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991.
Round C. I. Williams C. D. Latham K. Duke C. V. A. 《Journal of Thermal Analysis and Calorimetry》2000,63(2):329-338
The synthesis of pure silica ZSM-5 has been modified to produce highly crystalline material in the protonated form, necessary
for catalytic activity, directly from a low water fluoride gel. Tetrahedrally co-ordinated divalent species of nickel and
copper have been synthesised as salts of large organic cations and increasing mole fractions incorporated into the zeolite
gels. The products have been analysed and characterised using simultaneous thermogravimetric and derivative thermogravimetric
analysis (TG-DTG). The thermal decomposition under nitrogen of the metal associated cations, tetraethylammonium (TEA+), occluded within the zeolite channels is indicative and characteristic of the incorporation of heteroatoms into the zeolite
framework. Anomalous losses in the systems can be explained by Jahn–Teller distortions. The mass losses increased with increased
metal loading and were consistent with those reported in full water system, analysis also confirmed that the material was
hydrophobic and thermally stable.
Analysis by X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray fluorescence (XRF), Fourier transform infrared
spectroscopy (FTIR) and Atomic Absorption Spectroscopy (AAS) has confirmed the reliability of TG-DTG as a diagnostic tool.
The maximum levels of substitution achieved were (mass%) Ni 3.93 and Cu 4.38.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
992.
Ashwani Vij Jennifer L. Palmer Kamlesh Chauhan Richard Vaughan Williams 《Journal of chemical crystallography》2000,30(10):621-626
2,6-Dimethyl-1,3,5,7-cyclooctatetraene-1,3,5,7-tetracarboxylic acid 3, C14H14O9, was prepared by thermolysis of the corresponding semibullvalene and characterized by spectroscopic and single-crystal X-ray diffraction studies. The monohydrate of 3 crystallizes in the tetrahedral space group P-4n2, a = 11.0924(3) Å, c = 12.6799(5) Å, V = 1560.15(9) Å3, Z = 4. The cyclooctatetraene ring adopts a tub-shaped conformation with a crystallograpically imposed twofold rotational symmetry, and is composed of localized C=C double bonds in the 1,3,5, and 7 positions with an average interatomic distance of 1.327 (5) Å and C–C single bonds with an average interatomic distance of 1.489(5) Å. The average C=C–C angle in the ring is 122.6(3)°. Each symmetry generated eight-membered ring contains four carboxyl groups, two of which are coplanar with the methyl groups across the C=C ring atoms. However, across the C–C bonds the carboxyl groups and the methyl groups show a torsion angle of 64.3(4)°. The presence of a water molecule in the crystal lattice generates a three-dimensional network of close hydrogen bondings between water and the carboxyl groups of multiple rings. This creates a network of orthogonal 10-membered rings between the 8-membered rings. Two given cyclooctatetraene rings are intermolecularly hydrogen bonded not only directly through their carboxyl groups but also via a bridging water molecule. This effect is rare in polycarboxylic acids and their monohydrates which bond only with water or among themselves. 相似文献
993.
994.
Ning‐Hai Hu Katsuyuki Aoki Adegboye O. Adeyemo George N. Williams 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(9):1064-1066
In the title compound, 3‐[(4‐amino‐2‐methyl‐5‐pyrimidin‐1‐io)methyl]‐5‐(2‐hydroxyethyl)‐4‐methylthiazolium(2+) bis(tetrafluoroborate), C12H18N4OS2+·2BF4?, the divalent thiamine cation (in the F conformation) is associated with BF4? anions via two characteristic bridging interactions between the thiazolium and pyrimidinium rings, i.e. C—H?BF4??pyrimidinium and N—H?BF4??thiazolium interactions. Thiamine molecules are linked by N—H?O hydrogen bonds to form a helical chain structure. 相似文献
995.
996.
Variable temperature (300-40 K) 4-probe d.c. conduction studies on Cs2[Pt(CN)4](FHF)0.39 and Rb2[Pt(CN)4](FHF)0.40 are described. In these salts T3D occurs at a lower temperature than in K2[Pt(CN)4]Br0.3·3H2O and this is attributed to the absence of an inter-chain network of hydrogen bonded water molecules in the bifluorides. 相似文献
997.
Bintinger D Kees KH Masek GE Miller ES Thompson JR Vernon W White JT Eisner AM Palmer DA Sullivan MK Armitage JC Buijs A Van Driel MA Erné FC Langeveld WG Paar HP Sens JC Timmer J Van Uitert B Cain MP Ko W Lander RL Maeshima K McNeil RR Pellett DE Smith JR Williams MC Caldwell DO Joshi UP Lu A Schwitkis KA Yellin SJ 《Physical review letters》1985,54(8):763-766
998.
N. H. Tea F. A. B. Chaves U. Klostermann R. Giannetta M. B. Salamon J. M. Williams H. H. Wang U. Geiser 《Physica C: Superconductivity and its Applications》1997,280(4):281-288
The magnetic field dependence of the in-plane penetration depth λ|(H) for single crystal κ-(ET)2Cu[N(CN)2]Br has been measured at 3, 9.6, and 36 MHz. Over a limited range, λ| scales with a characteristic field H*(T) that coincides with a shoulder in the λ| vs. H curves. Above that field, λ| increases sharply toward a second inflection point at H**(T) that coincides with is close to the irreversibility line measured by magnetization. For fields larger than H** the penetration depth diverges, suggesting that the vortex lattice has melted. The field dependence at one frequency agrees qualitatively with a model of pinned vortices at low fields giving way to flux flow at higher fields. However, the observed frequency dependence deviates significantly from the predictions of this model, suggesting that collective effects play a major role. Our technique also yields a new measurement for the interplane penetration depth λ 300 μm, implying an anisotropy λ/λ| > 200. 相似文献
999.
M. A. Hartl D. J. Williams A. I. Acatrinei A. Stowe Luke L. Daemen Dr. 《无机化学与普通化学杂志》2007,633(1):120-126
The crystal structure of one of the simplest organoboron compounds, trimethyl borate does not appear to have been determined hitherto. The compound is of interest for the study of π‐donor ligands and their interaction with the π‐acceptor behavior of trigonal boron and the consequences of such interactions on molecular structure. We used powder neutron (with isotopically labeled material) and X‐ray diffraction to determine the crystal structure of trimethyl borate at 15 K and 200 K (neutron) and 200 K (X‐ray). The material is hexagonal (Z = 2) with a = b = 6.950(8) Å and c = 6.501(3) Å at 15 K. The unit cell volume is 272.00(1) Å3. The space group is P63/m (SG 176) at 15 K and 200 K. This is the first crystal structure solved on the Neutron Powder Diffractometer (NPDF) at the Lujan Center. 相似文献
1000.
Bally T Bernhard S Matzinger S Roulin JL Sastry GN Truttmann L Zhu Z Marcinek A Adamus J Kaminski R Gebicki J Williams F Chen GF Fulscher MP 《Chemistry (Weinheim an der Bergstrasse, Germany)》2000,6(5):858-868
The syn dimer of cyclobutadiene (tricyclo[4.2.0.0(2.5)]octa-3,7-diene, TOD) is subjected to ionization under different conditions and the resulting species are probed by optical and ESR spectroscopy. By means of quantum chemical modelling of the potential energy surfaces and the optical spectra, it is possible to assign the different products that arise spontaneously after ionization or after subsequent warming or illumination of the samples. Based on these findings, we propose a mechanistic scheme which involves a partitioning of the incipient radical cation of TOD between two electronic states. These two states engage in (near) activation-less decay to the more stable valence isomers, cyclooctatetraene (COT*+) and a bis-cyclobutenylium radical cation BCB*+. The latter product undergoes further rearrangement, first to tetracyclo[4.2.0.0(2,4).0(3,5]oct-7-ene (TCO*+) and eventually to bicyclo[4.2.0]octa-2,4,7-triene (BOT*+) which can also be generated photochemically from BCB*+ or TCO*+. The surprising departure of syn-TOD*+ from the least-motion reaction path leading to BOT*+ can be traced to strong vibronic interactions (second-order Jahn-Teller effects) which prevail in both possible ground states of syn-TOD*+. Such effects seem to be more important in determining the intramolecular reactivity of radical cations than orbital or state symmetry rules. 相似文献