全文获取类型
收费全文 | 18820篇 |
免费 | 3133篇 |
国内免费 | 2101篇 |
专业分类
化学 | 13617篇 |
晶体学 | 209篇 |
力学 | 1279篇 |
综合类 | 79篇 |
数学 | 1974篇 |
物理学 | 6896篇 |
出版年
2024年 | 41篇 |
2023年 | 372篇 |
2022年 | 444篇 |
2021年 | 628篇 |
2020年 | 719篇 |
2019年 | 701篇 |
2018年 | 622篇 |
2017年 | 557篇 |
2016年 | 966篇 |
2015年 | 887篇 |
2014年 | 1093篇 |
2013年 | 1371篇 |
2012年 | 1748篇 |
2011年 | 1711篇 |
2010年 | 1171篇 |
2009年 | 1113篇 |
2008年 | 1297篇 |
2007年 | 1130篇 |
2006年 | 1021篇 |
2005年 | 920篇 |
2004年 | 641篇 |
2003年 | 540篇 |
2002年 | 527篇 |
2001年 | 412篇 |
2000年 | 349篇 |
1999年 | 369篇 |
1998年 | 306篇 |
1997年 | 265篇 |
1996年 | 295篇 |
1995年 | 293篇 |
1994年 | 217篇 |
1993年 | 162篇 |
1992年 | 168篇 |
1991年 | 164篇 |
1990年 | 141篇 |
1989年 | 110篇 |
1988年 | 90篇 |
1987年 | 79篇 |
1986年 | 57篇 |
1985年 | 52篇 |
1984年 | 38篇 |
1983年 | 30篇 |
1982年 | 19篇 |
1981年 | 19篇 |
1980年 | 33篇 |
1978年 | 21篇 |
1977年 | 46篇 |
1976年 | 16篇 |
1975年 | 18篇 |
1974年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
在氨性溶液中,光照射对ZnTPPS的形成影响很大。光-极谱试验表明:光电流(i_p)与浓度(c)间有以下的关系:对Zn(NH_3)_4~(2+),i_p∝C_((Zn)(NH_3)_4)~(2+)_~(1/2),对H_2TPPS,i_p∝C_(H_2TPPS),ZnTPPS络合物还原波的i_p不明显。本文对其差异性和光电流产生的原因做了初步探讨。 相似文献
82.
The atomic structures of indium (In) on silicon (Si) (1 0 0)-(2 × 1) surface are investigated by the local density approximation using first-principles pseudopotentials. Total energy optimizations show that the energetically favored structure is the parallel ad-dimer model. The adsorption energy of In on ideal Si(1 0 0)-(1 × 1) surface is significantly higher than that on reconstructed Si(1 0 0)-(2 × 1) surface, suggesting that In adsorption does not break the Si-Si dimer bond of the substrate. When Si surface contains single dimer vacancy defects, In chain will be interrupted, leading to disconnected In nanowires. Displacive adsorption of In on Si(1 0 0) is also considered, and the calculation suggests that interdiffusion of In into Si substrate will not be favorable under equilibrium conditions. 相似文献
83.
Reactions of the hydrated electron, H atoms, 2-propanol, and methanol radicals with the TiO2 nano-particles have been studied either directly or by competition kinetics. The radicals were produced by radiolysis of 2-propanol, t-butanol, or methanol aqueous solutions in acid pH's. The reactions involve electron injection to the conduction band. As expected, the t-butanol radical is inert towards TiO2 under our conditions, while the other reducing radicals react with TiO2. The reactivity decreases in the order: eaq−>H>CH3COHCH3>CH2OH. Two TiO2 nanocrystallite sizes, with average diameters of 1.0 and 4.7 nm were compared. For equal concentrations (in terms of TiO2 molecules), the rate of electron injection shows relatively little dependency on particle size. The rates of interfacial electron transfer and transfer coefficient are also reported. 相似文献
84.
Single-crystalline layered lithium manganese oxide nanorods were prepared via a low-temperature molten salt synthesis method. The material was investigated by a variety of techniques, including X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectrum (XPS). 相似文献
85.
Rhizopus arrhizus lipase (EC 3.1.1.3; triacylglycerol hydrolase) was used in this study to investigate the hydrolysis of palm kernel olein in AOT-isooctane-water reversed micelle system at Wo = 13, pH = 7, and T = 30?C. The hydrolytic reaction obeys Michaelis-Menten kinetics for substrate concentrations in the range (0.175 and 0.877M). The apparentK m and Vmax for the substrate were 0.397M (equivalent to 9.06% w/v) and 5523 U/mg protein, respectively. Product inhibition with a dissociation constant of the enzyme-product complex,K I = 9.74 mM, was confirmed. Experimental results from the change of product concentrations with respect to time correlated sufficiently with those predicted theoretically from the rate equation for a reaction time up to 100 min. However, the discrepancy between the observed results and the predicted ones would increase with reaction time. Possible reasons for this deviation were discussed. 相似文献
86.
87.
Thin films of polystyrene (PS), poly(methyl methacrylate) (PMMA) and polystyrene-polyacrylonitrile copolymer (PS-AN), containing various embedded transition-metal complexes, have been studied by FTIR microscopy. The spatial distributions of the transition-metal carbonyl complexes throughout the thin organic polymer films have been determined by a two-dimensional IR mapping procedure. The spectral variations observed in the distribution of the metal carbonyls throughout the different polymer films are discussed. The IR data show that the technique used to prepare the organometallic-embedded thin films (viz. freeze-drying of solutions followed by hot mechanical pressing of the residues) does in general lead to homogeneous films which may eventually find industrial application, e.g. as membrane sensors for small molecules. 相似文献
88.
本文研究了一类二维非线性Schrodinger方程解的有限维行为,我们得到了此方程存在吸引子,并得到了此吸引子维数的上界估计 相似文献
89.
90.