全文获取类型
收费全文 | 1084篇 |
免费 | 32篇 |
国内免费 | 2篇 |
专业分类
化学 | 920篇 |
晶体学 | 10篇 |
力学 | 8篇 |
数学 | 29篇 |
物理学 | 151篇 |
出版年
2023年 | 5篇 |
2022年 | 5篇 |
2021年 | 4篇 |
2020年 | 8篇 |
2019年 | 15篇 |
2018年 | 5篇 |
2016年 | 17篇 |
2015年 | 14篇 |
2014年 | 28篇 |
2013年 | 53篇 |
2012年 | 80篇 |
2011年 | 66篇 |
2010年 | 35篇 |
2009年 | 31篇 |
2008年 | 68篇 |
2007年 | 69篇 |
2006年 | 72篇 |
2005年 | 80篇 |
2004年 | 62篇 |
2003年 | 70篇 |
2002年 | 68篇 |
2001年 | 17篇 |
2000年 | 19篇 |
1999年 | 7篇 |
1998年 | 18篇 |
1997年 | 12篇 |
1996年 | 14篇 |
1995年 | 8篇 |
1994年 | 9篇 |
1993年 | 5篇 |
1992年 | 8篇 |
1991年 | 9篇 |
1990年 | 5篇 |
1989年 | 8篇 |
1988年 | 5篇 |
1987年 | 7篇 |
1986年 | 7篇 |
1985年 | 7篇 |
1984年 | 17篇 |
1983年 | 8篇 |
1982年 | 8篇 |
1981年 | 10篇 |
1980年 | 8篇 |
1979年 | 11篇 |
1978年 | 5篇 |
1977年 | 5篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1974年 | 5篇 |
1973年 | 6篇 |
排序方式: 共有1118条查询结果,搜索用时 0 毫秒
121.
Thermal discoloration of cellulose (Avicel PH-101 and Whatman No. 42 filter paper) was studied in N2 at 160-280 °C with glycerol-treated and NaBH4-reduced samples, to understand the role of the reducing end. Thermal discoloration of glycerol-treated Avicel PH-101, in which some of the reducing ends were converted into glycosides (non-reducing ends), was suppressed compared with the original cellulose, and the level of suppression was directly related to the extent of glycosylation of the reducing ends. The stabilization efficiency of glycerol-treated Whatman No. 42 filter paper suggested that the reducing ends newly formed by reduction of the degree of polymerization (DP) (to about 200) during heat treatment contributed to the discoloration. The important role of the reducing ends in thermal discoloration was supported by the stabilization of Avicel PH-101 by reduction with NaBH4 (giving a reducing end content that was 2% of that of the original cellulose). Thermally induced discoloration was also inhibited by heating cellulose in suspension in the polyether tetraethyleneglycol dimethylether, which has been reported to inhibit the thermal degradation of reducing sugars. 相似文献
122.
We propose a modified mechanism for the inhibition of [NiFe]hydrogenase ([NiFe]H(2)ase) by CO. We present a model study, using a NiRu H(2)ase mimic, that demonstrates that (i) CO completely inhibits the catalytic cycle of the model compound, (ii) CO prefers to coordinate to the Ru(II) center rather than taking an axial position on the Ni(II) center, and (iii) CO is unable to displace a hydrido ligand from the NiRu center. We combine these studies with a reevaluation of previous studies to propose that, under normal circumstances, CO inhibits [NiFe]H(2)ase by complexing to the Fe(II) center. 相似文献
123.
124.
Ohno O Chiba T Todoroki S Yoshimura H Maru N Maekawa K Imagawa H Yamada K Wakamiya A Suenaga K Uemura D 《Chemical communications (Cambridge, England)》2011,47(46):12453-12455
Novel sesquiterpene alkaloids, halichonines A (1), B (2), and C (3), were identified from the marine sponge Halichondria okadai Kadota. By spectroscopic analyses and synthesis, their structures were revealed to include a 6,6-bicyclic ring system and two prenylated amine moieties. In addition, 2 induced apoptosis in HL60 human leukemia cells. 相似文献
125.
Shirakawa S Liu K Ito H Maruoka K 《Chemical communications (Cambridge, England)》2011,47(5):1515-1517
Efficient catalytic asymmetric synthesis of 1,1-disubstituted tetrahydro-β-carbolines has been achieved via asymmetric alkylation of 1-cyanotetrahydro-β-carbolines using a binaphthyl-modified N-spiro-type chiral phase-transfer catalyst. This is a valuable example of hitherto difficult highly enantioselective alkylations at α-carbon of the cyano group under phase-transfer conditions. 相似文献
126.
Uyama A Yamazoe S Shigematsu S Morimoto M Yokojima S Mayama H Kojima Y Nakamura S Uchida K 《Langmuir : the ACS journal of surfaces and colloids》2011,27(10):6395-6400
By alternate UV and visible light irradiation, reversible topographical changes were observed on a newly synthesized diarylethene microcrystalline surface between the rough crystalline surface of an open-ring isomer and flat eutectic surfaces. The contact angle changes of a water droplet between 80° and 150° and peak intensities changes of the open-ring isomer in XRD patterns within 2 h of repeating cycle were observed. The results indicated that reversibly photogenerated rod-shaped crystals on the surface were produced based on the lattice of the open-ring isomer crystals in the subphase. 相似文献
127.
Kausar A Nagano H Kuwahara Y Ogata T Kurihara S 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(2):508-515
In this paper the photocontrolled manipulation of solid materials on the surface of a liquid crystalline thin film is described. Three different types of films namely cholesteric liquid crystal (ChLC), compensated nematic liquid crystal (NLC) and nematic LC were used. The rotational and translational manipulation of the microscale solid object was induced by irradiation of light and mode of manipulation (either translational or rotational) was changed by changing the isomer of the azobenzene compound used to make the film. Rotational motion of the object was observed on the ChLC and compensated NLC films containing chirally pure azobenzene compound. The direction of rotational motion was controlled either by changing the optical isomer of the chiral azobenzene or by changing the irradiating light (from ultraviolet to visible). When racemic mixture of the chiral azobenzene compound was used, a translational motion of the object was observed. Even though the direction of the translational motion can be controlled by controlling irradiation position, more facile and precise manipulation of the objects was possible by spatially controlled irradiation of Ar(+) laser and diode UV laser. 相似文献
128.
Functionalized magnetic nanoparticles, composed of both inorganic and organic components, have recently been examined as promising platforms for detection and separation applications. This unique class of nanomaterials can retain not only beneficial features of both the inorganic and organic components, but can also provide the ability to systematically tune the properties of the hybrid materials through the combination of appropriate functional components. This tutorial review focuses on the recent development of functionalized magnetic nanoparticles for use in biological and environmental applications, in which these chromogenic and fluorogenic chemosensors can selectively detect and separate specific toxic metal ions. 相似文献
129.
130.
Yuichiro Haramoto Yoshiharu Kusakabe Masato Nanasawa Seiji Ujiie Stephan Mang Cladius Schwarzwalder 《Liquid crystals》2013,40(10):1393-1397
Side chain type ionic liquid crystalline polymers having a 4-(1,3-dioxan-2-yl)pyridinium structure in their mesogenic side chain were synthesized. These polymers exhibited the smectic A phase. The molecular weights of these ionic liquid crystalline polymers are very high, e.g. for compound 7 - 2 M w = 486 000. 相似文献