全文获取类型
收费全文 | 5361篇 |
免费 | 192篇 |
国内免费 | 30篇 |
专业分类
化学 | 4196篇 |
晶体学 | 53篇 |
力学 | 76篇 |
数学 | 347篇 |
物理学 | 911篇 |
出版年
2023年 | 23篇 |
2022年 | 22篇 |
2021年 | 54篇 |
2020年 | 65篇 |
2019年 | 94篇 |
2018年 | 54篇 |
2017年 | 47篇 |
2016年 | 110篇 |
2015年 | 97篇 |
2014年 | 133篇 |
2013年 | 284篇 |
2012年 | 314篇 |
2011年 | 383篇 |
2010年 | 207篇 |
2009年 | 238篇 |
2008年 | 382篇 |
2007年 | 375篇 |
2006年 | 415篇 |
2005年 | 362篇 |
2004年 | 336篇 |
2003年 | 271篇 |
2002年 | 270篇 |
2001年 | 61篇 |
2000年 | 46篇 |
1999年 | 40篇 |
1998年 | 40篇 |
1997年 | 55篇 |
1996年 | 54篇 |
1995年 | 43篇 |
1994年 | 33篇 |
1993年 | 40篇 |
1992年 | 26篇 |
1991年 | 33篇 |
1990年 | 18篇 |
1989年 | 18篇 |
1988年 | 24篇 |
1987年 | 28篇 |
1986年 | 39篇 |
1985年 | 55篇 |
1984年 | 46篇 |
1983年 | 20篇 |
1982年 | 47篇 |
1981年 | 51篇 |
1980年 | 42篇 |
1979年 | 39篇 |
1978年 | 32篇 |
1977年 | 26篇 |
1976年 | 23篇 |
1975年 | 15篇 |
1973年 | 18篇 |
排序方式: 共有5583条查询结果,搜索用时 15 毫秒
51.
Cross‐Coupling of Organolithium with Ethers or Aryl Ammonium Salts by C−O or C−N Bond Cleavage 下载免费PDF全文
Ze‐Kun Yang Dong‐Yu Wang Hiroki Minami Hiroyuki Ogawa Takashi Ozaki Dr. Tatsuo Saito Dr. Kazunori Miyamoto Dr. Chao Wang Prof. Dr. Masanobu Uchiyama 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(44):15693-15699
Various aryl‐, alkenyl‐, and/or alkyllithium species reacted smoothly with aryl and/or benzyl ethers with cleavage of the inert C?O bond to afford cross‐coupled products, catalyzed by commercially available [Ni(cod)2] (cod=1,5‐cyclooctadiene) catalysts with N‐heterocyclic carbene (NHC) ligands. Furthermore, the coupling reaction between the aryllithium compounds and aryl ammonium salts proceeded under mild conditions with C?N bond cleavage in the presence of a [Pd(PPh3)2Cl2] catalyst. These methods enable selective sequential functionalizations of arenes having both C?N and C?O bonds in one pot. 相似文献
52.
(R)-Tetrahydrozerumbone 2, which has a powerful balmy fragrance, contains a stereogenic carbon at the C2 position and can be easily prepared from zerumbone 1, one of the most important materials displaying an NMRDOS character. The reduction of 2 gave two diastereomers of tetrahydrozerumbol 3, and the optically active (>99%ee) alcohols were obtained by a lipase-catalyzed stereoselective transesterification of each racemic alcohol. A barrier to this development is a long reaction time (about four weeks) and the need to separate the diastereoisomers. The desired (2R)-form of 3 was efficiently obtained by a lipase-catalyzed transesterification under optimized conditions using a diastereomeric mixture of racemic 3 as the starting material without separation of the diastereomers. Using this method, the reaction of other zerumbone derivatives is greatly improved. 相似文献
53.
The photoluminescence (PL) properties of ZrO2 have been measured at different temperatures between 7 and 300 K, using various kinds of ZrO2 specimens: bulk crystal melt-grown by a large solar furnace, thermally oxidized zirconium plate (ZrO2 film crystal on Zr ) and nanocrystals (surface area: 35–45m2/g, diameter: 20–30 nm). The results clarify the deep and shallow energy level structures in the energy gap. Reversible UV-laser-light-induced spectral changes are observed for all of the specimens in different specimen-atmospheres (vacuum and O2 gas). The results elucidate the defect-effects of the PL properties and the PL enhancement mechanism in ZrO2 nanocrystals. 相似文献
54.
55.
56.
Budischowsky David Zwirchmayr Nele Sophie Hosoya Takashi Bacher Markus Hettegger Hubert Potthast Antje Rosenau Thomas 《Cellulose (London, England)》2021,28(10):6051-6071
Cellulose - Chromophores, colored substances of rather high stability that reduce brightness, are present in all kinds of cellulosic products, such as pulp, fibers, aged cellulosic material, and... 相似文献
57.
58.
Hiroshi Sakai Takashi Yamazaki Nobuya Machida Toshihiko Shigematsu Saburo Nasu 《Molecular Crystals and Liquid Crystals》2013,570(2):105-110
Abstract Mössbauer spectra of the FePS3-cobaltocene intercalation compound were measured in the temperature range of 300K to 10K. The spectra, distinct from those of pure FePS3, suggest the charge transfer from cobaltocene to Fe-S antibonding orbitals of the FePS3 host lattice. 相似文献
59.
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
60.
Kazuo Koyama Takashi Hirao Akira Toriba Kazuichi Hayakawa 《Biomedical chromatography : BMC》2013,27(5):583-588
The quality of starch‐containing foods may be significantly impaired by contamination with very small amounts of α‐amylase, which can enzymatically hydrolyze the starch and cause viscosity loss. Thus, for quality control, it is necessary to have an analytical method that can measure low amylase activity. We developed a sensitive analytical method for measuring the activity of α‐amylase (from Bacillus subtilis) in starch‐containing foods. The method consists of six steps: (1) crude extraction of α‐amylase by centrifugation and filtration; (2) α‐amylase purification by desalting and anion‐exchange chromatography; (3) reaction of the purified amylase with boron‐dipyrromethene (BODIPY)‐labeled substrate, which releases a fluorescent fragment upon digestion of the substrate, thus avoiding interference from starch derivatives in the sample; (4) stopping the reaction with acetonitrile; (5) reversed‐phase solid‐phase extraction of the fluorescent substrate to remove contaminating dye and impurities; and (6) separation and measurement of BODIPY fluorescence by HPLC. The proposed method could quantify α‐amylase activities as low as 10 mU/mL, which is enough to reduce the viscosity of starch‐containing foods. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献