全文获取类型
收费全文 | 779篇 |
免费 | 32篇 |
国内免费 | 18篇 |
专业分类
化学 | 506篇 |
晶体学 | 9篇 |
力学 | 16篇 |
综合类 | 3篇 |
数学 | 91篇 |
物理学 | 204篇 |
出版年
2023年 | 5篇 |
2022年 | 8篇 |
2021年 | 8篇 |
2020年 | 8篇 |
2019年 | 16篇 |
2018年 | 9篇 |
2017年 | 10篇 |
2016年 | 14篇 |
2015年 | 19篇 |
2014年 | 20篇 |
2013年 | 52篇 |
2012年 | 36篇 |
2011年 | 49篇 |
2010年 | 26篇 |
2009年 | 31篇 |
2008年 | 38篇 |
2007年 | 60篇 |
2006年 | 34篇 |
2005年 | 45篇 |
2004年 | 35篇 |
2003年 | 25篇 |
2002年 | 21篇 |
2001年 | 17篇 |
2000年 | 24篇 |
1999年 | 9篇 |
1998年 | 13篇 |
1997年 | 10篇 |
1996年 | 19篇 |
1995年 | 10篇 |
1994年 | 12篇 |
1993年 | 17篇 |
1992年 | 9篇 |
1991年 | 9篇 |
1990年 | 16篇 |
1989年 | 13篇 |
1988年 | 12篇 |
1987年 | 5篇 |
1986年 | 10篇 |
1985年 | 7篇 |
1984年 | 9篇 |
1983年 | 7篇 |
1982年 | 5篇 |
1981年 | 10篇 |
1980年 | 6篇 |
1979年 | 2篇 |
1976年 | 2篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有829条查询结果,搜索用时 31 毫秒
821.
Dr. Ivan E. Kareev Dr. Elena Laukhina Dr. Vyacheslav P. Bubnov Dr. Vyacheslav M. Martynenko Vega Lloveras Dr. José Vidal‐Gancedo Dr. Marta Mas‐Torrent Prof. Jaume Veciana Prof. Concepció Rovira 《Chemphyschem》2013,14(8):1670-1675
We show that electron transfer from the perchlorotriphenylmethide anion (PTM?) to Y@C82(C2v) is an instantaneous process, suggesting potential applications for using PTM? to perform redox titrations of numerous endohedral metallofullerenes. The first representative of a Y@C82‐based salt containing the complex cation was prepared by treating Y@C82(C2v) with the [K+([18]crown‐6)]PTM? salt. The synthesis developed involves the use of the [K+([18]crown‐6)]PTM? salt as a provider of both a complex cation and an electron‐donating anion that is able to reduce Y@C82(C2v). For the first time, the molar absorption coefficients for neutral and anionic forms of the pure isomer of Y@C82(C2v) were determined in organic solvents with significantly different polarities. 相似文献
822.
Modelling spatial and temporal variations in the water quality of an artificial water reservoir in the semiarid midwest of Argentina 总被引:1,自引:0,他引:1
Temporal and spatial patterns of water quality of an important artificial water reservoir located in the semiarid Midwest of Argentina were investigated using chemometric techniques. Surface water samples were collected at 38 points of the water reservoir during eleven sampling campaigns between October 1998 and June 2000, covering the warm wet season and the cold dry season, and analyzed for dissolved oxygen (DO), conductivity, pH, ammonium, nitrate, nitrite, total dissolved solids (TDS), alkalinity, hardness, bicarbonate, chloride, sulfate, calcium, magnesium, fluoride, sodium, potassium, iron, aluminum, silica, phosphate, sulfide, arsenic, chromium, lead, cadmium, chemical oxygen demand (COD), biochemical oxygen demand (BOD), viable aerobic bacteria (VAB) and total coliform bacteria (TC). Concentrations of lead, ammonium, nitrite and coliforms were higher than the maximum allowable limits for drinking water in a large proportion of the water samples. To obtain a general representation of the spatial and temporal trends of the water quality parameters at the reservoir, the three-dimensional dataset (sampling sites×parameters×sampling campaigns) has been analyzed by matrix augmentation principal component analysis (MA-PCA) and N-way principal component analysis (N-PCA) using Tucker3 and PARAFAC (Parallel Factor Analysis) models. MA-PCA produced a component accounting for the general behavior of parameters associated with organic pollution. The Tucker3 models were not appropriate for modelling the water quality dataset. The two-factor PARAFAC model provided the best picture to understand the spatial and temporal variation of the water quality parameters of the reservoir. The first PARAFAC factor contains useful information regarding the relation of organic pollution with seasonality, whereas the second factor also encloses information concerning lead pollution. The most polluted areas in the reservoir and the polluting sources were identified by plotting PARAFAC loadings as a function of the UTM (Universal Transverse Mercator) coordinates. 相似文献
823.
Feintuch A Shimon D Hovav Y Banerjee D Kaminker I Lipkin Y Zibzener K Epel B Vega S Goldfarb D 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2011,209(2):136-141
A spectrometer specifically designed for systematic studies of the spin dynamics underlying Dynamic Nuclear Polarization (DNP) in solids at low temperatures is described. The spectrometer functions as a fully operational NMR spectrometer (144 MHz) and pulse EPR spectrometer (95 GHz) with a microwave (MW) power of up to 300 mW at the sample position, generating a MW B(1) field as high as 800 KHz. The combined NMR/EPR probe comprises of an open-structure horn-reflector configuration that functions as a low Q EPR cavity and an RF coil that can accommodate a 30-50 μl sample tube. The performance of the spectrometer is demonstrated through some basic pulsed EPR experiments, such as echo-detected EPR, saturation recovery and nutation measurements, that enable quantification of the actual intensity of MW irradiation at the position of the sample. In addition, DNP enhanced NMR signals of samples containing TEMPO and trityl are followed as a function of the MW frequency. Buildup curves of the nuclear polarization are recorded as a function of the microwave irradiation time period at different temperatures and for different MW powers. 相似文献
824.
We shall study the following initial value problem:
where V(x) is a real short–range potential, whose radial derivative satisfies some supplementary assumptions. More precisely we shall
present a family of identities satisfied by the solutions to (0.1) that generalizes the ones proved in [12] and [21] in the
free case. As a by–product of these identities we deduce some uniqueness results for solutions to (0.1), and a lower bound
for the so-called local smoothing which becomes an identity in a precise asymptotic sense. 相似文献
825.
826.
L.C. Poças K.R. Campos S.L. Nogueira E. Piovesan R.A. Silva M.L. Vega Alexandre Marletta 《Journal of Non》2008,354(42-44):4852-4855
In this work we studied the properties of absorption and emission line shape of layer-by-layer (LBL) poly(p-phenylene vinylene) (PPV) on indium-tin oxide (ITO) electrode. To minimize the PPV thermal conversion effects during the polymer processing, we used a less aggressive leaving group in the precursor polymer; minimizing electrode degradation. LBL ITO/PPV films showed the same absorption and emission line shape compared with LBL PPV films deposited on non-metallic substrates (glass). With this analysis we indirectly observe the decrease in the ITO degradation. Atomic force microscopy (AFM) technique was used to analyze quantitatively the microscopic morphology of the film surface. Results indicated that the substrate topology is not affected, to a large extent, by the use of dodecylbenzensulfonate (DBS) ion. 相似文献
827.
Motivated in part by Eardley et al. (Commun Math Phys 106(1):137–158, 1986), in this note we obtain a rigidity result for globally hyperbolic vacuum spacetimes in arbitrary dimension that admit a timelike conformal Killing vector field. Specifically, we show that if M is a Ricci flat, timelike geodesically complete spacetime with compact Cauchy surfaces that admits a timelike conformal Killing field X, then M must split as a metric product, and X must be Killing. This gives a partial proof of the Bartnik splitting conjecture in the vacuum setting. 相似文献
828.
Kirstene A. Gultian Roshni Gandhi Tae Won B. Kim Sebastián L. Vega 《Macromolecular bioscience》2023,23(3):2200425
Although photopolymerization reactions are commonly used to form hydrogels, these strategies rely on light and may not be suitable for delivering therapeutics in a minimally invasive manner. Here, hyaluronic acid (HA) macromers are modified with norbornene (Nor) or tetrazine (Tet) and upon mixing click into covalently crosslinked Nor-Tet hydrogels via a Diels–Alder reaction. By incorporating a high degree of Nor and Tet substitution, Nor-Tet hydrogels with a broad range in elastic moduli (5 to 30 kPa) and fast gelation times (1 to 5 min) are achieved. By pre-coupling methacrylated HANor macromers with thiolated peptides via a Michael addition reaction, Nor-Tet hydrogels are peptide-functionalized without affecting their physical properties. Mesenchymal stem cells (MSCs) on RGD-functionalized Nor-Tet hydrogels adhere and exhibit stiffness-dependent differences in matrix mechanosensing. Fluid properties of Nor-Tet hydrogel solutions allow for injections through narrow syringe needles and can locally deliver viable cells and peptides. Substituting HA with enzymatically degradable gelatin also results in cell-responsive Nor-Tet hydrogels, and MSCs encapsulated in Nor-Tet hydrogels preferentially differentiate into adipocytes or osteoblasts, based on 3D cellular spreading regulated by stable (HA) and degradable (gelatin) macromers. 相似文献
829.
Hanfeng Zhou Panlong Li Dr. En Zhang Jonas Kunigkeit Xiongjun Zhou Katherina Haase Dr. Maria Rita Ortega Vega Shuwen Wang Xiaosa Xu Dr. Julia Grothe Prof. Stefan C. B. Mannsfeld Prof. Eike Brunner Prof. Katsumi Kaneko Prof. Stefan Kaskel 《Angewandte Chemie (International ed. in English)》2023,62(34):e202305397
Capacitive analogues of semiconductor diodes (CAPodes) present a new avenue for energy-efficient and nature-inspired next-generation computing devices. Here, we disclose the generalized concept for bias-direction-adjustable n- and p-CAPodes based on selective ion sieving. Controllable-unidirectional ion flux is realized by blocking electrolyte ions from entering sub-nanometer pores. The resulting CAPodes exhibit charge-storage characteristics with a high rectification ratio (96.29 %). The enhancement of capacitance is attributed to the high surface area and porosity of an omnisorbing carbon as counter electrode. Furthermore, we demonstrate the use of an integrated device in a logic gate circuit architecture to implement logic operations (‘OR’, ‘AND’). This work demonstrates CAPodes as a generalized concept to achieve p-n and n-p analogue junctions based on selective ion electrosorption, provides a comprehensive understanding and highlights applications of ion-based diodes in ionologic architectures. 相似文献