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101.
By analyzing high-speed video of the fruit fly, we discover a swimminglike mode of forward flight characterized by paddling wing motions. We develop a new aerodynamic analysis procedure to show that these insects generate drag-based thrust by slicing their wings forward at low angle of attack and pushing backwards at a higher angle. Reduced-order models and simulations reveal that the law for flight speed is determined by these wing motions but is insensitive to material properties of the fluid. Thus, paddling is as effective in air as in water and represents a common strategy for propulsion through aquatic and aerial environments. 相似文献
102.
Dmitry Grishenkov Leif KariLars-Åke Brodin Torkel B. BrismarGaio Paradossi 《Ultrasonics》2011,51(1):40-48
The focus of contrast-enhanced ultrasound research has developed beyond visualizing the blood pool and its flow to new areas such as perfusion imaging, drug and gene therapy, and targeted imaging. In this work comparison between the application of polymer- and phospholipid-shelled ultrasound contrast agents (UCAs) for characterization of the capillary microcirculation is reported. All experiments are carried out using a microtube as a vessel phantom. The first set of experiments evaluates the optimal concentration level where backscattered signal from microbubbles depends on concentration linearly. For the polymer-shelled UCAs the optimal concentration level is reached at a value of about 2 × 104 MB/ml, whereas for the phospholipid-shelled UCAs the optimal level is found at about 1 × 105 MB/ml.Despite the fact that the polymer shell occupies 30% of the radius of microbubble, compared to 0.2% of the phospholipid-shelled bubble, approximately 5-fold lower concentration of the polymer UCA is needed for investigation compared to phospholipid-shelled analogues. In the second set of experiments, destruction/replenishment method with varied time intervals ranging from 2 ms to 3 s between destructive and monitoring pulses is employed. The dependence of the peak-to-peak amplitude of backscattered wave versus pulse interval is fitted with an exponential function of the time γ = A(1 − exp(−βt)) where A represents capillary volume and the time constant β represents velocity of the flow. Taking into account that backscattered signal is linearly proportional to the microbubble concentration, for both types of the UCAs it is observed that capillary volume is linearly proportional to the concentration of the microbubbles, but the estimation of the flow velocity is not affected by the change of the concentration. Using the single capillary model, for the phospholipid-shelled UCA a delay of about 0.2-0.3 s in evaluation of the perfusion characteristics is found while polymer-shelled UCA provide response immediately. The latter at the concentration lower than 3.6 × 105 MB/ml have no statistically significant delay (p < 0.01), do not cause any attenuation of the backscattered signal or saturation of the receiving part of the system. In conclusion, these results suggest that the novel polymer-shelled microbubbles have a potential to be used for perfusion evaluation. 相似文献
103.
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105.
Benzylation of 1,2-ditosylhydrazine in DMF under various basic conditions results in a benzyl sulfone via intermediary sulfinate formation, providing new insights and allowing practical conclusions to be drawn. The half-lives of 1,2-ditosylhydrazine and several monotosylated hydrazides with 1,1,3,3-tetramethylguanidine in DMSO have been determined by 1H NMR spectroscopy and are found to vary from a few minutes to several months. In the course of this work a benzylated, partly detosylated compound has been identified and a 1,1,3,3-tetramethyl guanidine-containing side-product characterized. A contradictory report is also commented on. 相似文献
106.
I. Di Marco J. Minár J. Braun M. I. Katsnelson A. Grechnev H. Ebert A. I. Lichtenstein O. Eriksson 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,72(4):473-478
We investigate the role of magnetic fluctuations in the spectral properties of paramagnetic γ-Mn. Two methods are employed.
The Local Density Approximation plus Dynamical Mean-Field Theory together with the numerically exact quantum Monte-Carlo solver
is used as a reference for the spectral properties. Then the same scheme is used with the computationally less demanding perturbative
spin-polarized fluctuation-exchange solver in combination with the Disordered Local Moment approach, and photoemission spectra
are calculated within the one-step model. It is shown that the formation of local magnetic moments in γ-Mn is very sensitive
to the value of Hund’s exchange parameter. Comparison with the experimental photoemission spectra demonstrates that γ-Mn is
a strongly correlated system, with the Hubbard band formation, which cannot be described by the perturbative approach. However,
minor change of parameters would transform it into a weakly correlated system. 相似文献
107.
Leif J. Saethre Michele R. F. Siggel T. Darrah Thomas 《Journal of Electron Spectroscopy and Related Phenomena》1992,60(4):R1-R5
In earlier papers the atoms-in-molecules concept of Bader was used to show the inadequacies of the point-charge model for calculating potentials at atoms in molecules and, hence, for accounting for shifts in core-ionization energies in terms of atomic charges. Because questions have been raised about the suitability of the basis set that was used, part of these calculations has been repeated with the 6-31G** basis set. The conclusions of the earlier study are unchanged: the point-charge model does not accurately give the potentials at atoms in molecules. A multipole model gives better results, but needs to be carried at least to octupole terms. 相似文献
108.
Björn Alriksson Anders Sjöde Nils-Olof Nilvebrant Leif J. Jönsson 《Applied biochemistry and biotechnology》2006,130(1-3):599-611
Alkaline detoxification strongly improves the fermentability of dilute-acid hydrolysates in the production of bioethanol from
lignocellulose with Saccharomyces cerevisiae. New experiments were performed with NH4OH and NaOH to define optimal conditions for detoxification and make a comparison with Ca(OH)2 treatment feasible. As too harsh conditions lead to sugar degradation, the detoxification treatments were evaluated through
the balanced ethanol yield, which takes both the ethanol production and the loss of fermentable sugars into account. The optimization
treatments were performed as factorial experiments with 3-h duration and varying pH and temperature. Optimal conditions were
found roughly in an area around pH 9.0/60°C for NH4OH treatment and in a narrow area stretching from pH 9.0/80°C to pH 12.0/30°C for NaOH treatment. By optimizing treatment
with NH4OH, NaOH, and Ca(OH)2, it was possible to find conditions that resulted in a fermentability that was equal or better than that of a reference fermentation
of a synthetic sugar solution without inhibitors, regardless of the type of alkali used. The considerable difference in the
amount of precipitate generated after treatment with different types of alkali appears critical for industrial implementation. 相似文献
109.
S. Eriksson M. Trupke H. F. Powell D. Sahagun C. D.J. Sinclair E. A. Curtis B. E. Sauer E. A. Hinds Z. Moktadir C. O. Gollasch M. Kraft 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2005,35(1):135-139
We report on the integration of small-scale optical components
into silicon wafers for use in atom chips. We present an on-chip
fibre-optic atom detection scheme that can probe clouds with small
atom numbers. The fibres can also be used to generate microscopic
dipole traps. We describe our most recent results with optical
microcavities and show that a sufficiently high finesse can be achieved to
enable single-atom detection
on an atom chip. The key components have been fabricated by
etching directly into the atom chip silicon substrate. 相似文献
110.