全文获取类型
收费全文 | 6852篇 |
免费 | 1117篇 |
国内免费 | 811篇 |
专业分类
化学 | 4761篇 |
晶体学 | 72篇 |
力学 | 393篇 |
综合类 | 38篇 |
数学 | 781篇 |
物理学 | 2735篇 |
出版年
2024年 | 24篇 |
2023年 | 135篇 |
2022年 | 248篇 |
2021年 | 245篇 |
2020年 | 243篇 |
2019年 | 274篇 |
2018年 | 217篇 |
2017年 | 210篇 |
2016年 | 302篇 |
2015年 | 338篇 |
2014年 | 370篇 |
2013年 | 448篇 |
2012年 | 595篇 |
2011年 | 641篇 |
2010年 | 404篇 |
2009年 | 356篇 |
2008年 | 418篇 |
2007年 | 392篇 |
2006年 | 401篇 |
2005年 | 303篇 |
2004年 | 245篇 |
2003年 | 219篇 |
2002年 | 166篇 |
2001年 | 155篇 |
2000年 | 161篇 |
1999年 | 175篇 |
1998年 | 144篇 |
1997年 | 129篇 |
1996年 | 123篇 |
1995年 | 117篇 |
1994年 | 112篇 |
1993年 | 75篇 |
1992年 | 77篇 |
1991年 | 85篇 |
1990年 | 55篇 |
1989年 | 34篇 |
1988年 | 36篇 |
1987年 | 30篇 |
1986年 | 19篇 |
1985年 | 19篇 |
1984年 | 9篇 |
1983年 | 19篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有8780条查询结果,搜索用时 15 毫秒
991.
Jianghua Zeng Dingsheng Yuan Yingliang Liu Jingxing Chen Sanxiang Tan 《Frontiers of Chemistry in China》2009,4(2):127-131
Tungsten carbide (WC) nanocrystals have been prepared by a solvothermal method with Mg as the reductant and WO3 and anhydrous ethanol as the precursors. The effects of time and temperature on the synthesis of WC were investigated and
a probable formation mechanism was discussed. The obtained WC nanocrystals were characterized by X-ray diffraction, transmission
electron microscopy, energy dispersive spectroscopy and electrochemical methods. Hexagonal closepacked WC was successfully
synthesized when the temperature was as low as 500°C. The content of carbon was more than that of W, indicating that the composition
of the treated sample was C and WC only. The diameters of WC nanocrystals were ranged from 40 nm to 70 nm and the nanocrystals
were dispersed on carbon films. The electrochemical measurements reveal that WC nanocrystals obviously promote Pt/C electrocatalytic
ability for the oxygen reduction reaction.
__________
Translated from Chinese Journal of Catalysis, 2008, 29(7) (in Chinese) 相似文献
992.
In this paper, several sufficient conditions are obtained to guarantee that the n-dimensional cellular neural network can have even (?2n) memory patterns. In addition, the estimations of attractive domain of such stable memory patterns are obtained. These conditions, which can be directly derived from the parameters of the neural networks, are easily verified. A new design procedure for cellular neural networks is developed based on stability theory (rather than the well-known perceptron training algorithm), and the convergence in the new design procedure is guaranteed by the obtained local stability theorems. Finally, the validity and performance of the obtained results are illustrated by two examples. 相似文献
993.
2,2,6,6-Tetrafluoro-4-phenylmethylmorpholin-3-ones are obtained from a new single step, preparative route by reacting triethylene glycol di(trifluoromethanesulfonate), which contains poly -CF2O- groups, with benzylamine. Reaction of trifluoromethylsulfonate and trifluoromethoxy derivatives with benzylamine gave either the nucleophilically-substituted product or the product resulting from the basic hydrolysis of the difluoromethoxy group. Replacement of a fluoroether chain by a fluoroalkane gave rise to fluorinated phenylmethylpiperidine and phenylmethylazepine via the combination of trifluoromethanesulfonic fluoroalkyldiyl esters and benzylamine. 相似文献
994.
Z. H. Liu J. Chen L. S. Yu H. D. Jiang T. W. Yao S. Zeng 《Rapid communications in mass spectrometry : RCM》2009,23(13):1899-1906
Ginkgolic acids have been shown to possess allergenic as well as genotoxic and cytotoxic properties. The question arises whether the metabolism of ginkgolic acids in the liver could decrease or increase their toxicity. In this study, the in vitro metabolism of ginkgolic acid (15:1, GA), one component of ginkgo acids, was investigated as a model compound in Sprague‐Dawley rat liver microsomes. The metabolites were analyzed by ultra‐performance liquid chromatography coupled with photodiode array detector/negative‐ion electrospray ionization tandem mass spectrometry (UPLC‐PDA/ESI‐MS/MS) and hydrogen/deuterium (H/D) exchange. The result showed that the benzene ring remained unchanged and the oxidations occurred at the side alkyl chain in rat liver microsomes. At least eight metabolites were found. Among them, six phase I metabolites were tentatively identified. This study might be useful for the investigation of toxicological mechanism of ginkgolic acids. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
995.
In this paper, we extend the two-level Schwarz method to solve the variational inequality problems with nonlinear source terms, and establish a convergence theorem. The method converges within finite steps with an appropriate initial point. The numerical results show that the methods are efficient. 相似文献
996.
997.
储能器是一种储存能量的装置,随着高温超导悬浮轴承运用到飞轮储能器中,储能效率得到了大大的提高。它的主要结构是由高温超导体和永磁体组成。文中提出一种全新高温超导悬浮轴承,并研究其的力学性能,为新型超导悬浮轴承的研究与开发做好了基础准备。 相似文献
998.
999.
Liang Liu Dujuan Zeng Xianlong Wei Qing Chen Xide Li 《Acta Mechanica Solida Sinica》2009,22(6):584-592
Two kinds of clamping in micro/nano scale experiments are investigated in this paper, one based on electron-beam-induced deposition, and the other on the van der Waals interaction. The clamping strength and mechanism are analyzed both theoretically and experimentally. The influence of relative humidity on the micro/nano clamping and the method of electrostatic clamping are discussed. The clamping strength and performance of different clamping methods are compared considering the size and material of the clamped objects, and the application environments. 相似文献
1000.
研制半自动定容试液,半自动定位恒速注入KBK4,整个氢化过程不串空气,可用压力全方位喷射冲洗反应室。该装置定容定位准确,操作简便快速,适用于大批量样品分析。通过对8个GSD标准参考物质的分析,分析结果与参考值基本一致,RSD<6%。 相似文献