全文获取类型
收费全文 | 2215篇 |
免费 | 74篇 |
国内免费 | 14篇 |
专业分类
化学 | 1695篇 |
晶体学 | 35篇 |
力学 | 30篇 |
数学 | 204篇 |
物理学 | 339篇 |
出版年
2023年 | 11篇 |
2022年 | 13篇 |
2021年 | 18篇 |
2020年 | 27篇 |
2019年 | 40篇 |
2018年 | 27篇 |
2017年 | 25篇 |
2016年 | 46篇 |
2015年 | 42篇 |
2014年 | 48篇 |
2013年 | 130篇 |
2012年 | 140篇 |
2011年 | 136篇 |
2010年 | 70篇 |
2009年 | 80篇 |
2008年 | 169篇 |
2007年 | 148篇 |
2006年 | 125篇 |
2005年 | 117篇 |
2004年 | 104篇 |
2003年 | 96篇 |
2002年 | 78篇 |
2001年 | 24篇 |
2000年 | 39篇 |
1999年 | 19篇 |
1998年 | 27篇 |
1997年 | 32篇 |
1996年 | 25篇 |
1995年 | 24篇 |
1994年 | 14篇 |
1993年 | 19篇 |
1992年 | 26篇 |
1991年 | 21篇 |
1990年 | 18篇 |
1989年 | 13篇 |
1987年 | 23篇 |
1986年 | 10篇 |
1985年 | 20篇 |
1984年 | 22篇 |
1983年 | 19篇 |
1982年 | 24篇 |
1981年 | 20篇 |
1980年 | 30篇 |
1979年 | 30篇 |
1978年 | 18篇 |
1977年 | 11篇 |
1976年 | 14篇 |
1975年 | 13篇 |
1974年 | 10篇 |
1973年 | 11篇 |
排序方式: 共有2303条查询结果,搜索用时 312 毫秒
101.
Despite the fact that many transition-metal-catalyzed reactions of organosulfur compounds with internal alkynes are ineffective, cobalt carbonyl (Co2(CO)8) is an excellent catalyst for carbonylative cyclization of internal alkynes with carbon monoxide. When Co2(CO)8-catalyzed reactions of internal alkynes with organic thiols are conducted in acetonitrile under 4 MPa pressure of carbon monoxide, thiolative lactonization of internal alkynes successfully takes place with incorporation of two molecules of CO. This carbonylation provides a useful tool to prepare the corresponding α,β-unsaturated γ-thio-γ-lactones (butenolide derivatives) in good yields. In the cases of unsymmetrical alkynes, such as 2-octyne and 6-methyl-2-heptyne, the thiolative lactonization proceeds with moderate regioselectivity to give the butenolide derivatives on which the carbonyl group preferentially bonds to the less hindered acetylenic carbon. Mechanistic pathways about the present thiolative lactonization are also discussed. 相似文献
102.
Katsufumi Tanaka Takatoshi Morina Yuichiro Tanabe Ryuichi Akiyama 《Liquid crystals》2013,40(9):1019-1028
The concentration dependences of dielectric properties measured at 105 Hz and 106 Hz are reported for aqueous solutions of hydroxypropyl cellulose. Phase behaviour of the solutions was also observed with a polarizing optical microscope. For solutions with concentrations well above 40 wt %, polydomain textures, including the banded texture, were observed after a prehistory of deformation. No significant discontinuous changes in the dielectric constant, εr′, and loss factor, εr″, were found at the concentrations around the onset of the isotropic–cholesteric phase transition and in the biphasic region. In contrast, the steeper changes in εr′ and εr″ were found at the critical concentration for the fully developed cholesteric phase transition with the polydomain textures. 相似文献
103.
Kiyofumi Katagiri Keiko Ohta Kunihito Koumoto Kei Kurosu Yoshihiro Sasaki Kazunari Akiyoshi 《Colloid and polymer science》2013,291(6):1375-1380
Novel organic–inorganic hybrid nanoparticles consisting of polymer–hydrogel nanoparticles (nanogels) and iron oxide were developed for potential biomedical applications. Hybrid nanoparticles were prepared by a simple procedure using polysaccharide nanogels as a reactive site for iron oxide formation. The hybrid nanoparticles have a narrow size distribution with a diameter of approximately 30 nm and show high colloidal stability. These nanohybrid particles could be used as a contrast medium for magnetic resonance imaging or for magnetic hyperthermia therapy. 相似文献
104.
Yoshihiro Shigemasa Kuninori Oogaki Nasuo Ueda Ruka Hakashima Ken-Ichi Harada Naohito Takeda 《Journal of carbohydrate chemistry》2013,32(3):325-330
Abstract The formose reaction, by which a complex mixture of sugars and sugar alcohols (the so-called formose) are produced by the base-catalyzed condensation of formaldehyde, has received much attention in connection with the prebiotic synthesis of carbohydrates2 and the microbial utilization of formose.3–5 Formose, however, has not been useful yet, because of the complexity of this product mixture (Fig. 1a). Therefore, it seemed desirable to make the reaction more selective. 相似文献
105.
Yoshihiro Shigemasa Takaaki Ueda Hiroyuki Saimoto 《Journal of carbohydrate chemistry》2013,32(4):669-673
Abstract The formose reactions2 in N,N-dimethylformamide (DMF) catalyzed by 2-(dimethylamino)ethanol and thiamine hydrochloride, have been found to give rise to dihydroxyacetone and DL-glycero-tetrulose selectively at 1.1 M and 3.0 M of formaldehyde concentration, respectively. In our consecutive study on the formose reaction in DMF, it has been fortunately found that the distribution of products is able to be controlled by the amount of water added to the reaction mixture. We describe herein the first example of the favored formation of DL-2-C-hydroxymethyl-3-pentu-lose (GP-191) in the formose reaction using DMF-H2O solvent, and it's isolation and structure elucidation. 相似文献
106.
107.
108.
Yoshihiro Kon Toshiyuki Yokoi Masato Yoshioka Shinji Tanaka Yumiko Uesaka Takehisa Mochizuki Kazuhiko Sato Takashi Tatsumi 《Tetrahedron》2014
Selective oxidation of sulfides to sulfoxides and sulfones with hydrogen peroxide under organic solvent-free conditions was demonstrated by the MWW-type titanosilicate zeolite catalyst. Sulfides were oxidized smoothly to give sulfoxides with good selectivities at ambient temperature using 1.0–1.2 equiv of hydrogen peroxide with the MWW-type titanosilicate zeolite catalyst. Especially, the Ti-MWW with an interlayer-expanded structure (Ti-IEZ-MWW) catalyst showed high activity with good chemoselectivity for the oxidation of various sulfides. The catalyst is recyclable for at least five cycles, and the only byproduct is water. Sulfides were directly oxidized to give sulfones in high yields by 2.5 equiv of hydrogen peroxide with the MWW-type titanosilicate zeolite catalyst under organic solvent-free conditions. 相似文献
109.
Akter Sharmin Tanabe Tomoki Maejima Satoshi Kawauchi Satoko Sato Shunichi Hinoki Akinari Aosasa Suefumi Yamamoto Junji Nishidate Izumi 《Optical Review》2016,23(2):354-359
Optical Review - To quantify the changes in optical properties of in vivo rat liver tissue, we applied diffuse reflectance spectroscopy (DRS) system using single-reflectance fiber probe during... 相似文献
110.
Laser-induced breakdown spectroscopy (LIBS) is an analytical detection technique based on atomic emission spectroscopy to measure the elemental composition. LIBS has been extensively studied and developed due to the non-contact, fast response, high sensitivity, real-time and multi-elemental detection features. The development and applications of LIBS technique in Asia are summarized and discussed in this review paper. The researchers in Asia work on different aspects of the LIBS study in fundamentals, data processing and modeling, applications and instrumentations. According to the current research status, the challenges, opportunities and further development of LIBS technique in Asia are also evaluated to promote LIBS research and its applications. 相似文献