全文获取类型
收费全文 | 787篇 |
免费 | 9篇 |
国内免费 | 1篇 |
专业分类
化学 | 635篇 |
晶体学 | 15篇 |
力学 | 2篇 |
数学 | 58篇 |
物理学 | 87篇 |
出版年
2021年 | 4篇 |
2019年 | 7篇 |
2016年 | 9篇 |
2015年 | 8篇 |
2014年 | 9篇 |
2013年 | 56篇 |
2012年 | 21篇 |
2011年 | 36篇 |
2010年 | 15篇 |
2009年 | 24篇 |
2008年 | 42篇 |
2007年 | 28篇 |
2006年 | 30篇 |
2005年 | 38篇 |
2004年 | 26篇 |
2003年 | 33篇 |
2002年 | 35篇 |
2001年 | 5篇 |
2000年 | 11篇 |
1999年 | 11篇 |
1998年 | 14篇 |
1997年 | 8篇 |
1996年 | 15篇 |
1995年 | 4篇 |
1994年 | 7篇 |
1993年 | 4篇 |
1992年 | 6篇 |
1991年 | 12篇 |
1990年 | 7篇 |
1989年 | 10篇 |
1988年 | 7篇 |
1987年 | 7篇 |
1986年 | 4篇 |
1985年 | 20篇 |
1984年 | 18篇 |
1983年 | 12篇 |
1982年 | 20篇 |
1981年 | 15篇 |
1980年 | 27篇 |
1979年 | 23篇 |
1978年 | 19篇 |
1977年 | 23篇 |
1976年 | 5篇 |
1975年 | 13篇 |
1974年 | 7篇 |
1973年 | 8篇 |
1972年 | 3篇 |
1971年 | 3篇 |
1960年 | 2篇 |
1958年 | 3篇 |
排序方式: 共有797条查询结果,搜索用时 343 毫秒
731.
Romani AP Machado AE Hioka N Severino D Baptista MS Codognoto L Rodrigues MR de Oliveira HP 《Journal of fluorescence》2009,19(2):327-332
Potentially useful stead-state fluorimetric technique was used to determine the critical micellar concentrations (CMC(1) and CMC(2)) for two micellar media, one formed by SDS and the other by SDS/Brij 30. A comparative study based on conductimetric and surfacial tension measurements suggests that the CMC(1) estimated by the fluorimetric method is lower than the value estimated by these other techniques. Equivalent values were observed for SDS micelles without Brij 30 neutral co-surfactant. The use of acridine orange as fluorescent probe permitted to determine both CMC(1) and CMC(2). Based on it an explanation on aspects of micelle formation mechanism is presented, particularly based on a spherical and a rod like structures. 相似文献
732.
Ultrafast temperature rise after the deactivation of the electronically excited state of 2-hydroxybenzophenone in various solvents is investigated by two photothermal techniques; temperature lens and acoustic peak delay methods, and by the population grating technique. The results from these methods show that the thermalization process takes place by two phases; fast (<1 ps) and rather slow (30 ps) processes. From the solvent dependence of the thermalization rate, we suggest that these processes are related with the intermolecular interaction and the solvation structure around the photoexcited molecules. 相似文献
733.
Yoshiyuki Kani Shigeru Ohba Sayo Ito Yuzo Nishida 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(6):e233-e235
The four title CuII compounds are chloro[(2‐furylmethyl)bis(2‐pyridylmethyl)amine‐N,N′,N′′]copper(II) perchlorate, [CuCl(C17H17N3O)]ClO4, (I), chloro{2‐[bis(2‐pyridylmethyl)amino]ethanolato‐N,N′,N′′,O}copper(II) hemi[tetrachlorocopper(II)], [CuCl(C14H17N3O)][CuCl4]1/2, (II), chloro[(2‐morpholinoethyl)bis(2‐pyridylmethyl)amine‐N,N′,N′′,N′′′]copper(II) perchlorate, [CuCl(C18H24N4O)]ClO4, (III), and chloro[(2‐piperidinylethyl)bis(2‐pyridylmethyl)amine‐N,N′,N′′,N′′′]copper(II) hexafluorophosphate, [CuCl(C19H26N4)]PF6, (IV). They have tripodal potentially tetradentate ligands. In (I), the O atom of the furan moiety weakly coordinates to the Cu atom at a distance of 2.750 (3) Å. 相似文献
734.
Noboru Ohtani Masakazu Katsuno Takashi Aigo Tatsuo Fujimoto Hiroshi Tsuge Hirokatsu Yashiro Masatoshi Kanaya 《Journal of Crystal Growth》2000,210(4):613-622
Surface topography of the {0 0 0 1} facet plane of as-grown 6H- and 4H-SiC crystals was studied ex situ by Nomarski optical microscopy (NOM) and atomic force microscopy (AFM). The surface polarity and the polytype of grown crystals largely affect the growth surface morphology of SiC{0 0 0 1} via differences in several thermodynamic and kinetic parameters. NOM observations revealed giant steps of a few micrometers in height on the {0 0 0 1} growth facet, and it was found that a morphological transition of the growth facet occurred when the growth conditions were changed. AFM imaging of the stepped structure of SiC{0 0 0 1} detected steps of height equal to the unit c-lattice parameter (c=1.512 nm for 6H-SiC and 1.005 nm for 4H-SiC). They are fairly straight and very regularly arranged, giving rise to equidistant step trains. Upon nitrogen doping, these regular step trains on the 6H-SiC(0 0 0
)C and 4H-SiC(0 0 0
)C surfaces became unstable: the equidistant step trains were transformed into meandering macrosteps of height greater than 10 nm. In this paper, we discuss the mechanism of macrostep formation (step bunching) on the SiC{0 0 0 1} surfaces through the consideration of the interplay between step energetics (repulsive step interaction) and kinetics (asymmetric step kinetics) on the growing crystal surface and elucidate how they affect the growth surface morphology of the SiC{0 0 0 1} facet. 相似文献
735.
Yang Y Lowry M Schowalter CM Fakayode SO Escobedo JO Xu X Zhang H Jensen TJ Fronczek FR Warner IM Strongin RM 《Journal of the American Chemical Society》2006,128(43):14081-14092
The synthesis of new benzo[a]- and [b]xanthene dye frameworks is described. A unique benzo[a]xanthene, seminaphtho[a]fluorone (SNAFR-1), is studied in a variety of media. The optimization of solution parameters and excitation wavelengths allows SNAFR-1 to display red, green, and blue emission bands of approximately equal intensities and also to produce white light. Ratiometric red (anion) and green (neutral) emissions are observed upon varying solution pH. A pH-independent violet-blue emission band is due to the addition of nucleophiles to the benzylic carbon of SNAFR-1. 相似文献
736.
Kambe N Inoue T Takeda T Fujiwara S Sonoda N 《Journal of the American Chemical Society》2006,128(39):12650-12651
Dimetalated amides 1 (Y = O) were generated as the synthons of carbamoyllithiums 2 (Y = O) by the reaction of isocyanates with iBu2AlTenBu and a subsequent tellurium-lithium exchange reaction. A series of amide derivatives 3 (Y = O) were obtained by the trapping of dianion 1 with electrophiles. This transformation can be successfully applied to the generation and trapping of thiocarbamoyllithium synthons 1 (Y = S) as well as to the nucleophilic introduction of the parent carbamoyl moiety H2NC(O). 相似文献
737.
Jiang S Escobedo JO Kim KK Alptürk O Samoei GK Fakayode SO Warner IM Rusin O Strongin RM 《Journal of the American Chemical Society》2006,128(37):12221-12228
Several discreet sugar-boronate complexes exist in solution. This is due to the complex equilibria between isomeric species of even the simplest monosaccharides. In the current investigation, we determine the regio- and stereochemical features of the various equilibrating sugar isomers that induce signal transduction in boronic acid chemosensors such as 1 as well as 2 and 3. We present a unique example of a chemosensor (1) that is selective for ribose, adenosine, nucleotides, nucleosides, and congeners. As a result of this study, we are able to predict and achieve selective fluorescence and colorimetric responses to specific disaccharides as a consequence of their terminal sugar residue linkage patterns and configurations. We also find that the combined use of chemosensors exhibiting complementary reactivities may be used cooperatively to obtain enhanced selectivity for ribose and rare saccharides. 相似文献
738.
Three metal complexes, [M(II)Cl2(4NOPy-OMe)2] (M = Cu (1), Ni (2), and Co (3)), were prepared by mixing the corresponding metal chloride and 4-(N-tert-butyloxyamino)-2-(methoxymethylenyl)pyridine, 4NOPy-OMe, in 1:2 ratio. Complex 1 has two structures (complexes A and B) with similar coordination geometries, compressed octahedrons. In the crystal structure, complexes A and B locate alternately in short distances (C(radical)...C(beta) = 3.17 and 3.23 A) to form a 1-D chain structure. Complexes 2 and 3 are isomorphous and have a slightly distorted octahedral structure. In the crystal structure, both complexes have intermolecular short contacts (C(radical)...C(alpha) = 3.46 and 3.52 A for 2 and 3, respectively) to form the 2-D structures. The temperature dependence of the chi(mol)T values for the three complexes indicated that the magnetic interactions between the radicals and the metal ions within the complexes were ferromagnetic. By fitting a modified Fisher 1-D model to the data of the chi(mol)T vs T plot for 1, we estimated the intra- and intermolecular (intrachain) exchange coupling constants to be J1/kB = 60.2 and J2/kB = -7.02 K, respectively. On the other hand, complexes 2 and 3 showed steep increases of the chi(mol)T value below ca. 3 K, indicating that the long-range magnetic ordering is operating. The 1/chi(mol) vs T plot for 2 was analyzed by a Curie-Weiss model to give theta = 6.25 K and C = 2.02 cm3 K mol(-1) with g(Ni) = 2.25. Complex 3 was investigated in more detail using an orientated sample. Magnetic behavior strongly depends on the direction of the applied field, in which the c axis perpendicular to the ab plane is an easy axis for magnetization. Direct current (dc) and alternating current (ac) magnetic susceptibility measurements revealed that complex 3 had a magnetic phase transition of T(c) = 2.14 K and exhibited a glasslike magnetic behavior below T(c). 相似文献
739.
Kitamura N Sakuda E Yoshizawa T Iimori T Ohta N 《The journal of physical chemistry. A》2005,109(33):7435-7441
Electroabsorption and electrofluorescence spectroscopies were conducted for tri-9-anthrylborane (TAB) doped in poly(methyl methacrylate) films (1.0 mol %) to reveal the spectroscopic and excited-state properties of the compound. TAB showed three distinct absorption bands: bands I [(19 - 25) x 10(3) cm(-1)], II [(25-31) x 10(3) cm(-1)], and III (>31 x 10(3) cm(-1)). The electroabsorption spectrum demonstrated that the electronic transitions in bands I and III accompanied electric dipole moment changes (Deltamu), while the change in the molecular polarizability contributed mainly to electroabsorption band II. Because of the similarities of the electroabsorption spectrum of band II with that of anthracene itself, band II was assigned to the electronic transition to the locally excited (LE) state of the anthryl group. On the other hand, bands I and III were best described by the electronic transitions to the excited charge-transfer (CT) states. The study demonstrated furthermore that the Deltamu value of TAB accompanied by the lowest-energy electronic transition was as large as 7.8 D, which agreed very well with that determined by the solvent dependences of the absorption and fluorescence maximum energies of TAB (approximately 8.0 D, ref 1): Deltamu = 7.8-8.0 D. The results proved explicitly that the excited state of TAB was localized primarily on the p orbital of the boron atom. Despite the dipole moment change (Deltamu = 7.8-8.0 D) for the lowest-energy electronic transition (band I), the electrofluorescence of TAB accompanied the change in the molecular polarizability. The spectroscopic and excited-state properties of TAB including the curious behavior of the electrofluorescence spectrum as mentioned above were discussed on the basis of theoretical considerations. 相似文献
740.