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991.
The luminescence associated with the Eu3+ ion in K2EuCl5 has been studied at cryogenic temperatures under conditions of high resolution. Emission was observed to originate from both the 5D0 and 5D1 excited states, and transitions to the , and 7F4 ground levels were observed. The fine structure observed within these emission bands was found to be consistent with the existence of an effective C4 site symmetry for the emitting Eu(III) species, even though the crystal structure does not indicate the presence of a true or pseudo C4 axis. 相似文献
992.
Edward F. Cassidy Han X. Xiao Kurt C. Frisch Harry L. Frisch 《Journal of polymer science. Part A, Polymer chemistry》1984,22(10):2667-2683
Three-component IPN systems made from polyurethanes, epoxies, and poly(methacrylates) containing charge groups in the backbones of the constituent networks have been prepared. Specific attractive forces that occurred among the various networks helped to compatibilize them and aided in the formation of true homogeneous topologically interpenetrating polymer networks. These three-component polymer alloys, including full-IPN's, pseudo-IPN's, and graft-IPN's, were characterized by means of mechanical spectroscopy, electron microscopy, and stress–strain properties. In addition, some adhesion studies were carried out (lap shear strength and peel strength). A comparison of the different types of three-component polymer alloys showed that better properties were generally exhibited by the graft-IPN's and full-IPN's containing opposite charge groups. 相似文献
993.
van Delden RA Huck NP Piet JJ Warman JM Meskers SC Dekkers HP Feringa BL 《Journal of the American Chemical Society》2003,125(50):15659-15665
The photochemical control of ground- and excited-state chirality of (M)-cis-(1) and (P)-trans-(2)-2-nitro-7-(dimethylamino)-9-(2',3'-dihydro-1'H-naphtho[2,1-b]-thiopyran-1'-ylidene)-9H-thioxanthene is described. It is shown that while ground state chirality can be controlled photochemically by irradiation with light of different wavelengths, the excited state chirality can be tuned either photochemically in a similar way or by appropriate choice of solvent. In benzene solution, circularly polarized luminescence of the two isomers with opposite ground-state helicity, (M)-cis-1 and (P)-trans-2, revealed corresponding excited states of opposite helicity. On the contrary, in n-hexane solution, circularly polarized luminescence was identical for the two forms indicating identical excited state chirality. Circularly polarized luminescence (CPL), steady-state and time-dependent fluorescence, and time-resolved microwave conductivity (TRMC) measurements in both n-hexane and benzene are reported, which provide an explanation for the remarkable solvent dependence of excited-state chirality. 相似文献
994.
A novel catalyst-free,eco-friendly,on water protocol for the synthesis of 2,3-dihydro-1H-perimidines
Nissy Ann Harry Reeba Mary Cherian S. Radhika Gopinathan Anilkumar 《Tetrahedron letters》2019,60(33):150946
The first greenest methodology for the synthesis of 2,3-dihydro-1H-perimidines on water is described. 1,8-Diamino naphthalene was reacted with different types of aldehydes at room temperature to furnish the product in moderate to excellent yields in 30 min. A multi-gram scale reaction is also performed to ensure the scalability of the reaction. 相似文献
995.
Cell encapsulation within alginate beads has potential as a sustained release system for delivering therapeutic agents in vivo while protecting encapsulated cells from the immune system. There is, however, no in vitro model for cell-encapsulation therapy that provides a suitable platform for quantitative assessment of physiological responses to secreted factors. Here we introduce a new microfluidic system specifically designed to evaluate and quantify the pro-angiogenic potential of factors secreted from human fetal lung fibroblasts encapsulated in beads on an intact endothelial cell monolayer. We confirmed that cell-encapsulating beads induced an angiogenic response in vitro, demonstrated by a strong correlation between the encapsulated cell density in the beads and the length of the vascular lumen formed in vitro. Conditions established by in vitro tests were then further shown to exert a pro-angiogenic response in vivo using a subcutaneous mouse model, forming an extensive network of functional luminal structures perfused with red blood cells. 相似文献
996.
RJ Davidson EW Ainscough AM Brodie GB Jameson MR Waterland HR Allcock MD Hindenlang B Moubaraki KS Murray KC Gordon R Horvath GN Jameson 《Inorganic chemistry》2012,51(15):8307-8316
Two new cyclotriphosphazene ligands with pendant 2,2':6',2″-terpyridine (Terpy) moieties, namely, (pentaphenoxy){4-[2,6-bis(2-pyridyl)]pyridoxy}cyclotriphosphazene (L(1)), (pentaphenoxy){4-[2,6-terpyridin-4-yl]phenoxy}cyclotriphosphazene (L(2)), and their respective polymeric analogues, L(1P) and L(2P), were synthesized. These ligands were used to form iron(II) complexes with an Fe(II)Terpy(2) core. Variable-temperature resonance Raman, UV-visible, and M?ssbauer spectroscopies with magnetic measurements aided by density functional theory calculations were used to understand the physical characteristics of the complexes. By a comparison of measurements, the polymers were shown to behave in the same way as the cyclotriphosphazene analogues. The results showed that spin crossover (SCO) can be induced to start at high temperatures by extending the spacer length of the ligand to that in L(2) and L(2P); this combination provides a route to forming a malleable SCO material. 相似文献
997.
Corinne Boudon Jean-Paul Gisselbrecht Maurice Gross Lyle Isaacs Harry L. Anderson Rüdiger Faust Franois Diederich 《Helvetica chimica acta》1995,78(5):1334-1344
The first systematic electrochemical study by cyclic voltammetry (CV) and rotating-disk electrode (RDE) of the changes in redox properties of covalent fullerene derivatives ( 2 – 11 ) as a function of increasing number of addends is reported. Dialkynylmethanofullerenes 2 – 4 undergo multiple, fullerene-centered reduction steps at slightly more negative potentials than C60 ( 1 ; see Table and Fig. 1). The two C-spheres in the dumbbell-shaped dimeric fullerene derivative 4 show independent, identical redox characteristics. This highlights the insulating character of the sp3-C-atoms in methanofullerenes which prevent through-bond communication of substituent effects from the methano bridge to the fullerene sphere. In the series of mono- through hexakis-adducts 5 – 11 , formed by tether-directed remote functionalization, reductions become increasingly difficult and more irreversible with increasing number of addends (see Table and Fig. 2). Whereas, in 0.1M Bu4NPF6/CH2Cl2, the first reduction of mono-adduct 5 occurs reversibly at ?1.06 V vs. the ferrocene/ferricinium couple (Fc/Fc+), hexakis-adduct 11 is reduced irreversibly only at ? 1.87 V. Hence, with incremental functionalization of the fullerene, the LUMO of the remaining conjugated framework is raised in energy. Reduction potentials are also dependent on the relative spatial disposition of the addends on the surface of the fullerene sphere. Observed UV/VIS spectral changes and changes in the chemical reactivity along the series 5 – 11 are in accord with the results of electrochemical measurements. Further, with increasing number of addends, the oxidation of derivatives 5 – 11 becomes more reversible. Whereas oxidations are increasingly facilitated upon going from mono-adduct 5 (+1.22 V) to tris-adduct 7 (+0.90 V), they occur at nearly the same potential (+0.95 to +0.99 V) in the higher adducts 8 – 11 . This indicates that the oxidations occur in these compounds at a common sub-structural element, for which a ‘cubic’ cyclophane is proposed (see Fig. 3). This sub-structure is fully developed in hexakis-adduct 11 . 相似文献
998.
α-Functionalized 2-Methyl Phenylphosphines, 2-(HE? CH2)? C6H4? PH2 (E = O, NR, PH) II. Coordination Behaviour with Metal Carbonyles of Cr, Mo, W The preparation of different carbonyl substituted coordination compounds (M: Cr, Mo, W) of the phosphines 2-(HE? CH2)C6H4? PH2 (E = O, NPh, PH) is described. In one case, after deprotonation of a PH2 group a phosphine/phosphide migration of a W(CO)5 fragment is detected. 相似文献
999.
A parallel direct self-consistent field (SCF) algorithm for distributed memory computers is described. Key features of the algorithm are its ability to achieve a load balance dynamically, its modest memory requirements per processor, and its ability to utilize the full eightfold index permutation symmetry of the two-electron integrals despite the fact that entire copies of the Fock and density matrices are not present in each processor's local memory. The algorithm is scalable and, accordingly, has the potential to function efficiently on hundreds of processors. With the algorithm described here, a calculation employing several thousand basis functions can be carried out on a distributed memory machine with 100 or more processors each with just 4 MBytes of RAM and no disk. The Fock matrix build portion of the algorithm has been implemented on a 16-node Intel iPSC/2. Results from benchmark calculations are encouraging. The algorithm shows excellent load balance when run on 4, 8, or 16 processors and displays almost ideal speed-up in going from 4 to 16 processors. Preliminary benchmark calculations have also been carried out on an Intel Paragon. © 1995 by John Wiley & Sons, Inc. 相似文献
1000.
H. van Gemerden C. Davids Harry H. Tolkamp Wayland R. Swain Jaap Dorgelo 《Journal of Radioanalytical and Nuclear Chemistry》1995,195(2):371-371
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