全文获取类型
收费全文 | 1849篇 |
免费 | 71篇 |
国内免费 | 14篇 |
专业分类
化学 | 1160篇 |
晶体学 | 17篇 |
力学 | 34篇 |
数学 | 184篇 |
物理学 | 539篇 |
出版年
2023年 | 19篇 |
2022年 | 48篇 |
2021年 | 49篇 |
2020年 | 51篇 |
2019年 | 61篇 |
2018年 | 53篇 |
2017年 | 47篇 |
2016年 | 78篇 |
2015年 | 37篇 |
2014年 | 62篇 |
2013年 | 162篇 |
2012年 | 89篇 |
2011年 | 97篇 |
2010年 | 77篇 |
2009年 | 73篇 |
2008年 | 79篇 |
2007年 | 70篇 |
2006年 | 69篇 |
2005年 | 64篇 |
2004年 | 80篇 |
2003年 | 46篇 |
2002年 | 40篇 |
2001年 | 30篇 |
2000年 | 25篇 |
1999年 | 12篇 |
1998年 | 19篇 |
1997年 | 10篇 |
1996年 | 16篇 |
1995年 | 13篇 |
1994年 | 29篇 |
1993年 | 21篇 |
1992年 | 23篇 |
1991年 | 22篇 |
1990年 | 20篇 |
1989年 | 23篇 |
1988年 | 22篇 |
1987年 | 13篇 |
1986年 | 8篇 |
1985年 | 18篇 |
1984年 | 20篇 |
1983年 | 14篇 |
1982年 | 12篇 |
1981年 | 20篇 |
1980年 | 18篇 |
1979年 | 9篇 |
1978年 | 8篇 |
1977年 | 11篇 |
1975年 | 6篇 |
1974年 | 6篇 |
1971年 | 5篇 |
排序方式: 共有1934条查询结果,搜索用时 15 毫秒
71.
Thermolysis of a 2'-[(16)O]-O-benzoyl-[(17)O]-5'-O-(tert-butyldimethylsilyl)-O(2),3'-cyclouridine derivative gave the more stable 3'-[(17)O]-O-benzoyl-[(16)O]- 5'-O-(tert-butyldimethylsilyl)-O(2),2'-cyclouridine isomer, which was converted into 3'-[(17)O]-2'-azido-2'-deoxyuridine by deprotection and nucleophilic ring opening at C2' with lithium azide. The 5'-diphosphate was prepared by nucleophilic displacement of the 5'-O-tosyl group with tris(tetrabutylammonium) hydrogen pyrophosphate. Model reactions gave (16)O and (18)O isotopomers, and base-promoted hydrolysis of an O(2),2'-cyclonucleoside gave stereodefined access to 3'-[(18)O]-1-(beta-D-arabinofuranosyl)uracil. Inactivation of ribonucleoside diphosphate reductase with 2'-azido-2'-deoxynucleotides results in appearance of EPR signals for a nitrogen-centered radical derived from azide, and 3'-[(17)O]-2'-azido-2'-deoxyuridine 5'-diphosphate provides an isotopomer to perturb EPR spectra in a predictable manner. 相似文献
72.
The adsorption behavior and differential pulse cathodic adsorptive stripping voltammetry of the pesticide Chlorpyrifos (CP)
were investigated at the hanging mercury drop electrode (HMDE). The pesticide was accumulated at the HMDE and a well-defined
stripping peak was obtained at –1.2 V vs Ag/AgCl electrode at pH 7.50. A voltammetric procedure was developed for the trace
determination of Chlorpyrifos using differential pulse cathodic adsorptive stripping voltammetry (DP-CASV). The optimum working
conditions for the determination of the compound were established. The peak current was linear over the concentration range
9.90 × 10–8– 5.96 × 10–7 mol/L of Chlorpyrifos. The influence of diverse ions and some other pesticides was investigated. The analysis of Chlorpyrifos
in commercial formulations and treated waste water was carried out satisfactorily
Received: 10 July 1997 / Revised: 1 April 1998 / Accepted: 6 April 1998 相似文献
73.
74.
75.
76.
77.
Osman Ayop Mohamad Kamal A. Rahim Noor Asniza Murad Huda A. Majid 《Applied Physics A: Materials Science & Processing》2014,117(2):651-656
This paper presents the analysis of circular ring metamaterial absorber with the existing of copper lines. The structure is designed using lossy FR4 substrate with thin copper layers. The circular ring shape with copper lines is printed on the top surface of FR4 substrate, while at the bottom surface is printed with full copper ground plane. Parametric study is done to investigate the effect of copper lines on the resonance frequency. From the simulation, the circular ring metamaterial absorber with vertical copper lines can resonates at lower frequency, but this structure is polarized sensitive. This drawback can be improved by adding horizontal copper lines together with the vertical copper lines. The circular ring structure with vertical and horizontal copper lines is not only polarization insensitive, but it can works at wide operating angle of incident waves. 相似文献
78.
Triphenylphosphine catalyzes the reaction between 2-hydroxy-1-naphthaldehyde and π-deficient acetylenes to give the newly prepared benzo[f]chromenes. The mechanism for the formation of products is discussed. 相似文献
79.
Christina Schmidt A. M. Sarwaruddin Chowdhury† Klaus Neuking Gunther Eggeler 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(3):204-210
Thermomechanical cycles including programming, cooling, unloading and heating to trigger the 1WE were examined for a shape memory polymer (SMP), Tecoflex® (TFX EG-72D). Cycles were performed at 60°C with 50% and 225% strains and the recovery time of 10 min. Strains evolving with time were estimated during the thermomechanical treatments for the total 44 cycles using 50% strains and the total 50 cycles using 225% strains. Recovery ratios for 50% strains and 225% were also estimated. It turns out that programming, cooling, unloading and heating to trigger the 1WE causes an increase of irreversible strain and is associated with a corresponding decrease of the intensity of the 1WE in particular during the first thermomechanical cycles. In parallel scanning electron microscopic study using secondary electron imaging shows a very slight wavy surface structure evolved during cycling. 相似文献
80.
We develop a methodology for the estimation of extreme loss event probability and the value at risk, which takes into account both the magnitudes and the intensity of the extreme losses. Specifically, the extreme loss magnitudes are modeled with a generalized Pareto distribution, whereas their intensity is captured by an autoregressive conditional duration model, a type of self‐exciting point process. This allows for an explicit interaction between the magnitude of the past losses and the intensity of future extreme losses. The intensity is further used in the estimation of extreme loss event probability. The method is illustrated and backtested on 10 assets and compared with the established and baseline methods. The results show that our method outperforms the baseline methods, competes with an established method, and provides additional insight and interpretation into the prediction of extreme loss event probability. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献