全文获取类型
收费全文 | 1046篇 |
免费 | 26篇 |
国内免费 | 8篇 |
专业分类
化学 | 842篇 |
晶体学 | 7篇 |
力学 | 10篇 |
数学 | 69篇 |
物理学 | 152篇 |
出版年
2022年 | 8篇 |
2021年 | 14篇 |
2020年 | 8篇 |
2019年 | 19篇 |
2018年 | 16篇 |
2017年 | 6篇 |
2016年 | 20篇 |
2015年 | 15篇 |
2014年 | 30篇 |
2013年 | 48篇 |
2012年 | 55篇 |
2011年 | 60篇 |
2010年 | 31篇 |
2009年 | 23篇 |
2008年 | 46篇 |
2007年 | 61篇 |
2006年 | 50篇 |
2005年 | 63篇 |
2004年 | 67篇 |
2003年 | 46篇 |
2002年 | 57篇 |
2001年 | 16篇 |
2000年 | 15篇 |
1999年 | 12篇 |
1998年 | 8篇 |
1997年 | 12篇 |
1996年 | 24篇 |
1995年 | 11篇 |
1994年 | 12篇 |
1993年 | 7篇 |
1992年 | 11篇 |
1991年 | 7篇 |
1989年 | 5篇 |
1988年 | 17篇 |
1985年 | 12篇 |
1984年 | 12篇 |
1983年 | 9篇 |
1982年 | 18篇 |
1981年 | 6篇 |
1980年 | 9篇 |
1979年 | 8篇 |
1978年 | 7篇 |
1977年 | 5篇 |
1976年 | 6篇 |
1974年 | 7篇 |
1973年 | 7篇 |
1970年 | 5篇 |
1967年 | 5篇 |
1938年 | 4篇 |
1935年 | 4篇 |
排序方式: 共有1080条查询结果,搜索用时 0 毫秒
21.
Analysis of Spectral Reflectance Using Normalization Method from Endoscopic Spectroscopy System 总被引:2,自引:0,他引:2
Masao Sambongi Makoto Igarashi Takashi Obi Masahiro Yamaguchi Nagaaki Ohyama Masahiko Kobayashi Yasushi Sano Shigeaki Yoshida Kazuhiro Gono 《Optical Review》2002,9(6):238-243
Objective assessment of gastrointestinal mucosal color is extremely important in the endoscopic diagnosis of digestive tract disease. In this paper, we propose a method to clarify the spectral characteristics of gastric and colon cancer. A large number of spectral reflectance data of mucous membrane are measured by the endoscopic spectroscopy system (ESS) in the National Cancer Center Hospital East, Kashiwa, Japan and the Department of Internal Medicine, Self-Defense Force Center Hospital, Tokyo, Japan. We assume that early cancer appears primarily in the spectral data of short wavelength, because it is usually present in a superficial cell where short wavelength light is scattered more strongly than long wavelength light. To identify the features in the short wavelength components, the spectral reflectance was divided by the reflectance of a long wavelength. We investigated the possibility of distinguishing early cancer from normal spectral data through statistical analysis, employing the projection axis as the mean difference between them. Early cancer and normal spectral data were projected on the projection axis, and the Student’s T-test was applied to evaluate the mean of the distribution between these data. 相似文献
22.
A holographic photopolymer based on SU-8 epoxy resin as the binder and trimethylolpropane ethoxylate triacrylate as the monomer with an iodonium salt photoinitiator was studied. A diffraction efficiency of 93% and a refractive index modulation (Delta n) of 1.3 x 10(-2) were obtained from a 16 microm thick sample with write beam intensities of 50 mW/cm(2) at a wavelength of 514.5 nm, an exposure time of 60 s, and a postbaking at 65 degrees C for 1 h. The material exhibits good heat resistance in the range from 40 degrees C to 160 degrees C and long projected life. 相似文献
23.
Yousuke Fukaya Takashi Yanase Yasushi Kubota Shigeki Imai Taketoshi Matsumoto Hikaru Kobayashi 《Applied Surface Science》2010,256(18):5610-5613
We have developed the advanced nitric acid oxidation of Si (NAOS) method to form relatively thick (5-10 nm) SiO2/Si structure with good electrical characteristics. This method simply involves immersion of Si in 68 wt% nitric acid aqueous solutions at 120 °C with polysilazane films. Fourier transform infrared absorption (FT-IR) measurements show that the atomic density of the NAOS SiO2 layer is considerably high even without post-oxidation anneal (POA), i.e., 2.28 × 1022 atoms/cm2, and it increases by POA at 400 °C in wet-oxygen (2.32 × 1022 atoms/cm2) or dry-oxygen (2.30 × 1022 atoms/cm2). The leakage current density is considerably low (e.g., 10−5 A/cm2 at 8 MV/cm) and it is greatly decreased (10−8 A/cm2 at 8 MV/cm) by POA at 400 °C in wet-oxygen. POA in wet-oxygen increases the atomic density of the SiO2 layer, and decreases the density of oxide fixed positive charges. 相似文献
24.
A glycine receptor is involved in the organization of swimming movements in an invertebrate chordate
Background
Rhythmic motor patterns for locomotion in vertebrates are generated in spinal cord neural networks known as spinal Central Pattern Generators (CPGs). A key element in pattern generation is the role of glycinergic synaptic transmission by interneurons that cross the cord midline and inhibit contralaterally-located excitatory neurons. The glycinergic inhibitory drive permits alternating and precisely timed motor output during locomotion such as walking or swimming. To understand better the evolution of this system we examined the physiology of the neural network controlling swimming in an invertebrate chordate relative of vertebrates, the ascidian larva Ciona intestinalis. 相似文献25.
The Ag induced superstructures on the Si(111) surface have been studied by low energy electron diffraction constant momentum transfer averaging (LEED/CMTA) technique. The vertical displacements of the atoms are determined from the analysis of the specularly reflected (00) beam intensities. Unexpected behavior of the Ag atoms is clarified: For the √3 × √3-Ag surface it is verified that the Ag atoms are embedded in the first double layer of Si, leading to a considerable rearrangement of the substrate. In contrast, for the 3 × 1-Ag surface, the Ag atoms are riding on the Si surface and the reconstruction of the substrate is small. 相似文献
26.
27.
Tomohiro Suetsuna Seiichi SuenagaShinya Sakurada Koichi HaradaMaki Tomimatsu Toshihide Takahashi 《Journal of magnetism and magnetic materials》2011,323(13):1793-1798
Self-forming core/shell nanoparticles of magnetic metal/oxide with crystalline grain size of less than 40 nm were synthesized. The nanoparticles were highly concentrated in an insulating matrix to fabricate a nanocomposite, whose magnetic properties were investigated. The crystalline grain size of the nanoparticles strongly influenced the magnetic anisotropy field, magnetic coercivity, relative permeability, and loss factor (tan δ=μ″/μ′) at high frequency. The packing ratio of the magnetic metallic phase in the nanocomposite also influenced those properties. High permeability with low tan δ of less than 1.5% at up to 1 GHz was obtained in the case of the nanoparticles with crystalline grain size of around 15 nm with large packing ratio of the nanoparticles. 相似文献
28.
Kitajima K Yoshikawa T Seo Y Ohno Y Yano Y Miki A Kanda T Kanata N Azuma T Sugimura K 《Magnetic resonance imaging》2011,29(4):579-583
Budd-Chiari syndrome (BCS) is a rare disorder caused by the obstruction of hepatic venous outflow, leading to sinusoidal congestion, ischemic injury to liver cells and portal hypertension. Long-term survival largely depends on whether hepatocellular carcinoma occurs. A recently available liver-specific contrast medium, gadolinium-ethoxybenzyl-diethylenetriamine penta-acetic acid (Gd-EOB-DTPA), reportedly has high diagnostic capability for detection of malignant liver tumors. However, there has been no report of the sue of Gd-EOB-DTPA-enhanced magnetic resonance imaging (MRI) for BCS. We present a case of chronic BCS who underwent both gadopentetate dimeglumine (Gd-DTPA) and Gd-EOB-DTPA-enhanced MRI. Hepatic congestion and edema were seen as slightly hypointense areas on Gd-EOB-DTPA-enhanced hepatobiliary-phase images, although these areas were observed as slightly hyperintense on previously obtained Gd-DTPA-enhanced delayed-phase image. Reduced uptake of Gd-EOB-DTPA by hepatocytes in the region of congestion or edema may account for this difference, which should be recognized in image interpretations. 相似文献
29.
Fujimoto Yasushi Loewe M. Rojas J. C. 《Zeitschrift fur Physik C Particles and Fields》1994,61(3):495-509
Quasi-primary fields with dimensions that differ at most byO(1/N) and whose other quantum numbers are all equal, are called degenerate. Multiplets of such fields are produced by a chain of fusion processes. Forcing the fusion to run through different intermediate states leads to matrices of fusion and anomalous dimension amplitudes whose simultaneous diagonalization allows to resolve the degeneracy. 相似文献
30.
Yasushi Yokoya 《Physica D: Nonlinear Phenomena》2010,239(3-4):207-213
We studied the nature of fluctuations around the phase transition of vehicular traffic by analyzing a time series of successive variations of velocity, obtained from single-vehicle data measured by an onboard apparatus. We found that the probability density function calculated from the time series of variation of velocity is transformed irreversibly in the critical region, where a Gaussian distribution changes into a Lévy stable symmetrical distribution. The power-law tail in the Lévy distribution indicated that the time series of velocity variation exhibits the nature of the critical fluctuations generally observed in phase transitions driven far from equilibrium. Furthermore, single-vehicle data enabled us to calculate the time evolution of the local flux–density relation, which suggested that the vehicular traffic system spontaneously approaches a delicate balance between metastable states and congested-flow states. The nature of fluctuations enables us to understand mechanisms behind the spontaneous decay of the metastable branch at the phase transition. The power-law tail in the probability density function suggests that dynamical processes of vehicular traffic in the critical region are related to a time-discrete stochastic process driven by random amplification with additive external noise. 相似文献