全文获取类型
收费全文 | 6205篇 |
免费 | 1060篇 |
国内免费 | 812篇 |
专业分类
化学 | 4275篇 |
晶体学 | 43篇 |
力学 | 447篇 |
综合类 | 34篇 |
数学 | 765篇 |
物理学 | 2513篇 |
出版年
2024年 | 8篇 |
2023年 | 128篇 |
2022年 | 155篇 |
2021年 | 179篇 |
2020年 | 221篇 |
2019年 | 241篇 |
2018年 | 175篇 |
2017年 | 182篇 |
2016年 | 265篇 |
2015年 | 291篇 |
2014年 | 297篇 |
2013年 | 364篇 |
2012年 | 536篇 |
2011年 | 604篇 |
2010年 | 408篇 |
2009年 | 329篇 |
2008年 | 424篇 |
2007年 | 378篇 |
2006年 | 367篇 |
2005年 | 339篇 |
2004年 | 288篇 |
2003年 | 203篇 |
2002年 | 181篇 |
2001年 | 146篇 |
2000年 | 117篇 |
1999年 | 157篇 |
1998年 | 114篇 |
1997年 | 122篇 |
1996年 | 130篇 |
1995年 | 120篇 |
1994年 | 89篇 |
1993年 | 72篇 |
1992年 | 61篇 |
1991年 | 71篇 |
1990年 | 69篇 |
1989年 | 54篇 |
1988年 | 42篇 |
1987年 | 31篇 |
1986年 | 37篇 |
1985年 | 29篇 |
1984年 | 15篇 |
1983年 | 9篇 |
1982年 | 12篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1979年 | 1篇 |
1976年 | 2篇 |
1974年 | 1篇 |
1957年 | 3篇 |
排序方式: 共有8077条查询结果,搜索用时 515 毫秒
961.
为提高由NLDFT计算值确定活性炭孔径分布(PSD)的精度,根据测得的77K氮在非石墨化碳黑BP460和椰壳活性炭K05上的吸附数据,比较了吸附空间及壁面结构采取不同假设对计算结果的影响。结果表明,常规将活性炭吸附空间近似为无限尺寸的石墨化碳黑表面构成的狭缝孔,并由Lorenz-Berthelot混合法则确定相互作用参数,计算值在较低压力区域和试验值之间的偏差明显;而将吸附壁面结构近似为非石墨化碳黑,并由表面粗糙度和石墨晶格分布的误差函数修正相互作用参数后,计算结果和试验值吻合良好。分析结果时发现,归一化方法和考虑周边吸附质分子作用的加权函数是影响NLDFT计算结果准确性的关键因素。 相似文献
962.
搭建了一套研究金属和金属氧化物表面的超快激发态电子动力学和光化学动力学的飞秒双光子光电子能谱仪. 该装置将半球形电子能量分析仪和成像技术相结合,同时测量光电子的能量和角度分布.通过Mach-Zehnder干涉仪测量时间分辨的双光子光电子能谱获得超快激发电子态的动力学信息. 这一功能在Cu(111)上得到了证实. 另外还发展了一个通过实时测量双光子光电子能谱来研究表面光化学的方法,并成功应用到CH3CH2OH/TiO2(110)体系. 研究表明,只有将两种方法结合起来才能正确地研究光诱导的表面激发共振的动力学. 相似文献
963.
964.
Shi-liang Li Dao-xin Yao Yi-ming Qiu Hye Jung Kang E. W. Carlson Jiang-ping Hu Gen-fu Chen Nan-lin Wang Peng-cheng Dai 《Frontiers of Physics in China》2010,5(2):161-165
We use inelastic neutron scattering to study the low-energy spin excitations of polycrystalline samples of nonsuperconducting
CeFeAsO and superconducting CeFeAsO0.84F0.16. Two sharp dispersionless modes are found at 0.85 and 1.16 meV in CeFeAsO below the Ce antiferromagnetic (AF) ordering temperature
of T
N
Ce ˜ 4 K. On warming to above T
N
Ce ˜ 4 K, these two modes become one broad dispersionless mode that disappears just above the Fe ordering temperature T
N
Fe ˜ 140 K. For superconducting CeFeAsO0.84F0.16, where Fe static AF order is suppressed, we find a weakly dispersive mode center at 0.4 meV that may arise from short-range
Ce-Ce exchange interactions. Using a Heisenberg model, we simulate powder-averaged Ce spin wave excitations. Our results show
that we need both Ce spin wave and crystal electric field excitations to account for the whole spectra of low-energy spin
excitations. 相似文献
965.
The gradient method for the symmetric positive definite linear system
is as follows
where
is the residual of the system at xk and αk is the stepsize. The stepsize
is optimal in the sense that it minimizes the modulus
, where λ1 and λn are the minimal and maximal eigenvalues of A respectively. Since λ1 and λn are unknown to users, it is usual that the gradient method with the optimal stepsize is only mentioned in theory. In this
paper, we will propose a new stepsize formula which tends to the optimal stepsize as
. At the same time, the minimal and maximal eigenvalues, λ1 and λn, of A and their corresponding eigenvectors can be obtained.
This research was initiated while the first author was visiting The Hong Kong Polytechnic University.
This author was supported by the Chinese NSF grants (No. 40233029 and 101071104) and an innovation fund of Chinese Academy
of Sciences.
This author was supported by a grant from the Research Committee of the Hong Kong Polytechnic University (A-PC36). 相似文献
(1) |
966.
Li X Chen W Zhan Q Dai L Sowards L Pender M Naik RR 《The journal of physical chemistry. B》2006,110(25):12621-12625
The interactions of various polypeptides with individual carbon nanotubes (CNTs), both multiwall (MW) and single wall (SW), were investigated by atomic force microscopy (AFM). While adhesion forces arising from electrostatic attraction interactions between the protonated amine groups of polylysine and carboxylic groups on the acid-oxidized multi-wall carbon nanotubes (Ox-MWCNTs) dominate the interaction at a low pH, weaker adhesion forces via the hydrogen bonding between the neutral -NH2 groups of polylysine and -COO- groups of the Ox-MWCNTs were detected at a high pH. The adhesion force was further found to increase with the oxidation time for Ox-MWCNTs and to be negligible for oxidized single-wall carbon nanotubes (Ox-SWCNTs) because carboxylate groups were only attached onto the nanotube tips in the latter whereas onto both the nanotube tips and sidewall in the former. Furthermore, it was demonstrated that proteins containing aromatic moieties, such as polytryptophan, showed a stronger adhesion force with Ox-MWCNTs than that of polylysine because of the additional pi-pi stacking interaction between the polytryptophan chains and CNTs. 相似文献
967.
Fan L Song H Zhao H Pan G Yu H Bai X Li S Lei Y Dai Q Qin R Wang T Dong B Zheng Z Ren X 《The journal of physical chemistry. B》2006,110(26):12948-12953
An inorganic-organic hybrid semiconductor, ZnS/CHA (CHA = cyclohexylamine) nanocomposites was successfully synthesized via a solvothermal method using CHA as solvent, which yielded uniform and ultralong nanowires with widths of 100-1000 nm and lengths of 5-20 microm. Changing the reaction conditions could alter the morphology and optical properties of the nanocomposites. The periodic layer subnanometer structures were identified by high-resolution transmission electron microscopy (HR-TEM) images, with thickness of approximately 2 nm. The composites exhibited a very large blue-shift in their optical absorption edge as well as an exciton excitation band due to a strong quantum confinement effect caused by the internal subnanometer-scale structures. The pure hexagonal wurtzite ZnS nanowires were also obtained by extracting the ZnS/CHA nanocomposites with dimethyl formamide (DMF). In addition, the luminescent properties of exciton and defect-related transitions in different samples of ZnS/CHA were discussed in detail. 相似文献
968.
Coherent control of THz wave generation in ambient air 总被引:1,自引:0,他引:1
Our study of THz wave generation in the pulsed laser induced air plasma with individually controlled phase, polarization, and amplitude of the optical fundamental wave (omega) and its second harmonic (2omega) indicates that the third-order nonlinear optical process mixing the omega and 2omega beams in the ionized plasma is the main mechanism of the efficient THz wave generation. The polarity and the strength of the emitted THz field are completely controlled by the relative phase between the omega and 2omega waves. The measured THz field amplitude is proportional to the pulse energy of the fundamental beam and to the square root of the pulse energy of the second-harmonic beam once the total optical pulse energy exceeds the plasma formation threshold. The optimal THz field is achieved when all waves (omega, 2omega, and THz waves) are at the same polarization in the four-wave-mixing process. 相似文献
969.
We point out a novel manifestation of many-body correlations in the linear optical response of electrons confined in a quantum well. Namely, we demonstrate that along with the conventional absorption peak at a frequency omega close to the intersubband energy delta, there exists an additional peak at frequency h omega approximately = 2delta. This new peak is solely due to electron-electron interactions, and can be understood as excitation of two electrons by a single photon. The actual peak line shape is comprised of a sharp feature, due to excitation of pairs of intersubband plasmons, on top of a broader band due to absorption by two single-particle excitations. The two-plasmon contribution allows us to infer intersubband plasmon dispersion from linear absorption experiments. 相似文献
970.