全文获取类型
收费全文 | 1618篇 |
免费 | 43篇 |
国内免费 | 8篇 |
专业分类
化学 | 1145篇 |
晶体学 | 15篇 |
力学 | 20篇 |
数学 | 172篇 |
物理学 | 317篇 |
出版年
2022年 | 9篇 |
2021年 | 7篇 |
2020年 | 9篇 |
2019年 | 17篇 |
2018年 | 7篇 |
2017年 | 18篇 |
2016年 | 28篇 |
2015年 | 21篇 |
2014年 | 32篇 |
2013年 | 72篇 |
2012年 | 54篇 |
2011年 | 98篇 |
2010年 | 50篇 |
2009年 | 64篇 |
2008年 | 84篇 |
2007年 | 108篇 |
2006年 | 101篇 |
2005年 | 112篇 |
2004年 | 89篇 |
2003年 | 73篇 |
2002年 | 87篇 |
2001年 | 33篇 |
2000年 | 29篇 |
1999年 | 25篇 |
1998年 | 17篇 |
1997年 | 23篇 |
1996年 | 19篇 |
1995年 | 17篇 |
1994年 | 16篇 |
1993年 | 10篇 |
1992年 | 22篇 |
1991年 | 14篇 |
1990年 | 14篇 |
1989年 | 15篇 |
1988年 | 16篇 |
1987年 | 11篇 |
1986年 | 10篇 |
1985年 | 27篇 |
1984年 | 25篇 |
1983年 | 14篇 |
1982年 | 21篇 |
1981年 | 16篇 |
1980年 | 24篇 |
1979年 | 18篇 |
1978年 | 9篇 |
1977年 | 8篇 |
1976年 | 12篇 |
1975年 | 16篇 |
1974年 | 13篇 |
1973年 | 8篇 |
排序方式: 共有1669条查询结果,搜索用时 250 毫秒
1.
2.
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
3.
A new method for rotation and brightness invariant pattern recognition was proposed by applying multiple circular harmonic expansions to the joint transform correlator. The amplitudes of the multiple orders of circular harmonic expansions made from a detecting image were synthetically modified to respond to the same auto-correlation peaks. These modified circular harmonic expansions were arranged in the input plane as reference patterns together with an arbitrary target pattern, and the correlation signals between them were calculated in the subtracted joint transform correlator. The fraction of the correlation-peak intensities between the target and the references were extracted as a new discrimination parameter. This new parameter performs pattern recognition under rotation and brightness invariance with good discriminability. Its high discriminability has been proved in computer simulations using the face image patterns of many individuals. 相似文献
4.
Linear propagation of two pulses through methanol solution of aluminum phthalocyanine chloride is investigated using a modified white-light Michelson interferometer. The observed coherence time of the white light is 6 fs, and the separation between the two-excitation pulses is set to about 10 fs. The excitation is dependent on the phase-relation between the two pulses. We have observed an enhancement of the excitation when the two pulses are in-phase and strong suppression of the excitation when the two pulses are out of phase by π. 相似文献
5.
Betancourt L Takao T Hernandez L Padron G Shimonishi Y 《Journal of mass spectrometry : JMS》1999,34(3):169-174
High-resolution matrix-assisted laser desorption/ionization time-of-flight mass spectrometry was used to characterize the primary structure of the levansucrase (EC 2.4.1.10) secreted by Acetobacter diazotropicus SRT4. The technique permitted not only the reading frame of this enzyme, the amino acid sequence of which was deduced from DNA, but also the elucidation of an N-terminal blocking group and the position of a disulfide bridge between Cys309 and Cys365 among the three Cys residues. A free cysteine (Cys127) was identified by modifying an intact molecule with a sulfhydryl reagent, 5-(octyldithio)-2-nitrobenzoic acid, under non-reducing conditions. In addition, the enzyme obtained by site-directed mutagenesis at Asp279 to Asn279 was also identified by the above methods. Post-source decay analysis of the tryptic peptide containing the mutation site unequivocally revealed an Asn residue at position 279. 相似文献
6.
Small amounts of polycyclic aromatic hydrocarbons (PAHs) in aqueous solution were almost completely adsorbed on barium salts of copper (II) sulphophthalocyanines and cobalt (II) phthalocyanine, which were precipitated from the solution. Recoveries of the PAHs from the precipitates by thermal desorption gas chromatography were 71–95%. The method is useful for the concentration and analysis of medium molecular weight, thermally stable PAHs. 相似文献
7.
8.
9.
The structure and stereochemistry of scopadulin, a novel aphidicolane-type diterpene isolated from Scoparia dulcis L. have been established from spectral data and single-crystal X-ray analysis of its acetone solvate. 相似文献
10.
Properties and efficacies of novel aldose reductase (AR) inhibitors, M16209 (1-(3-bromobenzo[b]furan-2-ylsulfonyl)hydantoin) and M16287 (1-(3-chlorobenzo[b]furan-2-ylsulfonyl)hydantoin), were examined in vitro and in vivo, compared with known AR inhibitors, ONO-2235 and sorbinil. These four compounds inhibited partially purified aldose reductases from various origins, and the potencies of M16209 and M16287 were on the whole similar to ONO-2235, and were greater than that of sorbinil. The IC50 values of the four AR inhibitors did not substantially depend on the substrate used. Kinetic studies of inhibition of partially purified bovine lens (BLAR) revealed that M16209, M16287 and sorbinil were uncompetitive with glyceraldehyde and noncompetitive with nicotineamide adenine dinucleotide phosphate (NADPH), whereas ONO-2235 was noncompetitive with both glyceraldehyde and NADPH. Aldose reductase became less sensitive to the four inhibitors as enzyme purification progressed, although the susceptibility to inhibition was partially reversed by incubation with dithiothreitol. In addition, the four compounds slightly affected those enzymes of carbohydrate and glutathione metabolism which were tested. M16209 and M16287 prevented sorbitol accumulation in isolated rat tissues as potently as ONO-2235 and sorbinil. M16209 and M16287 were effective in the prevention of galactosemic cataracts and amelioration of diabetic neuropathy with almost the same potency, while ONO-2235 was effective only in neuropathy, and sorbinil was effective in galactosemic cataracts and diabetic neuropathy with a different potency. These results indicate that M16209 and M16287 are potent aldose reductase inhibitors, which could be applicable to treatment for diabetic complications. 相似文献