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121.
We classify spacelike hypersurfaces of the de Sitter space with constant scalar curvature and with two principal curvatures. Moreover, we prove that if Mn is a complete spacelike hypersurface with constant scalar curvature n(n−1)R and with two distinct principal curvatures such that the multiplicity of one of the principal curvatures is n−1, then R<(n−2)c/n. Additionally, we prove several rigidity theorems for such hypersurfaces. 相似文献
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Quantum Monte Carlo methods are used to investigate the binding of a positron to the alkali-metal hydrides, XH (X = Na and K). We obtain positron affinities for the NaH and KH molecules of 1.422(10) eV and 2.051(39) eV, respectively. These are considerably larger than the previous results of 1.035 eV and 1.273 eV obtained from multireference single- and double-excitation configuration interaction calculations. Together with our previous results for [LiH;e(+)] [Y. Kita et al., J. Chem. Phys. 131, 134310 (2009)], our study confirms the strong correlation between the positron affinity and dipole moment of alkali-metal hydrides. 相似文献
126.
Re(I) carbonyl-diimine complexes [Re(L-AA)(CO)(3)(N,N)](+) (N,N = bpy, phen) containing an aromatic amino acid (AA), phenylalanine (Phe), tyrosine (Tyr), or tryptophan (Trp), linked to Re by a pyridine-amido or imidazole-amido ligand L have been synthesized and their excited-state properties investigated by nanosecond time-resolved IR (TRIR) and emission spectroscopy. Near-UV optical excitation populates a Re(I)(CO)(3)→N,N (3)MLCT excited state *[Re(II)(L-AA)(CO)(3)(N,N(?-))](+). Decay to the ground state (50-300 ns lifetime) is the only excited-state deactivation process observed in the case of Phe and Tyr complexes, whereas the Trp-containing species undergo a Trp(indole)→*Re(II) electron transfer (ET) producing a charge-separated (CS) state, [Re(I)(L-Trp(?+))(CO)(3)(N,N(?-))](+). The ET occurs with a 8-40 ns lifetime depending on L, N,N, and the solvent. The CS state is characterized by ν(CO) IR bands shifted to lower wavenumbers from their respective ground-state positions and two bands at 1278 and 1497 cm(-1) tentatively attributed to Trp(?+). The amido bridge is affected by both the MLCT excitation and the subsequent ET, manifested by the shifts and intensity changes of the amide-I IR band at about 1680 cm(-1). The CS state decays to the ground state by a N,N(?-)→Trp(?+) back-ET the rates of which are comparable to those of the forward ET, 30-60 ns. This study independently demonstrates that Trp can act as an electron-hopping intermediate in photodriven ET systems based on Re-labeled proteins and supramolecules. Photoinduced ET in Trp-containing Re complexes also can be used to generate Trp(?+) and investigate its spectral properties and reactivity. 相似文献
127.
Maria Brzhezinskaya Alexander Firsov Karsten Holldack Torsten Kachel Rolf Mitzner Niko Pontius Jan‐Simon Schmidt Mike Sperling Christian Stamm Alexander Föhlisch Alexei Erko 《Journal of synchrotron radiation》2013,20(4):522-530
Aiming at advancing storage‐ring‐based ultrafast X‐ray science, over the past few years many upgrades have been undertaken to continue improving beamline performance and photon flux at the Femtoslicing facility at BESSY II. In this article the particular design upgrade of one of the key optical components, the zone‐plate monochromator (ZPM) beamline, is reported. The beamline is devoted to optical pump/soft X‐ray probe applications with 100 fs (FWHM) X‐ray pulses in the soft X‐ray range at variable polarization. A novel approach consisting of an array of nine off‐axis reflection zone plates is used for a gapless coverage of the spectral range between 410 and 1333 eV at a designed resolution of E/ΔE = 500 and a pulse elongation of only 30 fs. With the upgrade of the ZPM the following was achieved: a smaller focus, an improved spectral resolution and bandwidth as well as excellent long‐term stability. The beamline will enable a new class of ultrafast applications with variable optical excitation wavelength and variable polarization. 相似文献
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Mike A. Miller 《Colloid and polymer science》1937,80(3):327-333
Zusammenfassung Aus einer Reihe von Untersuchungen über Bildung, Niederschlagung, scheinbaren Bewegung und Austausch von kristallinem Jod
und unl?slichen kristallinen Jodiden in verschiedenen Gelen und anderen Mitteln wurde gefolgert, da? die Prozesse der Niederschlagung
des Reaktionsproduktes und der Diffusion dieses Produktes nicht voneinander getrennt werden k?nnen. Es wurde darauf hingewiesen,
da? die offensichtliche Wanderung von kristallinem Jod und unl?slichen kristallinen Jodiden in Gelstrukturen sich als eine
Folge der Wiederaufl?sung in einem Teil der Kristallmasse und der Wiederablagerung an einem andern Teile zu ergeben scheint.
Untersuchungen über den Austausch von kristallinem Jod durch unl?sliche Jodide und umgekehrt haben gezeigt, da? unter gewissen
passenden Diffusionsbedingungen, wie z. B. im Kiesels?uregel, sich pseudomorphe Kristalle bilden k?nnen. Pseudomorphe Kristalle
wurden in kapillaren R?umen zwischen Glasplatten nicht erhalten, obzwar sich eine ausgesprochene Neigung hierzu zeigte.
Material wurde dargelegt, um zu zeigen, da? sich verschiedene Arten von Jodablagerungen als eine Folge der Wirkung des Mittels
ergeben k?nnen. Diese Ablagerungen k?nnen sich von kolloiden bis zu makroskopischen Dimensionen und von sehr verzerrten bis
zu fast vollkommenen kristallinen Formen erstrecken. Unter gewissen Bedingungen scheinen sich Somatoide zu bilden. Umgebungen,
in denen diese Reaktionen ausgeführt wurden, waren a) verschiedene Gele, b) Schichten zwischen Glasplatten, c) Poren absorbierenden
Papiers und d) Membranoberfl?chen. 相似文献
130.
The bromination of 2,1,3-benzothiadiazoles in 47% hydrobromic acid at elevated temperature has led to a general preparative method for the synthesis in high yield of otherwise difficulty accessible brominated 2,1,3-benzothiadiazoles. The typical addition reaction is apparently eliminated under these reaction conditions and substitution takes place exclusively. Bromination of 2,1,3-benzothiadiazole occurs successively at positions 4 and 7. 4-Substituted 2,1,3-benzothia-diazoles are selectively brominated at position 7. 5-Bromo- and 5-methyl-2,1,3-benzothiadiazole are brominated consecutively at positions 4 and 7. 相似文献