全文获取类型
收费全文 | 1291篇 |
免费 | 28篇 |
国内免费 | 7篇 |
专业分类
化学 | 1029篇 |
晶体学 | 5篇 |
力学 | 18篇 |
数学 | 117篇 |
物理学 | 157篇 |
出版年
2023年 | 9篇 |
2022年 | 11篇 |
2021年 | 8篇 |
2020年 | 15篇 |
2019年 | 9篇 |
2018年 | 15篇 |
2017年 | 9篇 |
2016年 | 25篇 |
2015年 | 21篇 |
2014年 | 28篇 |
2013年 | 65篇 |
2012年 | 77篇 |
2011年 | 104篇 |
2010年 | 46篇 |
2009年 | 66篇 |
2008年 | 64篇 |
2007年 | 74篇 |
2006年 | 92篇 |
2005年 | 65篇 |
2004年 | 67篇 |
2003年 | 56篇 |
2002年 | 62篇 |
2001年 | 17篇 |
2000年 | 21篇 |
1999年 | 17篇 |
1998年 | 16篇 |
1997年 | 17篇 |
1996年 | 14篇 |
1995年 | 10篇 |
1994年 | 16篇 |
1993年 | 12篇 |
1992年 | 12篇 |
1991年 | 12篇 |
1990年 | 17篇 |
1989年 | 9篇 |
1988年 | 7篇 |
1987年 | 4篇 |
1986年 | 6篇 |
1985年 | 19篇 |
1984年 | 13篇 |
1983年 | 11篇 |
1982年 | 13篇 |
1981年 | 8篇 |
1980年 | 10篇 |
1979年 | 16篇 |
1975年 | 3篇 |
1974年 | 6篇 |
1973年 | 4篇 |
1971年 | 7篇 |
1968年 | 4篇 |
排序方式: 共有1326条查询结果,搜索用时 10 毫秒
61.
Photochromic acrylates containing both biphenylene and spiro-oxazine moieties with a chiral substituent and the related polymers were prepared and yielded photochromic chiral liquid crystalline systems. The photochromic acrylates containing both an undecamethylene group and a (2S, 3S)-2-chloro-3-methylpentanoyloxy group (A11SOP) or a (-)-menthoxyacetoxy group (A11SOM) gave a supercooled mesophase; the latter reflected right-handed visible light (blue colour) at room temperature. On the other hand, the photochromic acrylate containing both the (R)-(-)-2-methylpropylene and (2S, 3S)-2-chloro-3-methylpentanoyloxy groups (A3SOP) showed no mesophase. The related homopolymers, PA11SOP and PA11SOM, did not exhibit mesophases because of steric hindrance between the side groups of the polymers. However, only PA11SOM exhibited shear-induced birefringence under 100-104°C. Several copolymers consisting of the nematogenic monomer, 4-[4-(6-acryloyloxyhexyloxy)benzoyloxy]benzonitrile (A6CN), and A11SOP or A11SOM possessed a smectic phase due to reduction of the steric hindrance between the potentially smectogenic A11SOP or A11SOM moieties. 相似文献
62.
Chin-Soon Phan Takashi Kamada Takahiro Ishii Toshiyuki Hamada 《Natural product research》2019,33(6):808-813
One new compound, 12-epi-9-deacetoxyxenicin (1) along with a hydroperoxide product, 12-epi-9-deacetoxy-8-hydroperoxyxenicin (2) and two known sesquiterpenoids (3–4) were isolated from a population of Bornean soft coral Xenia sp. The structures of these secondary metabolites were elucidated based on their spectroscopic data. Compounds 1 and 2 showed cytotoxic activity against ATL cell line, S1T. In addition, compound 3 exhibited hyphal inhibition of Lagenidium thermophilum. 相似文献
63.
Makoto Nonomura Fumio Nakagawa Shinya Mizusawa Takashi Ohno Hiroyuki Kobayashi Toshiyuki Hobo 《International journal of environmental analytical chemistry》2013,93(4):371-379
Abstract Although cyanide compounds are not incorporated in photographic processing solutions, false detection of cyanide ion is often encountered during the determination of total cyanide by various standardized methods such as ISO, ANSI and JIS. Various organic compounds and nitrogen compounds in the processing solutions were examined because of this false detection. The results suggest that hydrogen cyanide is formed by a reaction between these compounds during the distillation process for the separation of total cyanide, even though ISO, ANSI and JIS were used. The results support the following three mechanisms of cyanide formation involved in the process: (1) Hydroxylammonium salts reacts with another ingredient, formaldehyde, to form formaldoxime, which then decomposes to HCN. (2) Hydroxylammonium is oxidized by air to form nitrite ion, which subsequently reacts with organic compounds such as aminocarboxylic acids and aromatic amines (the colour-developing agent) to form HCN. (3) Potassium permanganate oxidizes aromatic amines to form HCN. 相似文献
64.
The mechanism of the H2NO(2B1)→NO(2Π)+H2 reaction has been examined using ab initio molecular orbital methods. Ground-state and first-excited-state potential surfaces were plotted at the FOCI/cc-pVTZ level of theory as functions of two appropriate internal degrees of freedom. A conical intersection was found on the Cs pathway that is symmetric with respect to the plane perpendicular to the molecular plane of C2v H2NO(2B1). It is therefore considered that trajectories that start from H2NO(2B1) towards the product region detour around the conical intersection, pass through the neighborhood of the transition state that is located at the saddle point on the Cs pathway, and finally reach the products, NO(2Π)+H2. Thus we can explain the mechanism of the H2NO(2B1)→NO(2Π)+H2 reaction, which has remained unclear to date. 相似文献
65.
Hirata Kazuki Matsuda Atsunori Hirata Toshiyuki Tatsumisago Masahiro Minami Tsutomu 《Journal of Sol-Gel Science and Technology》2000,17(1):61-69
Highly proton-conductive elastic composites have been successfully prepared from H3PO4-doped silica gel and a styrene-ethylene-butylene-styrene (SEBS) block elastic copolymer. Ionic conductivities of the composites depended on the concentration of H3PO4 and the heat treatment temperature of the H3PO4-doped silica gel. It was found that H3PO4 added is present mainly as free orthophosphoric acid in the silica gel. The composite composed of H3PO4-doped silica gel with a molar ratio of H3PO4/SiO2 = 0.5 heat-treated at temperatures below 200°C and SEBS elastomer in 5 mass% showed a high conductivity of 10–5 S cm–1 at 25°C in an dry N2 atmosphere. The water adsorption during a storage in 25% relative humidity at room temperature for 1 day enhanced the ionic conductivities of composites by about one order of magnitude. Lower conductivities obtained in the composite with the H3PO4-doped silica gel heat-treated at 250°C for 1 h were due to the formation of crystalline Si3(PO4)4. The temperature dependence of conductivity of the composites was the Vogel-Tamman-Fulcher type, indicating that proton was transferred through a liquidlike phase formed in micropores of the H3PO4-doped silica gels. The temperature dependence of the modulus of the composite was similar to that of the SEBS elastomer. The thermoplastically deforming temperature of the composite was around 100°C, which was higher by 30°C than that of the SEBS elastomer. 相似文献
66.
cis-[Ru(NO)Cl(pyca)(2)] (pyca = 2-pyridinecarboxylato), in which the two pyridyl nitrogen atoms of the two pyca ligands coordinate at the trans position to each other and the two carboxylic oxygen atoms at the trans position to the nitrosyl ligand and the chloro ligand, respectively (type I shown as in Chart 1), reacted with NaOCH(3) to generate cis-[Ru(NO)(OCH(3))(pyca)(2)] (type I). The geometry of this complex was confirmed to be the same as the starting complex by X-ray crystallography: C(13.5)H(13)N(3)O(6.5)Ru; monoclinic, P2(1)/n; a = 8.120(1), b = 16.650(1), c = 11.510(1) A; beta = 99.07(1) degrees; V = 1536.7(2) A(3); Z = 4. The cis-trans geometrical change reaction occurred in the reactions of cis-[Ru(NO)(OCH(3))(pyca)(2)] (type I) in water and alcohol (ROH, R = CH(3), C(2)H(5)) to form [[trans-Ru(NO)(pyca)(2)](2)(H(3)O(2))](+) (type V) and trans-[Ru(NO)(OR)(pyca)(2)] (type V). The reactions of the trans-form complexes, trans-[Ru(NO)(H(2)O)(pyca)(2)](+) (type V) and trans-[Ru(NO)(OCH(3))(pyca)(2)] (type V), with Cl(-) in hydrochloric acid solution afforded the cis-form complex, cis-[Ru(NO)Cl(pyca)(2)] (type I). The favorable geometry of [Ru(NO)X(pyca)(2)](n)(+) depended on the nature of the coexisting ligand X. This conclusion was confirmed by theoretical, synthetic, and structural studies. The mono-pyca-containing nitrosylruthenium complex (C(2)H(5))(4)N[Ru(NO)Cl(3)(pyca)] was synthesized by the reaction of [Ru(NO)Cl(5)](2)(-) with Hpyca and characterized by X-ray structural analysis: C(14)H(24)N(3)O(3)Cl(3)Ru; triclinic, Ponemacr;, a = 7.631(1), b = 9.669(1), c = 13.627(1) A; alpha = 83.05(2), beta = 82.23(1), gamma = 81.94(1) degrees; V = 981.1(1) A(3); Z = 2. The type II complex of cis-[Ru(NO)Cl(pyca)(2)] was synthesized by the reaction of [Ru(NO)Cl(3)(pyca)](-) or [Ru(NO)Cl(5)](2)(-) with Hpyca and isolated by column chromatography. The structure was determined by X-ray structural analysis: C(12)H(8)N(3)O(5)ClRu; monoclinic, P2(1)/n; a = 10.010(1), b = 13.280(1), c = 11.335(1) A; beta = 113.45(1) degrees; V = 1382.4(2) A(3); Z = 4. 相似文献
67.
Joji Ohshita Takahiro Inoue Taisuke Uemura Toshiyuki Iida Atsutaka Kunai 《Silicon Chemistry》2003,2(3-4):147-149
Compounds having two benzocrown ether units bridged by an organosilicon bridge were prepared by the reactions of lithiated benzocrown derivatives with dichloromono- and disilanes in THF, and the ionochromic effects on their optical properties were studied. Of those, disilanylene-bridged benzocrown ethers exhibited clear ionochromism in the emission spectra and the intensity of the original emission band at about 320 nm decreased and a new broad band centered at 400 nm appeared, when selected alkali or alkali-earth metal ions were added into the acetonitrile solutions. In contrast to this, no significant changes were observed in the UV absorption spectra on addition of the metal ions. 相似文献
68.
Distribution of pirarubicin in human blood. 总被引:1,自引:0,他引:1
K Nagasawa N Kitada C Tsuji M Ogawa T Yokoyama N Ohnishi S Iwakawa K Okumura 《Chemical & pharmaceutical bulletin》1992,40(10):2866-2869
We investigated the distribution and stability of pirarubicin in human blood obtained from 12 healthy volunteers. The distribution of pirarubicin into blood cells showed marked temperature- and concentration-dependencies and the Arrhenius plot for pirarubicin uptake in blood was biphasic. Therefore, pirarubicin appears to be taken up into blood cells by a carrier-mediated system. Pirarubicin was mainly enzymatically metabolized to pirarubicinol in blood cells, but pirarubicin was not metabolized into doxorubicin in either blood or plasma. On the other hand, in plasma, pirarubicin was degraded to unknown inactive compounds instead of pirarubicinol. It is therefore suggested that blood cells serve to protect against the degradation of pirarubicin into inactive compounds in blood. Accordingly, when the monitoring of pirarubicin and its active metabolites is carried out in patients, both blood and plasma must be frozen immediately after blood collection. 相似文献
69.
Ionic liquids (ILs) have a wide variety of applications in energy storage and material production. ILs are composed of only cations and anions, without any molecular solvents, and are generally known as “designer liquids (solvents)” because their physicochemical properties can be tuned by the combination of ionic species. In recent several decades, research and development activities of rechargeable batteries have garnered considerable attention because certain groups of ILs exhibit high electrochemical stability and moderate ionic conductivity, rendering them suitable for application in high-voltage batteries. ILs with amide anions are representative electrolytes and are extensively researched by many research groups, including our group. This paper focuses on amide-based ILs as electrolytes for alkali-metal-ion rechargeable batteries, introducing their history, characteristics, and existing challenges to be addressed. 相似文献
70.
A flow analysis system involving the on-line configuration of an anion-exchange column has been examined to enrich and determine trace concentrations of zirconium of several ppm to hundred ppm levels in silicate rocks and minerals. About 100 mg of sample is decomposed by fusion with a mixture of boric acid and lithium carbonate and taken up with 1M hydrochloric acid to a total of 100 ml. Depending upon the concentration of zirconium, either a 1- or 4-ml aliquot is introduced into an aqueous carrier stream, merged with sulphuric acid and passed through a small volume anion-exchange column. The enriched zirconium is then back eluted with hydrochloric acid, colour-developed with Arsenazo III, and detected spectrophotometrically at 665 nm. 相似文献