全文获取类型
收费全文 | 58765篇 |
免费 | 10009篇 |
国内免费 | 1550篇 |
专业分类
化学 | 55804篇 |
晶体学 | 564篇 |
力学 | 1335篇 |
综合类 | 2篇 |
数学 | 4168篇 |
物理学 | 8451篇 |
出版年
2023年 | 140篇 |
2022年 | 302篇 |
2021年 | 617篇 |
2020年 | 1597篇 |
2019年 | 2893篇 |
2018年 | 1289篇 |
2017年 | 922篇 |
2016年 | 3876篇 |
2015年 | 3940篇 |
2014年 | 3996篇 |
2013年 | 5266篇 |
2012年 | 4637篇 |
2011年 | 4026篇 |
2010年 | 3902篇 |
2009年 | 3743篇 |
2008年 | 3888篇 |
2007年 | 3170篇 |
2006年 | 2793篇 |
2005年 | 2886篇 |
2004年 | 2527篇 |
2003年 | 2185篇 |
2002年 | 2794篇 |
2001年 | 1954篇 |
2000年 | 1761篇 |
1999年 | 664篇 |
1998年 | 279篇 |
1997年 | 315篇 |
1996年 | 338篇 |
1995年 | 271篇 |
1994年 | 277篇 |
1993年 | 281篇 |
1992年 | 269篇 |
1991年 | 208篇 |
1990年 | 159篇 |
1989年 | 144篇 |
1988年 | 142篇 |
1987年 | 118篇 |
1986年 | 98篇 |
1985年 | 176篇 |
1984年 | 126篇 |
1983年 | 105篇 |
1982年 | 132篇 |
1981年 | 94篇 |
1980年 | 86篇 |
1978年 | 96篇 |
1977年 | 109篇 |
1976年 | 101篇 |
1975年 | 112篇 |
1974年 | 83篇 |
1973年 | 106篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
911.
The determination of lanthanides by Inductively Coupled Plasma Mass Spectrometry (ICP‐MS) is complicated by several spectral overlaps from M+, MO+ or MOH+ ions formed in the ICP. Especially, it is essential to avoid the spectral interferences from lighter lanthanide and Ba polyatomic ions on middle or heavier lanthanides. To tackle this problem, we have developed a mathematical correction method, which reduces all the spectral overlaps from oxide species of Pr, Nd, Ce and Sm over Gd, Tb, Dy and Ho, and Gd, Tb over Yb and Lu. It can also successfully correct the oxide and hydroxide interference of Ba over Eu. The effectiveness of the proposed the mathematical correction scheme is demonstrated for the USGS Standard Rock samples AGV‐1 and G‐2. The results show that the experimental data obtained by applying the mathematical correction scheme for lanthanides is in good agreement with the reported values, using pneumatic and ultrasonic nebulisation methods, for their ICP‐MS analysis. 相似文献
912.
H. Poschenrieder H.‐D. Stachel B. Wiesend K. Polborn 《Journal of heterocyclic chemistry》2003,40(1):61-69
Ozonolysis of the pyrrolidinediones 4 afforded the pyrrolidinetriones 5 , which in the presence of Lewis acids were converted into maleimide 6 . Analogously, ozonolysis of the pyrrolidinones 7 gave the pyrrolidinediones 8 , which were converted into the pyridinetriones 11a, b via Lewis acid catalyzed isomerization to yield the trihydroxypyridones 10 and ensuing air oxidation. In solution two tautomeric forms of the pyridinetriones 11 may exist both of which represent hydroxy‐azabenzoquinones. In two steps compounds 11 were transformed into the azaquinone derivatives 19 . Representatives of another type of azaquinones are compounds 28a, b. These were generated in two steps from the pyridones 25 . The azaquinone 28a reacted easily with acidic compounds yielding the adducts 26, 27 and 29 or with 2‐butenal forming the cycloadduct 30 . 相似文献
913.
K. H. Kim J. H. Lee M. Y. Ko K. S. Shin J. S. Kang W. C. Mar J. R. Youm 《Chromatographia》2002,55(1-2):81-85
Summary A method for the assay of R-(+)- and S-(−)- metoprolol in human urine has been developed using gas chromatography-mass spectrometry.
The method involved purification by liquid-liquid extraction and derivatization with N-methyl-N-(trimethylsilyl)trifluoroacetamide
to form an O-silyl ether, followed by subsequent chiral derivatization with (−)-α-methoxy-α-(trifluoromethyl)phenylacetyl
chloride to form diastereomeric amide. The reaction was rapid and the diastereomeric derivatives were well resolved. Quantitation
was performed by selected-ion monitoring of fragment ions of the diastereomers in electron impact ionization mode. No racemization
was found during the reaction. The detection limit was 0.5 ng·mL−1. The intra-day variation ranged between 0.38 and 7.86% in relation to the measured concentration and inter-day variation
was 2.26–8.06%. The method has been applied to the determination of R-(+)-and S-(−)- metoprolol in human urine from healthy
volunteers dosed with racemic metoprolol tartrate. 相似文献
914.
Mathematical Programming - A Correction to this paper has been published: 10.1007/s10107-020-01587-x 相似文献
915.
Mathematical Programming - A clutter is k-wise intersecting if every k members have a common element, yet no element belongs to all members. We conjecture that, for some integer $$k\ge 4$$ , every... 相似文献
916.
Methodology and Computing in Applied Probability - We study an information asymmetry problem in a bond market. Especially we derive bond price dynamics of traders with different levels of... 相似文献
917.
918.
919.
920.
Balest R Cho K Ford WT Lohner M Park H Rankin P Smith JG Alexander JP Bebek C Berger BE Berkelman K Bloom K Browder TE Cassel DG Cho HA Coffman DM Crowcroft DS Dickson M Drell PS Dumas DJ Ehrlich R Elia R Gaidarev P Garcia-Sciveres M Gittelman B Gray SW Hartill DL Heltsley BK Henderson S Jones CD Jones SL Kandaswamy J Katayama N Kim PC Kreinick DL Lee T Liu Y Ludwig GS Masui J Mevissen J Mistry NB Ng CR Nordberg E Patterson JR Peterson D Riley D Soffer A Avery P Freyberger A Lingel K Prescott C 《Physical review letters》1995,75(21):3809-3813