全文获取类型
收费全文 | 1760篇 |
免费 | 155篇 |
国内免费 | 106篇 |
专业分类
化学 | 1129篇 |
晶体学 | 22篇 |
力学 | 82篇 |
综合类 | 8篇 |
数学 | 386篇 |
物理学 | 394篇 |
出版年
2023年 | 27篇 |
2022年 | 34篇 |
2021年 | 62篇 |
2020年 | 60篇 |
2019年 | 70篇 |
2018年 | 63篇 |
2017年 | 59篇 |
2016年 | 97篇 |
2015年 | 79篇 |
2014年 | 91篇 |
2013年 | 127篇 |
2012年 | 119篇 |
2011年 | 141篇 |
2010年 | 89篇 |
2009年 | 71篇 |
2008年 | 86篇 |
2007年 | 74篇 |
2006年 | 79篇 |
2005年 | 69篇 |
2004年 | 49篇 |
2003年 | 32篇 |
2002年 | 33篇 |
2001年 | 20篇 |
2000年 | 27篇 |
1999年 | 23篇 |
1998年 | 16篇 |
1997年 | 22篇 |
1996年 | 26篇 |
1995年 | 27篇 |
1994年 | 16篇 |
1993年 | 16篇 |
1992年 | 21篇 |
1991年 | 19篇 |
1990年 | 11篇 |
1989年 | 5篇 |
1987年 | 8篇 |
1986年 | 10篇 |
1985年 | 15篇 |
1984年 | 14篇 |
1983年 | 11篇 |
1982年 | 8篇 |
1981年 | 12篇 |
1980年 | 8篇 |
1979年 | 4篇 |
1978年 | 10篇 |
1977年 | 12篇 |
1976年 | 10篇 |
1975年 | 8篇 |
1974年 | 8篇 |
1973年 | 9篇 |
排序方式: 共有2021条查询结果,搜索用时 15 毫秒
51.
Dang Vu Giang 《Analysis Mathematica》1991,17(2):133-140
, . . [1] - . . 相似文献
52.
53.
Minh Duc Luong Jan Saeby Pierre Fombasso Andr Jacot-Guillarmod 《Helvetica chimica acta》1981,64(8):2741-2745
Phytochemistry of Genus Gentiana. XXVI. Identification of a New Di-O-glucosyl Cinnamoyl-C-glucosylflavone in the Leaves of Gentiana X marcailhouana RY . A new di-O-glucosyl cinnamoyl-C-glucosylflavone has been identified as 4′-O-β-D -glucosyl-2″-O-[2-O-β-D -glucosyl-2,4,5-trihydroxy-(E)-cinnamoyl]isoorientin ( 1 ). 相似文献
54.
Phytochemistry of genus Gentiana XXV: Study of the flavonic and xanthonic compounds in leaves of Gentiana X marcailhouana RY . New cinnamoyl-C-glucosyl-flavones Nine flavonic compounds: isoorientin ( 1 ), isovitexin ( 2 ), isoorientin-4′-O-β-D -glucoside ( 3 ), isovitexin-4′-O-β-D -glucoside ( 4 ), luteolin-7-O-β-D -glucoside ( 5 ), trans-cafeoyl-2′′-isoorientin ( 6 ), trans-feruloyl-2′′-isoorientin ( 7 ), trans-p-coumaroyl-2′′-isoorientin ( 8 ), p-O-β-D -glucosyl-trans-cafeoyl-2′′-isoorientin ( 9 ) and three xanthones: gentioside ( 10 ), isogentisine ( 11 ), mangiferin ( 12 ), have been identified from leaves of Gentiana X marcailhouana RY . Compounds 8 and 9 were described for the first time. The cyclitol L -(+)-bornesitol ( 13 ) has been also isolated. 相似文献
55.
Sonogashira cross-coupling of 6-chloro-1,3-dimethyllumazine with terminal alkynes gave 6-alkynyl derivatives in good yields. Oxidative amination of the latter with primary alkylamines was accompanied by the pyrrole-ring closure to form 1-R"-2-R-6,8-dimethylpyrrolo[3,2-g]pteridine-5,7(6H,8H)-diones. The addition of bromine to 6-alkynyllumazines afforded the corresponding dibromoalkenes whose treatment with sodium trithiocarbonate gave rise to 2-R-6,8-dimethylthieno[3,2-g]pteridine-5,7(6H,8H)-diones. The latter compounds are close analogs of the metabolite of molybdenum cofactor (molybdopterine). 相似文献
56.
57.
Tianyong Liu Qian Dang Xunhui Zhou Jin Li Zhen Ge Hang Che Prof. Shaobin Tang Prof. Yi Luo Prof. Jun Jiang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(23):6945-6953
Developing the low-cost and efficient single-atom catalysts (SACs) for nitrogen reduction reaction (NRR) is of great importance while remains as a great challenge. The catalytic activity, selectivity and durability are all fundamentally related to the elaborate coordination environment of SACs. Using first-principles calculations, we investigated the SACs with single transition metal (TM) atom supported on defective boron carbide nitride nanotubes (BCNTs) as NRR electrocatalysts. Our results suggest that boron-vacancy defects on BCNTs can strongly immobilize TM atoms with large enough binding energy and high thermal/structural stability. Importantly, the synergistic effect of boron nitride (BN) and carbon domains comes up with the modifications of the charge polarization of single-TM-atom active site and the electronic properties of material, which has been proven to be the essential key to promote N2 adsorption, activation, and reduction. Specifically, six SACs (namely V, Mn, Fe, Mo, Ru, and W atoms embedded into defective BCNTs) can be used as promising candidates for NRR electrocatalysts as their NRR activity is higher than the state-of-the art Ru(0001) catalyst. In particular, single Mo atom supported on defective BCNTs with large tube diameter possesses the highest NRR activity while suppressing the competitive hydrogen evolution reaction, with a low limiting potential of −0.62 V via associative distal path. This work suggests new opportunities for driving NH3 production by carbon-based single-atom electrocatalysts under ambient conditions. 相似文献
58.
59.
60.