全文获取类型
收费全文 | 2993篇 |
免费 | 672篇 |
国内免费 | 335篇 |
专业分类
化学 | 1405篇 |
晶体学 | 27篇 |
力学 | 126篇 |
综合类 | 31篇 |
数学 | 418篇 |
物理学 | 1993篇 |
出版年
2024年 | 6篇 |
2023年 | 34篇 |
2022年 | 76篇 |
2021年 | 58篇 |
2020年 | 69篇 |
2019年 | 68篇 |
2018年 | 87篇 |
2017年 | 125篇 |
2016年 | 119篇 |
2015年 | 134篇 |
2014年 | 242篇 |
2013年 | 213篇 |
2012年 | 214篇 |
2011年 | 276篇 |
2010年 | 216篇 |
2009年 | 222篇 |
2008年 | 225篇 |
2007年 | 228篇 |
2006年 | 188篇 |
2005年 | 183篇 |
2004年 | 128篇 |
2003年 | 134篇 |
2002年 | 86篇 |
2001年 | 82篇 |
2000年 | 58篇 |
1999年 | 54篇 |
1998年 | 59篇 |
1997年 | 60篇 |
1996年 | 48篇 |
1995年 | 54篇 |
1994年 | 43篇 |
1993年 | 23篇 |
1992年 | 32篇 |
1991年 | 19篇 |
1990年 | 16篇 |
1989年 | 18篇 |
1988年 | 10篇 |
1987年 | 20篇 |
1986年 | 11篇 |
1985年 | 12篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 10篇 |
1981年 | 9篇 |
1980年 | 9篇 |
1979年 | 5篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1974年 | 2篇 |
1973年 | 3篇 |
排序方式: 共有4000条查询结果,搜索用时 15 毫秒
101.
Simplified Solid-Phase Extraction Procedure and Liquid Chromatographic Determination of Celecoxib in Rat Serum 总被引:1,自引:0,他引:1
A simplified solid phase extraction method, eliminating a preliminary protein precipitation has been developed for the determination of celecoxib in rat plasma. The technique included a solid phase extraction of the serum samples on a [poly (divinylbenzene-co-N-vinylpyrrolidone)] sorbent. After conditioning, the cartridge was loaded with 0.5 mL of acidified serum containing internal standard. Elution was made with 1 mL of a mixture of acetonitrile and methanol (1/1, v/v). After evaporation of the eluate to dryness and reconstitution with methanol, the samples were analyzed on an octadecyl bonded phase with several mobile phases containing acetonitrile and a phosphate buffer. Detection was carried out using a Photodiode Array Detector. Full validation of the proposed method was provided (linearity range: 0.01–2 mg. L–1, average extraction efficiency: 92.4%; average intra-day variability: 4.6% with an accuracy of 94.8%; average interday variability: 5% with an accuracy of 95.3%, limit of detection: 0.005 mg. L–1, limit of quantification: 0.002 mg. L–1). The proposed method was successfully utilised to quantify celecoxib in rat plasma for a pharmacokinetic study.Revised: 26 January and 23 April 2004 相似文献
102.
Microdevices for manipulation and accumulation of micro- and nanoparticles by dielectrophoresis 总被引:1,自引:0,他引:1
Microfluidic devices with three-dimensional (3-D) arrays of microelectrodes embedded in microchannels have been developed to study dielectrophoretic forces acting on synthetic micro- and nanoparticles. In particular, so-called deflector structures were used to separate particles according to their size and to enable accumulation of a fraction of interest into a small sample volume for further analysis. Particle velocity within the microchannels was measured by video microscopy and the hydrodynamic friction forces exerted on deflected particles were determined according to Stokes law. These results lead to an absolute measure of the dielectrophoretic forces and allowed for a quantitative test of the underlying theory. In summary, the influence of channel height, particle size, buffer composition, electric field, strength and frequency on the dielectrophoretic force and the effectiveness of dielectrophoretic deflection structures were determined. For this purpose, microfluidic devices have been developed comprising pairs of electrodes extending into fluid channels on both top and bottom side of the microfluidic channels. Electrodes were aligned under angles varying from 0 to 75 degrees with respect to the direction of flow. Devices with channel height varying between 5 and 50 microm were manufactured. Fabrication involved a dedicated bonding technology using a mask aligner and UV-curing adhesive. Particles with radius ranging from 250 nm to 12 microm were injected into the channels using aqueous buffer solutions. 相似文献
103.
A piezoelectric chemical sensor array was developed using four quartz crystals. Gas chromatographic stationary phases were used as sensing materials and the array was connected to an artificial neural network (ANN). The application of the ANN method proved to be particularly advantageous if the measured property (mass, concentration, etc.) should not be connected exactly to the signal of the transducers of the piezoelectric sensor. The optimum structure of neural network was determined by a trial and error method. Different structures were tried with several neurons in the hidden layer and the total error was calculated. The optimum values of primary weight factors, learning rate (η=0.15), momentum term (μ=0.9), and the sigmoid parameter (β=1) were determined. Finally, three hidden neurons and 900 training cycles were applied. After the teaching process the network was used for identification of taught analytes (acetone, benzene, chloroform, pentane). Mixtures of organic compounds were also analysed and the ANN method proved to be a reliable way of differentiating the sensing materials and identifying the volatile compounds. 相似文献
104.
105.
Yueping?Fang Xiaogang?Wen Shihe?YangEmail author Qi?Pang Lu?Ding Jiannong?Wang Weikun?Ge 《Journal of Sol-Gel Science and Technology》2005,36(2):227-234
Uniform ZnO nanorods arrays are grown directly from and on Zn foils in pure water under hydrothermal conditions at a relatively
low temperature. The nanorods are 80–200 nm in diameter and ∼ 1 μm in length, which grow on the Zn foil along the [001] direction.
By changing the pure water to a urea solution, a Zn compound ([Zn5(OH)6(CO3)2], a precursor of ZnO nanoflowers film, is created by self-assembly. The ZnO nanoflowers film can be easily obtained by heating
the [Zn5(OH)6(CO3)2] compound in N2 at 350∘C for 5–6 hours. Possible growth processes of the ZnO nanorods arrays and the [Zn5(OH)6(CO3)2] nanoflowers are discussed. Photoluminescence properties of the as-prepared ZnO nanostructures have been measured. The ZnO
nanorods array synthesized using our method has minimal defects so that only band-gap emission is observed. However, the ZnO
nanoflowers film, obtained by heating the [Zn5(OH)6(CO3)2] nanoflower precursor in N2, is polycrystalline and displays strong defect-related emission. 相似文献
106.
Multichannel homogeneous immunoassay for detection of 2,4,6-trinitrotoluene (TNT) using a microfabricated capillary array electrophoresis chip 总被引:6,自引:0,他引:6
A high-throughput homogeneous immunoassay for the sensitive detection of 2,4,6-trinitrotoluene (TNT) has been developed using radial capillary array electrophoresis microdevices. Samples consisting of equilibrium mixtures of anti-TNT antibody (Ab), fluorescein-labeled TNT, and various concentrations of unlabeled TNT were electrokinetically injected into 48 channels of a radial capillary array electrophoresis microchannel plate. The rapid electrophoretic separation allows us to analyze the equilibrium ratio formed by the competition between the labeled and the unlabeled TNT for Ab binding. The simultaneous parallel TNT separations facilitate determination of a calibration curve for the TNT assay, which has high sensitivity (LOD, 1 ng/mL) and a wide dynamic range (1-300 ng/mL). 相似文献
107.
108.
A supercritical fluid extraction (SFE) method was developed in the present study as an effective sample pretreatment technique of petroleum distillates from fire debris. Three petroleum distillates were used as target analytes, including 95 unleaded gasoline, kerosene, and premium diesel. An orthogonal array (L16) experimental design was adopted to separately evaluate primary SFE experimental factors. The SFE efficiencies of petroleum distillates at various extraction conditions were examined and the optimized SFE conditions were identified. Experimental results demonstrated that the optimized SFE method not only provided an effective extraction method for the spiked sample, but also successfully recovered residues of petroleum distillates from fire debris. 相似文献
109.
《Electroanalysis》2005,17(3):239-245
Oxygen dependence of a tyrosinase‐based electrochemical biosensor for determination of phenol in aqueous and organic media was systematically investigated. The result demonstrated that the enzymatic coupling reaction rate of tyrosinase (deoxy form) and O2 to regenerate tyrosinase (oxy form) is a kinetically fast reaction, and the significant change of O2 concentration in aqueous solution did not affect the coupling reaction. The further increase of O2 concentration did not increase the overall oxidation reaction rate of the substrate at low substrate concentration (e.g.,<10 μM phenol) when O2 concentration was greater than 8.9 ppm. The oxygen dependence was observed in the case of high substrate concentration due to insufficient amount of O2 available for the regeneration of tyrosinase. In other words, the upper linear range is oxygen dependent for tyrosinase biosensors. The phenol biosensors employing microelectrodes had wider upper linear ranges than macroelectrodes in both aqueous and organic phase, which can be explained by the oxygen dependence. 相似文献
110.
Eun Jeong ChoFrank V Bright 《Analytica chimica acta》2002,470(1):101-110
We report a new, solid-state, integrated optical array sensor platform. By using pin printing technology in concert with sol-gel-processing methods, we form discrete xerogel-based microsensor elements that are on the order of 100 μm in diameter and 1 μm thick directly on the face of a light emitting diode (LED). The LED serves as the light source to excite chemically responsive luminophores sequestered within the doped xerogel microsensors and the analyte-dependent emission from within the doped xerogel is detected with a charge coupled device (CCD). We overcome the problem of background illumination from the LED reaching the CCD and the associated biasing that results by coating the LED first with a thin layer of blue paint. The thin paint layer serves as an optical filter, knocking out the LEDs red-edge spectral tail. The problem of the spatially-dependent fluence across the LED face is solved entirely by performing ratiometric measurements. We illustrate the performance of the new sensor scheme by forming an array of 100 discrete O2-responsive sensing elements on the face of a single LED. The combination of pin printing with an integrated sensor and light source platform results in a rapid method of forming (∼1 s per sensor element) reusable sensor arrays. The entire sensor array can be calibrated using just one sensor element. Array-to-array reproducibly is <8%. Arrays can be formed using single or multiple pins with indistinguishable analytical performance. 相似文献