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91.
[Reaction: see text]. A highly efficient synthetic method of carotenoid compounds has been developed on the basis of the sulfone coupling and double-elimination strategy. This method highlighted the sulfone-mediated coupling with the novel C(10) dialdehyde, 2,7-dimethyl-4-octenedial, which was easily prepared and efficiently utilized in the synthesis of the conjugated polyene chains. 相似文献
92.
Partha Guha 《Journal of Mathematical Analysis and Applications》2005,310(1):45-56
We show that all the Antonowicz-Fordy type coupled KdV equations have the same symmetry group and similar bi-Hamiltonian structures. It turns out that their configuration space is , where is the Bott-Virasoro group of orientation preserving diffeomorphisms of the circle, and all these systems can be interpreted as equations of a geodesic flow with respect to L2 metric on the semidirect product space . 相似文献
93.
The amplitude modulation as well as demodulation of an electromagnetic wave in a transversely magnetised piezoelectric semiconductor plasma has been studied in different wave number regions over a wide range of electron cyclotron frequency. 相似文献
94.
The parametric excitation of a helicon and an acoustic wave in a piezoelectric semiconductor-plasma in the presence of a strong magnetic field has been investigated using the coupled mode theory. The expressions for the threshold value of the electric field required for the onset of instability and for the growth rate well above the threshold have been obtained. It is observed that an acoustic wave of higher frequency and higher phase velocity than that of the pump wave cannot be excited. The analysis has been applied to the case of n type InSb sample where the threshold value of the electric field is found to be of the order 5.2 × 103 Vm?1 and the growth rate at an electric field 5.2 × 104 Vm?1 is of the order of 8.7 × 1010 sec?1. 相似文献
95.
Traditional quantitative structure-activity relationship (QSAR) models aim to capture global structure-activity trends present in a data set. In many situations, there may be groups of molecules which exhibit a specific set of features which relate to their activity or inactivity. Such a group of features can be said to represent a local structure-activity relationship. Traditional QSAR models may not recognize such local relationships. In this work, we investigate the use of local lazy regression (LLR), which obtains a prediction for a query molecule using its local neighborhood, rather than considering the whole data set. This modeling approach is especially useful for very large data sets because no a priori model need be built. We applied the technique to three biological data sets. In the first case, the root-mean-square error (RMSE) for an external prediction set was 0.94 log units versus 0.92 log units for the global model. However, LLR was able to characterize a specific group of anomalous molecules with much better accuracy (0.64 log units versus 0.70 log units for the global model). For the second data set, the LLR technique resulted in a decrease in RMSE from 0.36 log units to 0.31 log units for the external prediction set. In the third case, we obtained an RMSE of 2.01 log units versus 2.16 log units for the global model. In all cases, LLR led to a few observations being poorly predicted compared to the global model. We present an analysis of why this was observed and possible improvements to the local regression approach. 相似文献
96.
The advanced glycation end products (AGEs) of DNA nucleobases have received little attention, perhaps due to the fact that
adenine, guanine, cytosine and thymine do not dissolve under mild pH conditions. To maintain nucleobases in solution, alkaline
pH conditions are typically required. The objectives of this investigation were twofold: to study the susceptibility of DNA
nucleobases to nonenzymatic attack by different sugars, and to evaluate the factors that influence the formation of nucleobase
AGEs at pH 12, i.e., in an alkaline environment that promotes the aldo–keto isomerization and epimerization of sugars. Varying
concentrations of adenine, guanine, thymine and cytosine were incubated over time with constant concentrations of D-glucose, D-galactose or D/L-glyceraldehyde under different conditions of temperature and ionic strength. Incubation of the nucleobases with the sugars
resulted in a heterogeneous assembly of AGEs whose formation was monitored by UV/fluorescence spectroscopy. Capillary electrophoresis
and HPLC were used to resolve the AGEs of the DNA adducts and provided a powerful tool for following the extent of glycation
in each of the DNA nucleobases. Mass spectrometry studies of DNA adducts of guanine established that glycation at pH 12 proceeded
through an Amadori intermediate. 相似文献
97.
R. Bhattacharya A. Nag R. Guha A. Bhoumick S. De A. B. Bhattacharya 《Indian Journal of Physics》2010,84(11):1587-1595
The results of investigation of the variation of radio signal strengths during the solar eclipse on July 22, 2009 are reported
in this paper. Observations of the radio signals transmitted from different radio stations at different frequencies and received
at a particular observing site indicate a distinct change in signal strength around the time the eclipse umbra passes the
propagation paths. The three types of variations in the eclipse day and particularly during its peak period are different
from propagation under normal condition. The phenomena of signal variations, the noted “Inverted U-shape“ at one of the frequencies
before the occurrence of the eclipse and 13 to 15 minutes time difference between the enhancement of the signal strength and
the onset of eclipse are some interesting characteristics. The results are interpreted by ionospheric D-layer behavior at
such times. 相似文献
98.
This paper develops a new numerical technique to price an American option written upon an underlying asset that follows a bivariate diffusion process. The technique presented here exploits the supermartingale representation of an American option price together with a coarse approximation of its early exercise surface that is based on an efficient implementation of the least-squares Monte–Carlo algorithm (LSM) of Longstaff and Schwartz (Rev Financ Stud 14:113–147, 2001). Our approach also has the advantage of avoiding two main issues associated with LSM, namely its inherent bias and the basis functions selection problem. Extensive numerical results show that our approach yields very accurate prices in a computationally efficient manner. Finally, the flexibility of our method allows for its extension to a much larger class of optimal stopping problems than addressed in this paper. 相似文献
99.
Mikhail Belkin Hariharan Narayanan Partha Niyogi 《Random Structures and Algorithms》2013,43(4):407-428
We draw on the observation that the amount of heat diffusing outside of a heated body in a short period of time is proportional to its surface area, to design a simple algorithm for approximating the surface area of a convex body given by a membership oracle. Our method has a complexity of O*(n4), where n is the dimension, compared to O*(n8) for the previous best algorithm. We show that our complexity cannot be improved given the current state‐of‐the‐art in volume estimation. © 2013 Wiley Periodicals, Inc. Random Struct. Alg., 43, 407–428, 2013 相似文献
100.
In this paper, we develop a fourth order method for solving the systems of nonlinear equations. The algorithm is composed of two weighted-Newton steps and requires the information of one function and two first Fréchet derivatives. Therefore, for a system of n equations, per iteration it uses n?+?2n 2 evaluations. Computational efficiency is compared with Newton’s method and some other recently published methods. Numerical tests are performed, which confirm the theoretical results. From the comparison with known methods it is observed that present method shows good stability and robustness. 相似文献