全文获取类型
收费全文 | 1481篇 |
免费 | 66篇 |
国内免费 | 7篇 |
专业分类
化学 | 897篇 |
晶体学 | 6篇 |
力学 | 62篇 |
数学 | 321篇 |
物理学 | 268篇 |
出版年
2023年 | 10篇 |
2022年 | 33篇 |
2021年 | 44篇 |
2020年 | 52篇 |
2019年 | 21篇 |
2018年 | 30篇 |
2017年 | 22篇 |
2016年 | 69篇 |
2015年 | 61篇 |
2014年 | 79篇 |
2013年 | 85篇 |
2012年 | 100篇 |
2011年 | 122篇 |
2010年 | 85篇 |
2009年 | 67篇 |
2008年 | 99篇 |
2007年 | 89篇 |
2006年 | 66篇 |
2005年 | 65篇 |
2004年 | 57篇 |
2003年 | 40篇 |
2002年 | 36篇 |
2001年 | 20篇 |
2000年 | 11篇 |
1999年 | 12篇 |
1998年 | 9篇 |
1997年 | 14篇 |
1996年 | 16篇 |
1995年 | 8篇 |
1994年 | 7篇 |
1993年 | 11篇 |
1992年 | 14篇 |
1991年 | 11篇 |
1990年 | 7篇 |
1989年 | 6篇 |
1988年 | 13篇 |
1987年 | 6篇 |
1986年 | 7篇 |
1985年 | 13篇 |
1984年 | 9篇 |
1983年 | 9篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1972年 | 1篇 |
1964年 | 1篇 |
1916年 | 1篇 |
1914年 | 1篇 |
1899年 | 1篇 |
排序方式: 共有1554条查询结果,搜索用时 31 毫秒
121.
Porras MA Dubietis A Kucinskas E Bragheri F Degiorgio V Couairon A Faccio D Di Trapani P 《Optics letters》2005,30(24):3398-3400
We show that the angle-wavelength spectra of light filaments excited by ultrashort pulses experience a transition from X- to O-like structures when their carrier wavelengths are switched from normal to anomalous dispersion. Calculations confirm that the O-shaped conical emission follows the elliptic geometry of the nonlinear Schr?dinger equation with anomalous dispersion. 相似文献
122.
Nonlinear losses accompanying self-focusing substantially impact the dynamic balance of diffraction and nonlinearity, permitting the existence of localized and stationary solutions of the 2D + 1 nonlinear Schr?dinger equation, which are stable against radial collapse. These are featured by linear, conical tails that continually refill the nonlinear, central spot. An experiment shows that the discovered solution behaves as a strong attractor for the self-focusing dynamics in Kerr media. 相似文献
123.
Benati L Calestani G Leardini R Minozzi M Nanni D Spagnolo P Strazzari S 《Organic letters》2003,5(8):1313-1316
[reaction: see text] The radical chain reaction of benzenethiol with alkynylthiol esters provides a new, valuable protocol for the tin-free generation of acyl radicals that arise from intramolecular substitution at sulfur by the initial sulfanylvinyl radicals. 相似文献
124.
125.
Daniele Cauzzi Claudia Graiff Chiara Massera Giovanni Predieri Antonio Tiripicchio 《Journal of Cluster Science》2001,12(1):259-271
The reaction of [Ru3(CO)12] with Ph2(pyth)PSe (pyth=5-(2-pyridyl)-2-thienyl) allows to obtain two novel clusters [Ru3(3-Se)2(CO)7{P(pyth)Ph2}2] 1 and [Ru3(3-Se)(-PPh2)(-pyth)(CO)6{P(pyth)Ph2}] 2 in satisfactory yields. The first one exhibits the well-known bicapped, open triangular, 50-electron nido-core, whereas 2, whose crystal structure has been determined, shows the rather rare Ru3Se tetrahedron with the Ph2P and pyth fragments as side-bridging ligands. Morever cluster 2 belongs to the exiguous family of selenido-phosphido clusters not easily achievable by other routes. 相似文献
126.
Given a local quantum field theory net $ \mathcal{A} $ on the de Sitter spacetime dS
d
,
where geodesic observers are thermalized at Gibbons-Hawking temperature, we look
for observers that feel to be in a ground state, i.e., particle evolutions with positive
generator, providing a sort of converse to the Hawking-Unruh effect. Such positive
energy evolutions always exist as noncommutative flows, but have only a partial
geometric meaning, yet they map localized observables into localized observables.
We characterize the local conformal nets on dS
d
. Only in this case our positive
energy evolutions have a complete geometrical meaning. We show that each net
has a unique maximal expected conformal subnet, where our evolutions are thus
geometrical.
In the two-dimensional case, we construct a holographic one-to-one correspondence
between local nets $ \mathcal{A} $ on dS
2 and local conformal non-isotonic families
(pseudonets) $ \mathcal{B} $ on S
1. The pseudonet $ \mathcal{B} $ gives rise to two local conformal nets
$ \mathcal{B}_\pm $ on S
1, that correspond to the $ \frak{H}_\pm $ horizon components of $ \mathcal{A} $, and to the chiral
components of the maximal conformal subnet of $ \mathcal{A} $. In particular, $ \mathcal{A} $ is holographically
reconstructed by a single horizon component, namely the pseudonet is a net,
iff the translations on $ \frak{H}_\pm $ have positive energy and the translations on $ \frak{H}_\mp $ are
trivial. This is the case iff the one-parameter unitary group implementing rotations
on dS
2 has positive/negative generator.
Communicated by Klaus Fredenhagen
submitted 07/02/03, accepted: 07/07/03 相似文献
127.
128.
Michele Conti Michele Marconi Giulia Campanile Alessandro Reali Daniele Adami Raffaella Berchiolli Ferdinando Auricchio 《Meccanica》2017,52(3):633-644
Nitinol self-expanding stents are used for the endovascular management of peripheral artery diseases of the popliteal artery, which is located behind the knee joint. Unfortunately, the complex kinematics of the artery during the leg flexion leads to severe loading conditions, favouring the mechanical failure of the stent, calling for a specific biomechanical analysis. For this reason, in the present study we reconstruct by medical image analysis the patient-specific popliteal kinematics during leg flexion, which is subsequently exploited to compute the mechanical response of a stent model, virtually implanted in the artery by structural finite element analysis (FEA). The medical image analysis indicates a non-uniform configuration change of the artery during the leg flexion, leading to an increase of the vessel curvature above the knee. The computed mechanical response of the stent reflects the non-uniform configuration change of the artery as after the flexion the average stress is higher in the part of the stent located above the knee. Although the proposed analysis is limited to a case-study, it shows the capability of patient-specific FEA simulations to compute the mechanical response of a stent model subjected to the complex and severe loading conditions of the popliteal artery during leg flexion. 相似文献
129.
Alberto Damiano Daniele Struppa Adrian Vajiac Mihaela Vajiac 《Journal of Geometric Analysis》2009,19(2):288-300
We introduce the notion of antisyzygies, which studies the inverse problem of finding a system of PDEs, given compatibility
conditions. The system obtained possesses the property of removability of compact singularities. We write explicit computations
in the cases of the Cauchy-Fueter system and Maxwell’s system for electromagnetism, and we conclude with a study of systems
of non-maximal rank.
相似文献
130.
Daniele Di Corcia Veronica Morra Marco Pazzi Marco Vincenti 《Biomedical chromatography : BMC》2010,24(4):358-366
A fast screening protocol was developed and validated for the simultaneous determination of 15 β2‐agonists in human urine (bambuterol, cimbuterol, clenbuterol, fenoterol, formoterol, isoproterenol, mapenterol, metaproterenol, procaterol, ractopamine, ritodrine, salbutamol, salmeterol, terbutaline, tulobuterol). The overall sample processing includes deconjugation with enzyme hydrolysis, liquid–liquid extraction, followed by derivatization of the extract and detection of β2‐agonists trimethylsilyl‐derivatives by fast‐gas chromatography/electron impact–mass spectrometry (fast‐GC/EI‐MS). Sample extraction and derivatization were optimized with the purpose of improving recoveries and reaction yields for a variety of analytes with different structures simultaneously, while keeping the procedure simple and reliable. Validation parameters were determined for each analyte under investigation, including selectivity, linearity, intra‐ and inter‐assay precision, extraction recoveries and signal to noise ratio (S/N) at the lowest calibration level. Fast‐GC/MS sequences, based on the use of short columns, high carrier‐gas velocity and fast temperature ramping, allow considerable reduction of the analysis time (7 min), while maintaining adequate chromatographic resolution. The overall GC cycle time was less than 9 min, allowing a processing rate of 6 samples/h. High MS‐sampling rate, using a benchtop quadrupole mass analyzer, resulted in accurate peak shape definition under both scan and selected ion monitoring modes, and high sensitivity in the latter mode. The method was successfully tested on real samples arising from clinical treatments. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献