全文获取类型
收费全文 | 225529篇 |
免费 | 1976篇 |
国内免费 | 712篇 |
专业分类
化学 | 125913篇 |
晶体学 | 3310篇 |
力学 | 8561篇 |
综合类 | 6篇 |
数学 | 24349篇 |
物理学 | 66078篇 |
出版年
2021年 | 1879篇 |
2020年 | 2175篇 |
2019年 | 2489篇 |
2018年 | 3338篇 |
2017年 | 3253篇 |
2016年 | 4556篇 |
2015年 | 2662篇 |
2014年 | 4125篇 |
2013年 | 9728篇 |
2012年 | 7585篇 |
2011年 | 9314篇 |
2010年 | 6469篇 |
2009年 | 6257篇 |
2008年 | 8895篇 |
2007年 | 8937篇 |
2006年 | 8294篇 |
2005年 | 7573篇 |
2004年 | 6741篇 |
2003年 | 6117篇 |
2002年 | 5938篇 |
2001年 | 6087篇 |
2000年 | 4777篇 |
1999年 | 3546篇 |
1998年 | 3093篇 |
1997年 | 3111篇 |
1996年 | 2925篇 |
1995年 | 2390篇 |
1994年 | 2467篇 |
1993年 | 2501篇 |
1992年 | 2644篇 |
1991年 | 2714篇 |
1990年 | 2594篇 |
1989年 | 2573篇 |
1988年 | 2493篇 |
1987年 | 2467篇 |
1986年 | 2389篇 |
1985年 | 3106篇 |
1984年 | 3239篇 |
1983年 | 2602篇 |
1982年 | 2884篇 |
1981年 | 2759篇 |
1980年 | 2547篇 |
1979年 | 2751篇 |
1978年 | 2865篇 |
1977年 | 2888篇 |
1976年 | 2859篇 |
1975年 | 2711篇 |
1974年 | 2689篇 |
1973年 | 2828篇 |
1972年 | 1883篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
821.
S. V. Larionov L. I. Myachina L. A. Sheludyakova E. G. Boguslasvskii A. V. Tkachev S. N. Bizyaev 《Russian Journal of Coordination Chemistry》2004,30(12):846-849
Copper(II) compounds with the optically active diaminodioxime (H2L) derived from the monoterpenoid (+)-3-carene, Cu(H2L)(NO3)2 H2O (I), Cu(H2L)(ClO4)2 H2O (II), Cu(H2L)Br2 H2O (III), and Cu(H2L)SO40.5H2O (IV) with µeff equal to 1.81, 1.79, 1.71, and 1.8 µB, respectively, were prepared. Studies of the complexes by IR and EPR spectroscopy showed that I and II are mononuclear ionic complexes. Compound III apparently has polymeric structure (the CuN4Br2 coordination unit). According to EPR data, the Cu2+ ions in polycrystalline compounds III and IV undergo exchange interactions.Translated from Koordinatsionnaya Khimiya, Vol. 30, No. 12, 2004, pp. 897–900.Original Russian Text Copyright © 2004 by Larionov, Myachina, Sheludyakova, Boguslavskii, Tkachev, Bizyaev. 相似文献
822.
The reaction of aryl- or pyridylamines with ethyl orthoformate and malonanilic acid gave amides of 2-(N-arylcarbamoyl)-, 2-cyano-, 2-ethoxycarbonyl-3-arylaminoacrylic acids and their corresponding 3-pyridyl analogs. IR and PMR spectroscopy indicates that these compounds exist in the enamine form with strong intramolecular hydrogen bonds. Amides of 3-(2-pyridylamino)-2-ethoxycarbonylacrylic acid cyclize to give amides of pyrido[1,2-a]pyrimidine-3-carboxylic acid, which react with hydrazine hydrate to give amides of 3-aminopyrazole-4-carboxylic acid.Perm Pharmaceutical Institute, 614000 Perm. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 629–633, May, 1994. Original article submitted February 8, 1994. 相似文献
823.
Novel phase diagram calculations, in which the two phase-separated regions of polymer stabilized colloidal suspensions overlap under certain constraints of the reduction in the range of the steric interaction with increasing temperature, are presented. A phase diagram displaying liquid-vapour, liquid-solid and vapour-solid coexistence with two triple points, but no critical points is shown to exist in qualitative agreement with observations. 相似文献
824.
The antimonial drug (antimony potassium tartrate, antimony piperazine tartrate or antimony lithium thiomaleate) in aqueous solution or biological fluid is treated with sodium diethyldithiocarbamate in the presence of a suitable masking reagent, the pH is adjusted to 9 +/- 0.5. and the antimony complex extracted with n-hexane and determined by reversed-phase HPLC with an ODS column and detection at 254 nm. The limits of detection are 20 ng (for antimony potassium tartrate and antimony lithium thiomaleate) and 16 ng (for antimony piperazine tartrate). 相似文献
825.
The corresponding 1-alkoxyaziridines were synthesized by oxidation of methoxy-, ethoxy-, and isopropoxyamines with lead tetraacetate in the presence of 2-methyl-2-butene and 2,3-dimethyl-2-butene. The PMR spectra of the oxidation products were investigated, and the high pyramidal stability of nitrogen in these compounds was confirmed. The individual invertomers 1-alkoxy-2,2,3-trimethylaziridines were isolated by preparative gas-liquid chromatography.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1514–1519, November, 1972.The authors thank A. A. Potekhin, I. N. Somin, R. R. Kostikov, M. I. Komendantov, and M. A. Kuznetsov for their useful discussions. 相似文献
826.
The reaction takes place on Cd-containing Lewis sites, whereas the irreversible adsorption and condensation of product acetaldehyde on acidic OH groups of Cd-X, FAU catalyst results in deactivation. Preadsorbed ammonia moderates the deactivation, because it reacts with acetylene, and pyridine homologues are formed which block the accessible OH groups. Since in divalent cationic forms of clinoptilolite no OH groups are generated, Cd-clinoptilolite proved to be a catalyst of permanent activity.
, Cd, — OH FAU, Cd-X. , .. , OH . OH, Cd- .相似文献
827.
Molybdenum is extracted as the thiocyanate complex with the quaternary long-chain aliphatic amine Aliquat 336 in chloroform, followed by evaporation of the solvent, dissolution in MIBK, and atomic-absorption spectroscopy. The method is simple, rapid and sensitive, with few interference problems for the determination of the Mo content of soils and sediments in the range 0.1-1.0 ppm with a relative standard deviation better than 5% when 1-g samples are used. Quantitative extraction from large volumes of aqueous solution has also been confirmed, allowing the determination of Mo in natural waters in the ppM range. 相似文献
828.
All the second-order density matrix spin components for the spin-projected Slater determinant are presented as expansions in direct products of powers of unprojected spin- and residual electron density matrices. Spin components of the second-order transition density matrices between spin-projected Slater determinants built of orthogonal orbitals are also obtained. 相似文献
829.
N Sayem-el-Daher R E Simard L L'Heureux A G Roberge 《Journal of chromatography. A》1983,256(2):313-321
A fully automated, rapid and sensitive method was developed to analyze fourteen different biogenic amines in food. Using a Technicon C4 ion-exchange resin column (20 m X 0.5 cm), adapted to an automatic Technicon TSM amino acid analyzer, the following amines were separated and quantified: adrenaline, noradrenaline, 1,3-diaminopropane, putrescine, cadaverine, histamine, spermidine, dopamine, spermine, agmatine, tyramine, serotonin, phenethylamine and tryptamine. Five buffers were required to elute the amines using a gradient of pH from 5.6 to 12.7; the column temperature was maintained at 65 degrees C. The method was also assayed on ground beef, cheese and wine samples. Amines from cheese and ground beef samples were extracted with 0.6 M perchloric acid. No extraction of wine samples was necessary. 相似文献
830.
A simple method for the separation of hemoglobin chains from hemolysate or globin, by sodium dodecyl sulfate polyacrylamide gel electrophoresis, is described. The alpha, beta, and gamma chains can be clearly separated from each other. The alpha chain has the highest mobility, the beta chain has a slower mobility than the gamma chain, while the delta chain has about the same mobility as the beta chain. Hemoglobins with elongated chains can easily be detected by this method. Tak-beta, elongated by 11 residues, moves much more slowly than betaA but is much faster than alpha Constant Spring which is elongated by 31 residues. Screening of several individuals with slow-moving hemoglobins using this method led to the finding of a case with Hb Tak-beta thalassemia and other carriers of Hb Tak. 相似文献