全文获取类型
收费全文 | 2901篇 |
免费 | 156篇 |
国内免费 | 33篇 |
专业分类
化学 | 2223篇 |
晶体学 | 30篇 |
力学 | 53篇 |
数学 | 261篇 |
物理学 | 523篇 |
出版年
2023年 | 19篇 |
2022年 | 37篇 |
2021年 | 63篇 |
2020年 | 59篇 |
2019年 | 60篇 |
2018年 | 44篇 |
2017年 | 49篇 |
2016年 | 96篇 |
2015年 | 85篇 |
2014年 | 122篇 |
2013年 | 188篇 |
2012年 | 273篇 |
2011年 | 258篇 |
2010年 | 169篇 |
2009年 | 123篇 |
2008年 | 187篇 |
2007年 | 191篇 |
2006年 | 166篇 |
2005年 | 152篇 |
2004年 | 124篇 |
2003年 | 104篇 |
2002年 | 101篇 |
2001年 | 57篇 |
2000年 | 70篇 |
1999年 | 32篇 |
1998年 | 30篇 |
1997年 | 25篇 |
1996年 | 22篇 |
1995年 | 22篇 |
1994年 | 16篇 |
1993年 | 18篇 |
1992年 | 11篇 |
1991年 | 8篇 |
1990年 | 9篇 |
1989年 | 16篇 |
1988年 | 7篇 |
1987年 | 8篇 |
1986年 | 6篇 |
1985年 | 4篇 |
1983年 | 7篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 6篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1975年 | 3篇 |
1974年 | 5篇 |
1973年 | 5篇 |
排序方式: 共有3090条查询结果,搜索用时 15 毫秒
61.
For any -complexes and , we show that . We use this fact to compute generalized evaluation subgroups of generalized tori relative to a sphere.
62.
Gu P Haas P Hogan WP Kim SK Matthews JN Myung SS Schnetzer S Thomson GB Zou Y Arisaka K Roberts D Slater W Spencer MB Weaver M Briere RA Cheu E Harris DA Krolak P McFarland KS Roodman A Schwingenheuer B Somalwar SV Wah YW Winstein B Winston R Barker AR Swallow EC Bock GJ Coleman R Crisler M Enagonio J Ford R Hsiung YB Jensen DA O'Dell VR Ramberg E Tschirhart R Collins EM Gollin GD Nakaya T Yamanaka T 《Physical review letters》1996,76(23):4312-4315
63.
64.
The organic basic solution, 1 M tetramethylammonium hydroxide (TMAH) in methanol, was employed for the hydrolysis of extremely small amounts of lipids compared to the classical inorganic basic solution, 1 M KOH in ethanol. The hydrolysed fatty acids were derivatized as N(O)-tert.-butyldimethylsilyl (tBDMSi) esters with N-methyl-N-(tert.-butyldimethylsilyl) trifluoroacetamide (MTBSTFA) and compared with the classical derivatives, the methyl esters, made by the BF3-methanol method. Recoveries of fatty acids determined on the standard fatty acids and soybean oil hydrolysed with TMAH were high: about 1.1-2.1- and 2.0-5.4-times, respectively, in all fatty acids compared with the hydrolysis by KOH regardless of derivatization method. The relative standard deviations (RSDs) on the recoveries of standard fatty acids were less than 5% when hydrolysed with TMAH, regardless of derivatives, but when hydrolysed with KOH, RSDs were more than 5% for most fatty acids, especially for long-chain fatty acids. The RSDs on the recoveries of fatty acids on the soybean oil were also very high in the KOH hydrolysis. Fatty acid compositions of soybean oil were similar in the main fatty acids regardless of hydrolysis methods, but showed slightly different values, depending on the methods of derivatization. RSDs were also very high in the KOH hydrolysis. In view of these results, precision of analysis by KOH hydrolysis was very poor, so we could not rely on the data. On the other hand, the reliability of data by TMAH hydrolysis method was very high, so it is a useful new hydrolysis method for extremely small amounts of lipid samples. Both derivatives of 35 standard fatty acids were successfully separated on a HP-1 nonpolar capillary column. tBDMSi derivatives were completely resolved in 70 min by 295 degrees C. In the methyl ester derivatives it took about 80 min to get satisfying resolution, but these derivatives were completely resolved by 250 degrees C. The sensitivity of tBDMSi derivatives was about 1.5-6.3-times higher than that with methyl ester derivatives. The stability of tBDMSi derivatives was constant for about 144 h except arachidic, docosahexanoic, behenic and heneicosanoic acids, which were stable for only 86 h. 相似文献
65.
The urinary codeine-to-morphine ratios in fifteen volunteers administered codeine tablets at intervals were studied by gas chromatography (GC) and compared with one month's GC results for enzyme multiplied immunoassay technique (EMIT)-screened urine specimens in a mass-screening programme for abuse of opiate drugs, particularly heroin. It appears that when M less than 2 and C/M greater than 0 or when M greater than 2 and C/M greater than 0.5, where C and M are codeine and morphine concentrations in micrograms per 10 ml of urine, codeine consumption has to be presumed. 相似文献
66.
The mass spectral decomposition modes of a series of 2-imino-4-thiazolidinone derivatives are reported and discussed. The fragmentation patterns and mechanisms postulated have been confirmed by the analysis of the MIKE spectra and using DADI technique and the effects of heteroatoms and substituents on the MIKE spectrum of these compounds are compared with that of 3-substituted hydantoins. 相似文献
67.
Grace H.C. Woo 《Tetrahedron》2006,62(45):10507-10517
A novel and efficient protocol for the synthesis of the 3,8-diazabicyclo[3.2.1]octane system found in the naphthyridinomycin, dnacin, and tetrazomine families of alkaloids is described. The key transformation involves an intramolecular palladium-catalyzed allylic alkylation. The cyclization proceeds smoothly under mild conditions (20 mol % Pd2dba3, 1.5 equiv DBU, 65 °C, THF, 20 min) to afford 3,8-diazabicyclo[3.2.1]octanes in excellent yields (94-98%). 相似文献
68.
Won Sick Woo Sam Sik Kang Otto Seligmann V. Mohan Chari Hildebert Wagner 《Tetrahedron letters》1980,21(44):4255-4258
From the seeds of Phytolacca americana two new lignans, Americanin B and D, have been isolated and their structures elucidated mainly by spectroscopic methods 相似文献
69.
A core-shell structure was found in AM SURE™ resin, in which most amino groups were located at the skin layer. The AM SURE™ resin revealed better synthetic efficiency, compared to the noncore-shell type resin in the synthesis of the fragment 65-74 of acyl carrier protein, the fragment 27-35 of HIV (human immunodeficiency virus) fusion inhibitor (T-20) and the Jung-Redemann 10-mer. 相似文献
70.