全文获取类型
收费全文 | 30112篇 |
免费 | 4055篇 |
国内免费 | 2712篇 |
专业分类
化学 | 20479篇 |
晶体学 | 284篇 |
力学 | 1944篇 |
综合类 | 273篇 |
数学 | 3279篇 |
物理学 | 10620篇 |
出版年
2024年 | 105篇 |
2023年 | 590篇 |
2022年 | 908篇 |
2021年 | 987篇 |
2020年 | 1112篇 |
2019年 | 1081篇 |
2018年 | 911篇 |
2017年 | 813篇 |
2016年 | 1279篇 |
2015年 | 1268篇 |
2014年 | 1536篇 |
2013年 | 2050篇 |
2012年 | 2629篇 |
2011年 | 2657篇 |
2010年 | 1646篇 |
2009年 | 1632篇 |
2008年 | 1736篇 |
2007年 | 1659篇 |
2006年 | 1489篇 |
2005年 | 1227篇 |
2004年 | 940篇 |
2003年 | 789篇 |
2002年 | 751篇 |
2001年 | 561篇 |
2000年 | 558篇 |
1999年 | 651篇 |
1998年 | 578篇 |
1997年 | 574篇 |
1996年 | 659篇 |
1995年 | 506篇 |
1994年 | 464篇 |
1993年 | 388篇 |
1992年 | 371篇 |
1991年 | 322篇 |
1990年 | 255篇 |
1989年 | 202篇 |
1988年 | 157篇 |
1987年 | 136篇 |
1986年 | 127篇 |
1985年 | 118篇 |
1984年 | 88篇 |
1983年 | 61篇 |
1982年 | 41篇 |
1981年 | 36篇 |
1980年 | 18篇 |
1978年 | 19篇 |
1977年 | 23篇 |
1976年 | 20篇 |
1975年 | 28篇 |
1974年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
α-Aroyl substituted bis-ketene N,S-acetals 3–6 with a polymethylene linkage, N,N′-bis(1-methylthio-2-aroyl)vinyl polymethylene diamines, were synthesized by reactions between α-aroyl ketene dithioacetals 1 and polymethylene diamines 2 in moderate yields. © 1996 John Wiley & Sons, Inc. 相似文献
992.
Silica-supported polystannazane–copper complex has been prepared and used as a catalyst for the oxidation of methanol. The results showed that the catalyst could catalyze the oxidation of methanol to formaldehyde at a high yield and selectivity at 30°C and under 1 atm mild conditions. The N/Cu mole ratio in the complex, temperature and the amount of NaOH additive had much influence on the catalytic activity. The complex was stable during the reaction and could be used repeatedly. 相似文献
993.
Ying An Masahiro Suzuki Toshiki Koyama Kenji Hanabusa Hirofusa Shirai Mei-Yu Huang Ying-Jan Jiang 《先进技术聚合物》1996,7(8):652-656
The palladium cluster protected by silica-supported, crosslinking, partially phosphorylated poly(vinyl alcohol) (P-PVA) was prepared from a crosslinking P-PVA–Pd(II) complex by reduction in alcohol. The P-PVA–Pd complex and the palladium cluster protected by P-PVA were analyzed by electron spectroscopy, X-ray photoelectron spectrometry and transmission electron microscopy. The complex formation between the Pd(II) ion and phosphoric acid groups in P-PVA was important in the formation of a fine palladium cluster. Palladium clusters protected by silica-supported crosslinking P-PVA were used as catalysts for the hydrogenation of nitrobenzene or acrylic acid at 30°C under atmospheric pressure. The palladium cluster protected by crosslinking P-PVA supported on silica was the most active catalyst, was stable and had no by-products, compared with the palladium cluster protected by silica-supported noncrosslinking P-PVA or PVA. 相似文献
994.
Silica-supported mono-metal (such as Ni, Cu) complexes and mixed metal (such as Cu/Zn, Cu/Cr) complexes of chitosan have been prepared. It is found that these non-noble metal complexes could be used as efficient catalysts for the hydrogenation of aromatic nitro compounds. The effects of type of metal, reaction temperature and pressure, solvent, nitrogen/metal molar ratio in the complex catalysts on the yields from nitrobenzene to aniline have been examined. It was also found that catalysts are active for the catalytic hydrogenation of other aromatic nitro compounds such as 2-nitroanisole, 2-nitroaniline, 2-nitrotoluene and 1-chloro-4-nitrobenzene. 相似文献
995.
The epoxidation of styrene to styrene oxide at higher than 96% yield has been achieved by the catalysis by poly-(vinylbenzyl)acetylacetonate complexes of cobalt(II) or manganese(II) in the presence of isobutyraldehyde under an atmospheric pressure of molecular oxygen at room temperature. The kind of aldehyde and aldehyde/styrene molar ratio greatly influenced the reaction. The catalyst could be recycled, but after recycling for five times, the yield of styrene oxide decreased from 96.0% to 84.6%. 相似文献
996.
997.
998.
999.
Addition of C60 moiety, a powerful electron acceptor to poly(N-vinylcarbazole) (PVK) by chemical reaction modifies considerably the physical and chemical properties of PVK. The characterization techniques employed are UV-visible, IR, DSC, TGA, ESR, 13C-NMR spectroscopy, scanning electron microscopy, XRD, and cyclic voltammetry. The fullerenated PVK, which has a visibly earthy yellow cast when compared with the unreacted polymer, has a new structure in the UV-vis absorption spectrum with the active range extending from about 280 to 870 nm, its apparent temperature sensitivity is intriguing, and an unusual temperature dependence for the ESR spectrum is observed. Considerable difference of electronic structure between pure PVK and C60-PVK copolymer is indicated. The thermal stability and oxidation-reduction activation of pure PVK are enhanced by C60-chemical modification. © 1996 John Wiley & Sons, Inc. 相似文献
1000.