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61.
Michelini Mdel C Russo N Alikhani ME Silvi B 《Journal of computational chemistry》2004,25(13):1647-1655
The Density functional theory has been applied to characterize the structural features of Mo(1,2)-NH(3),-C(2)H(4), and -C(2)H(2) compounds. Coordination modes, geometrical structures, and binding energies have been calculated for several spin multiplets. It has been shown that in contrast to the conserved spin cases (Mo(1,2)-NH(3)), the interaction between Mo (or Mo(2)) and C(2)H(4) (or C(2)H(2)) are the low-spin (Mo-C(2)H(4) and -C(2)H(2)) and high-spin (Mo(2)-C(2)H(4) and -C(2)H(2)) complexes. In the ground state of Mo(1,2)-C(2)H(4) and -C(2)H(2), the metal-center always reacts with the C-C center. The spontaneous formation of the global minima is found to be possible due to the crossing between the potential energy surfaces (ground and excited states with respect to the metallic center). The bonding characterization has been performed using the topological analysis of the Electron Localization Function. It has been shown that the most stable electronic structure for a pi-acceptor ligand correlates with a maximum charge transfer from the metal center to the C-C bond of the unsaturated hydrocarbons, resulting in the formation of two new basins located on the carbon atoms (away from hydrogen atoms) and the reduction of the number of attractors of the C-C basin. The interaction between Mo(1,2) and C(2)H(4) (or C(2)H(2)) should be considered as a chemical reaction, which causes the multiplicity change. Contrarily, there is no charge transfer between Mo(1,2) and NH(3), and the partners are bound by an electrostatic interaction. 相似文献
62.
Fasih A. Siddiqi N. Lakshminarayanaiah Mohammad N. Beg 《Journal of polymer science. Part A, Polymer chemistry》1971,9(10):2853-2867
The permeability of various electrolytes through parchment-supported ferrocyanide membranes of manganese, cobalt, silver, and cadmium has been measured at 10, 15, 20, 25, and 30°C. The order of permeability at a given temperature was Cl- > NO3- > CNS- > CH3COO- > SO42- for both monovalent and divalent cations. For any given anion, the cations followed the sequence NH4+ > Li+ > Ba2+ > Ca2+ > Mg2+ > Al3+. This sequence has been correlated with the size of the hydrated ion. Further, the data have been considered from the standpoint of the theory of rate processes and the values for the entropy of activation (ΔS′) have been derived assuming an equilibrium distance of 3 Å in the membrane. The values of ΔS′ were all negative and decreased with increasing valence of the ions. This was interpreted to mean electrolyte permeation with partial immobilization in the membrane. 相似文献
63.
Mohammad R.?SaidiEmail author Mohammad?Nazari 《Monatshefte für Chemie / Chemical Monthly》2004,135(3):309-312
Summary. The solid LiClO4-mediated one-pot reaction of aldehydes with secondary amines and C nucleophiles afforded the corresponding aminoalkylation products in high yields. Unlike the previous reported procedure, the aminoalkylation of aldehyde was achieved in the presence of only 0.5 equivalents of solid lithium perchlorate in dichloromethane as the solvent with good to high yields at room temperature. 相似文献
64.
Irradiation of the red-light absorbing dye, methylene blue (MB), in the presence of the metal complex, cis-Rh(phen)2Cl2+ (BISPHEN), leads to irreversible photobinding of both reagents to DNA. Evidence from absorption and emission spectroscopy indicates that the dye is strongly complexed to the DNA at the concentrations used in the experiments and that this complex is unaffected by the presence of BISPHEN. The level of covalent binding is proportional to the absorbed light dose, with the quantum efficiency for covalent binding of BISPHEN to the DNA with 633 nm light equal to 3.5 x 10(-4). Electrospray ionization mass spectrum of a mixture of DNA fragments created by enzymatic degradation of DNA isolated following irradiation indicates that purine adducts are formed with both BISPHEN and the dye. In addition, UV-Vis and high-performance liquid chromatography analyses of the irradiated MB/BISPHEN/DNA mixture and isolated adducts show extensive conversion of the dye and metal complex to the corresponding N-demethylated and aquated derivatives, respectively. Triplet quenchers for MB, for example oxygen and benzoquinone, inhibit both the photoconjugation and the photochemistry of BISPHEN. A mechanism for the synergistic interaction is proposed that involves photoconjugation of both partners to the DNA following oxidation and reduction via electron transfer between 1MB*/DNA and 3MB*/BISPHEN. 相似文献
65.
66.
Ehsan A. H. Gomaa H. Schut A. Van Veen M. Mohsen U. Fromm P. Morshuis 《Journal of Radioanalytical and Nuclear Chemistry》1996,211(1):77-83
Using the positron annihilation lifetime technique, the annihilation parameters have been measured for epoxy and high density polyethylene (HDPE) as a function of AC electric field strength and the exposure time. The lifetime spectra have been resolved into three components, the longest component (I33) is attributed to the pick-off annihilation of o-Ps in the amorphous regions. The intermediate one (I22) is due to the annihilation of free positrons, while the shorter component (I11) stems from self annihilation of p-Ps. In HDPE, the o-Ps parameters 3 andI
3 are measured as a function of electric field strengths in the range from 10 to 100 kV/cm exposed for 24 hours. A decrease inI
3 of 8% is observed from zero to 50 kV/cm followed by an increase of the same order from 50 to 100 kV/cm. By investigating the effect of the exposure time from 2 to 24 hours at 16 and 50 kV/cm, the effect is confirmed and is attributed to the inhibition of o-Ps formation at lower field strength. In epoxy, the effect or exposure time onI
3 at 166 and 133 kV/cm shows a similar behavior as in HDPE. At 133 kV/cmI
3 decreases by only 2.5%. On the other hand, the changes in 3 occur at short exposure times. Again at large times the saturation is obtained. These effects are attributed to the expansion of free volume (increase of 3) competing at longer exposure times with other phenomena, such as liberation of free radicals, which reduce the o-Ps intensityI
3 through the conversion to p-Ps. The reactions between o-Ps and free radicals might also lead to free positrons, which could explain the increase ofI
2 and the decrease of 3 at longer exposure times. 相似文献
67.
Mohammad Ali Zolfigol Iraj Mohammadpoor-BaltorkDavood Habibi BiBi Fatemeh MirjaliliAbdolhamid Bamoniri 《Tetrahedron letters》2003,44(44):8165-8167
Primary and secondary trimethylsilyl ethers were converted to their corresponding ethers in the presence Nafion-H® with good to excellent yields under mild and heterogeneous conditions. 相似文献
68.
Liquid-liquid equilibrium data for mixtures of (ethylene carbonate + benzene + cyclohexane) at temperatures 303.15 and 313.15 K and (ethylene carbonate + BTX + cyclohexane) at temperature 313.15 K are reported, where the BTX is benzene, toluene and m-xylene. The compositions of liquid phases at equilibrium were determined by gas liquid chromatography. The selectivity factors and partition coefficients of ethylene carbonate for the extraction of benzene, toluene and m-xylene from (ethylene carbonate + BTX + cyclohexane) are calculated and presented. The obtained results are compared with the selectivity factors and partition coefficients of ethylene carbonate for the extraction of benzene from (ethylene carbonate + benzene + cyclohexane). The liquid-liquid equilibrium data were correlated with the UNIQUAC and NRTL activity coefficient models. The phase diagrams for the studied mixtures are presented and the correlated tie line results have been compared with the experimental data. The comparisons indicate the applicability of the UNIQUAC and NRTL activity coefficients model for liquid-liquid equilibrium calculations of the studied mixtures. The tie line data of the studied mixtures also were correlated using the Hand method. 相似文献
69.
Saira Shahzadi Moazzam H. Bhatti Khadija Shahid Saqib Ali Saadia R. Tariq Mohammad Mazhar Khalid M. Khan 《Monatshefte für Chemie / Chemical Monthly》2002,133(8):1089-1096
Summary. Tributyltin(IV) derivatives of six different pharmaceutically active carboxylates were synthesized. The complexes were characterized
by different analytical techniques (elemental analysis; infrared, NMR, and mass spectroscopy). 119Sn NMR data were also recorded in six different coordinating and non-coordinating solvents. The antibacterial activities of
the compounds were tested using ten different bacteria relative to the reference drugs ampicillin and cephalexin.
Received September 20, 2001. Accepted (revised) December 6, 2001 相似文献
70.
Low molecular weight organogels based on long-chain carbamates 总被引:2,自引:0,他引:2
Moniruzzaman M Sundararajan PR 《Langmuir : the ACS journal of surfaces and colloids》2005,21(9):3802-3807
Thermoreversible organogels were prepared from carbamates with alkyl side chains of different lengths. Gelation was possible only up to an alkyl side chain length of 12 carbons, beyond which crystallization occurs, due to the dominant van der Waals interaction between the alkyl chains. This is in contrast to other alkane-based organogels, in which gelating efficiency increased with the length of the alkane chain (see Abdallah, D. J.; Weiss, R. G. Adv. Mater. 2000, 12, 1237). The critical concentration for gelation decreases drastically with an increase in the side chain length. Xerogels of these show birefringent fibers with uniform cross section and unlimited growth in one direction. The extent of this unlimited growth is affected by the length of the alkyl side chain in the carbamate, which finally ceases the gel formation ability of the carbamate. Cryogenic scanning electron microscopy images of the gels are similar to those of xerogels. From X-ray diffraction of the fibers, we propose that the growth direction is along the plane of hydrogen bonds between the carbamate molecules. The thickness of the fibers depends on the length of the alkyl side chain. Morphological differences are seen between gels prepared by slow cooling and quenching of the solution. Thus, the morphology of the fibrous xerogels of the carbamates can be tailored for specific applications, by the choice of the alkyl side chain length and the rate of cooling the solution. 相似文献