全文获取类型
收费全文 | 4623篇 |
免费 | 463篇 |
国内免费 | 440篇 |
专业分类
化学 | 2991篇 |
晶体学 | 79篇 |
力学 | 171篇 |
综合类 | 30篇 |
数学 | 662篇 |
物理学 | 1593篇 |
出版年
2023年 | 94篇 |
2022年 | 133篇 |
2021年 | 155篇 |
2020年 | 169篇 |
2019年 | 140篇 |
2018年 | 135篇 |
2017年 | 141篇 |
2016年 | 188篇 |
2015年 | 167篇 |
2014年 | 194篇 |
2013年 | 276篇 |
2012年 | 336篇 |
2011年 | 330篇 |
2010年 | 208篇 |
2009年 | 248篇 |
2008年 | 264篇 |
2007年 | 239篇 |
2006年 | 191篇 |
2005年 | 190篇 |
2004年 | 124篇 |
2003年 | 114篇 |
2002年 | 111篇 |
2001年 | 88篇 |
2000年 | 75篇 |
1999年 | 71篇 |
1998年 | 52篇 |
1997年 | 47篇 |
1996年 | 72篇 |
1995年 | 71篇 |
1994年 | 60篇 |
1993年 | 62篇 |
1992年 | 64篇 |
1991年 | 59篇 |
1990年 | 54篇 |
1989年 | 45篇 |
1988年 | 36篇 |
1987年 | 36篇 |
1986年 | 34篇 |
1985年 | 40篇 |
1984年 | 43篇 |
1983年 | 29篇 |
1982年 | 23篇 |
1981年 | 17篇 |
1980年 | 18篇 |
1979年 | 24篇 |
1977年 | 15篇 |
1976年 | 17篇 |
1975年 | 15篇 |
1974年 | 17篇 |
1973年 | 25篇 |
排序方式: 共有5526条查询结果,搜索用时 15 毫秒
81.
We discuss the nonlinear propagation of relativistically intense electromagnetic waves into collisionless plasmas with special
emphasis on one dimensional plane wave solutions of the propagating, standing and modulated types. These solutions exhibit
a rich variety of phenomena associated with relativistic electron mass variation and coupling between transverse electromagnetic
and longitudinal fields. They have important applications to problems of laser propagation, self-focusing in overdense plasmas,
particle and photon acceleration and to electromagnetic radiation around pulsars. 相似文献
82.
Wu Wenwei Fan Yanjin Wu Xuehang Liao Sen Li Shushu 《Journal of Physics and Chemistry of Solids》2009,70(3-4):584-587
The layered nanocrystalline NH4MnPO4·H2O was obtained by grinding MnSO4·H2O and (NH4)3PO4·3H2O in the presence of surfactant PEG-400 via a solid-state reaction at room temperature, maintaining the mixture at room temperature for 12 h, washing the mixture with water, and drying at 60 °C. The resulting NH4MnPO4·H2O and its products of thermal decomposition were characterized using thermogravimetry and differential thermal analyses (TG/DTA), IR, X-ray powder diffraction (XRD), scanning electron microscopy (SEM), UV–vis, and magnetic susceptibility. The data showed that when dried at 60 °C for 5 h, highly crystallized orthorhombic NH4MnPO4·H2O (space group Pmnm(59)) was obtained with an average particle size of 45 nm and an average interlayer distance of 0.8701 nm. On the other hand, monoclinic nanocrystalline Mn2P2O7 with space group C2/m(12) was obtained when the product was calcined at 600 °C for 3 h. Magnetic susceptibility measurements from room temperature to 2.5 K point to ferrimagnetic ordering at TN~17 K. 相似文献
83.
In this paper, we study the 0+ nonet mesons as tetraquark states with interpolating currents inspired by the color-magnetic wave function. This wave function
is the eigenfunction of an effective color-magnetic Hamiltonian with the lowest eigenvalue, meaning that the state depicted
by this wave function is the most stable one and is the most probable to be observed in experiments. We perform an OPE calculation
up to dimension-eight condensates and find that the best QCD sum rule is achieved when the current inspired by the color-magnetic
wave function is a proper mixture of the tensor and pseudoscalar diquark-antidiquark bound states. Compared with previous
results, to sigma(600) and kappa(800), our results appear better, due to larger pole contribution. The direct instanton contributions
are also considered, which yields a consistent result with previous OPE results. Finally, we also discuss the h¢ \eta{^\prime} problem as a possible six-quark state. 相似文献
84.
S. Schwarz M. Block G. Bollen C. M. Campbell M. Facina R. Ferrer C. M. Folden III A. A. Kwiatkowski D. J. Morrissey G. K. Pang A. M. Prinke R. J. Ringle J. Savory P. H. Schury 《The European Physical Journal A - Hadrons and Nuclei》2009,42(3):323-326
The low-energy beam and ion trap facility LEBIT at NSCL/MSU is at present the only facility where precision experiments are performed with stopped rare isotope beams produced by fast-beam fragmentation. LEBIT combines high-pressure-gas stopping with advanced ion manipulation techniques to provide brilliant low-energy beams. So far these beams have mainly been used for mass measurements on short-lived rare isotopes with a 9.4T Penning trap mass spectrometer. Recent examples include 70m Br , located at the proton dripline, 32Si and the iron isotopes 63-65Fe . While the measurement of 32Si helps to solve a long-standing dispute over the validity of the isobaric multiplet mass equation (IMME) for the A = 32 , T = 2 multiplet, the mass measurements of 65m,g Fe marked the first time a nuclear isomeric state has been discovered by Penning trap mass spectrometry. 相似文献
85.
高超声速飞行器高温流场对激光武器毁伤效应的影响 总被引:2,自引:0,他引:2
以美国ABL系统激光武器为例,分析了高超声速飞行器高温流场气体影响激光武器毁伤效应的一些主要因素,包括气体击穿、等离子体屏蔽效应、烧蚀产物颗粒的影响。结果表明:通常情况下,流场电子数密度小于1017cm-3,流场本身等离子体特性不会引起对激光的等离子体屏蔽效应;只有在0.5 km射程以内和宽脉冲激光引起的高压流场(约10 MPa以上)气体击穿,才会导致明显的等离子体屏蔽效应,但在实际战场条件下这种情况一般不会发生;对采用烧蚀手段进行防热的飞行器而言,飞行高度大于10 km,并且基于自由来流流量的无量纲化烧蚀流量小于10-2左右时,烧蚀产物颗粒不会引起激光的衰减。 相似文献
86.
用高温熔融法制备了Tm3+/Ho3+/Yb3+共掺碲酸盐玻璃(TeO2-ZnO-La2O3)样品,测试了玻璃样品的吸收光谱和上转换发光光谱,分析了上转换发光机理.结果发现:在975 nm波长激光二极管(LD)激励下,制备的碲酸盐玻璃样品可以观察到强烈的红光(662 nm)、绿光(546 nm)和蓝光(480 nm)三基色上转换发光,红光对应于Tm3+离子
关键词:
碲酸盐玻璃
上转换发光
白光
3+/Ho3+/Yb3+共掺')" href="#">Tm3+/Ho3+/Yb3+共掺 相似文献
87.
Synthesis and characterization of Sr3Al2O6:Eu2+, Dy3+ phosphors prepared by sol-gel-combustion processing 下载免费PDF全文
A type of red luminescent Sr3Al2O6:Eu2+, Dy3+ phosphor powder is synthesised by sol-gel-combustion processing, with metal nitrates used as the source of metal ions and citric acid as a chelating agent of metal ions. By tracing the formation process of the sol-gel, it is found that it is necessary to reduce the amount of NO3- by dropping ethanol into the solution for forming a stable and homogeneous sol-gel. Thermogravimetric and Differential Scanning Calorimeter Analysis, x-ray diffractionmeter, scanning electron microscopy and photoluminescence spectroscopy are used to investigate the luminescent properties of the as-synthesised Sr3Al2O6:Eu2+, Dy3+. The results reveal that the Sr3Al2O6 crystallises completely when the combustion ash is sintered at 1250 C. The excitation and the emission spectra indicate that the excitation broadband lies mainly in a visible range and the phosphors emit a strong light at 618 nm under the excitation of 472 nm. The afterglow of (Sr0.94Eu0.03Dy0.03)3Al2O6 phosphors sintered at 1250 ℃ lasts for over 1000 s when the excited source is cut off. 相似文献
88.
89.
90.