全文获取类型
收费全文 | 586篇 |
免费 | 27篇 |
国内免费 | 3篇 |
专业分类
化学 | 469篇 |
晶体学 | 10篇 |
力学 | 19篇 |
数学 | 37篇 |
物理学 | 81篇 |
出版年
2023年 | 3篇 |
2022年 | 4篇 |
2021年 | 3篇 |
2019年 | 11篇 |
2018年 | 4篇 |
2017年 | 8篇 |
2016年 | 10篇 |
2015年 | 16篇 |
2014年 | 21篇 |
2013年 | 23篇 |
2012年 | 15篇 |
2011年 | 38篇 |
2010年 | 19篇 |
2009年 | 21篇 |
2008年 | 32篇 |
2007年 | 37篇 |
2006年 | 32篇 |
2005年 | 39篇 |
2004年 | 50篇 |
2003年 | 22篇 |
2002年 | 35篇 |
2001年 | 7篇 |
2000年 | 6篇 |
1999年 | 9篇 |
1998年 | 5篇 |
1997年 | 4篇 |
1996年 | 11篇 |
1995年 | 3篇 |
1994年 | 6篇 |
1993年 | 5篇 |
1992年 | 3篇 |
1991年 | 4篇 |
1989年 | 6篇 |
1988年 | 5篇 |
1987年 | 7篇 |
1986年 | 2篇 |
1985年 | 6篇 |
1984年 | 13篇 |
1983年 | 9篇 |
1982年 | 12篇 |
1981年 | 9篇 |
1980年 | 12篇 |
1979年 | 3篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1966年 | 2篇 |
排序方式: 共有616条查询结果,搜索用时 14 毫秒
611.
We previously found that a simple spiropyran derivative (1:1′,3′,3′-trimethyl-6-nitro-spiro-[2H-1-benzopyran-2,2′-indoline]) behaves as a selective and sensitive cyanide anion (CN−) receptor in aqueous media under UV irradiation13. The receptor, when irradiated by UV light in a water/MeCN mixture, creates a CN−-selective absorption band via a nucleophilic addition of CN− to 1 (formation of the 1-CN− species) and allows quantitative determination of very low levels of CN−. In the present work, effects of pH and water content on the response of 1 to anions were studied to clarify the detailed properties of 1. In aqueous media, 1 reacts selectively with CN−regardless of pH and water content, but the reaction is suppressed by a decrease in pH and an increase in water content due to the protonation of CN−. In contrast, in pure MeCN, addition of F− also creates a new absorption band, as does CN−. This is promoted via a nucleophilic interaction between 1 and F− in a 1:2 stoichiometry (formation of the 1-2F− species). The 1-CN− and 1-2F− species have different photochemical properties; the 1-CN− species is stable upon UV irradiation, while the UV irradiation of the 1-2F− species leads to a decomposition of the spiropyran platform. 相似文献
612.
Poly(squarate)s (PPS-1 and PPS-2) were synthesized by the reaction of squaryl dichloride with hydroquinone for PPS-1 and with 2,5-diethoxy-1,4-bis(trimethylsilyloxy)benzene for PPS-2, and the ionic conductivities, thermal properties, and electrochemical and thermal properties of their polymer electrolytes
with LiN(CF3SO2)2 were investigated. The ionic conductivity increased with increasing the lithium salt concentration for the PPS-1–LiN(CF3SO2)2 electrolyte, and the highest ionic conductivities of 8.60 × 10−5 S/cm at 100 °C and 9.57 × 10−8 S/cm at 30 °C were found at the [Li] to [O] ratio of 2:1. And also, the ionic conductivity for the PPS-1–LiN(CF3SO2)2 electrolyte increased with an increase in the lithium salt concentration, reached a maximum value at the [Li] to [O] ratio
of 1:2, and then decreased. The highest ionic conductivity was to be 1.04 × 10−5 S/cm at 100 °C and 1.71 × 10−8 S/cm at 30 °C, respectively. Both polymer electrolytes exhibited relatively better electrochemical and thermal stabilities.
Addition of the PPS-1 as a plasticizer into the poly(ethylene oxide) (PEO)–LiN(CF3SO2)2 electrolyte system suppressed the crystallization of PEO, and improved the ionic conductivity at room temperature.
Invited paper dedicated to Professor W. Weppner on his 65th birthday. 相似文献
613.
We have succeeded in achieving independent control of the repetition rate and optical frequency of a pulse laser by employing a regenerative mode-locking technique. By adopting a voltage-controlled microwave phase shifter or an optical delay line in a regenerative feedback loop we can control the repetition rate of the laser without directly disturbing the optical frequencies. We experimentally show how this independent control can be realized by employing a 40 GHz harmonically and regeneratively mode-locked fiber laser. 相似文献
614.
Poly(butylene sulfite) (poly-1) was synthesized by cationic ring-opening polymerization of butylene sulfite (1), which was prepared by the reaction of 1,4-butanediol and thionyl chloride, with trifluoromethanesulfonic acid (TfOH) in bulk. The polymer electrolytes composed of poly-1 with lithium salts such as bis(trifluoromethanesulfonyl)imide (LiN(SO2CF3)2, LiTFSI) and bis(fluorosulfonyl)imide (LiN(SO2F)2, LiFSI) were prepared, and their ionic conductivities, thermal, and electrochemical properties were investigated. Ionic conductivities of the polymer electrolytes for the poly-1/LiTFSI system increased with lithium salt concentrations, reached maximum values at the [LiTFSI]/[repeating unit] ratio of 1/10, and then decreased in further more salt concentrations. The highest ionic conductivity values at the [LiTFSI]/[repeating unit] ratio of 1/10 were 2.36?×?10?4 S/cm at 80 °C and 1.01?×?10?5 S/cm at 20 °C. On the other hand, ionic conductivities of the polymer electrolytes for the poly-1/LiFSI system increased with an increase in lithium salt concentrations, and ionic conductivity values at the [LiFSI]/[repeating unit] ratio of 1/1 were 1.25?×?10?3 S/cm at 80 °C and 5.93?×?10?5 S/cm at 20 °C. Glass transition temperature (T g) increased with lithium salt concentrations for the poly-1/LiTFSI system, but T g for the poly-1/LiFSI system was almost constant regardless of lithium salt concentrations. Both polymer electrolytes showed high transference number of lithium ion: 0.57 for the poly-1/LiTFSI system and 0.56 for the poly-1/LiFSI system, respectively. The polymer electrolytes for the poly-1/LiTFSI system were thermally more stable than those for the poly-1/LiFSI system. 相似文献
615.
Daiki Fukuhara Masataka Yamauchi Satoru G. Itoh Hisashi Okumura 《Journal of computational chemistry》2023,44(4):534-545
In the replica-permutation method, an advanced version of the replica-exchange method, all combinations of replicas and parameters are considered for parameter permutation, and a list of all the combinations is prepared. Here, we report that the temperature transition probability depends on how the list is created, especially in replica permutation with solute tempering (RPST). We found that the transition probabilities decrease at large replica indices when the combinations are sequentially assigned to the state labels as in the originally proposed list. To solve this problem, we propose to modify the list by randomly assigning the combinations to the state labels. We performed molecular dynamics simulations of amyloid-β(16–22) peptides using RPST with the “randomly assigned” list (RPST-RA) and RPST with the “sequentially assigned” list (RPST-SA). The results show the decreases in the transition probabilities in RPST-SA are eliminated, and the sampling efficiency is improved in RPST-RA. 相似文献
616.
The direct coupling reaction of D -ribosyl fluoride with typical π-excessive aromatic heterocycles such as furan, thiophene, pyrrole, benzofuran, benzothiophene, and indole and their trimethylsilyl derivatives was performed in the presence of boron trifluoride to afford the corresponding C-nucleosides in moderate to good yields. 相似文献