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991.
Investigation of the effect of power ultrasound on the nucleation of water during freezing of agar gel samples in tubing vials 总被引:1,自引:0,他引:1
Nucleation, as an important stage of freezing process, can be induced by the irradiation of power ultrasound. In this study, the effect of irradiation temperature (−2 °C, −3 °C, −4 °C and −5 °C), irradiation duration (0 s, 1 s, 3 s, 5 s, 10 s or 15 s) and ultrasound intensity (0.07 W cm−2, 0.14 W cm−2, 0.25 W cm−2, 0.35 W cm−2 and 0.42 W cm−2) on the dynamic nucleation of ice in agar gel samples was studied. The samples were frozen in an ethylene glycol-water mixture (−20 °C) in an ultrasonic bath system after putting them into tubing vials. Results indicated that ultrasound irradiation is able to initiate nucleation at different supercooled temperatures (from −5 °C to −2 °C) in agar gel if optimum intensity and duration of ultrasound were chosen. Evaluation of the effect of 0.25 W cm−2 ultrasound intensity and different durations of ultrasound application on agar gels showed that 1 s was not long enough to induce nucleation, 3 s induced the nucleation repeatedly but longer irradiation durations resulted in the generation of heat and therefore nucleation was postponed. Investigation of the effect of ultrasound intensity revealed that higher intensities of ultrasound were effective when a shorter period of irradiation was used, while lower intensities only resulted in nucleation when a longer irradiation time was applied. In addition to this, higher intensities were not effective at longer irradiation times due to the heat generated in the samples by the heating effect of ultrasound. In conclusion, the use of ultrasound as a means to control the crystallization process offers promising application in freezing of solid foods, however, optimum conditions should be selected. 相似文献
992.
We analyze the effect of higher derivative corrections to the near horizon geometry of the extremal vanishing horizon (EVH)
black hole solutions in four dimensions. We restrict ourselves to a Gauss–Bonnet correction with a dilation dependent coupling
in an Einstein–Maxwell-dilaton theory. This action may represent the effective action as it arises in tree level heterotic
string theory compactified to four dimensions or the K3 compactification of type II string theory. We show that EVH black
holes, in this theory, develop an AdS3 throat in their near horizon geometry. 相似文献
993.
Analysis of the magnetic losses in iron-based soft magnetic composites with MgO insulation produced by sol-gel method 总被引:3,自引:0,他引:3
Amir Hossein Taghvaei Azadeh Ebrahimi Kamal Janghorban 《Journal of magnetism and magnetic materials》2010,322(23):3748-3754
This work investigated the magnetic losses of heat treated iron-based soft magnetic composites with a thin MgO insulating layer produced by sol-gel method. The samples were characterized by energy dispersive X-ray spectroscopy, X-ray analysis and Fourier transform infrared spectroscopy. The results show that the surface of the powders contains a thin layer of MgO insulation. The loss results indicate that the hysteresis part for both the core loss and total loss factor was approximately the same for the MgO-insulated compacts and conventional SOMALOYTM samples with phosphate insulation after annealing at 600 °C. But the MgO-insulated compacts exhibited significantly lower eddy current contribution of both core loss and total loss factor with respect to SOMALOYTM samples after annealing. Also the contribution of eddy current in the iron particles for MgO insulated compacts (kp=0.91) was noticeably higher than this contribution for SOMALOYTM samples (kp=0.18) after annealing due to the higher electrical resistivity of the MgO-insulated compacts. 相似文献
994.
Hossein Hassani 《Physica A》2010,389(8):1601-1606
It is shown that the sum of the sample autocorrelation function at lag h≥1 is always for any stationary time series with arbitrary length T≥2 (Hassani, 2009 [1]). In this paper, the distribution of a set of the sample autocorrelation function using the properties of this quantity is considered. It is found that the distribution of a set of the sample autocorrelation estimates is not independent and identically distributed. This finding implies that the result of diagnostic check and model building using the traditional assumption of iid can be quite misleading. 相似文献
995.
996.
Hossein Salavati Shahram Tangestaninejad Majid Moghadam Valiollah Mirkhani Iraj Mohammadpoor-Baltork 《Ultrasonics sonochemistry》2010,17(2):453-459
A Keggin type polyoxometalate (POM) has been immobilized in the unique network structure of multi-wall carbon nanotubes (CNTs). The vanadium-containing polyphosphomolybdate (PVMo) supported on CNTs, which was prepared by a one-step solid-state reaction, was characterized by FT-IR, XRD, SEM and elemental analyses. These uniform nanoparticles have an average size 20–30 nm. Furthermore, due to the chemical interaction between PVMo and carboxylic acid groups, PVMo nanoparticles were successfully immobilized on the CNTs. Moreover, the obtained composite was found as an efficient catalyst for oxidation of hydrocarbons under reflux and ultrasonic irradiation (US) conditions. 相似文献
997.
Hossein Motavalli Amin Rezaei Akbarieh 《International Journal of Theoretical Physics》2010,49(9):2074-2079
We present a general construction for ladder operators for the special orthogonal functions based on Nikiforov-Uvarov mathematical
formalism. A list of creation and annihilation operators are provided for the well known special functions. Furthermore, we
establish the dynamic group associated with these operators. 相似文献
998.
Hossein Farajollahi Mehrdad Farhoudi Hossein Shojaie 《International Journal of Theoretical Physics》2010,49(10):2558-2568
We study longstanding problem of cosmological clock in the context of Brans–Dicke theory of gravitation. We present the Hamiltonian
formulation of the theory for a class of spatially homogeneous cosmological models. Then, we show that formulation of the
Brans–Dicke theory in the Einstein frame allows how an identification of an appropriate cosmological time variable, as a function
of the scalar field in the theory, can be emerged in quantum cosmology. The classical and quantum results are applied to the
Friedmann–Robertson–Walker cosmological models. 相似文献
999.
1000.
Hossein Movasati 《The Ramanujan Journal》2008,17(1):53-76
In the present article we define the algebra of differential modular forms and we prove that it is generated by Eisenstein
series of weight 2, 4 and 6. We define Hecke operators on them, find some analytic relations between these Eisenstein series
and obtain them in a natural way as coefficients of a family of elliptic curves. The fact that a complex manifold over the
moduli of polarized Hodge structures in the case h
10=h
01=1 has an algebraic structure with an action of an algebraic group plays a basic role in all of the proofs.
相似文献