全文获取类型
收费全文 | 1262篇 |
免费 | 121篇 |
国内免费 | 110篇 |
专业分类
化学 | 852篇 |
晶体学 | 20篇 |
力学 | 59篇 |
综合类 | 8篇 |
数学 | 237篇 |
物理学 | 317篇 |
出版年
2023年 | 22篇 |
2022年 | 52篇 |
2021年 | 42篇 |
2020年 | 52篇 |
2019年 | 46篇 |
2018年 | 50篇 |
2017年 | 46篇 |
2016年 | 72篇 |
2015年 | 57篇 |
2014年 | 70篇 |
2013年 | 87篇 |
2012年 | 74篇 |
2011年 | 99篇 |
2010年 | 65篇 |
2009年 | 56篇 |
2008年 | 62篇 |
2007年 | 56篇 |
2006年 | 62篇 |
2005年 | 54篇 |
2004年 | 36篇 |
2003年 | 25篇 |
2002年 | 19篇 |
2001年 | 15篇 |
2000年 | 23篇 |
1999年 | 18篇 |
1998年 | 14篇 |
1997年 | 13篇 |
1996年 | 19篇 |
1995年 | 23篇 |
1994年 | 12篇 |
1993年 | 17篇 |
1992年 | 16篇 |
1991年 | 17篇 |
1990年 | 9篇 |
1989年 | 5篇 |
1988年 | 4篇 |
1987年 | 5篇 |
1986年 | 6篇 |
1985年 | 8篇 |
1984年 | 5篇 |
1983年 | 8篇 |
1982年 | 7篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1978年 | 7篇 |
1977年 | 6篇 |
1976年 | 6篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1973年 | 5篇 |
排序方式: 共有1493条查询结果,搜索用时 15 毫秒
101.
Phu H. Dang Tho H. Le Phuong K.T. Phan Phuong T.T. Le Mai T.T. Nguyen Nhan T. Nguyen 《Tetrahedron letters》2017,58(16):1553-1557
Two acridones, paratrimerins C (1) and D (2), and two coumarins, paratrimerins E (3) and F (4), were isolated from the CHCl3 and EtOAc extracts of Paramignya trimera (Rutaceae), together with twelve known compounds (5–16). Their structures were elucidated on the basis of spectroscopic data. All isolated compounds possessed significant α-glucosidase inhibitory activity in a concentration-dependent manner, and showed more potent inhibitory activity, with IC50 values ranging from 14.6 to 112.2 μM, than the positive control acarbose (IC50, 214.5 μM). The biosynthesis of the isolated coumarins and acridones was proposed. 相似文献
102.
6,7-Dialkynyl-1,3-dimethylpteridine-2,4(1H,3H)-diones and 2,3-dialkynylquinoxalines have been shown to react with sodium azide in DMF at room temperature giving rise 9,11-dimethyl-[1,2,3]triazolo[1′,5′;1,2]pyrido[4,3-g]pteridine-8,10(9H,11H)-diones and [1,2,3]triazolo[1′,5′;1,2]pyrido[3,4-b]quinoxalines. A novel tandem cyclization involves 1,3-dipolar cycloaddition of an azide ion to the carbon-carbon triple bond followed by intramolecular nucleophilic addition of the intermediate 1,2,3-triazole N-anion to another CC bond. 相似文献
103.
T. A. Dang H.‐J. Lunk S. Roychowdhury T. A. Frisk T. J. Bard 《Surface and interface analysis : SIA》2010,42(1):45-51
Solid standards prepared by freeze‐drying consistently showed a high degree of homogeneity. The freezing process, completed in fractions of a second, preserves the original homogeneous distribution of the dopants, and the subsequent sublimation step would minimize any disturbance. Compared to those prepared by conventional methods such as blending and spiking, freeze‐dried standards exhibited superior lateral distribution and better uniform depth distribution. There is, however, a concentration constraint for achieving homogeneity. At 5% doping, segregation was observed in both lateral and depth distribution. Many tungsten standards doped with 10–28 elements ranging from 10 to 200 ppm were successfully prepared and used as controls for a number of analytical techniques including glow discharge mass spectrometry (GDMS) and d.c.‐arc optical emission spectroscopy (OES). Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
104.
105.
Plate impact experiments on the (210), (100), and (111) planes were performed to examine the role of crystalline anisotropy on the shock-induced decomposition of cyclotrimethylenetrinitramine (RDX) crystals. Time-resolved emission spectroscopy was used to probe the decomposition of single crystals shocked to peak stresses ranging between 7 and 20 GPa. Emission produced by decomposition intermediates was analyzed in terms of induction time to emission, emission intensity, and the emission spectra shapes as a function of stress and time. Utilizing these features, we found that the shock-induced decomposition of RDX crystals exhibits considerable anisotropy. Crystals shocked on the (210) and (100) planes were more sensitive to decomposition than crystals shocked on the (111) plane. The possible sources of the observed anisotropy are discussed with regard to the inelastic deformation mechanisms of shocked RDX. Our results suggest that, despite the anisotropy observed for shock initiation, decomposition pathways for all three orientations are similar. 相似文献
106.
Abstract
A new Cu(II) coordination polymer [Cu(3,5-pdc)(H2O)4·H2O] n 1 (3,5-pdc=3,5-pyridinedicarboxylic acid) has been synthesized by hydrothermal method and characterized by IR, elemental analysis, TG technique and X-ray crystallography. The crystallographic data for the compound 1: monoclinic P21/n, a = 11.361(5) ?, b = 7.095(3) ?, c = 14.575(6) ?, β = 107.630(4)°, V = 1,119.7(8) ?3, Z = 4, Dc = 1.891 Mg/m3, F(000) = 652, R 1 = 0.0374, wR 2 = 0.1083. Cu(II) atom has an distorted octahedral environment with N2O4 donor set of Cu(1) and O6 donor set of Cu(2), respectively. Each ligand is bound to two Cu(II) ions and each copper atom is coordinated by two ligands thereby generating a 1D zigzag chain. The 1D chain was interacted each other feathering three-dimensional supramolecular network through π···π interactions and multiform intermolecular hydrogen bonds. The luminescent properties of the title complex in the solid state were investigated. 相似文献107.
Song Dang Jiangbo Yu Lining Sun Jing Feng Hongjie Zhang 《Journal of luminescence》2011,131(9):1857-1863
The ligand 1-(2-naphthyl)-4,4,4-trifluoro-1,3-butanedionate (Htfnd) has been employed to synthesize six novel ternary-lanthanide complexes in which the synergic ligands were 1,10-phenanthroline-5,6-dione (dione) and 4,5-diazafluoren-9-one (dafone), respectively. Two series of complexes Ln(tfnd)3dione and Ln(tfnd)3dafone (Ln=Ho, Pr, Tm) were obtained. These complexes were characterized by elemental analysis, Fourier Transform Infrared spectra and diffused reflectance. After ligand-mediated excitation, Ln(tfnd)3dione and Ln(tfnd)3dafone all show the characteristic NIR luminescence of the corresponding Ln3+ ions (Ln=Ho, Pr, Tm). This can be attributed to the efficient energy transfer from ligands to central Ln3+ ions, via an antenna effect. The indirect energy transfer in the complexes has been investigated and the differences in the luminescence intensity between Ln(tfnd)3dione and Ln(tfnd)3dafone were discussed in detail. The excellent luminescent performances enable these NIR-luminescent complexes to have potential applications in optical amplification operating at 1300 or 1500 nm. 相似文献
108.
109.
In an attempt to examine the random version of the spectral theorem, the notion of random spectral measures and generalized random spectral measures are introduced and investigated. It is shown that each generalized random spectral measure on $(\mathbb C ,\mathcal{B}(\mathbb C ))$ admits a modification which is a random spectral measure. 相似文献
110.
水氯镁石脱水是镁资源利用的关键.其中一种重要的方法是向水氯镁石中添加助剂形成复盐及络合物脱水.通过缓慢冷却水氯镁石及盐酸苯胺的过饱和水溶液制备了水氯镁石-盐酸苯胺结晶物.通过TGDTA-FTIR联用技术分析了盐酸苯胺、水氯镁石以及盐酸苯胺-水氯镁石结晶物的热解过程,定性检测每步分解的逸出气体以推测反应过程.结果显示:盐酸苯胺在400℃以前仅发生物理变化;水氯镁石的热解分阶段进行,205℃以前发生脱去四个结晶水,205℃以后在脱水反应的同时发生水解反应生成HCl;盐酸苯胺-水氯镁石结晶物分阶段脱水、脱盐酸苯胺,整个过程没有水解现象发生,能够得到高纯度无水氯化镁. 相似文献