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71.
The differential cross sections for the elastic scattering of 3He ions on targets of 40Ca and 58Ni have been measured at incident energies of 27.7, 51.4, 73.2 and 83.5 MeV. The results of optical model analyses showed that only one unique potential (JR ≈ 330 MeV · fm3) with a surface absorptive term can provide acceptable fits to the large angle elastic scattering cross sections at 83.5 MeV. The particular geometrical set found at 83.5 MeV could not, however, give an adequate fit to the data with energy less than 40 MeV. Subsequent analyses indicated that a break in the energy dependence of the real potential is observed for the low energy data. Explicit energy dependent terms were obtained by fitting all the data simultaneously. These phenomenological potentials were also compared with the folded nucleon-nucleus potential. The influence of the α-particle channels on the elastic scattering of 3He ions at 83.5 MeV was also examined.  相似文献   
72.
[reactions: see text] A concise synthesis of highly functionalized cyclopentane derivatives via a Brook rearrangement mediated stereoselective linchpin cyclization reaction involving tert-butyldimethylsilyl-1,3-dithianyllithium and homochiral 1,4-bis-epoxides is described.  相似文献   
73.
Dimers of inclusion complexes were formed from a new cryptand and viologens (paraquats) driven by dipole-dipole and face-to-face pi-stacking interactions as shown by mass spectrometric characterization and X-ray analysis.  相似文献   
74.
Pincer-heterocyclic carbene complexes of Cr(III), of the form [2,6-(1-alkylimidazol-2-ylidene)pyridine]CrCl3, have been prepared and evaluated as catalysts for the oligomerization of ethylene to alpha-olefins. In combination with methylaluminoxane cocatalyst, exceptionally high activities are obtained, ranging up to ca. 40 000 g mmol-1 bar-1 h-1.  相似文献   
75.
The novel complex (eta 6-benzylamine)tricarbonylchromium(0) 11 was prepared in up to 66% yield by direct complexation with Cr(CO)6 in refluxing 1,4-dioxane. Imine derivatives of this complex were readily deprotonated at the benzylic position by diamide 5, and the resultant anions reacted regioselectively with electrophiles (Me3SiCl or MeI) to give fairly good yields of products substituted at the benzylic carbon. Products of up to 87% e.e. were obtained in these reactions, with the highest enantioselectivity being derived from the tert-butyl-substituted imine complex 25.  相似文献   
76.
A background-filtered version of the rotational-echo double resonance (REDOR) experiment is demonstrated. The experiment combines a traditional REDOR pulse sequence with a double-cross-polarization (DCP) sequence to select only those signals coming from spin pairs of interest. The relatively inefficient DCP sequence, which transfers polarization from (1)H to (15)N and subsequently to (13)C, is improved by the use of adiabatic passages through the (-1) sideband of the Hartmann-Hahn matching condition. The result is an efficient 2D-REDOR pulse sequence that does not require a reference experiment for removal of background signals. The data produced by the experiment are ideally suited to analysis by newly developed dipolar transform methods, such as the REDOR transform. The relevant features of the experiment are demonstrated on simple labeled amino acids. Relative efficiencies of several other potential filtering methods are also compared. Copyright 2000 Academic Press.  相似文献   
77.
A series of metal complexes containing potentially tetradentate phenoxyamine ligands is described. The ligands are found to bind to main-group metals and first-row transition-metal centres with variable denticity depending upon the requirements of the particular metal centre. Bidentate [Al(III)], tridentate [Mg(II), Ca(II), Zn(II)] and tetradentate [K(I), Cr(III), Fe(II), Co(II)] binding modes have been established unambiguously through single-crystal X-ray structure determinations.  相似文献   
78.
79.
In this study, methanol extracts (MEs) and essential oil (EO) of Angelica purpurascens (Avé-Lall.) Gill obtained from different parts (root, stem, leaf, and seed) were evaluated in terms of antioxidant activity, total phenolics, compositions of phenolic compound, and essential oil with the methods of 2,2-azino-bis(3ethylbenzo-thiazoline-6-sulfonic acid (ABTS•+), 2,2-diphenyl-1-picrylhydrazil (DPPH•) radical scavenging activities, and ferric reducing/antioxidant power (FRAP), the Folin–Ciocalteu, liquid chromatography−tandem mass spectrometry (LC−MS/MS), and gas chromatography-mass spectrometry (GC−MS), respectively. The root extract of A. purpurascens exhibited the highest ABTS•+, DPPH•, and FRAP activities (IC50: 0.05 ± 0.0001 mg/mL, IC50: 0.06 ± 0.002 mg/mL, 821.04 ± 15.96 µM TEAC (Trolox equivalent antioxidant capacity), respectively). Moreover, EO of A. purpurascens root displayed DPPH• scavenging activity (IC50: 2.95 ± 0.084 mg/mL). The root extract had the highest total phenolic content (438.75 ± 16.39 GAE (gallic acid equivalent), µg/mL)). Twenty compounds were identified by LC−MS/MS. The most abundant phenolics were ferulic acid (244.39 ± 15.64 μg/g extract), benzoic acid (138.18 ± 8.84 μg/g extract), oleuropein (78.04 ± 4.99 μg/g extract), and rutin (31.21 ± 2.00 μg/g extract) in seed, stem, root, and leaf extracts, respectively. According to the GC−MS analysis, the major components were determined as α-bisabolol (22.93%), cubebol (14.39%), α-pinene (11.63%), and α-limonene (9.41%) among 29 compounds. Consequently, the MEs and EO of A. purpurascens can be used as a natural antioxidant source.  相似文献   
80.
Reaction of Me(3)Al (one equivalent) with the bis(imino)phenol, [2,6-(ArNCH)(2)-4-MeC(6)H(2)OH] (I)(Ar = 2,6-Pr(i)(2)C(6)H(3)) in toluene at ambient temperature yields the yellow complex [Me(2)Al[2,6-(ArNCH)(2)-4-MeC(6)H(2)O]](1). Interaction of two equivalents of Me(3)Al in refluxing toluene affords the red complex [(Me(2)Al)(2)[2-ArNCH(Me)-6-(ArNCH)-4-MeC(6)H(2)O]](2). Similar interaction (two equivalents, refluxing toluene) of MeAlCl(2) or (i)Bu(3)Al with [2,6-(ArNCH)(2)-4-MeC(6)H(2)OH] affords [ClAl[2,6-(ArNCH)(2)-4-MeC(6)H(2)O](2)](3) or [(i)Bu(2)Al[2,6-(ArNCH)(2)-4-MeC(6)H(2)O]](4), respectively. Hydrolysis of 2 readily affords the iminoaminophenol ligand [2-(ArN=CH)-6-ArNHCH(Me)-4-MeC(6)H(2)OH](II), which reacts further with Me(3)Al to afford [Me(2)Al[2-ArNCH(Me)-6-(ArNCH)-4-MeC(6)H(2)O]](5). An X-ray study on reveals bidentate imino-alkoxide ligation about the distorted aluminium centre, whereas is a binuclear structure with tetrahedral aluminiums ligated by imino-alkoxide and amido-alkoxide ligand fragments, respectively. For and bidentate imino-alkoxide ligation is observed.  相似文献   
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