全文获取类型
收费全文 | 184640篇 |
免费 | 2256篇 |
国内免费 | 534篇 |
专业分类
化学 | 96881篇 |
晶体学 | 3239篇 |
力学 | 7525篇 |
综合类 | 4篇 |
数学 | 21866篇 |
物理学 | 57915篇 |
出版年
2021年 | 1500篇 |
2020年 | 1650篇 |
2019年 | 1859篇 |
2018年 | 2288篇 |
2017年 | 2391篇 |
2016年 | 3838篇 |
2015年 | 2379篇 |
2014年 | 3685篇 |
2013年 | 8715篇 |
2012年 | 6586篇 |
2011年 | 7765篇 |
2010年 | 5672篇 |
2009年 | 5574篇 |
2008年 | 7391篇 |
2007年 | 7185篇 |
2006年 | 6696篇 |
2005年 | 6033篇 |
2004年 | 5537篇 |
2003年 | 4952篇 |
2002年 | 4744篇 |
2001年 | 5425篇 |
2000年 | 4052篇 |
1999年 | 3100篇 |
1998年 | 2611篇 |
1997年 | 2485篇 |
1996年 | 2363篇 |
1995年 | 2209篇 |
1994年 | 2174篇 |
1993年 | 2072篇 |
1992年 | 2391篇 |
1991年 | 2335篇 |
1990年 | 2265篇 |
1989年 | 2193篇 |
1988年 | 2188篇 |
1987年 | 2188篇 |
1986年 | 2085篇 |
1985年 | 2765篇 |
1984年 | 2803篇 |
1983年 | 2463篇 |
1982年 | 2568篇 |
1981年 | 2381篇 |
1980年 | 2368篇 |
1979年 | 2490篇 |
1978年 | 2517篇 |
1977年 | 2423篇 |
1976年 | 2488篇 |
1975年 | 2405篇 |
1974年 | 2368篇 |
1973年 | 2536篇 |
1972年 | 1644篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
981.
Solubility of carbon dioxide in aqueous solutions of sodium chloride: Experimental results and correlation 总被引:2,自引:0,他引:2
The solubility of carbon dioxide in aqueous solutions of sodium chloride was measured in the temperature range from 40 to 160°C, up to 6 mol-kg salt solutions and total pressures up to 10 MPa. Pitzer's(1) equations as well as the Chen and Evans(2) model were used to correlate the new data. Results are reported and compared to literature data and correlations. 相似文献
982.
A series of unsaturated polyesters based on phthalic anhydride (PHA), maleic anhydride (MA), ethylene glycol (EG), diethylene glycol (DG), triethylene glycol (TG), propylene glycol (PG), styrene (Sty) and acrylonitrile (AN) were prepared. The molecular weights of the prepared polyesters were determined by end-group analysis. The effect of the structure of the resin on its curing behavior has been investigated. On the basis of the experimental study, the following were concluded: (1) The maximum curing temperature (Tmax) is related to the molecular weight of the glycol incorporated in these castings. In this context the Tmax was found to decrease with increasing the molecular weight. Meanwhile the time to peak temperature tmax was increasing. (2) The higher the percentage of AN in the crosslinking monomer system, the slower a resin cures. (3) The values of Tmax were found to be influenced to a large extent by the percentage of AN. 相似文献
983.
Mary Cheung Alex B. Young Alex G. Harrison 《Journal of the American Society for Mass Spectrometry》1994,5(6):553-557
O? and OH? react with fatty acid methyl esters (FAMES) under chemical ionization conditions both as Bronsted bases to form [M - H]? and as nucleophiles to form the carboxylate ion RCOO?. O? shows a much greater tendency to react as a nucleophile than does OH?. The [M - H]? ions fragment by elimination of CH3OH, with unsaturation in certain positions in the fatty acid hydrocarbon chain promoting this elimination for unknown reasons. The reaction of O? and OH? with triacylglycerols leads to [M - H]?, characteristic of the molecular mass, and to carboxylate ions characteristic of the fatty acid(s) present in the lipid. The presence of the three ester functions in the lipids greatly enhances the formation of carboxylate ions compared to the FAMES. 相似文献
984.
L. T. Eremenko L. B. Romanova M. E. Ivanova I. L. Eremenko S. E. Nefedov Yu. T. Struchkov 《Russian Chemical Bulletin》1994,43(4):619-623
An effective method of esterification of 1,4-cubanedicarboxylic acid with alkylsulfuric acids is proposed. The derivatives of alkanols with substantially different pKa Valus are obtained in high yields. Molecular structures of the esters obtained are confirmed by various methods. The X-ray study showed a remarkable effect of the nature of an alkyl radical on the geometry of the cubane core.Translated fromIzyestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp.668–672, April, 1994.The authors thank Dr. G. V. Lagodzinskaya for analyzing the NMR spectra and for useful discussions. 相似文献
985.
V. P. Bubnov I. S. Krainskii E. E. Laukhina E. B. Yagubskii 《Russian Chemical Bulletin》1994,43(5):746-750
The effect of the parameters of the electric arc (helium pressure, current and voltage, clearance between electrodes) and of the peculiarities of the setup design (arrangement of electrodes, distance between the arc and the cooling surface, temperature of the soot condensation surface) on the yield of fullerenes has been studied. Conditions for producing soot with a C60 and C70 content up to 43% (toluene extract) have been found.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 805–809, May, 1994.The authors are grateful to N. G. Spitsyna and A. V. Dubovitskii for the determination of the content of C60 and C70 fullerenes in the extract.The work was financially supported by the Russian Foundation for Basic Research (Project 93-03-18705). 相似文献
986.
987.
Flaked capillary columns with an OV-101/CE-Na{in3}PO{in4} hydrophobic-hydrophilic sorbent have been suggested. This sorbent provides for the analysis of polar and nonpolar substances, including amines and aminoalcohols, in aqueous and organic solvents. The efficiency of new columns was demonstrated for the analysis of 25 organic substances of various classes.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2169–2173, December, 1994.The work was financially supported by the Russian Foundation for Basic Research, Project No. 93-03-4969. 相似文献
988.
989.
M. M. Abdillahi M. S. Gharami M. A. B. Siddiqui 《Journal of Thermal Analysis and Calorimetry》1994,42(6):1275-1284
Confirmations of the successful synthesis of a particular zeolite demand investigation of the crystals by XRD, SEM, MAS-NMR and chemical analysis. In this work, we have used the DTA exothermic lattice breakdown of theA-zeolite, which gives typical peaks at around 900–1200°C for characterization. The effects ofpH, concentration, time of crystallization and temperature were studied and it was quickly and easily possible to distinguishA-zeolite formation from others originating from the synthesis matrix under different conditions by using DTA/TG analyses. The parameters were optimized for the synthesis of the zeolite and DTA measurements yielded enough information to identify theA-zeolite; this was confirmed by XRD and SEM. 相似文献
990.
Z. Szeglowski H. Bruchertseifer V. B. Brudanin G. V. Buklanov O. Constantinescu Dinh Thi Lien V. P. Domanov L. I. Guseva M. Hussonnois G. S. Tikhomirova I. Zvara Yu. Ts. Oganessian 《Journal of Radioanalytical and Nuclear Chemistry》1994,186(4):353-359
The short-lived isotopes of W and their descendants have been isolated from the products of the bombardment of144Sm with24Mg by a fast continuous ion-exchange method, using HF solution media. The feasibility of this method for isolation of element 106 is discussed. 相似文献