全文获取类型
收费全文 | 79919篇 |
免费 | 387篇 |
国内免费 | 382篇 |
专业分类
化学 | 25331篇 |
晶体学 | 793篇 |
力学 | 6820篇 |
数学 | 32327篇 |
物理学 | 15417篇 |
出版年
2022年 | 51篇 |
2021年 | 78篇 |
2020年 | 44篇 |
2019年 | 60篇 |
2018年 | 10454篇 |
2017年 | 10275篇 |
2016年 | 6121篇 |
2015年 | 897篇 |
2014年 | 346篇 |
2013年 | 423篇 |
2012年 | 3903篇 |
2011年 | 10604篇 |
2010年 | 5706篇 |
2009年 | 6124篇 |
2008年 | 6681篇 |
2007年 | 8856篇 |
2006年 | 342篇 |
2005年 | 1410篇 |
2004年 | 1613篇 |
2003年 | 2019篇 |
2002年 | 1062篇 |
2001年 | 270篇 |
2000年 | 310篇 |
1999年 | 171篇 |
1998年 | 214篇 |
1997年 | 166篇 |
1996年 | 221篇 |
1995年 | 137篇 |
1994年 | 91篇 |
1993年 | 111篇 |
1992年 | 67篇 |
1991年 | 72篇 |
1990年 | 64篇 |
1989年 | 71篇 |
1988年 | 64篇 |
1987年 | 67篇 |
1986年 | 70篇 |
1985年 | 67篇 |
1984年 | 68篇 |
1983年 | 47篇 |
1982年 | 62篇 |
1981年 | 57篇 |
1980年 | 65篇 |
1979年 | 53篇 |
1978年 | 44篇 |
1914年 | 45篇 |
1913年 | 40篇 |
1912年 | 40篇 |
1909年 | 41篇 |
1908年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
941.
Deokki Min Nils Hoivik Geir Uri Jensen Frode Tyholdt Camilla Haavik Ulrik Hanke 《Applied Physics A: Materials Science & Processing》2011,105(4):867-874
The dielectric properties of zirconium dioxide (ZrO2) ceramic thin films were characterized up to 50 GHz using coplanar waveguides (CPWs) and metal–insulator–metal (MIM) capacitors
with top circular electrodes. The ZrO2 films were deposited using a chemical solution onto high-resistivity Si wafers and metal layers. The real part of the dielectric
constant of approximately 22 and 26 was extracted at 50 GHz for CPW and MIM structures, respectively, and the loss tangent
was approximately 0.09 at 50 GHz. C–V and I–V measurements were carried out to determine low-frequency and DC dielectric properties. The measurement results indicate that
ZrO2 is a promising material to be used as a dielectric layer for radio-frequency (RF) microelectromechanical systems (MEMS) capacitive
switches. 相似文献
942.
J. Babington B. A. van Tiggelen 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2011,65(3):367-372
We consider a simple atomic two-body bound state system that is overall charge neutral
and placed in a static electric and magnetic field, and calculate the magneto-electric
response function as a function of frequency. This is done from first principles using a
two-particle Hamiltonian for both an harmonic oscillator and Coulomb binding potential. In
the high frequency limit, the response function falls off as
1/ω
2 whilst at low frequencies it tends to a constant
value. 相似文献
943.
A MARKOWICZ 《Pramana》2011,76(2):321-329
This paper reviews the major factors influencing the accuracy of the energy-dispersive X-ray fluorescence (EDXRF) analysis
including physical and chemical matrix effects (resulting from particle size, surface irregularity, mineralogy, moisture,
absorption and enhancement) as well as the correction procedures with emphasis on the analysis of unprepared samples. Quantification
methods for thin samples, samples with intermediate thickness and thick samples are presented including fundamental parameter
methods, influence coefficient algorithms, empirical coefficient algorithms and quantification methods based on scattered
primary radiation. Quality control procedures are also reviewed. 相似文献
944.
Nesreen Alzoghoul Alsmadi Aniket S. Wadajkar Weina Cui Kytai T. Nguyen 《Journal of nanoparticle research》2011,13(12):7177-7186
The objective of this research was to compare the effects of two different surfactants on the physicochemical properties of
thermo-responsive poly(N-isopropylacrylamide-acrylamide-allylamine) (PNIPAAm-AAm-AH)-coated magnetic nanoparticles (MNPs). Sodium dodecyl sulfate
(SDS) as a commonly used surfactant in nanoparticle formulation process and Pluronic F127 as an FDA approved material were
used as surfactants to synthesize PNIPAAm-AAm-AH-coated MNPs (PMNPs). The properties of PMNPs synthesized using SDS (PMNPs-SDS)
and PF127 (PMNPs-PF127) were compared in terms of size, polydispersity, surface charge, drug loading efficiency, drug release
profile, biocompatibility, cellular uptake, and ligand conjugation efficiency. These nanoparticles had a stable core–shell
structure with about a 100-nm diameter and were superparamagnetic in behavior with no difference in the magnetic properties
in both types of nanoparticles. In vitro cell studies showed that PMNPs-PF127 were more cytocompatible and taken up more by
prostate cancer cells than that of PMNPs-SDS. Cells internalized with these nanoparticles generated a dark negative contrast
in agarose phantoms for magnetic resonance imaging. Furthermore, a higher doxorubicin release at 40 °C was observed from PMNPs-PF127,
and the released drugs were pharmacologically active in killing cancer cells. Finally, surfactant type did not affect the
conjugation efficiency to the nanoparticles when folic acid was used as a targeting ligand model. These results indicate that
PF127 might be a better surfactant to form polymer-coated magnetic nanoparticles for targeted and controlled drug delivery. 相似文献
945.
Shufang Wang Huiling Li Kun Zhao Songqing Zhao Mingjing Chen Jingchun Chen Jianglong Wang Guangsheng Fu 《Applied Physics A: Materials Science & Processing》2011,105(2):407-410
A heterojunction was fabricated by growing a layer of Bi2Sr2Co2O
y
thin film on the 0.7 wt% Nb-doped SrTiO3 substrate. Such heterojunction showed good rectifying characteristics over a wide temperature range, and its transport mechanism
under the forward bias can be attributed to a space charge limited conduction mechanism via defects near the interface of
the heterojunction. Photovoltaic properties of the heterojunction were studied by using both continuous-wave and pulsed irradiations
and the results can be well explained by the photovoltaic effect of a p–n junction. 相似文献
946.
Aurelien Drezet 《Pramana》2007,68(3):389-396
In a paper by Home and Agarwal [1], it is claimed that quantum nonlocality can be revealed in a simple interferometry experiment
using only single particles. A critical analysis of the concept of hidden variable used by the authors of [1] shows that the
reasoning is not correct.
相似文献
947.
Using the Embedding Atom Method (EAM) for highly undercooled Ni3Al alloy, the melting point and the specific heat were studied by a molecular dynamics simulation. The simulation of melting
point was carried out by means of the sandwich method and the NVE ensemble method, and the results show a good agreement,
whereas are larger than the experimental value of 1663 K. This difference is attributed to the influence of surface melting
on experimental results, which causes the smaller measurements compared with the thermodynamic melting point. The simulated
specific heat of Ni3Al alloy weakly and linearly increases with the increase of undercooling in the temperature range from 800 K to 2000 K.
Supported by the National Natural Science Foundation of China (Grant No. 50395101) 相似文献
948.
We found, through extensive experimental studies, that the physical aging effects are absent in the relaxation of rubbing-induced
birefringence (RIB) in polystyrene (PS), and the relaxation involves very small length scale. A phenomenological model based
on individual birefringence elements is proposed for the RIB relaxation. The relaxation times (RTs) of the elements are found
to be independent of the thermal or stress history of the samples, either before or after the formation of the birefringence.
The RTs are also independent of the molecular weight, rubbing conditions, and film thickness, while the RTs distribution function
does depend on the molecular weight and rubbing conditions. The model provides quantitative interpretations that agree very
well with all the reported experimental results, and sheds important light on the novel behaviors of the RIB relaxation. The
absence of physical aging effects is probably due to the combined effects of small length scale of the RIB relaxation, and
the accelerated aging speed in the near surface region in which the RIB concentrates. 相似文献
949.
We present a density matrix of a mesoscopic RLC circuits to make it possible to analyze the connection between the initial
condition and the certain temperature. Our results show that the quantum state evolution will be closely related to the initial
condition; the system evolves to generalized coherent state if it is in ground state initially, and evolves to squeezed state
if it is in excited state initially. In addition, we also obtain squeezed minimum uncertainty state with satisfying certain
condition in mesoscopic RLC circuit. 相似文献
950.
P K Karmakar 《Pramana》2007,68(4):631-648
Application of inertia-induced acoustic excitation theory offers a new resonant excitation source channel of acoustic turbulence
in the transonic domain of plasma flow. In bi-ion plasmas like colloidal plasma, two well-defined transonic points exist corresponding
to the parent ion and the dust grain-associated acoustic modes. As usual, the modified ion acoustic mode (also known as dust
ion-acoustic (DIA) wave) dynamics associated with parent ion inertia is excitable for both nanoscale-and micronscale-sized
dust grains. It is found that the so-called (ion) acoustic mode (also known as dust-acoustic (DA) wave) associated with nanoscale
dust grain inertia is indeed resonantly excitable through the active role of weak but finite parent ion inertia. It is interestingly
conjectured that the same excitation physics, as in the case of normal plasma sound mode, operates through the active inertial
role of plasma thermal species. Details of the nonlinear acoustic mode analyses of current interest in transonic domains of
such impure plasmas in hydrodynamic flow are presented.
相似文献