全文获取类型
收费全文 | 1669篇 |
免费 | 34篇 |
国内免费 | 4篇 |
专业分类
化学 | 1113篇 |
晶体学 | 20篇 |
力学 | 19篇 |
数学 | 62篇 |
物理学 | 462篇 |
综合类 | 31篇 |
出版年
2022年 | 12篇 |
2021年 | 11篇 |
2020年 | 8篇 |
2019年 | 23篇 |
2018年 | 12篇 |
2016年 | 22篇 |
2015年 | 30篇 |
2014年 | 25篇 |
2013年 | 145篇 |
2012年 | 68篇 |
2011年 | 84篇 |
2010年 | 49篇 |
2009年 | 49篇 |
2008年 | 73篇 |
2007年 | 97篇 |
2006年 | 89篇 |
2005年 | 83篇 |
2004年 | 76篇 |
2003年 | 68篇 |
2002年 | 68篇 |
2001年 | 36篇 |
2000年 | 47篇 |
1999年 | 34篇 |
1998年 | 27篇 |
1997年 | 20篇 |
1996年 | 19篇 |
1995年 | 21篇 |
1994年 | 17篇 |
1993年 | 31篇 |
1992年 | 25篇 |
1991年 | 24篇 |
1990年 | 12篇 |
1989年 | 13篇 |
1988年 | 12篇 |
1987年 | 14篇 |
1986年 | 14篇 |
1985年 | 26篇 |
1984年 | 28篇 |
1983年 | 13篇 |
1981年 | 16篇 |
1980年 | 11篇 |
1979年 | 16篇 |
1978年 | 21篇 |
1977年 | 16篇 |
1976年 | 7篇 |
1975年 | 14篇 |
1974年 | 14篇 |
1972年 | 8篇 |
1970年 | 7篇 |
1969年 | 11篇 |
排序方式: 共有1707条查询结果,搜索用时 0 毫秒
21.
Cao B Hasegawa M Okada K Tomiyama T Okazaki T Suenaga K Shinohara H 《Journal of the American Chemical Society》2001,123(39):9679-9680
22.
23.
Tsugikazu Tomono Etsuo Hasegawa Eishun Tsuchida 《Journal of polymer science. Part A, Polymer chemistry》1974,12(5):953-965
Active hydrogen compounds such as hydroquinone (HQ), cyclohexanone (CH), acetophenone (AP), and 4,4′-methylene bis-N-methylaniline (MNA) polymerized with formaldehyde (F) and secondary diamines to produce Mannich base polyamine polymers. The HQ-containing polymers were oxidized to benzoquinone (BQ)-containing polymers and their redox properties were investigated in the desulfurization of hydrogen sulfide. 相似文献
24.
Isotropie Raman spectra of the symmetric C—H stretching bands of several organic molecules are measured in the neat liquid and in solvents including water. The linewidths are interpreted on the basis of the vibrational dephasing model, and intermolecular interactions between the solutes and solvents are discussed. 相似文献
25.
Hasegawa JY Takata K Miyahara T Neya S Frisch MJ Nakatsuji H 《The journal of physical chemistry. A》2005,109(14):3187-3200
Excited states of free-base porphyrin isomers, porphycene (Pc), corrphycene (Cor), and hemiporphycene (hPc), were studied by the Symmetry-Adapted Cluster (SAC)/SAC-Configuration Interaction (CI) method. The absorption peaks of the porphyrin isomers were assigned on the basis of the SAC-CI spectra. The X, Y, X', and Y' bands of the porphyrin isomers, which have weak intensities, are identified. The differences in the Q-band absorptions among the isomers were clearly explained by the four-orbital model. In Cor and hPc, the wave function of the B-band corresponds to the mixture of the four-orbital excitations and the optically forbidden excitation of free-base porphin (P), due to the molecular symmetry lowering in the isomers. The B-band character is described by the five-orbital model in Pc and the six-orbital model in Cor and hPc. Two tetrazaporphycenes and two ring-extended (dibenzo) porphycenes were designed, and the Q-band transition moment was successfully controlled. These examples show that the control of the four-orbital energy levels is the guiding principle for pigment design in porphyrin compounds. 相似文献
26.
27.
Masaki Hasegawa Kazuhiko Saigo Hirokazu Katsuki Noriyuki Yonezawa Toshio Kanoe 《Journal of polymer science. Part A, Polymer chemistry》1983,21(8):2345-2362
The ring-opening polyaddition reaction of anti and syn head-to-head Coumarin dimers with diamines and the photocleavage behavior of the resulting polyamides were investigated. Anti head-to-head Coumarin dimer successfully reacted with aliphatic and aromatic diamines in an aprotic polar solvent to give corresponding high molecular weight polyamides. The polyamides showed good film forming ability and exhibited solubility behavior typical of polyelectrolytes. Furthermore, these polyamides were found to undergo exclusively asymmetric photocleavage on the cyclobutane rings in the polymer main chain to give a fumaramide unit with elimination of 2,2′-dihydroxystilbene. On the other hand, syn head-to-head Coumarin dimer gave only low molecular weight polyamides. These polymerization and photocleavage behaviors were elucidated in comparison with those of model reactions. 相似文献
28.
Hasegawa E Takizawa S Iwaya K Kurokawa M Chiba N Yamamichi K 《Chemical communications (Cambridge, England)》2002,(17):1966-1967
Photoinduced electron transfer reaction of 2-bromomethyl-2-(3-butenyl)benzocyclic-1-alkanones with amines afforded 5-exo radical cyclization products while electron transfer reaction with samarium diiodide produced cyclopropanols. 相似文献
29.
T. Kambara K. Hasegawa H. Yoshioka Y. Kamiya T. Kotani K. Tabei 《Journal of Radioanalytical and Nuclear Chemistry》1977,36(1):87-94
Variations of125Sb valency states in HCl solutions were investigated by the use of the N-benzoyl-N-phenyl-hydroxylamine (BPHA) extraction
method.125Sb(V) is completely reduced to Sb(III) by one hour refluxing in conc. HCl.125Sb(III) is gradually oxidized to Sb(V) in solutions of low HCl concentrations by the effects of their own radiations. Natural
light promotes such oxidation reactions. By utilizing such oxidation-reduction effects125Sb(V) can be easily prepared from125Sb(III) and also125Sb(III) can be prepared by the reduction of Cl
aq
−
. Their valency states were stable on keeping them in brown-colored bottles at 6M HCl concentrations. 相似文献
30.
Kazutoshi Shindo Ryoko NakamuraIkuko Chinda Yasuo OhnishiSueharu Horinouchi Haruko TakahashiKazuo Iguchi Shigeaki HarayamaKensuke Furukawa Norihiko Misawa 《Tetrahedron》2003,59(11):1895-1900
The bphA1(2072)A2A3A4 gene cluster codes for a shuffled biphenyl dioxygenase holoenzyme with broad substrate specificity. These bphA1(2072)A2A3A4 genes were expressed in the actinomycetes Streptomyces lividans using a thiostrepton-inducible promoter PtipA. Biotransformation experiments of various aromatics including carboxylic acid or amine in their molecular structure, such as 1-naphthoic acid, 2-(1-naphthyl)acetic acid, diphenylamine, and 1-benzyl-4-piperidone, were performed using the recombinant S. lividans cells. These ionized aromatics were converted to the corresponding 1,2-dihydrodiol, mono- or tri-hydroxy forms in 48 h. The structure of the converted products was determined by their EI-MS, 1H- and 13C NMR analysis, and several products were found to be novel compounds. 相似文献