全文获取类型
收费全文 | 1400篇 |
免费 | 31篇 |
国内免费 | 10篇 |
专业分类
化学 | 989篇 |
晶体学 | 10篇 |
力学 | 28篇 |
数学 | 155篇 |
物理学 | 259篇 |
出版年
2023年 | 12篇 |
2022年 | 29篇 |
2021年 | 42篇 |
2020年 | 39篇 |
2019年 | 40篇 |
2018年 | 29篇 |
2017年 | 27篇 |
2016年 | 64篇 |
2015年 | 31篇 |
2014年 | 44篇 |
2013年 | 94篇 |
2012年 | 128篇 |
2011年 | 100篇 |
2010年 | 60篇 |
2009年 | 53篇 |
2008年 | 65篇 |
2007年 | 66篇 |
2006年 | 64篇 |
2005年 | 52篇 |
2004年 | 30篇 |
2003年 | 27篇 |
2002年 | 27篇 |
2001年 | 25篇 |
2000年 | 17篇 |
1999年 | 14篇 |
1998年 | 12篇 |
1996年 | 14篇 |
1995年 | 11篇 |
1994年 | 13篇 |
1992年 | 8篇 |
1991年 | 6篇 |
1990年 | 9篇 |
1989年 | 7篇 |
1988年 | 6篇 |
1987年 | 12篇 |
1986年 | 8篇 |
1985年 | 9篇 |
1984年 | 17篇 |
1983年 | 6篇 |
1981年 | 7篇 |
1980年 | 9篇 |
1978年 | 6篇 |
1977年 | 9篇 |
1976年 | 5篇 |
1975年 | 9篇 |
1974年 | 13篇 |
1973年 | 7篇 |
1972年 | 5篇 |
1971年 | 5篇 |
1970年 | 5篇 |
排序方式: 共有1441条查询结果,搜索用时 500 毫秒
61.
62.
This article reviews the solutions that have been studied for the implementation of nonreciprocal devices in integrated optics. These components, either isolators or circulators, use the nonreciprocal interaction between light and a magnetic medium. The only two isolators that have been experimented on to date are described in detail with their advantages and drawbacks, and some solutions are proposed to overcome the difficulties encountered. 相似文献
63.
Maíra Fasciotti Gustavo B. Sanvido Vanessa G. Santos Priscila M. Lalli Michael McCullagh Gilberto F. de Sá Romeu J. Daroda Martin G. Peter Marcos N. Eberlin 《Journal of mass spectrometry : JMS》2012,47(12):1643-1647
The use of CO2 as a massive and polarizable drift gas is shown to greatly improve peak‐to‐peak resolution (Rp‐p), as compared with N2, for the separation of disaccharides in a Synapt G2 traveling wave ion mobility cell. Near or baseline Rp‐p was achieved for three pairs of sodiated molecules of disaccharide isomers, that is, cellobiose and sucrose (Rp‐p = 0.76), maltose and sucrose (Rp‐p = 1.04), and maltose and lactose (Rp‐p = 0.74). Ion mobility mass spectrometry using CO2 as the drift gas offers therefore an attractive alternative for fast and efficient separation of isomeric disaccharides. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
64.
Maciej Makowski Krzysztof Pawełczak Paweł Kafarski Jolanta M. Dzik Barbara Gołos Małgorzata Balinska 《Phosphorus, sulfur, and silicon and the related elements》2013,188(8):1639-1651
The synthesis of six analogues of the potent thymidylate synthase (TS) inhibitor N -[4-[ N -[(3,4-dihydro-2-methyl-4-oxo-6-quinazolinoyl)-methyl]- N -prop-2-ynylamino]benzoyl]- L -glutamic acid 2 is described in which the glutamic acid residue has been replaced by DL -aminophosphonic acids. New antifolates were tested as inhibitors of TS isolated from mouse L1210 leukemic cells as well as inhibitors of growth mouse leukemic L5178Y cells. In general these modifications result in compounds that are considerably less potent than 2 as TS inhibitors with K i 's 0.17-1.10 w M. Very poor solubility in water limited their proper assay of growth cells inhibition. 相似文献
65.
Melinda Czikó Erzsébet-Sára Bogya Réka Barabás Liliana Bizo Răzvan Stefan 《Central European Journal of Chemistry》2013,11(11):1874-1874
The original version of the article was published in Cent. Eur. J. Chem. 11(10) (2013) pp. 1583–1598. Unfortunately, the original version of this article contains a mistake in the affiliation section. The affiliation for R?zvan Stefan is Veterinary Medicine Faculty, University of Agricultural Science and Veterinary Medicine, RO-400372 Cluj Napoca, Romania. 相似文献
66.
67.
Fayçal Boukhari Nacéra Tigrine‐Kordjani Brahim Youcef Meklati 《Helvetica chimica acta》2013,96(6):1168-1175
Walnut (Juglans regia L.) leaves are used traditionally as an herbal tea indicated for non‐insulin‐dependent diabetics. In recent years, the type‐II diabetes is occurring worldwide with increasing frequency. Thus, there is an urgent need to explore the new beneficial biomolecules on the human health. Our objective was to investigate, for the first time, the volatiles profile of Juglans regia L. leaves from Algiers region. The extraction of essential oil of fresh plant material was performed by microwave‐assisted hydrodistillation (MAHD), for the first time, a relatively recent method, then by the conventional hydrodistillation technique (HD) for comparison. The collected extracts were analyzed by GC‐FID and GC/MS using two capillary columns with different polarity. Extraction time of 1 h by MAHD provided higher yields (0.050±0.001% (w/w)) than by HD (0.030±0.006% (w/w)) after 3 h. A total of 38 compounds were identified using both techniques. Essential oils had similar qualitative but different quantitative composition in terms of chemical compounds. The MAHD method improved yield while reducing the extraction time. The sesquiterpenes were the dominant family in both MAHD and HD essential oils with β‐caryophyllene being the major constituent. Monoterpenes, including hydrocarbon and oxygenated, prevail in HD volatile fraction with β‐pinene and eucalyptol, respectively, as major components. 相似文献
68.
Vladimíra Novotná Věra Hamplová Miroslav Kašpar Milada Glogarová Karel Knížek Siegmar Diele 《Liquid crystals》2013,40(8):967-975
New mesogens composed of achiral bent molecules with thermally stable ester linkages, and laterally substituted by a methoxy group symmetrically near the central benzene ring, were synthesized. Texture, calorimetric, electro‐optical, X‐ray and dielectric measurements were performed. In most of studied compounds the antiferroelectric B2 phase was found on cooling from the isotropic phase, followed by the B7 phase at lower temperatures. Undulation of layers in the B7 phase was confirmed by precise synchrotron studies. 相似文献
69.
Kateřina Černovská Bedřich Košata Vladimíra Novotná Milada Glogarová 《Liquid crystals》2013,40(9):987-996
Several series of new benzofused thieno[3,2‐b]furan‐ and thieno[3,2‐b]thiophene‐based derivatives have been synthesized and their mesomorphic properties investigated. All the studied compounds exhibit a SmC* phase with very wide temperature interval. Additionally, some types of the compounds show the cholesteric, SmA or blue phase. In the ferroelectric SmC* phase we evaluated physical properties of relevance for possible applications. 相似文献
70.
Alexey Bobrovsky Valery Shibaev Věra Hamplová Miroslav Kašpar Vladimira Novotna Milada Glogarová 《Liquid crystals》2013,40(9):989-997
A photoinduced phase transition and helix untwisting in a new liquid crystal forming the SmC* phase were studied in detail. The compound consists of a cinnamoyl photosensitive fragment with C?=?C double bond capable of photoisomerisation and photocycloaddition. It was shown that ultraviolet (UV) irradiation (365 nm) induces an extreme decrease in phase transitions temperatures (SmC*–SmA*, SmA*–N*, N*–I). Vertically aligned samples in the SmC* phase cause selective light reflection in the visible spectral range. The light action results in a noticeable helix untwisting that causes a shift in the selective light reflection peak to the long-wavelength spectral region. The temperature dependence of spontaneous polarisation P s was measured and it was found that UV irradiation induces a decrease in the values of P s. Photo-optical phenomena taking place in the liquid crystal are attributed to the formation of photoproducts having low anisometry, which disrupts mesophases. 相似文献