒
1.
We study the growth morphology of thin macrostructure films which is known to be largely affected by the deposition conditions as thin film nucleation and formation is dependent on the kinetic energy and chemical free energy of the atoms. The ion-beam sputtering technique used for depositing thin layers is due to the advantage over other techniques, e.g. the independent control of many process parameters, such as the pressure and/or the energy of the ion-beam and the substrate temperature. Therefore, the dependence of various sputtering parameters such as: (i) sputtering pressure and/or the rate of deposition and (ii) the effect of substrate temperature on the growth has been studied by depositing a single layer of Al. The variations show some interesting dependencies on the structural parameters for the Al layer deposited which has been understood in terms of thin film growth and nucleation theory. 相似文献
2.
3.
Differentiation of functions w.r.t. finite atomless measures with compact support on the real line is introduced. The related harmonic calculus is similar to that of the classical Lebesgue case. As an application we obtain the Weyl exponent for the spectral asymptotics of the Laplacians w.r.t. linear Cantor-type measures with arbitrary weights. 相似文献
4.
5.
H.-J. Mai S. Wocadlo H.-C. Kang W. Massa K. Dehnicke C. Maichle-Mssmer J. Strhle D. Fenske 《无机化学与普通化学杂志》1995,621(5):705-712
Phosphanimine and Phosphoraneiminato Complexes of Iron. The Crystal Structures of [FeCl3(Me3SiNPEt3)], [FeCl2(Me3SiNPEt3)]2, [FeCl2(NPEt3)]2, and [Fe(O2C? CH3)2(NPEt3)]2 The phosphanimine complexes [FeCl3(Me3SiNPEt3)] (red-orange) and [FeCl2(Me3SiNPEt3)]2 (colourless) have been prepared by reactions of Me3SiNPEt3 with FeCl3 and FeCl2, respectively, in CH2Cl2 suspensions. Thermal decomposition of these donor-acceptor complexes in boiling toluene leads to the phosphoraneiminato complex [FeCl2(NPEt3)]2 (black), whereas [Fe(O2C? CH3)2(NPEt3)]2 (brown) is formed from iron(II) acetate and Me3SiNPEt3 in boiling acetonitrile. The complexes are characterized by IR spectroscopy and by crystal structure determinations. [FeCl3(Me3SiNPEt3)] (1) : Space group P21/c, Z = 8, structure determination with 4 673 unique reflections, R = 0.033. Lattice dimensions at ?15°C: a = 1 607.8, b = 1 602.0, c = 1 417.2 pm, β = 106.56°. 1 forms monomeric molecules with tetrahedrally coordinated iron atoms. Bond lengths in average: Fe? N = 196.9 pm, Fe? Cl = 219.7 pm. [FeCl2(Me3SiNPEt3)]2 (2) : Space group P21/c, Z = 4, structure determination with 4 992 unique reflections, R = 0.048. Lattice dimensions at 20°C: a = 1 457.9, b = 1 685.4, c = 1 507.3 pm, β = 116.74°. 2 forms dimeric molecules, which are associated by chloro bridges. The iron atoms are tetrahedrally coordinated with trans positions of the phosphanimine ligands. Both lengths in average: Fe? N = 202.2 pm, Fe? Clterminal = 224.7 pm, Fe? Cl bridge = 241.0 pm. [FeCl2(NPEt3)]2 (3): Space group P21/n, Z = 2, structure determination with 2763 unique reflections, R = 0.039. Lattice dimensions at ?70°C: a = 799.1, b = 1009.0, c = 1441.9 pm, β = 93.45°. 3 forms centrosymmetric dimeric molecules, in which the tetrahedrally coordinated iron atoms are associated by the nitrogen atoms of the phosphoraneiminato ligands. Bond lengths in average: Fe? N = 191.4 pm, Fe? Cl = 222.7 pm. [Fe(O2C? CH3)2(NPEt3]2 (4): Space group P21/n, Z = 2, structure determination with 3005 observed unique reflections, R = 0.034. Lattice dimensions at -65°C: a = 886.4, b = 1444.6 pm, β = 90.60°. 4 forms centrosymmetric dimeric molecules, in which the octahedrally coordinated iron atoms are associated by the nitrogen atoms of the phosphoraneiminato ligands with bond lengths Fe? N of 191.9 and 195.0 pm. The acetate groups are coordinated in a chelating fashion. 相似文献
6.
Pentaazadienido Complexes of Zinc, Cadmium, and Mercury. The Crystal Structure of [Cd(EtOC6H4-N5-C6H4OEt)2(py)2] and [Hg(tol-N5-tol)2(py)] The pentaazadienido complexes [M(EtOC6H4N5C6H4OEt)2] (M = Zn ( 1 ), Cd ( 2 )) are formed by the reaction of [M(NH3)4]2+ with [EtOC6H4N5C6H4OEt]? in aqueous ammonia. 2 crystallizes from pyridine as [Cd(EtOC6H4N5C6H4OEt)2py2] ( 3 ) with the triclinic space group P1 and a = 937.2(2); b = 1422.7(2); c = 2085.5(2) pm; α = 75.28(1)°; β = 94.74(1)°; γ = 99.75(1)°; Z = 2. The central Cd2+ ion of 3 exhibits an octahedral coordination by two pyridine ligands in cis arrangement and two (N1, N3)-2+ chelating pentaazadienide ions. The reaction of [HgI4]2 with the 1,5-di(tolyl)pentaazadienide anion in aqueous ammonia affords [Hg(p-tol-N5-tol)2] ( 4 ), which crystallizes from pyridine in form of [Hg(tol-N5-tol)2py] ( 5 ) with the space group P1 and a = 1176.2(4); b = 1203.1(3); c = 1295.6(5) pm; α = 100.77(3)°; β = 110.08(3)°; γ = 94.29(2)°; Z = 2. In 5 the Hg2+ cation is threefold coordinated by two monodentate (N3)-η1 pentaazadienid anions and one pyridine ligand. Within the N5 chains of the pentaazadienid anions of 3 and 5 localized N? N double bonds are found in the positions N1? N2 and N4? N5 with distances between 125 and 129 pm. 相似文献
7.
About the Structure and Reactivity of Diammonium Hexafluoromanganate(IV) Electrolytic oxidation of an aqueous suspension of MnF2 containing NH4F, and subsequent crystallization in 40% HF yields yellow crystals of (NH4)2MnF6. It crystallizes in the hexagonal K2MnF6 type structure with the space group P63mc and a = 5.903; c = 9.565 Å; Z = 2. With in situ powder diffraction studies it is shown, that (NH4)2MnF6 is gradually reduced in a NH3 atmosphere between 30 and 230 °C to afford (NH4)3MnF6, (NH4)2MnF5, and finally NH4MnF3. (NH4)3MnF6, thereby, forms a hitherto unknown cubic (a = 9.082 Å) high temperature modification with the cryolite type structure. Under N2 the thermal decomposition of (NH4)2MnF6 proceeds via NH4MnF4 to yield MnF2. 相似文献
8.
Gintaras Pivoriunas Ccilia Maichle‐Mssmer Simon Schwarz Joachim Strhle 《无机化学与普通化学杂志》2005,631(10):1743-1745
Synthesis and Crystal Structure of [(Ph3PAu)3NPPh3][PF6]2, a Gold(I) Phosphoraneiminato Complex The photolytic reaction of Ph3PAuN3 with Cr(CO)6 in THF yields the phosphoraneiminato complex [(Ph3PAu)3NPPh3]2+ in low yield as well as the cluster cation [(Ph3PAu)8]2+ as the main product. The phosphoraneiminato complex crystallizes from CH2Cl2 with [PF6]? ions as [(Ph3PAu)3NPPh3][PF6]2·CH2Cl2 in the triclinic space group with a = 1200.8(1), b = 1495.6(2), 2053.5(5), α = 86.97(2)°, β = 82.79(1)°, γ = 81.87(2)°, and Z = 2. The phosphoraneiminato ligand bridges through its N atom three Au atoms, which itself are connected to each other by weak aurophilic interactions. 相似文献
9.
Klaus van Benthem Stephan Krämer Wilfried Sigle Manfred Rühle 《Mikrochimica acta》2002,138(3-4):181-193
An understanding of the correlation between microstructures and properties of materials require the characterization of the
material on many different length scales. Often the properties depend primarily on the atomistics of defects, such as dislocations
and interfaces. The different techniques of transmission electron microscopy allow the characterization of the structure and
of the chemical composition of materials with high spatial resolution to the atomic level: high resolution transmission electron
microscopy allows the determination of the position of the columns of atoms (ions) with high accuracy. The accuracy which
can be achieved in these measurements depends not only on the instrumentation but also on the quality of the transmitted specimen
and on the scattering power of the atoms (ions) present in the analyzed column.
The chemical composition can be revealed from investigations by analytical microscopy which includes energy dispersive X-ray
spectroscopy, mainly quantitatively applied for heavy elements, and electron energy-loss spectroscopy. Furthermore, the energy-loss
near-edge structure of EELS data results in information on the local band structure of unoccupied states of the excited atoms
and, therefore, on bonding. A quantitative evaluation of convergent beam electron diffraction results in information on the
electron charge density distribution of the bulk (defect-free) material.
The different techniques are described and applied to different problems in materials science. It will be shown that nearly
atomic resolution can be achieved in high resolution electron microscopy and in analytical electron microscopy. Recent developments
in electron microscopy instrumentation will result in atomic resolution in the foreseeable future. 相似文献