全文获取类型
收费全文 | 1217篇 |
免费 | 153篇 |
国内免费 | 64篇 |
专业分类
化学 | 1024篇 |
晶体学 | 14篇 |
力学 | 40篇 |
综合类 | 2篇 |
数学 | 97篇 |
物理学 | 257篇 |
出版年
2023年 | 17篇 |
2022年 | 21篇 |
2021年 | 32篇 |
2020年 | 57篇 |
2019年 | 52篇 |
2018年 | 25篇 |
2017年 | 16篇 |
2016年 | 45篇 |
2015年 | 51篇 |
2014年 | 55篇 |
2013年 | 79篇 |
2012年 | 109篇 |
2011年 | 120篇 |
2010年 | 78篇 |
2009年 | 52篇 |
2008年 | 75篇 |
2007年 | 49篇 |
2006年 | 87篇 |
2005年 | 62篇 |
2004年 | 41篇 |
2003年 | 46篇 |
2002年 | 44篇 |
2001年 | 28篇 |
2000年 | 26篇 |
1999年 | 31篇 |
1998年 | 12篇 |
1997年 | 13篇 |
1996年 | 11篇 |
1995年 | 14篇 |
1994年 | 8篇 |
1993年 | 7篇 |
1992年 | 7篇 |
1991年 | 20篇 |
1990年 | 5篇 |
1989年 | 5篇 |
1988年 | 1篇 |
1987年 | 4篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1976年 | 1篇 |
1975年 | 4篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有1434条查询结果,搜索用时 15 毫秒
991.
Victor Udo Nna Ainul Bahiyah Abu Bakar Zaida Zakaria Zaidatul Akmal Othman Nur Asyilla Che Jalil Mahaneem Mohamed 《Molecules (Basel, Switzerland)》2021,26(11)
Diabetic nephropathy is reported to occur as a result of the interactions between several pathophysiological disturbances, as well as renal oxidative stress and inflammation. We examined the effect of Malaysian propolis (MP), which has anti-hyperglycemic, antioxidant and anti-inflammatory properties, on diabetes-induced nephropathy. Diabetic rats were either treated with distilled water (diabetic control (DC) group), MP (300 mg/kg b.w./day), metformin (300 mg/kg b.w./day) or MP + metformin for four weeks. We found significant increases in serum creatinine, urea and uric acid levels, decreases in serum sodium and chloride levels, and increase in kidney lactate dehydrogenase activity in DC group. Furthermore, malondialdehyde level increased significantly, while kidney antioxidant enzymes activities, glutathione level and total antioxidant capacity decreased significantly in DC group. Similarly, kidney immunoexpression of nuclear factor kappa B, tumor necrosis factor-α, interleukin (IL)-1β and caspase-3 increased significantly, while IL-10 immunoexpression decreased significantly in DC group relative to normal control group. Histopathological observations for DC group corroborated the biochemical data. Intervention with MP, metformin or both significantly mitigated these effects and improved renal function, with the best outcome following the combined therapy. MP attenuates diabetic nephropathy and exhibits combined beneficial effect with metformin. 相似文献
992.
Cycloartane glycosides from Cimicifuga dahurica. 总被引:1,自引:0,他引:1
Q W Zhang W C Ye W W Hsiao S X Zhao C T Che 《Chemical & pharmaceutical bulletin》2001,49(11):1468-1470
A new cycloartane bisdesmoside and two new trinorcycloartane glycosides, along with four known cycloartane compounds, were isolated from the rhizomes of Cimicifuga dahurica (Ranunculaceae). The structures of the new compounds were elucidated as 3-O-alpha-L-arabinopyranosyl cimigenol 15-O-beta-D-glucopyranoside, 24-hydroxy-12beta-acetoxy-25,26,27-trinorcycloartan-16,23-dione 3beta-O-alpha-L-arabinopyranoside, and 16alpha,24alpha-dihydroxy-12beta acetoxy-25,26,27-trinor-16,24-cyclocycloartan-23-one 3beta-O-alpha-L-arabinopyranoside by extensive NMR methods, FAB-MS, and hydrolysis. 相似文献
993.
994.
T. Toliński B. Andrzejewski G. Che?kowska J. Fr?ckowiak 《Journal of Physics and Chemistry of Solids》2006,67(4):751-755
The magnetic, electrical and electronic properties of the tetragonal ternary YbFe4Al8 compound have been investigated. This compound was supposed to be an antiferromagnetic superconductor due to the negative magnetization signal appearing at a low field of the field cooling mode, however, based on the measurements of the temperature dependence of magnetization and resistivity we do not confirm the presence of superconductivity in this material and we ascribe the negative magnetization to the complicated non-collinear magnetic structure. A switch to the antiferromagnetic order at about 150 K has been visible both on the M(T) and ρ(T) curves. The valence state of the Yb ions has been studied by X-ray photoemission spectroscopy. The valence band spectrum at the Fermi level exhibits the domination of the hybridized Yb(4f) and Fe(3d) states. 相似文献
995.
Two commercial turkey egg ovalbumins (TEOs) with different quantities of mannose, were further purified by reversed-phase high-performance liquid chromatography. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis for either of the purified glycoproteins showed one big wide band and one close small band. Capillary electrophoresis was used for the investigation of the separation of glycoforms of both glycoproteins. The best resolution of the glycoforms was obtained, reproducibly, with 100 mM borate, 1.8 mM 1,4-diaminobutane and pH 8.6 electrophoretic buffer. At least 13 glycoform peaks could be separated for either of the two glycoproteins. Their glycoform patterns were highly similar except for the conspicuous decrease in quantity of four glycoforms in the ovalbumin containing less mannose, compared to that of the other with more mannose. Coinjection electrophoresis of the two glycoproteins indicated that almost every glycoform peak of the former exactly overlapped with its corresponding glycoform peak of the latter. These results clearly indicated that the two TEOs possessed the same glycoform patterns but differed in quantity at least four glycoforms. It was found that the glycoform patterns were remarkably different between TEO and chicken egg ovalbumin. 相似文献
996.
997.
998.
Hari Prasad Rao Mohamed Ali Zanjanchi Pascale Massiani Denise Barthomeuf Suzanne Launay Anne Davidson Michel Che 《Research on Chemical Intermediates》1999,25(1):57-75
A progressive sintering of the porosity of both V-free and V-loaded AlPO4-5 samples is observed upon calcination in air at increasing temperatures. This sintering leads to the coexistence of porous
AlPO4-5 and dense tridymite. As established by cristallinity and pore volume measurements. the presence of vanadium decreases by
100 to 300°C the threshold temperature at which this sintering begins, in spite of the low V amount in the samples (V/(V+Al+P)
atomic ratio of 0.5–1%). This threshold temperature depends on the method used to introduce V (by hydrothermal synthesis,
under static conditions or agitation, and/or by grinding vanadia with a V-free AlPO4-5) and on the morphology of the AlPO4-5 crystals as observed by scanning electron microscopy. These factors are related to the dispersion of the V species within
the porosity. Since only very small amounts of intraporosity VIV species (VIV/VT<1%) are detected by ESR, whatever the extent of the Sintering which generates tridymite, it is concluded that the thermal
stability of V-loaded AlPO4-5 is determined by the dispersion of Vv species within the porosity. This conclusion is in line with earlier propositions made to explain the thermal behaviour of
V-loaded zeolites and V-contamined FCC catalysts. 相似文献
999.
Guey‐Sheng Liou Hung‐Ju Yen Ming‐Che Chiang 《Journal of polymer science. Part A, Polymer chemistry》2009,47(20):5378-5385
A series of near‐infrared (NIR) electrochromic aromatic poly(aryl ether)s containing N,N,N′,N′‐tetraphenyl‐p‐phenylenediamine (TPPA) moieties in the backbone were prepared from the high‐temperature polycondensation reactions of a biphenol monomer, 2,5‐bis(diphenylamino)hydroquinone, with difluoro compounds. The obtained polymers were readily soluble in many organic solvents and showed useful levels of thermal stability associated with high glass‐transition temperatures (182–205 °C) and high char yields (higher than 40% at 800 °C in nitrogen). The polymer films showed reversible electrochemical oxidation with high contrast ratio both in the visible range and NIR region, and also exhibited high coloration efficiency (CE), low switching time, and stability for electrochromic operation. The polyether TPPA‐a thin film revealed good CE in visible (CE = 217 cm2/C) and NIR (CE = 192 cm2/C) region with reversible electroactive stability (over 500 times within 5% loss relative to its initial injected charge). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5378–5385, 2009 相似文献
1000.
Xiao Ma Chao-Shan Da Lei Yi Ya-Ning Jia Qi-Peng Guo Li-Ping Che Feng-Chun Wu Jun-Rui Wang Wei-Ping Li 《Tetrahedron: Asymmetry》2009,20(12):1419-1424
Organocatalytic systems made up of six primary amine organocatalysts, derived from natural primary amino acids, in combination with 2,4-dinitrophenol (DNP) have proven to be efficient in the presence of brine without further addition of organic solvents. The system formed by 1f and DNP was the most efficient one; it can catalyze the direct aldol reaction with a broad range of ketones and aromatic aldehydes, giving the corresponding aldol products in high yields with up to nearly perfect diastereo- and enantioselectivities (up to 99/1 syn/anti, >99% ee). 相似文献