全文获取类型
收费全文 | 33266篇 |
免费 | 3531篇 |
国内免费 | 6085篇 |
专业分类
化学 | 29243篇 |
晶体学 | 1324篇 |
力学 | 791篇 |
综合类 | 232篇 |
数学 | 2081篇 |
物理学 | 9211篇 |
出版年
2024年 | 71篇 |
2023年 | 379篇 |
2022年 | 951篇 |
2021年 | 892篇 |
2020年 | 1127篇 |
2019年 | 1104篇 |
2018年 | 916篇 |
2017年 | 1263篇 |
2016年 | 1291篇 |
2015年 | 1172篇 |
2014年 | 1569篇 |
2013年 | 2823篇 |
2012年 | 1930篇 |
2011年 | 2377篇 |
2010年 | 1991篇 |
2009年 | 2266篇 |
2008年 | 2309篇 |
2007年 | 2288篇 |
2006年 | 2136篇 |
2005年 | 1993篇 |
2004年 | 1774篇 |
2003年 | 1453篇 |
2002年 | 1243篇 |
2001年 | 1054篇 |
2000年 | 1001篇 |
1999年 | 805篇 |
1998年 | 682篇 |
1997年 | 602篇 |
1996年 | 516篇 |
1995年 | 528篇 |
1994年 | 466篇 |
1993年 | 397篇 |
1992年 | 309篇 |
1991年 | 218篇 |
1990年 | 139篇 |
1989年 | 136篇 |
1988年 | 118篇 |
1987年 | 72篇 |
1986年 | 75篇 |
1985年 | 67篇 |
1984年 | 52篇 |
1983年 | 33篇 |
1982年 | 43篇 |
1981年 | 46篇 |
1980年 | 49篇 |
1979年 | 43篇 |
1978年 | 32篇 |
1977年 | 27篇 |
1976年 | 15篇 |
1973年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
971.
A nano‐crystalline In2O3 was synthesized using calcinations methods and was used as a photocatalyst to degrade sulfan blue (SB) dye. In addition, this study addresses the conditions of the degradation and the factors that influenced the catalysis. In2O3 was prepared by calcining In(OH)3 at heat ranges of 100–700 °C for 24 h. The In2O3 was characterized using field emission scanning electron microscopy (FE‐SEM), an X‐ray diffractometer (XRD), thermogravimetric analysis (TGA), and high‐resolution X‐ray photoelectron spectroscopy (HR‐XPS). The activities of these samples were tested for the photocatalytic degradation of SB dye. The results indicated that the In(OH)3 that was calcined at 300 °C for 24 h had the best performance. 相似文献
972.
Nourallah Hazeri Malek Taher Maghsoodlou Sayyed Mostafa Habibi‐Khorassani Jasem Aboonajmi Seyed Sajad Sajadikhah 《中国化学会会志》2013,60(4):355-358
Fe(NO3)3·9H2O is used as an efficient and effective catalyst for the one‐pot three‐component synthesis of highly functionalized piperidines from aromatic aldehydes, anilines and b–ketoesters in ethanol at ambient temperature. This procedure includes some important aspects like the easy work‐up, no need to column chromatography, simple and readily available precursors, and good to high yields. 相似文献
973.
Manuel Alberto Flores‐Hidalgo Daniel Glossman‐Mitnik D. H. Galvan Diana Barraza‐Jimenez 《中国化学会会志》2013,60(8):1082-1091
Density Functional Theory employing hybrid and M06 functionals in combination with three different basis sets is used to calculate the ground state of a cage like (ZnO)12 nanocluster which has been consistently reported as the more stable cluster for its particular size. B3LYP and B3PW91 hybrid functionals combined with 6‐31+G*, Lanl2dz and SDD basis sets are employed to treat the ZnO molecular system. Alternatively, three M06 functionals in combination with three basis sets are employed in the nanostructure calculations. Results obtained by treating ZnO sodalite cage nanocluster with M06 functionals demonstrated comparable quality to results obtained with hybrid functionals. Within this study, efficient theoretical DFT methods with the widely known hybrid and the recently created M06 meta‐hybrid functionals are employed to study nanostructured ZnO. Our resulting parameters provide a fresh approach performance wise on the different theoretical methods to treat transition metal nanostructures, particularly, ZnO nanoclusters geometry and electronic structure. 相似文献
974.
A simple and convenient method for the aromatization of Hantzsch 1,4-dihydropyridines to the corresponding pyridines is achieved via combination of aluminum or ferric nitrates and silica sulfuric acid as environmentally friendly and novel oxidizing media. This oxidation was carried out in dichloromethane under heterogeneous conditions with good to excellent yields. 相似文献
975.
A novel way of preparation for o-hydroxyarylketones with mild conditions and good yields by palladium-catalyzed coupling reaction of o-hydroxyarylaldehydes with hypervalent iodonium salts via the cleavage of the aldehyde C-H bond has been reported. 相似文献
976.
The base‐catalyzed Diels–Alder reactions of 4‐arylthio‐3‐hydroxy‐2‐pyrones are reported. Treatment of 4‐arylthio‐3‐hydroxy‐2‐pyrones and dienophiles with triethylamine gave 2‐arylthio‐2‐cyclohexenone derivatives by the Diels–Alder reaction involving a decarboxylation in excellent to reasonable yields. 相似文献
977.
A mild and highly efficient stereoselective reaction of 3,4,6‐tri‐O‐acetyl‐d‐glucal with a variety of nucleophiles, viz. alcohols, phenols, thiols, thiophenols, and allyl trimethyl silane (TMS), in the presence of 5 mol% of lanthanum(III) nitrate hexahydrate under solvent‐free conditions yielded the corresponding 2,3‐unsaturated glycopyranosides (pseudoglycals) in excellent yields. 相似文献
978.
Alex F. C. Flores Juliana L. Malavolta Leandro M. Frigo Morgana Doneda Darlene C. Flores 《合成通讯》2013,43(10):1198-1204
We develop an efficient method to synthesize novel propionyl-spaced bisheterocyclic compounds. It entails cyclocondensation of 3-(5-trifluoromethyl-1H-pyrazol-3-yl)propanoyl hydrazide obtained from levulinic acid, with 1,1,1-trifluoro-4-methoxy-3-alken-2-ones proceeding regiospecifically to 1-[(5-trifluoromethyl-5-hydroxy-3-substituted-4,5-dihydro-1H-pyrazol-1-yl)-3-(5-trifluoromethyl-1H-pyrazol-3-yl)propan-1-one derivatives. 相似文献
979.
Following our efforts towards the synthesis of new potential inhibitors of Xanthine Dehydrogenase (XDH), we describe here a general method for the preparation of N-(5-oxo-2,5-dihydro)pyrrol-3-yl glycines and N-(5-oxo-2,5-dihydro)pyrrol-3-yl glycine esters from glycine ethyl ester hydrochloride and various 4-hydroxy-5-oxo-2,5-dihydro-1H-pyrrole-3-carboxylic acid esters and carbonitriles. 相似文献
980.
An efficient, simple, and practical method has been developed for the deprotection of prenyl, geranyl, and phytyl ethers and esters of aromatic and aliphatic compounds using borontrifluoride–etherate (BF3 · OEt2) at room temperature in good to excellent yields for the first time. Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications® to view the free supplemental file. 相似文献