全文获取类型
收费全文 | 1169篇 |
免费 | 23篇 |
国内免费 | 1篇 |
专业分类
化学 | 791篇 |
晶体学 | 13篇 |
力学 | 12篇 |
数学 | 66篇 |
物理学 | 311篇 |
出版年
2021年 | 10篇 |
2019年 | 12篇 |
2018年 | 12篇 |
2016年 | 10篇 |
2015年 | 15篇 |
2014年 | 19篇 |
2013年 | 46篇 |
2012年 | 47篇 |
2011年 | 42篇 |
2010年 | 28篇 |
2009年 | 33篇 |
2008年 | 43篇 |
2007年 | 46篇 |
2006年 | 36篇 |
2005年 | 48篇 |
2004年 | 38篇 |
2003年 | 37篇 |
2002年 | 40篇 |
2001年 | 22篇 |
2000年 | 18篇 |
1999年 | 20篇 |
1998年 | 16篇 |
1997年 | 14篇 |
1996年 | 17篇 |
1995年 | 13篇 |
1994年 | 21篇 |
1993年 | 16篇 |
1992年 | 29篇 |
1991年 | 15篇 |
1990年 | 14篇 |
1989年 | 15篇 |
1988年 | 19篇 |
1987年 | 14篇 |
1986年 | 19篇 |
1985年 | 14篇 |
1984年 | 27篇 |
1983年 | 16篇 |
1982年 | 18篇 |
1981年 | 19篇 |
1980年 | 16篇 |
1979年 | 24篇 |
1977年 | 18篇 |
1976年 | 21篇 |
1975年 | 24篇 |
1974年 | 20篇 |
1973年 | 17篇 |
1972年 | 19篇 |
1971年 | 10篇 |
1966年 | 9篇 |
1965年 | 12篇 |
排序方式: 共有1193条查询结果,搜索用时 31 毫秒
991.
992.
Munehiro Inukai Masanori Tamura Satoshi Horike Masakazu Higuchi Susumu Kitagawa Koichi Nakamura 《Angewandte Chemie (International ed. in English)》2018,57(28):8687-8690
Design to store gas molecules, such as CO2, H2, and CH4, under low pressure is one of the most important challenges in chemistry and materials science. Herein, we describe the storage of CO2 in the cavities of a porous coordination polymer (PCP) using molecular rotor dynamics. Owing to the narrow pore windows of PCP, CO2 was not adsorbed at 195 K. As the temperature increased, the rotors exhibited rotational modes; such rotations dynamically expanded the size of the windows, leading to CO2 adsorption. The rotational frequencies of the rotors (k≈10?6 s) and correlation times of adsorbed CO2 (τ≈10?8 s) were elucidated via solid‐state NMR studies, which suggest that the slow rotation of the rotors sterically restricts CO2 diffusion in the pores. This restriction results in an unusually slow CO2 mobility close to solid state (τ≥10?8 s). Once adsorbed at room temperature, CO2 is robustly stored in the PCP under vacuum at 195–233 K because of the steric hindrance of the rotors. We also demonstrate that this mechanism can be applied to the storage of CH4. 相似文献
993.
Iida M Baba C Inoue M Yoshida H Taguchi E Furusho H 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(16):5047-5056
We have prepared novel ionic liquids of bis(N-2-ethylhexylethylenediamine)silver(I) nitrate ([Ag(eth-hex-en)(2)]NO(3) and bis(N-hexylethylenediamine)silver(I) hexafluorophosphate ([Ag(hex-en)(2)]PF(6)), which have transition points at -54 and -6 degrees C, respectively. Below these transition temperatures, both the silver complexes assume amorphous states, in which the extent of the vitrification is larger for the eth-hex-en complex than for the hex-en complex. The diffusion coefficients of both the complex cations, measured between 30 (or 35) and 70 degrees C, are largely dependent on temperature; the dependence is particularly large in the case of the eth-hex-en complex cation below 40 degrees C. Small-angle X-ray scattering studies showed that the bilayer structure of the metal complex is formed in the liquid state for both the silver complexes. A direct observation of the yellowish [Ag(eth-hex-en)(2)]NO(3) liquid by transmission electron microscopy (TEM) indicates the presence of nanostructures, as a microemulsion, of less than 5 nm. Such structures were not clearly observed in the [Ag(hex-en)(2)]PF(6) liquid. Although the [Ag(eth-hex-en)(2)]NO(3) liquid is sparingly soluble in bulk water, it readily incorporates a small amount of water up to [water]/[metal complex] = 7:1. Homogeneous and uniformly sized silver(0) nanoparticles in water were created by the reduction of the [Ag(eth-hex-en)(2)]NO(3) liquid with aqueous NaBH(4), whereas silver(0) nanoparticles were not formed from the [Ag(hex-en)(2)]PF(6) liquid in the same way. 相似文献
994.
Li JR Tao Y Yu Q Bu XH Sakamoto H Kitagawa S 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(9):2771-2776
A new multifunctional di-topic tetrazolate-based ligand, 2,3-di-1H-tetrazol-5-ylpyrazine (H(2)dtp) has been designed and synthesized. The solvothermal reaction of this ligand with ZnCl(2) gave a robust guest-free three-dimensional zeolite-like chiral metal-organic framework (MOF) complex, [Zn(dtp)], which crystallized in chiral space group P6(1) and possessed chiral open channels with nitrogen-rich walls and the diameter of approximately 4.1 A. This framework presents a unique uniform etd (8,3) topology, is the first example of its type in MOFs, and exhibits high thermal stability with the decomposition temperature above 380 degrees C and permanent porosity. It is interesting that this material is able to selectively adsorb O(2) and CO(2) over N(2) gas, being a rare example in MOFs. In addition, C(2)H(2) and MeOH adsorption results show that although the framework channel holds nitrogen-rich walls that may provide H-bonding sites, no NH H-bond effect between the guest molecules and microporous surface was observed. 相似文献
995.
Murphy JJ Furusho H Paton RM Nomura K 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(32):8985-8997
Various poly(macromonomer)s (PMMs) have been prepared by a repeating ring opening metathesis polymerization (ROMP) technique using the well-defined molybdenum initiators of the type, [Mo(CHCMe(2)Ph)(NAr)(OR)(2)] with OR=OCMe(3), OCMeC(CF(3))(2); Ar=2,6-iPr(2)C(6)H(3), 2,6-Me(2)C(6)H(3). The synthetic strategy is based on the polymerization of norbornene and its derivatives affording di- and triblock side chains bearing sugars (mannose, galactose, glucose etc.), linked via O- (ester), and glycosidase resistant C- (isoxazoline) glycosides. The efficient placement of norbornene units on the side chain termini and their conversion into PMMs, facilitated by the Mo alkylidenes, proceeded in a living manner with the quantitative initiation. The methodology was applied to prepare poly(macromonomer)-graft-PEG [PEG: poly(ethylene glycol)], by the attachment of a pseudo phenol terminus on the PMM main chain to PEG-Ms(2) [MsO(CH(2)CH(2)O)(n)Ms, Ms=MeSO(2)] using a "grafting to" approach. Removal of the acetal protecting groups from the sugar coating of a variety of supramolecular structures including PMMs, linear amphiphilic block copolymers (ABC) and a PMM-graft-PEGby using trifluroacetic acid/water (9:1), and suspension in water, prompted the spontaneous formation of spherical architectures by self-assembly of the amphiphilic PMMs as observed by transmission electron microscopy (TEM). The ability to uptake the hydrophobic dye (Nile Red) into the micellar cores of a variety of amphiphilic polymeric fragments is a significant step towards the production of sugar-coated nanospheres for cell-targeting biomimetic applications. 相似文献
996.
Morita N Fukui K Irikuchi J Sato H Takano Y Okamoto I Ishibashi H Tamura O 《The Journal of organic chemistry》2008,73(18):7164-7174
Ethyl glyoxylate O-tert-butyldimethylsilyloxime (8), on treatment with 2.2 equiv of BF3 x OEt2, generated N-boranonitrone E, which underwent intermolecular cycloaddition with alkenes 18 to afford isoxazolidines 19 in moderate to high yields. The cycloaddition of N-boranonitrone E with most of the alkenes gave 3,5-trans isoxazolidines as the major isomers via a concerted mechanism. However, in the case of 1-methylated cyclic alkenes (18j and 18l), the cycloaddition surprisingly furnished the 3,3a-cis-cycloadducts (19j and 19l) as major isomers. A possible explanation is that the reaction of 1-methylated cyclic alkenes proceeds mainly via a stepwise mechanism. This reaction of terminal alkenes is very useful for synthesis of 1,3-anti aminoalcohol derivatives by reductive cleavage of an N-O bond. 相似文献
997.
Liquid–liquid equilibria and tie-lines for the ternary (water + 1-propanol + α-pinene, β-pinene or limonene) and (water + 1-butanol + α-pinene, β-pinene or limonene) mixtures have been measured at T = 298.15 K. The experimental ternary liquid–liquid equilibrium data have been successfully represented using the additional ternary parameters as well as the binary parameters in terms of the extended and modified UNIQUAC models. 相似文献
998.
Shibata T Tahara YK Tamura K Endo K 《Journal of the American Chemical Society》2008,130(11):3451-3457
The intramolecular cycloaddition of 1,n-diene-ynes (n = 4-6), where alkyne and alkene moieties are connected by a 1,1-disubstituted alkene, was examined using a chiral rhodium catalyst, and various types of cycloadducts with quaternary carbon stereocenter(s) were obtained in high to excellent enantiomeric excess. In the case of 1,4-diene-ynes, tricyclic, bicyclic, and spirocyclic compounds were obtained depending upon the substituents at the 2-position of the 1,4-diene moiety and those at their alkyne termini. On the other hand, 1,5- and 1,6-diene-ynes gave tricyclic and bicyclic compounds, which included medium-sized ring systems. The mechanistic considerations for different reaction pathways and the synthetic transformation of tricyclic products into functionalized spirocyclic compounds are also described. The reaction of enediynes, where two alkyne moieties are connected by a 1,1-disubstituted alkene, was also examined, and sterically strained tricyclic compounds with two carbon stereocenters were obtained. 相似文献
999.
Mizumoto T Tamura T Kawai H Kajiyama A Itai S 《Chemical & pharmaceutical bulletin》2008,56(4):530-535
In this study, the taste-masking of famotidine, which could apply to any fast-disintegrating tablet, was investigated using the spray-dry method. The target characteristics of taste-masked particles were set as follows: the dissolution rate is not to be more than 30% at 1 min and not less than 85% at 15 min, and the particle size is not to be more than 150 microm in diameter to avoid a gritty feeling in the mouth. The target dissolution profiles of spray-dried particles consisting of Aquacoat ECD30 and Eudragit NE30D or triacetin was accomplished by the screening of formulas and the appropriate lab-scale manufacturing conditions. Lab-scale testing produced taste-masked particles that met the formulation targets. On the pilot scale, spray-dried particles with attributes, such as dissolution rate and particle size, of the same quality were produced, and reproducibility was also confirmed. This confirmed that the spray-dry method produced the most appropriate taste-masked particles for fast-disintegrating dosage forms. 相似文献
1000.
Kubo K Nakao A Ishii Y Yamamoto T Tamura M Kato R Yakushi K Matsubayashi GE 《Inorganic chemistry》2008,47(12):5495-5502
The electronic properties of cation radical salts derived from organometallic mixed-ligand complexes [(ppy)Au(S-S)](ppy- = C-dehydro-2-phenylpyridine(-); S-S(2-) = dithiolene ligand) with Au(III)-C sigma-bond were investigated. A 2:1 salt complex [(ppy)Au(C8H4S8)]2[PF6] (C8H4S8(2-) = 2-((4,5-ethylenedithio)-1,3-dithiole-2-ylidene)-1,3-dithiole-4,5-dithiolate(2-)) exhibited semiconductive behavior under ambient pressure (rho rt = 2.6 Omega cm, Ea = 0.03 eV). Magnetic measurements show that it is a Mott insulator close to the metal-insulator boundary. Raman and infrared spectra have revealed that the complex has a quasi-one-dimensional dimeric structure consisting of uniformly charged donor molecules. The complex exhibits metallic behavior at pressures above 0.8 GPa. In contrast, a similar compound [(ppy)Au(C8H4S6O2)]2[BF4] (C8H4S6O2(2-) = 2-((4,5-ethylenedioxy)-1,3-dithiole-2-ylidene)-1,3-dithiole-4,5-dithiolate(2-)) is a band insulator. 相似文献