全文获取类型
收费全文 | 203323篇 |
免费 | 1487篇 |
国内免费 | 432篇 |
专业分类
化学 | 104984篇 |
晶体学 | 3402篇 |
力学 | 10310篇 |
综合类 | 10篇 |
数学 | 21897篇 |
物理学 | 64639篇 |
出版年
2021年 | 1982篇 |
2020年 | 2018篇 |
2019年 | 2576篇 |
2018年 | 3666篇 |
2017年 | 3672篇 |
2016年 | 4821篇 |
2015年 | 2351篇 |
2014年 | 4327篇 |
2013年 | 8618篇 |
2012年 | 6845篇 |
2011年 | 8069篇 |
2010年 | 6484篇 |
2009年 | 6663篇 |
2008年 | 7665篇 |
2007年 | 7624篇 |
2006年 | 6718篇 |
2005年 | 5937篇 |
2004年 | 5652篇 |
2003年 | 5170篇 |
2002年 | 5166篇 |
2001年 | 5613篇 |
2000年 | 4144篇 |
1999年 | 3144篇 |
1998年 | 2706篇 |
1997年 | 2765篇 |
1996年 | 2549篇 |
1995年 | 2213篇 |
1994年 | 2331篇 |
1993年 | 2229篇 |
1992年 | 2529篇 |
1991年 | 2645篇 |
1990年 | 2558篇 |
1989年 | 2628篇 |
1988年 | 2532篇 |
1987年 | 2552篇 |
1986年 | 2415篇 |
1985年 | 3033篇 |
1984年 | 3111篇 |
1983年 | 2598篇 |
1982年 | 2565篇 |
1981年 | 2531篇 |
1980年 | 2337篇 |
1979年 | 2709篇 |
1978年 | 2673篇 |
1977年 | 2870篇 |
1976年 | 2873篇 |
1975年 | 2670篇 |
1974年 | 2608篇 |
1973年 | 2713篇 |
1972年 | 2090篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
981.
E. V. Kalneus A. A. Kipriyanov P. A. Purtov D. V. Stass Yu. N. Molin 《Applied magnetic resonance》2006,30(3-4):549-554
The paper presents the first resolved experimental magnetically affected reaction yield (MARY) spectrum for a system with nonequivalent nuclei, radical anion of pentafluorobenzene. This observation dispels the common apprehension that because of a rather involved energy level layout a system with not all nuclei magnetically equivalent cannot produce resolved MARY lines in nonzero fields, and greatly, increases the practical scope of level-crossing techniques for studies of spin-correlated radical pairs. The experimental finding is supported by schemes of energy levels calculated for this system. 相似文献
982.
A. Veiga N. Martínez P. Mendoza Zélis G. A. Pasquevich F. H. Sánchez 《Hyperfine Interactions》2006,167(1-3):905-909
A prototype of a programmable constant-velocity scaler is presented. This instrument allows the acquisition of partial Mössbauer spectra in selected energy regions using standard drivers and transducers. It can be fully operated by a remote application, thus data acquisition can be automated. The instrument consists of a programmable counter and a constant-velocity reference. The reference waveform generator is amplitude modulated with 13-bit resolution, and is programmable in a wide range of frequencies and waveforms in order to optimize the performance of the transducer. The counter is compatible with most standard SCA, and is configured as a rate-meter that provides counts per selectable time slice at the programmed velocity. As a demonstration of the instrument applications, a partial Mössbauer spectrum of a natural iron foil was taken. Only positive energies were studied in 512 channels, accumulating 20 s per channel. A line width of 0.20 mm/s was achieved, performing with an efficiency of 80%. 相似文献
983.
I. V. Kuchin N. B. Ur’ev 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2007,81(3):349-353
The main rules governing the redistribution of microparticles in disperse systems were revealed by computer simulation. These rules predetermine the character and properties of the structure being formed, which opens up the possibility to control the properties of disperse materials, including sorbents and catalysts based on high-dispersity solid phases. 相似文献
984.
985.
A fully coupled formulation combining reactive transport and an existing thermo-hydro-mechanical (THM) code is presented.
Special attention has been given to phenomena likely to be encountered in clay barriers used as part of containment systems
of nuclear waste. The types of processes considered include hydrolysis, complex formation, oxidation/reduction reactions,
acid/base reactions, precipitation/dissolution of minerals and cation exchange. Both kinetically-controlled and equilibrium-controlled
reactions have been incorporated. The total analytical concentrations (including precipitated minerals) are adopted as basic
transport variables and chemical equilibrium is achieved by minimizing Gibbs Free Energy. The formulation has been incorporated
in a general purpose computer code capable of performing numerical analysis of engineering problems. A validation exercise
concerning a laboratory experiment involving the heating and hydration of an expansive compacted clay is described. 相似文献
986.
N. Chai W.D. Kulatilaka S.V. Naik N.M. Laurendeau R.P. Lucht J.P. Kuehner S. Roy V.R. Katta J.R. Gord 《Applied physics. B, Lasers and optics》2007,88(1):141-150
We report the application of electronic-resonance-enhanced coherent anti-Stokes Raman scattering (ERE-CARS) for measurements
of nitric oxide concentration ([NO]) in three different atmospheric pressure flames. Visible pump (532 nm) and Stokes (591 nm)
beams are used to probe the Q-branch of the Raman transition. A significant resonance enhancement is obtained by tuning an
ultraviolet probe beam (236 nm) into resonance with specific rotational transitions in the (v’=0, v”=1) vibrational band of
the A2Σ+–X2Π electronic system of NO. ERE-CARS spectra are recorded at various heights within a hydrogen-air flame producing relatively
low concentrations of NO over a Hencken burner. Good agreement is obtained between NO ERE-CARS measurements and the results
of flame computations using UNICORN, a two-dimensional flame code. Excellent agreement between measured and calculated NO
spectra is also obtained when using a modified version of the Sandia CARSFT code for heavily sooting acetylene-air flames
(φ=0.8 to φ=1.6) on the same Hencken burner. Finally, NO concentration profiles are measured using ERE-CARS in a laminar,
counter-flow, non-premixed hydrogen-air flame. Spectral scans are recorded by probing the Q1 (9.5), Q1 (13.5) and Q1 (17.5) Raman transitions. The measured shape of the [NO] profile is in good agreement with that predicted using the OPPDIF
code, even without correcting for collisional effects. These comparisons between [NO] measurements and predictions establish
the utility of ERE-CARS for detection of NO in flames with large temperature and concentration gradients as well as in sooting
environments.
PACS 07.88.+y; 42.62.Fi; 42.65.Dr 相似文献
987.
988.
X.P. Hu X. Wang Z. Yan H.X. Li J.L. He S.N. Zhu 《Applied physics. B, Lasers and optics》2007,86(2):265-268
High power red light was generated from a periodically-poled stoichiometric LiTaO3 (PPSLT) by single-pass frequency doubling of a diode-side-pumped, Q-switched Nd:YAG laser at 1319 nm. An average power of
2.4 W of the 660 nm red light was obtained at the fundamental power of ∼5.4 W with the conversion efficiency up to 44.4% and
with low fluctuation down to 2%. The high efficiency and stability at the red output indicate that it is a practical method
to construct a reliable compact red laser.
PACS 42.70.Mp; 42.79.Nv; 42.55.Xi 相似文献
989.
S.-Y. Lee T.-H. Kim D.-I. Suh E.-K. Suh N.-K. Cho W.-K. Seong S.-K. Lee 《Applied Physics A: Materials Science & Processing》2007,87(4):739-742
We demonstrate GaN nanowire (NW) current rectifiers which were formed by assembling n-GaN nanowires on a patterned p-Si substrate
by means of alternating current (ac) dielectrophoresis. The dielectrophoresis was accomplished at a frequency of 10 kHz with
three different ac bias voltages (5, 10, and 15 Vp–p), indicating that the number of aligned GaN nanowires increased with increasing ac bias voltage. The n-GaN NW/p-Si diodes
showed well-defined current rectifying behavior with a forward voltage drop of 1.2–1.5 V at a current density of 200 A/cm2. We observed that the GaN NW diode functioned well as a half-wave rectifier.
PACS 71.20.Nr; 73.40.Cg; 73.40.Ei; 73.40.Kp 相似文献
990.
This work develops the dynamics of a perfectly elastic solid model for application to the outer crust of a magnetised neutron
star. Particular attention is given to the Noether identities responsible for energy-momentum conservation, using a formulation
that is fully covariant, not only (as is usual) in a fully relativistic treatment but also (sacrificing accuracy and elegance
for economy of degrees of gravitational freedom) in the technically more complicated case of the Newtonian limit. The results
are used to obtain explicit (relativistic and Newtonian) formulae for the propagation speeds of generalised (Alfven type)
magneto-elastic perturbation modes. 相似文献