全文获取类型
收费全文 | 4709篇 |
免费 | 165篇 |
国内免费 | 30篇 |
专业分类
化学 | 2626篇 |
晶体学 | 52篇 |
力学 | 186篇 |
数学 | 1163篇 |
物理学 | 877篇 |
出版年
2023年 | 45篇 |
2022年 | 128篇 |
2021年 | 141篇 |
2020年 | 131篇 |
2019年 | 160篇 |
2018年 | 157篇 |
2017年 | 145篇 |
2016年 | 199篇 |
2015年 | 153篇 |
2014年 | 212篇 |
2013年 | 346篇 |
2012年 | 316篇 |
2011年 | 331篇 |
2010年 | 179篇 |
2009年 | 199篇 |
2008年 | 238篇 |
2007年 | 206篇 |
2006年 | 159篇 |
2005年 | 130篇 |
2004年 | 129篇 |
2003年 | 97篇 |
2002年 | 92篇 |
2001年 | 78篇 |
2000年 | 60篇 |
1999年 | 39篇 |
1998年 | 31篇 |
1997年 | 38篇 |
1996年 | 53篇 |
1995年 | 42篇 |
1994年 | 34篇 |
1993年 | 42篇 |
1992年 | 36篇 |
1991年 | 38篇 |
1990年 | 31篇 |
1989年 | 23篇 |
1988年 | 29篇 |
1987年 | 37篇 |
1986年 | 39篇 |
1985年 | 35篇 |
1984年 | 29篇 |
1983年 | 26篇 |
1982年 | 33篇 |
1981年 | 31篇 |
1980年 | 22篇 |
1979年 | 39篇 |
1978年 | 28篇 |
1977年 | 24篇 |
1976年 | 23篇 |
1975年 | 20篇 |
1974年 | 14篇 |
排序方式: 共有4904条查询结果,搜索用时 15 毫秒
101.
Abstract Three new series of cyanoaryl 4-alkylthioxybenzoates have been synthesized and characterized. The 4-cyanophenyl series displays only transient mesomorphic properties while the 6-cyano-2-naphthyl and 4-cyanobiphenyl series exhibit the classical nematic and smectic A phases; a reentrant nematic phase is also found in the latter. Two other new series in which the position of the sulphur atom in the central rigid core has been varied were also prepared: the 4–[4′-cyanobenzoyloxy]-phenyl 4-alkylthiobenzoates and 4–[4′-alkylbenzoyloxy]phenyl 4-cyanothiobenzoates. As in the analogous benzoate series, the reentrant phenomenon with the sequence C, SAre, Nre, SA, N, I is observed with the nonyl derivatives. Comparisons between the alkoxybenzoates and the alkylthioxybenzoates are given. 相似文献
102.
Abdelhouad Oukhrib Laurence Bonnafoux Armen Panossian Sandrine Waifang Duc Hanh Nguyen Martine Urrutigoity Françoise Colobert Maryse Gouygou Frédéric R. Leroux 《Tetrahedron》2014
A new family of non-symmetrical disubstituted dibenzophospholes possessing different steric and electronic effects have been synthesized and characterized. Their preliminary evaluation in rhodium-catalyzed hydroformylation reactions is presented. 相似文献
103.
104.
Tuan-Anh Nguyen Øyvind Weiby Gregersen Ferdinand Männle Philippe Brachet 《Journal of Sol-Gel Science and Technology》2014,69(2):237-249
The substitution of fossil based packaging materials with materials from renewable sources is a topic of current interest. Polyhedral oligomeric silsesquioxanes with fatty acid moieties can have a renewable content of more than 90 % and are therefore called bio-POSS. In this study the bio-POSS octa-(ethyl erucamide) silsesquioxane was coated on a paperboard substrate as a liquid coating. The water resistance and the water vapour barrier properties of the paperboard were improved. Samples on which the bio-POSS coating layer was dried at 80 °C had a slightly higher water resistance and water vapour barrier than samples dried at room temperature. UV treatment of the coating layer had little effect. Solid state 1H-NMR of UV treated coatings showed no reaction of double bonds of bio-POSS in the coating layer. Multiple coating considerably enhanced the water resistance and water vapour barrier properties of the paperboard, due to an increase in the coating thickness and a reduction in number of pores on top coated surfaces. 相似文献
105.
D. Thao Nguyen Matthias Freitag Christian Gutheil Dr. Kai Sotthewes Dr. Bonnie J. Tyler Dr. Marcus Böckmann Mowpriya Das Friederike Schlüter Prof. Dr. Nikos L. Doltsinis Prof. Dr. Heinrich F. Arlinghaus Prof. Dr. Bart Jan Ravoo Prof. Dr. Frank Glorius 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(32):13754-13759
106.
Christian Decker Danielle Decker Trieu Nguyen Thi Viet Hien Le Xuan 《Macromolecular Symposia》1996,102(1):63-71
Different types of tridimensional polymer networks have been synthetised by photoinitiated cationic polymerisation of vinyl ether and epoxy-functionalised oligomers and polymers. The polymerisation kinetics was followed by real-time infrared (RTIR) spectroscopy, a technique that records directly conversion versus time profiles in a timescale as short as 1 s. The addition of a diacrylate monomer was shown to accelerate the ring-opening polymerisation of epoxidized polyisoprene, with formation of interpenetrating polymer networks having well contrasted properties. A dual polymer network has been generated by photocrosslinking of a polyisoprene functionalised with both epoxy and acrylate groups. 相似文献
107.
B. Liebl H. Mückter Ph.-T. Nguyen E. Doklea S. Islambouli B. Fichtl W. Forth 《应用有机金属化学》1995,9(7):531-540
We have compared the acute toxicities of the trivalent arsenic species arsenite, oxophenylarsine (PhAsO), 2-chlorovinyloxoarsine (ClvinAsO), methyloxoarsine (MeAsO), and of the pentavalent arsenic species arsenate, methyl- and phenyl-arsonic acid in rat kidney tubules (RKT) and Madin-Darby canine kidney (MDCK) cells. In RKT, PhAsO (1 μmol I−1, 60 min) almost completely (>90%) blocked gluconeogenesis without affecting cell viability as assessed by dye exclusion. In MDCK cells, PhAsO (2 μmol I−1) markedly inhibited glucose uptake (60% of controls) within 30 min, while cell viability, as assessed by formazan formation, was not affected within 180 min. MeAsO and CIvinAsO were similarly effective to PhAsO in both RKT and MDCK cells. Estimated IC50 values for the inhibition of gluconeogenesis were 0.55 (PhAsO), 0.69 (CIvinAsO) and 0.99 μmol I−1 (MeAsO) and for the inhibition of glucose uptake 1.23 (PhAsO). 2.62 (CIvinAsO) and 6.99 μmol I−1 (MeAsO). At longer storage times, aqueous solutions of MeAsO and of CIvinAsO, but not of PhAsO, gradually lost toxic activity in RKT and MDCK cells, especially at alkaline pH. Concomitantly, a gradual decrease in content as assessed by HPLC was detected. Roughly 10-fold higher concentrations of arsenite than of PhAsO were required for comparable effects on gluconeogenesis in RKT, whereas in MDCK cells about 100-fold higher concentrations were needed for similar inhibition of glucose uptake. Pentavalent arsenate and phenylarsonate were two orders of magnitude less effective than PhAsO in RKT, while methylarsonate had virtually no influence on gluconeogenic activity. In MDCK cells the pentavalent arsenic species showed effects only in the millimolar range. It is concluded (1) that different mechanisms are involved in the acute toxicity of oxoarsines and inorganic arsenic and (2) that PhAsO offers advantages as a model substance for mono-substituted trivalent arsenicals, because it is more stable and more readily detectable. 相似文献
108.
Marc A. Hillmyer Alto D. Benedicto SonBinh T. Nguyen Zhe Wu Robert H. Grubbs 《Macromolecular Symposia》1995,89(1):411-419
The copolymerization of both high- and low-strain cyclic olefins employing three ruthenium-based metathesis catalysts is desribed. The effect of the ligand environment as well as the nature of the carbene on the copolymerizations is discussed. 相似文献
109.
110.