全文获取类型
收费全文 | 1511篇 |
免费 | 57篇 |
国内免费 | 5篇 |
专业分类
化学 | 1107篇 |
晶体学 | 9篇 |
力学 | 32篇 |
数学 | 164篇 |
物理学 | 261篇 |
出版年
2023年 | 11篇 |
2022年 | 48篇 |
2021年 | 69篇 |
2020年 | 44篇 |
2019年 | 54篇 |
2018年 | 36篇 |
2017年 | 32篇 |
2016年 | 57篇 |
2015年 | 52篇 |
2014年 | 77篇 |
2013年 | 101篇 |
2012年 | 125篇 |
2011年 | 143篇 |
2010年 | 78篇 |
2009年 | 76篇 |
2008年 | 89篇 |
2007年 | 84篇 |
2006年 | 82篇 |
2005年 | 47篇 |
2004年 | 47篇 |
2003年 | 34篇 |
2002年 | 28篇 |
2001年 | 14篇 |
2000年 | 15篇 |
1999年 | 13篇 |
1998年 | 5篇 |
1997年 | 16篇 |
1996年 | 7篇 |
1995年 | 7篇 |
1994年 | 9篇 |
1993年 | 5篇 |
1992年 | 11篇 |
1991年 | 5篇 |
1990年 | 3篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1976年 | 3篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1969年 | 1篇 |
1965年 | 2篇 |
排序方式: 共有1573条查询结果,搜索用时 15 毫秒
261.
A. Magnus G. Carvalho F. Garcia P.J. von Ranke G.D. Loula A.A. Coelho F.C.G. Gandra 《Journal of magnetism and magnetic materials》2009,321(19):3014-3018
In this work, we report the theoretical and experimental investigations on the magnetic and magnetocaloric properties for Gd0.5Pr0.5Al2 compound in different magnetic fields. The magnetization features indicate that Gd0.5Pr0.5Al2 is ferrimagnetic at low temperatures. We also present data from X-ray magnetic circular dichroism (XMCD) experiments for this compound, with which we have confirmed that the magnetic moments of the Pr ions are antiparallel to the magnetic moments of the Gd ions. The magnetocaloric parameters, ΔTS and ΔST, were obtained from calorimetric data and both curves present normal and inverse magnetocaloric effect. A theoretical model for ferrimagnetic coupling, including the crystalline electrical field anisotropy, was used to describe the ΔTS and ΔST experimental results. 相似文献
262.
263.
In this work we perform an ab initio study of the electric field gradient (EFG) at the nucleus of Fe impurities in crystalline SnO. The Augmented Plane Waves plus Local Orbitals method is used to obtain the electronic structure of the doped system and the atomic relaxations introduced by the impurities in the SnO host in a fully self-consistent way. Most calculations are performed assuming that Fe ions replace the Sn atoms of the structure, in some cases including oxygen vacancies in order to discuss their role in the hyperfine interactions and in determining the local structure around Fe impurities. The case of interstitial Fe sites is also considered. Our predictions are compared with available Müssbauer spectroscopy results and also with theoretical and experimental results obtained for rutile SnO2 and TiO2. 相似文献
264.
Chirleanny M. Mendes Marília A. Brito Tatiana S. Porto Ana L. F. Porto Ranilson S. Bezerra Luiz B. CarvalhoJr. Ana M. A. Caneiro-Leão Maria G. Carneiro-da-Cunha 《Chemical Papers》2009,63(6):662-669
Intestine proteases of Nile tilapia (Oreochromis niloticus) were partially purified by heat treatment (purification factor of 3.5, enzyme activity remained almost constant) to reach the maximum activity and stability within an alkaline pH range of 7.2–11.0. The optimum temperature and stability over a 120 min period were found to be at 55°C and at 35–45°C, respectively. The proteases’ activity was not affected by a 1 vol. % saponin surfactant, inactivated by 0.01 g mL?1 sodium dodecylsulphate after 120 min, and it remained stable for 30 min in a 5 vol. % and 10 vol. % hydrogen peroxide solutions. The proteases were slightly activated by Ca2+, Mg2+, and K+ and the substrate most effectively hydrolysed was casein (40.0 U mg?1). A 24 full factorial design used to evaluated the influence of independent variables showed that the enzyme extract, detergent concentration and the incubation time had a significant influence on the enzymatic activity. The best conditions to be used concerning detergent additive were found with 0.3 mg mL?1 of protein and 3.0 mg mL?1 of detergent for 30 min in the presence of Astrus® detergent. 相似文献
265.
Fifere Adrian Tania Budtova Elena Tarabukina Mariana Pinteala Spulber Mariana Cristian Peptu Valeria Harabagiu Bogdan C. Simionescu 《Journal of inclusion phenomena and macrocyclic chemistry》2009,64(1-2):83-94
Carboxyl modified γ-cyclodextrin (CDSA) with a substitution degree of about 9.5 was prepared by the esterification of γ-cyclodextrin (CD) with succinic anhydride in pyridine at 90 °C. The chemical composition and the structure of CDSA were characterized by FT-IR, MALDI-TOF, X-ray diffraction pattern, potentiometric titration and TGA. Modified and native γ-cyclodextrin associate with fullerene (C60) in DMF-toluene mixture resulting 1:1 CDSA:C60 and CD:C60 inclusion complexes. Aqueous solutions of native cyclodextrin, carboxyl-modified cyclodextrin and their inclusion complexes with C60 were used as microgel solvent (or swelling agent) for controlled release application. The release of solutions was induced by shear stress and demonstrated using rheo-optical set-up. 相似文献
266.
Ferreira MC Gameiro J Nagib PR Brito VN Vasconcellos Eda C Verinaud L 《Photochemistry and photobiology》2009,85(1):227-233
The effect of HeNe laser on the extracellular matrix deposition, chemokine expression and angiogenesis in experimental paracoccidioidomycotic lesions was investigated. At days 7, 8 and 9 postinfection the wound of each animal was treated with a 632.8 nm HeNe laser at a dose of 3 J cm(-2). At day 10 postinfection, the wounds were examined by using histologic and immunohistochemical methods. Results revealed that laser-treated lesions were lesser extensive than untreated ones, and composed mainly by macrophages and lymphocytes. High IL-1beta expression was shown in the untreated group whereas in laser-treated animals the expression was scarce. On the other hand, the expression of CXCL-10 was found to be reduced in untreated animals and quite intensive and well distributed in the laser-treated ones. Also, untreated lesions presented vascular endothelial growth factor (VEGF) in a small area near the center of the lesion and high immunoreactivity for hypoxia-inducible factor-1 (HIF-1), whereas laser-treated lesions expressed VEGF surrounding blood vessels and little immunoreactivity for HIF-1. Laser-treated lesions presented much more reticular fibers and collagen deposition when compared with the untreated lesion. Our results show that laser was efficient in minimizing the local effects observed in paracoccidioidomycosis and can be an efficient tool in the treatment of this infection, accelerating the healing process. 相似文献
267.
Manuel A.V. Ribeiro da Silva Ana I.M.C. Lobo Ferreira Joana I.T.A. Cabral Ana Filipa L.O.M. Santos Ana Rita G. Moreno Tiago L.P. Galvão Inês M. Rocha Paula M.V. Fernandes Sílvia Q. Salgueiro Vanessa A.F. de Moura Isabel M.S.C. Oliveira Paula C. Cotelo Mariana R.A. Ribeiro 《The Journal of chemical thermodynamics》2009,41(9):984-991
268.
André Romero da Silva Natalia Mayumi Inada Daniel Rettori Mariana Ozello Baratti Anibal Eugenio Vercesi Renato Atilio Jorge 《Journal of photochemistry and photobiology. B, Biology》2009,94(2):101-112
In(III)-meso-tetraphenylporphyrin (InTPP) was encapsulated into nanoparticles (smaller than 200 nm) of poly(d,l-lactide-co-glycolide) (PLGA) using the emulsification–evaporation technique. The photodynamic efficacy of InTPP-loaded nanoparticles and its cellular uptake was investigated with LNCaP prostate tumour cells, in comparison with the free InTPP. The effects of incubation time (1–3 h), drug concentration (1.8–7.7 μmol/L) and incident light dose (15–45 J/cm2) with both encapsulated and free InTPP were studied. The type of cell death induced by the photochemical process using both encapsulated and free InTPP was also investigated. Cell viability was reduced more significantly with increasing values of these effects for InTPP-loaded nanoparticles than with the free drug. The cellular death induced by both encapsulated and free InTPP was preponderantly apoptotic. Confocal laser scanning microscopy data showed that the InTPP-loaded nanoparticles, as well free InTPP, were localized in the cells, and always in the perinuclear region. Encapsulated InTPP was measured by the intensity of fluorescence intensity of cell extracts and was three times more internalized into the cells than was the free InTPP. Electron paramagnetic resonance experiments corroborated the participation of singlet oxygen in the photocytotoxic effect of nanoparticles loaded with InTPP. 相似文献
269.
Mariana Macías-Alonso Nuria Esturau-Escofet Marcos Flores-Álamo Martín A. Iglesias-Arteaga Rafael Moreno-Esparza 《Journal of chemical crystallography》2011,41(10):1476-1482
Abstract
The crystal structure together with unambiguous assignation of 1H and 13C NMR signals of 3-epismilagenin acetate 4 and 23-oxo-3-epismilagenin acetate 5 are described. Compound 4, crystallized as orthorhombic system a = 10.535(1) ?, b = 13.775 (1) ?, c = 18.347 (1) ?, α = β = γ = 90°; with space group P2 1 2 1 2 1 ; while compound 5 crystallized as a monoclinic system a = 10.380(1) ?, b = 7.327(1) ?, c = 17.881(1) ?, α = γ = 90°, β = 99.56(1)°, with a space group P2 1 . The presence a carbonyl group at C(23) in compound 5 produces a significant deviation from the chair conformation observed in compound 4. The effects of the side chain modifications on the puckering parameters derived from are discussed. 相似文献270.
Mariana Antonova Anjan Biswas 《Communications in Nonlinear Science & Numerical Simulation》2009,14(3):734-748
The soliton perturbation theory is used to study the solitons that are governed by the generalized Korteweg–de Vries equation in the presence of perturbation terms. The adiabatic parameter dynamics of the solitons in the presence of the perturbation terms are obtained. 相似文献