全文获取类型
收费全文 | 201592篇 |
免费 | 1022篇 |
国内免费 | 371篇 |
专业分类
化学 | 101501篇 |
晶体学 | 3046篇 |
力学 | 10083篇 |
综合类 | 12篇 |
数学 | 22913篇 |
物理学 | 65430篇 |
出版年
2020年 | 2068篇 |
2019年 | 2511篇 |
2018年 | 3659篇 |
2017年 | 3759篇 |
2016年 | 4521篇 |
2015年 | 2140篇 |
2014年 | 3965篇 |
2013年 | 8097篇 |
2012年 | 6247篇 |
2011年 | 7378篇 |
2010年 | 6054篇 |
2009年 | 6183篇 |
2008年 | 7005篇 |
2007年 | 7007篇 |
2006年 | 6257篇 |
2005年 | 5577篇 |
2004年 | 5327篇 |
2003年 | 4857篇 |
2002年 | 5001篇 |
2001年 | 5655篇 |
2000年 | 4185篇 |
1999年 | 3265篇 |
1998年 | 2954篇 |
1997年 | 2769篇 |
1996年 | 2561篇 |
1995年 | 2424篇 |
1994年 | 2352篇 |
1993年 | 2347篇 |
1992年 | 2417篇 |
1991年 | 2773篇 |
1990年 | 2663篇 |
1989年 | 2735篇 |
1988年 | 2583篇 |
1987年 | 2611篇 |
1986年 | 2445篇 |
1985年 | 3054篇 |
1984年 | 3057篇 |
1983年 | 2624篇 |
1982年 | 2692篇 |
1981年 | 2591篇 |
1980年 | 2390篇 |
1979年 | 2707篇 |
1978年 | 2868篇 |
1977年 | 2940篇 |
1976年 | 3038篇 |
1975年 | 2808篇 |
1974年 | 2727篇 |
1973年 | 2909篇 |
1972年 | 2321篇 |
1971年 | 2117篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
Cr. Simionescu Tatiana Lixandru Lucia Tǎtaru I. Mazilu M. Vâţǎ 《Journal of organometallic chemistry》1982,238(4):363-381
The synthesis and study of some polyenes, polýiminoimides and Schiff polybases with ferrocene obtained by either polymerization or polycondensation are reported.The following monomers were used: ethynylferrocene, 1-chloro-1′-ethynyl-ferrocene, α-chloro-β-formyl-p-ferrocenylstyrene, p-ferrocenylphenylacetylene, p-ferrocenylacetophenone, 1,1′-diacetylferrocene and 1,1′-bis[β-(2-furyl)acryloyl]ferrocene which were characterized by spectral and thermodifferential analyses and Hückel MO calculations. The polymerization was performed in the presence of benzoyl and lauroyl peroxides, triisopropylboron and complex catalysts of [P(C6H5)3]2 NiX2 type. The ferrocene derivatives were polycondensed with biuret, 4,4′-diaminodiphenyl ether, 4,4′-diaminodiphenyl thioether, 4,4′-diamino-2,2′-dinitrodiphenyl disulphide in the presence of metallic salts and p-toluene sulphonic acid as catalysts.Polymers with either linear or tridimensional structure showing good thermal stability and semiconducting properties have been obtained. Some polymers show catalytical activity in the polymerization of chloroformylated vinylic derivatives. 相似文献
972.
The search for pharmacologically active compounds among substituted 2-benzyl-1,2,3,4-tetrahydroisoquinolines has been continued, and compounds possessing bile-stimulating activity have been found.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan, Tashkent, FAX (3712) 62 73 48. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 403–406, May–June, 1994. 相似文献
973.
O. Ya. Neiland B. Ya. Adamsone R. Yu. Dureya I. Ya. Gudele N. N. Zagorskaya 《Chemistry of Heterocyclic Compounds》1993,29(11):1316-1322
We have obtained previously unknown 1-methyl- and 1,3-dimethyl-5-diethylaminothiocarbonylthiobarbituric acids by reaction of sodium diethyldithiocarbamate with 5-phenyliodonium betaines of 1-methyl- and 1,3-dimethylbarbituric acids. Cyclization of these compounds upon heating in conc. H2SO4 gives methyl-substituted 5,7-dioxo(4H,6H)-1,3-dithiolo[4,5-d]pyrimidine-2-diethylimmonium hydrosulfates; the derivative of 1-methylbarbituric acid forms a mixture of 4-methyl- and 6-methyl-substituted compounds (21). We isolated perchlorates of 4-methyl- and 4,6-dimethyl-substituted derivatives in pure form. By treatment of the immonium salt with sodium sulfide or selenide, we obtained 4-methyl- and 4,6-dimethyl-5,7-dioxo(4H,6H)-1,3-dithiolo[4,5-d]pyrimidine-2-thiones and 4-methyl-, 6-methyl-, and 4,6-dimethyl-2-selenones. We characterized the isomeric 4- and 6-methyl-substituted selenones by electronic absorption spectra and ionization constants (7.65 and 4.0). The differences in the pK values and in the electronic absorption spectra makes it possible to distinguish the substitution site in N-mono-substituted derivatives of 5,7-dioxo(4H,6H)-1,3-dithiolo[4,5-d]pyrimidine.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1526–1533, November, 1993. 相似文献
974.
V. P. Tashchi T. I. Rukasov Yu. G. Orlova Yu. A. Putsykin Yu. A. Baskakov 《Chemistry of Heterocyclic Compounds》1982,18(6):566-568
2-(-Oximinoethyl)-2-methylthiirane was obtained by the reaction of 3,4-dibromo-3-methyl-2-butanone oxime with sodium sulfide. At the same time, the O-carbamoyl derivative of the ,-dibromo oxime was converted to the corresponding substituted ,-unsaturated oxime under the same conditions. Thiirane oxime, like its O-carbamoyl derivative, underwent the desulfuration that is characteristic for thirranes under the influence of tributylphosphine.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 751–753, June, 1982. 相似文献
975.
Acceleration of CO hydrogenation by oxygen over palladium catalysts can be accounted for by competing reactions taking place in the CO-H2O2 system.
, CO O2 , CO–H2–O2.相似文献
976.
U. M. Dzhemilev F. A. Selimov R. A. Khusnutdinov A. A. Fatykhov E. I. Andreikov G. A. Obanin 《Russian Chemical Bulletin》1992,41(5):895-902
Liquid-phase condensation of 3-, 4-, and 8-aminoquinolines with aliphatic and aromatic aldehydes catalyzed by transition and rare-earth metal complexes is an efficient method for synthesis of substituted 1,7- and 1,6-naphthyridines and 1,10-phenanthrolines.Institute of Organic Chemistry, Ural Branch, Russian Academy of Sciences, 450054 Ufa; Eastern Scientific-Research Institute of Coal Chemistry, 620219 Sverdlovsk. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 5, pp. 1139–1148, May, 1992. 相似文献
977.
W. Lautsch W. Broser W. Bandel W. Biedermann W. Gehrmann E. Schröder H. Gnichtel I. Zehmisch G. Kurth R. Krüger H. J. Kraege 《Colloid and polymer science》1954,138(3):129-142
Ohne Zusammenfassung
Die Arbeit wurde aus Mitteln des Marshall-Planes (ERP-Mittel) und mit Spenden aus dem „Fonds Chemie“ ausgeführt. Wir sprechen
den zust?ndigen Stellen für die Gew?hrung der Beihilfe unseren verbindlichsten Dank aus. Der Deutschen Forschungsgemeinschaft
danken wir für die überlassung einer Ultrazentrifuge, den Behring-Werken für die uns zur Verfügung gestellten Serumalbumin-
und -globulin-Pr?parate. 相似文献
978.
U. Steinike L. I. Barsova T. K. Jurik U. Kretchmar H. -P. Hennig U. Bol'mann 《Russian Chemical Bulletin》1990,39(7):1321-1324
Mechanical treatment of hydrargillite Al(OH)3 in a vibrational grinder and in a ball-mill grinder increases the dispersion, the specific surface area, and the unit-cell constants. An x-ray amorphous phase forms. Differences in the nature and in the concentration of paramagnetic centers arise on irradiation (77 K) of the mechanically treated samples. Anion vacancies and oxygen ions with disrupted short-range order appear in the mechanically treated samples. Their concentration increases with increased time of mechanical treatment. Pulsed thermal treatment of hydrargillite forms the Al2O3-Al(OH)3 system and anneals the mechanically induced defects.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1463–1467, July, 1990. 相似文献
979.
980.
N. A. Tyukavkina K. I. Lapteva V. A. Larina N. G. Devyatko 《Chemistry of Natural Compounds》1968,3(5):252-254
Summary The quantitative determination of quercetin and dihydroquercetin in the total flavonoids ofLatrix dahurica has been effected by the use of thin-layer chromatography on Kapron for separating the mixture with subsequent elution of the spots and colorimetry of the eluates obtained. The methanol-dimethylformamide (1:1) system was used as the eluate. It has been found that the flavonoids of the heartwood ofLatrix dahurica contain a predominating amount, 69% of dihydroquercetin, the amount of quercetin being 11%.Khimiya Prirodnykh Soedinenii, Vol. 3, No. 5, pp. 298–301, 1967 相似文献