全文获取类型
收费全文 | 4078篇 |
免费 | 77篇 |
国内免费 | 33篇 |
专业分类
化学 | 2701篇 |
晶体学 | 31篇 |
力学 | 208篇 |
数学 | 692篇 |
物理学 | 556篇 |
出版年
2021年 | 30篇 |
2020年 | 34篇 |
2019年 | 27篇 |
2018年 | 43篇 |
2017年 | 24篇 |
2016年 | 76篇 |
2015年 | 60篇 |
2014年 | 68篇 |
2013年 | 215篇 |
2012年 | 133篇 |
2011年 | 198篇 |
2010年 | 114篇 |
2009年 | 108篇 |
2008年 | 156篇 |
2007年 | 167篇 |
2006年 | 169篇 |
2005年 | 188篇 |
2004年 | 200篇 |
2003年 | 192篇 |
2002年 | 182篇 |
2001年 | 82篇 |
2000年 | 90篇 |
1999年 | 51篇 |
1998年 | 47篇 |
1997年 | 48篇 |
1996年 | 67篇 |
1995年 | 55篇 |
1994年 | 57篇 |
1993年 | 55篇 |
1992年 | 45篇 |
1991年 | 48篇 |
1990年 | 47篇 |
1989年 | 50篇 |
1988年 | 43篇 |
1987年 | 40篇 |
1986年 | 38篇 |
1985年 | 63篇 |
1984年 | 72篇 |
1983年 | 57篇 |
1982年 | 69篇 |
1981年 | 61篇 |
1980年 | 74篇 |
1979年 | 72篇 |
1978年 | 56篇 |
1977年 | 52篇 |
1976年 | 44篇 |
1975年 | 49篇 |
1974年 | 58篇 |
1973年 | 38篇 |
1972年 | 34篇 |
排序方式: 共有4188条查询结果,搜索用时 31 毫秒
181.
182.
We show almost sure simplicity of eigenvalues for several models of Anderson-type random Schrödinger operators, extending methods introduced by Simon for the discrete Anderson model. These methods work throughout the spectrum and are not restricted to the localization regime. We establish general criteria for the simplicity of eigenvalues which can be interpreted as separately excluding the absence of local and global symmetries, respectively. The criteria are applied to Anderson models with matrix-valued potential as well as with single-site potentials supported on a finite box. 相似文献
183.
A common problem encountered by synthetic chemists is to carry out a reaction at just one of two similar functional groups in the substrate molecule. Examples include protection/deprotection of just one hydroxyl group in a diol, addition to only one carbonyl of a diketone, etc. The problem, as depicted below, is to find conditions which maximize formation of the monoproduct (XP) while minimizing the amounts of diproduct (P2) and starting material (X2). 相似文献
184.
Roger M. Bialy Dr. Monsur M. Ali Prof. Dr. Yingfu Li Prof. Dr. John D. Brennan 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(22):5085-5092
We report a method to detect proteins via suppression of rolling circle amplification (RCA) by using an appropriate aptamer as the linear primer (denoted as an aptaprimer) to initiate RCA. In the absence of a protein target, the aptaprimer is free to initiate RCA, which can produce long DNA products that are detected via binding of a fluorescent intercalating dye. Introduction of a target causes the primer region within the aptamer to become unavailable for binding to the circular template, inhibiting RCA. Using SYBR Gold or QuantiFluor dyes as fluorescent probes to bind to the RCA reaction product, it is possible to produce a generic protein-modulated RCA assay system that does not require fluorophore- or biotin-modified DNA species, substantially reducing complexity and cost of reagents. Based on this modulation of RCA, we demonstrate the ability to produce both solution and paper-based assays for rapid and quantitative detection of proteins including platelet derived growth factor and thrombin. 相似文献
185.
Xuejie Zhang Yan Xu Andrew K. Abel Leslie S. Smith Roger Watt Amir Hussain Chengxiang Gao 《Entropy (Basel, Switzerland)》2020,22(12)
Extraction of relevant lip features is of continuing interest in the visual speech domain. Using end-to-end feature extraction can produce good results, but at the cost of the results being difficult for humans to comprehend and relate to. We present a new, lightweight feature extraction approach, motivated by human-centric glimpse-based psychological research into facial barcodes, and demonstrate that these simple, easy to extract 3D geometric features (produced using Gabor-based image patches), can successfully be used for speech recognition with LSTM-based machine learning. This approach can successfully extract low dimensionality lip parameters with a minimum of processing. One key difference between using these Gabor-based features and using other features such as traditional DCT, or the current fashion for CNN features is that these are human-centric features that can be visualised and analysed by humans. This means that it is easier to explain and visualise the results. They can also be used for reliable speech recognition, as demonstrated using the Grid corpus. Results for overlapping speakers using our lightweight system gave a recognition rate of over 82%, which compares well to less explainable features in the literature. 相似文献
186.
187.
188.
189.
Dr. Qaisar Nadeem Dr. Giuseppe Meola Dr. Henrik Braband Robin Bolliger Dr. Olivier Blacque Daniel Hernández-Valdés Prof. Dr. Roger Alberto 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(3):1213-1216
The labeling of (bio)molecules with metallic radionuclides such as 99mTc demands conjugated, multidentate chelators. However, this is not always necessary since phenyl rings can directly serve as integrated, organometallic ligands. Bis-arene sandwich complexes are generally prepared by the Fischer–Hafner reaction. In extension of this, we show that [99mTc(η6-C6R6)2]+-type complexes are directly accessible from water and [99mTcO4]−, even using arenes incompatible with Fischer–Hafner conditions. To unambiguously confirm the nature of these unprecedented 99mTc complexes, their rhenium homologous have been prepared by substituting naphthalene ligands in [Re(η6-C10H8)2]+ with the corresponding phenyl groups. The ease with which highly stable [99mTc(η6-C6R6)2]+ complexes are formed under standard labeling conditions enables a multitude of new potential imaging agents based on commercial pharmaceuticals or lead structures. 相似文献
190.
Tahya Bamine Edouard Boivin Christian Masquelier Laurence Croguennec Elodie Salager Dany Carlier 《Magnetic resonance in chemistry : MRC》2020,58(11):1109-1117
7Li, 31P, and 19F solid-state nuclear magnetic resonance (NMR) spectroscopy was used to investigate the local arrangement of oxygen and fluorine in LiVPO4F1-yOy materials, interesting as positive electrode materials for Li-ion batteries. From the evolution of the 1D spectra versus y, 2D 7Li radiofrequency-driven recoupling (RFDR) experiments combined, and a tentative signal assignment based on density functional theory (DFT) calculations, it appears that F and O are not randomly dispersed on the bridging X position between two X–VO4–X octahedra (X = O or F) but tend to segregate at a local scale. Using DFT calculations, we analyzed the impact of the different local environments on the local electronic structure. Depending on the nature of the VO4X2 environments, vanadium ions are either in the +III or in the +IV oxidation state and can exhibit different distributions of their unpaired electron(s) on the d orbitals. Based on those different local electronic structures and on the computed Fermi contact shifts, we discuss the impact on the spin transfer mechanism on adjacent nuclei and propose tentative signal assignments. The O/F clustering tendency is discussed in relation with the formation of short VIVO vanadyl bonds with a very specific electronic structure and possible cooperative effect along the chain. 相似文献