全文获取类型
收费全文 | 878篇 |
免费 | 5篇 |
国内免费 | 6篇 |
专业分类
化学 | 584篇 |
晶体学 | 11篇 |
力学 | 10篇 |
数学 | 46篇 |
物理学 | 238篇 |
出版年
2020年 | 4篇 |
2019年 | 9篇 |
2018年 | 12篇 |
2017年 | 7篇 |
2016年 | 5篇 |
2015年 | 5篇 |
2014年 | 19篇 |
2013年 | 30篇 |
2012年 | 26篇 |
2011年 | 55篇 |
2010年 | 25篇 |
2009年 | 19篇 |
2008年 | 60篇 |
2007年 | 50篇 |
2006年 | 49篇 |
2005年 | 46篇 |
2004年 | 42篇 |
2003年 | 34篇 |
2002年 | 37篇 |
2001年 | 29篇 |
2000年 | 18篇 |
1999年 | 12篇 |
1998年 | 7篇 |
1997年 | 6篇 |
1996年 | 6篇 |
1995年 | 13篇 |
1994年 | 18篇 |
1993年 | 15篇 |
1992年 | 14篇 |
1991年 | 13篇 |
1990年 | 13篇 |
1989年 | 11篇 |
1988年 | 8篇 |
1987年 | 9篇 |
1986年 | 19篇 |
1985年 | 17篇 |
1984年 | 13篇 |
1983年 | 8篇 |
1982年 | 10篇 |
1981年 | 12篇 |
1980年 | 11篇 |
1979年 | 6篇 |
1978年 | 7篇 |
1977年 | 12篇 |
1976年 | 8篇 |
1975年 | 4篇 |
1974年 | 6篇 |
1973年 | 9篇 |
1972年 | 4篇 |
1967年 | 3篇 |
排序方式: 共有889条查询结果,搜索用时 109 毫秒
141.
The crystal structure of calcium adipate monohydrate, Ca(C6H8O4)·H2O, has been determined by single crystal X-ray diffraction study. The crystals are triclinic witha=5.8990(3),b=6.7985(5),c=10.8212(6)Å,=78.999(5),=81.831(5), and =82.971(5)°, space group P¯1,Z=2,V=419.65(8)Å3,d
m=1.59,d
c=1.600 Mg m–3. The structure was refined by full-matrix least-squares techniques toR=0.040,R
w=0.058 for 1283 reflections withI3(I). Ca is coordinated to seven oxygen atoms and the coordination polyhedron is best described as pentagonal bipyramid. The coordinations of the two carboxylate groups in adipate ion are quite different. One carboxylate group binds three different Ca ions forming a four-membered chelate ring with one Ca ion and unidentate bridge bonds to two other Ca ions. The other carboxylate group links to two Ca ions through unidentate bonds. The structure is highly polymeric, but with a layertype structure parallel to (001) with the hydrocarbon chains sandwiched between the polar regions consisting of Ca, carboxylate and water molecules.Certain commercial materials and equipment are identified in this paper to specify the experimental procedure. In no instance does such identification imply recommendation or endorsement by the National Institute of Standards and Technology or the ADA Health Foundation or that the material or equipment identified is necessarily the best available for the purpose. 相似文献
142.
T. Kimura T. Sato M. Hirota S. Takagi 《Journal of Thermal Analysis and Calorimetry》2008,92(2):381-389
Excess enthalpies of sixteen binary mixtures between one each of methyl methylthiomethyl sulfoxide (MMTSO) and dimethyl sulfoxide
(DMSO) and one of ketone {CH3CO(CH2)nCH3, n=0 to 6 and CH3COC6H5} have been determined at 298.15 K. All the mixtures showed positive excess enthalpies over the whole range of mole fractions.
Excess enthalpies of ketone+MMTSO or DMSO increased with increasing the number of methylene radicals in the methyl alkyl ketone
molecules. Excess enthalpies of MMTSO+ketone are smaller than those of DMSO+ketone for the same ketone mixtures. The limiting
excess partial molar enthalpies of the ketone, H
1
E,∞, in all the mixtures with MMTSO were smaller than those of DMSO. Linear relationships were obtained between limiting excess
partial molar enthalpies and the number of methylene groups except 2-propanone. 相似文献
143.
144.
145.
Hori T Peng X Aratani N Takagi A Matsumoto T Kawai T Yoon ZS Yoon MC Yang J Kim D Osuka A 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(2):582-595
Starting from 1,3-phenylene linked diporphyrin zinc(II) complex 2ZA, repeated stepwise Ag I-promoted coupling reactions provided linear oligomers from 2nZA up to 128ZA. Of these zigzag shaped porphyrin arrays, the Ag I-promoted intramolecular cyclization reaction of 2 nZA (n=5, 6, 8, 9, 12, and 16) under dilute conditions gave the corresponding cyclic porphyrin wheels C2nZA (n=5, 6, 8, 9, 12, and 16), whereas large arrays 2nZA (n=24, 32, and 48) did not provide cyclic porphyrin products. These large discrete porphyrin arrays and wheels were fully characterized by means of 1H NMR spectroscopy, MALDI-TOF mass spectrometry, UV/Vis absorption spectroscopy, GPC-HPLC analysis, and the scanning tunneling microscopy (STM) technique. The STM images of C12ZA and C18ZA reveal their large circular structures. In the cyclic structures of C2nZA in solution, however, the gradual decrease in fluorescence quantum yields and fluorescence lifetimes are observed, reflecting some conformational heterogeneities. Collectively, the present work provides an important contribution to the construction of fully covalently linked large cyclic arranged porphyrin arrays with ample electronic interactions as a model of light-harvesting antenna. 相似文献
146.
Fredrickson Takagi R Johnsson M Lidin S 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(11):3434-3441
Compounds containing lone-pair elements such as Te(IV) are very interesting from the structural point of view, as the lone-pair nonbonding regions create low-dimensional geometrical arrangements. We have synthesized two new compounds with these features-Ba(2)Cu(2)Te(4)O(11)Br(2) (I) and Ba(2)Cu(2)Te(4)O(11-delta)(OH)(2delta)Br(2) (II, delta approximately equal to 0.57)-as members of the AE-M-Te-O-X (AE=alkaline-earth metal, M=transition metal, X=halide) family of compounds by solid-state reactions. Preliminary single-crystal X-ray analysis indicated that compound I crystallizes in the orthorhombic system, but attempts at refinement proved unsatisfactory. Closer inspection of the reciprocal lattice revealed systematic, non-crystallographic absences that indicate twinning. The structure is in fact triclinic, space group C_1 (equivalent to P_1), with unit cell parameters (at 120 K) of a=10.9027(9), b=15.0864(7), c=9.379(2) A, beta=106.8947 degrees . It is layered and built from [TeO(3)E] tetrahedra, [TeO(3+1)E] trigonal bipyramids (where E is the lone pair of Te(IV)), [CuO(4)] squares and irregular [BaO(10)Br] polyhedra. The crystal structure of II shows the same basic structure as I but contains additional oxygen, probably in the form of OH groups. The presence of satellites reveals that ordering on this O site creates an incommensurate modulation, primarily affecting Br and Te. The modulated structure of II was solved in the triclinic superspace group X$\bar 1$(alphabetagamma)0 with the vector q approximately equal to1/16 c*. 相似文献
147.
Kanno K Igarashi E Zhou L Nakajima K Takahashi T 《Journal of the American Chemical Society》2008,130(17):5624-5625
Selective synthesis of linear trienes from three different alkynes was achieved in one-pot procedure using the Zr/Cu system. Zirconacyclopentadiene prepared from two different alkynes such as an alkyl-substituted alkyne and an aryl-substituted alkyne reacted with NCS gave chlorodienylzirconocene. It reacted with the third alkyne with electron-withdrawing groups in the presence of CuCl to afford the corresponding linear triene. 相似文献
148.
Inoue Y Kogure M Matsumoto K Hamashima H Tsukada M Endo K Tanaka T 《Chemical & pharmaceutical bulletin》2008,56(5):692-694
Silver loaded zeolite (Ag-Z) was previously found to have effective bactericidal activity against Escherichia coli. To understand the mechanisms of bactericidal activity of Ag-Z, role of light irradiation was focused and investigated in this study. In this study, we focused on light irradiation. Antibacterial assay and spectroscopic study revealed that light irradiation enabled Ag-Z to reduce dioxygen to form a reactive oxygen species, which led to bactericidal activity. These results indicate that the onset of bactericidal activity can be controlled by light irradiation. 相似文献
149.
We investigated hydration and swelling behavior of a solid state photoresponsive copolymer in water by using a quartz crystal microbalance technique with dissipation measurement (QCM-D technique). On the gold film electrode of a quartz resonator, we deposited a thin layer of a pNSp-NIPAAm, which is a poly(N-isopropylacrylamide) (pNIPAAm) polymer partially modified with a photochromic chromophore, 6-nitrospiropyran (NSp). Using QCM-D measurements, we found that at a temperature of 19 °C both water adsorption and changes in the viscoelasticity of the solid pNSp-NIPAAm layer were induced when pNSp-NIPAAm was irradiated by 365 nm ultraviolet light, which triggers the photoisomerization of the NSp chromophore and makes the structure of the chromophore hydrophilic. At temperatures between 25 and 35 °C, this photo-induced hydration was not observed. These observations suggest that the photoisomerization of the NSp chromophores triggered the photo-induced hydration only when pNIPAAm component is sufficiently hydrophilic, at a temperature of 19 °C. 相似文献
150.
Miyamoto C Suzuki K Iwatsuki S Inamo M Takagi HD Ishihara K 《Inorganic chemistry》2008,47(5):1417-1419
The rate constants for a boronate ion were determined for the first time using the reaction systems of 3-nitrophenylboronic acid (3-NO2PhB(OH)2) with ethylene glycol (EG) and propylene glycol (PG) in an alkaline solution: the rate constants (25 degrees C, I = 0.10 M) for the reactions of 3-NO2PhB(OH)3- are 1.2 M(-1) s(-1) (EG) and 1.5 M(-1) s(-1) (PG), which are at least 10(3) times smaller than those for the reactions of 3-NO 2PhB(OH)2 [1.0 x 10(4) M(-1) s(-1) (EG) and 5.8 x 10(3) M(-1) s(-1) (PG)]. 相似文献