全文获取类型
收费全文 | 616篇 |
免费 | 99篇 |
国内免费 | 31篇 |
专业分类
化学 | 712篇 |
晶体学 | 7篇 |
物理学 | 27篇 |
出版年
2024年 | 2篇 |
2023年 | 4篇 |
2022年 | 9篇 |
2021年 | 10篇 |
2020年 | 13篇 |
2019年 | 33篇 |
2018年 | 26篇 |
2017年 | 16篇 |
2016年 | 26篇 |
2015年 | 27篇 |
2014年 | 45篇 |
2013年 | 58篇 |
2012年 | 39篇 |
2011年 | 43篇 |
2010年 | 32篇 |
2009年 | 29篇 |
2008年 | 33篇 |
2007年 | 35篇 |
2006年 | 49篇 |
2005年 | 43篇 |
2004年 | 47篇 |
2003年 | 30篇 |
2002年 | 6篇 |
2001年 | 5篇 |
2000年 | 12篇 |
1999年 | 3篇 |
1998年 | 6篇 |
1997年 | 6篇 |
1996年 | 10篇 |
1995年 | 11篇 |
1994年 | 5篇 |
1993年 | 10篇 |
1992年 | 5篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 4篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1984年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1974年 | 1篇 |
1972年 | 2篇 |
排序方式: 共有746条查询结果,搜索用时 15 毫秒
101.
Chinmay BhatSantosh G. Tilve 《Tetrahedron letters》2011,52(49):6566-6568
Synthesis of tropane alkaloids (−)-hygrine, (−)-norhygrine and sedum alkaloids (−)-pseudohygroline and (−)-hygroline is described from l-proline via Henry and Nef reactions. 相似文献
102.
The tunable self-assembly of a fullerene (C(60))-N,N-dimethylaminoazobenzene (DPNME) molecular system as a function of solvent polarity in THF/water binary solvent is reported. Gradual increase of the volume fraction of the nonsolvent water in a 1×10(-5) M THF solution of DPNME at a mixed dielectric constant ε(mix)≈42 resulted in initial redshifting of the (1)(π→π(*)) absorption band, which signified the 1D head-to-tail or J-type arrangement of the DPNME molecular system. Further increase in the solvent polarity to ε(mix)≈66 evidenced formation of an antiparallel head-to-tail or H-type molecular arrangement in conjunction with the J-aggregates, thereby establishing a solvent-polarity-dependent dynamic equilibrium between the monomer ? J-aggregate ? H-aggregate. The controlled aggregation was governed by the synergetic effect of intermolecular donor-acceptor interaction between the electron-deficient fullerene ring and the electron-rich N,N-dimethylamino-substituted aromatic ring; typically, van der Waals and π-π interactions between the molecules constituting a pair of dimers were envisaged. An agreement between the semiempirically calculated drastically reduced oscillator strength of the DPNME H-dimer in the antiparallel configuration (0.69 vs. 1.29 in the monomeric DPNME) and the experimental electronic absorption spectra beyond ε(mix)=66 further strengthened this assignment to the hitherto forbidden antiparallel H-dimer. Complementing the above, the periodicity of molecular self-assembly dictated a monoclinic unit cell in the single-crystal XRD packing pattern with a C2/c space group; the molecules packed laterally with mutual interdigitation with the donor (E)-N,N-dimethyl-4-(p-tolyldiazenyl)aniline (AZNME) parts in an antiparallel fashion (contrary to the usual expectation for H-aggregates) with strong inter- and intrapair van der Waals and π-π interactions between the constituent fullerene moieties. Unlike those of porphyrin/phthalocyanine bowl-like donor-initiated architectures, a rare class of DPNME dyadic supramolecular self-assemblies was realized with π-extended 2D fullerene networks, in which the linear geometry of the AZNME donor and the conformational rigidity of the fullerene acceptor played crucial roles. 相似文献
103.
104.
Piotr ?y?wa Ma?gorzata Kwiatkowska Piotr Kie?basiński Alexander Betz Annie-Claude Gaumont 《Tetrahedron letters》2007,48(3):351-355
A chiral racemic 2-phosphono-2,3-didehydrothiolane sulfoxide was used as a Michael acceptor in the reactions with several nucleophiles, in particular thiols. In most cases the reactions were fully diastereoselective. The relative configuration of the resulting adducts was determined. 相似文献
105.
Timothy D. White 《Tetrahedron letters》2005,46(34):5629-5632
1,4-Dien-3-ones encased within bridged bicyclic frameworks undergo efficient Nazarov electrocyclization upon treatment with TiCl4, but the resulting cyclopentenyl cations are trapped by chloride in preference to deprotonation. In contrast to the usual eliminative pathway, which destroys one of the stereocenters formed during electrocyclization, this process preserves both new centers and generates an additional one at the site of chloride trapping. Examples involving skeletal rearrangements and other Lewis acids are also discussed. 相似文献
106.
A. I. Matern V. V. Yanilkin V. N. Nastapova V. I. Morosov V. N. Charushin O. N. Chupakhin 《Russian Chemical Bulletin》2006,55(8):1498-1499
The electrochemical reduction of the 9-cyano-10-methylacridinium cation in acetonitrile yielded the corresponding radical,
which was rather stable at 20 °C and gave a resolved ESR spectrum. This radical reversibly dimerized in the temperature range
from 20 to −30 °C.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1444–1445, August, 2006. 相似文献
107.
Chun-Chih Wang 《Tetrahedron letters》2004,45(32):6203-6206
In the presence of CoX2(PPh3)2/3 PPh3 and zinc metal conjugated alkenes (CH2CHCOOR, CH2CHCN, CH2CHSO2Ph and CH2CHCONEt2) undergo reductive tail-to-tail dimerization to yield the corresponding saturated linear products. Under similar reaction conditions, vinylarenes (ArCHCH2) give stereoselective head-to-tail dimerization products, trans-1,3-diarylbut-1-ene, in good to excellent yields. 相似文献
108.
109.
《Tetrahedron letters》2005,46(19):3297-3300
Treatment of disulfide 7 with NaIO4 in EtOH at rt gave monosulfoxide 8 (95%), while at 50 °C it gave trans-bis-sulfoxide 6a (84%, >99% de). In contrast, treatment of 7 with MCPBA gave bis-sulfone 9 (95%). The anion of 6a reacted with benzaldehyde affording carbinol 10 (76%, >99% de). The absolute configuration of 8, 6a, and 10 was established by single crystal X-ray diffraction analyses. 相似文献
110.