全文获取类型
收费全文 | 14719篇 |
免费 | 539篇 |
国内免费 | 42篇 |
专业分类
化学 | 9996篇 |
晶体学 | 229篇 |
力学 | 464篇 |
综合类 | 1篇 |
数学 | 1114篇 |
物理学 | 3496篇 |
出版年
2024年 | 65篇 |
2023年 | 168篇 |
2022年 | 441篇 |
2021年 | 427篇 |
2020年 | 466篇 |
2019年 | 523篇 |
2018年 | 488篇 |
2017年 | 463篇 |
2016年 | 667篇 |
2015年 | 474篇 |
2014年 | 759篇 |
2013年 | 1259篇 |
2012年 | 1108篇 |
2011年 | 1148篇 |
2010年 | 760篇 |
2009年 | 587篇 |
2008年 | 721篇 |
2007年 | 721篇 |
2006年 | 560篇 |
2005年 | 490篇 |
2004年 | 378篇 |
2003年 | 312篇 |
2002年 | 252篇 |
2001年 | 155篇 |
2000年 | 130篇 |
1999年 | 99篇 |
1998年 | 71篇 |
1997年 | 99篇 |
1996年 | 94篇 |
1995年 | 73篇 |
1994年 | 68篇 |
1993年 | 93篇 |
1992年 | 97篇 |
1991年 | 77篇 |
1990年 | 68篇 |
1989年 | 71篇 |
1988年 | 49篇 |
1987年 | 45篇 |
1986年 | 42篇 |
1985年 | 63篇 |
1984年 | 62篇 |
1983年 | 53篇 |
1982年 | 47篇 |
1981年 | 37篇 |
1980年 | 45篇 |
1979年 | 62篇 |
1978年 | 48篇 |
1977年 | 53篇 |
1976年 | 41篇 |
1975年 | 34篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
261.
We consider the arrival time distribution defined through the quantum probability current for a Gaussian wave packet representing
free particles in quantum mechanics in order to explore the issue of the classical limit of arrival time. We formulate the
classical analogue of the arrival time distribution for an ensemble of free particles represented by a phase space distribution
function evolving under the classical Liouville's equation. The classical probability current so constructed matches with
the quantum probability current in the limit of minimum uncertainty. Further, it is possible to show in general that smooth
transitions from the quantum mechanical probability current and the mean arrival time to their respective classical values
are obtained in the limit of large mass of the particles. 相似文献
262.
A compact ultrafast terahertz (CUTE) free-electron laser (FEL) is being developed at the Raja Ramanna Centre for Advanced
Technology (RRCAT), Indore. The undulator required for the CUTE-FEL has recently been developed. We have designed, built and
characterized a variable gap, 5 cm period, 2.5 m long pure permanent magnet undulator in two identical segments. The tolerable
error in the magnetic field was 1% in rms, and we have measured it to be 0.7%. The obtained rms phase shake is around 2°.
To ensure that the trajectories do not have an exit error in position or angle, corrector coils have been designed. Shimming
coils have been applied for both the undulator segments to reduce the amplitude of the betatron oscillations in the vertical
trajectory. Details of novel corrector coils and soft iron shims are given and their performance is discussed.
相似文献
263.
A new integrated scheme based on resource-reservation and adaptive network flow routing to alleviate contention in optical burst switching networks is proposed. The objective of the proposed scheme is to reduce the overall burst loss in the network and at the same time to avoid the packet out-of-sequence arrival problem. Simulations are carried out to assess the feasibility of the proposed scheme. Its performance is compared with that of contention resolution schemes based on conventional routing. Through extensive simulations, it is shown that the proposed scheme not only provides significantly better burst loss performance than the basic equal proportion and hop-length based traffic routing algorithms, but also is void of any packet re-orderings. 相似文献
264.
In this contribution we report studies on the nature of binding of a small ligand/drug Nile blue (NB) with sodium dodecyl
sulfate (SDS) micelles, bis-(2-ethylehexyl) sulfosuccinate (AOT)/isooctane reverse micelles (RM) and a genomic DNA extracted
from Salmon sperm. With detailed steady state and picosecond resolved optical spectroscopic techniques, we examined the fluorescence
quenching of the ligand upon complexation with the SDS monomers and DNA. Polarization analyzed picosecond-resolved fluorescence
measurements reveal geometrical restriction on the probe in SDS micelles, AOT-RM and DNA. Steady state and time resolved studies
on the probe in nanocages of AOT RM with various degrees of hydration (w0) reveal the existence of NB as two distinct species namely, neutral and cationic. This study confirms that the emission of
NB in aqueous micelles and DNA solution is due to the cationic form of the drug. Our experiments clearly identified non-specific
electrostatic and intercalative modes of interaction of the probe with the DNA at lower and higher DNA concentrations respectively.
The nature of binding of NB in presence of the DNA and SDS micelles reveals that the binding affinity of the probe is higher
with the micelles than with the DNA. The complex rigidity of NB with DNA and its fluorescence quenching with DNA elucidate
a strong recognition mechanism between NB and DNA. 相似文献
265.
H. E. Stanley P. Kumar G. Franzese L. Xu Z. Yan M. G. Mazza S. V. Buldyrev S.-H. Chen F. Mallamace 《The European physical journal. Special topics》2008,161(1):1-17
We present evidence from experiments and computer
simulations supporting the hypothesis that water displays
polyamorphism, i.e., water separates into two distinct liquid
phases. This concept of a new liquid-liquid phase transition is
finding application to other liquids as well as water, such as
silicon and silica. Specifically, we investigate, the relation
between changes in dynamic and thermodynamic anomalies arising from
the presence of the liquid-liquid critical point in (i) Two models
of water, TIP5P and ST2, which display a first order liquid-liquid
phase transition at low temperatures; (ii) the Jagla model, a
spherically symmetric two-scale potential known to possess a
liquid-liquid critical point, in which the competition between two
liquid structures is generated by repulsive and attractive ramp
interactions; and (iii) A Hamiltonian model of water where the idea
of two length/energy scales is built in. This model also displays a
first order liquid-liquid phase transition at low temperatures
besides the first order liquid-gas phase transition at high
temperatures. We find a correlation between the dynamic fragility
crossover and the locus of specific heat maxima CPmax
(“Widom line”) emanating from the critical point. Our findings are
consistent with a possible relation between the previously
hypothesised liquid-liquid phase transition and the transition in
the dynamics recently observed in neutron scattering experiments on
confined water. More generally, we argue that this connection
between CPmax and the dynamic crossover is not limited to
the case of water, a hydrogen bonded network liquid, but is a more
general feature of crossing the Widom line, an extension of the
first-order coexistence line in the supercritical region.
Dedicated to Armin Bunde on the occasion of his 60th birthday. 相似文献
266.
D. M. Bhardwaj D. C. Jain S. Dalela Ravi Kumar N. L. Saini K. B. Garg 《Physica B: Condensed Matter》2004,350(4):366-374
We have made the XAFS measurements at the Cr–K-edge on natural Indian ruby single crystals (corundum) and its two irradiated samples with fluence 1×1012 Ni6+ and 5×1012 Ni6+ ions/cm2. Irradiated samples show interesting changes in their physical appearance. XANES measurements show progressive decrease in Δoct value on increase of Ni fluence in irradiated samples. EXAFS measurements on these samples show decrease in Cr–O distance on increase of Ni fluence. Lowering of Δoct value is correlated with the increase of Cr–O distance. 相似文献
267.
Brodzicka J Palka H Adachi I Aihara H Aulchenko V Bakich AM Barberio E Bay A Bedny I Bitenc U Bondar A Bracko M Browder TE Chang MC Chang P Chen A Chen WT Cheon BG Chiang CC Chistov R Cho IS Choi SK Choi Y Dalseno J Danilov M Dash M Drutskoy A Eidelman S Gabyshev N Go A Gokhroo G Golob B Ha H Haba J Hara T Hayasaka K Hayashii H Hazumi M Heffernan D Hoshi Y Hou WS Hyun HJ Iijima T Ikado K Inami K Ishikawa A Ishino H Itoh R Iwasaki M Iwasaki Y Joshi NJ Kah DH Kang JH Kawai H Kawasaki T Kichimi H 《Physical review letters》2008,100(9):092001
We report the observation of a new DsJ meson produced in B+-->D0DsJ-->D0D0K+. This state has a mass of M=2708+/-9(-10)(+11) MeV/c2, a width Gamma=108+/-23(-31)(+36) MeV/c2 and a 1- spin-parity. The statistical significance of this observation is 8.4 sigma. The results are based on an analysis of 449 x 10(6) BB events collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. 相似文献
268.
Neeraj Kumar Giri 《Optics Communications》2008,281(13):3547-3552
Upconversion emission and energy transfer processes in singly, doubly and triply doped tellurite glasses have been studied under 798 and 980 nm laser excitations. Emissions have been observed at 482, 544, 584, 655 nm and at 477, 655, 698, 800 nm corresponding to Tb3+: 5D4 → 7F6, 7F5, 7F4, 7FJ (J = 0, 1, 2, 3) and Tm3+: 1G4 → 3H6, 1G4 → 3F4, 3F3 → 3H6, 3H4 → 3H6 transitions, respectively. Among Tm3+, Yb3+and Tb3+ ions only Tm3+ has a ground state absorption at 798 nm excitation due to 3H4 ← 3H6 transition. For 980 nm excitation only Yb3+ can absorb the incident radiation. However, for both types of excitations, emission from all the three ions Tb, Yb and Tm has been observed. Possible mechanisms are proposed as follows: under 798 nm excitation Tm3+ ions are excited which excite Yb3+ ions through energy transfer. Finally “cooperative energy transfer” from a pair of Yb3+ ions to Tm3+ and Tb3+ ions takes place. Under 980 nm excitation Yb3+ ions absorb the incident energy and excite Tm3+ and Tb3+ ions via cooperative energy transfer. Variation of emission intensity with the ion concentrations of Yb3+, Tm3+ and Tb3+ has been studied. The lifetime of the 1G4 level has also been measured. 相似文献
269.
270.