全文获取类型
收费全文 | 1526篇 |
免费 | 42篇 |
国内免费 | 5篇 |
专业分类
化学 | 1211篇 |
晶体学 | 14篇 |
力学 | 10篇 |
数学 | 93篇 |
物理学 | 245篇 |
出版年
2023年 | 6篇 |
2022年 | 8篇 |
2021年 | 9篇 |
2020年 | 15篇 |
2019年 | 20篇 |
2018年 | 10篇 |
2016年 | 24篇 |
2015年 | 22篇 |
2014年 | 33篇 |
2013年 | 69篇 |
2012年 | 100篇 |
2011年 | 91篇 |
2010年 | 50篇 |
2009年 | 43篇 |
2008年 | 86篇 |
2007年 | 87篇 |
2006年 | 95篇 |
2005年 | 95篇 |
2004年 | 84篇 |
2003年 | 86篇 |
2002年 | 88篇 |
2001年 | 31篇 |
2000年 | 27篇 |
1999年 | 13篇 |
1998年 | 22篇 |
1997年 | 17篇 |
1996年 | 17篇 |
1995年 | 11篇 |
1994年 | 12篇 |
1993年 | 8篇 |
1992年 | 16篇 |
1991年 | 16篇 |
1990年 | 16篇 |
1989年 | 22篇 |
1988年 | 10篇 |
1987年 | 12篇 |
1986年 | 12篇 |
1985年 | 18篇 |
1984年 | 26篇 |
1983年 | 17篇 |
1982年 | 14篇 |
1981年 | 14篇 |
1980年 | 15篇 |
1979年 | 15篇 |
1978年 | 9篇 |
1977年 | 6篇 |
1975年 | 5篇 |
1974年 | 7篇 |
1973年 | 9篇 |
1968年 | 6篇 |
排序方式: 共有1573条查询结果,搜索用时 15 毫秒
21.
22.
23.
Miyabe H Nishimura A Ueda M Naito T 《Chemical communications (Cambridge, England)》2002,(14):1454-1455
The indium-mediated allylation and alkylation reactions of the Oppolzer camphorsultam derivative of glyoxylic oxime ether proceeded with excellent diastereoselectivity in aqueous media, providing a variety of enantiomerically pure alpha-amino acids. 相似文献
24.
Seiji Tsuzuki Kazumasa Honda Tadafumi Uchimaru Masuhiro Mikami Kazutoshi Tanabe 《Journal of the American Chemical Society》2002,124(1):104-112
A model chemistry for the evaluation of intermolecular interaction between aromatic molecules (AIMI Model) has been developed. The CCSD(T) interaction energy at the basis set limit has been estimated from the MP2 interaction energy near the basis set limit and the CCSD(T) correction term obtained by using a medium size basis set. The calculated interaction energies of the parallel, T-shaped,and slipped-parallel benzene dimers are -1.48, -2.46, and -2.48 kcal/mol, respectively. The substantial attractive interaction in benzene dimer, even where the molecules are well separated, shows that the major source of attraction is not short-range interactions such as charge-transfer but long-range interactions such as electrostatic and dispersion. The inclusion of electron correlation increases attraction significantly. The dispersion interaction is found to be the major source of attraction in the benzene dimer. The orientation dependence of the dimer interaction is mainly controlled by long-range interactions. Although electrostatic interaction is considerably weaker than dispersion interaction, it is highly orientation dependent. Dispersion and electrostatic interactions are both important for the directionality of the benzene dimer interaction. 相似文献
25.
Stannyl radical addition-cyclization of oxime ethers connected with olefin moieties was studied. The radical reactions proceeded effectively by the use of triethylborane as a radical initiator to provide the functionalized pyrrolidines via a carbon-carbon bond-forming process. 相似文献
26.
The partial molar free energy, enthalpy, and entropy of oxygen in niobium oxides with ratios from 2.47 to 2.50 were measured with a galvanic cell in the temperature range from 1084 to 1325 K. The partial molar enthalpies of oxygen of the Nb2O5?x and V phases were observed to be nearly independent of composition, indicating the presence of only weak interactions between defects. The value of the slope for the plots of log x in Nb2O5?x against log PO2 was observed to be which is interpreted in terms of a defect structure involving both singly ionized and doubly ionized oxygen vacancies. The previously proposed phase diagram in the vicinity of Nb2O5?x was confirmed by the present emf measurements. 相似文献
27.
Takaki K Itono Y Nagafuji A Naito Y Shishido T Takehira K Makioka Y Taniguchi Y Fujiwara Y 《The Journal of organic chemistry》2000,65(2):475-481
Three-component coupling of acylphosphonates and two carbonyl compounds leading to beta-hydroxyphosphonates has been achieved with low-valent samariums. Thus, acylphosphonates reacted with aldehydes in the presence of semicatalytic amounts of samarium metal or SmI(2) to give acyloxyphosphonates in good yields. The second coupling reaction of the acyloxyphosphonates with aldehydes or ketones promoted by SmI(2) afforded beta-hydroxyphosphonates instead of olefins. Moreover, these two reactions could be carried out in one pot. 相似文献
28.
Diethyl bromodifluoromethyl phosphonate reacts readily with cadmium metal to form a stable cadmium complex. Depending on solvent, this functionalized organocadmium reagent exhibits stability for days to months. It reacts with a variety of electrophiles and serves as a synthetically useful source for the introduction of the difluoromethylene phosphonate group into organic compounds.The synthetic utility of a wide variety of fluoromethylene phosphonium ylides has been a major effort in our laboratory over the past several years [1]. The generation and capture of difluoromethylene ylides () as a general route to difluoromethylene olefins has been of especial interest to us [2]. In an effort to increase the nucleophilicity of the ylide, we have attempted to prepare the analogous phosphonate ylide (). Although we have achieved modest success [3] by capture of () in the reaction of sodium dialkyl phosphites with diethyl bromodifluoromethylphosphonate (), attempts to pregenerate (), either from diethyl difluoromethylphosphonate () or (), have met with little success. () appears to have minimal stability even at low temperatures, and scale up processes of synthetic value would seem to be difficult. 相似文献
29.
Summary Alumina may be considerably modified by impregnating at 100°C in the alkali metal phosphate solution. The available solution for modification was the KOH–K2HPO4–AlPO4 (11.51M) solution or the NaOH–Na2 HPO4 (0.81.1 M or 11.5M) solution. The appreciable improvement on chromatograms was obtained by preheating of the alumina, especially above 800°C prior to impregnating A further modification may be made by ignition of the alumina impregnated. The x-ray diffraction studies revealed the phase transformation of the alumina inducing the modification, and the essential factor of the present modification method being the thermal treatment of the alumina at temperatures forming -alumina. 相似文献
30.
Urata S Irisawa J Takada A Shinoda W Tsuzuki S Mikami M 《The journal of physical chemistry. B》2005,109(36):17274-17280
The membranes of a perfluorosulfonic acid polymer swollen in 10-80 wt % methanol solution were investigated to elucidate the methanol effect on their morphologies, such as size of the solvent cluster, solvent location, and polymer structure, by using isothermal-isobaric molecular dynamics simulations. In higher methanol concentrations, we found less-spherical solvent aggregation and a more spread polymer structure because of the ampholytic nature of methanol. The partial radial distribution functions between solvent oxygen and fluorocarbons, which are composed of the main chain, clearly show that methanol is located closer to the polymer matrix than water. On the other hand, water is preferentially located in the vicinity of an acidic headgroup, SO(3)(-), compared with methanol, although both have similar attractive interaction energies to the acidic group. Furthermore, we discussed solvent dynamics and hydrogen bonding between sulfonic oxygen and solvent O-H groups. 相似文献