全文获取类型
收费全文 | 208篇 |
免费 | 12篇 |
专业分类
化学 | 142篇 |
晶体学 | 1篇 |
力学 | 5篇 |
数学 | 32篇 |
物理学 | 40篇 |
出版年
2023年 | 1篇 |
2022年 | 1篇 |
2021年 | 5篇 |
2020年 | 4篇 |
2019年 | 6篇 |
2018年 | 3篇 |
2017年 | 1篇 |
2016年 | 8篇 |
2015年 | 6篇 |
2014年 | 12篇 |
2013年 | 16篇 |
2012年 | 13篇 |
2011年 | 11篇 |
2010年 | 10篇 |
2009年 | 9篇 |
2008年 | 6篇 |
2007年 | 7篇 |
2006年 | 4篇 |
2005年 | 8篇 |
2004年 | 2篇 |
2003年 | 2篇 |
2002年 | 2篇 |
2001年 | 3篇 |
2000年 | 4篇 |
1999年 | 6篇 |
1998年 | 5篇 |
1997年 | 5篇 |
1996年 | 7篇 |
1995年 | 5篇 |
1994年 | 4篇 |
1993年 | 6篇 |
1992年 | 2篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 6篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1948年 | 1篇 |
1932年 | 1篇 |
1908年 | 1篇 |
1905年 | 2篇 |
1887年 | 1篇 |
排序方式: 共有220条查询结果,搜索用时 250 毫秒
141.
In this contribution, the model of the concrete deterioration due to the alkali silica reaction(ASR) at the microscale is set up. Based on a three-dimensional micro computer-tomography, a finite-element mesh is constructed at the micrometer length scale and 3D coupled Chemo-Themo-Mechanics model in the hardened cement paste(HCP) and computational homogenization of damage are addressed in this contribution. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
142.
Schieb H Weidlich S Schlechtingen G Linning P Jennings G Gruner M Wiltfang J Klafki HW Knölker HJ 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(48):14412-14423
Covalent coupling of β-secretase inhibitors to a raftophilic lipid anchor via a suitable spacer by using solid-phase peptide synthesis leads to tripartite structures displaying substantially improved inhibition of cellular secretion of the β-amyloid peptide (Aβ). Herein, we describe a series of novel tripartite structures, their full characterization by NMR spectroscopy and mass spectrometry, and the analysis of their biological activity in cell-based assays. The tripartite structure concept is applicable to different pharmacophores, and the potency in terms of β-secretase inhibition can be optimized by adjusting the spacer length to achieve an optimal distance of the inhibitor from the lipid bilayer. A tripartite structure containing a transition-state mimic inhibitor was found to be less potent on Aβ generation from Swedish-mutant amyloid precursor protein (APP) than from the wild-type protein. Moreover, our observations suggest that specific variants of Aβ are generated from wild-type APP but not from Swedish-mutant APP and are resistant to β-secretase inhibition. Efficient inhibition of Aβ secretion by tripartite structures in the absence of appreciable neurotoxicity was confirmed in a primary neuronal cell culture, thus further supporting the concept. 相似文献
143.
The reaction of the octachlorocyclotetraphosphazene, N4P4Cl8 (1), in three stoichiometries (1:1, 1:2 and 1:3) with the sodium derivative of the fluorinated diol, 2,2,3,3-tetrafluorobutane-1,4-diol (2), in THF solution at room temperature produced seven products, whose structures have been characterized by elemental analysis, mass spectrometry, 1H, 19F, 31P NMR spectroscopy and by X-ray crystallography, where suitable single crystals were obtained: the mono-spiro compound, N4P4Cl6(OCH2CF2CF2CH2O) (3), its ansa isomer (4), cis- and trans-bis-spiro derivatives N4P4Cl4(OCH2CF2CF2CH2O)2 (5 and 6), tris-spiro compound N4P4Cl2(OCH2CF2CF2CH2O)3 (7), its mono-spiro-bis-ansa isomer (8) and tetrakis-spiro compound N4P4(OCH2CF2CF2CH2O)4, (9). X-ray crystallographic studies confirmed that the structure of the mono-spiro-bis-ansa isomer (8) has been reported as a first example in the literature. The results of all reactions were compared with previous work on the reaction of hexachlorocyclotriphosphazene, N3P3Cl6 with the sodium derivative of the diol (2), in a 1:1.2 mole ratio in the in the same solvent, THF, and with the reaction of octafluorocyclotetraphosphazene, N4P4F8, with the silyl derivative of the diol (2), (Me3SiOCH2CF2)2, in a 1:0.4 mole ratio in THF. 相似文献
144.
Dr. Christopher S. Lancefield Bart Fölker Dr. Razvan C. Cioc Katarina Stanciakova Dr. Rosa E. Bulo Dr. Martin Lutz Dr. Marc Crockatt Prof. Pieter C. A. Bruijnincx 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(52):23686-23690
A novel route for the production of the versatile chemical building block phthalide from biorenewable furfuryl alcohol and acrylate esters is presented. Two challenges that limit sustainable aromatics production via Diels–Alder (DA) aromatisation—an unfavourable equilibrium position and undesired regioselectivity when using asymmetric addends—were addressed using a dynamic kinetic trapping strategy. Activated acrylates were used to speed up the forward and reverse DA reactions, allowing for one of the four DA adducts to undergo a selective intramolecular lactonisation reaction in the presence of a weak base. The adduct is removed from the equilibrium pool, pulling the system completely to the product with a fixed, desired regiochemistry. A single 1,2-regioisomeric lactone product was formed in up to 86 % yield and the acrylate activating agent liberated for reuse. The lactone was aromatised to give phthalide in almost quantitative yield in the presence of Ac2O and a catalytic amount of strong acid, or in 79 % using only catalytic acid. 相似文献
145.
B. V?lker P. Marton C. Els?sser M. Kamlah 《Continuum Mechanics and Thermodynamics》2011,23(5):435-451
To link the atomic level and the mesoscale within a knowledge-based multiscale modeling approach for ferroelectric materials,
a method is suggested to transfer results from first-principles calculations into a phase-field model. DFT calculations and
atomistic simulations are applied and provide a set of intrinsic and extrinsic material properties for PbTiO3 and tetragonal Pb(Zr0.5Ti0.5)O3. The Helmholtz free energy of the phase-field model that contains all crystallographic and domain wall information is discussed
in detail, and a sensitivity analysis is performed to identify the coefficients of the energy function. Then, a method is
developed to adjust the coefficients of the Helmholtz free energy solely based on results from first-principles calculations.
Full sets of adjusted energy coefficients for PbTiO3 and Pb(Zr0.5Ti0.5)O3 are presented and discussed, as well the limits of the suggested adjustment method. 相似文献
146.
147.
Tekgül Atakan Şarlar Kağan Küçük İlker 《Journal of Thermal Analysis and Calorimetry》2021,144(4):1109-1114
Journal of Thermal Analysis and Calorimetry - The structural, magnetic and magnetocaloric properties of $$\hbox {Ni}_{54}\hbox {Mn}_{14}\, \hbox {Ga}_{27}\hbox {Fe}_{5}$$ Heusler alloy as a... 相似文献
148.
In this note we give an elementary proof of the Fritz-John and Karush–Kuhn–Tucker conditions for nonlinear finite dimensional programming problems with equality and/or inequality constraints. The proof avoids the implicit function theorem usually applied when dealing with equality constraints and uses a generalization of Farkas lemma and the Bolzano-Weierstrass property for compact sets. 相似文献
149.
150.
Using a palladium(II)-catalyzed oxidative cyclization and a regioselective nickel-mediated prenylation as key steps, the first total synthesis of the 1-oxygenated carbazole alkaloid ekeberginine has been achieved in six steps and in 63% overall yield. 相似文献