全文获取类型
收费全文 | 249455篇 |
免费 | 5556篇 |
国内免费 | 3635篇 |
专业分类
化学 | 119311篇 |
晶体学 | 3352篇 |
力学 | 13372篇 |
综合类 | 307篇 |
数学 | 39724篇 |
物理学 | 82580篇 |
出版年
2020年 | 1520篇 |
2019年 | 1471篇 |
2018年 | 10855篇 |
2017年 | 11754篇 |
2016年 | 6580篇 |
2015年 | 2977篇 |
2014年 | 2716篇 |
2013年 | 6476篇 |
2012年 | 9908篇 |
2011年 | 19732篇 |
2010年 | 11906篇 |
2009年 | 11795篇 |
2008年 | 16845篇 |
2007年 | 20527篇 |
2006年 | 5532篇 |
2005年 | 12474篇 |
2004年 | 8094篇 |
2003年 | 7452篇 |
2002年 | 5250篇 |
2001年 | 4331篇 |
2000年 | 3456篇 |
1999年 | 2648篇 |
1998年 | 2249篇 |
1997年 | 2217篇 |
1996年 | 2256篇 |
1995年 | 2115篇 |
1994年 | 1802篇 |
1993年 | 1703篇 |
1992年 | 1855篇 |
1991年 | 1862篇 |
1990年 | 1781篇 |
1989年 | 1772篇 |
1988年 | 1779篇 |
1987年 | 1764篇 |
1986年 | 1645篇 |
1985年 | 2209篇 |
1984年 | 2349篇 |
1983年 | 1960篇 |
1982年 | 2267篇 |
1981年 | 2089篇 |
1980年 | 2123篇 |
1979年 | 2140篇 |
1978年 | 2259篇 |
1977年 | 2078篇 |
1976年 | 2146篇 |
1975年 | 2081篇 |
1974年 | 1910篇 |
1973年 | 2175篇 |
1972年 | 1304篇 |
1968年 | 1150篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
51.
Recently,the nested Mach–Zehnder interferometer[Phys.Rev.Lett.111,240402(2013)]was modified by adding Dove prisms in a paper[Quantum Stud.:Math.Found.2,255(2015)],and an interesting result is that,after the Dove prisms were inserted,a signal at the first mirror of the nested interferometer was obtained.But,according to the former original paper,the photons have never been present near that mirror.In this work,we interpret this result naturally by resorting to the three-path interference method.Moreover,we find that even though the photons have been somewhere,they can hide the trace of being there. 相似文献
52.
Youchao Wang Na Tian Weize Sun Boerhan Rena Xusheng Guo Yang Feng Chao Li Xuesong Wang Qianxiong Zhou 《Particle & Particle Systems Characterization》2020,37(5):2000045
Photoactivated chemotherapy (PACT) has appealing merits over traditional chemotherapy as well as photodynamic therapy (PDT) by virtue of its spatial and temporal control on drug activity and oxygen-independent mechanisms of action. However, the short photoactivation wavelengths, e.g., visible light–activated Ru(II)-based PACT agents, limit the clinical application severely. In this work, a facile construction of supramolecular nanoparticles from a poly(ethylene glycol) (PEG)-modified [Ru(dip)2(py-SO3)]+ (abbreviated as Ru-PEG, dip = 4,7-diphenyl-1,10-phenanthroline, py-SO3 = pyridine-2-sulfonate) and 1,3-phenylenebis(pyren-1-ylmethanone) (BP) is shown. While Ru-PEG may undergo photoinduced ligand dissociation and release anticancer species of [Ru(dip)2(H2O)2]2+, BP has extremely large two-photon absorption cross sections (δ2) in the NIR region and intense fluorescence over the wavelengths where Ru-PEG has strong absorption. Thus, two-photon excitation of BP followed by an efficient Förster resonance energy transfer (FRET) from BP to Ru-PEG may lead to a potent inactivation against cisplatin-resistant cancer cells and 3D multicellular tumor spheroids (MCTSs). The residue fluorescence of BP also allows the cellular uptake of the particles to be visualized. This work provides a universal and convenient strategy to realize theranostic PACT in the ideal phototherapeutic window of 650–900 nm. 相似文献
53.
54.
I. F. Golovnev E. I. Golovneva L. A. Merzhievsky V. M. Fomin V. E. Panin 《Physical Mesomechanics》2015,18(3):179-186
Molecular dynamics simulation was performed to study the formation of cluster structure, interfaces, and surfaces with different curvature radii in a perfect nanocrystal passed through by a nonlinear wave. It is shown that this process is a type of nanostructure self-organization in response to an external energy flux with subsequent development of a strong rotational field. 相似文献
55.
Gary W. Breton Lauren A. Hahn Kenneth L. Martin 《Acta Crystallographica. Section C, Structural Chemistry》2019,75(9):1208-1212
Tetrahydrotetrazoles are five‐membered‐ring heterocycles containing four contiguous saturated nitrogen atoms. Very few examples of such compounds have been reported in the literature. Our previous attempt at the synthesis of a member of this class of compound suggested that the N—N bonds may be more labile than expected. This finding raised the question as to whether the structures of any of the previously reported tetrahydrotetrazoles had been properly assigned. We have reproduced the synthesis of a reported tetrahydrotetrazole, namely 1,2‐di‐tert‐butyl 3‐phenyl‐1H,2H,3H,10bH‐[1,2,3,4]tetrazolo[5,1‐a]isoquinoline‐1,2‐dicarboxylate, C25H30N4O4, and have now confidently confirmed its structure via X‐ray crystallography. However, while sufficiently stable in the crystal phase, we discovered that it remains very labile in solution (having a half‐life of only 15 min at 20 °C in CDCl3). A tentative reaction pathway for its dissociation based on 1H NMR spectral evidence is provided. 相似文献
56.
Si-Yang Feng Tao Zheng Ai-Jing Sun Zuo-Xiang Wang 《Molecular Crystals and Liquid Crystals》2019,692(1):43-52
AbstractComplexes of [CdL2(NO3)2]·1.5H2O and [Ag2(μ-L)2(NO3)2] were synthesized by the reactions of 2-p-methylphenyl-5-(2-pyridyl)-1,3,4-thiadiazole (L) with Cd(NO3)2·4H2O and AgNO3, respectively. Their structures were determined by single crystal X-ray diffraction. The photophysical property and thermal stability were characterized by FT???IR, UV???Vis absorption, fluorescence, and thermogravimetric analysis (TGA). Both complexes belong to the triclinic system with space group p???1. The central metal of [CdL2(NO3)2]·1.5H2O has a distorted octahedral geometry [CdN4O2], while two central Ag(I) atoms of [Ag2(μ-L)2(NO3)2] exhibit distorted tetrahedral geometries [AgN3O]. 相似文献
57.
58.
E. V. Shadrina O. N. Malinkina T. G. Khonina A. B. Shipovskaya V. I. Fomina E. Yu. Larchenko N. A. Popova I. G. Zyryanova L. P. Larionov 《Russian Chemical Bulletin》2015,64(7):1633-1639
The biomimetic sol—gel synthesis of silicon—chitosan-containing glycerohydrogels was carried out using silicon tetraglycerolate as a precursor. It was found that chitosan accelerates gel formation in weakly acidic media. In more acidic media, the kinetics of the process changes according to the curve with a maximum, which can be attributed to different mechanisms of silanol condensation before and after the isoelectric point. The investigated silicon—chitosan-containing glycerohydrogels exhibit antibacterial, anti-inflammatory, and wound healing activity. The synthesized hybrid glycerohydrogels are promising materials for biomedical applications. 相似文献
59.
60.