全文获取类型
收费全文 | 91762篇 |
免费 | 17224篇 |
国内免费 | 9809篇 |
专业分类
化学 | 63312篇 |
晶体学 | 975篇 |
力学 | 5924篇 |
综合类 | 556篇 |
数学 | 10719篇 |
物理学 | 37309篇 |
出版年
2024年 | 114篇 |
2023年 | 2077篇 |
2022年 | 2192篇 |
2021年 | 3183篇 |
2020年 | 4109篇 |
2019年 | 3674篇 |
2018年 | 3293篇 |
2017年 | 2984篇 |
2016年 | 4704篇 |
2015年 | 4433篇 |
2014年 | 5365篇 |
2013年 | 6931篇 |
2012年 | 8484篇 |
2011年 | 8824篇 |
2010年 | 5861篇 |
2009年 | 5705篇 |
2008年 | 6115篇 |
2007年 | 5345篇 |
2006年 | 5021篇 |
2005年 | 4044篇 |
2004年 | 3127篇 |
2003年 | 2424篇 |
2002年 | 2244篇 |
2001年 | 1918篇 |
2000年 | 1701篇 |
1999年 | 1930篇 |
1998年 | 1624篇 |
1997年 | 1594篇 |
1996年 | 1545篇 |
1995年 | 1335篇 |
1994年 | 1146篇 |
1993年 | 1005篇 |
1992年 | 872篇 |
1991年 | 791篇 |
1990年 | 650篇 |
1989年 | 508篇 |
1988年 | 387篇 |
1987年 | 310篇 |
1986年 | 334篇 |
1985年 | 275篇 |
1984年 | 159篇 |
1983年 | 122篇 |
1982年 | 113篇 |
1981年 | 62篇 |
1980年 | 48篇 |
1979年 | 21篇 |
1978年 | 9篇 |
1976年 | 8篇 |
1975年 | 7篇 |
1957年 | 33篇 |
排序方式: 共有10000条查询结果,搜索用时 101 毫秒
981.
草酸锰分解过程的机理函数判别和动力学研究 总被引:6,自引:1,他引:6
用等温热重和线性升温热重分析法研究了草酸锰热分解过程,提出了判断其机理函数的3步判别法。经实验和理论分析证明,该反应受随机成核和晶核随后生长的过程(A_3a机理)支配,其活化能E=103.95 kJ/mol,频率因子A=4.448×10~8min~(-1).动力学补偿效应为IgA=0.09661E-1.2856 相似文献
982.
983.
984.
6-Acetoxy-4-alkenyl arenes undergo regio- and stereoselective intramolecular Friedel-Crafts reaction affording benzocycles in moderate to excellent yields in TFA/HOAc (3:1). It was observed that introduction of alkyls or phenyl group to the allylic acetate moiety facilitates the cyclization reaction. The optically active tricyclic (4bR,8aS)-4b,7,8,8a,9,10-hexahydrophenanthrene skeleton could also be easily obtained in excellent yields. 相似文献
985.
986.
La2O3对氧化铝透明陶瓷显微结构和透光性能的影响 总被引:4,自引:1,他引:4
采用传统无压烧结工艺在氢气氛下制备Al2O3透明陶瓷。实验结果表明:MgO和La2O3复合添加时,随着La2O3掺杂量的增加体积密度总体上保持上升的趋势。随着保温时间的延长,陶瓷的致密化程度增大,残余气孔逐步排出,晶粒进一步长大。采用La2O3和MgO复合添加比单独掺入MgO陶瓷样品透过率更高,掺杂效果更好。在烧结温度为1750℃,保温时问为1h条件下,在波艮为300~800nm测试范围内,陶瓷样品的全透过率大于82%,最大值为86%。 相似文献
987.
Effects of sugar inhibition on cellulases and β-glucosidase during enzymatic hydrolysis of softwood substrates 总被引:1,自引:0,他引:1
Zhizhuang Xiao Xiao Zhang David J. Gregg John N. Saddler 《Applied biochemistry and biotechnology》2004,115(1-3):1115-1126
A quantitative approach was taken to determine the inhibition effects of glucose and other sugar monomers during cellulase
and β-Glucosidase hydrolysis of two types of cellulosic material: Avicel and acetic acid-pretreated softwood. The increased
glucose content in the hydrolysate resulted in a dramatic increase in the degrees of inhibition on both β-Glucosidase and
cellulase activities. Supplementation of mannose, xylose, and galactose during cellobiose hydrolysis did not show any inhibitory
effects on β-Glucosidase activity. However, these sugars were shown to have significant inhibitory effects on cellulase activity
during cellulose hydrolysis. Our study suggests that high-substrate consistency hydrolysis with supplementation of hemicellulose
is likely to be a practical solution to minimizing end-product inhibition effects while producing hydrolysate with high glucose
concentration. 相似文献
988.
989.
Zhen-Qian Zhang Hong Li Juan Xu Su Yao Zheng-He Xu Jin-Gang Liu Liang-Nian Ji 《Transition Metal Chemistry》2007,32(6):776-780
The effects of copper ion on the interaction of [Ru(bpy)2HPIP]2+(bpy = 2,2′-bipyridine, HPIP = 2-(2-hydroxyphenyl) imidazo [4,5-f] [1, 10] phenanthroline) with DNA have been investigated
by electronic absorption spectroscopy and fluorescence spectroscopy. HPIP ligand of the complex with an intramolecular hydrogen
bond can bind Cu2+ in the absence of DNA, as revealed by the absorbance and fluorescence decrease for [Ru(bpy)2HPIP]2+. The resultant heterometallic complex binds to DNA via intercalation of HPIP into the DNA base pairs and its DNA-binding ability is stronger than [Ru(bpy)2HPIP]2+ itself. The DNA bound [Ru(bpy)2HPIP]2+ cannot bind Cu2+ at low Cu2+ concentration and the intramolecular hydrogen bond in HPIP is located inside the DNA helix. While the Cu2+ concentration is relative high, Cu2+ can quench the fluorescence of DNA bound [Ru(bpy)2HPIP]2+. The quenching reason is proposed. 相似文献
990.
Fabrication of hexaphenylsilole nanowires and their morphology-tunable photoluminescence. 总被引:1,自引:0,他引:1
Liping Heng Jin Zhai Anjun Qin Yuqi Zhang Yongqiang Dong Ben Zhong Tang Lei Jiang 《Chemphyschem》2007,8(10):1513-1518
Immersion of nanoporous alumina membranes into saturated solutions of hexaphenylsilole with subsequent solvent evaporation affords aligned organic nanowires. The luminescent properties of the hexaphenylsilole nanowires can be manipulated by varying their morphologies, which were controlled by changing the channel sizes of the alumina templates. 相似文献