全文获取类型
收费全文 | 487169篇 |
免费 | 7191篇 |
国内免费 | 1581篇 |
专业分类
化学 | 266309篇 |
晶体学 | 7025篇 |
力学 | 20115篇 |
综合类 | 10篇 |
数学 | 60587篇 |
物理学 | 141895篇 |
出版年
2021年 | 3224篇 |
2020年 | 3755篇 |
2019年 | 3901篇 |
2018年 | 4584篇 |
2017年 | 4452篇 |
2016年 | 7926篇 |
2015年 | 5992篇 |
2014年 | 8258篇 |
2013年 | 22651篇 |
2012年 | 17903篇 |
2011年 | 21536篇 |
2010年 | 14076篇 |
2009年 | 13634篇 |
2008年 | 19710篇 |
2007年 | 19752篇 |
2006年 | 18860篇 |
2005年 | 17267篇 |
2004年 | 15600篇 |
2003年 | 13696篇 |
2002年 | 13295篇 |
2001年 | 14255篇 |
2000年 | 11047篇 |
1999年 | 8645篇 |
1998年 | 7079篇 |
1997年 | 6798篇 |
1996年 | 6863篇 |
1995年 | 6178篇 |
1994年 | 5998篇 |
1993年 | 5794篇 |
1992年 | 6486篇 |
1991年 | 6222篇 |
1990年 | 5943篇 |
1989年 | 5757篇 |
1988年 | 5937篇 |
1987年 | 5643篇 |
1986年 | 5377篇 |
1985年 | 7641篇 |
1984年 | 7784篇 |
1983年 | 6452篇 |
1982年 | 6922篇 |
1981年 | 6790篇 |
1980年 | 6535篇 |
1979年 | 6742篇 |
1978年 | 6846篇 |
1977年 | 6689篇 |
1976年 | 6691篇 |
1975年 | 6520篇 |
1974年 | 6369篇 |
1973年 | 6660篇 |
1972年 | 4059篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
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
52.
53.
54.
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
55.
56.
Lithium Insertion Mechanism in Iron-Based Oxyfluorides with Anionic Vacancies Probed by PDF Analysis
Dr. Damien Dambournet Dr. Karena W Chapman Dr. Mathieu Duttine Dr. Olaf Borkiewicz Dr. Peter J Chupas Dr. Henri Groult 《ChemistryOpen》2015,4(4):443-447
The mechanism of lithium insertion that occurs in an iron oxyfluoride sample with a hexagonal–tungsten–bronze (HTB)-type structure was investigated by the pair distribution function. This study reveals that upon lithiation, the HTB framework collapses to yield disordered rutile and rock salt phases followed by a conversion reaction of the fluoride phase toward lithium fluoride and nanometer-sized metallic iron. The occurrence of anionic vacancies in the pristine framework was shown to strongly impact the electrochemical activity, that is, the reversible capacity scales with the content of anionic vacancies. Similar to FeOF-type electrodes, upon de-lithiation, a disordered rutile phase forms, showing that the anionic chemistry dictates the atomic arrangement of the re-oxidized phase. Finally, it was shown that the nanoscaling and structural rearrangement induced by the conversion reaction allow the in situ formation of new electrode materials with enhanced electrochemical properties. 相似文献
57.
Yingchun Wu Haipeng Li Xuecheng Wu Gérard Gréhan Lutz Mädler Cyril Crua 《Proceedings of the Combustion Institute》2019,37(3):3211-3218
Droplet evaporation characterization, although of great significance, is still challenging. The recently developed phase rainbow refractometry (PRR) is proposed as an approach to measuring the droplet temperature, size as well as evaporation rate simultaneously, and is applied to a single flowing n-heptane droplet produced by a droplet-on-demand generator. The changes of droplet temperature and evaporation rate after a transient spark heating are reflected in the time-resolved PRR image. Results show that droplet evaporation rate increases with temperature, from ?1.28 m2/s at atmospheric 293 K to a range of (?1.5, ?8) m2/s when heated to (294, 315) K, agreeing well with the Maxwell and Stefan–Fuchs model predictions. Uncertainty analysis suggests that the main source is the indeterminate gradient inside droplet, resulting in an underestimation of droplet temperature and evaporation rate. With the demonstration on simultaneous measurements of droplet refractive index as well as droplet transient and local evaporation rate in this work, PRR is a promising tool to investigate single droplet evaporation in real engine conditions. 相似文献
58.
J. Conrad J. Cohen-Tanugi L. E. Strigari 《Journal of Experimental and Theoretical Physics》2015,121(6):1104-1135
The launch of the gamma-ray telescope Fermi Large Area Telescope (Fermi-LAT) started a pivotal period in indirect detection of dark matter. By outperforming expectations, for the first time a robust and stringent test of the paradigm of weakly interacting massive particles (WIMPs) is within reach. In this paper, we discuss astrophysical targets for WIMP detection and the challenges they present, review the analysis tools which have been employed to tackle these challenges, and summarize the status of constraints on and the claimed detections in the WIMP parameter space. Methods and results will be discussed in comparison to Imaging Air Cherenkov Telescopes. We also provide an outlook on short term and longer term developments. 相似文献
59.
60.
Jigneshkumar P. Patel Zou Guo Xiang Shaw Ling Hsu Andrew B. Schoch Sena Ada Carleen Dean Matsumoto 《Journal of Polymer Science.Polymer Physics》2015,53(21):1519-1526
A uniform dispersion of reactants is necessary to achieve a complete reaction involving multicomponents. In this study, we have examined the role of plasticizer in the reaction of two seemingly unlikely reactants: a highly crystalline hexamethylenetetramine (HMTA) and a strongly hydrogen bonded phenol formaldehyde resin. By combining information from NMR, infrared spectroscopy and differential scanning calorimetry, we were able to determine the role of specific intermolecular interactions necessary for the plasticizer to dissolve the highly crystalline HMTA and to plasticize the phenol formaldehyde resin in this crosslinking reaction. The presence of the plasticizer increased the segmental mobility, disrupted the hydrogen bonded matrix, and freed the hydroxyl units, which further increased the solubility of the HMTA. Both the endothermic and exothermic transitions are accounted for in the calorimetric data obtained. For the first time, it is possible to obtain the effective molar ratio of each component needed to complete the crosslinking reaction efficiently. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1519–1526 相似文献