全文获取类型
收费全文 | 9316篇 |
免费 | 1381篇 |
国内免费 | 333篇 |
专业分类
化学 | 821篇 |
晶体学 | 45篇 |
力学 | 30篇 |
综合类 | 19篇 |
数学 | 79篇 |
物理学 | 5904篇 |
无线电 | 4132篇 |
出版年
2024年 | 13篇 |
2023年 | 31篇 |
2022年 | 75篇 |
2021年 | 137篇 |
2020年 | 157篇 |
2019年 | 74篇 |
2018年 | 97篇 |
2017年 | 274篇 |
2016年 | 300篇 |
2015年 | 292篇 |
2014年 | 644篇 |
2013年 | 413篇 |
2012年 | 869篇 |
2011年 | 767篇 |
2010年 | 541篇 |
2009年 | 619篇 |
2008年 | 912篇 |
2007年 | 849篇 |
2006年 | 874篇 |
2005年 | 663篇 |
2004年 | 523篇 |
2003年 | 411篇 |
2002年 | 194篇 |
2001年 | 194篇 |
2000年 | 155篇 |
1999年 | 129篇 |
1998年 | 125篇 |
1997年 | 100篇 |
1996年 | 93篇 |
1995年 | 68篇 |
1994年 | 82篇 |
1993年 | 62篇 |
1992年 | 58篇 |
1991年 | 43篇 |
1990年 | 47篇 |
1989年 | 31篇 |
1988年 | 21篇 |
1987年 | 16篇 |
1986年 | 17篇 |
1985年 | 14篇 |
1984年 | 12篇 |
1983年 | 10篇 |
1982年 | 8篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 4篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1971年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
191.
192.
《Comptes Rendus Physique》2016,17(8):934-945
Microcavity polaritons are mixed light–matter quasiparticles with extraordinary nonlinear properties, which can be easily accessed in photoluminescence experiments. Thanks to the possibility of designing the potential landscape of polaritons, this system provides a versatile photonic platform to emulate 1D and 2D Hamiltonians. Polaritons allow transposing to the photonic world some of the properties of electrons in solid-state systems, and to engineer Hamiltonians for photons with novel transport properties. Here we review some experimental implementations of polariton Hamiltonians using lattice geometries. 相似文献
193.
Changing the orientational order in liquid-crystal
elastomers leads to internal stresses and changes of the sample
shape. When this effect is induced by light, due to
photoisomerization of constituent molecular moieties, the
photomechanical actuation results. We investigate quantitatively
how the intensity and the polarization of light affect
photoactuation. By studying dissolved, as well as covalently
bonded azo-dyes, we determine the changes in absorption and the
response kinetics. For the first time we compare the response of
aligned monodomain, and randomly disordered polydomain nematic
elastomers, and demonstrate that both have a comparable
photoresponse, strongly dependent on the polarization of light.
Polarization-dependent photoactuation in polydomain elastomers
gives an unambiguous proof of its mechanism since it is the only
experiment that distinguishes from the associated thermal
effects. 相似文献
194.
G. Singla P. Scouflaire J.C. Rolon S. Candel 《Proceedings of the Combustion Institute》2007,31(2):2215-2222
Planar laser induced fluorescence (PLIF) of OH is used to examine flame stabilization in high pressure cryogenic flames formed by injecting a central jet of low speed liquid oxygen surrounded by a high speed gaseous stream of hydrogen or methane. In the LOx/GH2 experiments injection conditions are transcritical as the chamber pressure is above critical but the temperature is below critical . In the LOx/GCH4 experiments the chamber pressure and LOx injection temperature are below critical , . Hydrogen or methane are injected at room temperature LIF images delineate the flame edge in the injector nearfield. The two flames are stabilized in the vicinity of the liquid oxygen injector lip but the anchor point is found to lie closer to the lip in the LOx/GH2 case and its displacement from shot to shot is of a smaller amplitude than that corresponding to the LOx/GCH4 flame. Interpretation of these data is based on a previous analysis which indicates that stabilization is essentially controlled by a dimensionless group formed by comparing the lip thickness to the flame edge thickness Ψ = hs/δf. It is found that Ψ slightly exceeds unity in the LOx/GH2 case essentially fulfilling the stability condition while Ψ < 1 in the LOx/GCH4 case. In this last situation the flame is thicker than the characteristic thickness hs and it is therefore sensitive to the high speed methane stream. Anchoring is imperfect and the flame edge moves with the turbulent eddies shed from the lip. Global stabilization is achieved dynamically but the reactive layer is not well established and the large amplitude motion of the edge is a symptom of a possible lift-off. Theoretical estimates indicate that LOx/GCH4 flame stabilization requires a thicker lip size than the LOx/GH2 propellant couple. 相似文献
195.
Fluorescence imaging of cells and tissue can be used to evaluate β-NADH redox and location. At low temperature, β-NADH fluorescence
intensity increases and therefore sensitivity of imaging increases. In this paper, the temperature dependence of fluorescence
was evaluated for β-NADH in glycerol/water solution and in trehalose/sucrose glass. The average fluorescence lifetime for
NADH in glycerol/water is 0.66 ns, compared with 5.3 ns in trehalose/ sucrose at 20°C. Emission spectra were recorded from
290 to 12 K. The fluorescence of β-NADH in glycerol/water increases ∼16 fold and the emission shifts about 35 nm to the blue
as temperature decreases. Much smaller change is seen for fluorescence of β-NADH in sugar glass. Below 77 K, the β-NADH spectral
features did not change significantly with temperature change, and so no increase in sensitivity is obtained by going to very
low temperatures. It is suggested that the sensitivity of β-NADH fluorescence is related to water relaxation around the excited
state molecule. Differences in water in various tissues may contribute to β-NADH fluorescence changes when cells are altered. 相似文献
196.
培养兴趣,引导创新——《信息光学》理论教学改革实践 总被引:2,自引:0,他引:2
重点研究了针对《信息光学》理论性强的课程和学生在学习过程中兴趣下降以及一知半解等问题,着重从提高学生理论学习兴趣,引导学生创新为出发点,通过改进PPT课件,吸引学生注意,采用深入浅出、举一反三、师生互动、启发式教学方法、理论与实际相结合、教学科研相结合等多种方法和手段,帮助学生建立正确的物理概念,促进学生对数学公式所代表的物理意义的理解,达到改善理论教学效果的目的。同时结合创新性实验建设,培养创新型和复合型人才。 相似文献
197.
CCD抽样对傅里叶变换轮廓术的影响 总被引:1,自引:0,他引:1
从傅里叶变换轮廓术(FTP)原理入手,分析了傅里叶变换过程中频谱的产生,给出了CCD像元信号强度及其经抽样后的变形条纹的表达式,得出了变形条纹的傅里叶频谱式,其频谱是原连续函数的频谱在频域内的无限重复,即"频谱岛"。频谱中除了基频外,还产生了二级、三级等的高级频谱。给出了抽样条件及满足抽样条件的方法:当抽样频率与光栅基频的比值m>4时可以恢复物体的面形,反之不能;减小抽样间隔可以使m>4。给出了实验结果:当m=2.0883时,物体面形没有恢复;当m=16.6667时,物体面形得到了恢复。实验结果证明了理论分析的正确性。 相似文献
198.
Flat and crystalline materials with exceptional nonlinear optical(NLO) properties are highly desirable for their potential applications in integrated NLO photonic devices.Graphdiyne(GD),a new twodimensional(2 D) carbon allotrope,has recently evoked burgeoning research attention by virtue of its tunable bandgap along with a high carrier mobility and extended π-conjugation compared with most conventional optical materials.Here,we experimentally probe the third-order nonlinear optical response of GD dispersed in several common solvents(alcohols) using a femtosecond Z-scan technique.The measured nonlinear optical refractive index is in the order of ~10-8 cm2/W,which is approximately one order of magnitude higher than that of most 2 D materials.In particular,we find that different NLO responses can be observed from GD when dispersed in different solvents,with the strongest NLO response when dispersed in 1-propanol.It is proposed that some intrinsic properties of the solvents,such as the polarity and viscosity,could influence the NLO response of GD materials.Our experimental results confirm the assumptions on the NLO behavior in GD and demonstrate its great potential for future generations of Kerr-effect-based NLO materials and devices. 相似文献
199.
Maxim Polikarpov Irina Snigireva John Morse Vyacheslav Yunkin Sergey Kuznetsov Anatoly Snigirev 《Journal of synchrotron radiation》2015,22(1):23-28
For the first time, single‐crystal diamond planar refractive lenses have been fabricated by laser micromachining in 300 µm‐thick diamond plates which were grown by chemical vapour deposition. Linear lenses with apertures up to 1 mm and parabola apex radii up to 500 µm were manufactured and tested at the ESRF ID06 beamline. The large acceptance of these lenses allows them to be used as beam‐conditioning elements. Owing to the unsurpassed thermal properties of single‐crystal diamond, these lenses should be suitable to withstand the extreme flux densities expected at the planned fourth‐generation X‐ray sources. 相似文献
200.
提出了三种基于少模光纤的全光纤熔融模式选择耦合器. 根据模式匹配原理采用单模光纤与少模光纤熔融连接方式, 运用耦合模理论及光束传播法模拟分析了模式选择耦合器的结构参数对模式选择及耦合特性的影响, 实现了单模光纤中基模到少模光纤中不同阶模式的转换, 以满足不同的应用需求. 实验上以2× 2熔融光纤耦合器为例, 采用对称和非对称熔融拉锥方式, 分别实现了从基模到LP11, LP21模式的转换. 实验结果表明所得到的LP11, LP21模式在1530–1560 nm的波长带宽范围内均有较高的模式纯净度, 且模式耦合效率高于80%, 与理论模拟结果基本一致. 相似文献