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91.
Mobility and diffusion data for F? and Cl? ions in Xe gas at 300 K are used to test the well depths and the “width” of the XeF? well previously obtained by a fit to differential scattering cross sections. 相似文献
92.
Haneline MR Taylor RE Gabbaï FP 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(21):5189-5193
Trimeric perfluoro-ortho-phenylenemercury (1) constitutes one of the simplest trifunctional Lewis acidic hosts. In addition to cooperative effects arising from the proximity of the mercury(II) centers, the electron-withdrawing properties of the backbone and the accessibility of the electrophilic sites lead to the facile complexation of neutral and electron rich substrates. The planarity of the structure as well as its overall polarizability compounded with relativistic effects at mercury also permits the occurrence of non-covalent interactions and accounts for the tendency of this compound to form cofacial dimers. Collectively, the Lewis acidic properties of 1 as well as its ability to engage in non-covalent interactions can be held responsible for its ability to form extended binary supramolecular stacks with arenes. The photoluminescence observed in some of these supramolecular complexes corresponds to the phosphorescence of the aromatic substrate and indicate the occurrence of a mercury heavy atom effect. 相似文献
93.
Plieger PG Burrell AK Jameson GB Officer DL 《Dalton transactions (Cambridge, England : 2003)》2004,(2):319-326
A new series of meso-substituted diaryl free-base and metalloporphyrins have been prepared. Each arene has been substituted with both a methyl group in the ortho position and a formyl group in the meta position. Rotation of the arene units is prevented at room temperature due to the steric restrictions imposed by the flanking methyl groups at the porphyrin beta-pyrrolic positions on the methyl groups at the ortho position on the meso-substituted arene unit. This allowed the alpha alpha and alpha beta atropisomers of this porphyrin to be separated and characterised. X-Ray crystallographic determination of the structure of the free-base porphyrin revealed a very flat porphyrin core. Metallation resulted in the isolation and characterisation of the nickel, zinc and copper derivatives. The assignments of the alpha alpha and alpha beta isomers are confirmed by X-ray crystallographic determination of the structures of the Cu(II) analogues. The copper alpha alpha structure exhibits a very twisted porphyrin core, the copper alpha beta structure is also distorted, but to a lesser degree. The activation energy for rotation has been calculated for each of the 2H, Ni and Zn derivatives. The energy required to rotate the arene ring increases in the order Ni < Zn approximately 2H. No significant difference in the free energy of rotation was observed between experiments carried out with the alpha alpha and small alpha beta isomers. 相似文献
94.
α-Oxo-carboxylic acids undergo photo-oxidative decarboxylation from both C-1 and C-2 positions, and reaction does not involve singlet oxygen: a mechanism involving an electron transfer reaction is postulated. 相似文献
95.
Hui Yang Xing Chen Guoxiang Hu Wan-Ting Chen Siobhan J. Bradley Weijie Zhang Gaurav Verma Thomas Nann De-en Jiang Paul E. Kruger Xiangke Wang He Tian Geoffrey I. N. Waterhouse Shane G. Telfer Shengqian Ma 《Chemical science》2020,11(13):3523
Optimizing interfacial contacts and thus electron transfer phenomena in heterogeneous electrocatalysts is an effective approach for enhancing electrocatalytic performance. Herein, we successfully synthesized ultrafine β-Mo2C nanoparticles confined within hollow capsules of nitrogen-doped porous carbon (β-Mo2C@NPCC) and found that the surface layer of molybdenum atoms was further oxidized to a single Mo–O surface layer, thus producing intimate O–Mo–C interfaces. An arsenal of complementary technologies, including XPS, atomic-resolution HAADF-STEM, and XAS analysis clearly reveals the existence of O–Mo–C interfaces for these surface-engineered ultrafine nanostructures. The β-Mo2C@NPCC electrocatalyst exhibited excellent electrocatalytic activity for the hydrogen evolution reaction (HER) in water. Theoretical studies indicate that the highly accessible ultrathin O–Mo–C interfaces serving as the active sites are crucial to the HER performance and underpinned the outstanding electrocatalytic performance of β-Mo2C@NPCC. This proof-of-concept study opens a new avenue for the fabrication of highly efficient catalysts for HER and other applications, whilst further demonstrating the importance of exposed interfaces and interfacial contacts in efficient electrocatalysis.Ultrafine β-Mo2C nanostructures encapsulated in N-doped carbon capsules featuring O–Mo–C interfaces as the active sites for HER have been unveiled. 相似文献
96.
The kinetics of conversion of an edge-linked double cube, in this case [{Mo(3)PdS(4)(H(2)O)(9)}(2)](8+), to the corresponding single cube [Mo(3)(PdX)S(4)(H(2)O)(9)](4+), has been studied for the first time. Reaction is induced by six reagents X = CO, two water-soluble phosphines, Cl(-), Br(-), and NCS(-), which complex at the tetrahedral Pd. The first stage of reaction is fast and is accompanied by color changes, e.g. purple to dark blue in the case of Cl(-), assigned as double to single cube conversion. With X = CO and the two phosphines, when absorbance changes are intense enough for stopped-flow monitoring with reactants at =1 mM, rate constants 10(-)(5) k/M(-)(1) s(-)(1) at 25 degrees C are as follows: CO, 1.11; PTA, 27.8; P(C(6)H(4)SO(3))(3)(3)(-), 9.6; at I = 2.00 (Li(pts)). The reactions are independent of [H(+)] in the range 0.30-2.00 M, and no substitution at the Mo's is observed. The first stages with X = Cl(-), Br(-), and NCS(-) were too fast to monitor, but equilibrium constants K(1)/M(-)(1) were determined, Cl(-) (490), Br(-) (8040), and NCS(-) (630), by UV-vis spectrophotometry. Two subsequent kinetic stages are assigned to substitution at the Mo's. Similar behavior is observed for [Mo(3)FeS(4)(H(2)O)(10)](4+), which was selected because substitution at the Fe is also fast and there is no known double-cube formation. For both Mo(3)Pd and Mo(3)Fe the latter two stages can be explained by substitution at nonidentical (two alpha and one beta) H(2)O's on each Mo or by the presence of mixed-valent Mo(III)(2)Mo(IV) forms which are sufficiently long-lived to give a kinetic discrimination. In the case of NCS(-) an additional step, 0.015 s(-)(1), independent of [NCS(-)] is assigned to the isomerization Pd-NCS --> Pd-SCN. On removal of e.g. Cl(-) by chromatography or addition of Ag(+), the double cube re-forms. 相似文献
97.
V. L. Spate M. M. Mason C. L. Reams C. K. Baskett J. S. Morris D. S. Mills 《Journal of Radioanalytical and Nuclear Chemistry》1994,179(2):315-322
In this study we report on the comparison between the total selenium in serum (total Se) with that which is apparently bound to high molecular weight (>12,000 D) species, presumably proteins (bound Se). Nine hundred seventy seven (977) serum samples arising out of a population-based epidemiological study were prepared in duplicate for the determination of total Se by pipeting directly into irradiation vials; and separate duplicate aliquots were dialyzed against DI water for the determination of bound Se. All samples were analyzed by neutron activation analysis via77mSe (17.4 s). A small dialyzable Se component (6%) (free Se), defined as the difference between the total Se minus the bound Se, was identified. 相似文献
98.
V. Karimäki R. Kinnunen M. Korkea-aho J. Tuominiemi G. W. van Apeldoorn D. Harting D. J. Holthuizen B. J. Pijlgroms P. Johnson P. Mason P. Michaelides Ch. Michaelidou H. Muirhead G. D. Patel G. Ekspong T. Moa S. Nilsson 《Zeitschrift fur Physik C Particles and Fields》1981,9(2):117-129
Inclusive production of ?0,K *±(892), andf is studied in \(\bar p\) p interactions at 12 GeV/c. The inclusive cross sections for ?0,K *±(892), andf are found to be 6.7±0.3 mb, 1.0±0.2 mb, and 1.4±0.3 mb, respectively. The differential cross sections are presented as a function of c.m. rapidity, Feynmanx and square of the transverse momentump T 2 . Comparison with the correspondingpp data shows some interesting differences which can be attributed to the \(\bar p\) p annihilation. The results are compared with the predictions of the quark fusion model. 相似文献
99.
Geoffrey A. Lawrance 《Transition Metal Chemistry》1986,11(10):396-399
Summary The Co(NH3)5[OC(NH2)2]3+ cation in aqueous acid reacts with chlorine and hypochlorous acid, with two sequential steps observed in each case. Rate constants for both steps show a first-order dependence on [oxidant], with k1/k2 always <20, but varying with the choice of reactant and acid. Rate constants with Cl2 as reactant are faster than with HOCl, possibly related to preferential attack by Cl+ compared with OCl– on the bound urea. Competition by ions (HSO
4
–
, Cl– or NO
3
–
) measured by product analysis of reactions conducted in 1 M acid produced competition ratios R (R=[CoX]/[CoOH2][X]) which are similar to values determined with a range of leaving groups previously, indicating a mechanistic constancy. No formation of Co(NH3)5Cl2+ was observed in reactions conducted in H2SO4 or HNO3, implying that free Cl– is not generated at the reaction site and captured by the metal ion. Electronic and vibrational spectra of the intermediate formed in the two stage reaction is indicative of a change from an O-bound to an N-bound ligand in forming that intermediate, although it cannot be a simple isomerization due to the dependence on [oxidant]. A possible mechanism is discussed. 相似文献
100.
Bingham RJ Findlay JB Hsieh SY Kalverda AP Kjellberg A Perazzolo C Phillips SE Seshadri K Trinh CH Turnbull WB Bodenhausen G Homans SW 《Journal of the American Chemical Society》2004,126(6):1675-1681
In the present study we examine the thermodynamics of binding of two related pyrazine-derived ligands to the major urinary protein, MUP-I, using a combination of isothermal titration calorimetry (ITC), X-ray crystallography, and NMR backbone (15)N and methyl side-chain (2)H relaxation measurements. Global thermodynamics data derived from ITC indicate that binding is driven by favorable enthalpic contributions, rather than the classical entropy-driven hydrophobic effect. Unfavorable entropic contributions from the protein backbone and side-chain residues in the vicinity of the binding pocket are partially offset by favorable entropic contributions at adjacent positions, suggesting a "conformational relay" mechanism whereby increased rigidity of residues on ligand binding are accompanied by increased conformational freedom of side chains in adjacent positions. The principal driving force governing ligand affinity and specificity can be attributed to solvent-driven enthalpic effects from desolvation of the protein binding pocket. 相似文献