全文获取类型
收费全文 | 5517篇 |
免费 | 191篇 |
国内免费 | 30篇 |
专业分类
化学 | 4352篇 |
晶体学 | 50篇 |
力学 | 76篇 |
数学 | 347篇 |
物理学 | 913篇 |
出版年
2023年 | 23篇 |
2022年 | 22篇 |
2021年 | 56篇 |
2020年 | 65篇 |
2019年 | 96篇 |
2018年 | 54篇 |
2017年 | 47篇 |
2016年 | 110篇 |
2015年 | 97篇 |
2014年 | 133篇 |
2013年 | 284篇 |
2012年 | 314篇 |
2011年 | 383篇 |
2010年 | 209篇 |
2009年 | 240篇 |
2008年 | 385篇 |
2007年 | 376篇 |
2006年 | 416篇 |
2005年 | 363篇 |
2004年 | 335篇 |
2003年 | 272篇 |
2002年 | 271篇 |
2001年 | 84篇 |
2000年 | 66篇 |
1999年 | 58篇 |
1998年 | 70篇 |
1997年 | 68篇 |
1996年 | 67篇 |
1995年 | 54篇 |
1994年 | 36篇 |
1993年 | 40篇 |
1992年 | 25篇 |
1991年 | 34篇 |
1990年 | 20篇 |
1989年 | 18篇 |
1988年 | 24篇 |
1987年 | 29篇 |
1986年 | 40篇 |
1985年 | 57篇 |
1984年 | 48篇 |
1983年 | 20篇 |
1982年 | 50篇 |
1981年 | 51篇 |
1980年 | 43篇 |
1979年 | 38篇 |
1978年 | 29篇 |
1977年 | 26篇 |
1976年 | 23篇 |
1975年 | 15篇 |
1973年 | 18篇 |
排序方式: 共有5738条查询结果,搜索用时 437 毫秒
991.
Takashi Nakamura Keiji Yashiro Kazuhisa Sato Junichiro Mizusaki 《Journal of solid state chemistry》2009,182(5):1121-299
In order to elucidate the relation between thermodynamic quantities, the defect structure, and the defect equilibrium in La2−xSrxNiO4+δ, statistical thermodynamic calculation is carried out and calculated results are compared to those obtained from experimental data. Partial molar enthalpy of oxygen and partial molar entropy of oxygen are obtained from δ-P(O2)-T relation by using Gibbs-Helmholtz equation. Statistical thermodynamic model is derived from defect equilibrium models proposed before by authors, localized electron model and delocalized electron model which could well explain the variation of oxygen content of La2−xSrxNiO4+δ. Although assumed defect species and their equilibrium are different, the results of thermodynamic calculation by localized electron model and delocalized electron model show minor difference. Calculated results by the both models agree with the thermodynamic quantities obtained from oxygen nonstoichiometry of La2−xSrxNiO4+δ. 相似文献
992.
Sasaki T Kubo M Kikukawa T Kamiya M Aizawa T Kawano K Kamo N Demura M 《Photochemistry and photobiology》2009,85(1):130-136
Halorhodopsin (HR) is a transmembrane seven-helix retinal protein, and acts as an inward light-driven Cl− pump. HR from Natronomonas pharaonis (NpHR) can be expressed in Escherichia coli inner membrane in large quantities. Here, we showed that NpHR forms the trimer structure even in the presence of 0.1% (2 m m ) to 1% (20 m m ) dodecyl-β- d -maltoside (DDM), whose concentrations are much higher than the critical micelle concentration (0.17 m m ). This conclusion was drawn from the following observations. (1) NpHR in the DDM solution showed an exciton-coupling circular dichroism (CD) spectrum. (2) From the elution volume of gel filtration, the molecular mass of the NpHR–DDM complex was estimated. After evaluation of the mass of the bound DDM molecules, the mass of NpHR calculated was approximately equal to that of the trimer. (3) The cross-linked NpHR by glutaraldehyde gave the SDS-PAGE corresponding to the trimer. Mass spectra of these samples also support the notion of the trimer. Using the membrane fractions expressing NpHR ( Escherichia coli and Halobacterium salinarum ), CD spectra showed exciton-coupling, which suggests strongly the trimer structure in the cell membrane. 相似文献
993.
Takashi Masuda Yasuo Matsuki Tatsuya Shimoda 《Journal of colloid and interface science》2009,340(2):298-305
Cyclopentasilane (CPS) and polydihydrosilane, which consist of hydrogen and silicon only, are unique materials that can be used to produce intrinsic silicon film in a liquid process, such as spin coating or an ink-jet method. Wettability and solubility of general organic solvents including the above can be estimated by Hamaker constants, which are calculated according to the Lifshitz theory. In order to calculate a Hamaker constant by the simple spectral method (SSM), it is necessary to obtain absorption frequency and function of oscillator strength in the ultraviolet region. In this report, these physical quantities were obtained by means of an optical method. As a result of examination of the relation between molecular structures and ultraviolet absorption frequencies, which were obtained from various liquid materials, it was concluded that ultraviolet absorption frequencies became smaller as electrons were delocalized. In particular, the absorption frequencies were found to be very small for CPS and polydihydrosilane due to σ-conjugate of their electrons. The Hamaker constants of CPS and polydihydrosilane were successfully calculated based on the obtained absorption frequency and function of oscillator strength. 相似文献
994.
Kaoru Honda Jaeheung Cho Prof. Dr. Takahiro Matsumoto Dr. Jungyun Roh Hideki Furutachi Dr. Takehiko Tosha Dr. Minoru Kubo Dr. Shuhei Fujinami Prof. Takashi Ogura Prof. Teizo Kitagawa Prof. Masatatsu Suzuki Prof. 《Angewandte Chemie (International ed. in English)》2009,48(18):3304-3307
In the nick(el) of time : Bis(μ‐oxo) dinickel(III) complexes 2 (see scheme), generated in the reaction of 1 with H2O2, are capable of hydroxylating the xylyl linker of the supporting ligand to give 3 . Kinetic studies reveal that hydroxylation proceeds by electrophilic aromatic substitution. The lower reactivity than the corresponding μ‐η2:η2‐peroxo dicopper(II) complexes can be attributed to unfavorable entropy effects.
995.
Yasushi Yokoyama Prof. Dr. Tatsuya Shiozawa Yutaka Tani Dr. Takashi Ubukata Dr. 《Angewandte Chemie (International ed. in English)》2009,48(25):4521-4523
Into my arms : Photochemical cyclization of diarylethenes that have two chiral side arms showed up to 100 % de (see scheme). Introduction of these chiral side arms onto the carbon atoms where ring closure occurs is a general strategy for the highly diastereoselective cyclization of diarylethenes.
996.
Hiroaki Kitagishi Dr. Yasuaki Kakikura Hiroyasu Yamaguchi Dr. Koji Oohora Akira Harada Prof. Dr. Takashi Hayashi Prof. Dr. 《Angewandte Chemie (International ed. in English)》2009,48(7):1170-1170
Supramolecular protein polymers consisting of cytochrome b562 monomers with heme covalently attached to the protein surface are presented by T. Hayashi and co‐workers in their Communication on page 1271 ff. Not only one‐dimensional hemoprotein fibers with submicrometer lengths have been prepared, but when a heme triad was added as a pivot molecule, two‐dimensional protein assembly networks resulted, which cover over 100 square micrometers.
997.
Isamu Shiina Takashi Katoh Shunsuke Nagai Minako Hashizume 《Chemical record (New York, N.Y.)》2009,9(6):305-320
Various intermediates for the synthesis of erythronolide A, an aglycon of erythromycin A, are prepared from the corresponding seco‐acids using 2‐methyl‐6‐nitrobenzoic anhydride (MNBA) in the presence of 4‐(dimethylamino)pyridine (DMAP) with or without triethylamine. The efficiency of the MNBA lactonization is assessed by studying this method and comparing the results with those of the other established macrocyclization protocols. It has been finally concluded that (i) the conformationally appropriate substrate for the monomeric cyclization gave the desired lactone in excellent yield under mild reaction conditions in the presence of MNBA and DMAP, (ii) the highly‐strained substrate for the cyclization also afforded the monomeric lactone in relatively good yield at 100°C in toluene, and (iii) the seco‐acid having stable linear conformation, which preferred dimerizing more than forming the monomeric lactone, provided the corresponding diolide in high yield with the constant ratio of the monomer to dimeric lactone (approximately 1/5). © 2009 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 9: 305–320; 2009: Published online in Wiley InterScience ( www.interscience.wiley.com ) DOI 10.1002/tcr.200900017 相似文献
998.
Abe M Hattori M Takegami A Masuyama A Hayashi T Seki S Tagawa S 《Journal of the American Chemical Society》2006,128(24):8008-8014
A detailed study of the regioselectivity of 1,2-oxygen migration was conducted using the unsymmetrically substituted singlet 2,2-dialkoxy-1,3-diarylcyclopentane-1,3-diyls 5. The alkoxy group selectively migrates to the electron-donating p-methoxyphenyl-substituted carbon. The regioselective migration of oxygen clearly indicates a hyperconjugative resonance structure, that is, zwitterionic characteristics, in singlet 2,2-dialkoxy-1,3-diyls. This represents the first attempt to experimentally probe the contribution of hyperconjugation to stabilizing the singlet state. 相似文献
999.
Matsuo Y Muramatsu A Kamikawa Y Kato T Nakamura E 《Journal of the American Chemical Society》2006,128(30):9586-9587
A series of conical molecules featuring a [60]fullerene/ferrocene hybrid and five aralkyl side chains (Fe[C60{C6H4-(OCO-C6H3-(OR)2-3,4)-4}5]Cp) have been synthesized and examined for their structural and electrochemical properties as well as their ability to form supramolecular structures in crystals and liquid crystals. When the R group on the side is a methyl group, the compound forms crystals in which the dipolar conical molecules are stacked head-to-tail to form a columnar structure. When the R group is as long as a C18H38 group, the compound forms liquid crystals. Oxidation of the liquid crystalline compound by an aminium salt [(4-BrC6H4)3N][SbCl6] produces the corresponding paramagnetic Fe(III) compound that also exhibits liquid crystalline properties. 相似文献
1000.
Funasaki N Uratsuji I Okuno T Hirota S Neya S 《Chemical & pharmaceutical bulletin》2006,54(8):1155-1161
The masking mechanisms of the bitter taste of propantheline bromide (PB) and oxyphenonium (OB) bromide by native and modified cyclodextrins, saccharides, surfactants, organic acids, nonionic and anionic polymers, and other compounds were investigated with ion selective electrodes. The intensity of the bitter taste for a mixed solution of cyclodextrin with PB or OB was quantitatively explained from the observed electromotive force with the following assumptions: the complex and the masking agent do not have any tastes and the bitter taste is independent of other tastes. Sodium dodecyl sulfate reduced the bitter taste remarkably, and this reduction was also explicable on the basis of the same mechanism. Sodium taurodeoxycholate enhanced the bitter taste, because of its strong bitterness, although it formed 1 : 1 complexes with PB and OB. The masking mechanism of saccharides was ascribed to overcoming the weak bitterness of the drug by the strong sweetness. Lambda-carrageenan suppressed the bitter taste remarkably. This suppression was ascribed to the binding of PB and OB to lambda-carrageenan, the effect of the solution viscosity on the bitter taste, and the covering of the bitter taste receptor by lambda-carrageenan. It was suggested that the moderate masking by other polymers was attributable to the effect of the solution viscosity or the receptor covering. Native and modified beta-cyclodextrins, sodium dodecyl sulfate, lambda-carrageenan, Tween 20, and sodium carboxymethyl cellulose are good masking agents for the bitter tastes of PB and OB. The drug ion selective electrode is a useful tool for understanding of the masking mechanism of the bitter taste, screening of masking agents, and estimation of appropriate concentrations of the masking agents. 相似文献