全文获取类型
收费全文 | 1114篇 |
免费 | 32篇 |
国内免费 | 1篇 |
专业分类
化学 | 858篇 |
晶体学 | 10篇 |
力学 | 2篇 |
数学 | 19篇 |
物理学 | 258篇 |
出版年
2023年 | 12篇 |
2022年 | 8篇 |
2021年 | 9篇 |
2020年 | 10篇 |
2019年 | 16篇 |
2018年 | 13篇 |
2016年 | 18篇 |
2015年 | 18篇 |
2014年 | 21篇 |
2013年 | 49篇 |
2012年 | 44篇 |
2011年 | 50篇 |
2010年 | 33篇 |
2009年 | 27篇 |
2008年 | 66篇 |
2007年 | 55篇 |
2006年 | 63篇 |
2005年 | 52篇 |
2004年 | 52篇 |
2003年 | 58篇 |
2002年 | 33篇 |
2001年 | 40篇 |
2000年 | 22篇 |
1999年 | 16篇 |
1998年 | 8篇 |
1997年 | 15篇 |
1996年 | 11篇 |
1995年 | 13篇 |
1994年 | 16篇 |
1993年 | 13篇 |
1992年 | 15篇 |
1991年 | 14篇 |
1990年 | 17篇 |
1989年 | 17篇 |
1988年 | 12篇 |
1987年 | 15篇 |
1986年 | 7篇 |
1985年 | 21篇 |
1984年 | 14篇 |
1983年 | 9篇 |
1982年 | 12篇 |
1981年 | 16篇 |
1980年 | 10篇 |
1979年 | 9篇 |
1978年 | 12篇 |
1977年 | 11篇 |
1976年 | 8篇 |
1975年 | 8篇 |
1974年 | 12篇 |
1973年 | 6篇 |
排序方式: 共有1147条查询结果,搜索用时 218 毫秒
61.
62.
Kitaura R Iwahori F Matsuda R Kitagawa S Kubota Y Takata M Kobayashi TC 《Inorganic chemistry》2004,43(21):6522-6524
A new three-dimensional (3-D) jungle-gym-like open metal-organic framework has been synthesized from a two-dimensional (2-D) layer compound using a heterogeneous pillar insertion reaction. Both the starting 2-D layer and the resulting 3-D open compounds have been characterized using X-ray crystallography. 相似文献
63.
64.
[reaction: see text] Phosphates from 3-substituted 4,4,4-trifluorobut-2-en-1-ols were found to be effective for construction of CF3-containing quaternary carbon centers by way of Cu(I)-catalyzed Grignard reactions in the presence of catalytic amounts of CuCN and trimethylsilyl chloride (TMSCl) in an anti S(N)2' manner. 相似文献
65.
The degradation of unsaturated polyesters crosslinked with styrene was performed in sub-critical water (SCW) in the absence and presence of organic additives. The unsaturated polyesters were de-crosslinked by hydrolysis of ester chains to form polystyrene derivatives on SCW treatment at 300 °C. With an increase in treating time, carboxylic acid groups in the polystyrene derivatives were turned into carboxylic anhydride groups in SCW. The de-crosslinking rate was much enhanced on SCW treatment in the presence of hydroxy compounds with a long alkyl chain and alkylamines, while carboxylic acids, benzenesulfonate salts, and quaternary ammonium salts were ineffective even though they had a long alkyl chain. The degree of de-crosslinking was reduced in the presence of diamines and amino acids because re-crosslinking at both ends of the additive molecules proceeded. 相似文献
66.
67.
Adriano Francisco Barbosa Arnaldo César Pereira Lauro Tatsuo Kubota César Ricardo Teixeira Tarley 《Talanta》2007,71(4):1512-1519
The present paper proposes the application of multiwall carbon nanotubes (MWCNTs) as a solid sorbent for lead preconcentration using a flow system coupled to flame atomic absorption spectrometry. The method comprises the preconcentration of Pb (II) ions at a buffered solution (pH 4.7) onto 30 mg of MWCNTs previously oxidized with concentrated HNO3. The elution step is carried out with 1.0 mol L−1 HNO3. The effect of the experimental parameters, including sample pH, sampling flow rate, buffer and eluent concentrations were investigated by means of a 24 full factorial design, while for the final optimization a Doehlert design was employed. Under the best experimental conditions the preconcentration system provided detection and quantification limits of 2.6 and 8.6 μg L−1, respectively. A wide linear range varying from 8.6 up to 775 μg L−1 (r > 0.999) and the respective precision (relative standard deviation) of 7.7 and 1.4% for the 15 and 200 μg L−1 levels were obtained. The characteristics obtained for the performance of the flow preconcentration system were a preconcentration factor of 44.2, preconcentration efficiency of 11 min−1, consumptive index of 0.45 mL and sampling frequency estimated as 14 h−1. Preconcentration studies of Pb (II) ions in the presence of the majority foreign ions tested did not show interference, attesting the good performance of MWCNTs. The accuracy of the method was assessed from analysis of water samples (tap, mineral, physiological serum and synthetic seawater) and common medicinal herbs submitted to the acid decomposition (garlic and Ginkgo Biloba). The satisfactory recovery values obtained without using analyte addition method confirms the feasibility of this method for Pb (II) ions determination in different type of samples. 相似文献
68.
This paper describes the development of a new system for amperometric determination of phenolic compounds, and its application for monitoring these compounds in paper mill effluent. The method was based on a flow system, a dialysis sampler, and a laccase-based biosensor. The performance of this system was investigated with respect to pH, ionic strength, working potential, and flow-rate dependence. The biosensor showed an excellent long-term stability allowing measurements for over than 3 months. The sensitivity of laccase-based biosensor was tested for phenol, p-chlorophenol, guaiacol and chloroguaiacol; the detector presented selective measurements of micromolar concentration of these compounds. The integration of a dialysis membrane sampling in the system protected the biosensor surface from fouling and gave independence of sample conditions that commonly influence the biosensor performance. These favorable characteristics allowed its application for direct measurements in complex media with no sample pretreatment. This ability was confirmed employing this system in a continuous analysis of phenolic compounds during the remediation of paper mill effluent by ozonization process. 相似文献
69.
H Harada K Iizuka T Kamijo K Akahane R Yamamoto Y Nakano A Tsubaki T Kubota I Shimaoka H Umeyama 《Chemical & pharmaceutical bulletin》1990,38(11):3042-3047
The experimental details for the synthesis of human renin inhibitors are described. In order to avoid metabolic degradation of the Phe-His (P3-P2) amide bond in transition-state analogs, structurally modified acyl residues (P4-P3) were incorporated into the inhibitors. Compound 1a, which contained 2-(1-naphthylmethyl)-3-(N-phenethylcarbamoyl)propionyl residue (P4-P3) with a retro-inverso amide bond, L-histidine, and norstatine isoamylamide residue (P1-P1) as a transition-state mimic, had potent human renin inhibitory activity, and it lowered blood pressure when administered orally to common marmosets. 相似文献
70.
Kubota Y Nelson JK Perticone D Poling R Schrenk S Crawford G Fulton R Jensen T Johnson DR Kagan H Kass R Malchow R Morrow F Whitmore J Wilson P Bortoletto D Brown D Dominick J McIlwain RL Miller DH Modesitt M Ng CR Schaffner SF Shibata EI Shipsey IP Battle M Kroha H Sparks K Thorndike EH Wang C Alam MS Kim IJ Li WC Nemati B Romero V Sun CR Wang P Zoeller MM Goldberg M Haupt T Horwitz N Jain V Mestayer MD Moneti GC Rozen Y Rubin P Skwarnicki T Stone S Thusalidas M Yao W Zhu G Barnes AV Bartelt J 《Physical review D: Particles and fields》1991,44(3):593-600