全文获取类型
收费全文 | 2127篇 |
免费 | 635篇 |
国内免费 | 286篇 |
专业分类
化学 | 1056篇 |
晶体学 | 22篇 |
力学 | 75篇 |
综合类 | 31篇 |
数学 | 276篇 |
物理学 | 1588篇 |
出版年
2024年 | 5篇 |
2023年 | 27篇 |
2022年 | 60篇 |
2021年 | 47篇 |
2020年 | 60篇 |
2019年 | 55篇 |
2018年 | 76篇 |
2017年 | 99篇 |
2016年 | 91篇 |
2015年 | 102篇 |
2014年 | 187篇 |
2013年 | 149篇 |
2012年 | 185篇 |
2011年 | 216篇 |
2010年 | 173篇 |
2009年 | 162篇 |
2008年 | 172篇 |
2007年 | 175篇 |
2006年 | 141篇 |
2005年 | 147篇 |
2004年 | 106篇 |
2003年 | 106篇 |
2002年 | 63篇 |
2001年 | 63篇 |
2000年 | 43篇 |
1999年 | 38篇 |
1998年 | 39篇 |
1997年 | 43篇 |
1996年 | 35篇 |
1995年 | 40篇 |
1994年 | 26篇 |
1993年 | 15篇 |
1992年 | 24篇 |
1991年 | 14篇 |
1990年 | 12篇 |
1989年 | 10篇 |
1988年 | 7篇 |
1987年 | 11篇 |
1986年 | 8篇 |
1985年 | 6篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 3篇 |
排序方式: 共有3048条查询结果,搜索用时 16 毫秒
101.
In this paper,microphase behavior of an ABC triblock copolymer,polystyrene-block-poly(2-vinylpyridine)-block-poly(ethylene oxide),namely PS-b-P2VP-b-PEO,was systematically studied during spin-coating and solvent vapor annealing based on various parameters,including the types of the solvent,spin speed and thickness.The morphological features and the microdomain location of the different blocks were characterized by atomic force microscope (AFM) and high resolution transmission electron microscopy (HRTEM).With increasing thickness,the order-order transition from nanopores array to the pattern of nanostripes was observed due to microdomain coarsening.These processes of pattern transformation were based on the selectivity of toluene for different blocks and on the contact time between solvent molecules and the three blocks.This work provides different templates for preparation of gold nanoparticle array on silicon wafer,which can be adopted as an active surface-enhanced Raman scattering (SERS) substrate for poly(3-hexylthiophene) (P3HT). 相似文献
102.
In this paper, we propose a compensated pixelwise calibration that integrates the effects of the camera housing temperature. The results of this calibration are compared on black body images to classic two points Non Uniformity Correction based calibrations, compensated or not. It is shown that the proposed approach leads to a significant improvement in the thermal resolution with a reduction in the mean error as well as the standard deviation. The approach is finally challenged on a real case measurement focusing on thermoelasticity. The gain in terms of accuracy measurement is highlighted by comparing the proposed calibration to classic calibrations and the scope of interest of this new calibration is discussed. 相似文献
103.
Local field surface plasmon excitation of pair arrays of silver nanospheres was studied using three-dimensional finite-difference time-domain method. The near-field enhancement was associated with the radius of nanosphere and the incident wavelength, the highest of which always appeared in the penultimate gaps, regardless of the number of the pairs. The surface plasmon resonance could be controlled and tuned by radius of nanosphere and incident wavelength. 相似文献
104.
With the three-dimensional symmetry and wide potential application, spherical array signal processing has been a hot research area for years. This paper devotes to the direction-of-arrival (DOA) estimation of the spherical arrays. Based on the orthogonality of the sensors’ location, MUSIC algorithm in spherical space is proposed, named as SH-MUSIC. Similar to beamspace MUSIC, spherical harmonics transformation is operated before MUSIC algorithm and a better performance is gotten because SH-MUSIC utilizes the array configuration’s orthogonality. On account of the transformation matrix’s orthogonality, spherical harmonics transformation is suggested to be operated firstly in other improved MUSIC algorithms without rejection, and it is demonstrated in beamspace MUSIC. In addition, owing to the tiny error between the steering vectors and the spherical harmonics with high order, sphere array data models including open sphere and rigid sphere are constructed. Simulation proves SH-MUSIC to be effective. Moreover, experimental data from a rigid sphere microphone array is dealt with by SH-MUSIC and the DOAs are estimated accurately. 相似文献
105.
Recent advances in miniaturization of analytical systems and newly emerging technologies offer platforms with greater automation and multiplexing capabilities than traditional biological binding assays. Multiplexed bioanalytical techniques provide control agencies and food industries with new possibilities for improved, more efficient monitoring of food and environmental contaminants. This review deals with recent developments in planar-array and suspension-array technologies, and their applications in detecting pathogens, food allergens and adulterants, toxins, antibiotics and environmental contaminants. 相似文献
106.
Multi‐layered Youden rectangles are introduced. These new designs include double and triple Youden rectangles as subdesigns. Though many double Youden rectangles are known, the triples, introduced in 1994, have to now yielded few nontrivial examples. Two infinite series of multi‐layered Youden rectangles are constructed, and so also many new triple Youden rectangles. 相似文献
107.
A simple and quick ultra performance liquid chromatography method (UPLC) has been developed for determination of methyl paraben (MP) and its major metabolites p‐hydroxybenzoic acid (pHBA) and phenol (Phe), following its biotransformations in Eisenia foetida. After different exposure time to paper contact test, the presence of methyl paraben and his biotransformation products in adult earthworms was monitored. Determination of its metabolites was achieved with a BEH (bridged ethane‐silicon hybrid) C18 column (2.1×50 mm i.d., 1.7 µm particle size), using methanol/water/phosphoric acid as mobile phase, under a gradient elution program, and a PDA (photo‐diode array) detection (quantification with MaxPlot in the range 210–400 nm). The absorption of MP did not exceed 30% and in the first 4–6 h after exposure only minute amounts of pHBA and Phe were detected in the worm homogenates. After 48 h of exposures, almost 70% of absorbed MP was already metabolized to Phe and around 20% could be found as pHBA. 相似文献
108.
Chemical imaging systems help to solve many challenges in various scientific fields. Able to deliver rapid spatial and chemical information, modern infrared spectrometers using Focal Plane Array detectors (FPA) are of great interest. Considering conventional infrared spectrometers with a single element detector, we can consider that the diffraction-limited spatial resolution is more or less equal to the wavelength of the light (i.e. 2.5-25 μm). Unfortunately, the spatial resolution of FPA spectroscopic setup is even lower due to the detector pixel size. This becomes a real constraint when micron-sized samples are analysed. New chemometrics methods are thus of great interest to overcome such resolution drawback, while keeping our far-field infrared imaging spectrometers. The aim of the present work is to evaluate the super-resolution concept in order to increase the spatial resolution of infrared imaging spectrometers using FPA detectors. The main idea of super-resolution is the fusion of several low-resolution images of the same sample to obtain a higher-resolution image. Applying the super-resolution concept on a relatively low number of FPA acquisitions, it was possible to observe a 30% decrease in spatial resolution. 相似文献
109.
《Analytical letters》2012,45(15):2707-2715
Abstract A simple and efficient HPLC analysis method has been developed to simultaneously analyse complicated multi-vitamin preparations, including vitamin B complexes, vitamin C, orotic acid, methionine, calcium pantothenate, nicotinamide, biotin, folic acid and rutin, without using expensive ion pairing reagent. Diode array detector and adjustment of the mobile phase to pH 5.6 are required in the study. This method has been validated with good linearity, reproducibility, recovery and accuracy for analysis of commercial multi-vitamin products. 相似文献
110.
《Analytical letters》2012,45(11):1879-1890
Abstract An efficient and simple high performance liquid chromatography method was developed for determination of Ephedrine. Noscapine, Promethazine and Bromhexine in cough syrup. Cough syrup samples could be cleaned up by anionic exchange solid phase extraction disk. The method has been validated with good recovery, linearity, reproducibility and selectivity for simultaneous determination of common antihistamines in over-the-counter cough syrup mixtures. 相似文献