全文获取类型
收费全文 | 215篇 |
免费 | 20篇 |
国内免费 | 11篇 |
专业分类
化学 | 101篇 |
晶体学 | 6篇 |
数学 | 6篇 |
物理学 | 32篇 |
综合类 | 101篇 |
出版年
2024年 | 1篇 |
2023年 | 6篇 |
2022年 | 8篇 |
2021年 | 10篇 |
2020年 | 8篇 |
2019年 | 9篇 |
2018年 | 6篇 |
2017年 | 8篇 |
2016年 | 8篇 |
2015年 | 6篇 |
2014年 | 4篇 |
2013年 | 12篇 |
2012年 | 16篇 |
2011年 | 15篇 |
2010年 | 15篇 |
2009年 | 14篇 |
2008年 | 20篇 |
2007年 | 18篇 |
2006年 | 12篇 |
2005年 | 6篇 |
2004年 | 7篇 |
2003年 | 8篇 |
2002年 | 3篇 |
2001年 | 6篇 |
2000年 | 9篇 |
1999年 | 3篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1987年 | 1篇 |
排序方式: 共有246条查询结果,搜索用时 15 毫秒
161.
162.
Solvothermal Synthesis,Crystal Structure,and Luminescent Properties of Three Heterometallic Lanthanide‐Transition‐Metal Frameworks Constructed from Three Types of CuBr Motifs 下载免费PDF全文
Three three‐dimensional (3D) heterometallic lanthanide‐transition‐metal (hetero‐Ln‐TM) compounds with the formula [Ln6(Cu4Br3)(Cu2Br2)2(Cu2Br)(IN)20(H2O)12] · 2H2O [Ln = Gd ( 1 ), Ln = Sm ( 2 ), Ln = Eu ( 3 )] based on the linkages of one‐dimensional Ln organic chain and CumBrn units were synthesized by mixing Ln2O3 with isonicotinic acid (HIN = pyridine‐4‐carboxylic acid) under hydrothermal condition. During the synthesis, two ligands were used: the isonicotinate (IN–) stabilizes the cluster and links the one‐dimensional Ln organic chains and CumBrn motif, whereas Br– anions play a very important role in the formation of the distinct CumBrn units. It is interesting that there are three different Cu‐Br motifs: a closed four‐membered ring [Cu2Br2] subunit, a linear [Cu2Br] subunit, an S‐sharp [Cu4Br3] subunit. Strong fluorescence of compounds 2 and 3 suggests an efficient energy transfer from the ligand to Eu3+ ions. The luminescent investigation indicates that 2 and 3 are excellent candidates for fluorescent materials. 相似文献
163.
《Acta Crystallographica. Section C, Structural Chemistry》2017,73(7):536-540
Two new salts, namely 2,6‐diamino‐4‐chloropyrimidinium 2‐carboxy‐3‐nitrobenzoate, C4H6ClN4+·C8H4NO6−, (I), and 2,6‐diamino‐4‐chloropyrimidinium p‐toluenesulfonate monohydrate, C4H6ClN4+·C7H7O3S−·H2O, (II), have been synthesized and characterized by single‐crystal X‐ray diffraction. In both crystal structures, the N atom in the 1‐position of the pyrimidine ring is protonated. In salt (I), the protonated N atom and the amino group of the pyrimidinium cation interact with the carboxylate group of the anion through N—H…O hydrogen bonds to form a heterosynthon with an R 22(8) ring motif. In hydrated salt (II), the presence of the water molecule prevents the formation of the familiar R 22(8) ring motif. Instead, an expanded ring [i.e. R 32(8)] is formed involving the sulfonate group, the pyrimidinium cation and the water molecule. Both salts form a supramolecular homosynthon [R 22(8) ring motif] through N—H…N hydrogen bonds. The molecular structures are further stabilized by π–π stacking, and C=O…π, C—H…O and C—H…Cl interactions. 相似文献
164.
165.
166.
167.
In order to obtain better detection results of heterodyne, we used phase IQ quadrature demodulation algorithm to process the data which detected by laser heterodyne. Based on laser heterodyne interferometer, processing the data in the interferometer phase IQ quadrature demodulation algorithm from the signal to noise ratio, sampling rate, sampling rate, filter order and cutoff frequency, verify the effects of these system parameters to the phase precision, and choose the best parameters to obtain a better phase precision through experiment as: the signal to noise ratio is 25 dB, the IF signal frequency is 98.3 MHz, 98.5 MHz, 99.1 MHz, 99.5 MHz and 100 MHz, the sampling rate is 512–2048, the cutoff frequency and order of the filter are 0.11 and 40, respectively. 相似文献
169.
Vladimir Pozdnyakov 《Discrete Applied Mathematics》2008,156(1):93-102
A new martingale technique is developed to find formulas for the expected value and generating function of the waiting time until one observes a gapped pattern (or a structured motif) in an i.i.d. sequence of random letters from a finite alphabet. 相似文献
170.
Valeri T. Stefanov 《Discrete Applied Mathematics》2011,159(8):826-831
Structured motifs with arbitrary number of boxes are considered. In particular, such motifs are of interest in molecular biology for identifying gene promoters along genomes. Neat closed-form expressions for relevant distributions associated with occurrences of structured motifs are derived. Our methodology is based on developing a suitable semi-Markov embedding of the problem. A numerical example is also provided. 相似文献