全文获取类型
收费全文 | 715篇 |
免费 | 11篇 |
国内免费 | 2篇 |
专业分类
化学 | 557篇 |
晶体学 | 7篇 |
力学 | 17篇 |
数学 | 53篇 |
物理学 | 94篇 |
出版年
2020年 | 3篇 |
2017年 | 4篇 |
2016年 | 9篇 |
2015年 | 11篇 |
2014年 | 12篇 |
2013年 | 29篇 |
2012年 | 30篇 |
2011年 | 31篇 |
2010年 | 7篇 |
2009年 | 13篇 |
2008年 | 32篇 |
2007年 | 24篇 |
2006年 | 35篇 |
2005年 | 32篇 |
2004年 | 35篇 |
2003年 | 23篇 |
2002年 | 35篇 |
2001年 | 17篇 |
2000年 | 9篇 |
1999年 | 12篇 |
1998年 | 14篇 |
1997年 | 6篇 |
1996年 | 4篇 |
1995年 | 6篇 |
1994年 | 9篇 |
1993年 | 10篇 |
1992年 | 10篇 |
1991年 | 6篇 |
1990年 | 7篇 |
1989年 | 6篇 |
1988年 | 6篇 |
1987年 | 7篇 |
1986年 | 12篇 |
1985年 | 18篇 |
1984年 | 17篇 |
1983年 | 6篇 |
1982年 | 23篇 |
1981年 | 17篇 |
1980年 | 14篇 |
1979年 | 17篇 |
1978年 | 19篇 |
1977年 | 16篇 |
1976年 | 6篇 |
1975年 | 9篇 |
1974年 | 13篇 |
1973年 | 5篇 |
1972年 | 7篇 |
1971年 | 4篇 |
1968年 | 3篇 |
1967年 | 4篇 |
排序方式: 共有728条查询结果,搜索用时 15 毫秒
721.
Masashi Haruki Kunio NakanishiShigemitsu Mano Shin-ichi KiharaShigeki Takishima 《Fluid Phase Equilibria》2011,305(2):152-160
The phase behaviors of the hexane + polydispersed polyethylene (PE) systems were measured to clarify the effect of the molecular weight distribution (MWD) of PE on liquid-liquid (LL) phase boundaries. The weight fraction for the PE portion of a maximum LL phase separation pressure in the LL phase boundary decreased as the polydispersity of PE increased. Moreover, depression of the phase separation pressure from the maximum phase separation pressure on the higher PE weight fraction side was more drastic as the polydispersity of the PE increased. The LL phase boundaries were correlated using the Sanchez-Lacombe equation of state (S-L EOS). For the correlations, the polydispersed PEs were regarded as mixtures of 16 types of monodispersed PEs with different molecular weights, and the characteristic parameters of the S-L EOS, P*, ρ* and T*, were assigned the same values for all monodispersed PEs even though the molecular weights differed. However, the interaction parameters of the hexane-PE pairs depended on the molecular weight of the PE and the temperature. The correlated results capably reproduced the effect of the MWD of the PE on the LL phase boundaries for the hexane + polydispersed PE systems. 相似文献
722.
The PsbP and PsbQ proteins are extrinsic subunits of the photosystem II (PSII) supercomplex, which are found in green plants including higher plants and green algae. These proteins are thought to have evolved from their cyanobacterial homologs; cyanoP and cyanoQ respectively. It has been suggested that the functions of PsbP and PsbQ have largely changed from those of cyanoP and cyanoQ. In addition, multiple isoforms and homologs of PsbP and PsbQ were found in green plants, indicating that the acquisition of PsbP and PsbQ in PSII is not a direct path but a result of intensive functional divergence during evolution from cyanobacterial endosymbiont to chloroplast. In this review, we highlight newly introduced topics related to the functions and structures of both PsbP and PsbQ proteins. The present data suggest that PsbP together with PsbQ have specific and important roles in coordinating the activity of the donor and acceptor sides of PSII and stabilizing the active form of the PSII-light-harvesting complex II (LHCII) supercomplex. 相似文献
723.
The C-3 C-11 segment
of (+)-aplasmomycin was synthesized stereoselectively starting from (+)-pantolactone (
) and the C-3 C-17 segment
was synthesized via coupling of
and
. 相似文献
724.
N Kanekiyo T Kuwada T Choshi J Nobuhiro S Hibino 《The Journal of organic chemistry》2001,66(26):8793-8798
The total syntheses of beta-carboline alkaloids, (R)-(-)-pyridindolols (1, 5, and 6) are described. The two key steps involved are (1) a thermal electrocyclic reaction of the 3-alkenylindole-2-aldoxime 10 and (2) a thermal cyclization of 3-alkynylindole-2-aldoxime 11 to construct the beta-carboline N-oxides 8, which upon heating with acetic anhydride and sequential treatment with trifluoromethanesulfonic anhydride gave the triflates 18. The Stille coupling reaction of 18 with vinylstannane, followed by cleavage of MOM ether, afforded the 1-ethenyl-3-hydroxymethyl-beta-carboline (7a). Subsequent acetylation of 7a yielded the acetate 7b, which was subjected to the Sharpless asymmetric 1,2-dihydroxylation by AD-mix-beta to produce (R)-(-)-pyridindolol K2 (6). Selective acetylation of 6 was effected by Ac(2)O and collidine to form (R)-(-)-pyridindolol K1 (5). By contrast, hydrolysis of 6 provided (R)-(-)-pyridindolol (1). 相似文献
725.
726.
727.
Yasuyuki Yamada Hiroaki Nakajima Chisa Kobayashi Yoshiaki Shuku Kunio Awaga Shigehisa Akine Kentaro Tanaka 《Chemistry (Weinheim an der Bergstrasse, Germany)》2023,29(1):e202203272
A C4h symmetrically substituted phthalocyanine, 1,8,15,22-tertrakis(2,4-dimethylpent-3-oxy)phthalocyanine (H2TdMPPc), was used to synthesize Tb3+-phthalocyanine double-decker complexes ([Tb(TdMPPc)2]s). Because H2TdMPPc has C4h symmetry, S,S, R,R, and meso isomers of [Tb(TdMPPc)2] were obtained depending on the difference in the direction of the coordination plane of two C4h-type phthalocyanines with respect to a central Tb3+ ion. We investigated the physical properties of these [Tb(TdMPPc)2] isomers, including their single-ion magnetic properties, and found that the spin-reversal energy barrier (Ueff) of the meso isomer was apparently higher than that of the enantiomers. Detailed crystal structural analyses indicated that the meso isomer has a more symmetrical structure than do the enantiomers, thereby suggesting that the higher Ueff of the meso isomer originated from the more highly symmetrical structure. 相似文献
728.