全文获取类型
收费全文 | 2347篇 |
免费 | 106篇 |
国内免费 | 11篇 |
专业分类
化学 | 1530篇 |
晶体学 | 13篇 |
力学 | 77篇 |
数学 | 333篇 |
物理学 | 467篇 |
综合类 | 44篇 |
出版年
2023年 | 19篇 |
2022年 | 36篇 |
2021年 | 53篇 |
2020年 | 60篇 |
2019年 | 71篇 |
2018年 | 53篇 |
2017年 | 40篇 |
2016年 | 102篇 |
2015年 | 68篇 |
2014年 | 81篇 |
2013年 | 145篇 |
2012年 | 161篇 |
2011年 | 170篇 |
2010年 | 103篇 |
2009年 | 85篇 |
2008年 | 151篇 |
2007年 | 130篇 |
2006年 | 108篇 |
2005年 | 111篇 |
2004年 | 106篇 |
2003年 | 82篇 |
2002年 | 93篇 |
2001年 | 30篇 |
2000年 | 34篇 |
1999年 | 19篇 |
1998年 | 25篇 |
1997年 | 19篇 |
1996年 | 17篇 |
1995年 | 14篇 |
1994年 | 10篇 |
1993年 | 13篇 |
1992年 | 11篇 |
1991年 | 18篇 |
1990年 | 8篇 |
1989年 | 14篇 |
1988年 | 9篇 |
1987年 | 4篇 |
1986年 | 7篇 |
1985年 | 12篇 |
1984年 | 17篇 |
1983年 | 8篇 |
1982年 | 13篇 |
1981年 | 14篇 |
1980年 | 18篇 |
1979年 | 15篇 |
1978年 | 20篇 |
1977年 | 8篇 |
1976年 | 8篇 |
1974年 | 9篇 |
1973年 | 9篇 |
排序方式: 共有2464条查询结果,搜索用时 125 毫秒
951.
Ronan Vicquelin Benoît Fiorina Nasser Darabiha Olivier Gicquel Denis Veynante 《Comptes Rendus Mecanique》2009,337(6-7):329-339
A new modeling strategy is developed to introduce tabulated chemistry methods in the LES of turbulent premixed combustion. The objective is to recover the correct laminar flame propagation speed of the filtered flame front when the subgrid scale turbulence vanishes. The filtered flame structure is mapped by 1D filtered laminar premixed flames. Closure of the filtered progress variable and the energy balance equations are carefully addressed. The methodology is applied to 1D and 2D filtered laminar flames. These computations show the capability of the model to recover the laminar flame speed and the correct chemical structure when the flame wrinkling is completely resolved. The model is then extended to turbulent combustion regimes by introducing subgrid scale wrinkling effects on the flame front propagation. Finally, the LES of a 3D turbulent premixed flame is performed. To cite this article: R. Vicquelin et al., C. R. Mecanique 337 (2009). 相似文献
952.
Cara L Ryan David C Baranowski Babykumari P Chitramuthu Suneil Malik Zhi Li Mingju Cao Sandra Minotti Heather D Durham Denis G Kay Christopher A Shaw Hugh PJ Bennett Andrew Bateman 《BMC neuroscience》2009,10(1):1-22
Background
Progranulin is a secreted high molecular weight growth factor bearing seven and one half copies of the cysteine-rich granulin-epithelin motif. While inappropriate over-expression of the progranulin gene has been associated with many cancers, haploinsufficiency leads to atrophy of the frontotemporal lobes and development of a form of dementia (frontotemporal lobar degeneration with ubiquitin positive inclusions, FTLD-U) associated with the formation of ubiquitinated inclusions. Recent reports indicate that progranulin has neurotrophic effects, which, if confirmed would make progranulin the only neuroprotective growth factor that has been associated genetically with a neurological disease in humans. Preliminary studies indicated high progranulin gene expression in spinal cord motor neurons. However, it is uncertain what the role of Progranulin is in normal or diseased motor neuron function. We have investigated progranulin gene expression and subcellular localization in cultured mouse embryonic motor neurons and examined the effect of progranulin over-expression and knockdown in the NSC-34 immortalized motor neuron cell line upon proliferation and survival.Results
In situ hybridisation and immunohistochemical techniques revealed that the progranulin gene is highly expressed by motor neurons within the mouse spinal cord and in primary cultures of dissociated mouse embryonic spinal cord-dorsal root ganglia. Confocal microscopy coupled to immunocytochemistry together with the use of a progranulin-green fluorescent protein fusion construct revealed progranulin to be located within compartments of the secretory pathway including the Golgi apparatus. Stable transfection of the human progranulin gene into the NSC-34 motor neuron cell line stimulates the appearance of dendritic structures and provides sufficient trophic stimulus to survive serum deprivation for long periods (up to two months). This is mediated at least in part through an anti-apoptotic mechanism. Control cells, while expressing basal levels of progranulin do not survive in serum free conditions. Knockdown of progranulin expression using shRNA technology further reduced cell survival.Conclusion
Neurons are among the most long-lived cells in the body and are subject to low levels of toxic challenges throughout life. We have demonstrated that progranulin is abundantly expressed in motor neurons and is cytoprotective over prolonged periods when over-expressed in a neuronal cell line. This work highlights the importance of progranulin as neuroprotective growth factor and may represent a therapeutic target for neurodegenerative diseases including motor neuron disease. 相似文献953.
Hamaker interaction energies and cutoff distances have been calculated for disordered carbon films, in contact with purely dispersive (diiodomethane) or polar (water) liquids, using their experimental dielectric functions ε (q, ω) obtained over a broad energy range. In contrast with previous works, a q-averaged <ε (q, ω) > q is derived from photoelectron energy-loss spectroscopy (XPS-PEELS) where the energy loss function (ELF) < Im[?1/ε (q, ω)] > q is a weighted average over allowed transferred wave vector values, q, given by the physics of bulk plasmon excitation. For microcrystalline diamond and amorphous carbon films with a wide range of (sp3/sp2 + sp3) hybridization, non-retarded Hamaker energies, A 132 (L < 1 nm), were calculated in several configurations, and distance and wavenumber cutoff values were then calculated based on A 132 and the dispersive work of adhesion obtained from contact angles. A geometric average approximation, H 0?CVL ?=?(H 0?CVC H 0?LVL )1/2, holds for the cutoff separation distances obtained for carbon-vacuum-liquid (CVL), carbon-vacuum-carbon (CVC) and liquid-vacuum-liquid (LVL) equilibrium configurations. The linear dependence found for A CVL, A CLC and A CLV values as a function of A CVC, for each liquid, allows predictive relationships for Hamaker energies (in any configuration) using experimental determination of the dispersive component of the surface tension, \( {\gamma}_{CV}^d \), and a guess value of the cutoff distance H 0?CVC of the solid. 相似文献
954.
Simulations of monodisperse and polydisperse (μ
2(A) = 0.13±0.002) 2D foam samples undergoing simple shear are performed using the 2D viscous froth (VF) model. These simulations
clearly demonstrate shear localisation. The dependence of localisation length on the product λV (shearing velocity V times the wall drag coefficient λ) is examined and is shown to agree qualitatively with published experimental data. A wide range of localisation lengths is
found at low λV, an effect which is attributed to the existence of distinct yield and limit stresses. The general continuum model is extended
to incorporate such an effect and its parameters are subsequently related to those of the VF model. A Herschel–Bulkley exponent
of a = 0.3 is shown to accurately describe the observed behaviour. The localisation length is found to be independent of λV for monodisperse foam samples. 相似文献
955.
Mounir Aytouna Denis Bartolo Gerard Wegdam Daniel Bonn Salima Rafaï 《Experiments in fluids》2010,48(1):49-57
We study the impact and subsequent retraction of aqueous surfactant-laden drops upon high-speed impact on hydrophobic surfaces.
Without surfactants, a rapid expansion of the drop due to the fluid inertia is followed by a rapid retraction, due to the
wetting incompatibility. With surfactants, the retraction can be partly or completely inhibited. We provide quantitative measurements
showing that both the expansion and the retraction dynamics depend not only on the equilibrium surface tension (ST) but also
on the dynamic tension of the surfactant solutions; the latter varies significantly between different surfactants. 相似文献
956.
Mariani C Vandenboomgaerde M Jourdan G Souffland D Houas L 《Physical review letters》2008,100(25):254503
A novel method to set highly accurate initial conditions has been designed in the context of shock tube experiments for the Richtmyer-Meshkov instability study. Stereolithography has been used to design the membrane supports which initially materialize the gaseous interface. The visualizations of both heavy-light and light-heavy sinusoidal interfaces were carried out with laser sheet diagnostics. Experiments are in very good agreement with theory and simulations for the heavy-light case, but probably due to the membrane effects, quickly deviate from them in the light-heavy configuration. 相似文献
957.
New fluctuation properties arise in problems where both spatial integration and energy summation are necessary ingredients. The quintessential example is given by the short-range approximation to the first order ground state contribution of the residual Coulomb interaction. The dominant features come from the region near the boundary where there is an interplay between Friedel oscillations and fluctuations in the eigenstates. Quite naturally, the fluctuation scale is significantly enhanced for Neumann boundary conditions as compared to Dirichlet. Elements missing from random plane wave modeling of chaotic eigenstates lead surprisingly to significant errors, which can be corrected within a purely semiclassical approach. 相似文献
958.
The Jarzynski equality and the Crooks fluctuation theorem enable the calculation of the change in a system's free energy from nonequilibrium path integrals. These relations consider processes where the system is driven out of equilibrium by a mechanical external agent while remaining in contact with a thermal reservoir at a fixed temperature. We generalize these relations to describe processes driven by any type of external agent, be it thermal or mechanical. Attention is given to the case of a system, initially in equilibrium, that is driven through a temperature change by a heat reservoir. The results are cast in a form applicable to experiments. 相似文献
959.
Peisi Keg Anup Lohani Denis Fichou Yeng Ming Lam Yiliang Wu Beng S. Ong Subodh G. Mhaisalkar 《Macromolecular rapid communications》2008,29(14):1197-1202
A solution processible polymer—poly(3,3‴‐didodecylquaterthiophene) (PQT‐12) is investigated at the liquid/solid interface using the scanning tunneling microscopy (STM). Two‐dimensional ordered films made up of self‐assembled domains, with dimensions of 100 nm × 50 nm adsorbed on highly oriented pyrolytic graphite (HOPG) were formed. These domains consist of parallel lamellar polymer chains, with the alkyl chains forming interdigitated structures, along with U‐shaped and closed ring segments of the polymer chains. A polymer chain packing model is proposed herein, which attempts to propose a correlation between the packing of long chains and charge mobilities. These STM results could help in understanding the relationship between the extended conjugation and molecular organization of the PQT‐12 chains.
960.
Mechanical, calorimetric, dynamic mechanical and dielectric properties were measured in starch and amylose films plasticized by different glycerol contents. Low-temperature relaxation was found to be highly dependent on plasticizer level and related to unusual mechanical properties. 相似文献