全文获取类型
收费全文 | 8229篇 |
免费 | 1584篇 |
国内免费 | 1294篇 |
专业分类
化学 | 6172篇 |
晶体学 | 125篇 |
力学 | 446篇 |
综合类 | 55篇 |
数学 | 1185篇 |
物理学 | 3124篇 |
出版年
2024年 | 11篇 |
2023年 | 166篇 |
2022年 | 208篇 |
2021年 | 265篇 |
2020年 | 309篇 |
2019年 | 302篇 |
2018年 | 258篇 |
2017年 | 281篇 |
2016年 | 433篇 |
2015年 | 434篇 |
2014年 | 569篇 |
2013年 | 651篇 |
2012年 | 811篇 |
2011年 | 842篇 |
2010年 | 575篇 |
2009年 | 514篇 |
2008年 | 604篇 |
2007年 | 467篇 |
2006年 | 479篇 |
2005年 | 416篇 |
2004年 | 363篇 |
2003年 | 281篇 |
2002年 | 246篇 |
2001年 | 214篇 |
2000年 | 151篇 |
1999年 | 200篇 |
1998年 | 136篇 |
1997年 | 105篇 |
1996年 | 112篇 |
1995年 | 117篇 |
1994年 | 99篇 |
1993年 | 64篇 |
1992年 | 63篇 |
1991年 | 60篇 |
1990年 | 70篇 |
1989年 | 49篇 |
1988年 | 33篇 |
1987年 | 28篇 |
1986年 | 31篇 |
1985年 | 16篇 |
1984年 | 15篇 |
1983年 | 15篇 |
1982年 | 8篇 |
1981年 | 11篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1928年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Wenwu Zhao Shilie Pan Jian Han Jiyong Yao Yun Yang Junjie Li Min Zhang Lian Han Zhang Yin Hang 《Journal of solid state chemistry》2011,184(11):2849-2853
A new compound, Pb2BO3F, has been grown by high temperature solution method from the PbO–PbF2–B2O3 system for the first time. The crystal structure of this compound has been identified by single crystal X-ray diffraction analysis. It crystallizes in the hexagonal system, space group P63/m (No. 176) with unit-cell parameters a=7.2460(3) Å, c=14.5521(17) Å, Z=6, V=661.69(9) Å3. Its structure was solved by the direct methods and refined to R1=0.0163 and wR2=0.0367. The structure of Pb2BO3F consists of the distorted PbO3F2 groups and BO3 triangles, which are all symmetric with each other in the gestalt structure to the extent that the Pb2BO3F compound crystallizes in the symmetric space group. The powder X-ray diffraction pattern of the Pb2BO3F has been measured. The BO3 functional groups presented in the sample were identified by FTIR spectrum. The DTA curve of Pb2BO3F suggests that Pb2BO3F melts congruently at 448 °C. 相似文献
992.
A differential pulse voltammetric method was developed for the simultaneous determination of paracetamol, 4-aminophenol and dopamine at pH 7.0 using a glassy carbon electrode (GCE) coated with gold nanoparticles (AuNPs) and a layered double hydroxide sodium modified with dodecyl sulfate (SDS-LDH). The modified electrode displays excellent redox activity towards paracetamol, and the redox current is increased (and the corresponding over-potential decreased) compared to those of the bare GCE, the AuNPs-modified GCE, and the SDS-LDH-modified GCE. The modified electrode enables the determination of paracetamol in the concentration range from 0.5 to 400???M, with a detection limit of 0.13???M (at an S/N of 3). The sensor was successfully applied to the stimultaneous determination of paracetamol and dopamine, and of paracetamol and 4-aminophenol, respectively, in pharmaceutical tablets and in spiked human serum samples. Figure
1. Gold nanoparticles and organophillic layered double hydroxide modified glassy carbon electrode was fabricated. 2. The modified electrode displayed excellent redox activity towards paracetamol. 3. This electrode was successfully applied to the simultaneous determination of paracetamol and dopamine, and of paracetamol and 4-aminophenol, respectively 相似文献
993.
Feng Zhang Xing Liu Jian Zhou Xian-Hong Yin Jun He 《Monatshefte für Chemie / Chemical Monthly》2011,22(1):763-768
Abstract
Two new transition-metal thiogermanates [M(dap)3]4Ge4S10Cl4 (M = Co, Ni; dap = 1,2-propanediamine) have been solvothermally synthesized and structurally characterized. The two thiogermanates are isostructural and consist of discrete Ge4S104− adamantane-like ions, free Cl− ions, and [M(dap)3]2+ cations as counterions. The Ge4S104− anion is built from corner-sharing connection of four GeS44− tetrahedra. Although some chalcogenidogermanates have been obtained by use of in situ generated transition-metal complexes as structure-directing agents under mild solvothermal conditions, their anions are usually dimeric [Ge2Q6]4− (Q = S, Se) species. The new thiogermanates are rare examples of adamantane-like (Ge4S104−) thiogermanates combined with transition-metal complexes. Their optical properties have been investigated by UV–Vis spectra. 相似文献994.
Yin YingZhuo Chai Hai-Feng WangPeng Li Chang-Wu ZhengGang Zhao Yue-Peng Cai 《Tetrahedron》2011,67(19):3337-3342
A highly enantioselective [4+2] cycloaddition reaction of β,γ-unsaturated α-keto esters with oxazolones was realized with readily available cinchona alkaloids as the catalysts. Using this reaction, a series of highly functionalized δ-lactones with adjacent α-quaternary-β-tertiary stereocenters were obtained in high yields (up to 97%) and with good-to-excellent enantioselectivities (up to 97% ee). 相似文献
995.
Stephen G. Davies James A. LeePaul M. Roberts James E. ThomsonJingda Yin 《Tetrahedron》2011,67(34):6382-6403
The doubly diastereoselective conjugate addition of the antipodes of lithium N-benzyl-N-(α-methylbenzyl)amide to a range of enantiopure α,β-unsaturated esters [derived from Corey’s 8-phenylmenthol chiral auxiliary] and enantiopure α,β-unsaturated hydroxamates [derived from our ‘chiral Weinreb amide’ auxiliary (S)-N-1-(1′-naphthyl)ethyl-O-tert-butylhydroxylamine] has been used as a mechanistic probe to determine the reactive conformations of these acceptors. 相似文献
996.
以脱镁叶绿酸-a甲酯为起始原料,通过3-位乙烯基与氧化苯甲腈和4-取代氧化苯甲腈的1,3-偶极环加成反应,分别得到3-位异噁唑基取代的二氢卟吩衍生物以及其他形式的加成产物,对其脱镁叶绿酸的E-环结构修饰则转换成相应的二氢卟吩-p6衍生物;脱镁叶绿酸-a甲酯经空气氧化和重排反应形成了红紫素-18-内酰胺,再与4-取代氧化苯甲腈进行相同的环加成反应,也以理想的产率生成标题化合物.所得新的二氢卟吩衍生物的化学结构均经UV,IR,1H NMR 及元素分析得以证实,并对相应的反应提出可能的反应机理. 相似文献
997.
998.
999.
1000.
ZHANG Tao ZHANG Ji-Ming JIANG Hai-Hui SHI Xiang-Li WU Hai-Ming XU Qing-Juan MA Wan-Yong ZHOU Jian-Hua 《结构化学》2011,30(3):443-447
Using geometrical optimization and DFT method at the B3LYP/6-31G (d) level, nineteen equilibrium geometries were identified, and three transition states of dissociation reaction of C3O6 clusters were also found. The vibrational frequencies and intrinsic reaction coordinate (IRC) verification at the same level were computed to verify the transitions. And then we calculated the dissociation energies and analyzed the dissociation channels. The computational results show that the dissociation energies of C3O6 isomers relative to three CO2 are between 1.509 × 103 and 10.61 × 103 kJ·kg-1, and the energy barriers of the reactions are 92.857, 131.138 and 185.793 kJ·mol-1. Both the high dissociation energies and high energy barriers show that C3O6 clusters studied in this paper are stable enough to be used as high-energy-density materials. 相似文献