全文获取类型
收费全文 | 1540篇 |
免费 | 361篇 |
国内免费 | 212篇 |
专业分类
化学 | 784篇 |
晶体学 | 32篇 |
力学 | 99篇 |
综合类 | 34篇 |
数学 | 54篇 |
物理学 | 1110篇 |
出版年
2024年 | 5篇 |
2023年 | 19篇 |
2022年 | 72篇 |
2021年 | 68篇 |
2020年 | 87篇 |
2019年 | 48篇 |
2018年 | 50篇 |
2017年 | 79篇 |
2016年 | 100篇 |
2015年 | 93篇 |
2014年 | 119篇 |
2013年 | 133篇 |
2012年 | 94篇 |
2011年 | 123篇 |
2010年 | 93篇 |
2009年 | 96篇 |
2008年 | 74篇 |
2007年 | 94篇 |
2006年 | 91篇 |
2005年 | 71篇 |
2004年 | 60篇 |
2003年 | 70篇 |
2002年 | 54篇 |
2001年 | 37篇 |
2000年 | 46篇 |
1999年 | 31篇 |
1998年 | 25篇 |
1997年 | 29篇 |
1996年 | 31篇 |
1995年 | 22篇 |
1994年 | 14篇 |
1993年 | 17篇 |
1992年 | 17篇 |
1991年 | 9篇 |
1990年 | 8篇 |
1989年 | 4篇 |
1988年 | 6篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1982年 | 4篇 |
1980年 | 3篇 |
1979年 | 5篇 |
1975年 | 1篇 |
排序方式: 共有2113条查询结果,搜索用时 31 毫秒
31.
研制一种新型可移动式微量氧分析仪检定装置。该装置由标准气体、零点气、脱氧纯化器、减压阀、调节阀、4通阀、5通阀、不锈钢管路、流量控制系统、移动平台等组成。该装置气密性好,15 min内可将装置内氧气浓度由20.9%降至不大于0.1μmol/mol,对于0~10μmol/mol的微量氧分析仪检定结果的扩展不确定度为Urel=1.7%FS(k=2)。该装置满足气体标准物质的连续切换和在线检定的需要,检定时间短,结果准确可靠,可为在线式和非在线式微量氧分析仪的量值溯源提供有效保障。 相似文献
32.
Osaka T 《Chemical record (New York, N.Y.)》2004,4(6):346-362
This overview describes the results of our recent study of the application of electrochemical nanotechnology to the fabrication of magnetic recording materials, interconnects in ultra-large-scale integrated (ULSI) devices, energy storage materials, and on-chip biosensors. It is important to note that electrochemical processes play significant roles in developing and fabrication such sophisticated materials and devices. In the field of magnetic recording, electrodeposition methods for preparing CoNiFe and CoFe soft magnetic thin films with a high saturation magnetic flux density were newly developed, and the significant issues for obtaining those films are highlighted. In the area of ULSI interconnects, we developed a technique using a self-assembled monolayer (SAM) for direct bonding of the interconnect layer to SiO2, and proposed a novel electroless deposition method for fabricating a diffusion barrier layer. In the field of batteries, electrodeposited SnNi alloy was proposed as a future anode material for Li batteries, and electrochemical MEMS processes were shown to be useful for fabricating micro-sized direct methanol fuel cells (DMFCs) as portable batteries for electronics applications. In the area of chemical sensors, we developed a new process for fabricating field effect transistors (FETs) modified with SAMs for on-chip biosensing applications. 相似文献
33.
Guodong Feng Yanfu Huan Yanbo Cao Shuhua Wang Xinghua Wang Jie Jiang Aimin Yu Qinhan Jin Hongmei Yu 《Microchemical Journal》2004,76(1-2):17
An unique miniature simultaneous microwave plasma torch (MPT) atomic emission spectrometer employing linear UV intensified charge-coupled device (ICCD) array detector has been developed and studied preliminarily. The detection limits and precisions of the spectrometer for Ag, Al, Ba, Ca, Cr, Cu, Fe, Mg, Mn, Sr and V by using different CCD exposure times have been determined. An analysis of a practical sample has been carried out. The preliminary results demonstrate that such simultaneous spectrometer has advantages of saving sample and time, especially suitable for use as detector for chromatography and in combination with flow injection systems. Taking analytical figures of merit and portability into accounts, the miniature simultaneous MPT system will have extended application areas and greater competition potential as compared with commercialized scanning MPT spectrometers. 相似文献
34.
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
35.
一种新的滤纸基质固体表面低温荧光(燐光)测定装置 总被引:1,自引:0,他引:1
对自行研制的铜制滤纸基质低温荧光(燐光)测定的样品支架,进行了滤纸基质固体表面低温荧光测定的可行性研究。与同类冷冻装置和室温装置比较,本装置用于滤纸基质固体表面低温荧光(燐光)测定具有以下优点;样品的分析周期大大地缩短,由45min缩短为5-6min;装置简单、便宜耐用;操作简便,简化了室温测定时的滤纸干燥程序,应用范围广,方法的重现性好,检样分析结果的相对标准偏差RSD%小于10%,荧光(燐光)分析灵敏度高,检出限低,线性范围宽。 相似文献
36.
Tumbiolo S Gal JF Maria PC Zerbinati O 《Analytical and bioanalytical chemistry》2004,380(5-6):824-830
The aim of the study was to analyse BTEX compounds (benzene, toluene, ethylbenzene, xylenes) in air by solid phase micro-extraction/gas chromatography/mass spectrometry (SPME/GC/MS), and this article presents the features of the calibration method proposed. Examples of real-world air analysis are given. Standard gaseous mixtures of BTEX in air were generated by dynamic dilution. SPME sampling was carried out under non-equilibrium conditions using a Carboxen/PDMS fibre exposed for 30 min to standard gas mixtures or to ambient air. The behaviour of the analytical response was studied from 0 to 65 g/m3 by adding increasing amounts of BTEX to the air matrix. Detection limits range from 0.05 to 0.1 g/m3 for benzene, depending on the fibre. Inter-fibre relative standard deviations (reproducibility) are larger than 18%, although the repeatability for an individual fibre is better than 10%. Therefore, each fibre should be considered to be a particular sampling device, and characterised individually depending on the required accuracy. Sampling indoor and outdoor air by SPME appears to be a suitable short-delay diagnostic method for volatile organic compounds, taking advantage of short sampling time and simplicity. 相似文献
37.
38.
Robert S. Pomeroy Jeffrey D. Kolczynski Jonathan V. Sweedler M. Bonner Denton 《Mikrochimica acta》1989,99(3-6):347-353
A unique simultaneous emission spectrograph is utilized to perform qualitative and quantitative analysis on trace quantities of solid particulates. The atomic emission spectroscopic system consists of a direct current plasma source and an echelle spectrograph with a charge injection device detector, enabling the system to simultaneously measure the wavelength range from 220 nm to 520 nm with 0.02 nm resolution at 300 nm. Monitoring all wavelengths simultaneously allows the qualitative and quantitative determination of most major and minor constituent in a trace quantity of sample with little prior knowledge about the sample. The ability to perform qualitative and quantitative analysis on particulates is demonstrated by evaluating NBS certified coal fly ash, as well as a sample taken from the respirator air filter at an acute care unit in a hospital.Presented in part at the 1989 European Winter Conference on Plasma Spectrochemistry, Reutte, Austria 相似文献
39.
40.
Hiroto Tachikawa Hiroshi Kawabata Kazumi Matsushige 《Journal of organometallic chemistry》2005,690(12):2895-2904
The structures and electronic states of phenyl-capped terthiophene (denoted by P3T) and the ionic species of P3T have been investigated by means of density functional theory (DFT) and direct MO dynamics calculations. P3T is one of the high-performance molecular devices, which has been utilized as a semi-conductor. The calculations indicated that the neutral P3T has a non-planar structure whose the phenyl rings in both ends of thiophene chain are largely deviated from the molecular plane. The cation and anion radicals, dication and dianion were considered as its ionic states. The structure for cation radical of P3T is close to more planar than that of neutral P3T. The structures for anion radical, dication and dianion take a pure planar structure. The first excitation energy of neutral P3T is calculated to be 2.90 eV at the TD-B3LYP/6-31G(d)//B3LYP/6-311+G(d) level, while the P3T cation and anion radicals have lower excitation energies (1.22 and 1.10 eV, respectively). The direct MO dynamics calculation showed that neutral, cation and anion hold near planar structure at 300 K. On the other hand, oligothiophene (n = 5) and its ionic species are strongly deformed from the planar structure, and thiophene rings in both ends of chain rotate rapidly by thermal activation. The mechanism of the electron conductivity in P3T was discussed on the basis of theoretical results. 相似文献