全文获取类型
收费全文 | 5760篇 |
免费 | 1269篇 |
国内免费 | 457篇 |
专业分类
化学 | 2973篇 |
晶体学 | 15篇 |
力学 | 76篇 |
综合类 | 14篇 |
数学 | 62篇 |
物理学 | 4346篇 |
出版年
2024年 | 34篇 |
2023年 | 54篇 |
2022年 | 291篇 |
2021年 | 321篇 |
2020年 | 353篇 |
2019年 | 309篇 |
2018年 | 260篇 |
2017年 | 327篇 |
2016年 | 384篇 |
2015年 | 354篇 |
2014年 | 611篇 |
2013年 | 524篇 |
2012年 | 433篇 |
2011年 | 446篇 |
2010年 | 348篇 |
2009年 | 373篇 |
2008年 | 365篇 |
2007年 | 356篇 |
2006年 | 228篇 |
2005年 | 184篇 |
2004年 | 137篇 |
2003年 | 113篇 |
2002年 | 94篇 |
2001年 | 65篇 |
2000年 | 85篇 |
1999年 | 71篇 |
1998年 | 62篇 |
1997年 | 55篇 |
1996年 | 45篇 |
1995年 | 28篇 |
1994年 | 25篇 |
1993年 | 17篇 |
1992年 | 22篇 |
1991年 | 16篇 |
1990年 | 21篇 |
1989年 | 14篇 |
1988年 | 11篇 |
1987年 | 13篇 |
1986年 | 3篇 |
1985年 | 10篇 |
1984年 | 11篇 |
1983年 | 1篇 |
1982年 | 9篇 |
1980年 | 2篇 |
1975年 | 1篇 |
排序方式: 共有7486条查询结果,搜索用时 0 毫秒
1.
2.
通过分析计算,设计了一种大口径宽视场折射式红外相机光学系统。该系统设计用于超长线阵扫描红外相机的地面演示成像,它能同时对短波2μm—3μm、中波3μm—4.5μm双波段成像,且同时具有24°的大视场和150mm的宽口径,成像质量接近衍射极限。该系统在航天遥感领域应用广泛。 相似文献
3.
K. Dayananda R. Dhamodharan K. Vijayakumaran T. Rajamannar 《Journal of polymer science. Part A, Polymer chemistry》2004,42(21):5413-5423
A monolayer of covalently anchored, novel, binaphthyl ketone is used as a surface‐confined photochemical radical generator (PRG) for anchoring a variety of polymers to silicon surfaces. The precursor PRG is synthesized by the application of a facile and novel method for the oxidation of sterically hindered benzylic hydrocarbons to carbonyl compounds. Oxidation was carried out with a stoichiometric amount of potassium peroxydisulfate, in the presence of a catalytic amount of copper sulfate in an acetonitrile/water mixture. The PRG synthesized is characterized by 1H NMR, UV, and Fourier transform infrared (FTIR). The covalently attached monolayers are characterized by X‐ray photoelectron spectroscopy, ellipsometry, and water contact angle measurements. The method developed is applicable to the preparation of a monolayer of a variety of polymers on a wide range of substrates carrying surface hydroxyl groups. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5413–5423, 2004 相似文献
4.
5.
6.
Recently, molecular imaging has been rapidly developed to studyphysiological and pathological processes in vivo at the cellularand molecular levels. Among molecular imaging modalities, opticalimaging has attracted a major attention for its unique advantages.In this paper, we establish a mathematical framework for multispectralbioluminescence tomography (BLT) that allows simultaneous studiesof multiple optical reporters. We show solution existence, uniquenessand continuous dependence on data as well as the limiting behaviourswhen the regularization parameter approaches zero or when thepenalty parameter approaches infinity. Then, we propose twonumerical schemes for multispectral BLT and derive error estimatesfor the corresponding solutions. 相似文献
7.
《Magnetic resonance in chemistry : MRC》2003,41(8):585-588
A novel, radical responsive MRI contrast agent based on a gadolinium chelate conjugated to a liposome through a disulfide linker was synthesized, with the aim of pursuing the in vivo mapping of radicals. The liposome was prepared by incorporating a thiol‐activated phospholipid, which was subsequently reacted with a gadolinium chelate containing a free thiol group. The long reorientational motion of the supramolecular adduct endows the paramagnetic agent with a relaxivity significantly higher than that of the free complex. The disulfide bond represents a radical‐sensitive moiety and a large decrease in contrast efficacy (T1 relaxivity) is shown upon its cleavage. A preliminary assessment of the system was made by means of in vitro gamma‐irradiation and thiol–disulfide bond exchange with dithiothreitol. Both methods showed a clear dose‐dependent decrease in T1‐relaxivity. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
8.
《Surface and interface analysis : SIA》2004,36(9):1304-1313
For rough heterogeneous samples, the contrast observed in XPS images may result from both changes in elemental or chemical composition and sample topography. Background image acquisition and subtraction are frequently utilized to minimize topographical effects so that images represent concentration variations in the sample. This procedure may significantly increase the data acquisition time. Multivariate statistical methods can assist in resolving topographical and chemical information from multispectral XPS images. Principal component analysis (PCA) is one method for identification of the highest correlation/variation between the images. Topography, which is common to all of the images, will be resolved in the first most significant component. The score of this component contains spatial information about the topography of the surface, whereas the loading is a quantitative representation of the topography contribution to each elemental/chemical image. The simple‐to‐use self‐modelling mixture analysis (Simplisma) method is a pure variable method that searches for the source of most differences in the data and therefore has the potential to distinguish between chemical and topographical phases in images. The mathematical background correction scheme is developed and validated by comparing results to the experimental background correction for samples with differing degrees of topography. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
9.
10.
Endoscopic Observation of Tissue by Narrowband Illumination 总被引:6,自引:0,他引:6
Kazuhiro Gono Kenji Yamazaki Nobuyuki Doguchi Tetsuo Nonami Takashi Obi Masahiro Yamaguchi Nagaaki Ohyama Hirohisa Machida Yasushi Sano Shigeaki Yoshida Yasuo Hamamoto Takao Endo 《Optical Review》2003,10(4):211-215
We propose a new illumination method for a medical endoscope: narrow band imaging (NBI), in which the spectral bandwidth of the filtered light is narrowed. To confirm how the spectral specifications of the filtered light influence a reproduced image, an experiment was conducted observing the endoscopic images of the back mucosa of a human tongue. In addition, the effect of NBI on endoscopic images was investigated through preliminary clinical tests in colonoscopy and upper gastrointestinal endoscopy. It has been shown that NBI can enhance the capillary pattern and the crypt pattern on the mucosa. These patterns are useful features for diagnosing an early cancer. 相似文献