全文获取类型
收费全文 | 861篇 |
免费 | 26篇 |
国内免费 | 4篇 |
专业分类
化学 | 718篇 |
晶体学 | 7篇 |
力学 | 1篇 |
数学 | 60篇 |
物理学 | 105篇 |
出版年
2024年 | 1篇 |
2023年 | 13篇 |
2022年 | 87篇 |
2021年 | 95篇 |
2020年 | 36篇 |
2019年 | 30篇 |
2018年 | 29篇 |
2017年 | 30篇 |
2016年 | 36篇 |
2015年 | 30篇 |
2014年 | 36篇 |
2013年 | 61篇 |
2012年 | 44篇 |
2011年 | 67篇 |
2010年 | 26篇 |
2009年 | 41篇 |
2008年 | 49篇 |
2007年 | 37篇 |
2006年 | 31篇 |
2005年 | 27篇 |
2004年 | 20篇 |
2003年 | 7篇 |
2002年 | 8篇 |
2001年 | 6篇 |
2000年 | 3篇 |
1999年 | 3篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1996年 | 4篇 |
1995年 | 1篇 |
1993年 | 1篇 |
1991年 | 6篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1987年 | 1篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1966年 | 1篇 |
1963年 | 1篇 |
排序方式: 共有891条查询结果,搜索用时 31 毫秒
61.
Lung transplantation is a necessary step for the patients with the end stage of chronic obstructive pulmonary disease. The use of artificial lungs is a promising alternative to natural lung transplantation which is complicated and is restricted by low organ donations. For successful lung engineering, it is important to choose the correct combination of specific biological cells and a synthetic carrier polymer. The focus of this study was to investigate the interactions of human lung epithelial cell line NCl-H292 that is involved in lung tissue development with the biodegradable poly(ε-caprolactone) before and after its chemical modification to evaluate potential for use in artificial lung formation. Also, the effect of polymer chemical modification on its mechanical and surface properties has been investigated. The poly(ε-caprolactone) surface was modified using aminolysis followed by immobilization of gelatin. The unmodified and modified polymer surfaces were characterized for roughness, tensile strength, and NCl-H292 metabolic cell activity. The results showed for the first time the possibility for NCI-H292 cells to adhere on this polymeric material. The resazurin assay showed that the metabolic activity at 24?h postseeding of 80% in the presence of the unmodified and greater than 100% in the presence of the modified polymer was observed. The roughness of the poly(ε-caprolactone) increased from 4 to 26?nm and the film strength increased from 0.01 to 0.045 kN when the material was chemically modified. The results obtained to date show potential for using modified poly(ε-caprolactone) as a scaffold for lung tissue engineering. 相似文献
62.
Sebastian Mendrek Aleksandra Mendrek Hans-Juergen Adler Andrzej Dworak Dirk Kuckling 《Colloid and polymer science》2010,288(7):777-786
Temperature-sensitive poly(glycidol)-b-poly(N-isopropylacrylamide) block copolymers (PGl55PNIPAAmy) were synthesised and their aqueous solutions investigated by different methods including differential scanning calorimetry
(DSC), UV-VIS spectroscopy as well as dynamic and static light scattering. The cloud point temperature (T
c) depended on the composition of the investigated block copolymers and increased with decreasing length of the PNIPAAm block
in PGl55PNIPAAmy copolymers. In contrast, the enthalpy of phase separation of PNIPAAm segments measured by DSC decreased with decreasing length
of the PNIPAAm block in the polymer. These findings can be correlated with the behaviour of homo-PNIPAAm with similar molecular
weights indicating that the influence of PGl on the local environment and phase separation of PNIPAAm chains is similar to
the influence observed for PNIPAAm chains bearing different low molecular weight end group. Using DLS measurement, it was
shown that the aggregation process depended on the PGl/PNIPAAm block ratio. If the PGl/PNIPAAm ratio was low, stable core-shell
aggregates were formed. In contrast, the tendency to formation of large unstable, loose aggregates was observed for copolymers
with high PGl/PNIPAAm ratio. 相似文献
63.
Aleksandra Zivkovic 《Tetrahedron letters》2010,51(29):3769-3771
Fingolimod (FTY720) and its analogue derivatives are not only promising therapeutics in sphingolipid signaling but also valuable tools for understanding the roles of sphingolipids in (patho)physiological conditions. A practical method for the synthesis of the ether analogue of FTY720 is described. Our final synthetic approach allows high yield and efficient synthesis of O-FTY in only four steps without chromatographic purifications. 相似文献
64.
65.
Agata L. Starosta Viktoriya V. Karpenko Anna V. Shishkina Aleksandra Mikolajka Natalia V. Sumbatyan Frank Schluenzen Galina A. Korshunova Alexey A. Bogdanov Daniel N. Wilson 《Chemistry & biology》2010,17(5):504-514
Highlights? Macrolides exhibit nascent polypeptide chain–dependent inhibition ? Peptides can form specific interactions with the ribosomal tunnel ? A covalent bond between tylosin and the ribosome is necessary for inhibitory activity 相似文献
66.
István Ilisz Zoltán Pataj Róbert Berkecz Aleksandra Misicka Dagmara Tymecka Ferenc Fülöp Hee Jung Choi Myung Ho Hyun Antal Péter 《Journal of chromatography. A》2010,1217(7):1075-1082
Reversed-phase high-performance liquid chromatographic methods were developed for the separation of enantiomers of eleven unnatural β2-amino acids on a new chiral stationary phase, using the 11-methylene-unit spacer of aminoundecylsilica gel for the bonding of (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid as selector. The nature and concentration of the acidic and organic modifiers, the pH, the mobile phase composition, and the structures of the analytes substantially influenced the retention and resolution. Separations were carried out at constant mobile phase compositions in the temperature range 7–40 °C and the changes in enthalpy, Δ(ΔH°), entropy, Δ(ΔS°), and free energy, Δ(ΔG°) were calculated. The elution sequence was determined in some cases: the S enantiomers eluted before the R enantiomers. 相似文献
67.
Faugeras C Amado M Kossacki P Orlita M Kühne M Nicolet AA Latyshev YI Potemski M 《Physical review letters》2011,107(3):036807
Magneto-Raman-scattering experiments from the surface of graphite reveal novel features associated to purely electronic excitations which are observed in addition to phonon-mediated resonances. Graphene-like and graphite domains are identified through experiments with ~1 μm spatial resolution performed in magnetic fields up to 32 T. Polarization resolved measurements emphasize the characteristic selection rules for electronic transitions in graphene. Graphene on graphite displays the unexpected hybridization between optical phonon and symmetric across the Dirac point inter Landau level transitions. The results open new experimental possibilities--to use light scattering methods in studies of graphene under quantum Hall effect conditions. 相似文献
68.
Winnerl S Orlita M Plochocka P Kossacki P Potemski M Winzer T Malic E Knorr A Sprinkle M Berger C de Heer WA Schneider H Helm M 《Physical review letters》2011,107(23):237401
We study the carrier dynamics in epitaxially grown graphene in the range of photon energies from 10 to 250 meV. The experiments complemented by microscopic modeling reveal that the carrier relaxation is significantly slowed down as the photon energy is tuned to values below the optical-phonon frequency; however, owing to the presence of hot carriers, optical-phonon emission is still the predominant relaxation process. For photon energies about twice the value of the Fermi energy, a transition from pump-induced transmission to pump-induced absorption occurs due to the interplay of interband and intraband processes. 相似文献
69.
We study the possibility of cavitation in the non-conformal N=2?SU(N) theory which is a mass deformation of N=4SU(N) Yang-Mills theory. The second order transport coefficients are known from the numerical work using AdS/CFT by Buchel and collaborators. Using these and the approach of Rajagopal and Tripuraneni, we investigate the flow equations in a (1+1)-dimensional boost invariant set up. We find that the string theory model does not exhibit cavitation before phase transition is reached. We give a semi-analytic explanation of this finding. 相似文献
70.
Piotr Gwiazda Agnieszka Świerczewska-Gwiazda Petra Wittbold Aleksandra Zimmermann 《Journal of Functional Analysis》2014
We consider scalar balance laws with a dissipative source term. The flux function may be discontinuous with respect to both the space variable x and the unknown quantity u. We formulate the definition of entropy weak solutions and provide existence and uniqueness to the considered problem. The problem is formulated in the framework of multi-valued mappings. The notion of entropy measure-valued solutions is used to prove the so-called contraction principle and comparison principle. 相似文献