全文获取类型
收费全文 | 2550篇 |
免费 | 113篇 |
国内免费 | 15篇 |
专业分类
化学 | 1943篇 |
晶体学 | 22篇 |
力学 | 37篇 |
综合类 | 16篇 |
数学 | 230篇 |
物理学 | 430篇 |
出版年
2023年 | 20篇 |
2022年 | 14篇 |
2021年 | 41篇 |
2020年 | 54篇 |
2019年 | 56篇 |
2018年 | 38篇 |
2017年 | 31篇 |
2016年 | 60篇 |
2015年 | 57篇 |
2014年 | 64篇 |
2013年 | 132篇 |
2012年 | 170篇 |
2011年 | 166篇 |
2010年 | 93篇 |
2009年 | 104篇 |
2008年 | 184篇 |
2007年 | 158篇 |
2006年 | 163篇 |
2005年 | 155篇 |
2004年 | 131篇 |
2003年 | 109篇 |
2002年 | 105篇 |
2001年 | 38篇 |
2000年 | 46篇 |
1999年 | 30篇 |
1998年 | 33篇 |
1997年 | 31篇 |
1996年 | 29篇 |
1995年 | 16篇 |
1994年 | 21篇 |
1993年 | 16篇 |
1992年 | 23篇 |
1991年 | 12篇 |
1990年 | 22篇 |
1989年 | 13篇 |
1988年 | 15篇 |
1987年 | 20篇 |
1986年 | 12篇 |
1985年 | 26篇 |
1984年 | 22篇 |
1983年 | 19篇 |
1982年 | 20篇 |
1981年 | 22篇 |
1980年 | 21篇 |
1979年 | 11篇 |
1978年 | 9篇 |
1977年 | 10篇 |
1976年 | 10篇 |
1975年 | 5篇 |
1974年 | 6篇 |
排序方式: 共有2678条查询结果,搜索用时 78 毫秒
101.
Synthesis and Rearrangement of P‐Nitroxyl‐Substituted PIII and PV Phosphanes: A Combined Experimental and Theoretical Case Study 下载免费PDF全文
Tobias Heurich Dr. Zheng‐Wang Qu Dr. Senada Nožinović Dr. Gregor Schnakenburg Dr. Hideto Matsuoka Prof. Dr. Stefan Grimme Prof. Dr. Olav Schiemann Prof. Dr. Rainer Streubel 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(29):10102-10110
Low‐temperature generation of P‐nitroxyl phosphane 2 (Ph2POTEMP), which was obtained by the reaction of Ph2PH ( 1 ) with two equivalents of TEMPO, is presented. Upon warming, phosphane 2 decomposed to give P‐nitroxyl phosphane P‐oxide 3 (Ph2P(O)OTEMP) as one of the final products. This facile synthetic protocol also enabled access to P‐sulfide and P‐borane derivatives 7 and 13 , respectively, by using Ph2P(S)H ( 6 ) or Ph2P(BH3)H ( 11 ) and TEMPO. Phosphane sulfide 7 revealed a rearrangement to phosphane oxide 8 (Ph2P(O)STEMP) in CDCl3 at ambient temperature, whereas in THF, thermal decomposition of sulfide 7 yielded salt 10 ([TEMP‐H2][Ph2P(S)O]). As well as EPR and detailed NMR kinetic studies, indepth theoretical studies provided an insight into the reaction pathways and spin‐density distributions of the reactive intermediates. 相似文献
102.
T. Arun Kumar V.S.S. Sastry Ken Ishikawa Hideo Takezoe N.V. Madhusudana 《Liquid crystals》2013,40(8):971-979
We report experimental studies on defects in a nematic liquid crystal with negative dielectric anisotropy mounted in a cell with perfluoropolymer-coated surfaces. The sample exhibits a discontinuous anchoring transition from planar to homeotropic on cooling at zero or a small electric field, and above a cross-over voltage a continuous ‘inverse Freedericksz transition’, at which the director starts tilting in opposite directions at the two surfaces. Defects of strength ±1/2 are either annihilated or expelled when the director tilts. On the other hand, disclination lines of ±1 which end in partial point defects (boojums) at the surfaces in the planar alignment regime acquire point defects of strength ±1 at the midplane of the cell when the director tilts. At a low enough temperature, the homeotropic anchoring becomes strong, and an electric field above the Freedericksz threshold generates the usual umbilic defects, which follow the dynamic scaling laws found in earlier studies. 相似文献
103.
104.
105.
Kyoichi Hanada Juntaro Nogami Prof. Dr. Kazunori Miyamoto Norihiko Hayase Dr. Yuki Nagashima Yusuke Tanaka Dr. Atsuya Muranaka Prof. Dr. Masanobu Uchiyama Prof. Dr. Ken Tanaka 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(36):9313-9319
The enantioselective synthesis of aza[6] and [7]helicene-like molecules have been achieved by the cationic rhodium(I)/axially chiral biaryl bisphosphine complex-catalyzed intramolecular [2+2+2] cycloaddition of cyanodiynes. This protocol was successfully applied to the diastereo- and enantioselective synthesis of an S-shaped double aza[6]helicene-like molecule with a high ee value of 89 %. Although no epimerization and racemization were observed in the double carbo[6]helicene-like molecule at 80 °C, epimerization and racemization of the double aza[6]helicene-like molecule proceeded at 80 °C. This double aza[6]helicene-like molecule showed good fluorescent quantum yields and chiroptical responses under both neutral and acidic conditions. 相似文献
106.
Hyoe Hatakeyama Shigeo Hirose Tatsuko Hatakeyama Kunio Nakamura Ken Kobashigawa Noriyuki Morohoshi 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(4):743-750
Abstract Polyurethane (PU) sheets and foams having plant components in their network were prepared by using the following procedure. Polyethylene glycol (PEG) was mixed with one of the following; molasses, lignin, woodmeal, or coffee grounds. The mixture obtained was reacted with diphenylmethane diisocyanate (MDI) at room temperature, and precured PUs were prepared. The precured PUs were heat-pressed and PU sheets were obtained. In order to make PU foam, the above mixture was reacted with MDI after the addition of plasticizer, surfactant (silicone oil), catalyst (di-n-butyltin dilaurate), and droplets of water under vigorous stirring. The glass transition temperature, tensile and compression strengths, and Young's modulus of the PU sheets and foams increased with an increasing amount of plant components. This suggests that saccharide and lignin residues act as hard segments in PUs. It was found that the PUs obtained were biodegradable in soil. The rate of biodegradation of the PUs derived from molasses and coffee grounds was between that of cryptomeria (Cryptomeria japonica) and beech (Fagus sieboldi). 相似文献
107.
Ken Jones 《Chromatographia》2017,80(10):1597-1597
108.
Relatively few constructions are known of negative Latin square type Partial Difference Sets (PDSs), and most of the known constructions are in elementary abelian groups. We present a product construction that produces negative Latin square type PDSs, and we apply this product construction to generate examples in p-groups of exponent bigger than p. 相似文献
109.
Dr. Yoichi Hoshimoto Keita Ashida Yukari Sasaoka Dr. Ravindra Kumar Prof. Dr. Ken Kamikawa Prof. Dr. Xavier Verdaguer Prof. Dr. Antoni Riera Prof. Dr. Masato Ohashi Prof. Dr. Sensuke Ogoshi 《Angewandte Chemie (International ed. in English)》2017,56(28):8206-8210
The nickel(0)-catalyzed carbonylative cycloaddition of 1,5- and 1,6-ene-imines with carbon monoxide (CO) is reported. Key to this reaction is the efficient regeneration of the catalytically active nickel(0) species from nickel carbonyl complexes such as [Ni(CO)3L]. A variety of tri- and tetracyclic γ-lactams were thus prepared in excellent yields with 100 % atom efficiency. Preliminary results on asymmetric derivatives promise potential in the synthesis of enantioenriched polycyclic γ-lactams. 相似文献
110.
Hiroaki Shimomoto Dai Fukami Tomomi Irita Ken‐ichi Katsukawa Takabumi Nagai Shokyoku Kanaoka Sadahito Aoshima 《Journal of polymer science. Part A, Polymer chemistry》2012,50(8):1547-1555
Various types of fluorine‐containing star‐shaped poly(vinyl ether)s were successfully synthesized by crosslinking reactions of living polymers based on living cationic polymerization. Star polymers with fluorinated arm chains were prepared by the reaction between a divinyl ether and living poly(vinyl ether)s with fluorine groups (C4F9, C6F13, and C8F17) at the side chain using cationogen/Et1.5AlCl1.5 in a fluorinated solvent (dichloropentafluoropropanes), giving star‐shaped fluorinated polymers in high yields with a relatively narrow molecular weight distribution. The concentration of living polymers for the crosslinking reaction and the molar feed ratio of a bifunctional vinyl ether to living polymers affected the yield and molecular weight of the star polymers. Star polymers with block arms were prepared by a linking reaction of living block copolymers of a fluorinated segment and a nonfluorinated segment. Heteroarm star‐shaped polymers containing two‐ or three‐arm species were synthesized using a mixture of different living polymer species for the reaction with a bifunctional vinyl ether. The obtained polymers underwent temperature‐induced solubility transitions in various organic solvents, and their concentrated solutions underwent sol–gel transitions, based on the solubility transition of a thermoresponsive fluorinated segment. Furthermore, a slight amount of fluorine groups were shown to be effective for physical gelation when those were located at the arm ends of a star polymer. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献