全文获取类型
收费全文 | 58200篇 |
免费 | 3774篇 |
国内免费 | 2567篇 |
专业分类
化学 | 33629篇 |
晶体学 | 935篇 |
力学 | 2916篇 |
综合类 | 189篇 |
数学 | 5854篇 |
物理学 | 21018篇 |
出版年
2023年 | 466篇 |
2022年 | 863篇 |
2021年 | 1094篇 |
2020年 | 1142篇 |
2019年 | 1127篇 |
2018年 | 1203篇 |
2017年 | 1152篇 |
2016年 | 1694篇 |
2015年 | 1391篇 |
2014年 | 1830篇 |
2013年 | 3124篇 |
2012年 | 3292篇 |
2011年 | 3785篇 |
2010年 | 2598篇 |
2009年 | 2551篇 |
2008年 | 2945篇 |
2007年 | 2821篇 |
2006年 | 2554篇 |
2005年 | 2129篇 |
2004年 | 1879篇 |
2003年 | 1618篇 |
2002年 | 1542篇 |
2001年 | 1780篇 |
2000年 | 1405篇 |
1999年 | 1259篇 |
1998年 | 1015篇 |
1997年 | 990篇 |
1996年 | 948篇 |
1995年 | 828篇 |
1994年 | 818篇 |
1993年 | 659篇 |
1992年 | 711篇 |
1991年 | 695篇 |
1990年 | 619篇 |
1989年 | 545篇 |
1988年 | 559篇 |
1987年 | 524篇 |
1986年 | 468篇 |
1985年 | 524篇 |
1984年 | 527篇 |
1983年 | 387篇 |
1982年 | 423篇 |
1981年 | 402篇 |
1980年 | 349篇 |
1979年 | 417篇 |
1978年 | 388篇 |
1977年 | 402篇 |
1976年 | 396篇 |
1975年 | 349篇 |
1973年 | 345篇 |
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
991.
Z. Slanina 《Journal of Radioanalytical and Nuclear Chemistry》1990,142(2):525-529
Evaluation has been carried out of the component of the second virial coefficient of steam related to the formation of dimers. The necessary equilibrium constants of dimerization have been evaluated within the MCY-B water pair interaction potential. The calculated isotopic difference in the second virial coefficient reflects the qualitative features found by observation but, nevertheless, the calculation quite distinctly overestimates the value of this isotopic difference as compared with the observation. The nature of these differences and the relation to the state behaviour of water are discussed. 相似文献
992.
Z. I. Mavlyankulova U. N. Zainutdinov S. I. Mukhamedkhanova V. B. Leont'ev Kh. A. Aslanov 《Chemistry of Natural Compounds》1980,16(1):37-40
The acetylation of lagochilin and its derivatives with acetic anhydride in the presence of pyridine has been studied by PMR spectroscopy. It has been shown that the manifestation of the polyfunctionality of lagochilin in acetylation reactions with acetic anhydride is connected with a change in the nature of the process of solvation of the reaction forms with the subsequent replacement of the hydrogen atoms of the hydroxy groups by acetyl groups.V. I. Lenin Tashkent State University. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 46–49, January–February, 1980. 相似文献
993.
3,4—亚甲二氧基苯甲酸锡酯的合成及表征 总被引:3,自引:0,他引:3
3,4-亚甲二氧基苯甲酸及其取代物与三苯基氢氧化锡或二丁基化锡反应合成了5个锡酯,通过元素分析,IR和^1HNMR对其进行了表征。 相似文献
994.
M. E. Élyashberg Yu. Z. Karasev É. R. Martirosyan 《Journal of Structural Chemistry》1995,36(3):502-509
Major axioms underlying structure elucidation of molecules by their characteristic spectral data are considered. The amount
of information obtained by solving the problem on structure elucidation of molecules serves as a basis to evaluate the quality
of solution. Conditions for computer-aided solution of problems using expert systems (ES) are analyzed. Reasons for incorrect
or zero solutions and for inconsistencies leading to negative results are examined. The role of additional information as
a necessary condition for correct solution is discussed. On the basis of this analysis, a general strategy for structure elucidation
of molecules by their spectra using ES is suggested. The principal idea is to use the iteration method, gradually increasing
the rigidity of constraints. Strategies named ARCHEOLOGIST and SCULPTOR are discussed. Examples are given.
Russian Scientific Research Institute of Organic Synthesis. Translated fromZhurnal Strukturnoi Khimii, Vol. 36, No. 3, pp. 548–558, May–June, 1995.
Translated by L. Smolina 相似文献
995.
The high thermal neutron flux provided by the CIRUS reactor (1×1013 n cm–2s–1) has been used to determine elements having long half-lives or poor thermal neutron crosssections. Selective cooling time and the use of a high resolution HPGe detector in conjunction with a PC based MCA unit have made it possible to analyze many elements in a single irradiation run. The method developed has been used for the analysis of ores such as Ilmenite, Rutile, Sillimanite, Garnet, Zircon and Monazite. 相似文献
996.
G.Z. Suleimanov V.V. Bashilov A.A. Musaev V.I. Sokolov O.A. Reutov 《Journal of organometallic chemistry》1980,202(2):C61-C63
The molecular structures of the L-menthyl ester of S-α-bromomercuriphenyl-acetic acid, diastereomer II, [α]20D ?18°, and of the related L-menthyl ester of α-bromobis(triphenylphosphine)platinummeruriphenylacetic acid, VI, have been investigated by the X-ray method. Insertion of L2Pt carbenoid appears to occur into the HgBr bond in II and two phosphine ligands in the product VI occupy cis positions in a planar square around the platinum atom. The HgPt distance is 2.50 Å; there is intermolecular HgBr coordination in II, the distance being 3.23 Å. 相似文献
997.
G. Rasulić Lj. Milanović S. Jovanović G. Novohatni V. Krivokuća Z. Marjanović 《Journal of Thermal Analysis and Calorimetry》1985,30(1):73-82
A study was made of the changes in the active component of a commercial catalyst for methane reforming by means of steam, as a function of its duration of use and of its position in an industrial reactor. The samples for examination were taken after 3, 8, 9 and 20 months of catalyst use, and from seven different levels in the reformer tube, ranging from the top to the bottom.DTA, TG, IR spectroscopy, X-ray diffraction and surface area determination were used to follow the catalyst changes.
Zusammenfassung Veränderungen der aktiven Komponente eines kommerziellen Katalysators zur Methanreformierung mittels Wasserdampf wurden in Abhängigkeit von der Betriebsdauer und der Lage im industriellen Reaktor untersucht. Proben für die Untersuchung wurden nach 3-, 8-, 9- und 20-monatiger Betriebsdauer aus 7 verschiedenen Höhen vom Boden bis zum Kopf des Reformer-Rohres entnommen. Veränderungen des Katalysators wurden mittels DTA, TG, IR-Spektroskopie, Röntgendiffraktometrie und Oberflächenmessungen verfolgt.
, - , @2 . 3, 8, 9 20 -, -. , , , , , .相似文献
998.
An accurate and simple method has been developed for the determination of Pt, Ru, Ir and other elements employing instrumental neutron activation analysis (INAA). Nondestructive analysis has been carried out for the determination of these elements in different rock samples such as Dolerite, Dyke Dolerite, Country Basalt, Hyaloclastite, Trachyte, Ijolite, Spillite, Diorite and Lamprophyre from various locations like Daman, Tapti, Murud, Talasari, Ranala and Bassein in Maharashtra state. High flux provided by the CIRUS reactor (1×1013 n cm–2s–1) has been used for thermal neutron bombardment followed by radioassaying of the (n,) products on a HPGe detector coupled to a PC-based MCA unit. 相似文献
999.
The fluorimetric determination of mercury ions with o-vanillin-8-aminoquinoline (OVAQ) in aqueous solutions was investigated. Hg(II) could react with the fluorescent reagent OVAQ
(λex/em = 278/314 nm) to form a nonfluorescent complex in an ethanol-water medium of pH 6.00. The linear range of the proposed method
was from 2.5 to 80 μg/L, and the detection limit was 0.80 μg/L. The interferences of 24 foreign ions were also studied. The
method was successfully applied to the determination of Hg(II) in sludge.
The text was submitted by the authors in English. 相似文献
1000.
The optical properties of pregnenes containing different substituents at C-17 (—SCN, —SAc, —SC(CH3)2O—, —Br, —OAc, —N3) have been investigated with the help of the CD spectra. It is shown that the sign and value of the Cotton effect of the carbonyl chromophore n → π* transition is determined by the nature of the substituent at C-17. 相似文献