全文获取类型
收费全文 | 490880篇 |
免费 | 6002篇 |
国内免费 | 1774篇 |
专业分类
化学 | 259941篇 |
晶体学 | 7498篇 |
力学 | 21801篇 |
综合类 | 8篇 |
数学 | 58537篇 |
物理学 | 150871篇 |
出版年
2020年 | 3489篇 |
2019年 | 3728篇 |
2018年 | 4414篇 |
2017年 | 4234篇 |
2016年 | 7193篇 |
2015年 | 5183篇 |
2014年 | 7761篇 |
2013年 | 21845篇 |
2012年 | 16500篇 |
2011年 | 20428篇 |
2010年 | 13533篇 |
2009年 | 13440篇 |
2008年 | 18800篇 |
2007年 | 19031篇 |
2006年 | 18255篇 |
2005年 | 16551篇 |
2004年 | 15050篇 |
2003年 | 13343篇 |
2002年 | 13169篇 |
2001年 | 14840篇 |
2000年 | 11382篇 |
1999年 | 9123篇 |
1998年 | 7492篇 |
1997年 | 7347篇 |
1996年 | 7230篇 |
1995年 | 6585篇 |
1994年 | 6327篇 |
1993年 | 6258篇 |
1992年 | 6738篇 |
1991年 | 6743篇 |
1990年 | 6301篇 |
1989年 | 6099篇 |
1988年 | 6446篇 |
1987年 | 6012篇 |
1986年 | 5749篇 |
1985年 | 8140篇 |
1984年 | 8322篇 |
1983年 | 6859篇 |
1982年 | 7270篇 |
1981年 | 7229篇 |
1980年 | 6913篇 |
1979年 | 7197篇 |
1978年 | 7240篇 |
1977年 | 7203篇 |
1976年 | 7190篇 |
1975年 | 6864篇 |
1974年 | 6784篇 |
1973年 | 6955篇 |
1972年 | 4446篇 |
1971年 | 3490篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
Mathematical Notes - 相似文献
103.
Ding Q. Yao M. Wu Sh. Zeng M. Xue N. Wu D. Xu J. 《Journal of Applied Spectroscopy》2022,89(4):712-718
Journal of Applied Spectroscopy - Based on partial least squares (PLS) analysis, the effects of different smoothing points and different preprocessing methods on the accuracy and precision of the... 相似文献
104.
Transport in Porous Media - The theme of coupling problems for adsorption, absorption and thermochemical transport in porous media is very important for engineering applications. Based on the... 相似文献
105.
106.
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
107.
108.
Monodisperse aqueous upconverting nanoparticles (UCNPs) were covalently immobilized on aldehyde modified cellulose paper via reduction amination to develop a luminescence resonance energy transfer (LRET)-based nucleic acid hybridization assay. This first account of covalent immobilization of UCNPs on paper for a bioassay reports an optically responsive method that is sensitive, reproducible and robust. The immobilized UCNPs were decorated with oligonucleotide probes to capture HPRT1 housekeeping gene fragments, which in turn brought reporter conjugated quantum dots (QDs) in close proximity to the UCNPs for LRET. This sandwich assay could detect unlabeled oligonucleotide target, and had a limit of detection of 13 fmol and a dynamic range spanning nearly 3 orders of magnitude. The use of QDs, which are excellent LRET acceptors, demonstrated improved sensitivity, limit of detection, dynamic range and selectivity compared to similar assays that have used molecular fluorophores as acceptors. The selectivity of the assay was attributed to the decoration of the QDs with polyethylene glycol to eliminate non-specific adsorption. The kinetics of hybridization were determined to be diffusion limited and full signal development occurred within 3 min. 相似文献
109.
Nitin P. Lobo K.V. Ramanathan T. Narasimhaswamy 《Magnetic resonance in chemistry : MRC》2020,58(11):988-1009
In this review, methods to obtain the orientational order of topologically variant molecular mesogens using by one- and two-dimensional (2D) solid-state 13C nuclear magnetic resonance (NMR) spectroscopy are described. Besides 13C chemical shifts, the 13C─1H dipolar couplings measured from 2D-separated local field (SLF) technique are used for computing the order parameters of a variety of mesogens. The investigated molecules are composed of a variable number of rings in the core, that is, core ranging from simply one ring to five rings. Among the mesogens investigated, a special focus has been placed on mesogens with thiophene rings, which are gaining popularity as liquid crystalline organic semiconductors. The replacement of a phenyl ring by thiophene in the core has a dramatic influence on molecular topology, as observed from the measured order parameters. The review highlights the advantages of the 2D SLF method for understanding the local dynamics and for mapping the topology of mesogens through the measured order parameters. SLF NMR studies of as many as 24 molecular mesogens that vary in terms of the molecular structure as well as topology are covered in the review. Order parameters of the rings have been estimated from the 13C─1H dipolar couplings in the nematic, smectic A, smectic C, and tilted hexatic phases as well as in B1 and B2 mesophases of various mesogens. It is anticipated that, in the years to come, the 2D SLF method would provide advanced molecular information on structurally complex mesogens that are emerging in liquid crystal science through the incessant efforts of synthetic chemists. The mini review covers the orientational order of topologically variant molecular mesogens determined by 1D and 2D solid-state 13C NMR spectroscopy. Accordingly, rod-like, bent-core, and thiophene mesogens were subjected to 2D SLF measurements to get the order parameters from which the topology was established. The replacement of phenyl ring by thiophene and its influence on order parameters as well as on molecular topology is also discussed. 相似文献
110.
Renny Mathew Karolina A. Uchman Lydia Gkoura Chris J. Pickard Maria Baias 《Magnetic resonance in chemistry : MRC》2020,58(11):1018-1025
A combined experimental and computational approach was used to distinguish between different polymorphs of the pharmaceutical drug aspirin. This method involves the use of ab initio random structure searching (AIRSS), a density functional theory (DFT)-based crystal structure prediction method for the high-accuracy prediction of polymorphic structures, with DFT calculations of nuclear magnetic resonance (NMR) parameters and solid-state NMR experiments at natural abundance. AIRSS was used to predict the crystal structures of form-I and form-II of aspirin. The root-mean-square deviation between experimental and calculated 1H chemical shifts was used to identify form-I as the polymorph present in the experimental sample, the selection being successful despite the large similarities between the molecular environments in the crystals of the two polymorphs. 相似文献