全文获取类型
收费全文 | 1171篇 |
免费 | 32篇 |
专业分类
化学 | 590篇 |
晶体学 | 18篇 |
力学 | 23篇 |
数学 | 186篇 |
物理学 | 386篇 |
出版年
2020年 | 16篇 |
2019年 | 16篇 |
2018年 | 11篇 |
2017年 | 9篇 |
2016年 | 52篇 |
2015年 | 42篇 |
2014年 | 47篇 |
2013年 | 119篇 |
2012年 | 35篇 |
2011年 | 16篇 |
2010年 | 27篇 |
2009年 | 29篇 |
2008年 | 28篇 |
2007年 | 23篇 |
2006年 | 35篇 |
2005年 | 17篇 |
2004年 | 12篇 |
2003年 | 15篇 |
2002年 | 31篇 |
2001年 | 20篇 |
2000年 | 22篇 |
1999年 | 18篇 |
1998年 | 23篇 |
1997年 | 19篇 |
1996年 | 18篇 |
1995年 | 19篇 |
1994年 | 16篇 |
1993年 | 15篇 |
1992年 | 27篇 |
1991年 | 16篇 |
1990年 | 17篇 |
1989年 | 11篇 |
1988年 | 11篇 |
1987年 | 14篇 |
1986年 | 14篇 |
1985年 | 17篇 |
1984年 | 19篇 |
1982年 | 15篇 |
1981年 | 18篇 |
1980年 | 17篇 |
1979年 | 18篇 |
1978年 | 19篇 |
1977年 | 13篇 |
1976年 | 19篇 |
1975年 | 21篇 |
1974年 | 21篇 |
1973年 | 9篇 |
1972年 | 9篇 |
1971年 | 8篇 |
1969年 | 18篇 |
排序方式: 共有1203条查询结果,搜索用时 15 毫秒
121.
N. Aissaoui F. Haas R. M. Freeman C. Beck A. Morsad B. Djerroud R. Čaplar G. A. Monnehan A. Hachem M. Youlal 《Zeitschrift für Physik A Hadrons and Nuclei》1994,348(3):237-238
The 16 O+ 15 N reaction products have been studied by the γ-ray detection method in the CM energy range 15.5 to 36.1 MeV and by the kinematical coincidence method at energies ranging from E CM =20.6 to 33.5MeV. The γ-ray yield excitation function of the 16O 3? inelastic channel shows the existence of resonant structures. Two structures with ~ 1.6 MeV width are observed in the large angle elastic scattering excitation function, they are correlated with the resonances seen in the inelastic channel. Angular momentum assignments were made from the elastic backward angular distributions. 相似文献
122.
123.
Electrochemical Activity of Wedelolactone and Probing its Interaction with DNA Using Voltammetry at a Carbon Electrode
下载免费PDF全文
![点击此处可从《Electroanalysis》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Wedelolactone (WLA) is a polyphenolic coumestan derivative found in extracts of plants used in traditional medicine. Due to its cytostatic activity, WLA is one of natural compounds tested as potential anticancer drugs. In this work we for the first time studied electrochemical properties of WLA using cyclic (CV) and square‐wave (SWV) voltammetry at the basal‐plane pyrolytic graphite electrode. A reversible pair of peaks, corresponding to catechol/o‐benzoquinone redox system, was observed using CV around 0.275 V vs. Ag|AgCl|3 M KCl reference electrode. Measurements of SWV signal of WLA in the presence of single‐ or double‐stranded DNA suggested a weak interaction without evident preference for double‐stranded DNA. An indirect assay, employing electroactive DNA intercalator doxorubicin as competitor, confirmed absence of intercalative DNA binding of WLA. 相似文献
124.
125.
Jiří Čmelík Zdeňka Nainarová Petr Ryšánek 《International journal of environmental analytical chemistry》2015,95(12):1090-1098
The developed and tested method is based on the acid volatile sulphur (AVS) releasing from a sample of sediment by acidification with hydrochloric acid and sequential absorption of released hydrogen sulphide into the absorption solution of sodium hydroxide. Total sulphur absorbed in the absorption solution is subsequently determined by inductively coupled plasma optical emission spectrometry (ICP-OES) technique. The method was tested using both model and real samples of the river sediment. Obtained results were compared with the results of iodometric determination as the method routinely used for the AVS determination. In case of using ICP-OES with purge and trap, there is no spectral interference of calcium; therefore for the determination of sulphur, it is possible to use atomic emission line of sulphur S I 180.7 nm. The tested method provides the results comparable with the iodometric method within the range of tested concentrations. The detection limit (LOD) of this method is 0.09 mg· S2? ? L?1 in the absorption solution which corresponds to 0.23 mg S2?·kg?1 in a sediment. Value of LOD is comparable with the iodometric determination. 相似文献
126.
Čížková M Kolivoška V Císařová I Šaman D Pospíšil L Teplý F 《Organic & biomolecular chemistry》2011,9(2):450-462
A modular approach to the construction of monocationic quaternary N-heteroaromatic frameworks was developed capitalizing on a direct pyridine-type nitrogen quaternization followed by metal-catalyzed [2+2+2] cycloaddition with gaseous acetylene. The flexibility of the route is demonstrated on 12 diverse scaffolds based on pyridinium, quinolinium, thiazolium, benzothiazolium, imidazolium, and pyrimidinium. Electrochemical study revealed a quinolinium redox system with two electrochemically distinct forms that are interconverted by a homogeneous chemical reaction triggered by fast electron transfers (reduction at -0.7 V and oxidation at -0.05 V). 相似文献
127.
Vladan Čelebonović 《高压研究》2013,33(1-6):693-695
Abstract Using the mass and radius of Uranus, as determined by Voyager, and a particular semiclassical theory of dense matter, a model of its interior has been developed. Details of the model, the underlying theory and possible sources of discrepancies with recent work on this topic are briefly presented. 相似文献
128.
Preconcentration was effected using a 50 mm × 2 mm i.d. minicolumn packed with a spherical cellulose sorbent with chemically bound quinolin-8-ol function groups (Ostorb Oxin). The column was connected to the nebulizer of the atomic absorption spectrometer and the sample solution and eluent (2 M hydrochloric acid) were sucked through it at a flow-rate of 2–3 ml min?1 by utilizing the negative pressure of the nebulizer. The experimental design was tested with the determination of traces of copper. Peak-area and peak-height measurements were compared. Owing to the simple calibration, the former method was used for quantification. The dynamic range was from 0.3 ng ml?1 (detection limit) to 5 μg ml?1 (breakthrough). The reproducibility in the concentration range 25 ng ml?1-5 μg ml?1 was better than 5%. Water-soluble inorganic salts, ammonia and sodium hydroxide were analysed. The accuracy of the results was checked by anodic-stripping voltammetry and by electrothermal AAS. 相似文献
129.
In this paper we report the first chemoselective asymmetric hydrogenation of (1-bromo-1-alkenyl)boronic esters, which constitutes a new route to (α-bromoalkyl)boronic esters. The study demonstrates that excellent chemoselectivities along with full conversions can be obtained for hydrogenation of alkyl substituted derivatives with iridium–PˆN complexes. Moreover, acyclic alkyl derivatives afford (α-bromoalkyl)boronic esters in good enantioselectivities ranging from 64 to 73% ee. A cyclic alkyl derivative was obtained only in a nearly racemic form. The (1-bromo-1-alkenyl)boronic esters appear to be less reactive towards homogenous hydrogenation conditions than their chloro analogues as demonstrated by the higher catalyst loadings required to achieve full conversions for alkyl derivatives and lower conversions observed for the aryl substituted derivatives. 相似文献
130.
Dr. Paul S. Wheatley Dr. Pavla Chlubná‐Eliášová Dr. Heather Greer Prof. Wuzong Zhou Dr. Valerie R. Seymour Dr. Daniel M. Dawson Prof. Sharon E. Ashbrook Dr. Ana B. Pinar Dr. Lynne B. McCusker Dr. Maksym Opanasenko Prof. Jiří Čejka Prof. Russell E. Morris 《Angewandte Chemie (International ed. in English)》2014,53(48):13210-13214
Zeolites are important materials whose utility in industry depends on the nature of their porous structure. Control over microporosity is therefore a vitally important target. Unfortunately, traditional methods for controlling porosity, in particular the use of organic structure‐directing agents, are relatively coarse and provide almost no opportunity to tune the porosity as required. Here we show how zeolites with a continuously tuneable surface area and micropore volume over a wide range can be prepared. This means that a particular surface area or micropore volume can be precisely tuned. The range of porosity we can target covers the whole range of useful zeolite porosity: from small pores consisting of 8‐rings all the way to extra‐large pores consisting of 14‐rings. 相似文献