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51.
We introduce a generalization of the notion of a Koszul algebra, which includes graded algebras with relations in different
degrees, and we establish some of the basic properties of these algebras. This class is closed under twists, twisted tensor
products, regular central extensions and Ore extensions. We explore the monomial algebras in this class and we include some
well-known examples of algebras that fall into this class. 相似文献
52.
Lu Zhang J. Z. Liu I. C. Chang R. N. Shelton 《Physica C: Superconductivity and its Applications》1996,260(3-4):283-289
Temperature-dependent magnetic relaxation was studied in a La2CuO4+δ crystal in the low-temperature range 2–10 K. The experimental data exhibited a non-vanishing magnetic relaxation in the low-temperature limit. These data could be well interpreted by a quantum-creep theory, suggesting the non-vanishing relaxation at low temperatures due to quantum tunneling of vortices. The effective Euclidean action determined as /|d ln M/d ln t| showed a quadratic temperature dependence. The quantitative analysis of the effective Euclidean action yields a classical activation energy, crossover temperature and zero-temperature quantum-tunneling rate. 相似文献
53.
The pressure dependence of the superconducting transition temperature, Tc, is determined for eight metallic glasses in the series (Nb1?xTax)55T45, where T Rh, Ir. From these data we estimate the Grüneisen parameter, γG, and the volume dependence of the electron-phonon coupling constant, λ. Pressure is observed to affect Tc through both γG and λ. 相似文献
54.
The thermal decomposition of biguanide, the biguanidinium chlorides, sulphates and carbonate have been studied. Biguanide decomposes in definite steps, producing an almost quantitative yield of ammonia leaving initially a solid residue, melamine, which then sublimes unchanged at higher temperatures. The biguanidinium chlorides and sulphates are thermally more stable than the parent base and do not decompose in well-defined steps, whereas the carbonate is thermally less stable than the parent base but does decompose in definite steps. In addition, the fragmentation of biguanide and biguanidinium carbonate in a mass spectrometer is reported. 相似文献
55.
Vibratory measurements of the structures of the ear are key to understanding much of the pathology in mouse models of hearing loss. Unfortunately the high-speed sampling required to interrogate the high end of the mouse hearing spectrum is beyond the reach of most optical coherence tomography (OCT) systems. To address this issue, we have developed an algorithm that enables phase-sensitive OCT measurements over the full range of the mouse hearing spectrum (4-90 kHz). The algorithm phase-locks the line-trigger to the acoustic stimulation and then uses interleaved sampling to reconstruct the signal with higher temporal sampling. The algorithm was evaluated by measuring the vibratory response of mouse tympanic membrane to a pure tone stimulus. 相似文献
56.
Treating chloromethylated polystyrene beads with anthranilic acid and then palladium chloride gives a material capable of catalyzing the cis-hydrogenation of alkynes. Hydrogenation of phenylacetylene (10mmol) with 0.017 g-atom (based on Pd) of catalyst at room temperature and 30 psig for 7.3 h resulted in 82 % styrene and 14% ethylbenzene. Methylphenylacetylene was converted to cis-1-phenylpropene (60%) and n-propylbenzene (17 %). Several other alkynes were also converted to cis alkenes. The catalyst is less selective than the Lindlar catalyst, but is air stable and stores well. 相似文献
57.
Separation of peptides by high-pressure liquid chromatography for the identification of a hemoglobin variant 总被引:1,自引:0,他引:1
High-pressure liquid chromatography on a reversed-phase column has been used to separate the tryptic peptides of a human hemoglobin variant which was then identified as hemoglobin E. 相似文献
58.
Fred Ames Shelton 《The Journal of the Operational Research Society》1987,38(3):269-275
Acceptance of the adaptive-filtering parameter-estimation process has been mixed. Much of the variability between studies may result from the particular learning factor selected and may be further affected by the type of standardization used. The author presents a modification of the Makridakis and Wheelwright adaptive-filtering algorithm. This modified algorithm provides superior performance and simplifies the selection of the learning factor when used with simple autoregressive processes. 相似文献
59.
Sazanovich IV Alamiry MA Best J Bennett RD Bouganov OV Davies ES Grivin VP Meijer AJ Plyusnin VF Ronayne KL Shelton AH Tikhomirov SA Towrie M Weinstein JA 《Inorganic chemistry》2008,47(22):10432-10445
A combination of picosecond time-resolved infrared spectroscopy, picosecond transient absorption spectroscopy, and nanosecond flash photolysis was used to elucidate the nature and dynamics of a manifold of the lowest excited states in Pt(phen-NDI)Cl 2 ( 1), where NDI = strongly electron accepting 1,4,5,8-naphthalene-diimide group. 1 is the first example of a Pt (II)-diimine-diimide dyad. UV/vis/IR spectroelectrochemistry and EPR studies of electrochemically generated anions confirmed that the lowest unoccupied molecular orbital (LUMO) in this system is localized on the NDI acceptor group. The lowest allowed electronic transition in Pt(phen-NDI)Cl 2 is charge-transfer-to-diimine of a largely Pt-->phen metal-to-ligand charge-transfer (MLCT) character. Excitation of 1 in the 355-395 nm range initiates a series of processes which involve excited states with the lifetimes of 0.9 ps ( (1)NDI*), 3 ps ( (3)MLCT), 19 ps (vibrational cooling of "hot" (3)NDI and of "hot" NDI ground state), and 520 mus ( (3)NDI). Excitation of 1 with 395 nm femtosecond laser pulses populates independently the (1)MLCT and the (1)NDI* excited states. A thermodynamically possible decay of the initially populated (1)MLCT to the charge-transfer-to-NDI excited state, [Pt (III)(phen-NDI (-*))Cl 2], is not observed. This finding could be explained by an ultrafast ISC of the (1)MLCT to the (3)MLCT state which lies about 0.4 eV lower in energy than [Pt (III)(phen-NDI (-*))Cl 2]. The predominant decay pathway of the (3)MLCT is a back electron transfer process with approximately 3 ps lifetime, which also causes partial population of the vibrationally hot ground state of the NDI fragment. The decay of the (1)NDI* state in 1 populates vibrationally hot ground state of the NDI, as well as vibrationally hot (3)NDI. The latter relaxes to form (3)NDI state, that is, [Pt(phen- (3)NDI)Cl 2]*, which possesses a remarkably long lifetime for a Pt (II) complex in fluid solution of 520 mus. The IR signature of this excited state includes the nu(CO) bands at 1607 and 1647 cm (-1), which are shifted considerably to lower energies if compared to their ground-state counterparts. The assignment of the vibrational bands is supported by the density-functional theory calculations in CH 2Cl 2. Pt(phen-NDI)Cl 2 acts as a modest photosensitizer of singlet oxygen. 相似文献
60.
H.C. Hamaker S.D. Bader G. Zajac R.N. Shelton A.J. Bevolo H.E. Horng 《Solid State Communications》1983,48(7):589-591
Auger and photoemission studies for Y(Rh1?xRux)4B4 superconductors elucidate the mechanism for the abrupt drop in Tc near x=0.5. The B -states admix more strongly with Ru than Rh -states, thereby yielding low-Tc values for Ru-rich compounds due to broadening of the -band feutures. These effects underlie a previous suggestion that the preservation of Rh4 tetrahedral units is essential for high-Tc values in ternary boride compounds. 相似文献