全文获取类型
收费全文 | 1689篇 |
免费 | 64篇 |
国内免费 | 8篇 |
专业分类
化学 | 1332篇 |
晶体学 | 31篇 |
力学 | 24篇 |
数学 | 171篇 |
物理学 | 203篇 |
出版年
2023年 | 9篇 |
2022年 | 11篇 |
2021年 | 14篇 |
2020年 | 23篇 |
2019年 | 31篇 |
2018年 | 17篇 |
2017年 | 21篇 |
2016年 | 39篇 |
2015年 | 36篇 |
2014年 | 41篇 |
2013年 | 97篇 |
2012年 | 113篇 |
2011年 | 115篇 |
2010年 | 55篇 |
2009年 | 68篇 |
2008年 | 116篇 |
2007年 | 108篇 |
2006年 | 101篇 |
2005年 | 94篇 |
2004年 | 95篇 |
2003年 | 82篇 |
2002年 | 65篇 |
2001年 | 12篇 |
2000年 | 29篇 |
1999年 | 13篇 |
1998年 | 24篇 |
1997年 | 23篇 |
1996年 | 18篇 |
1995年 | 15篇 |
1994年 | 7篇 |
1993年 | 10篇 |
1992年 | 17篇 |
1991年 | 12篇 |
1990年 | 12篇 |
1989年 | 12篇 |
1988年 | 7篇 |
1987年 | 16篇 |
1986年 | 6篇 |
1985年 | 14篇 |
1984年 | 14篇 |
1983年 | 17篇 |
1982年 | 20篇 |
1981年 | 12篇 |
1980年 | 24篇 |
1979年 | 15篇 |
1978年 | 14篇 |
1976年 | 11篇 |
1975年 | 8篇 |
1974年 | 5篇 |
1973年 | 8篇 |
排序方式: 共有1761条查询结果,搜索用时 15 毫秒
231.
Yoshihiro Ochi 《Proceedings of the American Mathematical Society》2006,134(1):31-37
We prove that for any abelian variety defined over a number field that is not isogenous to a product of CM elliptic curves, the pontrjagin dual of the Selmer group of the abelian variety over the trivializing extension has no nonzero pseudo-null submodules.
232.
Imanishi A Suzuki H Murakoshi K Nakato Y 《The journal of physical chemistry. B》2006,110(42):21050-21054
Dye-sensitized photocurrents at (100)-, (001)-, and (110)-cut TiO(2) rutile surfaces were increased by photoetching of TiO(2), but the increasing ratio strongly depended on the cut crystal faces and the illumination intensity for the photoetching. For the (110)-cut surface, the photocurrent increase was moderately large and in proportion to the increase in the surface area of TiO(2) induced by the photoetching, irrespective of the illumination intensity for the photoetching. On the other hand, the photocurrent increases for the (001)- and (100)-cut surfaces, especially that for the (001)-cut surface, were prominent and largely exceeded the increases in the surface area. The results were explained by taking into account the following factors: (1) The (001)- and (100)-cut surfaces were thermodynamically unstable in contrast to the (110)-cut surface and had thicker inactive surface layers (or higher densities of surface defects), produced by surface reconstruction during heat treatment of TiO(2) at 550 degrees C in a hydrogen atmosphere for getting n-type semiconductivity. (2) Photoetching not only increased the surface area through formation of nanoholes and grooves at the surface but also effectively removed the thin inactive surface layers (or surface defects). 相似文献
233.
[reaction: see text] Novel rod-shaped polycyano-oligo(phenyleneethynylene)s were synthesized by Pd cross-coupling reaction. Polycyano groups were found to greatly improve the emission efficiency (Phi(f)) of OPEs. By the end donor modification, we achieved the creation of very intense blue light-emitting fluorophore with the SMe group (Phi(f) = 0.972, log epsilon 4.89, lambda(em) 455 nm) and very intense yellow light-emitting fluorophore with the NMe(2) group (Phi(f) = 0.999, log epsilon 4.75, lambda(em) 555 nm). Contrasting Phi(f) solvent dependency of 6 and 7 and a linear relationship between Phi(f) and sigma(p)-X over the whole region of sigma(p)-X were also found. 相似文献
234.
A phosphorus-containing hybrid porphyrin was successfully prepared via the BF3-promoted dehydrative condensation between sigma4-phosphatripyrrane and 2,5-bis[hydroxy(phenyl)methyl]thiophene. The NMR and UV-vis absorption spectra, electrochemical measurements, and DFT calculations revealed that the sigma3-P,N2,S-hybrid porphyrin exhibits high aromaticity as an 18pi-electron system in terms of both geometric and magnetic criteria. [structure: see text] 相似文献
235.
A novel in-needle sample preparation device has been developed for the determination of volatile aldehydes in gaseous samples.
The needle device is designed for the gas chromatographic (GC) analysis of aldehydes and ketones commonly found in typical
in-house environments. In order to prepare the extraction device, a bundle of polymer-coated filaments was longitudinally
packed into a specially designed needle. Derivatization reactions were prompted by 2,4-dinitrophenylhydrazine (NDPH) included
in the needle, and so the aldehydes and ketones were derivatized to the corresponding hydrazones and extracted with the extraction
needle. A reproducible extraction needle preparation process was established, along with a repeatable derivatization/extraction
process that ensures the successful determination of aldehydes. The storage performance of the extraction needle was also
evaluated at room temperature for three days. The results demonstrate the successful application of the fiber-packed extraction
device to the preparation of a gaseous sample of aldehydes, and the future possibility of applying the extraction device to
the analysis of in-house environments. 相似文献
236.
Sonoda Y Hirayama F Arima H Yamaguchi Y Saenger W Uekama K 《Chemical communications (Cambridge, England)》2006,(5):517-519
We describe a novel approach for the selective isolation of Ostwald's intermediate metastable polymorphs occurring during an early stage of crystallization, by utilizing the inclusion complex formed with a cyclic oligosaccharide derivative, 2,6-di-O-methyl-beta-cyclodextrin. 相似文献
237.
Uzawa H Nagatsuka T Hiramatsu H Nishida Y 《Chemical communications (Cambridge, England)》2006,(13):1381-1383
Glucuronidase-catalyzed transglycosylation was examined by using 4-nitrophenyl beta-D-glucuronide (D-GlcA-O-pNP) as the glycosyl donor; when pNP 6-O-sulfo-beta-D-gluco- and D-galacto-pyranosides were used as the acceptors, a bovine enzyme was found to construct beta-D-GlcA-(1-3)-linkages with the 6-O-sulfo-sugars in both a site- and beta-selective way. 相似文献
238.
Imahori H Mitamura K Umeyama T Hosomizu K Matano Y Yoshida K Isoda S 《Chemical communications (Cambridge, England)》2006,(4):406-408
A silica microparticle has been successfully employed as a nanoscaffold to self-organize porphyrin and C60 molecules on a nanostructured SnO2 electrode which exhibits efficient photocurrent generation. 相似文献
239.
240.
Hiromitsu Terao Yoshihiko Kai Kazuyo Kita Yoshihiro Furukawa 《Hyperfine Interactions》2010,198(1-3):93-101
The crystals of 4-NH2PyHSbI4 (Py = C5H4N) have been investigated by means of 127I NQR, 1H NMR T 1 and DTA. The crystals can exist in two modifications of β and α(I) at room temperatures. The α(I)-phase is a metastable state which is obtained when the stable β form is heated. The α(I)-phase undergoes a first-order type phase transition of α(I) $\leftrightarrow \alpha $ (II) at 272 K (on heating), while the β-phase is stable down to 77 K. Four and two 127I (m = ±1/2 $\leftrightarrow \pm $ 3/2) NQR lines have been found for the β- and α(II)-phases, respectively. One half of them is assignable to the terminal I atom(s) and the other to the bridging I atom(s) in each phase. All the resonance lines of the α(II)-phase underwent a disappearance above ca. 240 K and no resonance line was observed in the α(I)-phase. The second moment M 2 value of 1H NMR spectra with 8 G2 at 290 K shows that the 4-NH2PyH?+? cations reside in the rigid lattice in the β-phase. In contrast, in the α(I)-phase the cation rotates about an axis more symmetric than pseudo threefold axis. The activation energy of 21 kJ mol???1 was estimated for the reorientational motion in the α(I)-phase from the 1H NMR T 1 measurements. The nature of phase transitions in the 4-NH2PyHSbI4 is discussed in comparison with that in 4-NH2PyHSbBr4. 相似文献