全文获取类型
收费全文 | 5849篇 |
免费 | 386篇 |
国内免费 | 405篇 |
专业分类
化学 | 2045篇 |
晶体学 | 19篇 |
力学 | 622篇 |
综合类 | 77篇 |
数学 | 2216篇 |
物理学 | 1661篇 |
出版年
2023年 | 52篇 |
2022年 | 125篇 |
2021年 | 97篇 |
2020年 | 139篇 |
2019年 | 130篇 |
2018年 | 78篇 |
2017年 | 154篇 |
2016年 | 179篇 |
2015年 | 131篇 |
2014年 | 219篇 |
2013年 | 332篇 |
2012年 | 231篇 |
2011年 | 259篇 |
2010年 | 177篇 |
2009年 | 297篇 |
2008年 | 350篇 |
2007年 | 319篇 |
2006年 | 329篇 |
2005年 | 266篇 |
2004年 | 186篇 |
2003年 | 208篇 |
2002年 | 224篇 |
2001年 | 186篇 |
2000年 | 171篇 |
1999年 | 152篇 |
1998年 | 158篇 |
1997年 | 135篇 |
1996年 | 114篇 |
1995年 | 77篇 |
1994年 | 71篇 |
1993年 | 68篇 |
1992年 | 74篇 |
1991年 | 50篇 |
1990年 | 43篇 |
1989年 | 26篇 |
1988年 | 49篇 |
1987年 | 40篇 |
1986年 | 24篇 |
1985年 | 87篇 |
1984年 | 104篇 |
1983年 | 58篇 |
1982年 | 97篇 |
1981年 | 93篇 |
1980年 | 54篇 |
1979年 | 54篇 |
1978年 | 51篇 |
1977年 | 33篇 |
1976年 | 23篇 |
1974年 | 16篇 |
1973年 | 21篇 |
排序方式: 共有6640条查询结果,搜索用时 31 毫秒
1.
2.
João Marcos G. Barbosa Milenna K. Fernandes Rodrigues Lurian C. David Taynara C. e Silva Danielly A. Fortuna Lima Naiara Z. Pereira Emmanuel B. D'Alessandro Anselmo E. de Oliveira Paulo H. Jorge da Cunha Maria Clorinda S. Fioravanti Nelson R. Antoniosi Filho 《Biomedical chromatography : BMC》2020,34(11):e4935
An innovative volatolomic approach employs the detection of biomarkers present in cerumen (earwax) to identify cattle intoxication by Stryphnodendron rotundifolium Mart., Fabaceae (popularly known as barbatimão). S. rotundifolium is a poisonous plant with the toxic compound undefined and widely distributed throughout the Brazilian territory. Cerumen samples from cattle of two local Brazilian breeds (‘Curraleiro Pé-Duro’ and ‘Pantaneiro’) were collected during an experimental intoxication protocol and analyzed using headspace (HS)/GC–MS followed by multivariate analysis (genetic algorithm for a partial least squares, cluster analysis, and classification and regression trees). A total of 106 volatile organic metabolites were identified in the cerumen samples of bovines. The intoxication by S. rotundifolium influenced the cerumen volatolomic profile of the bovines throughout the intoxication protocol. In this way, it was possible to detect biomarkers for cattle intoxication. Among the biomarkers, 2-octyldecanol and 9-tetradecen-1-ol were able to discriminate all samples between intoxicated and nonintoxicated bovines. The cattle intoxication diagnosis by S. rotundifolium was accomplished by applying the cerumen analysis using HS/GC–MS, in an easy, accurate, and noninvasive way. Thus, the proposed bioanalytical chromatography protocol is a useful tool in veterinary applications to determine this kind of intoxication. 相似文献
3.
Qi Yongcheng 《数学年刊B辑(英文版)》1998,19(4):499-510
1.IntroductionLet{X.,n21}beasequenceoflidry'swithanondegeneratedistributionfunctionF(x).Supposethereexistsomeconstantsan>0,b.6RandsomeacERsuchthatwhereG.standsforoneoftheextremevaluedistributions:Heretheindex7ERisarealparameter(interpret(1 box)--'/ryase--"for7~0).Theestimationoftheextreme-valueindex7isveryimportantbothintheextremevaluetheoryandinpractice.Manystatistics,suchasHillestimator(forcaseac>0),PickandsestimatorandDekkers-EinmahLdeHaan'smomentestimatorwhicharebasedonafinitesample,… 相似文献
4.
5.
氪灯、氙灯光谱强度分布和光谱效率测量是反映氪灯、氙灯性能的关键指标。介绍了一套新型的氪灯、氙灯光谱强度分布和光谱效率检测系统。该系统是一套测量连续发光灯和脉冲闪光灯发光性能及效果的综合检测设备。该检测单元采用计算机进行操控,人机界面良好,便于检验人员进行氪灯和氙灯光谱强度分布和光谱效率的批量检测。检验人员利用该系统可进行装机模拟试验和可靠性试验,可对氪灯和氙灯的性能进行必要的分析研究,不断地积累了氪灯和氙灯的检验数据和经验。 相似文献
6.
LIU Jixue ZHANG Sanguo & CHEN Xiru Department of Statistics Finance University of Science Technology of China Hefei China Department of Mathematics Graduate School of Chinese Academy of Sciences Beijing China 《中国科学A辑(英文版)》2006,49(6):752-769
This paper studies the linear EV model when replicate observations are made only on independent variables. We construct the estimates of regression coefficients and prove the consistency and asymptotic normality under some proper conditions. Results obtained reveal the difference between the case where the independent and dependent variables are observed repeatedly and simultaneously and the case studied in this article. 相似文献
7.
We obtain a solution of the DGLAP equation for the gluon at low x first by expanding the gluon in a Taylor series and then using the method of characteristics. We test its validity by comparing
it with that of Glück, Reya and Vogt. The convergence criteria of the approximation used are also discussed. We also calculate
εF
2(x,Q)2/ε In Q
2 using its approximate relations with the gluon distribution at low x. The predictions are then compared with the HERA data. 相似文献
8.
9.
本文利用聚集型状态方程,克拉贝龙方程以及临界条件推出聚集活性参量方程.分析结果表明,医药的药理活性是可以用聚集活性参量予以定量表征.本文给出了某些医药的主要的药物成分,如氧化亚氮 乙醚、氯仿和水杨酸甲酯等嘛醉剂),一氧化氮(硝酸甘油)、乙醇胺(医药活性剂)和多巴胺(神经递质)的生物活性数据.实践经验表明,这些化学品分别在生命体的心血管系统、神经系统和免疫系统中起着重要的药理功能作用.这表明,本文研究的内容在医药学研究领域有其重要意义. 相似文献
10.
S. K. Godunov V. T. Zhukov O. B. Feodoritova 《Computational Mathematics and Mathematical Physics》2006,46(6):971-982
An algorithm is constructed for calculating invariant subspaces of symmetric hyperbolic systems arising in electromagnetic, acoustic, and elasticity problems. Discrete approximations are calculated for subspaces that correspond to minimal eigenvalues and smooth eigenfunctions. Difficulties related to the presence of an infinite-dimensional kernel in the differential operator are successfully handled. The efficiency of the algorithm is demonstrated using acoustics equations. 相似文献