全文获取类型
收费全文 | 12511篇 |
免费 | 1117篇 |
国内免费 | 702篇 |
专业分类
化学 | 8439篇 |
晶体学 | 121篇 |
力学 | 499篇 |
综合类 | 51篇 |
数学 | 1484篇 |
物理学 | 3736篇 |
出版年
2023年 | 159篇 |
2022年 | 293篇 |
2021年 | 284篇 |
2020年 | 308篇 |
2019年 | 326篇 |
2018年 | 253篇 |
2017年 | 264篇 |
2016年 | 404篇 |
2015年 | 415篇 |
2014年 | 485篇 |
2013年 | 722篇 |
2012年 | 899篇 |
2011年 | 1025篇 |
2010年 | 651篇 |
2009年 | 676篇 |
2008年 | 769篇 |
2007年 | 734篇 |
2006年 | 647篇 |
2005年 | 562篇 |
2004年 | 532篇 |
2003年 | 455篇 |
2002年 | 404篇 |
2001年 | 330篇 |
2000年 | 270篇 |
1999年 | 206篇 |
1998年 | 162篇 |
1997年 | 139篇 |
1996年 | 175篇 |
1995年 | 131篇 |
1994年 | 150篇 |
1993年 | 124篇 |
1992年 | 117篇 |
1991年 | 96篇 |
1990年 | 106篇 |
1989年 | 82篇 |
1988年 | 90篇 |
1987年 | 61篇 |
1986年 | 69篇 |
1985年 | 95篇 |
1984年 | 69篇 |
1983年 | 68篇 |
1982年 | 49篇 |
1981年 | 46篇 |
1980年 | 47篇 |
1979年 | 34篇 |
1977年 | 37篇 |
1976年 | 37篇 |
1975年 | 34篇 |
1974年 | 48篇 |
1973年 | 44篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
J. Ren P. C. W. Fung C. Chang G. X. Shen G. Lu F. H. Y. Chan K. J. Liu J. Shen 《Applied magnetic resonance》2007,32(3):243-255
Electron paramagnetic resonance (EPR) spin trapping technology is a sensitive and unambiguous method for detection of nitric
oxide (NO). Due to the short lifetime, NO must be trapped before EPR measurement. There are two EPR spin trapping techniques
used currently, including the detections of EPR signals of diethyldithiocarbamate-iron-nitric oxide (DETC2-Fe2+-NO) and nitrosyl hemoglobin (HbNO). In this study, we firstly investigated the kinetics of the EPR signal of DETC2-Fe2+-NO in normal and ischemia-reperfused kidneys. In normal rat kidneys, the signal of DETC2-Fe2+-NO was found at 5 min after the spin trappers Fe2+/DETC were administrated, the peak concentration was at 15 min and the period with relatively stable signal intensity was
at the time range from 15 to 70 min. In the ischemia-reperfused rat kidneys, the signal of DETC2-Fe2+-NO was increased at 30 min of ischemia and decreased at 60 min of ischemia after the occlusion of renal artery (corresponding
to the time course of 60 and 90 min after Fe2+/DETC injection respectively). We then investigated the EPR signal of HbNO in blood. No characteristic HbNO signal was found
in the rats of the sham control and 30 min of ischemia. An HbNO signal occurred in the rats exposed to 60 min of ischemia
and it became pronounced with increased duration of reperfusion. The signal intensity reached a plateau at 150 min of reperfusion.
The results suggest that the DETC2-Fe2+-NO signal can be only suitable for the NO measurement in the short-term ischemia-reperfusion model, whereas the HbNO signal
can be applied to represent NO in the relatively long-term ischemia-reperfusion model. In addition, NG-nitro-L-arginine (L-NAME) and allopurinol were used to identify the source of NO. By detecting the HbNO signal, we demonstrated
that the activation of xanthine oxidase is an important source of NO formation at the long-term period of ischemia and reperfusion.
Authors' address: Jiangang Shen, School of Chinese Medicine, University of Hong Kong, 10 Sassoon Road, Hong Kong SAR, China 相似文献
952.
Gun Sang Jeon Chia-Chen Chang Jainendra K. Jain 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,55(3):271-282
We review and extend the composite fermion theory for semiconductor quantum dots in high magnetic fields. The mean-field model
of composite fermions is unsatisfactory for the qualitative physics at high angular momenta.
Extensive numerical calculations demonstrate that the microscopic CF theory,
which incorporates interactions between composite fermions, provides an excellent qualitative and quantitative account
of the quantum dot ground state down to the largest angular momenta studied,
and allows systematic improvements by inclusion of mixing between composite
fermion Landau levels (called Λ levels). 相似文献
953.
测量了氢气离子转动分辨的真空紫外脉冲场电离光电子谱.涵盖了15.30?18.09 eV能量范围内的H2+(X2§+g , v+=0?18,N+=0?5)?H2(X1§+g , v00=0, J00=0?4)的电离跃迁. 通过基于Buckingham-Orr-Sichel(BOS)模型的光谱拟合和对氢气离子振动带H2+(X2§+g ,v+=0?18)的转动光谱的分析, 发现实验上只观察到对应于¢N=N+-J00=0,§2的转动跃迁. 振动量子数v+ 越高,¢N=0的转动跃迁越占主导地位, 而转动谱线强度受邻 相似文献
954.
W.Y. Zhang C.H. Chiu L.C. Zhang K. Biswas H. Ehrenberg W.C. Chang J. Eckert 《Journal of magnetism and magnetic materials》2007
The effect of refractory element addition on phase transformation, crystallization behavior and magnetic properties of Pr8.5Fe81.5B10 (addition-free) and Pr8.5Fe81.5M2B10 (M=V, Cr, Nb, Zr, Ti) ribbons has been investigated. The annealed addition-free ribbon as well as the samples with V or Cr additions are mainly composed of the metastable Pr2Fe23B3 phase, whereas annealed ribbons with Nb, Zr or Ti additions primarily consist of Pr2Fe14B and a minor amount of Fe3B/boride. The complete suppression of the metastable Pr2Fe23B3 phase due to Nb, Zr or Ti additions leads to a significant enhancement of the magnetic properties. For example, the remanence, the coercivity and the energy product are remarkably increased from 2.5 kG, 0.4 kOe and 0.2 MG Oe for the addition-free material to 9.2 kG, 4.7 kOe and 7.6 MG Oe for the specimens with Nb addition. The successful elimination of the metastable Pr2Fe23B3 phase is believed to profit from two factors: (a) Nb, Zr or Ti atoms substitute the Pr site, comparatively increase the Pr content, and thus inhibit the nucleation of Pr-lean Pr2Fe23B3 phases, and (b) the formation of Nb, Zr, or Ti borides consumes some part of B, which hinders the generation of the B-rich Pr2Fe23B3 phase. 相似文献
955.
Composite coating of Ni-Co/Al2O3 was deposited in Ce2(SO4)3 containing electrolyte by pulse reverse current (PRC) method. The effect of Ce2(SO4)3 in electrolyte on morphology, microstructure, composition, micro-hardness and residual macrostress of composite coating was investigated. The results indicates that with addition of Ce2(SO4)3 in electrolyte, the composite coating becomes uniform, compact and possesses finer grains, the composite content of Al2O3 is enhanced, the micro-hardness of composite coating is improved, while the residual macrostress is decreased. 相似文献
956.
Surface status and size influences of nickel nanoparticles on sulfur compound adsorption 总被引:1,自引:0,他引:1
Metallic nickel nanoparticles were incorporated on mesoporous silica to remove sulfur compounds in diesel selectively. In the first method, nickel nanoparticles were formed on mesoporous silica SBA-15 by impregnation and subsequent reduction of nickel nitrate. The sulfur adsorption capacity was strongly dependent on the nickel loading and the average nickel particle size. In the second method, nickel nanoparticles were synthesized in solution in the presence of a capping agent and then incorporated in mesoporous silica MCF by sonication. Although these particles maintain their sizes on the MCF surface after heat treatment, capping agent remaining on the Ni particle surface might interfere the adsorption of sulfur compounds. 相似文献
957.
In this report, we demonstrate the efficient generation of collinearly propagating photon pairs in a bulk periodically poled potassium titanyl phosphate pumped by a cw laser. The detected coincidence counts are more than 7400/s with 3.58 mW pump power in a Hanbury-Brown-Twiss-type experiment. The estimated photon pair production rate is about 0.73 MHz/mW. This is very promising for some applications, such as quantum key distribution, proof of the Bell-inequality, preparation of single photon states in broadband wave packets, Franson-type interference and so on. 相似文献
958.
Al-doped ZnO (AZO) transparent conductive thin films were grown by magnetron sputtering with AZO (98 wt.% ZnO, 2 wt.% Al2O3) ceramic target in Ar + H2 ambient at a relatively low temperature of 100 °C. To investigate the dependence of crystalline and properties of as-grown AZO films on the H2-flux, X-ray diffraction (XRD), X-ray photoemission spectrometer (XPS), Hall and transmittance spectra measurements were employed to analyze the AZO samples deposited with different H2-flux. The results indicate that H2-flux has a considerable influence on the transparent conductive properties of AZO films. The resistivity of 4.15 × 10−4 Ω cm and the average transmittance of more than 94% in the visible range were obtained with the optimal H2-flux of 1.0 sccm. Such a low temperature growing method present here may be especially useful for some low-melting point photoelectric devices and substrates. 相似文献
959.
Electrodynamic Analysis of Dissipative Electromagnetic Materials Based on Fractional Derivative
下载免费PDF全文
![点击此处可从《中国物理快报》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The generalized Lagrangian is defined in a dissipative electromagnetic medium on the basis of the combination of dynamical analysis and fractional derivative. Lorentz medium models are obtained by formulating relevant Euler-Lagrange equations. The invariance is obtained subsequently by investigating the invariance of time variation in the system, and then the relation between the related Hamiltonian and electromagnetic energy density is investigated. Canonical equations are obtained eventually. The electrodynamic interpretation on dissipative electromagnetic systems is revealed. 相似文献
960.
Kyung Ah Jeon Hyo Jeong Son Chang Eun Kim Jong Hoon Kim Sang Yeol Lee 《Physica E: Low-dimensional Systems and Nanostructures》2007,37(1-2):222
ZnO nanowires were fabricated on c-plane (0 0 0 1), a-plane (1 1 2¯ 0) sapphire, and boron doped p-type (1 0 0) Si substrates in vacuum furnace by simple physical vapor deposition. Room temperature photoluminescence spectra of the nanowires show the near band-edge emission and the deep-level green light emission. The ZnO nanowires formed on sapphire (1 1 2¯ 0) substrates exhibited enhancement on optical properties and better crystalline structures than those of nanowires grown on other substrates. The formation mechanism and the effect of substrate direction on structural and optical properties of the nanowires are discussed. 相似文献