全文获取类型
收费全文 | 50966篇 |
免费 | 1626篇 |
国内免费 | 23篇 |
专业分类
化学 | 30904篇 |
晶体学 | 349篇 |
力学 | 844篇 |
综合类 | 1篇 |
数学 | 9567篇 |
物理学 | 10950篇 |
出版年
2023年 | 352篇 |
2022年 | 344篇 |
2021年 | 527篇 |
2020年 | 726篇 |
2019年 | 694篇 |
2018年 | 1054篇 |
2017年 | 962篇 |
2016年 | 1787篇 |
2015年 | 1503篇 |
2014年 | 1506篇 |
2013年 | 3300篇 |
2012年 | 3082篇 |
2011年 | 2956篇 |
2010年 | 2002篇 |
2009年 | 1701篇 |
2008年 | 2590篇 |
2007年 | 2325篇 |
2006年 | 2122篇 |
2005年 | 2108篇 |
2004年 | 1843篇 |
2003年 | 1524篇 |
2002年 | 1330篇 |
2001年 | 1030篇 |
2000年 | 1019篇 |
1999年 | 729篇 |
1998年 | 573篇 |
1997年 | 492篇 |
1996年 | 657篇 |
1995年 | 473篇 |
1994年 | 547篇 |
1993年 | 503篇 |
1992年 | 518篇 |
1991年 | 445篇 |
1990年 | 486篇 |
1989年 | 390篇 |
1988年 | 387篇 |
1987年 | 355篇 |
1986年 | 349篇 |
1985年 | 490篇 |
1984年 | 459篇 |
1983年 | 366篇 |
1982年 | 368篇 |
1981年 | 370篇 |
1980年 | 306篇 |
1979年 | 302篇 |
1978年 | 311篇 |
1977年 | 311篇 |
1976年 | 315篇 |
1974年 | 278篇 |
1973年 | 286篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
Albert Lévai Gábor Tóth Áron Szőllősy Tibor Timár 《Monatshefte für Chemie / Chemical Monthly》1990,121(5):403-411
Summary Arylsulfonyloxy-2,2-dimethyl-2H-chromenes (26–35) have been synthesized by reduction of arylsulfonyloxy-2,2-dimethyl-4-chromanones (6–15) followed by dehydration.
Synthese von Benzopyranderviaten. 15. Mitt.: Darstellung von Arylsulfonyloxy-2,2-dimethyl-2H-chromenen
Zusammenfassung Reduktion von Arylsulfonyloxy-2,2-dimethyl-4-chromanonen (6–15) und anschließende Dehydratisierung liefert Arylsulfonyloxy-2,2-dimethyl-2H-chromene (26–35).相似文献
962.
J. Šňupárek L. Mrkvičková O. Quadrat Z. Walterová P. Bradna 《Colloid and polymer science》2000,278(12):1205-1210
Model ethyl acrylate–methacrylic acid copolymer latices and latices of particles cross-linked by copolymerizing small amounts
of water-soluble N,N′-methylenebisacrylamide were prepared by nonseeded semicontinuous emulsion copolymerization. Dynamic and static light scattering
measurements indicated a slightly higher degree of polydispersity in the case of cross-linked particles, especially in the
initial stages of polymerization. The hydrodynamic volume of the alkalinized particles controlling the viscosity properties
of the dispersions decreased with the time of polymerization and in the case of cross-linked copolymer almost reached a constant
value at about 1 h. The different character of the particle structure was confirmed by differences in particle disintegration
after alkali addition or in the presence of methanol.
Received: 2 February 1999/Accepted: 28 June 2000 相似文献
963.
Kubíček Vladimír Kučová Daria Císarř Prřemysl Burešová Vlasta 《Mikrochimica acta》2003,142(4):273-276
An ion-pair extraction spectrophotometry method was developed for the determination of fenpiverine bromide in tablets. To determine this substance it was necessary to find experimental conditions that would allow eliminating the influence of other components of the tablets. Attention was paid to the fact that a suitable pH of water phase was necessary to achieve high selectivity.Received December 11, 2002; accepted April 24, 2003
Published online July 28, 2003 相似文献
964.
Fluorimetric and UV methods of detection for liquid chromatographic determination of phenothiazines (chlorpromazine, acetopromazine and propionylpromazine) were developed. The effects of several experimental parameters on the separation and the sensitivity of the methods were evaluated. The detection limits ranged from 31 to 350 ng ml−1. Optimized methods were successfully applied to determination of the promazines in bovine liver samples. 相似文献
965.
[reaction: see text] A new route to oxcarbazepine (Trileptal), the most widely prescribed antiepileptic drug, starting from commercially available 2'-aminoacetophenone and 1,2-dibromobenzene, is reported. The sequentially accomplished key steps are palladium-catalyzed intermolecular alpha-arylation of ketone enolates and intramolecular N-arylation reactions. After several experiments to establish the best conditions for both arylation processes, the target oxcarbazepine is obtained in a satisfactory overall yield, minimizing the number of steps and employing scalable catalytic procedures developed in partially aqueous media. 相似文献
966.
Ruiz-Medina A Ortega-Barrales P Fernández-de Córdova ML Molina-Díaz A 《Journal of AOAC International》2002,85(2):369-374
A simple, rapid, inexpensive, and automated flow-through solid-phase spectroscopic sensing device is proposed for the sequential determination of 2 vitamins: thiamine and ascorbic acid. The vitamins are concentrated on ion-exchange gels, thiamine on Sephadex SP C-25, and ascorbic acid on Sephadex QAE A-25; both solid supports are packed in 2 different flow cells. The absorbance is monitored directly on the solid phase with a double-beam spectrophotometer at 250 nm, without derivatization or additional elution. With the use of 2 carrier/self-eluting solutions (0.1 5M sodium acetate/acetic acid and 0.18M citric acid/K2HPO4) and a sample volume of 1000 microL, the sensor responds linearly in the range of 0.5-15 and 3-50 microg/mL with detection limits of 0.14 and 0.36 microg/mL for thiamine and ascorbic acid, respectively. When the method was applied to synthetic samples and pharmaceutical preparations, precise and accurate values were obtained. 相似文献
967.
Gy. Marosi R. Lágner Gy. Bertalan P. Anna A. Tohl 《Journal of Thermal Analysis and Calorimetry》1996,47(4):1155-1161
Nucleating and transcrystallization behaviour of additives in engineering PP composites and the effect of modified interfacial structure is the subject of this series of papers. The first part concentrates on polypropylene/liquid crystalline polyester blends. Increased crystallisation temperature and degree of crystallinity of polypropylene is characteristic to the blends containing different amount of LCP additive. Transcrystallization process governs the formation of crystalline structure in these systems in course of isothermal crystallisation at 132C. The nucleating effect of LCP gives rise to more uniform crystalline structure in the polypropylene phase.The financial support of the OTKA 014194 is acknowledged with gratitude. 相似文献
968.
A. Bumbálová A. Pikulíková M. Komová A. Muchová 《Journal of Radioanalytical and Nuclear Chemistry》1992,164(6):357-364
Determination of Cr, Fe, Cu, Zn and Pb in drinking water preconcentrated on a chelating ion exchanger of Czechoslovak production is described. The analytical system consisted of a radionuclide source238Pu, a Si/Li semiconductor detector and a multichannel analyzer. Results are compared with trehshold limit values recommended for drinking water. 相似文献
969.
Barluenga J Diéguez A Rodríguez F Flórez J Fañanás FJ 《Journal of the American Chemical Society》2002,124(31):9056-9057
Eight-membered carbocycles with up to five new stereogenic centers are enantioselectively obtained following a one-pot procedure that involves the coupling of three components: an alkenyl Fischer carbene complex, a ketone enolate, and allyl lithium. 相似文献
970.
I. Labádi E. Pál R. Tudose O. Costisor 《Journal of Thermal Analysis and Calorimetry》2006,83(3):681-686
The
thermal behaviour of the mixed-ligand complexes of cobalt(II) and copper(I)
ions with antipyrine derivatives of 1,2-ethanediamine or piperazine (BAMP
and TAMEN), with water and with 2-mercapto-benzothiazole (Hmbt) was investigated.
The complexes contain 2-mercaptobenzothiazole (Hmbt, in the case of cobalt(II)
ion) or dimercaptobenzothiazine (mbt–mbt, in the case of copper(I) ion)
molecules as ligands and perchlorate (ClO4–) or
thiocyanate (SCN – ) ion as counterion. By heating, water and ligands
release the solid phase at lower temperature. At higher temperatures process
of different organic reactions of ligands (e.g. polymerization, polycondensation)
could be suggested to interpret the relative high final mass values. 相似文献