全文获取类型
收费全文 | 1460篇 |
免费 | 78篇 |
国内免费 | 10篇 |
专业分类
化学 | 1225篇 |
晶体学 | 16篇 |
力学 | 10篇 |
数学 | 100篇 |
物理学 | 197篇 |
出版年
2023年 | 11篇 |
2022年 | 12篇 |
2021年 | 10篇 |
2020年 | 29篇 |
2019年 | 31篇 |
2018年 | 15篇 |
2017年 | 15篇 |
2016年 | 50篇 |
2015年 | 37篇 |
2014年 | 27篇 |
2013年 | 72篇 |
2012年 | 70篇 |
2011年 | 96篇 |
2010年 | 56篇 |
2009年 | 62篇 |
2008年 | 107篇 |
2007年 | 98篇 |
2006年 | 93篇 |
2005年 | 89篇 |
2004年 | 75篇 |
2003年 | 63篇 |
2002年 | 64篇 |
2001年 | 26篇 |
2000年 | 31篇 |
1999年 | 11篇 |
1998年 | 17篇 |
1997年 | 9篇 |
1996年 | 15篇 |
1995年 | 15篇 |
1994年 | 10篇 |
1993年 | 11篇 |
1992年 | 12篇 |
1991年 | 10篇 |
1990年 | 14篇 |
1989年 | 6篇 |
1988年 | 14篇 |
1987年 | 9篇 |
1986年 | 6篇 |
1985年 | 14篇 |
1984年 | 21篇 |
1983年 | 8篇 |
1982年 | 18篇 |
1981年 | 20篇 |
1980年 | 10篇 |
1979年 | 10篇 |
1978年 | 8篇 |
1977年 | 5篇 |
1974年 | 5篇 |
1973年 | 8篇 |
1972年 | 6篇 |
排序方式: 共有1548条查询结果,搜索用时 15 毫秒
1.
2.
Intramolecular (2+2) photocycloaddition of β-stilbazoles tethered by silyl chains took place with high efficiency. Complexation with dicarboxylic acid or catechol further enhanced both the efficiency and stereoselectivity. 相似文献
3.
Tetraoctylammonium cation forms a room-temperature molten salt (RTMS) with 2,4,6-trinitrophenolate anion. The RTMS is immiscible with water (W) and forms a stable RTMS/W interface. It has been shown that the RTMS/W interface can be electrochemically polarized. A well-defined voltammetric wave due to the transfer of thiocyanate ion across the RTMS/W interface was observed within the potential window. This is the first example of a polarized RTMS/W interface. 相似文献
4.
The double-bond conversion of UV-cured resins prepared from pentaerythritol triacrylate (PETA) was determined by pyrolysis-gas chromatography in the presence of an organic alkali, tetramethylammonium hydroxide (TMAH). The pyrogram of the uncured prepolymer compound, consisting of PETA and a photoinitiator, 2,2-dimethoxy-2-phenylacetophenone, contained specific products reflecting the original acrylate structure, such as methyl acrylate (MA) and methyl ethers of pentaerithritol. Meanwhile, in pyrograms of the UV-cured PETA, the yields of MA considerably decreased. The double-bond conversions of the cured resins, irradiated with various UV dosages, were calculated based on the relative yields of MA among specific products in the pyrograms. The conversions determined by this approach were analyzed by comparing them with those estimated by Fourier-transform infrared spectroscopy. 相似文献
5.
Tsutomu Nakanishi Hajime Okamoto Maki Kasahara Kyozaburo Takeda 《Journal of Polymer Science.Polymer Physics》2003,41(22):2829-2849
We theoretically investigated the polymorphy of the stereostructures of a periodic polymer. Using the polymer's internal conformation parameters of bond lengths, bond angles, and internal rotation angles, we extended the mathematical treatment for designing polymer backbones. We considered those periodic polymers whose unit cell consists of one (m = 1), two (m = 2), or three (m = 3) kinds of atoms. Moreover, for these three types of polymers, we supposed two catenation types for the skeleton atoms; one is a “homorotatory” sequence and the other is a “heterorotatory” one. To specify the backbone's stereostructure, we introduced several conformation parameters such as the helical pitch number n, the translation distance d, and the inclination angle of the skeleton plane Θ. By combining these parameters, we can systematically understand the variety and the possible polymorphy in the stereostructure of a periodic polymer backbone. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2829–2849, 2003 相似文献
6.
Yan Yin Otoo Yamada Shunsuke Hayashi Kazuhiro Tanaka Hidetoshi Kita Ken‐Ichi Okamoto 《Journal of polymer science. Part A, Polymer chemistry》2006,44(12):3751-3762
A series of branched/crosslinked sulfonated polyimide (B/C‐SPI) membranes were prepared and evaluated as proton‐conducting ionomers based on the new concept of in situ crosslinking from sulfonated polyimide (SPI) oligomers and triamine monomers. Chemical branching and crosslinking in SPI oligomers with 1,3,5‐tris(4‐aminophenoxy)benzene as a crosslinker gave the polymer membranes very good water stability and mechanical properties under an accelerated aging treatment in water at 130 °C, despite their high ion‐exchange capacity (2.2–2.6 mequiv g?1). The resulting polymer electrolytes displayed high proton conductivities of 0.2–0.3 S cm?1 at 120 °C in water and reasonably high conductivities of 0.02–0.03 S cm?1 at 50% relative humidity. In a single H2/O2 fuel‐cell system at 90 °C, they exhibited high fuel‐cell performances comparable to those of Nafion 112. The B/C‐SPI membranes also displayed good performances in a direct methanol fuel cell with methanol concentrations as high as 50 wt % that were superior to those of Nafion 112. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3751–3762, 2006 相似文献
7.
8.
Dehydration of zinc biladienone was catalyzed by zinc acetate, while the reverse reaction was catalyzed by triethylamine. The transformation can be performed thermally without catalyst, and the ratio of the hydrated form to the dehydrated form depended on the solvents: the dehydrated form is favored in CHCl3 and CH2Cl2, while the hydrated form is favored in hexane, pyridine, and DMF. Kinetic studies on the thermal transformation of zinc biladienone from its hydrated blue form to the dehydrated yellow-brown form were performed in toluene and THF. The rate law was half order with respect to the zinc biladienone concentration in toluene, while first order in THF, leading to a slow transformation in concentrated solution in toluene. 相似文献
9.
Novel catalytic asymmetric sulfoxidation in water using the hypervalent iodine reagent iodoxybenzene
Tohma H Takizawa S Morioka H Maegawa T Kita Y 《Chemical & pharmaceutical bulletin》2000,48(3):445-446
A new catalytic asymmetric oxidation of sulfides to sulfoxides in water using the hypervalent iodine(V) reagent iodoxybenzene (PhIO2) has been developed. This methodology is distinctly different from the previously reported use of cyclodextrins or biological catalysts and provides a new route to asymmetric sulfoxidation in water. 相似文献
10.