全文获取类型
收费全文 | 1787篇 |
免费 | 39篇 |
国内免费 | 7篇 |
专业分类
化学 | 1387篇 |
晶体学 | 29篇 |
力学 | 20篇 |
数学 | 122篇 |
物理学 | 275篇 |
出版年
2022年 | 8篇 |
2021年 | 18篇 |
2019年 | 20篇 |
2018年 | 13篇 |
2016年 | 22篇 |
2015年 | 19篇 |
2014年 | 27篇 |
2013年 | 65篇 |
2012年 | 71篇 |
2011年 | 86篇 |
2010年 | 57篇 |
2009年 | 37篇 |
2008年 | 78篇 |
2007年 | 95篇 |
2006年 | 101篇 |
2005年 | 111篇 |
2004年 | 85篇 |
2003年 | 59篇 |
2002年 | 82篇 |
2001年 | 15篇 |
2000年 | 20篇 |
1999年 | 25篇 |
1998年 | 28篇 |
1997年 | 20篇 |
1996年 | 28篇 |
1995年 | 25篇 |
1994年 | 16篇 |
1993年 | 26篇 |
1992年 | 16篇 |
1991年 | 13篇 |
1990年 | 12篇 |
1989年 | 14篇 |
1988年 | 19篇 |
1987年 | 21篇 |
1986年 | 18篇 |
1985年 | 37篇 |
1984年 | 41篇 |
1983年 | 26篇 |
1982年 | 32篇 |
1981年 | 31篇 |
1980年 | 24篇 |
1979年 | 29篇 |
1978年 | 31篇 |
1977年 | 26篇 |
1976年 | 37篇 |
1975年 | 28篇 |
1974年 | 27篇 |
1973年 | 26篇 |
1972年 | 13篇 |
1971年 | 9篇 |
排序方式: 共有1833条查询结果,搜索用时 0 毫秒
1.
By extracting combinatorial structures in well-solved nonlinear combinatorial optimization problems, Murota (1996,1998) introduced the concepts of M-convexity and L-convexity to functions defined over the integer lattice. Recently, Murota–Shioura (2000, 2001) extended these concepts to polyhedral convex functions and quadratic functions in continuous variables. In this paper, we consider a further extension to more general convex functions defined over the real space, and provide a proof for the conjugacy relationship between general M-convex and L-convex functions.Mathematics Subject Classification (1991): 90C10, 90C25, 90C27, 90C35This work is supported by Grant-in-Aid of the Ministry of Education, Culture, Sports, Science and Technology of Japan 相似文献
2.
3.
Abstract— A new method of using hydroxylamine as the reagent was developed to determine the concentrations of chlorophylls a and b in plant extracts accurately and sensitively. The method is based on the principle that hydroxylamine reacts in a short time with the aldehyde group of chlorophyll b in 95 per cent methanol at pH 5.8 to afford a derivative having a red band similar in position to the red band of chlorophyll a , while the spectrum of chlorophyll a is unaffected by the treatment with hydroxylamine. The method includes the measurements of absorbanlce for the mixture of a plant extract with hydroxylamine and for the reagent blank at a single wavelength, 666 mμ, and the concentrations of chlorophylls a and b are calculated from the absorbance value for the reagent blank and the increment of absorbance due to the reaction. By measuring this increment directly by difference photometry, one can determine a low concentration of chlorophyll b relative to chlorophyll a . The contents of chlorophylls in matured and etiolated leaves were determined by the method, and the errors included in this method were shown to be smaller than those in a commonly used technique including the measurements at two different wavelengths. 相似文献
4.
Synthesis and structures of the title compounds 2a–d are described. In spite of non-parallel orientation of the two base rings, fairly large hypochromism was observed for 2a–d. 相似文献
5.
The hydrothermal syntheses of the alkali metal molybdenum bronzes from starting solids (HxMoO3) with structural affinities to the desired products were investigated. Single-phase potassium blue and red bronzes were prepared by the hydrothermal treatments at around 430 K, and characterized by powder X-ray diffraction, IR spectroscopy, and SEM. The formation processes of these two bronzes during the hydrothermal treatments were found to differ. The blue bronze was formed by a structure-inheriting solid-state route from HxMoO3 with x<0.3, whereas the red bronze was formed for x>0.3 through a solution dissolution/deposition route via the formation of MoO3+MoO2. 相似文献
6.
7.
Shinji Inagaki Yoshiaki Fukushima Kazuo Kuroda Kazuyuki Kuroda 《Journal of colloid and interface science》1996,180(2):623
The first and second adsorption–desorption isotherms of water vapor on a new mesoporous material derived from kanemite have been measured. The isotherms show unusual type V isotherms and large hysteresis. The type V isotherms, which have never been observed for the other adsorbates, suggest that the mesoporous material has a hydrophobic surface, although the hydrophobicity decreased after treatment with water vapor because of rehydration of the surface. The significantly large hysteresis could be explained by the difference in contact angle between adsorption and desorption. 相似文献
8.
[structure: see text] A highly convergent synthetic route to the FGHIJKLM ring fragment of ciguatoxins has been developed, which relied on extensive use of the B-alkyl Suzuki-Miyaura coupling reaction. 相似文献
9.
A new type of atomic absorption spectrometry using the Zeeman effect of sample materials is proposed. A magnetic field was applied to the sample vapor in the direction perpendicular to the propagation of light emitted from an atomic spectral source. Absorption of radiation polarized perpendicular and parallel to the magnetic field was observed alternatively. The absorption difference was proportional to the true atomic absorption, and was not interfered with by any other molecular absorption and light scattering, i.e., background absorption. The background absorption could be monitored at exactly the same wavelength as an atomic absorption line. Suitable magnetic field strength was found for each line of the various elements. 相似文献
10.
Chiral urea compounds 10a-g were synthesized as catalysts for conjugate addition of pyrrolidine (2) to gamma-crotonolactone (3). In the presence of a catalytic amount of the chiral ureas, this hetero-Michael reaction was greatly accelerated. Asymmetric induction was observed with the catalysts 10e, 10f, and 10g. 相似文献