全文获取类型
收费全文 | 1581篇 |
免费 | 84篇 |
国内免费 | 7篇 |
专业分类
化学 | 1240篇 |
晶体学 | 25篇 |
力学 | 41篇 |
数学 | 91篇 |
物理学 | 275篇 |
出版年
2024年 | 13篇 |
2023年 | 29篇 |
2022年 | 108篇 |
2021年 | 111篇 |
2020年 | 38篇 |
2019年 | 62篇 |
2018年 | 54篇 |
2017年 | 52篇 |
2016年 | 89篇 |
2015年 | 59篇 |
2014年 | 68篇 |
2013年 | 93篇 |
2012年 | 126篇 |
2011年 | 120篇 |
2010年 | 70篇 |
2009年 | 57篇 |
2008年 | 78篇 |
2007年 | 73篇 |
2006年 | 70篇 |
2005年 | 72篇 |
2004年 | 46篇 |
2003年 | 44篇 |
2002年 | 30篇 |
2001年 | 9篇 |
2000年 | 8篇 |
1999年 | 7篇 |
1998年 | 3篇 |
1997年 | 7篇 |
1996年 | 5篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1993年 | 2篇 |
1992年 | 5篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 5篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1985年 | 3篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 2篇 |
1981年 | 11篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1970年 | 1篇 |
1965年 | 1篇 |
1935年 | 1篇 |
1934年 | 1篇 |
排序方式: 共有1672条查询结果,搜索用时 31 毫秒
111.
Cho T Yoshida M Kohagura J Hirata M Numakura T Higaki H Hojo H Ichimura M Ishii K Islam KM Itakura A Katanuma I Nakashima Y Saito T Tatematsu Y Yoshikawa M Kojima Y Tokioka S Yokoyama N Tomii Y Imai T Pastukhov VP Miyoshi S;GAMMA Group 《Physical review letters》2005,94(8):085002
Vortexlike turbulent structures in hot-ion mode plasmas with several keV are observed in the case with a radially produced weak shear of electric fields E(r). However, a strong E(r) shear formation due to a high ion-confining potential phi(c) production clears up these vortices together with plasma-confinement improvement and disappearance of both drift-wave and turbulencelike Fourier spectral signals. These findings are based on three-time progress in phi(c) in comparison to phi(c) attained 1992-2002. The significant advance of phi(c) is well extended in line with proposed potential-formation physics scalings. 相似文献
112.
113.
Nonperturbative corrections from loop quantum cosmology (LQC) to the scalar matter sector are already known to imply inflation. We prove that the LQC modified scalar field generates exponential inflation in the small scale factor regime, for all positive definite potentials, independent of initial conditions and independent of ambiguity parameters. For positive semidefinite potentials it is always possible to choose, without fine-tuning, a value of one of the ambiguity parameters such that exponential inflation results, provided zeros of the potential are approached at most as a power law in the scale factor. In conjunction with the generic occurrence of bounce at small volumes, particle horizon is absent, thus eliminating the horizon problem of the standard big bang model. 相似文献
114.
We report here the low temperature emission spectra in the heterometal dinuclear 3d-4f assembled molecular system [(acac)2CrIII(μ-ox)LnIII(HBpz3)2] (Cr(ox)Ln:acac−=acetylacetonate, ox2−=oxalate, HBpz3−=hydrotris(pyrazol-1-yl)borate; Ln=La, Nd, Ho, Er , Tm and Yb) in comparison with those of Na[Cr(acac)2(ox)] and [(HBpz3)2Ln(μ-ox)Ln(HBpz3)2](Ln=Nd and Er). From 10 to 150 K the Cr(ox)Ln complexes show a broad emission band around 800 nm from the 2E state of Cr(III) moiety. At room temperature no 2E-4A2 emission was observed in the Cr(ox)Ln except for the La and Lu complexes. On warming from 10 to 300 K rapid quenching of the 2E-4A2 emission of Cr(III) is suggested to result from the energy transfer from Cr to Ln in the Cr(ox)Ln. The excitation spectra and the life-time were also measured with monitoring the 4f-4f emission peaks of the Cr(ox)Yb complex. 相似文献
115.
116.
Q. Md. Alfred T. Chakravarty G. Singh S. K. Sanyal 《International Journal of Infrared and Millimeter Waves》2007,28(10):881-887
In radar, planar phased array antenna plays vital role in electronic scanning in the azimuth and elevation direction to the
horizon. In most operations using planar phased array both the coordinates of azimuth and elevation, are steered electronically.
In this paper a conceptual schematic of a phased array antenna with programmable time delay units has been presented. It is
shown that by suitably exploiting the time delay matrix one can have electronic beam rotation around the target axis as required
in conical scan. Thus both the elevation and azimuth motors in conical scan system are replaced by electronic scanning. Heuristically,
we have selected eight consecutive points for beam rotation in a polygon shape and can also be extended almost circular shape
by increasing number of array elements and phase shifter (delays) in the delay matrix. The array requires dual control of
phase gradient and individual phase values. The whole array is controlled by micro-controller. This presents exciting possibilities
in radar operation. 相似文献
117.
The wake of a streamwise oscillating cylinder is presently investigated. The Reynolds number investigated is 300, based on
the cylinder diameterd. The cylinder oscillates at an amplitude of 0.5d and a frequencyf
e/fs=1.8, wheref
e is the cylinder oscillating frequency andf
s is the natural vortex shedding frequency of a stationary cylinder. Under these conditions the flow is essentially two dimensional.
A two-dimensional direct numerical simulation (DNS) scheme has been developed to calculate the flow. The DNS results display
a street of binary vortices, each containing two counter-rotating vortical structures, symmetrical about the centerline, which
is in excellent agreement with measurements. The drag and lift on the cylinder have been examined. The time averaged drag
and lift are 1.4 and 0, respectively, which are the same as those on a stationary cylinder at the sameRe. However, the fluctuating drag was high, about 2.68. It has been found that, being symmetrically formed about the centerline,
the binary vortices induce an essentially zero fluctuating lift, which may have a profound implication in flow control and
engineering. 相似文献
118.
Michael A. Olatunji Mayeen U. Khandaker Ekramul H. N. M. Mahmud Yusoff Md. Amin Janet A. Ademola Deborah O. Olorode 《Journal of Radioanalytical and Nuclear Chemistry》2018,316(3):933-945
Polypyrrole is incorporated with activated carbon in large size dopant solution and investigated for 137Cs removal studies. Adsorption experiments showed optimum conditions within 240 min contact time, pH 6, 0.2 g adsorbent and?≤?100 mg/l adsorbate dose, respectively, while the kinetic data followed pseudo-first-order model. Isotherm data were reproducible by the Langmuir isotherm yielding 23 mg/g maximum sorption capacity. Regeneration of adsorbent was attempted and indicated promising results within three cycles. The surface behavior has also been examined and revealed a well-ordered structure under gamma irradiation. This is a cheap adsorbent to consider and has also proven to possess higher sorption capacity than most highly-cost inorganic materials in use. 相似文献
119.
Construction of 6/7 fused bicycles featuring C/D rings of micrandilactone C and rubrifloradilactone B is reported through IMDA reaction of properly designed substrates. Also a route to the construction of a tricycle having A/B ring of nortriterpenoids of schisandra family is reported using RCM and a bromonium ion initiated cycloetherification reaction as the key steps. 相似文献
120.
Yuhei Horio Md. Mijanur Rahman Yurei Imai Yoshihiro Hishikawa Takashi Minemoto 《Current Applied Physics》2017,17(10):1341-1346
The output energy of photovoltaic (PV) modules is influenced by the spectral irradiance distribution of the solar spectrum under outdoor conditions. To rate the precise output energy of PV modules, the correction of short circuit current (ISC) based on actual environmental conditions is needed, because ISC significantly depends on the shape of the spectral irradiance distribution. The average photon energy (APE) is a zero-dimensional index for spectral irradiance distribution, and APE value uniquely describes the shape of a solar spectrum. Thus, APE has an impact on ISC of PV modules. In this contribution, the relationship between APE coefficient and ISC of the multi-crystalline silicon, single-crystalline silicon, heterojunction intrinsic thin-layer, back contact, copper indium selenide and cadmium telluride PV modules has explored. It is revealed that APE value changes the ISC of PV modules which appeared to have immense possibilities of ISC correction using APE coefficient. This new approach can be very effective for precise rating the output energy of PV modules under actual outdoor conditions. 相似文献