全文获取类型
收费全文 | 834篇 |
免费 | 29篇 |
专业分类
化学 | 508篇 |
晶体学 | 9篇 |
力学 | 19篇 |
数学 | 93篇 |
物理学 | 234篇 |
出版年
2023年 | 6篇 |
2022年 | 21篇 |
2021年 | 28篇 |
2020年 | 13篇 |
2019年 | 18篇 |
2018年 | 15篇 |
2017年 | 14篇 |
2016年 | 38篇 |
2015年 | 20篇 |
2014年 | 32篇 |
2013年 | 52篇 |
2012年 | 65篇 |
2011年 | 64篇 |
2010年 | 30篇 |
2009年 | 31篇 |
2008年 | 47篇 |
2007年 | 53篇 |
2006年 | 40篇 |
2005年 | 42篇 |
2004年 | 42篇 |
2003年 | 23篇 |
2002年 | 21篇 |
2001年 | 10篇 |
2000年 | 21篇 |
1999年 | 11篇 |
1998年 | 13篇 |
1997年 | 9篇 |
1996年 | 8篇 |
1995年 | 15篇 |
1994年 | 4篇 |
1993年 | 12篇 |
1992年 | 10篇 |
1991年 | 2篇 |
1990年 | 6篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1982年 | 2篇 |
1981年 | 7篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1936年 | 1篇 |
排序方式: 共有863条查询结果,搜索用时 15 毫秒
771.
Oliveira IM Silva JP Feitosa E Marques EF Castanheira EM Real Oliveira ME 《Journal of colloid and interface science》2012,374(1):206-217
A recently described non-viral gene delivery system [dioctadecyldimethylammonium bromide (DODAB)/monoolein (MO)] has been studied in detail to improve knowledge on the interactions between lamellar (DODAB) and non-lamellar-forming (MO) lipids, as a means to enhance their final cell transfection efficiency. Indeed, the morphology, fluidity, and size of these cationic surfactant/neutral lipid mixtures play an important role in the ability of these systems to complex nucleic acids. The different techniques used in this work, namely dynamic light scattering (DLS), fluorescence spectroscopy, differential scanning calorimetry (DSC), cryogenic transmission electron microscopy (cryo-TEM), light microscopy (LM), and surface pressure-area isotherms, allowed fully characterization of the phase behavior and aggregate morphology of DODAB/MO mixtures at different molar ratios. Overall, the results indicate that the final morphology of DODAB/MO aggregates depends on the balance between the tendency of DODAB to form zero-curvature bilayer structures and the propensity of MO to form non-bilayer structures with negative curvature. These results also show that in the MO-rich region, an increase in temperature has a similar effect on aggregate morphology as an increase in MO concentration. 相似文献
772.
Hapiuk D Marques MA Melinon P Flores-Livas JA Botti S Masenelli B 《Physical review letters》2012,108(11):115903
The issue of p doping in nanostructured cagelike ZnO is investigated by state-of-the-art calculations. Our study is focused on one prototypical structure, namely, sodalite, for which we show that p-type doping is possible for elements of the V, VI, and VII columns of the periodic table. However, some dopants tend to form dimers, thus impairing the stability of this kind of doping. This difference of behavior is discussed, and two criteria are proposed to ensure stable p doping. 相似文献
773.
Phase-shifted Bragg grating waveguides (PSBGWs) were formed in bulk fused silica glass by femtosecond laser direct writing to produce narrowband (22±3) pm filters at 1550 nm. Tunable π and other phase shifts generated narrow passbands in controlled positions of the Bragg stopband, while the accurate placement of multiple cascaded phase-shift regions yielded a rectangular-shaped bandpass filter. A waveguide birefringence of (7.5±0.3)×10(-5) is inferred from the polarization-induced spectral shifting of the PSBGW narrowband filters. 相似文献
774.
Let (Cn)n?0 be the Lucas sequence Cn+2=aCn+1+bCn for all n?0, where C0=0 and C1=1. For 1?k?m−1 let
775.
E. Marques De Sá 《Discrete Mathematics》1981,34(3):275-281
The main result consists of a combinatorial characterization of weakly cyclic matrices of odd index. The case of even index is also considered. 相似文献
776.
Maria de Ftima V. Marques rica Gervasoni Chaves 《Journal of polymer science. Part A, Polymer chemistry》2003,41(10):1478-1485
Because of the great economic interest in propylene‐based polymers and the possibility of designing materials with desired properties with metallocene catalyst mixtures, we investigated the characteristics of polypropylenes produced by mixtures of SiMe2Ind2ZrCl2: dimethylsilane‐bis(indenyl) zirconocene ( 1 ) and Et(Flu)(Cp)ZrCl2: ethylidene (fluorenyl cyclopentadienyl) zirconocene ( 2 ) in different proportions. The polymers were fractionated with solvents, and the fractions were characterized. We observed that the polymers produced by the different mixed systems showed lower weight‐average molecular weights and only slightly broader molecular weight distributions than polypropylenes synthesized by the individual catalysts. We concluded that catalyst 1 acted independently of catalyst 2 , producing polymers with the same isotacticity. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1478–1485, 2003 相似文献
777.
Jo?o P. Marques Gon?alo Caeiro Isabelle Gener José M. Lopes and Fernando Ram?a Ribeiro 《Reaction Kinetics and Catalysis Letters》2005,86(2):389-396
Summary A commercial NaBEA sample was exchanged, at different levels, with NH4+cations through conventional and microwave promoted methods. The dependence of the acidic and catalytic properties of the
HNaBEA samples with the exchange degree was analyzed. It was observed that the catalytic activity of the exchanged samples
for methylcyclohexane cracking depends on the exchange method, whereas surface acidity, determined by pyridine adsorption
followed by IR spectroscopy and temperature programmed desorption of NH3, do not. 相似文献
778.
Karine L. Marques Cherrine K. Pires João L. M. Santos José L. F. C. Lima 《International journal of environmental analytical chemistry》2013,93(2):77-85
Abstract This paper presents a novel technique for measuring soluble inorganic monophosphate in water based on high performance liquid chromatography and flow injection detection (IC-FI). The IC-FI technology was applied to irrigation water from the Macalister Research Farm in South Eastern Australia. Overland flow was measured exiting two irrigation bays. Inorganic monophosphate constituted over 97% of the DRP component and between 86–93% of the total phosphorus. Similar results were obtained from a channel that drained the excess irrigation water from the farm. This work supports the findings of others that show DRP contributes a large portion of the P in runoff from grazing systems. Additionally, it confirms this fraction is dominated by immediately bioavailable inorganic monophosphate, something that previously could only be inferred due to the limitations of the chemistry applied. 相似文献
779.
N.P.C. Marques J.C.F. Pereira 《Numerical Methods for Partial Differential Equations》2006,22(4):971-982
The concept of a representative spectrum is introduced in the context of Newton‐Krylov methods. This concept allows a better understanding of convergence rate accelerating techniques for Krylov‐subspace iterative methods in the context of CFD applications of the Newton‐Krylov approach to iteratively solve sets of non‐linear equations. The dependence of the representative spectrum on several parameters such as mesh, Mach number or discretization techniques is studied and analyzed. © 2005 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2006 相似文献
780.
Aromatic hydroxylamines and sterically bulky aliphatic hydroxylamines react with aroyl cyanides to give exclusively the -acyl derivatives. 相似文献