全文获取类型
收费全文 | 757篇 |
免费 | 22篇 |
专业分类
化学 | 583篇 |
晶体学 | 10篇 |
力学 | 19篇 |
数学 | 111篇 |
物理学 | 56篇 |
出版年
2023年 | 5篇 |
2022年 | 30篇 |
2021年 | 28篇 |
2020年 | 14篇 |
2019年 | 13篇 |
2018年 | 15篇 |
2017年 | 11篇 |
2016年 | 29篇 |
2015年 | 16篇 |
2014年 | 19篇 |
2013年 | 37篇 |
2012年 | 41篇 |
2011年 | 41篇 |
2010年 | 29篇 |
2009年 | 39篇 |
2008年 | 47篇 |
2007年 | 43篇 |
2006年 | 50篇 |
2005年 | 41篇 |
2004年 | 32篇 |
2003年 | 38篇 |
2002年 | 30篇 |
2001年 | 11篇 |
2000年 | 5篇 |
1999年 | 8篇 |
1998年 | 9篇 |
1997年 | 5篇 |
1996年 | 12篇 |
1995年 | 7篇 |
1994年 | 7篇 |
1993年 | 5篇 |
1992年 | 2篇 |
1991年 | 6篇 |
1990年 | 3篇 |
1989年 | 8篇 |
1988年 | 6篇 |
1987年 | 4篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1984年 | 7篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 3篇 |
1971年 | 1篇 |
排序方式: 共有779条查询结果,搜索用时 15 毫秒
721.
Elías Quezada Giovanna Delogu Dolores Viña Lourdes Santana Gianni Podda Maria Joao Matos Carmen Picciau 《Helvetica chimica acta》2009,92(7):1309-1314
Arenofurans have important biological and pharmacological activities. Compared to benzofurans, the reports on the synthesis of benzodifurans are rather limited. Here, we report the synthesis of a linear and an angular 3,3′‐bis(carboxymethyl)substituted benzodifuran and 4′‐carboxymethyl‐substituted angelicins from phloroglucinol, using 4‐halomethyl‐substituted dipyrones as key intermediates in the synthetic route. This strategy shows that the stability of a pyrone ring depends on the type of substituent at C(4) and the conditions used. 相似文献
722.
Giovanna Jona-Lasinio 《Journal of multivariate analysis》2001,77(2):315
In this paper an exploratory technique based on the diagonalization of cross-variogram matrices is described. Through the definition of a model for the analysis and simulation of multivariate spatial data, a test procedure for the assumption of isotropy of multivariate spatial data is proposed. Applications to simulated and real data are reported. 相似文献
723.
We study the relationship between chaotic behavior and the Central Limit Theorem (CLT) in the Kuramoto model. We calculate sums of angles at equidistant times along deterministic trajectories of single oscillators and we show that, when chaos is sufficiently strong, the Pdfs of the sums tend to a Gaussian, consistently with the standard CLT. On the other hand, when the system is at the “edge of chaos” (i.e. in a regime with vanishing Lyapunov exponents), robust q-Gaussian-like limit distributions naturally emerge, consistently with recently proved generalizations of the CLT. 相似文献
724.
We study the regularity of the solutions u of a class of P.D.E., whose prototype is the prescribed Levi curvature equation in ℝ2
n
+1. It is a second-order quasilinear equation whose characteristic matrix is positive semidefinite and has vanishing determinant
at every point and for every function u∈C
2. If the Levi curvature never vanishes, we represent the operator ℒ associated with the Levi equation as a sum of squares
of non-linear vector fields which are linearly independent at every point. By using a freezing method we first study the regularity
properties of the solutions of a linear operator, which has the same structure as ℒ. Then we apply these results to the classical
solutions of the equation, and prove their C
∞ regularity.
Received: October 10, 1998; in final form: March 5, 1999?Published online: May 10, 2001 相似文献
725.
Simona Argentiere Laura Blasi Giuseppe Ciccarella Giovanna Barbarella Roberto Cingolani Giuseppe Gigli 《Macromolecular Symposia》2009,281(1):69-76
Summary: Nanometer-sized poly(acrylic acid) (PAA) hydrogels were synthesized by emulsion polymerization of methyl acrylate and subsequent acid hydrolysis, and their pH-dependent swelling behaviour was studied by dynamic light scattering. To determine the suitability of PAA nanogels as pH-sensitive carriers for biomedical applications, loading and release of an oligothiophene fluorophore and its albumin conjugate onto the PAA nanogels were investigated as a function of pH by absorption and photoluminescence measurements. It was observed that loading and release processes of both the oligothiophene and its conjugate could be controlled by changing pH of their solutions. 相似文献
726.
Burcin Bozal‐Palabiyik Mariagrazia Lettieri Bengi Uslu Giovanna Marrazza 《Electroanalysis》2019,31(8):1458-1464
In this study, we report the development of a sensitive label‐free impedimetric sensor based on molecularly imprinted polymer (MIP) as biomimetic receptor coupled with screen‐printed electrodes (SPEs) for the detection of vascular endothelial growth factor (VEGF). Firstly, electropolymerization of o‐phenylenediamine (o‐PD) in the presence of VEGF molecule by cyclic voltammetry was performed onto graphite screen‐printed electrodes. The solvent extraction of the target was then carried out. The MIP based sensor was characterized by electrochemical techniques and scanning electron microscopy (SEM). Using optimized experimental conditions, the single‐use MIP‐based sensor showed a good analytical performance for VEGF detection from 20 to 200 pg mL?1 with limit of detection of 0.08 pg mL?1. Finally, the developed MIP‐based sensor in human serum samples was also tested. 相似文献
727.
Olatz Olaizola Igor Iriarte Giovanna Zanella Enrique Gmez‐Bengoa Iaki Ganboa Mikel Oiarbide Claudio Palomo 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(40):14388-14392
A catalyst‐driven one‐pot reaction sequence is developed for the enantio‐ and diastereoselective synthesis of tetrasubstituted cyclohexenes from simple unsaturated ketones or thioesters. The method involves a tertiary amine/squaramide‐catalyzed α‐selective addition of transiently generated trienolates to nitroolefins, subsequent base‐catalyzed double bond isomerization, and an intramolecular (vinylogous) 1,6‐addition reaction, a rare key carbocyclization step that proceeded with essentially perfect stereocontrol. 相似文献
728.
Giovanna Guidoboni Marcello Guidorzi Mariarosaria Padula 《Journal of Mathematical Fluid Mechanics》2012,14(1):1-32
We prove a continuous dependence theorem for weak solutions of equations governing a fluid–structure interaction problem in
two spatial dimensions. The proof is based on a priori estimates which, in particular, convey uniqueness of weak solutions. The estimates are obtained using Eulerian coordinates,
without remapping the problem into a fixed domain. 相似文献
729.
Emilia Garofalo Giovanna Maria Russo Luciano Di Maio Loredana Incarnato 《Macromolecular Symposia》2007,247(1):110-119
This work focuses on the study of uniaxial elongational flow and its effects on morphology and stiffness of polyamide-6 based nanocomposites prepared by melt compounding. The elongational flow characterization was realized by converging flow method and fiber spinning technique. During the haul-off tests, fibers of the neat polyamide-6 and the hybrids (at 3 and 6 wt% of silicate) were collected at different draw ratios. Mechanical properties of the produced fibers were investigated and correlated to their nanostructure through analytical techniques sensitive to different aspects of morphology, such as DSC and TEM analysis. Rheological results, obtained with a capillary rheometer, indicate that the shear viscosity decreases with the silicate loading, while the extentional viscosity increases. Moreover, the presence of the silicate in polymer matrix leads to enhancements of draw-down force and reduction of the breaking draw ratio. In hybrid fibers an enhanced degree of exfoliation of the filler was observed upon drawing. Moreover, DSC analyses suggest that the crystalline structure of the fibers is the result of two opposite effects: the presence of the silicate which stabilizes the γ form and the drawing which promotes the α crystal phase. The degree of silicate exfoliation and the amount of the different crystal phases strongly affect the tensile properties of the fibers. 相似文献
730.
Ryhänen SJ Säily VM Parry MJ Luciani P Mancini G Alakoskela JM Kinnunen PK 《Journal of the American Chemical Society》2006,128(26):8659-8663
While much is known about the self-assembly of lipids on nanoscale, our understanding of their biologically relevant mesoscale organization remains incomplete. Here, we show for a cationic gemini lipid a sharp and reversible transition from small vesicles with an average diameter of approximately 40 nm to giant vesicles (GVs) with an average diameter of approximately 11 microm. This transition is dependent on proper [NaCl] and specific temperature. Below this transition and in the vicinity of the air/water interface, a series of mesoscale morphological transitions was observed, revealing complex structures resembling biological membranes. On the basis of microscopy experiments, a tentative [NaCl] versus temperature shape/size phase diagram was constructed. To explain this unprecedented transition, we propose a novel mechanism whereby a specific interaction of Cl(-) counterion with the cationic gemini surfactant initiates the formation of a commensurate solute counterion lattice with low spontaneous curvature. In keeping with the high bending rigidity of NaCl crystal, this tightly associated ionic lattice enslaves membrane curvature and the mesoscale 3-D organization of this lipid. 相似文献