全文获取类型
收费全文 | 5126篇 |
免费 | 82篇 |
国内免费 | 9篇 |
专业分类
电工技术 | 253篇 |
综合类 | 10篇 |
化学工业 | 988篇 |
金属工艺 | 88篇 |
机械仪表 | 81篇 |
建筑科学 | 74篇 |
能源动力 | 169篇 |
轻工业 | 302篇 |
水利工程 | 24篇 |
石油天然气 | 12篇 |
无线电 | 548篇 |
一般工业技术 | 797篇 |
冶金工业 | 1343篇 |
原子能技术 | 157篇 |
自动化技术 | 371篇 |
出版年
2023年 | 20篇 |
2022年 | 72篇 |
2021年 | 83篇 |
2020年 | 35篇 |
2019年 | 44篇 |
2018年 | 45篇 |
2017年 | 47篇 |
2016年 | 77篇 |
2015年 | 35篇 |
2014年 | 97篇 |
2013年 | 201篇 |
2012年 | 141篇 |
2011年 | 207篇 |
2010年 | 139篇 |
2009年 | 178篇 |
2008年 | 176篇 |
2007年 | 150篇 |
2006年 | 135篇 |
2005年 | 126篇 |
2004年 | 117篇 |
2003年 | 121篇 |
2002年 | 115篇 |
2001年 | 143篇 |
2000年 | 106篇 |
1999年 | 149篇 |
1998年 | 554篇 |
1997年 | 346篇 |
1996年 | 252篇 |
1995年 | 134篇 |
1994年 | 146篇 |
1993年 | 131篇 |
1992年 | 75篇 |
1991年 | 67篇 |
1990年 | 60篇 |
1989年 | 59篇 |
1988年 | 58篇 |
1987年 | 55篇 |
1986年 | 50篇 |
1985年 | 47篇 |
1984年 | 39篇 |
1983年 | 39篇 |
1982年 | 45篇 |
1981年 | 46篇 |
1980年 | 27篇 |
1979年 | 35篇 |
1978年 | 24篇 |
1977年 | 28篇 |
1976年 | 54篇 |
1973年 | 16篇 |
1972年 | 16篇 |
排序方式: 共有5217条查询结果,搜索用时 0 毫秒
71.
Kojima Shuichi; Takagi Nobuyuki; Minagawa Tetsuya; Fushimi Noriko; Miura Kin-ichiro 《Protein engineering, design & selection : PEDS》1999,12(10):857-862
We have previously shown that replacing the P1-site residue(Ala) of chicken ovomucoid domain 3 (OMCHI3) with a Met or Lysresults in the acquisition of inhibitory activity toward chymotrypsinor trypsin, respectively. However, the inhibitory activitiesthus induced are not strong. In the present study, we introducedadditional amino acid replacements around the reactive siteto try to make the P1-site mutants more effective inhibitorsof chymotrypsin or trypsin. The amino acid replacement AspTyrat the P2' site of OMCHI3(P1Met) resulted in conversion to a35000-fold more effective inhibitor of chymotrypsin with aninhibitor constant (Ki) of 1.17x1011 M. The Ki valueof OMCHI3(P1Met, P2'Ala) indicated that the effect on the interactionwith chymotrypsin of removing a negative charge from the P2'site was greater than that of introducing an aromatic ring.Similarly, enhanced inhibition of trypsin was observed whenthe AspTyr replacement was introduced into the P2' site of OMCHI3(P1Lys).Two additional replacements, AspAla at the P4 site and ArgAlaat the P3' site, made the mutant a more effective inhibitorof trypsin with a Ki value of 1.44x109 M. By contrast,ArgAla replacement at the P3' site of OMCHI3(P1Met, P2'Tyr)resulted in a greatly reduced inhibition of chymotrypsin, andAspAla replacement at the P4 site produced only a small changewhen compared with a natural variant of OMCHI3. These resultsclearly indicate that not only the P1-site residue but alsothe characteristics, particularly the electrostatic properties,of the amino acid residues around the reactive site of the proteaseinhibitor determine the strength of its interactions with proteases.Furthermore, amino acids with different characteristics arerequired around the reactive site for strong inhibition of chymotrypsinand trypsin. 相似文献
72.
Electro-rheological (ER) effect of a blend composed of two liquid crystalline materials with different molecular weights is described in this article. The results indicated that ER effect of the blend was observed at the temperature range where each neat sample did not show ER effect. Furthermore, both storage modulus (G′) and loss modulus (G″) decreased drastically at the temperature range for the blend in dynamic viscoelastic measurements. We show that steady ER effect could be obtained by using a blend made up of two liquid crystalline components, whereas remarkable increment in shear stress was not observed for each component under applied electric field. 相似文献
73.
Hideya Nakamura 《Chemical engineering science》2007,62(11):3043-3056
This paper describes the numerical analysis of particle mixing in a rotating fluidized bed (RFB). A two-dimensional discrete element method (DEM) and computational fluid dynamics (CFD) coupling model were proposed to analyze the radial particle mixing in the RFB. Spherical polyethylene particles (Geldart group B particles) were used as model particles under the assumptions that they were cohesionless and mono-disperse with their diameter of 0.5 mm.The validity of the proposed model was confirmed by the comparison between the calculated degree of particle mixing and the experimental one, which was obtained by measuring the lightness of the recorded image taken by a high-speed video camera. Effects of the operating parameters (gas velocity, centrifugal acceleration, particle bed height, and vessel radius) on the radial particle mixing rate were numerically analyzed. The radial particle mixing rate was found to be strongly affected by the bubble characteristics, especially by the bubble size. The mathematical model for the rate coefficient of particle mixing as functions of operating parameters was empirically proposed. The radial particle mixing rate in a RFB could be well correlated by the three dimensionless numbers: dimensionless acceleration (Ac), bubble Froude number (Frb), and dimensionless radius on the surface of particle bed (βs). 相似文献
74.
Naofumi Nakamura 《应用聚合物科学杂志》1991,42(5):1341-1350
Ketalization reaction of poly(vinyl alcohol) (PVA) by aliphatic ketones, dimethylsulfoxide (DMSO) as solvent, under the presence of acidic catalyst, in homogeneous system was carried out and the synthesis of polyvinylketals were successfully performed. The equilibrium constant at 40°C is ca. 0.07 in the case of methyl n-propyl ketone (nPK) and methyl n-butyl ketone (nBK), but is ca. 0.05 in the case of methyl i-propyl ketone (iPK) and ca. 0.01 in the case of methyl i-butyl ketone (iBK) and methyl t-butyl ketone (tBK), respectively. Moreover, the ketalization degree of polyvinylketal by iBK and tBK reached to only ca. 35 mol % as the maximum. It seems that these were due to steric hindrance of bulky side chain of ketones. But the heat of reaction is 7.5 kcal/mol in all aliphatic ketones, it seems to proceed the same ketalization reaction mechanism. Films prepared from the polyvinylketals were soaked in water and degree of swelling, solubility, and hydrolysis of films were measured. The reaction of film with water, in acidic side, at first the film swells, and then, as the deketalization reaction proceeds, the film dissolves in water. The dissolution time is controlled by the kind of ketones, ketalization degree, and pH of water which reveals that deketalization reaction proceeds proportional to proton concentration. It is more difficult to dissolve highly ketalized polyvinylketals obtained by propyl ketones and butyl ketones than that by acetone. The hydrolysis of polyvinylketal film proceeds in the order as follows: acetone > MEK > nPK > iPK ≒ nBK > iBK > tBK. This phenomenon seems to be affected by hydrophobicity of the film surface which depends upon the kind of the original ketones. 相似文献
75.
The complexation between poly(ethylene oxide) (PEO) and poly(acrylic acid) (PAA) was made by using double the molar quantity of either polymer component at pH 2 where the resulting complex completely precipitates. After the removal of the precipitate, PEO or PAA remaining in the supernatant was subjected to gel permeation chromatography to investigate the change in the molecular weight distribution (MWD) caused by the complexation. No remarkable difference is observed in the MWD curves for PEO[1] (Mw=1.37 × 104) before and after the complexation with PAA[1] (Mw=1.10 × 103) and PAA[2] (Mw=4.16 × 105). However, the MWD curves of PEO[2] (Mw=1.26 × 105) and PAA[2] become shortened and shift to the low molecular weight side after the complexation with PAA[1] or [2] and PEO[2], respectively. This tendency is enhanced by increasing the complexation temperature. From these results, it is indicated that the complexation between PEO and PAA deals with an equilibrium reaction, and the equilibrium constant is dependent on the chain length of both polymer components and also on the complexation temperature. 相似文献
76.
Yamauchi Toshihiro Akao Yohei Yoshitani Ryota Nakamura Yuichi Hashimoto Masaki 《International Journal of Information Security》2021,20(4):461-473
International Journal of Information Security - Cyberattacks, especially attacks that exploit operating system vulnerabilities, have been increasing in recent years. In particular, if administrator... 相似文献
77.
Combustion, Explosion, and Shock Waves - Zero-dimensional computations of nanosecond-order ignition using a nanosecond discharge are performed with two constraints. The effects of these constraints... 相似文献
78.
Gabriela Brunosi Medeiros Paulo Ricardo de Souza Karina Miyuki Retamiro Celso Vataru Nakamura Edvani Curti Muniz Elisângela Corradini 《应用聚合物科学杂志》2021,138(36):50898
The production of polymer fibers from the combination of zein and PEO might have great potential in the field of biomaterial. Zein/PEO fibers were obtained in this work through solution electrospinning. An experimental design, 24-1, was used for evaluating the influences of PEO content in the blend, distance from the needle tip to the collector, applied electric voltage and solution flow for average fiber diameter and relative-yield process. Beyond this, the relationship between PEO content in the blend and the fiber properties were evaluated through FTIR, DSC, TG, tensile tests, and cytotoxic tests. The factor that exerts the greatest effect on the average fiber diameter response was the electrical voltage. The increase in PEO content in the blend decreased the thermal stability and increased the degree of the fibers' crystallinity. The mechanical tests showed that fibers with higher elongation were obtained at richer PEO blends. The fibers presented cytocompatible characteristics. 相似文献
79.
Y. Sakamoto T. Hisamoto M. Ura R. Nakamura T.B. Flanagan 《Journal of Alloys and Compounds》1993,200(1-2):141-146
Thermodynamic quantities were determined for the absorption of hydrogen in Pd-5.5at.%Li and Pd-7.2at.%Li alloys, the latter alloy being in the two-phase field of saturated -Pd(Li,s) solid solution and the ordered Pd7Li phase. Data were also determined for the Pd-10.6at.%Li alloy which consists only of the ordered Pd7Li phase. The data were determined from measurements of pressure-composition isotherms at temperatures between 273 K and 463 K and hydrogen pressures up to 1000 Torr. The Pd---Li alloys dissolve considerable amounts of hydrogen and form a more stable hydride phase than Pd despite the lattice contraction which occurs on alloying Pd with Li. The hydrogen solubility in the ordered Pd7Li phase alone is a little smaller than that in the two-phase mixture. The large hydrogen absorption of Pd---Li alloys, which does not depend on the presence of ordered Pd7Li, may be attributed to (i) an attractive H---Li pair interaction, (ii) a decrease in the strain energies necessary for hydrogen occupation of the interstices, because of the similar lattice parameters of the -Pd(Li,s) and ordered Pd7Li phases, and the large compressibility of Pd---Li alloys, and (iii) the valence of 1 of Li in Pd compared with 3 for, for example, Y in Pd. 相似文献
80.
S. Nakashima Y. Ikeda S. Hirose H. Nakamura T. Ito 《Journal of Materials Engineering and Performance》1992,1(2):211-218
Kawasaki Steel Corporation and Kawatetsu Mining Co., Ltd. have developed a new refining process to extract iron oxide from
iron ore to meet the increase in demand for iron oxide for high- grade hard ferrites. This article discusses the quality of
iron oxides and the characteristics of the hard ferrite magnets produced from them. 相似文献