全文获取类型
收费全文 | 1585篇 |
免费 | 46篇 |
国内免费 | 8篇 |
专业分类
化学 | 1247篇 |
晶体学 | 14篇 |
力学 | 13篇 |
数学 | 97篇 |
物理学 | 268篇 |
出版年
2022年 | 16篇 |
2021年 | 14篇 |
2020年 | 20篇 |
2019年 | 28篇 |
2018年 | 19篇 |
2017年 | 12篇 |
2016年 | 33篇 |
2015年 | 29篇 |
2014年 | 34篇 |
2013年 | 69篇 |
2012年 | 84篇 |
2011年 | 92篇 |
2010年 | 54篇 |
2009年 | 55篇 |
2008年 | 93篇 |
2007年 | 83篇 |
2006年 | 84篇 |
2005年 | 88篇 |
2004年 | 101篇 |
2003年 | 74篇 |
2002年 | 81篇 |
2001年 | 33篇 |
2000年 | 23篇 |
1999年 | 26篇 |
1998年 | 17篇 |
1997年 | 15篇 |
1996年 | 19篇 |
1995年 | 10篇 |
1994年 | 21篇 |
1993年 | 20篇 |
1992年 | 21篇 |
1991年 | 14篇 |
1990年 | 9篇 |
1989年 | 17篇 |
1988年 | 13篇 |
1987年 | 11篇 |
1986年 | 12篇 |
1985年 | 18篇 |
1984年 | 16篇 |
1983年 | 18篇 |
1982年 | 9篇 |
1981年 | 17篇 |
1980年 | 14篇 |
1979年 | 18篇 |
1978年 | 9篇 |
1977年 | 19篇 |
1976年 | 13篇 |
1975年 | 11篇 |
1974年 | 7篇 |
1967年 | 4篇 |
排序方式: 共有1639条查询结果,搜索用时 15 毫秒
81.
Tokuyuki Kuroda Koji Hisamura Ikuo Matsukuma Hiroshi Nishikawa Makoto Morimoto Tadashi Ashizawa Nobuhiro Nakamizo Yoshio Otsuji 《Journal of heterocyclic chemistry》1992,29(5):1133-1142
Seventeen compounds having a variety of substituents at the 3- and 5′-positions of 2′-deoxy-5-fluorouridine (5-FUdR) and 5-fluorouridine (5-FUR) were synthesized, and their γ-radiolysis in aqueous solutions were studied. The compounds having thioureido (RNHCSNH, R H, PhCH2, acyl) and thiocarbonylamino (XCSNH, X PhCH2S, PhO) groups at the 3-position of 5-FUdR were efficiently cleaved to give 5-FUdR with high G values upon γ-irradiation of their aqueous solutions. The active species for these cleavage reactions were hydrated electron (e− aq), H• and HO•. However, the compounds having a dimethylsulfoxyimino group at 3-position of 5-FUdR and 5-FUR afforded 5-FUdR and 5-FUR only under the radiolysis conditions where e− aq becomes a principal active species. The compound having a 2-benzoylthiazoylthiocarbonylamino group at the 3-position of 5-FUdR showed the highest reactivity toward HO.. The mechanisms of these γ-radiolysis reactions are discussed. The examination of anticellular activities of γ-irradiated compounds having a thiocarbonylamino group at the 3-position of 5-FUdR toward murine Sarcoma 180 cells revealed that these compounds may be utilized as a candidate for a radiation-induced drug (RID). 相似文献
82.
83.
Utilizing the unique features of the scanning atom probe (SAP) the binding states of the biomolecules, leucine and methionine, are investigated at atomic level. The molecules are mass analyzed by detecting a single atom and/or clustering atoms field evaporated from a specimen surface. Since the field evaporation is a static process, the evaporated clustering atoms are closely related with the binding between atoms forming the molecules. For example, many thiophene radicals are detected when polythiophene is mass analyzed by the SAP. In the present study the specimens are prepared by immersing a micro cotton ball of single walled carbon nanotubes (SWCNT) in the leucine or methionine solution. The mass spectra obtained by analyzing the cotton balls exhibit singly and doubly ionized carbon ions of SWCNT and the characteristic fragments of the molecules, CH3, CHCH3, C4H7, CHNH2 and COOH for leucine and CH3, SCH3, C2H4, C4H7, CHNH2 and COOH for methionine. 相似文献
84.
85.
Sato S Ogura Y Miyanaga A Sugimoto T Tanaka K Moriyama H 《Journal of chromatography. A》2002,956(1-2):53-58
Ion chromatography (IC) has been a powerful tool for measuring ionic species in environmental samples such as tap, river and drain waters. Suppressor modules (membrane and disposable column types) have been used for reducing the background of a baseline. A new type of suppressor device, which has a suppressor resin and switching valve was developed. Fresh ionic resin is introduced into a groove for each analysis to perform the suppression of the working eluent. The eluent composition for obtaining higher sensitivity and better resolutions among ionic species and carbonate ion was also investigated. Although carbonate buffers are used for ion separation in general, the separation of carbonate ion from other ions was not achieved. A borate eluent resulted in good resolutions and higher sensitivity. A new column was also developed for obtaining higher column efficiency and resolution. The optimization of anion separation using a new IC system (IC-2001) that consists of a new suppressor device, an anion-exchange column (TSKgel SuperIC-Anion, 150x4.6 mm), an autosampler, a conductivity cell and a pump in a compact module is described. 相似文献
86.
Koichi KikuchiHiroyuki Nishikawa Isao IkemotoTakashi Toita Hiroki AkutsuShin'ichi Nakatsuji Jun-ichi Yamada 《Journal of solid state chemistry》2002,168(2):503-508
Three FeCl4 salts based on non-tetrathiafulvalene (TTF) donors, 2,5-bis(1,3-dithiolan-2-ylidene)-1,3,4,6-tetrathiapentalene (BDH-TTP) and 2,5-bis(1,3-dithian-2-ylidene)-1,3,4,6-tetrathiapentalene (BDA-TTP), have been prepared and characterized as κ-(BDH-TTP)2FeCl4, β-(BDA-TTP)2FeCl4, and (BDA-TTP)3FeCl4 · PhCl. The κ-(BDH-TTP)2FeCl4 salt, with a room-temperature conductivity (σrt) of 39 S cm−1, is metallic down to 1.5 K, and its magnetic susceptibility obeys the Curie-Weiss law with a Curie constant (C) of 4.25 emu K mol−1 and a Weiss constant (θ) of 0.041 K. β-(BDA-TTP)2FeCl4 exhibits metallic behavior (σrt=9.4 S cm−1) with a sharp metal-to-insulator (MI) transition (TMI=113 K) and antiferromagnetic ordering with the Néel temperature of near 8.5 K, whereas the solvated (BDA-TTP)3FeCl4 · PhCl salt is a semiconductor with a thermal activation energy of 0.11 eV (σrt=2.0× 10−2 S cm−1) and exhibits Curie-Weiss behavior (C=4.42 emu K mol−1, θ=−0.35 K). 相似文献
87.
Exposure of tertiary thioamides to (E)-1-hexenyl(phenyl)-lambda 3-iodane results in vinylic SN2 reaction to give the inverted (Z)-S-vinylthioimidonium salts, which under alkaline hydrolysis (Na2CO3 or K2CO3) selectively afford amides, while (Z)-S-vinyl thioesters are obtained in high yields via the hydrolysis under acidic conditions (HCl). 相似文献
88.
Periodic mesoporous benzene-silicas with large pores of 6.0 to 7.4 nm in diameter are synthesized using triblock copolymer as a template. These mesoporous materials have a well-defined hexagonal rod morphology and high thermal stability up to 823 K in air. 相似文献
89.
[structure: see text] 8,11-Dideoxytetrodotoxin, an unnatural tetrodotoxin analogue, was synthesized in a highly stereoselective manner from a common intermediate in our synthetic studies on tetrodotoxin. The synthesis features neighboring group participation of trichloroacetamide for stereoselective hydroxylation, protection of ortho ester, and guanidine installation with Boc-protected isothiourea. 相似文献
90.
[reaction: see text] Treatment of 1,6-enynes with tetramethallylchromate induces a cyclization reaction with concurrent introduction of a methallyl group. A catalytic amount of CrCl(3) combined with methallylmagnesium chloride also achieves this cyclization process. The resultant cyclic organometallic species undergo further functionalization upon reaction with electrophiles. 相似文献