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The rates of deactivation of CO(v=1) by 4He and by 3He have been measured between 300 K and 80 K using a pulsed laser fluorescence technique. The results show the usual strong deviation from Landau—Teller behaviour and a marked isotope effect. Comparison is made with theoretical predictions including a one-dimensional treatment which takes account of attractive forces. The present results are compared also with earlier work on the deactivation of CO by H2, HD and D2. It has been found that at and below 300 K D2 is less efficient than 4He in the (VT) deactivation of CO (v=1) and HD is anomalously efficient. The latter effect is attributed to the involvement of rotational transitions. 相似文献
106.
John A. Chenery Asghar Fakhr Malcolm I. Wood C.J.S.M. Simpson 《Chemical physics letters》1983,96(2):143-147
The thermal decomposition of CO2 and OCS has been studied using a shock tube and cw CO probe laser. The energies of activation are in good agreement with the values of other workers. It has been shown that the CO formed from OCS has an initial non-thermal vibrational distribution with a large excess in ν = 0. 相似文献
107.
J.A. Simpson R.A. Cowley D.A. Jehan R.C.C. Ward M.R. Wells D.F. McMorrow K.N. Clausen T.R. Thurston Doon Gibbs 《Zeitschrift für Physik B Condensed Matter》1996,101(1):35-46
The effect of competing crystal-field anisotropies on magnetic order has been investigated in a series of Ho/Er superlattices using a combination of x-ray and neutron scattering techniques. For temperatures in the interval TN(Er)≤T≤TN(Ho) the Ho basal-plane order propagates coherently through the paramagnetic Er over a typical length scale of 1000 Å. At low temperatures the Ho moments retain their bulk-like helical configuration, whereas the magnetic structure in the Er blocks has both basal-plane and c-axis components. Below TN(Er), the coherence length of the basal-plane order decreases on cooling, while the longitudinal component of the Er moments fails to order across the Ho block. It is argued that these results require an extension of current models of indirect exchange in superlattices to explicitly include the superlattice band structure. 相似文献
108.
Stochasticity is an inherent feature of complex systems with nanoscale structure. In such systems information is represented by small collections of elements (e.g., a few electrons on a quantum dot), and small variations in the populations of these elements may lead to big uncertainties in the information. Unfortunately, little is known about how to work within this inherently noisy environment to design robust functionality into complex nanoscale systems. Here, we look to the biological cell as an intriguing model system where evolution has mediated the trade-offs between fluctuations and function, and in particular we look at the relationships and trade-offs between stochastic and deterministic responses in the gene expression of budding yeast (Saccharomyces cerevisiae). We find gene regulatory arrangements that control the stochastic and deterministic components of expression, and show that genes that have evolved to respond to stimuli (stress) in the most strongly deterministic way exhibit the most noise in the absence of the stimuli. We show that this relationship is consistent with a bursty two-state model of gene expression, and demonstrate that this regulatory motif generates the most uncertainty in gene expression when there is the greatest uncertainty in the optimal level of gene expression. 相似文献
109.
Brungart DS Chang PS Simpson BD Wang D 《The Journal of the Acoustical Society of America》2006,120(6):4007-4018
When a target speech signal is obscured by an interfering speech wave form, comprehension of the target message depends both on the successful detection of the energy from the target speech wave form and on the successful extraction and recognition of the spectro-temporal energy pattern of the target out of a background of acoustically similar masker sounds. This study attempted to isolate the effects that energetic masking, defined as the loss of detectable target information due to the spectral overlap of the target and masking signals, has on multitalker speech perception. This was achieved through the use of ideal time-frequency binary masks that retained those spectro-temporal regions of the acoustic mixture that were dominated by the target speech but eliminated those regions that were dominated by the interfering speech. The results suggest that energetic masking plays a relatively small role in the overall masking that occurs when speech is masked by interfering speech but a much more significant role when speech is masked by interfering noise. 相似文献
110.
The temporally overlapping, ultrafast electronic and vibrational dynamics of a model five-coordinate, high-spin heme in a nominally isotropic solvent environment has been studied for the first time with three complementary ultrafast techniques: transient absorption, time-resolved resonance Raman Stokes, and time-resolved resonance Raman anti-Stokes spectroscopies. Vibrational dynamics associated with an evolving ground-state species dominate the observations. Excitation into the blue side of the Soret band led to very rapid S2 --> S1 decay (sub-100 fs), followed by somewhat slower (800 fs) S1 --> S0 nonradiative decay. The initial vibrationally excited, non-Boltzmann S0 state was modeled as shifted to lower energy by 300 cm(-1) and broadened by 20%. On a approximately 10 ps time scale, the S0 state evolved into its room-temperature, thermal distribution S0 profile largely through VER. Anti-Stokes signals disappear very rapidly, indicating that the vibrational energy redistributes internally in about 1-3 ps from the initial accepting modes associated with S1 --> S0 internal conversion to the rest of the macrocycle. Comparisons of anti-Stokes mode intensities and lifetimes from TRARRS studies in which the initial excited state was prepared by ligand photolysis [Mizutani, T.; Kitagawa, T. Science 1997, 278, 443, and Chem. Rec. 2001, 1, 258] suggest that, while transient absorption studies appear to be relatively insensitive to initial preparation of the electronic excited state, the subsequent vibrational dynamics are not. Direct, time-resolved evaluation of vibrational lifetimes provides insight into fast internal conversion in hemes and the pathways of subsequent vibrational energy flow in the ground state. The overall similarity of the model heme electronic dynamics to those of biological systems may be a sign that the protein's influence upon the dynamics of the heme active site is rather subtle. 相似文献