全文获取类型
收费全文 | 4862篇 |
免费 | 134篇 |
国内免费 | 13篇 |
专业分类
化学 | 2672篇 |
晶体学 | 47篇 |
力学 | 149篇 |
数学 | 495篇 |
物理学 | 1646篇 |
出版年
2023年 | 38篇 |
2022年 | 78篇 |
2021年 | 81篇 |
2020年 | 97篇 |
2019年 | 97篇 |
2018年 | 97篇 |
2017年 | 74篇 |
2016年 | 132篇 |
2015年 | 89篇 |
2014年 | 127篇 |
2013年 | 289篇 |
2012年 | 253篇 |
2011年 | 299篇 |
2010年 | 185篇 |
2009年 | 168篇 |
2008年 | 241篇 |
2007年 | 239篇 |
2006年 | 252篇 |
2005年 | 210篇 |
2004年 | 155篇 |
2003年 | 137篇 |
2002年 | 112篇 |
2001年 | 93篇 |
2000年 | 87篇 |
1999年 | 59篇 |
1998年 | 46篇 |
1997年 | 45篇 |
1996年 | 52篇 |
1995年 | 54篇 |
1994年 | 49篇 |
1993年 | 62篇 |
1992年 | 50篇 |
1991年 | 42篇 |
1990年 | 56篇 |
1989年 | 43篇 |
1988年 | 43篇 |
1987年 | 42篇 |
1985年 | 53篇 |
1984年 | 48篇 |
1983年 | 43篇 |
1982年 | 40篇 |
1981年 | 46篇 |
1980年 | 51篇 |
1979年 | 35篇 |
1978年 | 44篇 |
1977年 | 38篇 |
1976年 | 40篇 |
1975年 | 33篇 |
1974年 | 40篇 |
1973年 | 40篇 |
排序方式: 共有5009条查询结果,搜索用时 0 毫秒
21.
22.
23.
24.
25.
26.
Costin CD Olund RK Staggemeier BA Torgerson AK Synovec RE 《Journal of chromatography. A》2003,1013(1-2):77-91
We report a microchip-based detection scheme to determine the diffusion coefficient and molecular mass (to the extent correlated to molecular size) of analytes of interest. The device works by simultaneously measuring the refractive index gradient (RIG) between adjacent laminar flows at two different positions along a microchannel. The device, referred to as a microscale molecular mass sensor (micro-MMS), takes advantage of laminar flow conditions where the mixing of two streams occurs essentially by diffusion across the boundary between the two streams. Two flows merge on the microchip, one containing solvent only, referred to as the mobile phase stream and one which contains the analyte(s) of interest in the solvent, i.e. the sample stream. As these two streams merge and flow parallel to each other down the microchannel a RIG is created by the concentration gradient. The RIG is further influenced by analyte diffusion from the sample stream into the mobile phase stream. Measuring the RIG at a position close to the merging point (upstream signal) and simultaneously a selected distance further down the microchannel (downstream signal) provides real-time data related to the extent a given analyte has diffused, which can be readily correlated to analyte molecular mass by taking the ratio of the downstream-to-upstream signals. For the dual-beam RIG measurements, a diode laser output is coupled to a single mode fiber optic splitter with two output fibers. Light from each fiber passes through a graded refractive index (GRIN) lens forming a collimated beam that then passes through the microchannel and then on to a position sensitive detector (PSD). The RIG at both detection positions deflects the two collimated probe beams. The deflection angle of each beam is then measured on two separate PSDs. The micro-MMS was evaluated using polyethylene glycols (PEGs), sugars, and as a detector for size-exclusion chromatography (SEC). Peak purity can be readily identified using the micro-MMS with SEC. The limit of detection was 0.9 ppm (PEG at 11 840 g/mol) at the upstream detection position corresponding to a RI limit of detection (LOD) (3sigma) of 7-10(-8) RI. The pathlength for the RIG measurement was 200 microm and the angular LOD was 0.23 micro(rad) with a detection volume of 8 nl at both positions. The average molecular mass resolution was 9% (relative standard deviation) for a series of PEGs ranging in molecular mass from 106 to 22 800 g/mol. With this excellent mass resolution, small molecules such as monosaccharides, disaccharides, and so on, are readily distinguished. The sensor is demonstrated to readily determine unknown diffusion coefficients. 相似文献
27.
A least-squares method in the matrix form is described for the simultaneous determination of rifampicin and isoniazid in a mixture. The method allows the rapid analysis of binary pharmaceutical formulations with minimum error. The concentration of each component in the mixture has been determined spectrophotometrically by measuring the absorbance of the mixture at 5-nm intervals from 230 to 290 nm. To calculate the matrix of the proportionality constant a standard mixture was used for each component. All data analyses were performed on a personal computer. 相似文献
28.
Photocatalytic polypyrrole-TiO2-nanoparticles composite thin film generated at the air-water interface 总被引:1,自引:0,他引:1
Chowdhury D Paul A Chattopadhyay A 《Langmuir : the ACS journal of surfaces and colloids》2005,21(9):4123-4128
Herein, we report a new method of generation of TiO(2) nanoparticles (NPs) incorporated thin films of polypyrrole (PPy) at the air-water interface. Aqueous TiO(2) NPs when treated with H(2)O(2) and left in a chamber of pyrrole vapor resulted in the formation of a film at the interface, in addition to bulk precipitate. Spectroscopic, X-ray diffraction, and electron microscopic measurements establish the formation of a thin film of PPy with the incorporation of TiO(2) NPs. The TiO(2)-containing PPy films when transferred onto glass substrates were able to photo catalyze the decomposition of aqueous organic dyes: methyl orange and methylene blue. Further, these films could also photo catalyze the oxidation of iodide to triiodide ions in aqueous potassium iodide solution. We find that the PPy-TiO(2) composite films catalyze the reactions in the presence of light more efficiently than a suspension of TiO(2) NPs. 相似文献
29.
30.
Chowdhury Wasimul Q. Idehara Kenji Maeda Isamu Umeda Fusako Yagi Kiyohito Miura Yoshiharu Mizoguchi Tadashi 《Applied biochemistry and biotechnology》1996,57(1):361-366
Applied Biochemistry and Biotechnology - A marine photosynthetic bacterium,Rhodopseudomonas sp. strain W-1S, accumulated polyhydroxybutyrate (PHB) to 56% of the dry cell weight under microaerobic... 相似文献