全文获取类型
收费全文 | 793篇 |
免费 | 33篇 |
国内免费 | 2篇 |
专业分类
化学 | 600篇 |
晶体学 | 3篇 |
力学 | 26篇 |
数学 | 65篇 |
物理学 | 134篇 |
出版年
2023年 | 4篇 |
2022年 | 5篇 |
2021年 | 16篇 |
2020年 | 14篇 |
2019年 | 13篇 |
2018年 | 5篇 |
2017年 | 7篇 |
2016年 | 29篇 |
2015年 | 23篇 |
2014年 | 25篇 |
2013年 | 37篇 |
2012年 | 61篇 |
2011年 | 73篇 |
2010年 | 34篇 |
2009年 | 23篇 |
2008年 | 57篇 |
2007年 | 35篇 |
2006年 | 43篇 |
2005年 | 31篇 |
2004年 | 32篇 |
2003年 | 24篇 |
2002年 | 27篇 |
2001年 | 3篇 |
2000年 | 8篇 |
1998年 | 3篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1993年 | 8篇 |
1992年 | 5篇 |
1991年 | 6篇 |
1990年 | 4篇 |
1989年 | 6篇 |
1988年 | 10篇 |
1987年 | 4篇 |
1986年 | 4篇 |
1985年 | 8篇 |
1984年 | 9篇 |
1983年 | 8篇 |
1982年 | 12篇 |
1981年 | 9篇 |
1980年 | 16篇 |
1979年 | 9篇 |
1978年 | 13篇 |
1977年 | 8篇 |
1976年 | 7篇 |
1975年 | 4篇 |
1974年 | 10篇 |
1973年 | 12篇 |
1924年 | 2篇 |
1901年 | 2篇 |
排序方式: 共有828条查询结果,搜索用时 46 毫秒
791.
Gas-liquid selective oxidations with oxygen under explosive conditions in a micro-structured reactor
The gas-liquid oxidation of cyclohexane is performed at high temperature (>200 degrees C) and pressure (up to 25 bar) using pure oxygen in a Pyrex capped silicon etched microreactor which allows convenient screen reaction conditions well above the flammability limit. 相似文献
792.
Jacquot C McGinley CM Plata E Holman TR van der Donk WA 《Organic & biomolecular chemistry》2008,6(22):4242-4252
Lipoxygenases catalyse the oxidation of polyunsaturated fatty acids and have been invoked in many diseases including cancer, atherosclerosis and Alzheimer's disease. Currently, no X-ray structures are available with substrate or substrate analogues bound in a productive conformation. Such structures would be very useful for examining interactions between substrate and active site residues. Reported here are the syntheses of linoleic acid analogues containing a sulfur atom at the 11 or 14 positions. The key steps in the syntheses were the incorporation of sulfur using nucleophilic attack of metallated alkynes on electrophilic sulfur compounds and the subsequent stereospecific tantalum-mediated reduction of the alkynylsulfide to the cis-alkenylsulfide. Kinetic assays performed with soybean lipoxygenase-1 showed that both 11-thialinoleic acid and 14-thialinoleic acid were competitive inhibitors with respect to linoleic acid with K(i) values of 22 and 35 microM, respectively. On the other hand, 11-thialinoleic acid was a noncompetitive inhibitor with respect to arachidonic acid with K(is) and K(ii) values of 48 and 36 microM, respectively. 11-Thialinoleic acid was also a noncompetitive inhibitor of human 15-lipoxygenase-1 with arachidonic acid (K(is) = 11.4 microM, K(ii) = 18.1 microM) or linoleic acid as substrate (K(is) = 20.1 microM, K(ii) = 20.0 microM), and a competitive inhibitor of human 12-lipoxygenase with arachidonic acid as substrate (K(i) = 2.5 microM). The presence of inhibitor did not change the regioselectivity of soybean lipoxygenase-1, human 12- or 15-lipoxygenase-1. 相似文献
793.
Korchowiec B Corvis Y Viitala T Feidt C Guiavarch Y Corbier C Rogalska E 《The journal of physical chemistry. B》2008,112(43):13518-13531
Interactions of phenantrene, anthracene, pyrene, chrysene, and benzo[a]pyrene (polyaromatic hydrocarbons) with model phospholipid membranes were probed using the Langmuir technique. The lipid monolayers were prepared using 1,2-dipalmitoyl-sn-glycero-3-phosphocholine, 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine, 1,2-dipalmitoyl-sn-glycero-3-phosphoglycerol, 1,2-dipalmitoyl-sn-glycero-3-phosphoserine, 1,2-myristoyl-sn-glycero-3-phosphoethanolamine, 1,2-dilauroyl-sn-glycero-3-phosphocholine, and cholesterol. Surface pressure and electrical surface potential were measured on mixed phospholipid/PAH monolayers spread on a pure water subphase. The morphology of the mixed monolayers was followed with Brewster angle microscopy. Polarization-modulation infrared reflection-absorption spectroscopy spectra obtained on DPPE/benzo[a]pyrene showed that the latter interacts with the carbonyl groups of the phospholipid. On the other hand, the activity of phospholipase A2 toward DLPC used as a probe to locate benzo[a]pyrene in the monolayers indicates that the polyaromatic hydrocarbons are not accessible to the enzyme. The results obtained show that all PAHs studied affect the properties of the pure lipid, albeit in different ways. The most notable effects, namely, film fluidization and morphology changes, were observed with benzo[a]pyrene. In contrast, the complexity of mixed lipid monolayers makes the effect of PAHs difficult to detect. It can be assumed that the differences observed between PAHs in monolayers correlate with their toxicity. 相似文献
794.
New dispiro compounds: synthesis and properties 总被引:1,自引:0,他引:1
We report the synthesis and structural characterization of two dispiro compounds. These two positional isomers have been designed and synthesized through an efficient method. Because of the rigidity and orthogonality of the spiro bridge, both molecules exhibit a well-defined architecture which consists of two fluorene rings connecting to an indenofluorenyl unit via two sp3 carbon atoms. The structural, electrochemical, optical, and thermal properties of these dispiro isomers are discussed. 相似文献
795.
Nonlinear Dynamics - The objective of this contribution is to compare two methods proposed recently in order to build efficient reduced-order models for geometrically nonlinear structures. The... 相似文献
796.
Nonlinear Dynamics - Analytical study of ball vibration absorber behavior is presented in the paper. The dynamics of trajectories of a heavy ball moving without slipping inside a spherical cavity... 相似文献
797.
The present paper provides a spectral comparison between abdominal human skin (Transkin) and pig ear skin using confocal Raman microspectroscopy at 660 nm. Pig ear skin is usually utilized as a substitute for human skin for active ingredients assessment in dermatological and cosmetics fields. Herein, the comparison is made at the level of the stratum corneum (SC), the SC/epidermis junction and the viable epidermis. The 660 nm excitation source appears to be the most appropriate wavelength for such skin characterization. From Raman signatures of both skin types, a tentative assignment of vibrations was performed in the fingerprint and the high wavenumber spectral regions. Significant differences were highlighted for lipid content in in-depth spectra and for hyaluronic acid (HA) and carotenoid in SC spectra. Marked tissular variability was also revealed by certain Raman vibrations. These intrinsic molecular data probed by confocal Raman microspectroscopy have to be considered for further applications such as cutaneous drug permeation. 相似文献
798.
We report the synthesis and spectroscopic characterization of nanohybrid structures consisting of an azobenzene compound grafted on the surface of zinc oxide nanoparticles. Characteristic bathochromic shifts indicate that the azobenzene photochromic molecules self-assemble onto the surface of the nanocrystals. The extent of packing is dependent on the shape of the nanoparticle. ZnO nanorods, with flat facets, enable a tighter organization of the molecules in the self-assembled monolayer than in the case of nanodots that display a more curvated shape. Consistently, the efficiency of photochromic switching of the self-assembled monolayer on ZnO nanoparticles is also shown to be strongly affected by nanoparticle shape. 相似文献
799.
Samira Zeroual Nathalie Bouet Fabien Tuyèras Cyril Peltier Nadia Ouddai Philippe Ochsenbein Carlo Adamo Philippe P. Lainé Ilaria Ciofini 《Theoretical chemistry accounts》2012,131(2):1107-10
With the aim of designing new inorganic photosensitizers for photovoltaic applications, the structural and electronic properties
of two Ru(II) complexes containing terpyridine-based ligands derived from expanded pyridiniums both branched—polyphenyl—and
fused—polycyclic—were investigated by the means of density functional theory (DFT) and time-dependent DFT (TD-DFT). In particular,
the structure and electronic absorption of the fused architectures—including the isolated ligand and its complex—were compared
with those of their respective branched precursors with the aim to account for the their enhanced electronic features in the
visible spectral region. The theoretical insights gained into the “large-surface” ligand and its associated complex open the
route for a joint experimental and theoretical design of new inorganic photosensitizers based on fused expanded pyridiniums. 相似文献