全文获取类型
收费全文 | 25481篇 |
免费 | 6153篇 |
国内免费 | 2243篇 |
专业分类
化学 | 8098篇 |
晶体学 | 382篇 |
力学 | 764篇 |
综合类 | 110篇 |
数学 | 654篇 |
物理学 | 23869篇 |
出版年
2024年 | 44篇 |
2023年 | 164篇 |
2022年 | 436篇 |
2021年 | 523篇 |
2020年 | 580篇 |
2019年 | 530篇 |
2018年 | 599篇 |
2017年 | 841篇 |
2016年 | 1001篇 |
2015年 | 952篇 |
2014年 | 1501篇 |
2013年 | 1920篇 |
2012年 | 1587篇 |
2011年 | 2050篇 |
2010年 | 1437篇 |
2009年 | 1678篇 |
2008年 | 1872篇 |
2007年 | 2056篇 |
2006年 | 1771篇 |
2005年 | 1421篇 |
2004年 | 1384篇 |
2003年 | 1171篇 |
2002年 | 1196篇 |
2001年 | 983篇 |
2000年 | 984篇 |
1999年 | 859篇 |
1998年 | 701篇 |
1997年 | 565篇 |
1996年 | 555篇 |
1995年 | 435篇 |
1994年 | 370篇 |
1993年 | 283篇 |
1992年 | 285篇 |
1991年 | 214篇 |
1990年 | 172篇 |
1989年 | 138篇 |
1988年 | 117篇 |
1987年 | 107篇 |
1986年 | 65篇 |
1985年 | 58篇 |
1984年 | 61篇 |
1983年 | 22篇 |
1982年 | 39篇 |
1981年 | 49篇 |
1980年 | 16篇 |
1979年 | 14篇 |
1978年 | 10篇 |
1976年 | 9篇 |
1974年 | 9篇 |
1973年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
G. Bruno P. Capezzuto G. Cicala F. Cramarossa 《Plasma Chemistry and Plasma Processing》1986,6(2):109-125
Plasma-chemical reduction of SiCl4 in mixtures with H2 and Ar has been studied by optical emission spectroscopy (OES) and laser interferometry techniques. It has been found that the Ar:H2 ratio strongly affects the plasma composition as well as the deposition (r
D) and etch (r
E) rates of Si: H, Cl films and that the electron impact dissociation is the most important channel for the production of SiClx species, which are the precursors of the film growth. Chemisorption of SiClx and the reactive surface reaction SiClx+H–SiCl(x–1)0+HCl are important steps in the deposition process. The suggested deposition model givesr
D [SiClx][H], in agreement with the experimental data. Etching of Si: H, Cl films occurs at high Ar: H2 ratio when Cl atoms in the gas phase become appreciable and increases with increasing Cl concentration. The etch rate is controlled by the Cl atom chemisorption step. 相似文献
62.
A novel method for the determination of proteins in aqueous solutions has been developed based on the enhancement of resonance light scattering (RLS) of Ag nanoparticles in the presence of proteins. Factors including acidity of the media, concentration of Ag hydrosol, reaction time, temperature, and interference of non-protein substances were investigated. Under the optimal conditions, with the enhanced RLS signals at 452nm, the linear ranges of calibration curves were 0–0.8µgmL–1 for bovine serum albumin (BSA), 0–1.2µgmL–1 for human serum albumin (HSA), and 0–2.5µgmL–1 for human -IgG (-IgG), respectively. The detection limits were 1.3ngmL–1 for BSA, 10ngmL–1 for HAS, and 5.7ngmL–1 for -IgG.This method has been applied to the analysis of synthetic samples and real human serum samples, and the results were in good agreement with those reported by the hospital, indicating that the method presented here is not only sensitive and simple, but also reliable and suitable for practical applications. 相似文献
63.
64.
Mass determination by mass spectrometric methods (electrospray ionization mass spectrometry (ESI-MS), matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS)) of sodiumdodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE)-separated proteins is a well known procedure and reliable protocols are available. In our efforts to use the established methods to determine the molecular mass of the disulfide bridged, heterodimeric glycoprotein GP3 and to determine the carbohydrate content of each protein subunit we developed an in-gel chemical deglycosylation method. For this purpose we established experimental conditions that allow maximum extraction of the high molecular mass protein subunits and developed a routine method to apply the HF-pyridine deglycosylation protocol to proteins isolated from polyacrylamide gel pieces. The novel protocol and extraction procedure described can be used to analyze O-glycosylated proteins up to 150 kDa after SDS-PAGE separation. 相似文献
65.
PRODUCTION OF LIGHTOLEFINS FROM CO_2 HYDROGENATION OVER Fe/SILICALITE-2 CATALYST Ⅱ. PROMOTION EFFECT OF MnO PROMOTER 下载免费PDF全文
IntroductionItilasbeenshot'-nthattileadditionofMnOpromotertoFocatal}stcanresultinaremarkableimprovementinthesclectivit}'to11ghtalkenesforCOh}!drogenationll'l.Ho-c'cvcr.thecadetofMnOonCH4formationandCOconversionisvery'ambigUouslltolMoreover.MnOpromotergrca… 相似文献
66.
A. Fruchtman J. L. Hirshfield 《International Journal of Infrared and Millimeter Waves》1981,2(5):905-913
A finite spread in axial momentum for the electron beam in a free electron laser amplifier is shown to decrease the small-signal gain. For millimeter and sub-millimeter wave amplifiers, where exponential growth dominates the gain, it is shown that the gain is approximately 3 db below that for a cold beam if the relative momentum spread (u/u)1/2 = (Go/248)1/2 (o/L), where Go1 is the gain in db for the cold-beam case, o is the magnetic wiggler period, and L is the amplifier length. Exact numerical examples are given for representative FEL amplifiers at 35 and 550 GHz.This research was sponsored by the U.S. Office of Naval Research, and by the U.S.-Israel Binational Science Foundation. 相似文献
67.
68.
由光的波动方程证明,若介质为旋光物质,则其极化率张量χ一定有非对角对称的共轭虚元素,并导出了旋光晶体的寻常折射率no与左旋光折射率nL和右旋光折射率nR之间的关系.将理论分析结果与实验数据相对照,结果完全吻合. 相似文献
69.
利用光栅最小偏向角法测光波波长 总被引:1,自引:0,他引:1
本文导出斜入射时,光栅谱线存在最小偏向角的条件及最小偏向角与波长间的关系,据此精确测定了光波波长,并在实验中通过与垂直入射法的比较显出其优越性。 相似文献
70.
The rational design of small building block molecules and understanding their molecular assemblies are of fundamental importance in creating new stimuli-responsive organic architectures with desired shapes and functions. Based on the experimental results of light-induced conformational changes of four types of triangular azo dyes with different terminal functional groups, as well as absorption and fluorescence characteristics associated with their molecular assemblies, we report that aggregation-active emission enhancement (AIEE)-active compound (1) substituted with sterically crowded tert-butyl (t-Bu) groups showed approximately 35% light-induced molecular switching and had a strong tendency to assemble into highly stable hexagonal structures with AIEE characteristics. Their sizes were regulated from nanometer-scale hexagonal rods to micrometer-scale sticks depending on the concentration. This is in contrast to other triangular compounds with bromo (Br) and triphenylamine (TPA) substituents, which exhibited no photoisomerization and tended to form flexible fibrous structures. Moreover, non-contact exposure of the fluorescent hexagonal nanorods to ultraviolet (UV) light led to a dramatic hexagonal-to-amorphous structure transition. The resulting remarkable variations, such as in the contrast of microscopic images and fluorescence characteristics, were confirmed by various microscopic and spectroscopic measurements. 相似文献