全文获取类型
收费全文 | 1676篇 |
免费 | 19篇 |
国内免费 | 9篇 |
专业分类
化学 | 1384篇 |
晶体学 | 13篇 |
力学 | 21篇 |
数学 | 83篇 |
物理学 | 203篇 |
出版年
2020年 | 10篇 |
2018年 | 11篇 |
2017年 | 10篇 |
2016年 | 12篇 |
2015年 | 8篇 |
2014年 | 16篇 |
2013年 | 73篇 |
2012年 | 46篇 |
2011年 | 74篇 |
2010年 | 44篇 |
2009年 | 41篇 |
2008年 | 74篇 |
2007年 | 84篇 |
2006年 | 96篇 |
2005年 | 92篇 |
2004年 | 97篇 |
2003年 | 63篇 |
2002年 | 75篇 |
2001年 | 20篇 |
2000年 | 33篇 |
1999年 | 26篇 |
1998年 | 23篇 |
1997年 | 19篇 |
1996年 | 18篇 |
1995年 | 20篇 |
1994年 | 20篇 |
1993年 | 20篇 |
1992年 | 15篇 |
1991年 | 20篇 |
1990年 | 12篇 |
1989年 | 13篇 |
1988年 | 29篇 |
1987年 | 20篇 |
1986年 | 18篇 |
1985年 | 34篇 |
1984年 | 36篇 |
1983年 | 14篇 |
1982年 | 38篇 |
1981年 | 51篇 |
1980年 | 34篇 |
1979年 | 26篇 |
1978年 | 31篇 |
1977年 | 24篇 |
1976年 | 34篇 |
1975年 | 20篇 |
1974年 | 30篇 |
1973年 | 21篇 |
1971年 | 7篇 |
1970年 | 8篇 |
1967年 | 8篇 |
排序方式: 共有1704条查询结果,搜索用时 15 毫秒
91.
Fukuji Higashi Toshio Mashimo 《Journal of polymer science. Part A, Polymer chemistry》1986,24(7):1697-1701
The reaction promoted by thionyl chloride and pyridine could selectively activate carboxyl groups of hydroxybenzoic acids to give polyesters of high inherent viscosities up to 3.8. Favorable conditions were studied in terms of the temperatures for the initial reaction with the acids and subsequent aging at room temperature. Copolymers of several combinations of hydroxybenzoic acids with high molecular weights were obtained in quantitative yield by carrying out the polycondensation at 80°C for 3 h. The reaction could also produce high molecular polyesters in a simpler process without the initial activation of dicarboxylic acids by adding a mixture of these monomers to the condensing agent, and a tough film- and fiberforming polymer was obtained from 4,4′-dihydroxyphenylsulfone of low nucleophilicity whose polymer of high molecular weight is difficult to obtain. The process was also successfully applied to the direct copolycondensations of hydroxybenzoic acids, aromatic dicarboxylic acids, and bisphenols to produce polyesters of ηinh up to 5.6. 相似文献
92.
Toshio Ogawa Masakazu Sakai Wataru Ishitobi 《Journal of polymer science. Part A, Polymer chemistry》1986,24(1):109-118
Molecular weight distribution of Nylon 12 was determined with hexafluoroisopropanol/toluene mixture as eluent by gel permeation chromatography. Calibration curve for Nylon 12 was easily obtained from that of polystyrene because the method of universal calibration was applicable among these polymers. The molecular weight distributions of Nylon 12 were always broader than expected by the theory of polymerization, i.e., most probable distribution. This result was not caused by broadening effect in gel permeation chromatography, but by polymerization itself. 相似文献
93.
Tsukasa Matsunaga YURI HATAKEYAMA Michi Ohta Toshio Mori Osamu Nikaido 《Photochemistry and photobiology》1993,57(S1):934-940
Abstract— We established a monoclonal antibody(DEM–1) that recognizes UV-induced DNA damage other than cyclobutane pyrimidine dimers or(6–4)photoproducts. The binding ofDEM–1 antibody to 254 nm UV-irradiated DNA increased with subsequent exposure to UV wavelengths longer than 310 nm, whereas that of the 64M-2 antibody specific for the(6–4)photoproduct decreased with this treatment. Furthermore, the increase inDEM–1 binding was inhibited by the presence of the 64M-2 antibody during the exposure. We concluded that theDEM–1 antibody specifically recognized the Dewar photoproduct, which is the isomeric form of the(6–4)photoproduct. TheDEM–1 antibody, however, also bound to DNA irradiated with high fluences of 254 nm UV, suggesting that 254 nm UV could induce Dewar photoproducts without subsequent exposure to longer wavelengths of UV. Furthermore, an action spectral study demonstrated that 254 nm was the most efficient wavelength for Dewar photoproduct induction in the region from 254 to 365 nm, as well as cyclobutane dimers and(6–4)photoproducts, although the action spectrum values in the U V-B region were significantly higher compared with those for cyclobutane dimer and(6–4)photoproduct induction. 相似文献
94.
Tomoko Sotomatsu Yoshiyuki Murata Toshio Fujita 《Journal of computational chemistry》1991,12(1):135-138
The AM1 calculation was done for ortho-substituted toluenes (o-X-C6H4-CH3) and ortho-substituted tert-butylbenzenes (o-X-C6H4-t-Bu). The difference in the calculated heat of formation between o-X-C6H4-CH3 and o-X-C6H4-t-Bu was used as a theoretical steric index for ortho-X. The correlation of this theoretical steric index with the empirical steric parameter sets such as our recently defined Es(AMD) and the Taft–Kutter–Hansch (TKH) Es was examined. In spite of the simplicity of the model system, the theoretical index was linear with the Es(AMD) constant with a correlation coefficient of r = 0.972 for 17 substituents of various structures. Including the phenyl group, the correlation with the TKH Es constant was r = 0.948. The theoretically calculated index was shown to serve as a measure of the ortho steric effect. 相似文献
95.
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
96.
James P. Kutney Toshio Honda Peter M. Kazmaier Norman J. Lewis Brian R. Worth 《Helvetica chimica acta》1980,63(2):366-374
The synthesis and conformational analysis of (3′R)-3-hydroxyleurosidine ( 5 ), (3′S)-3-hydroxyleurosidine ( 10 ), (3′S)-3-acetoxy-4′-deoxyleurosidine ( 15 ), (3′R)-3-acetoxy-4′-deoxyleurosidine ( 23 ), (3′R)-3-acetoxy-4′-deoxyvinblastine ( 16 ), (3′S)-3-acetoxy-4′-deoxyleurosidine ( 28 ) is discussed. 相似文献
97.
Yoshiharu Abe Toshio Masuda Toshinobu Higashimura 《Journal of polymer science. Part A, Polymer chemistry》1989,27(13):4267-4279
(o-Methylphenyl)acetylene polymerized with high yields in the presence of W and Mo catalysts. W catalysts were more active than the corresponding Mo catalysts. The weight-average molecular weight of the polymer formed with W(CO)6–CCl4–hv reached 8 × 105, being higher than the maximum value (ca. 2 × 105) for poly(phenylacetylene). The polymer had the structure $\rlap{--} [{\rm CH} \hbox{=\hskip-1pt=} {\rm C}(o - {\rm CH}_3 {\rm C}_6 {\rm H}_4 )\rlap{--} ]_n $. The stereochemical structure of the main chain could be determined by 13C-NMR; the cis content varied in a range of 41–61% depending on the polymerization conditions. The present polymer was thermally more stable than poly(phenylacetylene) according to thermogravimetric analysis. Interestingly, this polymer possessed deeper color than poly(phenylacetylene), and showed a fairly strong absorption in the visible region. 相似文献
98.
Ionizing radiations, which have already been utilized for the sterilization of medical supplies as well as gas fumigation, should be the final candidate to decontaminate “hybrid” biomaterials containing bio-active materials including enzymes because irradiation induces neither heat nor substances affecting the quality of the materials and our health. In order to check the feasibility of 60Co-gamma rays on these materials, we selected commercial proteases including papain and bromelain hybridized with commercial activated chitosan beads and demonstrated that these enzyme-hybrids suspended in water showed the significant radiation durability of more than twice as much as free enzyme solution at 25-kGy irradiation. Enhanced thermal and storage stability of the enzyme hybrids were not affected by the same dose level of irradiation, either, indicating that commercial irradiation sterilization method is applicable to enzyme hybrids without modification. 相似文献
99.
Sako M Kihara T Tanisaki M Maki Y Miyamae A Azuma T Kohda S Masugi T 《The Journal of organic chemistry》2002,67(3):668-673
The UV irradiation of pyrrolnitrin (1a), which is an antibiotic clinically useful against dermatophytosis and possesses a unique 2-(pyrrol-3-yl)nitrobenzene moiety in the molecule, in an anhydrous aprotic solvent resulted in the exclusive formation of transient 7,4'-dichlorospiro[1,3-dihydrobenzo(c)isoxazole-3,3'-pyrrolin-2'-one] (2a) via the intramolecular oxidation of the juxtaposed pyrrole ring by the triplet-excited nitro group. The irradiation in an aqueous aprotic solvent, however, allowed the concurrent occurrence of intramolecular cyclization by the singlet-excited nitro group in 1a and the hydroxylation at the 2-position of the pyrrole ring by water to afford 3,7-dichloro-8-hydroxy-8,8a-dihydropyrrolo[2,3-b]indol-2-one (3a), accompanied by the formation of 2a. Elongation of the irradiation time in these photoreactions caused a rapid consumption of the products, 2a and 3a, to give undetermined polar polymeric products. The present results indicate that the photodegradation of 1a is significantly influenced by the presence of water in the reaction media and by the nature of its excited state. Thus, the loss of the antifungal activities by the photosensitive antibiotic 1a was chemically proved. 相似文献
100.
[structure: see text] 8,11-Dideoxytetrodotoxin, an unnatural tetrodotoxin analogue, was synthesized in a highly stereoselective manner from a common intermediate in our synthetic studies on tetrodotoxin. The synthesis features neighboring group participation of trichloroacetamide for stereoselective hydroxylation, protection of ortho ester, and guanidine installation with Boc-protected isothiourea. 相似文献