全文获取类型
收费全文 | 3621篇 |
免费 | 106篇 |
国内免费 | 8篇 |
专业分类
电工技术 | 196篇 |
综合类 | 6篇 |
化学工业 | 1124篇 |
金属工艺 | 94篇 |
机械仪表 | 89篇 |
建筑科学 | 88篇 |
矿业工程 | 2篇 |
能源动力 | 129篇 |
轻工业 | 400篇 |
水利工程 | 10篇 |
石油天然气 | 2篇 |
无线电 | 233篇 |
一般工业技术 | 602篇 |
冶金工业 | 403篇 |
原子能技术 | 108篇 |
自动化技术 | 249篇 |
出版年
2023年 | 18篇 |
2021年 | 67篇 |
2020年 | 38篇 |
2019年 | 45篇 |
2018年 | 64篇 |
2017年 | 57篇 |
2016年 | 84篇 |
2015年 | 45篇 |
2014年 | 105篇 |
2013年 | 207篇 |
2012年 | 146篇 |
2011年 | 222篇 |
2010年 | 135篇 |
2009年 | 183篇 |
2008年 | 189篇 |
2007年 | 164篇 |
2006年 | 134篇 |
2005年 | 148篇 |
2004年 | 133篇 |
2003年 | 131篇 |
2002年 | 122篇 |
2001年 | 84篇 |
2000年 | 66篇 |
1999年 | 71篇 |
1998年 | 151篇 |
1997年 | 102篇 |
1996年 | 83篇 |
1995年 | 62篇 |
1994年 | 70篇 |
1993年 | 60篇 |
1992年 | 42篇 |
1991年 | 28篇 |
1990年 | 27篇 |
1989年 | 31篇 |
1988年 | 28篇 |
1987年 | 33篇 |
1986年 | 42篇 |
1985年 | 35篇 |
1984年 | 30篇 |
1983年 | 28篇 |
1982年 | 28篇 |
1981年 | 12篇 |
1980年 | 19篇 |
1979年 | 24篇 |
1978年 | 17篇 |
1977年 | 21篇 |
1976年 | 29篇 |
1974年 | 15篇 |
1973年 | 11篇 |
1972年 | 10篇 |
排序方式: 共有3735条查询结果,搜索用时 15 毫秒
71.
Kazuyori Urabe Hiromi Nakano Hiroyasu Morita 《Journal of the American Ceramic Society》2002,85(2):423-429
Structural modulations in solid solutions of C3 S doped with various amounts of ZnO were investigated via the selected-area electron diffraction method. Three monoclinic modifications (M(I), M(II), and M(III)) were identified in the solid solutions. The modifications had pseudohexagonal subcells that were modulated to form supercells. Coordinates of the reflections attributable to the supercells could be expressed by the following linear combinations of vectors of the reciprocal lattices: m1 (−2 a */5.4 + 2 b */5.4 − 7 c */5.4) for M(I), m2 (− a */5 + b */5 − c *) for M(II), and m3 (− a */6 + b */6 + 7 c */6) for M(III), m1 and m2 =±1 and ±2, and m3 =±1, ±2, and ± 3. All the monoclinic modifications possessed structural modulations of a one-dimensional type. The modulation waves could be detected as wavy contrasts by high-resolution transmission electron microscopy. 相似文献
72.
This article describes cationic ring‐opening copolymerization of a bicyclic orthoester having hydroxy group (BOE‐OH) and glycidyl phenyl ether (GPE), and the volume shrinkage behavior during the copolymerization. THF soluble polyethers [poly(BOE‐OH‐co‐GPE)] were obtained by the copolymerizations at 80–180°C, while crosslinked poly(BOE‐OH‐co‐GPE) was obtained by the copolymerizations at 220–250°C. This crosslinking reaction may originate from the dehydration of methylol groups in the side chain of poly(BOE‐OH‐co‐GPE). The volume shrinkage during the cationic copolymerization reduced as the increase of the BOE‐OH feed ratio. By contrast, the volume shrinkage on the crosslinking polymerization was almost independent on the BOE‐OH feed ratio. Poly(BOE‐OH‐co‐GPE)s with higher BOE‐OH composition showed lower thermal weight loss temperature owing to the release of H2O by dehydration of methylol groups. The BOE‐OH component in the THF soluble poly(BOE‐OH‐co‐GPE)s lowered the glass transition temperature (Tg), while that in the crosslinked poly(BOE‐OH‐co‐GPE) increased the Tg probably because of the higher crosslinking density. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1356–1361, 2006 相似文献
73.
Synthesis of poly(tetrahydrofuran-b-ε-caprolactone) macromonomer via the Sml2-induced transformation
Summary A novel well-defined macromonomer consisting of different types of monomers in polymerization mechanisms was synthesized for the first time through the SmI2-induced transformation. The macromonomer, -methacryloylpoly-(tetrahydrofuran-b--caprolactone), was prepared by the reaction of methacryloyl chloride with living poly(tetrahydrofuran-b--caprolactone) [poly(THF-b-CL)] which was obtained by the two-electron reduction of the cationic growing center of poly(THF) by samarium iodide (SmI2) followed by the polymerization of CL. 1H NMR analysis indicated the quantitative introduction of the methacryloyl group onto the polymer end. The molecular weight distribution of the macromonomer was relatively narrow, and the unit ratio of THF to CL could be controlled by both polymerization time of THF and the amount of CL, resulting from the living nature of both CL- and THF-polymerizations. Radical copolymerization of the produced macromonomers with methyl methacrylate in the presence of AIBN resulted in a polymethacrylate backbone grafted with poly(THF-b-CL) block copolymers. 相似文献
74.
The polymers 3 having pyridine moieties in the main chain were synthesized by the reaction of the organocobalt polymers 1 having cobaltacyclopentadiene moieties in the main chain with various nitriles 2. When brown colored 1 and excess 2 were heated in tetrahydrofuran at 80 °C for 24 h and then at 150 °C for 12 h in a sealed tube, the polymers 3 were obtained by the precipitation with methanol in good yields. From the spectroscopic measurements, the resulting polymers
3 were found to contain 35 – 90% of the pyridine moieties depending on the structures of 1.
Received: 7 July 1997/Revised: 14 August 1997/Accepted: 25 August 1997 相似文献
75.
The diffusion and adsorption of C.I. Direct Yellow 12 and Blue 15 in water-swollen ordinary cellophane sheets were examined at various ionic strengths. The concentration dependence of apparent diffusion coefficients, Dc, for these dyes was obtained from the diffusion profiles in the substrate, which were measured by the use of the cylindrical film roll method. The decrease of apparent porosity with an increase in the amounts of adsorption was observed. To explain the diffusion/adsorption behaviors of these systems, a variable porosity model was proposed and was applied to analyze the concentration dependence of Dc's. The diffusion/adsorption behaviors of these dyes could be quantitatively described by this model at relatively low ionic strengths. At higher ionic strengths and/or lower values of C, i.e., at the large values of Cim/Cm, where the C's are the concentrations of immobilized (suffix im) and mobile (suffix m) species, it needed to introduce the concept of dynamic equilibria which occurred simultaneously with diffusion but deviated from the true equiliblia measured by the adsorption experiments. 相似文献
76.
Prediction of the biologically active sites in eclosion hormone from the silkworm, Bombyx mori 总被引:1,自引:0,他引:1
Kikuchi T; Okamoto M; Geiser M; Schmitz A; Gohda K; Takai M; Morita T; Horii K; Fujita N 《Protein engineering, design & selection : PEDS》1997,10(3):217-222
The structure-activity relationship of eclosion hormone from the silkworm,
Bombyx mori, was analyzed. First, the probable active residues in silkworm
eclosion hormone and also tobacco hornworm eclosion hormone were predicted
by the average distance map method. To examine the contributions of those
residues to the activity of silkworm eclosion hormone, Gly-substituted
mutants for those predicted residues were produced by site-directed
mutagenesis and their activities were evaluated by a bioassay. Finally,
Glu12, Met24 and Phe25 were estimated to be the crucial residues for the
eclosion hormone activity. The possibility of the development of a blocker
of an eclosion hormone receptor on the basis of the present work is also
discussed.
相似文献
77.
The diffusion of a reactive disperse dye with a vinylsulfonyl group accompanied by simultaneous reaction with the amino end groups in nylon 6 was examined by the method of cylindrical film roll at 70°C and pH 2.2–8.0. The experimental diffusion profiles of the active and fixed species of the dye in nylon 6 were confirmed to be described by the diffusion equation accompanied by the chemical reaction with substrate taking the limited amount of the end groups into account, where the active species of dye were assumed to react only with the free base of amino end groups. The completion of the reaction with the amino end groups was observed in the first layer from the surface at pH 6.0–8.0. The value of diffusion coefficient was constant (8.0 × 10?10 cm2/s) at all the pH's. The product of the second-order rate constant, k2, of reaction of the dye and the dissociation constant, Ka, of the amino end groups was constant (k2Ka = 4.0 × 10?9 s?1) at pH 2.2–8.0. The k2 values of the reaction with various substrates for vinylsulfonyl and monochlorotriazinyl-reactive dyes were compared and the practical dyeing conditions were discussed. 相似文献
78.
The radiation-induced copolymerization of the methyl chloride salt of N,N-dimethylaminoethyl methacrylate (DMAEM·MC) with acrylamide (AAm) was used to prepare a cationic polymer flocculant. The polymerization rate increased with increasing dose rate, polymerization temperature, monomer concentration and mole fraction of AAm in the monomer mixture. The molecular weight of the copolymer was also found to increase with monomer concentration and mole fraction of AAm, but at high concentration and fraction of AAm, intermolecular crosslinking tends to occur during the polymerization to form water-insoluble copolymer. A water-soluble copolymer having various molecular weights and cationic strengths can be synthesized by selecting suitable reaction conditions; i.e., this radiation process can provide a much higher molecular weight copolymer with a wide range of cationic strength. The flocculation effect was evaluated using sludge from wastewater of sugar manufacture. It was found that the radiation-polymerized copolymer DMAEM·MC–AAm has an excellent flocculation effect. 相似文献
79.
Reverse osmosis separations of phenol (9.4 to 108 ppm), p-cresol (108 ppm), and p-chlorophenol (129 ppm) were studied using Loeb-Sourirajan-type porous cellulose acetate membranes, and single-solute aqueous feed solutions at 500 psig and the indicated solute concentrations. It was found that, by dissociating the solute by changing the pH of the feed solution, all the above phenols could be separated by reverse osmosis. Solute separation increased with increase in the degree of dissociation of the solute in the feed solution; and, by the appropriate choice of pore size on the membrane surface, separations of phenol approaching the degree of dissociation of phenol in the feed solution could be obtained under the operating conditions used. Similar experiments using aniline (93 ppm) as the solute showed that dissociation of solute molecules in the feed solution could be a technique generally applicable for the reverse osmosis separation of nonionic solutes in aqueous solution. The effects of operating pressure in the range 250 to 1500 psig and pore size on the membrane surface on the separation of un-ionized phenol and p-chlorophenol showed that, with respect to single-solute aqueous feed solutions of phenols, the component whose relative acidity was greater was preferentially sorbed at the cellulose acetate membrane—aqueous solution interface, and the solute concentration in the membrane-permeated product solution was a function of the extent and mobility of each of the sorbed species. 相似文献
80.
Hakoshima Toshio; Tanaka Masahiro; Itoh Takeshi; Tomita Ken-khi; Amisaki Takashi; Nishikawa Satoshi; Morioka Hiroshi; Uesugi Sei-ichi; Ohtsuka Eiko; Ikehara Morio 《Protein engineering, design & selection : PEDS》1991,4(7):793-799
Hydrophobic effects on binding of ribonuclease Tl to guaninebases of several ribonucleotides have been proved by mutatinga hydrophobic residue at the recognition site and by measuringthe effect on binding. Mutation of a hydrophobic surface residueto a more hydrophobic residue (Tyr45 Trp) enhances thebinding to ribonucleotides, including mononucleotide inhibitorand product, and a synthetic substrate-analog trinudeotide aswell as the binding to dinucleotide substrates and RNA. Enhancementson binding to non-substrate ribonucleotides by the mutationhave been observed with free energy changes ranging from 2.2 to 3 .9 kJ/mol. These changes are in good agreementwith that of substrate binding, 2.3 kJ/mol, which iscalculated from Michaelis constants obtained from kinetic studies.It is shown, by comparing the observed and calculated changesin binding free energy with differences in the observed transferfree energy changes of the amino acid side chains from organicsolvents to water, that the enhancement observed on guaninebinding comes from the difference in the hydrophobic effectsof the side chains of tyrosine and tryptophan. Furthermore,a linear relationship between nucleolytic activities and hydrophobicityof the residues (Ala, Phe, Tyr, Trp) at position 45 is observed.The mutation could not change substantially the base specificityof RNase Tl, which exhibits a prime requirement for guaninebases of substrates. 相似文献