全文获取类型
收费全文 | 10553篇 |
免费 | 1670篇 |
国内免费 | 1935篇 |
专业分类
化学 | 6061篇 |
晶体学 | 110篇 |
力学 | 375篇 |
综合类 | 148篇 |
数学 | 953篇 |
物理学 | 2498篇 |
无线电 | 4013篇 |
出版年
2024年 | 39篇 |
2023年 | 169篇 |
2022年 | 230篇 |
2021年 | 296篇 |
2020年 | 307篇 |
2019年 | 381篇 |
2018年 | 286篇 |
2017年 | 345篇 |
2016年 | 394篇 |
2015年 | 499篇 |
2014年 | 555篇 |
2013年 | 756篇 |
2012年 | 861篇 |
2011年 | 769篇 |
2010年 | 782篇 |
2009年 | 691篇 |
2008年 | 790篇 |
2007年 | 756篇 |
2006年 | 708篇 |
2005年 | 607篇 |
2004年 | 560篇 |
2003年 | 585篇 |
2002年 | 791篇 |
2001年 | 691篇 |
2000年 | 453篇 |
1999年 | 243篇 |
1998年 | 140篇 |
1997年 | 82篇 |
1996年 | 73篇 |
1995年 | 54篇 |
1994年 | 46篇 |
1993年 | 26篇 |
1992年 | 37篇 |
1991年 | 39篇 |
1990年 | 25篇 |
1989年 | 16篇 |
1988年 | 28篇 |
1987年 | 7篇 |
1986年 | 7篇 |
1985年 | 10篇 |
1984年 | 8篇 |
1983年 | 6篇 |
1982年 | 4篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1975年 | 1篇 |
1936年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
991.
An alternative approach to synthesize pedamide,a key building block of pederin was described.Iodine-induced asymmetric heterocyclization was used as the key step to construct the skeleton,a tetrahydropyran ring with three chiral centers.Brown's asymmetric allylation and Lewis acid-mediated allylation were investigated to introduce chains and chiral alcohols.Sharpless dihydroxylation decorated the side chain.And high optically pure target was obtained by removing the epimers formed in these reactions on c... 相似文献
992.
A new macrolide glycoside,cuneataside F was isolated from the n-butanol extract of the stem of Sargentodoxa cuneata. The structure was elucidated on the basis of extensive 1D and 2D NMR as well as HRESI-MS spectroscopic analysis. 相似文献
993.
994.
Xiangyu Xu Dianqing Li Jiaqing Song Yanjun Lin Zhi Lv Min Wei Xue Duan 《Particuology》2010,8(3):198-201
A clean method for preparing layered double hydroxides (LDHs) has been developed, featured by using the hydroxides of two different metals as starting materials by atom-economic reaction. The reactions were carried out under hydrothermal conditions in either a high pressure autoclave or a microwave digester. The compositions, structural parameters and thermal behavior of the resulting LDHs are very similar to those of materials produced by using the separate nucleation and aging steps (SNAS) method. The major advantage of the new method is that no by-product is produced, so that filtration and washing processes are unnecessary. The consequent reduction in water consumption is beneficial to the environment. 相似文献
995.
996.
In this paper we consider a double fronts free boundary problem for a parabolic equation with a non-local source and absorption. The long time behaviors of the solutions are given and the properties of the free boundaries are discussed. Our results show that if the initial value is sufficiently large, then the solution blows up in finite time, while the global fast solution exists for sufficiently small initial data, and the intermediate case with suitably large initial data gives the existence of the global slow solution. 相似文献
997.
The thermodynamics of the association between 4,4′,4″-tris(dimethyl-amino)triphenylmethyl chloride (crystal violet or CV) and sodium bis(2-ethylhexyl)-sulfosuccinate (aerosol OT or AOT) in water/AOT/n-decane microemulsion and the kinetics of the basic hydrolysis of CV in a water-in-oil microemulsion were investigated by UV–vis spectroscopic measurements. An association model of CV and AOT was used to analyze the experimental data to obtain the association constants at various temperatures. By taking the association into account, the “actual” rate constants and the activation energies of the basic hydrolysis of CV in the media of water/AOT/oil were obtained. The difference in thermodynamics and kinetics between the two media of water/AOT/n-decane and water/AOT/isooctane is discussed. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 294–300, 2008 相似文献
998.
粗糙集代数与MV代数 总被引:2,自引:0,他引:2
讨论粗糙集代数与MV代数的关系以及由粗糙集代数构造MV代数的方法.粗糙集代数本身具有格结构,证明了在适当选取蕴涵及乘积运算之后,粗糙集代数就成为MV代数. 相似文献
999.
In pH 5.5 phosphate buffer solution,N-n-undecyl-N'-(sodium-p-amino-benzenesulfonate)thiourea(UPT)produced a pair of redox peaks on the bare glassy carbon electrode.At the multi-walled carbon nanotube(MWNT)modified electrode,the electrochemical behavior of UPT enhanced greatly.In the presence of bovine serum albumin (BSA),the peak currents of UPT decreased linearly due to the formation of a super-molecular complex.This method was successfully applied to the determination of BSA in a bovine serum sample. 相似文献
1000.
§ 1.Introduction Allgraphsconsideredinthispaperarefinite,undirected ,unloopedandsimplegraphs.WedenotethechromaticpolynomialofagraphGbyP(G ,λ)orP(G) .WesaygraphsGandHtobechromatiallyequivalentifP(G) =P(H) .ThechromaticuniquenessofagraphGisestablishedifitcanbeded… 相似文献