全文获取类型
收费全文 | 2689篇 |
免费 | 68篇 |
国内免费 | 12篇 |
专业分类
化学 | 1987篇 |
晶体学 | 44篇 |
力学 | 47篇 |
数学 | 160篇 |
物理学 | 531篇 |
出版年
2022年 | 13篇 |
2021年 | 22篇 |
2020年 | 18篇 |
2019年 | 33篇 |
2018年 | 12篇 |
2017年 | 19篇 |
2016年 | 34篇 |
2015年 | 43篇 |
2014年 | 53篇 |
2013年 | 148篇 |
2012年 | 122篇 |
2011年 | 137篇 |
2010年 | 83篇 |
2009年 | 82篇 |
2008年 | 150篇 |
2007年 | 156篇 |
2006年 | 154篇 |
2005年 | 161篇 |
2004年 | 132篇 |
2003年 | 105篇 |
2002年 | 115篇 |
2001年 | 63篇 |
2000年 | 63篇 |
1999年 | 46篇 |
1998年 | 42篇 |
1997年 | 26篇 |
1996年 | 39篇 |
1995年 | 26篇 |
1994年 | 36篇 |
1993年 | 33篇 |
1992年 | 34篇 |
1991年 | 31篇 |
1990年 | 22篇 |
1989年 | 29篇 |
1988年 | 13篇 |
1987年 | 18篇 |
1986年 | 25篇 |
1985年 | 44篇 |
1984年 | 38篇 |
1983年 | 25篇 |
1982年 | 45篇 |
1981年 | 40篇 |
1980年 | 23篇 |
1979年 | 32篇 |
1978年 | 21篇 |
1977年 | 22篇 |
1976年 | 26篇 |
1975年 | 19篇 |
1974年 | 19篇 |
1973年 | 25篇 |
排序方式: 共有2769条查询结果,搜索用时 15 毫秒
1.
2.
3.
In this study we examined the unsteady and chaotic characteristics of the natural convection field in vertical slots at large
Prandtl number. In the computation, temperature dependence of viscosity was partially taken into consideration. As a result
we discovered that the spatial region where a significant temperature fluctuation is detected corresponds to the spatial region
where the secondary cells exist. The largest Lyapunov exponents calculated from the temperature on the center line have a
local maximum at the lower region of the enclosure when the viscosity change was considered. These characteristics agree well
with the experimental ones that have been observed by authors (Ishida, Kure and Kimoto 2001). 相似文献
4.
5.
Er-Si-O crystalline compounds, which exhibit superlattice structures and sharp and strong Er-related 1.54 μm photoluminescence (PL) spectra at room temperature have been formed by self-assembling growth mechanism. Oxidation of the starting materials which have Si and Er at an atomic ratio of 2:1 are prepared and then oxidation and succeeding high-temperature annealing in Ar above 1250 °C cause a self-assembled superlattice-structured Er-Si-O crystalline compounds. The control of the ratio of Si and Er, as well as the following oxidation and annealing processes, is found to be sensitive to the crystalline properties, PL spectra and electrical properties. In this study, Er-Si-O crystalline thin films are formed on Si substrates by sol-gel and MOMBE methods, and their crystalline properties such as crystalline orientation and concentration ratio of Er, Si and O are investigated. Crystalline Er-Si-O films of high orientation are successfully grown on Si(1 0 0) and its inclined surface. The PL and excitation spectra, fluorescence decay and the electrical properties are found to be strongly related to the crystalline properties. Excess O causes a broader 1.54 μm PL spectra, slower fluorescence decay, lower carrier-mediated excitation and higher resistivity. A precise control of O is found to be necessary to grow superlattice-structured Er-Si-O compounds, which are semiconducting and are excitable via carrier-mediated excitation mechanism. 相似文献
6.
N Murakami T Morimoto H Imamura T Ueda S Nagai J Sakakibara N Yamada 《Chemical & pharmaceutical bulletin》1991,39(9):2277-2281
Seven new monogalactosyl diacylglycerols (1-7) and six new digalactosyl diacylglycerols (11-16) were isolated from an axenically cultured cyanobacterium, P. tenue. Their structures were elucidated on the basis of physicochemical evidence and the results of enzymatic hydrolysis using a lipase (from Rhizopus arrhizus). Comparison of antialgal activity for P. tenue between monogalactosyl diacylglycerols (1-8) and digalactosyl diacylglycerols (11-19) revealed that the former showed more potent activity than the latter. 相似文献
7.
Takeshi Murashige Hideo Fujikake Hiroto Sato Hiroshi Kikuchi Taiichiro Kurita Fumio Sato 《Optical Review》2004,11(6):349-352
We have confirmed light diffraction of aligned polymer fibers obtained by a phase separation of an anisotropic-phase solution of liquid crystal and polymer. He—Ne laser light passing through the polymer fibers was scattered in the axis vertical to the fibers, and had two peaks of light intensity symmetrical to the center of the transmitting laser spot. The two peaks were found to be caused by light diffraction due to the periodic polymer-fiber dispersion because the peaks corresponded to values calculated by intervals between the fibers. The periodical fiber networks are considered to be formed by anisotropic spinodal decomposition. This effect can be used to measure the dispersion order of the polymer fibers. © 2004 The Optical Society of Japan 相似文献
8.
Shigeyuki Toki Igors Sics Benjamin S. Hsiao Syozo Murakami Masatoshi Tosaka Sirilux Poompradub Shinzo Kohjiya Yuko Ikeda 《Journal of Polymer Science.Polymer Physics》2004,42(6):956-964
The molecular orientation and strain‐induced crystallization of synthetic rubbers—polyisoprene rubber, polybutadiene rubber, and butyl rubber [poly(isobutylene isoprene)]—during uniaxial deformation were studied with in situ synchrotron wide‐angle X‐ray diffraction. The high intensity of the synchrotron X‐rays and the new data analysis method made it possible to estimate the mass fractions of the strain‐induced crystals and amorphous chain segments in both the oriented and unoriented states. Contrary to the conventional concept, the majority of the molecules (50–75%) remained in an unoriented amorphous state at high strains. Each synthetic rubber showed a different behavior of strain‐induced crystallization and molecular orientation during extension and retraction. Our results confirmed the occurence of strain‐induced networks in the synthetic rubbers due to the inhomogeneity of the crosslink distribution. The strain‐induced networks containing microfibrillar crystals and oriented amorphous tie chains were responsible for the ultimate mechanical properties. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 956–964, 2004 相似文献
9.
Takayuki Nakai Yoshiko Murakami Yoshiaki Sasaki Isamu Fujiwara Shoji Tagashira 《Analytical sciences》2004,20(1):235-237
The extraction and separation of copper(II), zinc(II), cobalt(II), and cadmium(II) were investigated. Both copper(II) and zinc(II) formed ammine-complexes, while cadmium(II) and cobalt(II) formed hydroxide precipitates in an ammonia medium. By the addition of sodium dodecylsulfate (SDS), a copper(II) complex formed an ion-pair (copper-ammine-DS), which was extracted into the SDS phase. However, a zinc(II) complex did not form an ion-pair, and was soluble in water. Copper(II) ion was recovered by stripping (back-extraction) after the addition of hydrochloric acid. This method was applied to the separation of copper(II) in a brass alloy. 相似文献
10.
Curved Ferroelectric Liquid Crystal Matrix Displays Driven by Field-Sequential-Color and Active-Matrix Techniques 总被引:1,自引:0,他引:1
Hideo Fujikake Hiroto Sato Takeshi Murashige Yoshihide Fujisaki Taiichiro Kurita Tadahiro Furukawa Fumio Sato 《Optical Review》2006,13(1):14-19
This paper describes a curved field-sequential-color matrix display using fast-response ferroelectric liquid crystal. Black
matrix and transparent electrode patterns were formed on a thin plastic substrate by a transfer method from a glass substrate.
While a composite film of liquid crystal and micro-polymers of walls and fibers was formed between the flexible substrates
by printing, laminating and curing processes of a solution of monomers and liquid crystal, the mechanical stability was enhanced
by use of multi-functional monomers to form large display panels. The image pixels of the matrix panel were driven by an active
matrix scheme using an external switch transistor array at a frequency of 180 Hz for intermittent three-primary-color backlight
illumination. The flexible A4-paper-sized color display with 24 × 16 pixels and 60 Hz field frequency was demonstrated by
illuminating it with sequential three-primary-color lights from light-emitting diodes of the backlight. Our display system
is useful in various information displays because of its freedom of setting and location. 相似文献