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141.
Photo-oxidation of α,β-unsaturated thiones yields the corresponding ketones as the only product. Studies carried out on three systems, namely thioketones, α,β-unsaturated thiones and thioketenes, have revealed that there exists a similarity in their mechanism of oxidation. It has been suggested that the thiocarbonyl chromophore is the site of attack by singlet oxygen in α,β-unsaturated thiones and that the adjacent C-C double bond is inert under these conditions. Absence of sulphine during the oxidation of α,β-unsaturated thiones is attributed to the electronic factors operating on the zwitterionic/diradical intermediate. While α,β-unsaturated ketones are poorly reactive, α,β-unsaturated thiones are highly reactive toward singlet oxygen. 相似文献
142.
Pichandi Ashokkumar Prof. Dr. Vayalakkavoor T. Ramakrishnan Prof. Dr. Perumal Ramamurthy 《Chemphyschem》2011,12(2):389-396
To explore the anion‐recognition ability of the phenolic hydroxyl group and the amino hydrogen, we synthesized three different acridinedione (ADD) based anion receptors, 1 , 2 and 3 , having OH, NH, and combination of OH and NH groups, respectively. Absorption, emission and 1H NMR spectral studies revealed that receptor 1 , having only a phenolic OH group, shows selective deprotonation of the hydroxyl proton towards F?, which results in an “ON–OFF”‐type signal in the fluorescence spectral studies. Receptor 2 , which only has an amino hydrogen, also shows deprotonation of the amino hydrogen with F?, whereas receptor 3 (having both OH and NH groups) shows head‐to‐tail intermolecular hydrogen bonding of OH and NH groups with F? prior to deprotonation. The observation of hydrogen bonding of the OH and NH groups in a combined solution of 1 and 2 with F? in a head‐to‐tail hetero‐intermolecular fashion, and the absence of head‐to‐head and tail‐to‐tail intermolecular hydrogen bonding in 1 and 2 with F?, prove that the difference in the acidity of the OH and NH protons leads to the formation of an intermolecular hydrogen‐bonding complex with F? prior to deprotonation. The presence of this hydrogen‐bonding complex was confirmed by absorption spectroscopy, 3D emission contour studies, and 1H NMR titration. 相似文献
143.
The self-organization of cucurbit[n]uril (n = 7 and 8, CBs) complexes was probed by electrospray mass spectrometry. The self-association of CB complexes is a general phenomenon but shows some dependence on the absence, presence, and type of included guest molecules. 相似文献
144.
145.
Adler SS Afanasiev S Aidala C Ajitanand NN Akiba Y Alexander J Amirikas R Aphecetche L Aronson SH Averbeck R Awes TC Azmoun R Babintsev V Baldisseri A Barish KN Barnes PD Bassalleck B Bathe S Batsouli S Baublis V Bazilevsky A Belikov S Berdnikov Y Bhagavatula S Boissevain JG Borel H Borenstein S Brooks ML Brown DS Bruner N Bucher D Buesching H Bumazhnov V Bunce G Burward-Hoy JM Butsyk S Camard X Chai JS Chand P Chang WC Chernichenko S Chi CY Chiba J Chiu M Choi IJ Choi J Choudhury RK Chujo T 《Physical review letters》2006,96(3):032301
The PHENIX experiment has measured midrapidity ([FORMULA: SEE TEXT]) transverse momentum spectra ([FORMULA: SEE TEXT]) of electrons as a function of centrality in Au+Au collisions at [FORMULA: SEE TEXT]. Contributions from photon conversions and from light hadron decays, mainly Dalitz decays of pi0 and eta mesons, were removed. The resulting nonphotonic electron spectra are primarily due to the semileptonic decays of hadrons carrying heavy quarks. Nuclear modification factors were determined by comparison to nonphotonic electrons in p+p collisions. A significant suppression of electrons at high pT is observed in central Au+Au collisions, indicating substantial energy loss of heavy quarks. 相似文献
146.
Adler SS Afanasiev S Aidala C Ajitanand NN Akiba Y Alexander J Amirikas R Aphecetche L Aronson SH Averbeck R Awes TC Azmoun R Babintsev V Baldisseri A Barish KN Barnes PD Bassalleck B Bathe S Batsouli S Baublis V Bazilevsky A Belikov S Berdnikov Y Bhagavatula S Boissevain JG Borel H Borenstein S Brooks ML Brown DS Bruner N Bucher D Buesching H Bumazhnov V Bunce G Burward-Hoy JM Butsyk S Camard X Chai JS Chand P Chang WC Chernichenko S Chi CY Chiba J Chiu M Choi IJ Choi J Choudhury RK Chujo T 《Physical review letters》2006,96(3):032302
The azimuthal distribution of identified pi0 and inclusive photons has been measured in [FORMULA: SEE TEXT] Au+Au collisions with the PHENIX experiment at the Relativistic Heavy-Ion Collider (RHIC). The second-harmonic parameter (nu2) was measured to describe the observed anisotropy of the azimuthal distribution. The measured inclusive photon is consistent with the value expected for the photons from hadron decay and is also consistent with the lack of direct photon signal over the measured pT range 1-6 GeV/c. An attempt is made to extract nu2 of direct photons. 相似文献
147.
148.
Chong KC Sivaguru J Shichi T Yoshimi Y Ramamurthy V Scheffer JR 《Journal of the American Chemical Society》2002,124(12):2858-2859
Three different approaches to asymmetric induction in the cis-to-trans photoisomerization of a number of 1-benzoyl-2,3-diphenylcyclopropane derivatives are reported: the use of chiral inductors and covalent chiral auxiliaries in MY zeolites and the use of ionic chiral auxiliaries in crystals. High levels of asymmetric induction were achieved using the latter two methods-up to 71% through the use of covalent chiral auxiliaries in zeolites and a remarkable 99% via the solid state ionic chiral auxiliary approach. In the zeolite method, the diastereomeric excess was found to depend strongly on the nature of the zeolite cation, M(+), and in the ionic chiral auxiliary approach, evidence is presented that it is the fixed orientation of the benzoyl group with respect to the cyclopropane ring that controls enantioselectivity in the crystalline state-a finding that is directly relevant to theoretical work on this topic. 相似文献
149.
Sivaguru J Scheffer JR Chandarasekhar J Ramamurthy V 《Chemical communications (Cambridge, England)》2002,(8):830-831
Alkali ion-exchanged Y-zeolites significantly enhance asymmetric induction in the photoisomerization of a number of cis-1,2-diphenylcyclopropane derivatives containing a distant chiral auxiliary. 相似文献
150.
Evgeny I. Kvasyuk Tamara I. Kulak Galina T. Zaitseva Igor A. Mikhailopulo Ramamurthy Charubala Wolfgang Pfleiderer 《Tetrahedron letters》1984,25(34):3683-3686
The trimer of 2′, 5′-oligoadenylic acid with a (2-carboxyethyl)ethylidene group ({=1}{=6}) at the 2′-terminal adenosine moiety and its 3′-deoxyadenosine analog ({=1}{=7}) have been synthesized by the phosphotriester method. 相似文献