全文获取类型
收费全文 | 452篇 |
免费 | 4篇 |
国内免费 | 1篇 |
专业分类
化学 | 243篇 |
晶体学 | 7篇 |
力学 | 19篇 |
数学 | 77篇 |
物理学 | 111篇 |
出版年
2022年 | 5篇 |
2021年 | 3篇 |
2019年 | 5篇 |
2018年 | 6篇 |
2017年 | 6篇 |
2015年 | 8篇 |
2014年 | 6篇 |
2013年 | 20篇 |
2012年 | 27篇 |
2011年 | 21篇 |
2010年 | 13篇 |
2009年 | 8篇 |
2008年 | 28篇 |
2007年 | 26篇 |
2006年 | 22篇 |
2005年 | 22篇 |
2004年 | 15篇 |
2003年 | 11篇 |
2002年 | 18篇 |
2001年 | 16篇 |
2000年 | 7篇 |
1997年 | 3篇 |
1996年 | 6篇 |
1994年 | 4篇 |
1993年 | 5篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 4篇 |
1988年 | 5篇 |
1987年 | 11篇 |
1986年 | 6篇 |
1985年 | 9篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 14篇 |
1980年 | 8篇 |
1979年 | 7篇 |
1978年 | 12篇 |
1977年 | 6篇 |
1976年 | 8篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1972年 | 3篇 |
1971年 | 5篇 |
1968年 | 2篇 |
1967年 | 3篇 |
1961年 | 2篇 |
排序方式: 共有457条查询结果,搜索用时 31 毫秒
101.
Kar S Sarkar B Ghumaan S Roy D Urbanos FA Fiedler J Sunoj RB Jimenez-Aparicio R Kaim W Lahiri GK 《Inorganic chemistry》2005,44(24):8715-8722
The bis-bidentate bridging function of gbha2- with N,O-/N,O- coordination was observed for the first time in the complex (mu-gbha)[Ru(III)(acac)2]2 (1). Density functional theory calculations of 1 yield a triplet ground state with a large (deltaE > 6000 cm(-1)) singlet-triplet gap. Intermolecular antiferromagnetic coupling was observed (J approximately -5.3 cm(-1)) for the solid. Complex 1 undergoes two one-electron reduction and two one-electron oxidation steps; the five redox forms [(mu-gbha)[Ru(acac)2]2]n (n = -2, -1, 0, +1, +2) were characterized by UV-vis-NIR spectroelectrochemistry (NIR = near infrared). The paramagnetic intermediates were also investigated by electron paramagnetic resonance (EPR) spectroscopy. The monoanion with a comproportionation constant K(c) of 2.7 x 10(8) does not exhibit an NIR band for a Ru(III)/Ru(II) mixed-valent situation; it is best described as a 1,4-diazabutadiene radical anion containing ligand gbha*3-, which binds two ruthenium(III) centers. A Ru(III)-type EPR spectrum with g1 = 2.27, g2 = 2.21, and g3 = 1.73 is observed as a result of antiferromagnetic coupling between one Ru(III) and the ligand radical. The EPR-active monocation (K(c) = 1.7 x 10(6)) exhibits a broad (deltanu(1/2) = 2600 cm(-1)) intervalence charge-transfer band at 1800 nm, indicating a valence-averaged (Ru3.5)2 formulation (class III) with a tendency toward class II (borderline situation). 相似文献
102.
Flow inhomogeneity and axial development in low-pressure chromatographic columns have been studied by magnetic resonance imaging velocimetry. The columns studied included (a) an 11.7-mm I.D. column packed with either 50 microm diameter porous polyacrylamide, or 99 or 780 microm diameter impermeable polystyrene beads, and (b) a 5-mm I.D. column commercially packed with 10 microm polymeric beads. The packing methods included gravity settling, slurry packing, ultrasonication, and dry packing with vibration. The magnetic resonance method used averaged apparent fluid velocity over both column cross-sections and fluid displacements greater than one particle diameter and hence permits assessment of macroscopic flow non-uniformities. The results confirm that now non-uniformities induced by the conical distributor of the 11.7-mm I.D. column or the presence of voids at the column entrance relax on a length scale of the column radius. All of the 11.7-mm I.D. columns examined exhibit near wall channeling within a few particle diameters of the wall. The origins of this behavior are demonstrated by imaging of the radial dependence of the local porosity for a column packed with 780 microm beads. Columns packed with the 99-microm beads exhibit reduced flow in a region extending from ten to three-to-five particle diameters from the wall. This velocity reduction is consistent with a reduced porosity of 0.35 in this region as compared to approximately 0.43 in the bulk of the column. Ultrasonicated and dry-packed columns exhibit enhanced flow in a region located between approximately eight and 20 particle diameters from the wall. This enhancement maybe caused by packing density inhomogeneity and/or particle size segregation caused by vibration during the packing process. No significant non-uniformities on length scales of 20 microm or greater were observed in the commercially packed column packed with 10 microm particles. 相似文献
103.
The structure of triphenylphosphine — (1 — (di(trifluoromethyl) — hydroxymethyl) — cyclopentadienyl) — (1,2 — di(carboxymethyl)ethylene — 1 — yl) — ruthenium (0) has been studied by single-crystal X-ray diffraction techniques. This compound, [C5 H4(CF3)2 COH] Ru(PPh3)C2(CO2Me)2H, crystallizes in the triclinic space groupP¯1 witha =10.131,b= 15.107,c= 10.798 Å, = 102.14, = 107.04, = 89.64° andZ = 2. The structure was refined by block-diagonal least-squares methods to a finalR value of 0.042, including hydrogen atoms. The compound contains a dicarboxymethylethylene ligand coordinated to ruthenium both through a ketonic oxygen and through a metal--carbon -bond. An intramolecular hydrogen bond is observed. Details of the structure are reported, and the structures of several Ru(0) complexes are compared. 相似文献
104.
105.
106.
N. Kalaiselvi P. Periasamy R. Thirunakaran B. Ramesh Babu T. Prem Kumar N. G. Renganathan M. Raghavan N. Muniyandi 《Ionics》2001,7(4-6):451-455
Layered transition metal oxides of the formula LiMO2 have good lithium insertion properties for which reason LiCoO2 and LiNiO2 have been exploited in practical lithium rocking chair batteries. Another member of the LiMO2 series, LiFeO2, should be an attractive cathode material considering the cheapness and environment-friendliness of iron compounds. Its rock-salt
structure, however, does not allow significant amounts of lithium to be reversibly intercalated in its structure. Synthesis
of layered LiFeO2 and study of its lithium intercalating properties have been of limited success. Therefore, an attempt has been made here
to study LiCo1−yFeyO2 solid solutions (0 ≤ y ≤ 0.4) as prospective cathode materials. XRD, FTIR, Atomic absorption spectroscopy, Particle size
and Surface area analysis were carried out in this regard towards the physical characterization of the entire series of LiCo1−yFeyO2 compounds. The electrochemical discharge capacity of these materials is explained as a function of the iron content. 相似文献
107.
D. Yebassa S. Balakrishnan E. Feresenbet D. Raghavan P. R. Start S. D. Hudson 《Journal of polymer science. Part A, Polymer chemistry》2004,42(6):1310-1321
The primary objective of this study was to improve montmorillonite clay‐platelet separation in vinyl ester resin matrix by organically modifying the nanoclay platelet with a partially reactive onium salt. The reactive onium salt (ω‐undecylenyl amine hydrochloride) was synthesized from commercial ω‐undecylenyl alcohol through a series of synthetic conversions. Nonreactive onium salt (undecyl amine hydrochloride) was made from commercial undecyl amine. These salts were characterized with 1H and 13C NMR and Fourier transform infrared techniques. The relative amounts of exfoliated, intercalated, and as‐treated clay and the size of the clay particle aggregates depended significantly on the composition of clay and the processing conditions. When the clay was ion‐exchanged with a mixture of reactive and nonreactive onium salts, a partially exfoliated vinyl ester resin polymer nanocomposite was formulated. The addition of a comonomer styrene and high‐intensity ultrasonic mixing produced vinyl ester nanocomposite with the highest degree of clay‐platelet exfoliation. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1310–1321, 2004 相似文献
108.
The interaction of two commercially available phosphate ester dispersants with calcined alumina has been investigated using the techniques of flow calorimetry and electrophoresis. Flow calorimetric experiments have shown that these dispersants chemically interact with the surface of calcined alumina. The electrical charging of alumina particles in an iso-octane solution containing a phosphate ester indicates that an acid-base interaction mechanism is operative in this system. 相似文献
109.
A previously described procedure for the determination of the positions of coupling in the dimeric one-electron reduction products of 1-alkylpyridinium ions has been extended to the examination of the coupling positions in the dimeric species resulting from one-electron reduction of ring-substituted 1-alkylpyridinium ions. 相似文献
110.