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61.
We study the asymptotic behaviour of the trajectories of the second order equation ${\ddot{x}(t)+\gamma \dot{x}(t)+\nabla\phi(x(t))+\varepsilon(t)x(t)=g(t)}We study the asymptotic behaviour of the trajectories of the second order equation [(x)\ddot](t)+g[(x)\dot](t)+?f(x(t))+e(t)x(t)=g(t){\ddot{x}(t)+\gamma \dot{x}(t)+\nabla\phi(x(t))+\varepsilon(t)x(t)=g(t)} , where γ > 0, g ? L1([0,+¥[;H){g \in L^1([0,+\infty[;H)}, Φ is a C
2 convex function and e{\varepsilon} is a positive nonincreasing function. 相似文献
62.
63.
Th. Abdel‐Moghny S. M. Desouky M. Ramzi 《Journal of Dispersion Science and Technology》2013,34(3):397-405
This work pertains to study the asphaltenes aggregates' settling behavior of crude oil in absence and presence of oil‐soluble surfactants including long‐chain fatty acid in the form of amidation and estrification. First, the onset points as a function of light absorbed asphaltenes aggregates were quantified before and after adding asphaltenes dispersants using ultra violet spectroscopy, and the photograph fractal‐like aggregate structures were quantified using Carl Zeiss Trinocular microscope. Second the shear rates against shear stress induced aggregation were also measured in absence and presence of different concentrations of asphaltenes dispersants using Brookfield digital rheometer model LVDV‐III+. The results reviled that the asphaltenes aggregates are found to depend on toluene–heptane ratios. In absence of dispersant the accumulated and aggregates clusters of asphaltenes are formed at heptane: toluene ratio of 50∶50. Whereas, in the presence of dispersant the asphaltenes are solvated at heptane: toluene ratio of 60∶40, followed by appearance of stronger and dots aggregates clusters at a ratio of 70∶30, and finally, a larger aggregates growing at heptane: toluene ratio of 80∶20. The dispersant solvates the asphaltenes and maintains them in solution, while their surface activity remains high. This means that the dispersant apparently functioned well in decreasing the degree of flocculation and precipitation beyond the critical micelle concentration (CMC) of asphaltenes at 0.0027 g/L. Also, the reduction in the viscosity in presence of dispersant suggests that the asphaltenes aggregates are highly porous and very fragile. 相似文献
64.
Rami W. Chakroun Alexandra Sneider Caleb F. Anderson Feihu Wang Pei‐Hsun Wu Denis Wirtz Honggang Cui 《Angewandte Chemie (International ed. in English)》2020,59(11):4434-4442
Self‐assembly of peptide‐based building units into supramolecular nanostructures creates an important class of biomaterials with robust mechanical properties and improved resistance to premature degradation. Yet, upon aggregation, substrate–enzyme interactions are often compromised because of the limited access of macromolecular proteins to the peptide substrate, leading to either a reduction or loss of responsiveness to biomolecular cues. Reported here is the supramolecular design of unsymmetric reverse bolaamphiphiles (RBA) capable of exposing a matrix metalloproteinase (MMP) substrate on the surface of their filamentous assemblies. Upon addition of MMP‐2, these filaments rapidly break into fragments prior to reassembling into spherical micelles. Using 3D cell culture, it is shown that drug release is commensurate with cell density, revealing more effective cell killing when more cancer cells are present. This design platform could serve as a cell‐responsive therapeutic depot for local chemotherapy. 相似文献
65.
The reaction of 1, 2-dibromo-1, 2-bis(4-methoxyphenyl)ethane with alcohols was associated with rearrangement to give the corresponding bis(4-methoxyphenyl)acetals. In boiling ethylene glycol 4,4′-dimethoxy-deoxybenzoin was also obtained due to an aldehyde-ketone rearrangement. 4,4′-Dimethoxybenzophenone was also formed being apparently derived from the acetals. The mechanism of formation of the acetals has been discussed. 相似文献
66.
Bonačić-Koutecký V Kulesza A Gell L Mitrić R Antoine R Bertorelle F Hamouda R Rayane D Broyer M Tabarin T Dugourd P 《Physical chemistry chemical physics : PCCP》2012,14(26):9282-9290
We focus on the functional role of small silver clusters in model hybrid systems involving peptides in the context of a new generation of nanostructured materials for biosensing. The optical properties of hybrids in the gas phase and at support will be addressed with the aim to bridge fundamental and application aspects. We show that extension and enhancement of absorption of peptides can be achieved by small silver clusters due to the interaction of intense intracluster excitations with the π-π* excitations of chromophoric aminoacids. Moreover, we demonstrate that the binding of a peptide to a supported silver cluster can be detected by the optical fingerprint. This illustrates that supported silver clusters can serve as building blocks for biosensing materials. Moreover, the clusters can be used simultaneously to immobilize biomolecules and to increase the sensitivity of detection, thus replacing the standard use of organic dyes and providing label-free detection. Complementary to that, we show that protected silver clusters containing a cluster core and a shell liganded by thiolates exhibit absorption properties with intense transitions in the visible regime which are also suitable for biosensing applications. 相似文献
67.
Amlie I. S. Sobczak Kondwani G. H. Katundu Fladia A. Phoenix Siavash Khazaipoul Ruitao Yu Fanuel Lampiao Fiona Stefanowicz Claudia A. Blindauer Samantha J. Pitt Terry K. Smith Ramzi A. Ajjan Alan J. Stewart 《Chemical science》2021,12(11):4079
Zn2+ is an essential regulator of coagulation and is released from activated platelets. In plasma, the free Zn2+ concentration is fine-tuned through buffering by human serum albumin (HSA). Importantly, the ability of HSA to bind/buffer Zn2+ is compromised by co-transported non-esterified fatty acids (NEFAs). Given the role of Zn2+ in blood clot formation, we hypothesise that Zn2+ displacement from HSA by NEFAs in certain conditions (such as type 2 diabetes mellitus, T2DM) impacts on the cellular and protein arms of coagulation. To test this hypothesis, we assessed the extent to which increasing concentrations of a range of medium- and long-chain NEFAs reduced Zn2+-binding ability of HSA. Amongst the NEFAs tested, palmitate (16 : 0) and stearate (18 : 0) were the most effective at suppressing zinc-binding, whilst the mono-unsaturated palmitoleate (16 : 1c9) was markedly less effective. Assessment of platelet aggregation and fibrin clotting parameters in purified systems and in pooled plasma suggested that the HSA-mediated impact of the model NEFA myristate on zinc speciation intensified the effects of Zn2+ alone. The effects of elevated Zn2+ alone on fibrin clot density and fibre thickness in a purified protein system were mirrored in samples from T2DM patients, who have derranged NEFA metabolism. Crucially, T2DM individuals had increased total plasma NEFAs compared to controls, with the concentrations of key saturated (myristate, palmitate, stearate) and mono-unsaturated (oleate, cis-vaccenate) NEFAs positively correlating with clot density. Collectively, these data strongly support the concept that elevated NEFA levels contribute to altered coagulation in T2DM through dysregulation of plasma zinc speciation.Zn2+ is an essential regulator of coagulation. In plasma, Zn2+ availability is fine-tuned by human serum albumin (HSA). Here we show that elevated fatty acid levels contribute to altered coagulation in type-2 diabetes through Zn2+ mishandling by HSA. 相似文献
68.
Fluorination of tetralin over cobalt trifluoride at 250° in a stirred reactor gave the known cis- and trans- perfluorodecalins and two known fluorobicyclo[4,4,0]dec-1(6)-enes. Also obtained were five new heptadecafluorobicyclo[4,4,0]decanes. Dehydrofluorinations of these gave five new hexadecafluorobicyclo[4,4,0]decenes of which one, the 1(2)- isomer, rearranged readily to the 1(6)- isomer. 相似文献
69.
An analytical solution for the nonspecific-binding-facilitated diffusion-controlled rate of association of a protein with a specific site on a circular DNA is derived. Nonspecific binding is modeled by a short-range attractive surface potential. The protein undergoes diffusion in the bulk solution and in the surface layer. The association rate for a circular DNA is compared to the counterpart for a linear DNA, in which the ends of the surface layer are treated as reflecting. As expected, when the DNA length is long, the shape of the DNA does not affect the association rate. For a shorter length, the association rate for the linear DNA is modestly higher than the circular counterpart. The higher rate of the linear DNA is possibly due to its more open shape, which affords it a higher ability to draw the protein from the bulk to its surface. The analytical solution is verified by Brownian dynamics simulations. 相似文献
70.
Mohamed Ramzi Gert Jan Vroege Hendrik N.W. Lekkerkerker 《Macromolecular Symposia》2001,166(1):209-216
Measurements of viscosity were carried out using several solutions of cellulose in different concentrations of phosphoric acid at different temperatures. The intrinsic viscosity [η]0, a measure for the size of a single chain and the Huggins constant kH, a measure for the interaction between chains were derived. 相似文献