全文获取类型
收费全文 | 3362篇 |
免费 | 134篇 |
国内免费 | 53篇 |
专业分类
化学 | 2027篇 |
晶体学 | 46篇 |
力学 | 103篇 |
数学 | 605篇 |
物理学 | 768篇 |
出版年
2023年 | 25篇 |
2022年 | 38篇 |
2021年 | 58篇 |
2020年 | 65篇 |
2019年 | 60篇 |
2018年 | 41篇 |
2017年 | 43篇 |
2016年 | 90篇 |
2015年 | 75篇 |
2014年 | 101篇 |
2013年 | 180篇 |
2012年 | 226篇 |
2011年 | 255篇 |
2010年 | 137篇 |
2009年 | 131篇 |
2008年 | 220篇 |
2007年 | 175篇 |
2006年 | 170篇 |
2005年 | 144篇 |
2004年 | 145篇 |
2003年 | 126篇 |
2002年 | 110篇 |
2001年 | 67篇 |
2000年 | 73篇 |
1999年 | 59篇 |
1998年 | 27篇 |
1997年 | 48篇 |
1996年 | 39篇 |
1995年 | 49篇 |
1994年 | 52篇 |
1993年 | 53篇 |
1992年 | 57篇 |
1991年 | 42篇 |
1990年 | 38篇 |
1989年 | 32篇 |
1988年 | 23篇 |
1987年 | 18篇 |
1986年 | 21篇 |
1985年 | 32篇 |
1984年 | 31篇 |
1982年 | 15篇 |
1981年 | 17篇 |
1980年 | 15篇 |
1979年 | 21篇 |
1978年 | 18篇 |
1977年 | 9篇 |
1976年 | 11篇 |
1975年 | 11篇 |
1974年 | 15篇 |
1973年 | 10篇 |
排序方式: 共有3549条查询结果,搜索用时 15 毫秒
61.
Kinetic eigenmodes of plasma oscillations in a weakly collisional plasma, described by a collision operator of the Fokker-Planck type, are obtained in closed form for initial-value as well as for boundary-value problems. These eigenmodes, which are smooth and compose a complete discrete spectrum, play the same role for weakly collisional plasmas as the Case-Van Kampen modes do for collisionless plasmas. 相似文献
62.
The purpose of the present study was to describe the effects ofacute laryngitis on some aerodynamic, acoustic, and perceptual measures. Eleven subjects with diagnosed acute laryngitis due to upper respiratory infection were recorded during a laryngitic episode and 1 week to 10 days after amelioration of the laryngitic condition. Fundamental frequency values, collapsed across the five vowels, were significantly reduced in the laryngitic compared with the normal speaking condition. The decrease in fundamental frequency associated with acute laryngitis suggests an increase in the mass of the vocal folds. In addition, aerodynamic values differed significantly for the laryngitic condition compared with the normal speaking condition, suggesting the presence of laryngeal hypofunction. Perceptual data indicated that speakers in the laryngitic condition were judged to have a hoarse voice when compared with the normal speaking condition. 相似文献
63.
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
64.
The preconcentration of analytes is important in biochemical analysis as it offers the ability to detect for trace species,
and increase signal-to-noise ratios when using optical sensing on fluorophores. A strong advantage of the evaporation technique
lies in its ability to operate without the need of any energy source; albeit major challenges exist on how to increase the
surface area exposure to air for heightened evaporation, ensure no further increases once specified analyte concentrations
have been achieved, and not needing any intervening membranes. We demonstrate here that the droplet creation and retraction
approach in capillary based microplates offers such abilities whilst at the same time facilitating mixing. 相似文献
65.
Using molecular dynamics simulations, we investigate the oscillatory behaviors of carbon nanotube oscillators containing sp3-hybridized defects formed by hydrogen chemisorption. It is found that the presence of these defects significantly affects the kinetic and potential energies of the nanotube systems, which in turn affects their oscillation periods and frequencies. We have also studied the oscillatory characteristics of the oscillators containing sp3-hybridized Stone-Wales defects. Our results show that it is possible to control the motion of the inner nanotube by introducing sp3-hybridized defects on the outer nanotube, which provides a potential way to tune the oscillatory behavior of nanotube oscillators. 相似文献
66.
PbTiO3 thin films were successfully deposited on the LaNiO3 (LNO) substrates by the liquid-phase deposition (LPD) method and post-annealing at various temperatures. The structure, morphology and composition of the films were investigated by some analytical techniques. The as-deposited films are amorphous and composed of densely packed spherical particles. The films with the grain size of 180 nm start to decompose and crystallize into perovskite structure at 450 °C and show a perovskite single phase with tetragonal structure after annealing at 650 °C. X-ray photoelectron spectroscopy (XPS) analysis reveals that the as-deposited film contains fluorine and carbon as major impurities. Fluorine could be completely eliminated by annealing at 650 °C in air. 相似文献
67.
Altitude-resolved volume mixing ratio profiles of CFC-113 have recently become available on a global scale with the Atmospheric Chemistry Experiment (ACE) satellite mission. However, the accuracy of the retrieval is currently limited by the uncertainties on the spectroscopic parameters of CFC-113. This paper reports on the geometrical structure, harmonic frequencies and intensities in the mid-infrared region of the two conformers of CFC-113 and the evaluation of whether theoretical calculations reproduce measurements. The calculations are performed using density functional theory at the B3LYP/6-311+G(3df) level. The molecular geometry parameters, the enthalpy difference and the potential barrier between conformers are calculated. The harmonic frequency of the normal modes of vibration are presented and accurately compared to experimental data. Overtones and combination bands are assigned in the 1200-2500 cm−1 region. 相似文献
68.
Yunn-Hwa Ma Ya-Wun Hsu Yeu-Jhy Chang Mu-Yi Hua Jyh-Ping Chen Tony Wu 《Journal of magnetism and magnetic materials》2007
Targeted delivery of thrombolytic drug to the site of emboli exhibits potential to greatly reduce hemorrhagic side effect. A rat embolic model with an easy access of a magnet was established for study of the efficacy of magnetic drug targeting. In anesthetized rats, a whole blood clot produced in vitro was injected from the right iliac artery and lodged in the left iliac artery. Intra-arterial infusion of recombinant tissue plasminogen activator (rt-PA) thereafter significantly reversed the iliac flow within 15 min. Placement of an NdFeB magnet above the left iliac artery caused magnetic nanoparticle retention against hemodynamic dragging force in the presence and absence of the clot. Our results suggest the feasibility of this rat embolic model for the study of magnetic targeted delivery of thrombolytic drugs. 相似文献
69.
The adsorption and thermal decomposition of perfluorodimethyl ether, (CF3)2O, on a high-surface-area Al2O3 surface was investigated by FTIR under both vacuum and pressure conditions. IR spectra in the 4000-1050 cm−1 range were collected and the spectral assignments were assisted by quantum chemical ab initio calculations. The spectral evidence indicated that (CF3)2O decomposed to form adsorbed fluoroformate, FCOO (ads). Increases of temperature (up to 525 K) caused the FCOO (ads) to convert to hydrogen formate, HCOO (ads). Surface hydroxyl groups participated in the decomposition of (CF3)2O and the conversion of FCOO (ads) to HCOO (ads). A decomposition mechanism is proposed. 相似文献
70.
The structure of the automorphism group of a simple TAI algebra is studied. In particular, we show that is isomorphic (as a topological group) to an inverse limit of discrete abelian groups for a unital, simple, AH algebra with
bounded dimension growth. Consequently, is totally disconnected.
Another consequence of our results is the following: Suppose A is the transformation group C*-algebra of a minimal Furstenberg transformation with a unique invariant probability measure. Then the automorphism group
of A is an extension of a simple topological group by the discrete group . 相似文献