全文获取类型
收费全文 | 1691篇 |
免费 | 46篇 |
国内免费 | 11篇 |
专业分类
化学 | 1231篇 |
晶体学 | 17篇 |
力学 | 19篇 |
数学 | 173篇 |
物理学 | 308篇 |
出版年
2022年 | 10篇 |
2021年 | 10篇 |
2020年 | 13篇 |
2019年 | 16篇 |
2017年 | 19篇 |
2016年 | 33篇 |
2015年 | 24篇 |
2014年 | 32篇 |
2013年 | 94篇 |
2012年 | 60篇 |
2011年 | 89篇 |
2010年 | 48篇 |
2009年 | 62篇 |
2008年 | 90篇 |
2007年 | 110篇 |
2006年 | 99篇 |
2005年 | 117篇 |
2004年 | 96篇 |
2003年 | 72篇 |
2002年 | 79篇 |
2001年 | 26篇 |
2000年 | 30篇 |
1999年 | 25篇 |
1998年 | 19篇 |
1997年 | 19篇 |
1996年 | 29篇 |
1995年 | 13篇 |
1994年 | 11篇 |
1992年 | 26篇 |
1991年 | 10篇 |
1990年 | 13篇 |
1989年 | 13篇 |
1988年 | 10篇 |
1987年 | 12篇 |
1985年 | 26篇 |
1984年 | 21篇 |
1983年 | 14篇 |
1982年 | 23篇 |
1981年 | 17篇 |
1980年 | 27篇 |
1979年 | 18篇 |
1978年 | 12篇 |
1977年 | 13篇 |
1976年 | 14篇 |
1975年 | 17篇 |
1974年 | 14篇 |
1973年 | 9篇 |
1968年 | 12篇 |
1967年 | 15篇 |
1966年 | 10篇 |
排序方式: 共有1748条查询结果,搜索用时 187 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.
5.
Kentaro Suzuya Tomoaki Kamiyama Takemi Yamamura Kiyohito Okamura Kenji Suzuki 《Journal of Non》1992,150(1-3):167-171
A small-angle X-ray scattering (SAXS) study was performed to reveal the nanometer scale hybrid structure of Si---Ti---C---O fibers prepared by the pyrolysis of polytitanocarbosilane. The SAXS profile for Si---Ti---C---O fibers is attributed to two different types of scattering entities: an anisotropic contribution from long filaments with diameters hundreds to thousands of Ångströms and an isotropic contribution from β-SiC fine clusters of about a nanometer in diameter. A drastic degradation in the tensile strength of the fibers is correlated to the characteristic variations in their long-and medium-range structure. 相似文献
6.
7.
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
8.
V. P. Ladygin T. Uesaka T. Saito M. Hatano A. Yu. Isupov H. Kato N. B. Ladygina Y. Maeda A. I. Malakhov J. Nishikawa T. Ohnishi H. Okamura S. G. Reznikov H. Sakai N. Sakamoto S. Sakoda Y. Satou K. Sekiguchi K. Suda A. Tamii N. Uchigashima K. Yako 《Physics of Atomic Nuclei》2006,69(8):1271-1278
RIKEN Accelerator Research Facility data on the tensor analyzing power T 20 of the dd → 3Hen and dd → 3Hp reactions at zero angle for deuteron kinetic energies of 140, 200, and 270 MeV are reported. The observed positive sign of T 20 clearly demonstrates the sensitivity to the D/S-wave ratio in the 3He and 3H wave functions in the energy range of the experiment. Data on T 20 for the 3Hen channel are in agreement with those for the 3Hp channel within the experimental errors. 相似文献
9.
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
10.