全文获取类型
收费全文 | 870篇 |
免费 | 15篇 |
国内免费 | 7篇 |
专业分类
化学 | 379篇 |
晶体学 | 1篇 |
力学 | 52篇 |
综合类 | 2篇 |
数学 | 243篇 |
物理学 | 215篇 |
出版年
2022年 | 11篇 |
2021年 | 14篇 |
2020年 | 12篇 |
2018年 | 15篇 |
2017年 | 9篇 |
2016年 | 18篇 |
2015年 | 16篇 |
2014年 | 19篇 |
2013年 | 39篇 |
2012年 | 20篇 |
2011年 | 37篇 |
2010年 | 38篇 |
2009年 | 29篇 |
2008年 | 30篇 |
2007年 | 33篇 |
2006年 | 41篇 |
2005年 | 23篇 |
2004年 | 25篇 |
2003年 | 20篇 |
2002年 | 28篇 |
2001年 | 23篇 |
2000年 | 25篇 |
1999年 | 12篇 |
1998年 | 18篇 |
1997年 | 12篇 |
1996年 | 11篇 |
1995年 | 14篇 |
1994年 | 15篇 |
1993年 | 6篇 |
1992年 | 10篇 |
1991年 | 10篇 |
1990年 | 9篇 |
1989年 | 7篇 |
1987年 | 6篇 |
1986年 | 8篇 |
1985年 | 10篇 |
1984年 | 10篇 |
1983年 | 7篇 |
1982年 | 8篇 |
1981年 | 9篇 |
1978年 | 11篇 |
1975年 | 11篇 |
1974年 | 9篇 |
1973年 | 9篇 |
1972年 | 6篇 |
1970年 | 9篇 |
1969年 | 13篇 |
1968年 | 8篇 |
1965年 | 8篇 |
1916年 | 10篇 |
排序方式: 共有892条查询结果,搜索用时 15 毫秒
41.
Sequential Voltammetric Determination of Uranium,Cadmium and Lead by Using the ex situ Bismuth Film Electrode: Application to Phosphate Fertilizers 下载免费PDF全文
Cristiane L. Jost Lara M. di Martos Luis Ferraz Paulo Cícero do Nascimento 《Electroanalysis》2016,28(2):287-295
A sequential voltammetric procedure for the determination of uranium, cadmium and lead was investigated at an ex situ bismuth film electrode (BiFE). First, the adsorptive stripping voltammetry was applied to assay the U(VI)‐cupferron complex in the differential pulse mode (detection limit of 1.0 µg L?1, 200 s accumulation time). Through the manipulation of the same aliquot of the sample, efforts were made to quantify cadmium and lead by square wave anodic stripping voltammetry. Detection limits of 2.03 µg L?1 for Cd (II) and 2.43 µg L?1 for Pb (II) were calculated (100 s accumulation time). The methodology was successfully applied to phosphate fertilizer samples after open vessel wet decomposition (HNO3/H2O2). The following value ranges were evaluated: U (VI) 37.2–150 mg kg?1, Pb (II) 78.3–204 mg kg?1 and Cd (II) 44.1–71.6 mg kg?1. Validation was performed by using the standard reference materials SRM‐695 – phosphate fertilizer – and SRM‐1643e – water. 相似文献
42.
43.
Dr. Dominique Laniel Dr. Florian Trybel Dr. Adrien Néri Yuqing Yin Andrey Aslandukov Dr. Timofey Fedotenko Saiana Khandarkhaeva Dr. Ferenc Tasnádi Dr. Stella Chariton Dr. Carlotta Giacobbe Dr. Eleanor Lawrence Bright Dr. Michael Hanfland Dr. Vitali Prakapenka Prof. Dr. Wolfgang Schnick Prof. Dr. Igor A. Abrikosov Prof. Dr. Leonid Dubrovinsky Prof. Dr. Natalia Dubrovinskaia 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(62):e202201998
Non-metal nitrides are an exciting field of chemistry, featuring a significant number of compounds that can possess outstanding material properties. These properties mainly rely on maximizing the number of strong covalent bonds, with crosslinked XN6 octahedra frameworks being particularly attractive. In this study, the phosphorus–nitrogen system was studied up to 137 GPa in laser-heated diamond anvil cells, and three previously unobserved phases were synthesized and characterized by single-crystal X-ray diffraction, Raman spectroscopy measurements and density functional theory calculations. δ-P3N5 and PN2 were found to form at 72 and 134 GPa, respectively, and both feature dense 3D networks of the so far elusive PN6 units. The two compounds are ultra-incompressible, having a bulk modulus of K0=322 GPa for δ-P3N5 and 339 GPa for PN2. Upon decompression below 7 GPa, δ-P3N5 undergoes a transformation into a novel α′-P3N5 solid, stable at ambient conditions, that has a unique structure type based on PN4 tetrahedra. The formation of α′-P3N5 underlines that a phase space otherwise inaccessible can be explored through materials formed under high pressure. 相似文献
44.
Ferenc Krdi 《Journal of heterocyclic chemistry》1991,28(6):1549-1552
Methylquinolines 1–4 were chlorinated by heating with phosphorus pentachloride in chlorobenzenes to side-chain halogen derivatives 5–14 . Methyl groups of compounds 1–4 can be chlorinated to chloromethyl, dichloromethyl or trichloromethyl groups depending on their positions and the reaction conditions. 相似文献
45.
Syntheses of 5H-[1,2,4]triazolo[5′,1′:2,3][1,3]thiazino[5,4-c]quinolines 8, 5H-[1,2,4]triazolo[3′,4′:2)3][1,3]thiazino[5,4-c]quinolines 9, 5H-[1,2,4]triazolo[5′,1′:2,3][1,3]thiazino[5,6-c]quinolines 14 and 5H-[1,2,4]triazolo[3′,4′:2,3][1,3]thiazino[5,6-c]quinolines 15 are described starting from 4-chloro-3-chloromethylquinaldine (4) and 1,2,4-triazole-5-thiols 5 taking advantage of different reactivity of the chlorine atoms of 4 under different reaction conditions. The structures of products 8, 9, 14 and 15 and the intermediates leading to them were confirmed by desulfurization, unequivocal syntheses and nmr spectroscopy as well. 相似文献
46.
F. LattanziC. di Lauro M. HermanJ.Vander Auwera 《Journal of Molecular Spectroscopy》2002,216(2):308-314
A detailed investigation of the high-resolution infrared spectrum of ethane revealed the occurrence of features belonging to the hot perpendicular system (ν4+ν8)−ν4 between 1400 and 1510 cm−1. Transition lines of the subbranches with K″ΔK from −7 to 4, exhibiting torsional splittings of several tenths of a cm−1, were observed and measured in this region. The observed line splittings are strongly influenced by the interaction between the ν4+ν8 and 2ν4+ν12 states and change with the values of K″ΔK, depending on the zero-order energy separation of the interacting levels. We found by numerical extrapolation that splittings still occur far from resonance, showing that the intrinsic torsional splittings of the combining states ν4+ν8 and ν4 are quite different. We determined the intrinsic torsional splitting of ν4+ν8 to be less than 0.083 cm−1, compared with 0.236 cm−1 estimated for the ν4 state. This result is in agreement with the expected effects of torsional Coriolis and head-tail coupling and is consistent with previous observations on vibrationally degenerate states of ethane-like molecules. 相似文献
47.
During the ultrasonic non-destructive evaluation of complex materials, like multilayer or composite materials, the behavior of the ultrasonic waves at the interface of samples is strongly dependent upon the anisotropy as well as the attenuation characteristics of the propagation media. In the generally arbitrary case, the incident wave is assumed to be inhomogeneous. Therefore the application of the Snell-Descartes laws requires to consider the real as well as the imaginary parts of all the quantities encountered during the study. In that aim, we use a representation of the complex slowness curves so-called slowness interface curves which point out the evolution of the interaction of the waves at the interface with the inhomogeneity factors, i.e. the imaginary part of the slowness vectors. The continuous distortion of the curves with the inhomogeneity factor increasing is an interesting approach of these complicated phenomena. 相似文献
48.
提出一种交互式自动挖掘知识的模型,论述了该模型的原理、实现机制,并讨论了模型中数据宝藏和影响域及其相互关系.该模型同时具有在线性与深入挖掘的优点,能灵活有效地满足实际应用的需求. 相似文献
49.
Sandra di Rocco 《Mathematische Nachrichten》1996,179(1):47-56
A k-very ample line bundle L on a Del Pezzo Surface is numerically characterized, improving the results of Biancofiore— Ceresa in [7]. 相似文献
50.
László Légrádi 《Fresenius' Journal of Analytical Chemistry》1973,265(4):272
Ohne Zusammenfassung
Determination of minute amounts of phenol-2,4-disulphonic acid in the presence of phenol-4-sulphonic acid相似文献