全文获取类型
收费全文 | 3166篇 |
免费 | 85篇 |
国内免费 | 23篇 |
专业分类
化学 | 2083篇 |
晶体学 | 23篇 |
力学 | 101篇 |
数学 | 570篇 |
物理学 | 497篇 |
出版年
2022年 | 34篇 |
2021年 | 34篇 |
2020年 | 29篇 |
2019年 | 44篇 |
2018年 | 31篇 |
2017年 | 22篇 |
2016年 | 58篇 |
2015年 | 64篇 |
2014年 | 57篇 |
2013年 | 141篇 |
2012年 | 119篇 |
2011年 | 165篇 |
2010年 | 86篇 |
2009年 | 59篇 |
2008年 | 127篇 |
2007年 | 137篇 |
2006年 | 169篇 |
2005年 | 164篇 |
2004年 | 133篇 |
2003年 | 135篇 |
2002年 | 119篇 |
2001年 | 55篇 |
2000年 | 53篇 |
1999年 | 33篇 |
1998年 | 31篇 |
1997年 | 46篇 |
1996年 | 52篇 |
1995年 | 42篇 |
1994年 | 41篇 |
1993年 | 47篇 |
1992年 | 48篇 |
1991年 | 44篇 |
1990年 | 33篇 |
1989年 | 37篇 |
1988年 | 39篇 |
1987年 | 23篇 |
1986年 | 25篇 |
1985年 | 46篇 |
1984年 | 39篇 |
1983年 | 42篇 |
1982年 | 40篇 |
1981年 | 43篇 |
1980年 | 50篇 |
1979年 | 35篇 |
1978年 | 47篇 |
1977年 | 35篇 |
1976年 | 38篇 |
1975年 | 32篇 |
1974年 | 41篇 |
1973年 | 42篇 |
排序方式: 共有3274条查询结果,搜索用时 0 毫秒
141.
142.
Electrochemical Sensing of Uric Acid Using Glassy Carbon Modified with Multiwall Carbon Nanotubes Dispersed in Polyethylenimine 下载免费PDF全文
Alejandro Gutiérrez Maria L. Lozano Laura Galicia Nancy F. Ferreyra Gustavo A. Rivas 《Electroanalysis》2014,26(10):2191-2196
This work reports the advantages of using glassy carbon electrodes modified with multiwall carbon nanotubes (MWCNT) dispersed in polyethylenimine (PEI). The presence of MWCNTs wrapped by PEI largely facilitated the strong adsorption of uric acid (UA) and allowed its highly sensitive and selective quantification even in the presence of high excess of ascorbic acid. The selected conditions for the electrochemical sensing were 5 s accumulation at ?0.300 V under stirring and quantification in a 0.050 M phosphate buffer solution pH 7.40 by differential pulse voltammetry adsorptive‐stripping after medium exchange. The platform allowed the successful application in the quantification of UA in urine. 相似文献
143.
Paul Cowper Yu Jin Michael D. Turton Gabriele Kociok‐Khn Simon E. Lewis 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2016,128(7):2610-2614
Azulenesulfonium salts may be readily prepared from the corresponding azulenes by an SEAr reaction. These azulene sulfonium salts are bench‐stable species that may be employed as pseudohalides for cross‐coupling. Specifically, their application in Suzuki–Miyaura reactions has been demonstrated with a diverse selection of coupling partners. These azulenesulfonium salts possess significant advantages in comparison with the corresponding azulenyl halides, which are known to be unstable and difficult to prepare in pure form. 相似文献
144.
Stephen D. Pastor David N. Rahni Nancy Khoury Stephen A. Koch 《Phosphorus, sulfur, and silicon and the related elements》2013,188(8):1951-1956
The X-ray crystallographic analysis of 6,6-dimethyl-2,4,8,10-tetra-tert-octyl-dibenzo[d,f][1,3,2]dioxagermepin, 1 is reported. In the solid-state conformation of 1, the dihedral angle about the C─C sp2-sp 2 σ bond connecting the two aryl rings is 50.1°. The observed C2 symmetry in the solid-state conformation of 1 is consistent with the previously suggested solution conformation. 相似文献
145.
Emily F. Evans Norman J. Lewis Isabelle Kapfer Gregor Macdonald Richard J. K. Taylor 《合成通讯》2013,43(11):1819-1825
A mild and efficient procedure is described for the removal of the tert-butoxycarbonyl (BOC) group using boron trifluoride etherate and molecular sieves in dichloromethane at room temperature. The scope of this procedure is explored for the deprotection of a variety of amines including amino acid derivatives. 相似文献
146.
147.
148.
Lewis Couchman Sarah L. Belsey Simon A. Handley Robert J. Flanagan 《Analytical and bioanalytical chemistry》2013,405(29):9455-9466
Therapeutic drug monitoring (TDM) requires timely results in order to be clinically helpful. Such assays, when carried out using mass spectrometry-based methods, typically involve a batched sample approach with multipoint calibration. Isotopic internal calibration offers the possibility of open-access mass spectrometric analysis with consequent shortening of turnaround times. We measured plasma clozapine and N-desmethylclozapine (norclozapine) concentrations in (1) external quality assessment (EQA) samples (N?=?22) and (2) patient samples (N?=?100) using liquid chromatography-tandem mass spectrometry with isotopic internal calibration (ICAL-LC-MS/MS). Analyte concentrations were calculated from graphs of the response of three internal calibrators (clozapine-D4, norclozapine-D8, and clozapine-D8) against concentration. Precision (% RSD) and accuracy (% nominal concentrations) for the ICAL-LC-MS/MS method were <5 % and 104–112 %, respectively for both analytes. There was excellent agreement with consensus mean and with ‘spiked’ values on analysis of the EQA samples (R 2?=?0.98 and 0.97, respectively, inclusive of clozapine and norclozapine results). In the patient samples, comparison against traditionally calibrated HPLC-UV and LC-MS/MS methods showed excellent agreement (R 2?=?0.97 or better) with small albeit significant mean differences (<0.041 and <0.042 mg/L for clozapine and norclozapine, respectively). These differences probably reflect discrepancies in the in-house preparation of calibrators and/or interference in the UV method. Internal calibration offers a novel and attractive alternative to traditionally calibrated batch analysis in analytical toxicology. The method described has been validated for use in the high-throughput TDM of clozapine and norclozapine, and allows for (1) same-day reporting of results and (2) significant cost savings. Figure
A typical internal calibration curve produced using three different isotopically-labelled analogues of clozapine and norclozapine (clozapine-D4, norclozapine-D8 and clozapine-D8) and interpolation of the clozapine and norclozapine concentrations from an extracted patient sample (calculated clozapine and norclozapine 0.47 and 0.31 mg/L, respectively) 相似文献
149.
Benjamin M. Gridley Dr. Graeme J. Moxey Dr. William Lewis Prof. Alexander J. Blake Dr. Deborah L. Kays 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(34):11446-11453
The synthesis and characterization of the first series of low‐coordinate bis(terphenyl) complexes of the Group 12 metals, [Zn(2,6‐Naph2C6H3)2] ( 1 ), [Cd(OEt2)(2,6‐Naph2C6H3)2] ( 2 ) and [Hg(OEt2)(2,6‐Naph2C6H3)2] ( 3 ) (Naph=1‐C10H7) are described. The naphthyl substituents of the terphenyl ligands confer considerable steric bulk, and as a result of limited flexibility introduce multiple conformations to these unusual systems. In the solid state, complex 1 features a two‐coordinate Zn centre with the ligands oriented in a syn/anti conformation, whereas the three‐coordinate distorted T‐shaped complexes 2 and 3 feature the ligands in the syn/syn configurations. The results of DFT calculations are in good agreement with the solid‐state configurations for these complexes and support the spectroscopic measurements, which indicate several conformers in solution. 相似文献
150.
Daniele Giallombardo Adam C. Nevin William Lewis Christopher C. Nawrat Russell R.A. Kitson Christopher J. Moody 《Tetrahedron》2014
A synthesis of the naturally occurring xanthone toxyloxanthone B is described, in which the key step is the regioselective addition of a methyl salicylate to a substituted benzyne, followed by cyclization of the intermediate aryl anion to form the xanthone, the regiochemistry of the aryne addition being confirmed by X-ray crystallography. Subsequent introduction of the pyran ring by [3,3]-rearrangement and deprotection completed the synthesis. 相似文献