全文获取类型
收费全文 | 1019篇 |
免费 | 33篇 |
国内免费 | 1篇 |
专业分类
化学 | 670篇 |
晶体学 | 16篇 |
力学 | 24篇 |
数学 | 63篇 |
物理学 | 280篇 |
出版年
2021年 | 9篇 |
2020年 | 11篇 |
2019年 | 10篇 |
2018年 | 8篇 |
2017年 | 7篇 |
2016年 | 20篇 |
2015年 | 18篇 |
2014年 | 18篇 |
2013年 | 45篇 |
2012年 | 45篇 |
2011年 | 53篇 |
2010年 | 35篇 |
2009年 | 22篇 |
2008年 | 41篇 |
2007年 | 48篇 |
2006年 | 32篇 |
2005年 | 57篇 |
2004年 | 48篇 |
2003年 | 26篇 |
2002年 | 39篇 |
2001年 | 18篇 |
2000年 | 51篇 |
1999年 | 10篇 |
1998年 | 8篇 |
1997年 | 7篇 |
1996年 | 8篇 |
1995年 | 18篇 |
1994年 | 21篇 |
1993年 | 17篇 |
1992年 | 21篇 |
1991年 | 22篇 |
1990年 | 9篇 |
1989年 | 10篇 |
1988年 | 8篇 |
1987年 | 12篇 |
1986年 | 12篇 |
1985年 | 18篇 |
1984年 | 11篇 |
1983年 | 13篇 |
1982年 | 13篇 |
1981年 | 6篇 |
1980年 | 11篇 |
1979年 | 11篇 |
1978年 | 17篇 |
1977年 | 10篇 |
1976年 | 17篇 |
1975年 | 18篇 |
1974年 | 15篇 |
1973年 | 5篇 |
1923年 | 4篇 |
排序方式: 共有1053条查询结果,搜索用时 468 毫秒
151.
D.A. McKeown I.S. Muller H. Gan Z. Feng Carol Viragh I.L. Pegg 《Journal of Non》2011,357(14):2735-2743
X-ray absorption spectroscopy (XAS) was used to characterize vanadium (V) and chromium (Cr) environments in low activity nuclear waste (LAW) glasses synthesized under a variety of redox conditions. V2O5 was added to the melt to improve sulfur incorporation from the waste; however, at sufficiently high concentrations, V increased melt foaming, which lowered melt processing rates. Foaming may be reduced by varying the redox conditions of the melt, while small amounts of Cr are added to reduce melter refractory corrosion. Three parent glasses were studied, where CO-CO2 mixtures were bubbled through the corresponding melt for increasing time intervals so that a series of redox-adjusted-glasses was synthesized from each parent glass. XAS data indicated that V and Cr behaviors are significantly different in these glasses with respect to the cumulative gas bubbling times: V4+/Vtotal ranges from 8 to 35%, while Cr3+/Crtotal can range from 15 to 100% and even to population distributions including Cr2+. As Na-content decreased, V, and especially, Cr became more reduced, when comparing equivalent glasses within a series. The Na-poor glass series show possible redox coupling between V and Cr, where V4+ populations increase after initial bubbling, but as bubbling time increases, V4+ populations drop to near the level of the parent glass, while Cr becomes more reduced to the point of having increasing Cr2+ populations. 相似文献
152.
Ondrej Stranik Daniela Iacopino Robert Nooney Colette McDonagh Brian D. MacCraith 《Journal of fluorescence》2010,20(1):215-223
In this paper, we describe a novel technique for depositing metal nanoparticles (NPs) on a planar substrate whereby the NPs
are micro-patterned on the surface by a simple stamp-printing procedure. The method exploits the attractive force between
negatively charged colloidal metal NPs and positively-charged polyelectrolyte layers which have been selectively deposited
on the surface. Using this technique, large uniform areas of patterned metal NPs, with different plasmonic properties, were
achieved by optimisation of the stamping process. We report the observation of unusual fluorescence emission from these structures.
The emission was measured using epifluorescence microscopy. Fluorescence lifetime behaviour was also measured. Furthermore,
the μ-patterned NPs exhibited blinking behaviour under 469 nm excitation and the fluorescence spectrum was multi-peaked. It
has been established that the fluorescence is independent of the plasmon resonance properties of the NPs. As well as optimising
the novel NP μ-patterning technique, this work discusses the origin and characteristics of the anomalous fluorescence behaviour
in order to characterise and minimise this unwanted background contribution in the use of metal NPs for plasmonic enhancement
of fluorescence for optical biochip applications. 相似文献
153.
Albert Y Jin Ursula I Tuor David Rushforth Jaspreet Kaur Robert N Muller Jodie Lee Petterson Sébastien Boutry Philip A Barber 《BMC neuroscience》2010,11(1):12
Background
The link between early blood- brain barrier (BBB) breakdown and endothelial cell activation in acute stroke remain poorly defined. We hypothesized that P-selectin, a mediator of the early phase of leukocyte recruitment in acute ischemia is also a major contributor to early BBB dysfunction following stroke. This was investigated by examining the relationship between BBB alterations following transient ischemic stroke and expression of cellular adhesion molecule P-selectin using a combination of magnetic resonance molecular imaging (MRMI), intravital microscopy and immunohistochemistry. MRMI was performed using the contrast, gadolinium diethylenetriaminepentaacetic acid (Gd-DTPA) conjugated to Sialyl Lewis X (Slex) where the latter is known to bind to activated endothelium via E- or P selectins. Middle cerebral artery occlusion was induced in male C57/BL 6 wild-type (WT) mice and P-selectin-knockout (KO) mice. At 24 hours following middle cerebral artery occlusion, T1 maps were acquired prior to and following contrast injection. In addition to measuring P- and E-selectin expression in brain homogenates, alterations in BBB function were determined immunohistochemically by assessing the extravasation of immunoglobulin G (IgG) or staining for polymorphonuclear (PMN) leukocytes. In vivo assessment of BBB dysfunction was also investigated optically using intravital microscopy of the pial circulation following the injection of Fluorescein Isothiocyanate (FITC)-dextran (MW 2000 kDa). 相似文献154.
155.
High‐quality single‐crystal and polycrystalline chemical‐vapor‐deposition diamond detectors with platinum contacts have been tested at the white‐beam X28C beamline at the National Synchrotron Light Source under high‐flux conditions. The voltage dependence of these devices has been measured under both DC and pulsed‐bias conditions, establishing the presence or absence of photoconductive gain in each device. Linear response consistent with the theoretically determined ionization energy has been achieved over eleven orders of magnitude when combined with previous low‐flux studies. Temporal measurements with single‐crystal diamond detectors have resolved the nanosecond‐scale pulse structures of both the NSLS and the APS. Prototype single‐crystal quadrant detectors have provided the ability to simultaneously resolve the X‐ray beam position and obtain a quantitative measurement of the flux. 相似文献
156.
Alexandre Boulay Sophie Laine Nadine Leygue Eric Benoist Sophie Laurent Luce Vander Elst Robert N. Muller Béatrice Mestre-Voegtle Claude Picard 《Tetrahedron letters》2013
In the design of dual-imaging probes, the first functionalized and neutral heterobimetallic Re(I)–Gd(III) complex, highly soluble in aqueous solutions, has been prepared. This system exhibits interesting photophysical properties (λem = 578 nm, ? = 1.4%) for optical imaging and substantial higher relaxivity (r1 = 6.6 mM−1 s−1 at 0.47 T and 37 °C) than the clinically used MRI contrast agents. Moreover, this system incorporates an aromatic ester functionality suitable for bioconjugation. 相似文献
157.
Darbandi Masih Laurent Sophie Busch Martin Li Zi-An Yuan Ying Krüger Michael Farle Michael Winterer Markus Vander Elst Luce Muller Robert N. Wende Heiko 《Journal of nanoparticle research》2013,15(5):1-9
Quasi-critical fluctuations occur close to critical points or close to continuous phase transitions. In three-dimensional systems, precision tuning is required to access the fluctuation regime. Lowering the dimensionality enhances the parameter space for quasi-critical fluctuations considerably. This enables one to make use of novel properties emerging in fluctuating systems, such as giant susceptibilities, Casimir forces or novel quasi-particle interactions. Examples are discussed ranging from simple metal–adsorbate systems to unconventional superconductivity in iron-based superconductors. 相似文献
158.
The photoluminescence spectrum of a single quantum dot was recorded as a secondary resonant laser optically dressed either the vacuum-to-exciton or the exciton-to-biexciton transitions. High-resolution polarization-resolved measurements using a scanning Fabry-Pérot interferometer reveal splittings of the linearly polarized fine-structure states that are nondegenerate in an asymmetric quantum dot. These splittings manifest as either triplets or doublets and depend sensitively on laser intensity and detuning. Our approach realizes complete resonant control of a multiexcitonic system in emission, which can be either pulsed or continuous wave, and offers direct access to the emitted photons. 相似文献
159.
Encapsulation-dehydration was applied to cryopreserve 14 diverse algal strains, representing eukaryotic terrestrial microalgae; of these 12 survived to form cell colonies after recovery from cryostorage. Surviving algae had varying degrees of tolerance to osmotic dehydration and desiccation in this vitrification-based cryoprotective strategy. The extent of algal regrowth was affected by the mode of desiccation (silica gel or air-flow), the duration of evaporative desiccation and exposure to light during early recovery phase. This paper: (i) demonstrates the versatility of the encapsulation/dehydration method to cryopreserve diverse microalgae; (ii) confirms the successful transfer of this cryostorage technology to the Culture Collection of Algae at Gottingen University (SAG); and (iii) recommends encapsulation/dehydration as a feasible alternative to controlled rate cooling for preserving algae held in international culture collections. 相似文献
160.
Grant E. Muller 《Mathematical Methods in the Applied Sciences》2020,43(8):4995-5009
Under the Basel III regime, a commercial bank is considered adequately capitalized if it maintains a ratio of capital to total risk-weighted assets or capital adequacy ratio (CAR) of at least 8%. We model a commercial bank that complies with Basel III's minimum capital requirement on an interval for . The bank model is achieved via a specific rate of capital influx that fixes the bank's CAR at the minimum prescribed level of 8%. On the basis of this capital influx rate, we derive models for the bank's asset portfolio and capital dynamics required for maintaining the CAR at the minimum prescribed level. For the aforementioned bank, we further study a deposit insurance (DI) pricing problem with a coverage horizon equal to years. More specifically, we employ a multiperiod DI pricing model to approximate the cost of DI for the bank on the interval , where the constant (minimum) CAR is maintained. We study the behaviours of the models leading to the constant (minimum) CAR, and the behaviour of the DI premium estimate by means of numerical simulations. In the simulation study pertaining to the DI premium estimate specifically, we determine the effects of changes in the bank's initial leverage level (deposit-to-asset ratio), the DI coverage horizon, and the volatility of the asset portfolio on the DI premium estimate. 相似文献