全文获取类型
收费全文 | 2895篇 |
免费 | 119篇 |
国内免费 | 347篇 |
专业分类
化学 | 2291篇 |
晶体学 | 24篇 |
力学 | 8篇 |
综合类 | 16篇 |
数学 | 646篇 |
物理学 | 376篇 |
出版年
2024年 | 9篇 |
2023年 | 71篇 |
2022年 | 58篇 |
2021年 | 79篇 |
2020年 | 154篇 |
2019年 | 122篇 |
2018年 | 111篇 |
2017年 | 125篇 |
2016年 | 113篇 |
2015年 | 80篇 |
2014年 | 147篇 |
2013年 | 563篇 |
2012年 | 179篇 |
2011年 | 182篇 |
2010年 | 147篇 |
2009年 | 161篇 |
2008年 | 149篇 |
2007年 | 170篇 |
2006年 | 147篇 |
2005年 | 108篇 |
2004年 | 112篇 |
2003年 | 75篇 |
2002年 | 33篇 |
2001年 | 26篇 |
2000年 | 28篇 |
1999年 | 18篇 |
1998年 | 23篇 |
1997年 | 24篇 |
1996年 | 14篇 |
1995年 | 24篇 |
1994年 | 11篇 |
1993年 | 10篇 |
1992年 | 13篇 |
1991年 | 17篇 |
1990年 | 10篇 |
1989年 | 7篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 5篇 |
1976年 | 5篇 |
1975年 | 2篇 |
1974年 | 2篇 |
排序方式: 共有3361条查询结果,搜索用时 15 毫秒
931.
932.
933.
《Tetrahedron letters》2014,55(52):7186-7189
The reaction of α,β-unsaturated ketoximes with fluoroalkanosulfonyl fluorides in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) underwent the Beckmann rearrangement smoothly to afford the corresponding acid-sensitive enamides in moderate to excellent yields, which provides a new efficient method for the preparation of acid-sensitive enamides. 相似文献
934.
Mohammad Ali Zolfigol Arash Ghorbani Choghamarani 《Phosphorus, sulfur, and silicon and the related elements》2013,188(7):1623-1629
A combination of silica sulfuric acid and sodium nitrite in the presence of wet SiO 2 was used as an effective nitrosating agent for the nitrosation of g -diketones to their corresponding f -nitroso or f -oximinoketones under mild and heterogenous conditions in moderate to excellent yields. 相似文献
935.
M. M. Alavi Nikje M. A. Bigdeli H. Imanieh 《Phosphorus, sulfur, and silicon and the related elements》2013,188(8):1465-1468
Substituted α-aryl-N-methylnitrones are prepared by the condensation reaction of N-methylhydroxylamine hydrochloride and benzaldehydes in solvent-free media using silica-gel–NaOH catalyst system. The yields are excellent regardless of the electron-donating or electron-accepting nature of the substituents on benzaldehyde. Similar ketones are unreactive under these conditions, rendering chemoselectivity of the method. 相似文献
936.
A novel onoceranoid triterpene, named lamesticumin G (1) along with four known compounds (2–5) were isolated from the ethyl acetate extract of the fruit peels of Lansium parasiticum. The structure of lamesticumin G (1) was fully characterised using spectroscopic data. Lamesticumin G (1) inhibited α-glucosidase (maltase) with IC50 value of 2.27 mM, while 2–5 showed no inhibition. 相似文献
937.
利用紫外光解(UV)作为预处理工艺来强化生物过滤塔(BF)和生物滴滤塔(BTF)对疏水性化合物α-蒎烯的去除,基于试验数据对滤塔内α-蒎烯的传质行为和微生物活性进行了模型和理论分析.Michaelis-Menten动力学分析表明,α-蒎烯在UV-BTF内的气相饱和常数为1.0gm-3,是其在BTF内的20倍,而α-蒎烯在BF内的气相饱和常数略大于UV-BF内相应数值.UV-BTF的理论临界进气浓度为555.22mgm-3,高于其他处理系统.微生物代谢活性和比耗氧速率分析表明,UV-BTF内的微生物世代时间明显缩短,α-蒎烯及其光解产物的最大比耗氧速率分别达到了1.16、0.34、0.41和0.25mgO2mg-1DWh-1,略高于其他处理系统中相应数值的150%-200%.以上模型拟合数据从理论上说明UV光解工艺能减轻α-蒎烯在BTF内的传质抑制效应,进而提高整体宏观去除能力;但是由于BF工艺的自身特性和累积臭氧的毒害效应,UV光解不适合作为BF的预处理工艺. 相似文献
938.
Davut Avcı Sümeyye Altürk Fatih Sönmez Ömer Tamer Adil Başoğlu Yusuf Atalay Belma Zengin Kurt Necmi Dege 《应用有机金属化学》2020,34(4):e5412
A series of mixed-ligand M(II) complexes containing 1,10-phenanthroline (phen) and 3-methylpyridine-2-carboxylic acid (3-mpaH) or 6-methylpyridine-2-carboxylic acid (6-mpaH), namely [Co(3-mpa)2(phen)]·3H2O ( 1 ), [Hg(6-mpa)2(phen)]·2H2O ( 2 ), [Mn(6-mpa)2(phen)]·2H2O ( 3 ), [Co(6-mpa)2(phen)]·H2O ( 4 ) and [Ni(6-mpa)2(phen)]·H2O ( 5 ), were synthesized for the first time. Among them, 1 was obtained as single crystals. The structural characterization for 1 was conducted using X-ray diffraction and that for 2 – 5 using mass spectrometry. The IC50 values for α-glucosidase inhibition of 1 – 5 were obtained as 0.161 to >600 μM. The spectral properties were also investigated using Fourier transform infrared and UV–visible spectra. Furthermore, to investigate the geometrical parameters, spectral and electronic properties and second- and third-order nonlinear optical parameters for 1 – 5 , density functional calculations were applied. 相似文献
939.
Mădălina Mihalache Ovidiu Oprea Cornelia Guran Alina M. Holban 《Comptes Rendus Chimie》2018,21(1):32-40
The four divalent nickel complexes having α-ketoglutaric acid (H2A) and 1-(o-tolyl)biguanide (TB) ligands have been synthesized, characterized, and tested for antibacterial and antitumor activity.The proposed formulas for these complexes are [Ni(TB)(HA)(H2O)2]Cl (C1), [Ni(TB)(HA)(H2O)2]Br (C2), [Ni(TB)(HA)]NO3·H2O (C3), and [Ni(TB)(HA)]CH3COO (C4), where HA represents deprotonated H2A.For the four complexes and for the ligands used in the synthesis, the antibacterial activity against Staphylococcus aureus ATCC 25923 and Pseudomonas aeruginosa ATCC 27853 and antitumor activity in HeLa tumor cells were tested. A moderate cytotoxic effect of C3 and C4 complexes has been observed on the development and metabolic activity of HeLa cells, whereas C1 and C2 ligands have a very low effect on them.The synthesized complexes (obtained) inhibit adherence to the inert substrate of bacterial strains S. aureus and P. aeruginosa; therefore, they may be candidates for (potential) therapeutic applications. 相似文献
940.
Dr. Hua Wu Dr. Qian Wang Prof. Dr. Jieping Zhu 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(21):5952-5955
We report an unprecedented organocatalytic enantioselective acyloin rearrangement of α,α-disubstituted α-hydroxy acetals. In the presence of a catalytic amount of chiral binol-derived N-triflyl phosphoramide, α-hydroxy acetals rearranged to α-alkoxy ketones in good to high yields with high enantioselectivities. Formation of an ion pair between the in situ generated oxocarbenium ion and the chiral phosphoramide anion was proposed to be responsible for the highly efficient transfer of chirality. Conditions for removal of cyclohexyl and cyclopentyl groups from the corresponding α-alkoxy ketones were uncovered underpinning their potential general utility as hydroxy protecting groups. Conversion of the rearranged products to the enantioenriched α-hydroxy ketone, 1,2-diol, β-amino alcohol and 1,4-dioxane was also documented. 相似文献