全文获取类型
收费全文 | 748篇 |
免费 | 23篇 |
国内免费 | 2篇 |
专业分类
化学 | 563篇 |
晶体学 | 7篇 |
力学 | 14篇 |
数学 | 96篇 |
物理学 | 93篇 |
出版年
2023年 | 4篇 |
2022年 | 7篇 |
2021年 | 11篇 |
2020年 | 11篇 |
2019年 | 9篇 |
2018年 | 12篇 |
2017年 | 7篇 |
2016年 | 15篇 |
2015年 | 20篇 |
2014年 | 20篇 |
2013年 | 31篇 |
2012年 | 49篇 |
2011年 | 43篇 |
2010年 | 28篇 |
2009年 | 38篇 |
2008年 | 42篇 |
2007年 | 38篇 |
2006年 | 47篇 |
2005年 | 55篇 |
2004年 | 44篇 |
2003年 | 40篇 |
2002年 | 24篇 |
2001年 | 9篇 |
2000年 | 18篇 |
1999年 | 10篇 |
1998年 | 7篇 |
1997年 | 5篇 |
1996年 | 7篇 |
1995年 | 9篇 |
1994年 | 6篇 |
1993年 | 9篇 |
1992年 | 7篇 |
1991年 | 6篇 |
1990年 | 6篇 |
1989年 | 8篇 |
1987年 | 3篇 |
1985年 | 5篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1981年 | 3篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 8篇 |
1975年 | 4篇 |
1974年 | 8篇 |
1973年 | 4篇 |
1972年 | 4篇 |
1971年 | 3篇 |
1941年 | 2篇 |
排序方式: 共有773条查询结果,搜索用时 15 毫秒
81.
Here, we present a fast and simple hydrogen peroxide assay that is based on time-resolved fluorescence. The emission intensity of a complex consisting of terbium ions (Tb3+) and phthalic acid (PA) in HEPES buffer is quenched in the presence of H2O2 and this quenching is concentration-dependent. The novel PATb assay detects hydrogen peroxide at a pH range from 7.5 to 8.5 and with a detection limit of 150 nmol L−1 at pH 8.5. The total assay time is less than 1 min. The linear range of the assay can be adapted by a pH adjustment of the aqueous buffer and covers a concentration range from 310 nmol L−1 to 2.56 mmol L−1 in total which encompasses four orders of magnitude. The assay is compatible with high concentrations of all 47 tested inorganic and organic compounds. The PATb assay was applied to quantify H2O2 in polluted river water samples. In conclusion, this fast and easy-to-use assay detects H2O2 with high sensitivity and precision. 相似文献
82.
A design for a passive, air-breathing microfluidic fuel cell utilizing formic acid (FA) as a fuel is described and its performance characterized. The fuel cell integrates high surface area platinum (cathode) and palladium-platinum (anode) alloy electrodes within a PDMS microfluidic network that keeps them fully immersed in a liquid electrolyte. The polymer network that comprises the device also serves as a self-supporting membrane through which FA and oxygen are supplied to the alloy anode and cathode, respectively, by passive permeation from external sources. The cell is based on a planar form-factor and in its operation exploits FA concentration gradients that form across the PDMS membrane. These latter gradients allow the device to operate stably, producing a nearly constant limiting power density of ~0.2 mW/cm2, without driven laminar flow of fluids or the incorporation of an in-channel separator between the anodic and the cathodic compartments. The power output of this elementary device in air is subject to electrolyte mass transport impacts, which can be reduced for a given design rule by decreasing the internal ohmic resistance of the cell. The results suggest that operational stability can be improved by decreasing the kinetic losses imposed on the cathode side of the cell due to FA crossover and modalities for doing so, such as by increasing the efficiency of fuel capture at the anode. 相似文献
83.
Klodian Xhanari Kristin Syverud Gary Chinga-Carrasco Kristofer Paso Per Stenius 《Cellulose (London, England)》2011,18(2):257-270
Adsorption isotherms of single and double chain cationic surfactants with different chain length (cetyltrimethyl-, didodecyl-
and dihexadecyl ammonium bromide) onto cellulose nanofibrils were determined. Nanofibrillated cellulose, also known as microfibrillated
cellulose (MFC), with varying contents of carboxyl groups (different surface charge) was prepared by TEMPO-mediated oxidation
followed by mechanical fibrillation. The fibril charge was characterized by potentiometric and conductometric titration. Surfactant
adsorption was verified by Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS). Wetting
and adhesion of water onto fibril films was determined by contact angle measurements. Small aggregates (admicelles) of surfactant
were shown to form on the nanofibril surfaces, well below critical micelle concentrations. The results demonstrate the possibility
of using cationic surfactants to systematically control the degree of water wettability of cellulose nanofibrils. 相似文献
84.
A valveless microdevice has been developed for the integration of solid phase extraction (SPE) and polymerase chain reaction (PCR) on a single chip for the short tandem repeat (STR) analysis of DNA from a biological sample. The device consists of two domains--a SPE domain filled with silica beads as a solid phase and a PCR domain with an ~500 nL reaction chamber. DNA from buccal swabs was purified and amplified using the integrated device and a full STR profile (16 loci) resulted. The 16 loci Identifiler? multiplex amplification was performed using a non-contact infrared (IR)-mediated PCR system built in-house, after syringe-driven SPE, providing an ~80-fold and 2.2-fold reduction in sample and reagent volumes consumed, respectively, as well as an ~5-fold reduction in the overall analysis time in comparison to conventional analysis. Results indicate that the SPE-PCR system can be used for many applications requiring genetic analysis, and the future addition of microchip electrophoresis (ME) to the system would allow for the complete processing of biological samples for forensic STR analysis on a single microdevice. 相似文献
85.
Xhanari K Syverud K Chinga-Carrasco G Paso K Stenius P 《Journal of colloid and interface science》2011,356(1):58-62
The nature of layers formed by cellulose nanofibrils that had been surface modified (hydrophobized) at the oil/water (o/w) interface was investigated. The aim of the study was to clarify the mechanism underlying the excellent ability of these nanoparticles to stabilize emulsions. Layers of hydrophobized nanofibrillated cellulose spread at the o/w interface were deposited on glass slides by the Langmuir-Blodgett deposition technique. Overall evaluation of layer structures was performed by image analysis based on a Quadtree decomposition of images obtained from a flatbed scanner. A more detailed characterization of the layer structures was performed by Atomic Force Microscopy (AFM), and Field-Emission Scanning Electron Microscopy (FE-SEM). The results show that nanofibrils that were able to stabilize emulsions occur as single, dispersed fibrils or form large, network-like aggregates at the o/w interface. Fibrils that were insufficiently hydrophobized and therefore did not stabilize emulsions were only partially deposited and formed small, compact aggregates. We conclude that it is likely that the network formation is the main mechanism by which the fibrils prevent coalescence of emulsion droplets. 相似文献
86.
Maddox AF Erickson KA Tanski JM Waterman R 《Chemical communications (Cambridge, England)》2011,47(42):11769-11771
Reaction of (N(3)N)ZrX complexes (X = amido, Cl(-), CH(3)(-)) with carbodiimide substrates results in insertion into an Zr-N bond of the triamidoamine ligand rather than the Zr-X bond as has been observed for related (N(3)N)ZrX complexes (X = PR(2)(-), AsR(2)(-)). 相似文献
87.
Trace detection and physicochemical characterization of protein aggregates have a large impact in understanding and diagnosing many diseases, such as ageing-related neurodegeneration and systemic amyloidosis, for which the formation of protein aggregates is one of the pathological hallmarks. Here we demonstrate an innovative label-free method for detecting and characterizing small amounts of early stage protein aggregates using a Raman active nanofluidic device. Sub-micrometre channels formed by a novel elastomeric collapse technique enable the separation and concentration of matured protein aggregates from small protein molecules. The Raman enhancement by gold nanoparticle clusters fixed below a micro/nanofluidic junction allows characterization of intrinsic properties of protein aggregates at concentration levels (~fM) much lower than can be done with traditional analytical tools. With our device we show for the first time the concentration dependence of protein aggregation over these low concentration ranges. We expect that our method could facilitate definitive diagnosis and possible therapeutics of diseases at early stages. 相似文献
88.
89.
FTIR microspectroscopy, with synchrotron radiation as a source, was used for the first time to study changes in plant structure induced by organic contaminants. Sunflower (Helianthus annuus L.) plants were grown hydroponically in the presence of benzotriazole. Changes in the plant structure due to uptake, incorporation, and/or transformation of benzotriazole were observed. False color intensity maps of benzotriazole treated secondary root sections showed changes in plant structure, as well as the presence of aromatic CH peaks due to incorporation of benzotriazole within the plant. The presence of the characteristic benzotriazole CH out-of-plane bending mode suggests that the contaminant aromatic ring remains intact upon the uptake by the plant. Simultaneously, the changes in the lignin structure suggest that the plant suffered damage by the uptake of the benzotriazole. Spectral variations between the untreated and benzotriazole treated sunflowers were uncovered using principal components analysis (PCA). PCA also revealed clustering according to the different benzotriazole treatments. 相似文献
90.
We show that the value function of a singular stochastic
control problem is equal to the integral of the value function
of an associated optimal stopping problem. The connection is
proved for a general class of diffusions using the
method of viscosity solutions. 相似文献