全文获取类型
收费全文 | 9170篇 |
免费 | 1866篇 |
国内免费 | 1640篇 |
专业分类
化学 | 6611篇 |
晶体学 | 253篇 |
力学 | 641篇 |
综合类 | 128篇 |
数学 | 1039篇 |
物理学 | 4004篇 |
出版年
2024年 | 24篇 |
2023年 | 129篇 |
2022年 | 319篇 |
2021年 | 378篇 |
2020年 | 419篇 |
2019年 | 365篇 |
2018年 | 356篇 |
2017年 | 383篇 |
2016年 | 468篇 |
2015年 | 544篇 |
2014年 | 692篇 |
2013年 | 834篇 |
2012年 | 851篇 |
2011年 | 933篇 |
2010年 | 765篇 |
2009年 | 699篇 |
2008年 | 761篇 |
2007年 | 694篇 |
2006年 | 584篇 |
2005年 | 462篇 |
2004年 | 358篇 |
2003年 | 267篇 |
2002年 | 270篇 |
2001年 | 258篇 |
2000年 | 175篇 |
1999年 | 141篇 |
1998年 | 85篇 |
1997年 | 89篇 |
1996年 | 81篇 |
1995年 | 57篇 |
1994年 | 34篇 |
1993年 | 42篇 |
1992年 | 22篇 |
1991年 | 29篇 |
1990年 | 23篇 |
1989年 | 14篇 |
1988年 | 11篇 |
1987年 | 13篇 |
1986年 | 10篇 |
1985年 | 11篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1975年 | 1篇 |
1971年 | 2篇 |
1957年 | 2篇 |
1936年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Wu J Huang J Xiao Q Zhang S Xiao Z Li Q Long L Huang L 《Magnetic resonance in chemistry : MRC》2004,42(7):659-662
Ten phenylethanoid glycosides, including two new ones, isolated from the aerial parts of the mangrove plant Acanthus ilicifolius were identified. The first complete assignments of the 1H and 13C NMR chemical shifts for these glycosides were achieved by means of 2D NMR techniques, including 1H-1H COSY, TOCSY, HSQC and HMBC spectra. 相似文献
82.
二苄亚砜硝酸钕Nd(NO_3)_3·[(C_6H_5CH_2)_2S0]属三斜晶系,P1空间群,晶胞参数:a=9.835(2),b=12.445(2),c=19.971(5)A,α=104.13(2)°,β=90.34(2)°γ=74.96(1)°Z=2。晶体结构用重原子法解出,经最小二乘修正后R因子为0.031。钕离子由九个氧配位,形成稍歪扭的三帽三方棱柱配位多面体,其中一个三角面由三个二苄亚砜(DBSO)提供的氧形成,其他氧原子则由硝酸根提供。平均Nd-O(DBSO)=2.379A,Nd-O(NO_3)=2.536A。 相似文献
83.
用比较力场分析研究了N-亚硝基化合物的结构与致癌活性的关系,考察了网络结构和探针原子对结果的影响.结果表明,立体效应和静电作用场是描述其致癌活性和进行结构性能关系研究的最重要的结构参数。 相似文献
84.
85.
The nonlinear optical membrane used for image processing was prepared using tetraethyl silicate by sol-gel method under mild conditions. Ru(bpy)3Cl2 (bpy, bipyridine) was immobilized in the sol-gel matrix. This light-excitable membrane containing Ru(bpy)3Cl2 as photocatalyst could catalyze the Belousov-Zhabotinsky reaction by illumination. Our results indicated that a fine-definition image processing could be autoperformed when projecting a picture on this medium. The imaging process was an image evolution process, which was similar to that of the human vision process. 相似文献
86.
87.
Chen Xia DU Zhi Qiang WANG Qi XIN Yang Jie WU Wen Lian LI Department of Chemistry Zhengzhou University Zhengzhou Changchun institute of optics Fine Mechanics Physics Chinese Academy of Sciences Changchun 《中国化学快报》2005,(5)
In recent years, the interest in developing luminescent lanthanide complexes has been greatly stimulated by their potential use in electroluminescent displays1. Europium complexes appear most attractive in view of the high photoluminescent efficiency and the high monochromatic red light that are widely exploited in full-color displays2. It has been approved that the second ligand plays an important role in europium complexes, the synergistic complexation of the second ligand can not only lead … 相似文献
88.
89.
Zhang Q Carpenter CJ Kemper PR Bowers MT 《Journal of the American Chemical Society》2003,125(11):3341-3352
The sequential association energies for one through six water molecules clustering to Na(2)I(+), as well as one and two water molecules clustering to Na(3)I(2)(+), are measured. The association energies show a pairwise behavior, indicating a symmetric association of water molecules to the linear Na(2)I(+) and Na(3)I(2)(+) ions. This pairwise behavior is well reproduced by Density Functional Theory (DFT) calculations. DFT calculations also suggest that a significant separation of charge for the Na-I ion pair occurs when four or more water molecules cluster to a single sodium center. Two different solvent-separated ion pairs have been identified with the DFT calculations. Experiments also show that the dissolution processes, loss of a neutral NaI unit, occurs when six or more water molecules have been added to Na(2)I(+) cluster. However, one or two water molecules are able to detach an NaI unit from the Na(3)I(2)(+) cluster. The difference in solubility of the Na(2)I(+) and Na(3)I(2)(+) ions is due to the difference in the energies required to lose an NaI unit from these two species. The experiment also confirms that the loss of a neutral NaI unit, instead of an Na(+) ion, occurs during the dissolution processes of Na(3)I(2)(+). The microsolvation schemes proposed to explain our experimental observations are supported by DFT and phase space theory (PST) calculations. 相似文献
90.
Cerium-doped terbium aluminum garnet phosphors, Tb3Al5O12:Ce3+ (TAG:Ce3+), were prepared with different methods: co-precipitation (CP), half dry-half wet (HDHW), sol-combustion (SC) and Pechini method plus conventional solid state reaction (SS) method. Comparative study on the phase-formation, particle size, morphologies and luminescent characteristics of the phosphors synthesized with different methods was carried out by means of XRD, FE-SEM and photoluminescence (PL) analysis and SC method was confirmed by the comparison of the results to be an easy and an effective process for preparing efficient and nano-sized Tb3Al5O12:Ce3+ phosphors. Various factors influencing particle size, morphology and PL of the phosphors, such as precursor preparation, reaction temperature and heating time, were also investigated. Light-emitting diodes (LEDs) were fabricated with each phosphor and a ∼460 nm emitting InGaN chip. The LEDs from SS, HDHW and CP exhibit strong white emission while those from SC and Pechini emit yellow, revealing that the emission characteristics of LEDs are influenced not only by the morphology and the particle size of the phosphors, but also by the preparing process of the phosphors. 相似文献