全文获取类型
收费全文 | 1770篇 |
免费 | 42篇 |
国内免费 | 1篇 |
专业分类
化学 | 1144篇 |
晶体学 | 20篇 |
力学 | 42篇 |
数学 | 153篇 |
物理学 | 454篇 |
出版年
2024年 | 2篇 |
2023年 | 9篇 |
2022年 | 49篇 |
2021年 | 62篇 |
2020年 | 39篇 |
2019年 | 42篇 |
2018年 | 45篇 |
2017年 | 47篇 |
2016年 | 82篇 |
2015年 | 52篇 |
2014年 | 86篇 |
2013年 | 97篇 |
2012年 | 108篇 |
2011年 | 143篇 |
2010年 | 85篇 |
2009年 | 85篇 |
2008年 | 98篇 |
2007年 | 111篇 |
2006年 | 82篇 |
2005年 | 71篇 |
2004年 | 64篇 |
2003年 | 27篇 |
2002年 | 36篇 |
2001年 | 18篇 |
2000年 | 33篇 |
1999年 | 12篇 |
1998年 | 21篇 |
1997年 | 12篇 |
1996年 | 14篇 |
1995年 | 21篇 |
1994年 | 17篇 |
1993年 | 11篇 |
1992年 | 10篇 |
1991年 | 21篇 |
1990年 | 16篇 |
1989年 | 10篇 |
1988年 | 10篇 |
1987年 | 10篇 |
1986年 | 9篇 |
1985年 | 9篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 5篇 |
1980年 | 6篇 |
1979年 | 2篇 |
1977年 | 4篇 |
1975年 | 4篇 |
1957年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有1813条查询结果,搜索用时 15 毫秒
991.
Adriano F. Lima Fernanda G. Basso Ana P. D. Ribeiro Vanderlei S. Bagnato Josimeri Hebling Giselle M. Marchi Carlos A. de Souza Costa 《Photochemistry and photobiology》2014,90(1):201-206
The aim of this study was to evaluate the effect of low‐level laser therapy (LLLT) on odontoblast‐like cells exposed to a bleaching agent. Mouse dental papilla cell‐23 cells were seeded in wells of 24‐well plates. Eight groups were established according to the exposure to the bleaching agent and LLLT (0, 4, 10 and 15 J cm?2). Enamel–dentin disks were adapted to artificial pulp chambers, which were individually placed in wells containing Dulbecco's modified Eagle's medium (DMEM). A bleaching agent (35% hydrogen peroxide [BA35%HP]) was applied on enamel (15 min) to obtain the extracts (DMEM + BA35%HP components diffused through enamel/dentin disks). The extracts were applied (1 h) to the cells, and then subjected to LLLT. Cell viability (Methyl tetrazolium assay), alkaline phosphatase (ALP) activity, as well as gene expression of ALP, fibronectin (FN) and type I collagen, were evaluated. The bleaching procedures reduced the cell viability, ALP activity and gene expression of dentin proteins. Laser irradiation did not modulate the cell response; except for FN, as LLLT decreased the gene expression of this protein by the cells exposed to the BA35%HP. It can be concluded that BA35%HP decreased the activities of odontoblasts that were not recovered by the irradiation of the damaged cells with low‐level laser parameters tested. 相似文献
992.
Odair P. Ferreira Larissa Otubo Acrisio L. Aguiar Jose J. A. Silva Josue Mendes Filho Antonio G. Souza Filho Solange B. Fagan Oswaldo L. Alves 《Journal of nanoparticle research》2009,11(8):2163-2170
We have studied the interaction of benzonitrile with as-prepared and purified single-walled carbon nanotubes (SWCNTs). As-prepared
SWCNTs, when suspended in benzonitrile, lead to a red colored dispersion which contains fragments composed mostly of amorphous
carbon and carbon-coated catalyst, thus suggesting that benzonitrile is a solvent that can be used as one step of the purification
process. Optical spectroscopic data (infrared, Raman, absorption) showed that purified carbon nanotubes interact weakly with
benzonitrile. These experimental results are confirmed by first principles calculations that predict a very weak adsorption
process through π–π interaction instead of through the free electron pair of the nitrile. 相似文献
993.
994.
Fernando O. Souza Reinaldo M. Palhares Petr Ya. Ekel 《Chaos, solitons, and fractals》2009,41(5):2387-2393
This paper deals with the stability analysis of delayed uncertain Cohen–Grossberg neural networks (CGNN). The proposed methodology consists in obtaining new robust stability criteria formulated as linear matrix inequalities (LMIs) via the Lyapunov–Krasovskii theory. Particularly one stability criterion is derived from the selection of a parameter-dependent Lyapunov–Krasovskii functional, which allied with the Gu’s discretization technique and a simple strategy that decouples the system matrices from the functional matrices, assures a less conservative stability condition. Two computer simulations are presented to support the improved theoretical results. 相似文献
995.
An atomistic simulation study of oxygen-vacancy migration in perovskite electrolytes based on LaGaO3
Abstract Static lattice simulation techniques were used to calculate the energetic barriers for oxygen-vacancy migration in the perovskite-type
oxide LaGaO3 substituted with alkaline earth cations. The calculated migration energies are found to vary with the number and size of
the substituting cations in the immediate neigbourhood of the migrating defect. It is argued that not only the size but also
the charge of the cations constituting the saddle-point configuration play a role in determining the migration energy.
Graphical abstract
相似文献
996.
A two-scale model for predicting the multiple crack growth in viscoelastic solids due to an impact is presented. The cracks
are considered only at the local scale through the use of a micromechanical viscoelastic cohesive zone model. The multiscale
model has been implemented in a finite-element code. In order to minimize the computation time, the local finite-element meshes
are solved in parallel by multiple processors. An example problem is given in order to demonstrate the capabilities of the
model.
Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 45, No. 2, pp. 211–222, March–April, 2009. 相似文献
997.
We classify the quadratic extensions and the finite groups G for which the group ring [G] of G over the ring of integers of K has the property that the group of units of augmentation 1 is hyperbolic. We also construct units in the ℤ-order of the quaternion algebra , when it is a division algebra. 相似文献
998.
A. J. Tertuliano C. F. Lagatta I. F. Machado R. M. Souza 《Experimental Mechanics》2017,57(7):1071-1079
Niobium carbide (NbC) has high wear and corrosion resistance and retains these characteristics at high temperatures. In industrial applications, as well as in academia, NbC can be found in various configurations, such as carbides dispersed in the microstructure of steel or as sintered components. The aim of this study is to use the instrumented indentation (nanoindentation) technique to evaluate the properties of carbides present in the martensitic matrix of a cast steel or as a sintered specimen. In the case of the cast alloy, the sample had an MC-type carbide volume fraction of approximately 5%. In the second case, the NbC specimen was sintered using spark-plasma sintering (SPS). Additional specimen characterization was conducted using X-ray diffraction (XRD) and scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDX). Nanoindentation analyses were conducted with loads up to 10 mN, allowing hardness impressions with dimensions significantly smaller than the size of the carbides in the cast specimens. The results indicated relatively uniform values of 22 GPa and 348 GPa for the hardness and reduced elastic modulus of the sintered specimen, respectively. The EDX analysis results of the cast specimen indicated that the MC-type carbides had regions with different chemical compositions. Differences in the carbide chemical compositions were also observed when different regions of the cast specimen were compared. Nevertheless, similar properties were obtained in all regions, with a trend for the carbides in the cast specimen to present a higher hardness and lower modulus than those in the sintered specimen. 相似文献
999.
Ian?A.?Frigaard Kristofer?G.?PasoEmail author Paulo?R.?de Souza Mendes 《Rheologica Acta》2017,56(3):259-282
Yield stress fluid flows occur in a great many operations and unit processes within the oil and gas industry. This paper reviews this usage within reservoir flows of heavy oil, drilling fluids and operations, wellbore cementing, hydraulic fracturing and some open-hole completions, sealing/remedial operations, e.g., squeeze cementing, lost circulation, and waxy crude oils and flow assurance, both wax deposition and restart issues. We outline both rheological aspects and relevant fluid mechanics issues, focusing primarily on yield stress fluids and related phenomena. 相似文献
1000.
M.M. Cavalcanti V.N. Domingos Cavalcanti M.A. Jorge Silva A.Y. de Souza Franco 《Journal of Differential Equations》2018,264(11):6535-6584
In this paper we discuss the asymptotic stability as well as the well-posedness of the damped wave equation posed on a bounded domain Ω of , subject to a locally distributed viscoelastic effect driven by a nonnegative function and supplemented with a frictional damping acting on a region A of Ω, where in A. Assuming that is constant, considering that the well-known geometric control condition holds and supposing that the relaxation function g is bounded by a function that decays exponentially to zero, we prove that the solutions to the corresponding partial viscoelastic model decay exponentially to zero, even in the absence of the frictional dissipative effect. In addition, in some suitable cases where the material density is not constant, it is also possible to remove the frictional damping term , that is, the localized viscoelastic damping is strong enough to assure that the system is exponentially stable. The semi-linear case is also considered. 相似文献