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B. Schmid B. Dorner D. Visser M. Steiner 《Zeitschrift für Physik B Condensed Matter》1992,86(2):257-262
The magnetic excitations in CsFeBr3 have been measured with inelastic scattering of cold neutrons to high precision at 80 mK. The fact that the lowest frequency mode softens with decreasing temperature but stabilizes at 0.11 THz below 2.5 K is the indication that CsFeBr3 remains a SGS system forT0.From dispersion curves measured earlier in a magnetic field along the chain axis experimental intensities were derived and in turn correlation lengths. Correlation lengths were also calculated using the new parameters for exchange and anisotropy. The experimental results and the calculations both show that the correlation lengths increase for increasing magnetic field, flatten off around the phase transformation at 4.1 Tesla with a maximum of about 35 Å and then decrease again for higher fields. No critical phenomena connected with this phase transformation could be detected.The Mirror Mode published earlier was found to be of spurious origin due to double scattering. It does not exist. 相似文献
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Syntheses and Structures of Trilithium Cyclotriphosphazenates Equipped with 2‐Halo‐aryl Substituents
Hexakis (2‐halo‐anilino) cyclotriphosphazenes (2‐X‐C6H4NH)6P3N3 {X = F ( 1d ), Cl ( 1e ), Br ( 1f )} were prepared by refluxing mixtures of hexachloro cyclotriphosphazene, 2‐haloaniline and triethylamine in toluene and characterized by single crystal X‐ray diffraction. 1d , 1e and 1f were reacted with nBuLi in thf. Reactions were monitored with 31P NMR. Addition of three equivalents of nBuLi yields lithium complexes of trianionic phosphazenates [{(thf)2Li}3{(2‐X‐C6H4N)3(2‐X‐C6H4NH)3P3N3}] {X= F ( 2d ), Cl ( 2e ) and Br ( 2f )}. 2d , 2e and 2f were structurally characterized by X‐ray diffraction, which reveals monomeric cis‐metalated phosphazenates featuring central P3N3 ring systems of chair conformation. Lithium ions reside in three N(eq)‐P‐N(endo) chelation sites at one face of the P3N3 ring system. Li…X distances are rather long (> 3Å) indicating no Li‐X interactions. 相似文献
56.
The Crystal Structure of Nitrogen Triiodide-1-Pyridine NI3 · C5H5N The crystal structure of NI3 · C5H5N like “Nitrogen Triiodide” NI3 · NH3 contains NI4 tetrahedra as essential structure elements. The tetrahedra are connected by common corners, forming indefinite chains. The pyridine molecule is bonded by its lone electron pair to one of the two iodine atoms that do not participate in the connection of the tetrahedra. Different from NI3 · NH3 there are very weak intermolecular interactions between iodine atoms of neighbouring chains. 相似文献
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Tsirelson Vladimir Abramov Yury Zavodnik Valery Stash Adam Belokoneva Elena Stahn Jochen Pietsch Ullrich Feil Dirk 《Structural chemistry》1998,9(4):249-254
The critical points in the model electron density distributions of LiF, NaF, NaCl, and MgO crystals, constructed from accurate X-ray diffraction data, are determined. For LiF and MgO they are compared with those obtained from a Hartree–Fock electron density calculation. Both experiment and theory show the same type of critical points on the bond lines. The topological features in areas between structural units, where the electron density is low and near-uniform, turn out to be model dependent and cannot be established well with the data available. Topological analysis of procrystals (hypothetical systems consisting of spherical atoms or ions placed on the same sites as atoms in real crystal) show that (3, –1) critical points, usually connected with bonding interaction, are observed on interatomic lines in these nonbonded systems as well. 相似文献
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Samoylova E Lippert H Ullrich S Hertel IV Radloff W Schultz T 《Journal of the American Chemical Society》2005,127(6):1782-1786
The excited-state dynamics of adenine and thymine dimers and the adenine-thymine base pair were investigated by femtosecond pump-probe ionization spectroscopy with excitation wavelengths of 250-272 nm. The base pairs showed a characteristic ultrafast decay of the initially excited pi pi* state to an n pi* state (lifetime tau(pi pi*) approximately 100 fs) followed by a slower decay of the latter with tau(n pi*) approximately 0.9 ps for (adenine)2, tau(n pi*) = 6-9 ps for (thymine)2, and tau(n pi*) approximately 2.4 ps for the adenine-thymine base pair. In the adenine dimer, a competing decay of the pi pi* state via the pi sigma* state greatly suppressed the n pi* state signals. Similarities of the excited-state decay parameters in the isolated bases and the base pairs suggest an intramonomer relaxation mechanism in the base pairs. 相似文献
59.
R. Grau S. W. Moissejew A. P. Georgijewski A. M. Michailowa A. Miermeister G. Buogo Maria Maitilasso C. Wilhelm G. Steiner F. Th. van Voorst J. Peltzer J. H. Glynn G. L. Taylor G. S. Adair Muriel E. Adair G. Kieselbach H. Diller und R. Stäsche 《Fresenius' Journal of Analytical Chemistry》1943,125(7-8):306-309
Ohne Zusammenfassung 相似文献
60.
The landscape of synchrotron radiation facilities in Europe is diverse. In addition to the flagship ESRF, several national facilities exist or came into operation recently. In contrast to ESRF, which is financed for use by member countries, access of foreign users to national facilities is not easy. Even if their proposals pass the review process, they can only perform the experiments if funding is allocated to cover not only travel expenses, board and lodging of the experimenters, but also some compensation for the facility's operational costs; this is because national facilities are primarily funded for the home-country's users at that nation's costs. 相似文献