全文获取类型
收费全文 | 2180篇 |
免费 | 90篇 |
国内免费 | 8篇 |
专业分类
化学 | 1365篇 |
晶体学 | 13篇 |
力学 | 118篇 |
数学 | 352篇 |
物理学 | 430篇 |
出版年
2023年 | 12篇 |
2022年 | 25篇 |
2021年 | 51篇 |
2020年 | 52篇 |
2019年 | 38篇 |
2018年 | 36篇 |
2017年 | 40篇 |
2016年 | 73篇 |
2015年 | 77篇 |
2014年 | 68篇 |
2013年 | 114篇 |
2012年 | 138篇 |
2011年 | 163篇 |
2010年 | 76篇 |
2009年 | 87篇 |
2008年 | 146篇 |
2007年 | 125篇 |
2006年 | 106篇 |
2005年 | 110篇 |
2004年 | 83篇 |
2003年 | 63篇 |
2002年 | 58篇 |
2001年 | 29篇 |
2000年 | 29篇 |
1999年 | 14篇 |
1998年 | 17篇 |
1997年 | 21篇 |
1996年 | 21篇 |
1995年 | 19篇 |
1994年 | 21篇 |
1993年 | 25篇 |
1992年 | 15篇 |
1991年 | 18篇 |
1990年 | 20篇 |
1989年 | 16篇 |
1988年 | 15篇 |
1987年 | 10篇 |
1986年 | 10篇 |
1985年 | 10篇 |
1984年 | 19篇 |
1983年 | 10篇 |
1982年 | 12篇 |
1981年 | 24篇 |
1980年 | 13篇 |
1979年 | 13篇 |
1978年 | 10篇 |
1977年 | 12篇 |
1975年 | 9篇 |
1974年 | 12篇 |
1973年 | 8篇 |
排序方式: 共有2278条查询结果,搜索用时 937 毫秒
121.
Chencheng Dai Yuanmiao Sun Gao Chen Adrian C. Fisher Zhichuan J. Xu 《Angewandte Chemie (International ed. in English)》2020,59(24):9418-9422
Nitrates are widely used as fertilizer and oxidizing agents. Commercial nitrate production from nitrogen involves high‐temperature‐high‐pressure multi‐step processes. Therefore, an alternative nitrate production method under ambient environment is of importance. Herein, an electrochemical nitrogen oxidation reaction (NOR) approach is developed to produce nitrate catalyzed by ZnFexCo2?xO4 spinel oxides. Theoretical and experimental results show Fe aids the formation of the first N?O bond on the *N site, while high oxidation state Co assists in stabilizing the absorbed OH? for the generation of the second and third N?O bonds. Owing to the concerted catalysis, the ZnFe0.4Co1.6O4 oxide demonstrates the highest nitrate production rate of 130±12 μmol h?1 gMO?1 at an applied potential of 1.6 V versus the reversible hydrogen electrode (RHE). 相似文献
122.
Stereoscopic particle image velocimetry applied to liquid flows 总被引:7,自引:5,他引:7
A twin-camera stereoscopic system has been developed to extend conventional high image-density Particle Image Velocimetry (PIV) to three-dimensional vectors on planar domains. The stereoscopic velocimeter performs with extremely high accuracy. Translation tests have yielded errors (rms) of 0.2% of full-scale for the in-plane displacement, and 0.8% of full-scale for the out-of-plane component, both of which agree with the errors predicted by an uncertainty analysis. In addition, modified techniques in hardware and software have enabled the stereoscopic system to perform successfully when acquiring images through a thick liquid layer, wherein previously the aberrations arising due to the liquid-air interface have restricted the use of such systems. With these techniques, the stereoscopic system, in combination with a simple method for image-shifting, is able to accurately measure threedimensional velocity fields in liquids. This is demonstrated by measurements of the helical, three-dimensional flow induced by a rotating disk in glycerine. 相似文献
123.
Gabriela Pin-Zrate Fernanda Reyes-Riquelme Ma Beatriz Snchez-Monroy Mnica Velasco-Torrez Mariano Martínez-Vzquez Christian Adrian Crdenas-Monroy Beatriz Hernandez-Tllez Katia Jarquín-Yez Miguel ngel Herrera-Enríquez Andrs Eliú Castell-Rodríguez 《Molecules (Basel, Switzerland)》2022,27(4)
Dendritic cells are antigen-presenting cells, which identify and process pathogens to subsequently activate specific T lymphocytes. To regulate the immune responses, DCs have to mature by the recognition of TLR ligands, TNFα or IFNγ. These ligands have been used as adjuvants to activate DCs in situ or in vitro, with toxic effects. It has been shown that some molecules affect the immune system, e.g., Masticadienonic acid (MDA) and 3α-hydroxy masticadienoic acid (3α-OH MDA) triterpenes naturally occurring in several medicinal plants, since they activate the nitric oxide synthase in macrophages and induce T lymphocyte proliferation. The DCs maturation induced by MDA or 3a-OH MDA was determined by incubating these cells with MDA or 3α-OH MDA, and their phenotype was afterwards analyzed. The results showed that only 3α-OH MDA was able to induce DCs maturation. When mice with melanoma were inoculated with DCs/3α-OH MDA, a decreased tumor growth rate was observed along with an extended cell death area within tumors compared to mice treated with DCs incubated with MDA. In conclusion, it is proposed that 3α-OH MDA may be an immunostimulant molecule. Conversely, it is proposed that MDA may be a molecule with anti-inflammatory properties. 相似文献
124.
A study of the effect of step excrescences and free‐stream disturbances on boundary layer stability
下载免费PDF全文
![点击此处可从《国际流体数值方法杂志》网站下载免费的PDF全文](/ch/ext_images/free.gif)
In this work, a study of the mechanism by which free‐stream acoustic and vorticity disturbances interact with a boundary layer flow developing over a flat plate featuring a step excrescence located at a certain distance from a blunt leading edge is included. The numerical tool is a high‐fidelity implicit numerical algorithm solving for the unsteady, compressible form of the Navier–Stokes equations in a body‐fitted curvilinear coordinates and employing high‐accurate compact differencing schemes with Pade‐type filters. Acoustic and vorticity waves are generated using a source term in the momentum and energy equations, as opposed to using inflow boundary conditions, to avoid spurious waves that may propagate from boundaries. The results show that the receptivity to surface step excrescences is largely the result of an overall adverse pressure gradient posed by the step, and that the free‐stream disturbances accelerate the generation of instabilities in the downstream. As expected, it is found that the acoustic disturbance interacting with the surface imperfection is more efficient in exciting the Tollmien–Schlichting waves than the vorticity disturbance. The latter generates Tollmien–Schlichting waves that are grouped in wave packets consistent with the wavelength of the free‐stream disturbance. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
125.
126.
Sonic boom focusing phenomenon can be predicted using the solution to the nonlinear Tricomi equation which is a hybrid (hyperbolic‐elliptic) second‐order partial differential equation. In this paper, the hyperbolic conservation law form is derived, which is valid in the entire domain. In this manner, the presence of two regions where the equation behaves differently (hyperbolic in the upper and elliptic in the lower half‐plane) is avoided. On the upper boundary, a new mixed boundary condition for the acoustic pressure is employed. The discretization is carried out using a discontinuous Galerkin (DG) method combined with a Runge–Kutta total‐variation diminishing scheme. The results show the accuracy of DG methods to solve problems involving sharp gradients and discontinuities. Comparisons with analytical results for the linear case, and other numerical results using classical explicit and compact finite difference schemes and weighted essentially non‐oscillatory schemes are included. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
127.
Ciprian Dragan Adrian Samuila Subhankar Das Dan Iancu Mihai Bilici Lucian Dascalescu 《Journal of Electrostatics》2009,67(2-3):184-188
The aim of this study is to refine the understanding of the tribo-electrostatic phenomena that can affect the efficiency of suction-type dilute-phase transport systems. The study was conducted with mm-size ABS-PC particles, a granular material originating from genuine information technology wastes. The tribo-charging process was modelled using the response surface method of experimental design. The controlled variables were the granular material feed rate and the aspirating air speed rate. The monitored variable was the charge imparted to a well-defined section of the duct and which is equal to the charge transferred to the particles passing through that section of the pneumatic transport system. An induction type sensor connected to an electrometer has been employed for the measurements. The data were processed by a virtual instrument developed in LabView. A commercial software package was employed for estimating the effects of the various factors and predicting the optimum operating conditions, which were then confirmed by a final experiment. 相似文献
128.
Shankari V. Rajagopal Kurt M. Fujiwara Ruwan Senaratne Kevin Singh Zachary A. Geiger David M. Weld 《Annalen der Physik》2017,529(8)
Ultracold atomic physics experiments offer a nearly ideal context for the investigation of quantum systems far from equilibrium. We describe three related emerging directions of research into extreme non‐equilibrium phenomena in atom traps: quantum emulation of ultrafast atom‐light interactions, coherent phasonic spectroscopy in tunable quasicrystals, and realization of Floquet matter in strongly‐driven lattice systems. We show that all three should enable quantum emulation in parameter regimes inaccessible in solid‐state experiments, facilitating a complementary approach to open problems in non‐equilibrium condensed matter. 相似文献
129.
Adrian K. Y. Lam Craig A. Hutton Richard A. J. O'Hair 《Rapid communications in mass spectrometry : RCM》2010,24(17):2591-2604
A combination of electrospray ionisation (ESI), multistage and high‐resolution mass spectrometry experiments was used to compare the gas‐phase chemistry of the amino acids histidine (1), 2‐oxo‐histidine (2), and 2‐thioxo‐histidine (3). Collision‐induced dissociation (CID) of all three different proton‐bound heterodimers of these amino acids led to the relative gas‐phase proton affinity order of: histidine >2‐thioxo‐histidine >2‐oxo‐histidine. Density functional theory (DFT) calculations confirm this order, with the lower proton affinities of the oxidised histidine derivatives arising from their ability to adopt the more stable keto/thioketo tautomeric forms. All protonated amino acids predominately fragment via the combined loss of H2O and CO to yield a1 ions. Protonated 2 and 3 also undergo other small molecule losses including NH3 and the imine HN=CHCO2H. The observed differences in the fragmentation pathways are rationalised through DFT calculations, which reveal that while modification of histidine via the introduction of the oxygen atom in 2 or the sulfur atom in 3 does not affect the barriers against the loss of H2O+CO, barriers against the losses of NH3 and HN=CHCO2H are lowered relative to protonated histidine. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
130.
An ultra-high speed, time-resolved particle image velocimetry (PIV) system is developed to measure velocity fields created
by explosive detonators. When initiated into a gas, the detonators generate blast waves that propagate outwards from the origin
of initiation at supersonic speeds. The PIV system consists of a custom eight-pulse Nd:YAG laser system and an ultra-high
speed camera system comprising four dual-frame CCD cameras optically combined to share a single optic axis. The system is
capable of sampling the flow field four times at up to 333 MHz or eight times at up to 8 MHz. System development is discussed,
and preliminary application to the complex flow behind the blast wave from an exploding bridge wire detonator is demonstrated. 相似文献