全文获取类型
收费全文 | 886篇 |
免费 | 11篇 |
国内免费 | 3篇 |
专业分类
化学 | 601篇 |
晶体学 | 9篇 |
力学 | 14篇 |
数学 | 168篇 |
物理学 | 108篇 |
出版年
2022年 | 8篇 |
2021年 | 6篇 |
2020年 | 6篇 |
2018年 | 7篇 |
2016年 | 14篇 |
2015年 | 12篇 |
2014年 | 9篇 |
2013年 | 55篇 |
2012年 | 27篇 |
2011年 | 32篇 |
2010年 | 11篇 |
2009年 | 9篇 |
2008年 | 18篇 |
2007年 | 28篇 |
2006年 | 28篇 |
2005年 | 29篇 |
2004年 | 24篇 |
2003年 | 39篇 |
2002年 | 28篇 |
2001年 | 10篇 |
2000年 | 9篇 |
1998年 | 6篇 |
1997年 | 19篇 |
1996年 | 6篇 |
1995年 | 10篇 |
1993年 | 10篇 |
1992年 | 13篇 |
1991年 | 13篇 |
1990年 | 11篇 |
1989年 | 12篇 |
1988年 | 9篇 |
1987年 | 11篇 |
1985年 | 18篇 |
1984年 | 31篇 |
1983年 | 16篇 |
1982年 | 20篇 |
1981年 | 25篇 |
1980年 | 22篇 |
1979年 | 13篇 |
1978年 | 22篇 |
1977年 | 22篇 |
1976年 | 15篇 |
1975年 | 13篇 |
1974年 | 13篇 |
1973年 | 40篇 |
1972年 | 7篇 |
1970年 | 8篇 |
1969年 | 7篇 |
1968年 | 8篇 |
1934年 | 9篇 |
排序方式: 共有900条查询结果,搜索用时 31 毫秒
51.
The effects of quasi-periodicity on the splitting of invariant manifolds are examined. We have found that some harmonics that could be expected to be dominant in some ranges of the perturbation parameter actually are nondominant. It is proved that, under reasonable conditions, this is due to the arithmetic properties of the frequencies. 相似文献
52.
Nera Cagnoli Paolo Ceccherelli Massimo Curini Maria Carla Marcotullio Ernest Wenkert 《合成通讯》2013,43(11):1261-1271
Copper oxide-catalyzed decomposition of 1-diazoacetyl-1-methyl-3-methylenecyclohexanes produces strained tricycles whose reduction or hydrolysis affords 6-bicyclo[3.2.1]octanones. 相似文献
53.
Ernest L. Eliel 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-2):73-95
Abstract Earlier work concerned with a highly stereoselective asymmetric synthesis based on a 1,3-oxathiane as the ciral auxiliary reagent is reviewed and recent applications to the synthesis of the four stereoisomers of malyngolide, of (R)-(+)-γ-caprolactone (a pheromone of the Trogoderma glabrum beetle) and of (S)-(+)-mevalolactone are presented. The mechanism underlying this asymmetric synthesis is discussed briefly. 相似文献
54.
The kinetics of the noncatalyzed reaction between α, ω -dicarboxypoly-amide-11 and α, ω -dihydroxypolyoxyalkylenes is investigated by using the reactions of 11-dodecylamidoundecanoic acid with 1-dodecanol, 2-tridecanol, α-dodecyl-ω-hydroxypolyoxyethylene or α-dodecyl-ω;-hydroxypolyoxypropylene as models. Kinetic data fit a 3rd overall order (2 in acid and 1 in alcohol). Rate constants and activation parameters are determined and compared. 相似文献
55.
Whereas the Diels-Alder reaction has been in vogue as a facile method of six-membered ring construction for many years, its application to a one-step cis-octalone synthesis was precluded by discouraging, early reports on the conditions required for the interaction of dienes with 2-cyclohexenones and on the yields of the resultant adducts.1,2 It is quite conceivable that these observations were responsible in part for the minimization of use of an otherwise attractive route toward angularly alkylated six-membered polycycles in the field of steroid total synthesis. The discovery of Lewis acid catalysis of the cycloaddition of α, β-unsaturated carbonyl compounds3 has rekindled interest in the above reactions.4 The following discussion illustrates octalone 相似文献
56.
The two-step process of hydrogenation of l-alkyl-3-acylpyridinium salts and cyclization of the resultant 1, 4, 5, 6-tetrahydropyridines has been the foundation of a general scheme of alkaloid synthesis.1 Its application in the indole alkaloid field has yielded ready access to tetrahydro-β-carboline systems, e.g. 1a → 2 → eburnamonine.2 Since acid treatment of Nb -acyl derivatives of substances related to la has been shown to lead to products of indole β-cyclization3, it became of interest to test the cyclization behavior of the vinylogous imide lb, prepared by the dicyclohexylcarbodiimide-induced acylation of 3-acetyl-1, 4, 5, 6-tetrahydropyridine4 with indoleacetic acid. Treatment of lb with boron trifluoride gave a 62 yield of ketolactam 3a. Thus a two-step entry into the pentacyclic Aspidosperma alkaloid skeleton is on hand. 相似文献
57.
58.
Ernest Z. Manson Kyama C. Mutinda Joseph K. Gikunju Aleksandra Bocian Konrad K. Hus Vladimír Petrílla Jaroslav Legth James H. Kimotho 《Molecules (Basel, Switzerland)》2022,27(3)
The administration of toxin-specific therapy in snake envenoming is predicated on improved diagnostic techniques capable of detecting specific venom toxins. Various serological tests have been used in detecting snakebite envenoming. Comparatively, enzyme-linked immunosorbent assay (ELISA) has been shown to offer a wider practical application. We report an inhibition ELISA for detecting three-finger toxin (3FTx) proteins in venoms of African spitting cobras. The optimized assay detected 3FTxs in N. ashei (including other Naja sp.) venoms, spiked samples, and venom-challenged mice samples. In venoms of Naja sp., the assay showed inhibition, implying the detection of 3FTxs, but showed little or no inhibition in non-Naja sp. In mice-spiked samples, one-way ANOVA results showed that the observed inhibition was not statistically significant between spiked samples and negative control (p-value = 0.164). Similarly, the observed differences in inhibition between venom-challenged and negative control samples were not statistically significant (p-value = 0.9109). At an LOD of 0.01 µg/mL, the assay was able to confirm the presence of 3FTxs in the samples. Our results show a proof of concept for the use of an inhibition ELISA model as a tool for detecting 3FTxs in the venoms of African spitting cobra snakes. 相似文献
59.