全文获取类型
收费全文 | 20785篇 |
免费 | 1947篇 |
国内免费 | 2588篇 |
专业分类
化学 | 21553篇 |
晶体学 | 247篇 |
力学 | 356篇 |
综合类 | 97篇 |
数学 | 352篇 |
物理学 | 2715篇 |
出版年
2024年 | 44篇 |
2023年 | 228篇 |
2022年 | 464篇 |
2021年 | 758篇 |
2020年 | 1078篇 |
2019年 | 819篇 |
2018年 | 597篇 |
2017年 | 614篇 |
2016年 | 726篇 |
2015年 | 667篇 |
2014年 | 767篇 |
2013年 | 1438篇 |
2012年 | 1837篇 |
2011年 | 968篇 |
2010年 | 809篇 |
2009年 | 1049篇 |
2008年 | 1135篇 |
2007年 | 1266篇 |
2006年 | 1116篇 |
2005年 | 1010篇 |
2004年 | 1017篇 |
2003年 | 855篇 |
2002年 | 778篇 |
2001年 | 594篇 |
2000年 | 596篇 |
1999年 | 501篇 |
1998年 | 459篇 |
1997年 | 434篇 |
1996年 | 455篇 |
1995年 | 457篇 |
1994年 | 332篇 |
1993年 | 292篇 |
1992年 | 252篇 |
1991年 | 165篇 |
1990年 | 117篇 |
1989年 | 87篇 |
1988年 | 89篇 |
1987年 | 83篇 |
1986年 | 57篇 |
1985年 | 50篇 |
1984年 | 46篇 |
1983年 | 23篇 |
1982年 | 42篇 |
1981年 | 30篇 |
1980年 | 31篇 |
1979年 | 23篇 |
1978年 | 13篇 |
1977年 | 10篇 |
1976年 | 10篇 |
1973年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
Investigation on ultrafast thrid—order optical nonlinearity of metal(dmit)2/mnt)2 Charge transfer complexes 下载免费PDF全文
We have investigated the transient third-order optical nonlinearity of the solutions of Metal(dmit)2/(mnt)2 salts in acetone by employing femtosecond optical Kerr gate measurement at 830nm wavelength.An order of enhancement on the second-order hyperppolarizability is found for the above salts with central atoms of Cu and Ni.We have suggested an explanation for the enhancement based on the extension of electronic conjugation by the entring Cu or Ni atom. 相似文献
103.
Metal ion uptake properties of polystyrene-supported chelating polymer resins functionalized with (i) glycine, (ii) hydroxy
benzoic acid, (iii) Schiff base and (iv) diethanol amine have been investigated. The effects of pH, time and initial concentration
on the uptake of metal ions have been studied. The uptake of metal ion depends on pH. The resins are more selective at pH
10 for Pb(II) and Hg(II), whereas at pH 6 they are found to be Cd(II) and Cr(VI) selective. Metal ion uptake properties of
resins follow Freundlich’s equation. The resins are recyclable and are therefore employed for the removal of heavy metal pollutants
from industrial waste water. 相似文献
104.
Jean-Marc Kern Jean-Pierre Sauvage Gerard Bidan Bernadette Divisia-Blohorn 《Journal of polymer science. Part A, Polymer chemistry》2003,41(22):3470-3477
This article provides an overview of the fundamental principles of the synthesis of metallocatenanes and metallorotaxanes. It also describes the synthesis and properties of electronic conducting polymers—polypyrrole and polythiophene—built around metallocatenanes and metallorotaxanes. The particular properties of this new class of polymers, including the possibility of transmetallation reactions being performed with them and the observation of electronic coupling between the metal centers and the conducting matrix, are discussed. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3470–3477, 2003 相似文献
105.
In many Italian archaeological sites dated between the sixth and third centuries BC, unworked lumps of Cu-based materials are sometimes found, the so called Aes Rude, which according to archaeological considerations were appreciated as currency, as a medium of exchange and as a form of saving. The microchemical investigation of these ancient artefacts discloses their nature as apparently not usable for any functional applications or possible use. Indeed, Aes Rude resemble ordinary copper material, but microchemical results indicate that they are constituted by highly ferruginous leaded copper, making them useless for producing other metal objects by means of casting or hot and cold working. Notwithstanding this intrinsic negative feature, the production of these intractable Cu-based alloys was deliberately carried out to maximise the process yield in terms of produced metal from an impure and unselected metal ore by tailoring the smelting process parameters. With these considerations in mind, the microchemical investigation of these ancient iron–copper alloys gives evidence of the passage from the acceptance of an artefact value based on its true nature or potential use to the acceptance of the value based only on its appearance or form irrespective of its present or future use. This information could contribute to a better understanding of the evolution of human thought and economic and social interactions. 相似文献
106.
Lanthanide Complexes for Oligomerization of Phenyl Isocyanate 总被引:1,自引:0,他引:1
IntroductionThestudyonthereactivitiesoflanthanidecomplexesto wardisocyanateshasattractedmuchattention .Ithasbeenre portedthatlanthanidealkoxides,1anddivalentdiaza pentadi enyllanthanidecomplexes2 canbeusedasthesinglecompo nentinitiatorsforisocyanatespolymerization .Recentlyourre searchgrouphasalsofoundthatlanthanoceneamide ,3diva lentaryloxideofsamarium4 ,5anddivalentsamarocene6 areallactivefortheoligomerizationofphenylisocyanate,andtheactivespeciesforthesethreesystemswereallsuccessfullyisolat… 相似文献
107.
N. A. Anikin A. S. Mendkovich M. B. Kuzminskiy A. M. Andreev 《Russian Chemical Bulletin》2008,57(2):428-430
A new fast computational method for mass calculations of docking complexes by the AM1/PM3 semiempirical methods is proposed.
The computation time is shortened by at least an order of magnitude compared to alternative schemes of quantum chemical calculations.
The root-mean-square deviation of the AM1 calculated energies of formation of complexes from the results obtained by conventional
diagonalization procedure is at most 0.4 kcal mol−1.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 418–420, February, 2008. 相似文献
108.
Abed Al-Aziz Al-Quntar 《Journal of organometallic chemistry》2005,690(10):2504-2514
This article describes our recent methods for the synthesis of substituted vinylphosphonates by reacting 1-alkynylphosphnates with group (IV) complexes. cis-Vinylphosphonates, 1,3-butadienylphosphonates, 1-(hydroxymethyl)vinylphosphonates, 2-(hydroxymethyl)vinylphosphonates, (E) 3-oxo-1-alkenylphosphonates were produced as a result of the reactions between zirconium complexes and 1-alkynylphosphonates. On the other hand, titanium complexes afford 3-aminovinylphoshonates, 1,4-bis-phosphonates, and various other di- and tri-substituted vinylphosphonates. An evaluation of access of these recently synthesized vinylphosphonates as MMP-2 inhibitors has shown that certain compounds are very potent and promising. 相似文献
109.
合成了多个基于钴氰化锌的双金属氰化络合物(DMC)催化剂,并对催化剂的结晶形态进行了表征.考察了制备过程中,有机配体及其引入方式,温度,搅拌速度对DMC催化剂形态的影响.其中有机配体对DMC催化剂形态的影响是最主要的.有机配体中富电子原子的电负性的强弱和数量共同影响着DMC催化剂的形态.该类原子的电负性越强,得到的DMC催化剂的结晶性越差,无定型部分的比例越高,并且单个原子的电负性强弱比该类原子的数量在此间的影响更大.而在有机配体预先存在的情况下,该沉淀体系则更有利于无定型部分的产生.在30℃左右的沉淀反应温度下,得到的DMC催化剂的无定型部分比例最高.在有机配体存在的情况下,搅拌速度对DMC催化剂形态的影响有限.并且发现存在于有机配体中的DMC催化剂随着时间的推移,形态会发生变化.初步揭示了DMC催化剂的形态与其催化活性间的关系.而无定型态的DMC催化剂更有利于PO的聚合. 相似文献
110.
Historical perspectives for the chemistry of diene complexes of early transition metals developed at Osaka University in the period after 1970s were reviewed briefly and personally. Preparative chemistry of this field commenced from the magnesium-diene 1:1 compounds and quickly extended to almost all the early transition metals. By the studies operated together with other researchers, unique features of these diene complexes, especially their bonding and structure, selective reactions, and catalysis performances are described. 相似文献