全文获取类型
收费全文 | 22303篇 |
免费 | 813篇 |
国内免费 | 16篇 |
专业分类
化学 | 14686篇 |
晶体学 | 170篇 |
力学 | 372篇 |
数学 | 3795篇 |
物理学 | 4109篇 |
出版年
2023年 | 148篇 |
2022年 | 148篇 |
2021年 | 235篇 |
2020年 | 328篇 |
2019年 | 349篇 |
2018年 | 457篇 |
2017年 | 408篇 |
2016年 | 836篇 |
2015年 | 649篇 |
2014年 | 685篇 |
2013年 | 1463篇 |
2012年 | 1419篇 |
2011年 | 1423篇 |
2010年 | 867篇 |
2009年 | 799篇 |
2008年 | 1254篇 |
2007年 | 1299篇 |
2006年 | 1150篇 |
2005年 | 1060篇 |
2004年 | 955篇 |
2003年 | 740篇 |
2002年 | 646篇 |
2001年 | 495篇 |
2000年 | 463篇 |
1999年 | 341篇 |
1998年 | 229篇 |
1997年 | 222篇 |
1996年 | 292篇 |
1995年 | 207篇 |
1994年 | 236篇 |
1993年 | 197篇 |
1992年 | 195篇 |
1991年 | 179篇 |
1990年 | 171篇 |
1989年 | 153篇 |
1988年 | 143篇 |
1987年 | 139篇 |
1986年 | 134篇 |
1985年 | 196篇 |
1984年 | 198篇 |
1983年 | 124篇 |
1982年 | 131篇 |
1981年 | 141篇 |
1980年 | 140篇 |
1979年 | 96篇 |
1978年 | 95篇 |
1977年 | 104篇 |
1976年 | 83篇 |
1975年 | 86篇 |
1973年 | 71篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Inês Nunes Nuno Mesquita Sandra Cabo Verde Maria João Trigo Armando Ferreira Maria Manuela Carolino António Portugal Maria Luísa Botelho 《Radiation Physics and Chemistry》2012,81(12):1943-1946
Parchments are important documents that give testimony for History; therefore these materials should be respected and preserved. Considering incremental biodeterioration problems that have to be faced daily, the Archive of the University of Coimbra (AUC) is involved in different scientific projects in order to evaluate and determine new methods for document decontamination and preservation.The aim of this study was to evaluate gamma radiation effects on the colour and texture of the AUC parchment documents. The assessment of these effects was used to estimate the maximum gamma radiation dose (Dmax) that could guarantee parchment documents′ decontamination treatment, without significant alteration of their physical properties. Parchment samples were exposed to gamma radiation doses ranging from 10 to 30 kGy. The texture and colour of samples were assessed before and after the irradiation procedure, using a texture analyser and an electronic colorimeter. Hardness and springiness were determined based on texture spectra. Lightness (L?), Chroma (C), greenness vs. redness (a*) and yellowness vs. blueness (b*) values were obtained from colorimetric measures. Results indicate no significant effects of gamma radiation on the texture and colour of parchment for the studied doses. 相似文献
992.
Ranking fuzzy numbers is often a necessary step in many mathematical models, and a large number of ranking methods have been proposed to perform this task. However, few comparative studies exist and nowadays it is still unknown how similar ranking methods are in practice, i.e., how likely they are to induce the same ranking. In this study, by means of numerical simulations, we try to answer this question. We shall discover that there are some very similar methods as well as some outliers. We end the paper interpreting the results and giving some recommendations on the use of ranking methods. 相似文献
993.
994.
Vidal-Iglesias Francisco J. Montiel Vicente Solla-Gullón José 《Journal of Solid State Electrochemistry》2016,20(4):1107-1118
Journal of Solid State Electrochemistry - The influence of the metal loading (i.e. interparticle distance) of shape-controlled Pt nanoparticles on their electrocatalytic properties is evaluated for... 相似文献
995.
Ramon Carbó-Dorca 《Journal of mathematical chemistry》2012,50(9):2339-2341
A simple argument proves that quantum similarity measures, performed on any density function (DF) tag set of a given quantum object set, create a hologram of such DF tag set. 相似文献
996.
Suely L. Galdino Maria C. A. Lima Alexandre J. S. Góes Ivan R. Pitta Cuong Luu-Duc 《光谱学快报》2013,46(7-8):1013-1021
In the present investigation, a study of the electron impact mass spectrometry data is reported for seven compounds of a series of some 3-(4-chlorobenzyl)-5-benzylidene-imidazolidine-2, 4-diones and 3-(4-fluoro or chlorobenzyl)-5-benzylidene-thiazolidine-2, 4-diones previously synthesized. 相似文献
997.
Jordi Badosa Josep Calbó Richard Mckenzie Ben Liley Josep‐Abel González Bruce Forgan Charles N. Long 《Photochemistry and photobiology》2014,90(4):941-951
Cloud effects on UV Index (UVI) and total solar radiation (TR) as a function of cloud cover and sunny conditions (from sky images) as well as of solar zenith angle (SZA) are assessed. These analyses are undertaken for a southern‐hemisphere mid‐latitude site where a 10‐years dataset is available. It is confirmed that clouds reduce TR more than UV, in particular for obscured Sun conditions, low cloud fraction (<60%) and large SZA (>60°). Similarly, local short‐time enhancement effects are stronger for TR than for UV, mainly for visible Sun conditions, large cloud fraction and large SZA. Two methods to estimate UVI are developed: (1) from sky imaging cloud cover and sunny conditions, and (2) from TR measurements. Both methods may be used in practical applications, although Method 2 shows overall the best performance, as TR allows considering cloud optical properties. The mean absolute (relative) differences of Method 2 estimations with respect to measured values are 0.17 UVI units (6.7%, for 1 min data) and 0.79 Standard Erythemal Dose (SED) units (3.9%, for daily integrations). Method 1 shows less accurate results but it is still suitable to estimate UVI: mean absolute differences are 0.37 UVI units (15%) and 1.6 SED (8.0%). 相似文献
998.
999.
The sesquiterpene (+)-gossonorol is prepared in only three synthetic steps in 60% overall yield and 82% ee from commercially available reagents. The key asymmetric step is the catalytic enantioselective addition of dimethylzinc to 5-methyl-1-(2-methylphenyl)hex-4-en-1-one catalyzed by chiral isoborneolsulfonamide ligands in the presence of titanium tetraisopropoxide. The modular approach allows the synthesis not only of the aforementioned natural product but also other products arising from the corresponding processes of ethylation, phenylation, and ethynylation, just by changing the final nucleophilic reagent and using the same isoborneol type ligand. 相似文献
1000.
Radosław Bonikowski Józef Kula Anna Bujacz Anna Wajs-Bonikowska Małgorzata Zakłos-Szyda Stanisław Wysocki 《Tetrahedron: Asymmetry》2012,23(14):1038-1045
Ten enantiomerically pure hydroindene-derived compounds obtained by the transformation of (+)-carotol, the main constituent of carrot seed essential oil, were examined for their ability to inhibit the growth of myeloid leukaemia (HL-60) cancer cell lines. All compounds showed significant activity, which was comparable to the most active volatile organic compounds, such as trans–trans-farnesol, citral and nerolidol. Based on the bioactivity and molecular modelling, a 3D QSAR pharmacophore model was generated. 相似文献