全文获取类型
收费全文 | 1426篇 |
免费 | 86篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 56篇 |
综合类 | 1篇 |
化学工业 | 417篇 |
金属工艺 | 32篇 |
机械仪表 | 32篇 |
建筑科学 | 23篇 |
矿业工程 | 1篇 |
能源动力 | 61篇 |
轻工业 | 137篇 |
水利工程 | 2篇 |
石油天然气 | 3篇 |
无线电 | 96篇 |
一般工业技术 | 269篇 |
冶金工业 | 194篇 |
原子能技术 | 58篇 |
自动化技术 | 132篇 |
出版年
2023年 | 28篇 |
2022年 | 44篇 |
2021年 | 75篇 |
2020年 | 38篇 |
2019年 | 43篇 |
2018年 | 59篇 |
2017年 | 50篇 |
2016年 | 57篇 |
2015年 | 51篇 |
2014年 | 45篇 |
2013年 | 94篇 |
2012年 | 76篇 |
2011年 | 96篇 |
2010年 | 63篇 |
2009年 | 62篇 |
2008年 | 61篇 |
2007年 | 55篇 |
2006年 | 37篇 |
2005年 | 32篇 |
2004年 | 33篇 |
2003年 | 34篇 |
2002年 | 17篇 |
2001年 | 15篇 |
2000年 | 14篇 |
1999年 | 21篇 |
1998年 | 91篇 |
1997年 | 43篇 |
1996年 | 36篇 |
1995年 | 20篇 |
1994年 | 13篇 |
1993年 | 23篇 |
1992年 | 9篇 |
1991年 | 4篇 |
1990年 | 5篇 |
1989年 | 7篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 8篇 |
1980年 | 7篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1976年 | 7篇 |
1975年 | 3篇 |
1973年 | 2篇 |
1972年 | 2篇 |
排序方式: 共有1514条查询结果,搜索用时 31 毫秒
91.
T Inoue H Yatsuki T Kusakabe K Joh Y Takasaki N Nikoh T Miyata K Hori 《Canadian Metallurgical Quarterly》1997,339(1):226-234
Two distinct types of cDNAs for fructose-1,6-bisphosphate (FBP) aldolase, Ce-1 and Ce-2, have been isolated from nematode Caenorhabditis elegans, and the respective recombinant aldolase isozymes, CE-1 and CE-2, have been purified and characterized. The Ce-1 and Ce-2 are 1282 and 1248 bp in total length, respectively, and both have an open reading frame of 1098 bp, which encodes 366 amino acid residues. The entire amino acid sequences deduced from Ce-1 and Ce-2 show a high degree of identity to one another and to those of vertebrate and invertebrate aldolases. The highest sequence diversity was found in the carboxyl-terminal region that corresponds to one of the isozyme group-specific sequences of vertebrate aldolase isozymes that play a role in determining isozyme-specific functions. Southern blot analysis suggests that CE-1 and CE-2 are encoded by different genes. Concerning general or kinetic properties, CE-2 is quite different from CE-1. CE-1 exhibits unique characteristics which are not identical to any aldolase isozymes previously reported, whereas CE-2 is similar to vertebrate aldolase C. These results suggest that CE-2 might preserve the properties of a progenitor aldolase with a moderate preference for FBP over fructose 1-phosphate (F1P) as a substrate, whereas CE-1 evolved to act as an intrinsic enzyme that exhibits a much broader substrate specificity than dose CE-2. 相似文献
92.
A self-administered questionnaire study of 333 workers (male 253, female 80) in a manufacturing company was carried out one month after informing the workers of the results of their medical checkups in 1993. The questionnaire included several items such as recalled abnormal findings of health examination and ways of overcoming the abnormal findings, recalled results of their medical checkups in 1992, self-confidence in their recollection of the results, and the usefulness of medical checkups. The following were investigated: the relationship between actual as well as recalled results of medical checkups in 1992 and the recollection of them after one year, the effects of examinations after medical checkups in 1992 on their recollection of the checkup results after one year, the effects of actual as well as recalled 1992 checkup results on the recollection of the results one month after informing the workers of the results of their medical checkups in 1993, assurance of correct recollection of the results, the relationship between the usefulness of medical checkups, explanation of abnormal findings and the percentage of correct answers to the results of medical checkups in 1993 one month after informing the workers of their results. It was found that the percentage of correct answers to the results after one year was significantly lower than that after one month in 1992. The rate decreased with the increase in the number of abnormal items in medical checkups. Moreover, the rate also decreased when the results were abnormal. Further examinations in addition to the medical checkups influenced their recollection somewhat after one year. The results that the workers still remembered in 1992 had a stronger effect on their recalling the results one month after informing them in 1993 than the actual results in 1992. The workers' confidence in their recollection of the results was untrustworthy in the same way as their recollection of the results, and they were not able to maintain the recollection of the correct results, although many of the workers realized the usefulness of the medical checkups. Our results suggest that explanation of abnormal medical findings in 1993 was effective because the percentage of partial concordance between actual and recalled results was much higher in the workers who received the explanation than in the workers who did not receive it. 相似文献
93.
The phylogenetic position of Dictyostelium inferred from 18S rRNA data contradicts that from protein data. Protein trees always show the close affinity of Dictyostelium with animals, fungi, and plants, whereas in 18S rRNA trees the branching of Dictyostelium is placed at a position before the massive radiation of protist groups including the divergence of the three kingdoms. To settle this controversial issue and to determine the correct position of Dictyostelium, we inferred the phylogenetic relationship among Dictyostelium and the three kingdoms Animalia, Fungi, and Plantae by a maximum-likelihood method using 19 different protein data sets. It was shown at the significance level of 1 SE that the branching of Dictyostelium antedates the divergence of Animalia and Fungi, and Plantae is an outgroup of the Animalia-Fungi-Dictyostelium clade. 相似文献
94.
On the basis of a theory previously developed by the authors for the indentation hardness of glass matrix, particulate composites, an attempt was made to interpret published hardness data for a ZnO-Al2O3-SiO2 glass-ceramic in which gahnite (ZnAl2O4) crystal particles are dispersed in a glass matrix as a major crystalline phase. The elastic moduli for gahnite were estimated using both the bulk modulus-molar volume relationship and the density-Poisson's ratio relationship, established for oxide crystals. After determining the variation of the matrix Young's modulus with heat-treatment, the variation of the overall hardness with volume fraction of crystal phase as well as the crystal-size effect were discussed. The hardness behaviour of the present glass-ceramic could be interpreted well in terms of the properties and amounts of the constituent phases and the microstructural effects. 相似文献
95.
Various image coding schemes have been studied for digital transmission of videophone signals. The Hadamard transform, which is now studied for the transmission of pictures such as those from satellites, has been considered too complicated for public use, though the characteristics such as the ratio of bit-rate reduction are more desirable than those of differential pulse-code modulation (DPCM). We have found a very simple scheme of the transform, where digitized videophone signals are transformed to Hadamard components all digitally just byn digital adders and some shift registers for 2nth-order transform. For example, three adders are necessary for eighth-order transform. It is extendable to two-dimensional transform with ease. We have made an experimental model running in real time. Experiments and theoretical calculation have shown that 3 bits/sample are required for good picture quality in the case of two-dimensional(4 times 2) th transform and 0.5 bits more for one-dimensional eighthorder transform. 相似文献
96.
Koichi Hatada Tatsuki Kitayama Kinzo Fujikawa Koji Ohta Heimei Yuki 《Polymer Bulletin》1978,1(2):97-102
Summary Copolymer of methyl methacrylate-d8(M1) with a small amount of trityl methacrylate(M2) was radically prepared in tetrahydrofuran and converted into the copolymer of methyl methacrylate-d8 with a small amount of undeuterated methyl methacrylate by the selective hydrolysis of the trityl group and subsequent methylation with diazomethane. From the 1H NMR spectrum of the derived copolymer the assigned coisotactic parameters 12 and 21 were determined to be 0.14 and 0.61, respectively. This may be the first example of the unequivocal determination of assigned configurational parameters in cross propagation for copolymerization. 相似文献
97.
Silica films with a single-crystalline mesoporous structure 总被引:1,自引:0,他引:1
Miyata H Suzuki T Fukuoka A Sawada T Watanabe M Noma T Takada K Mukaide T Kuroda K 《Nature materials》2004,3(9):651-656
Films of mesoporous materials attract broad interest because of their wide applicability in the fields of optics and electronics. Although many of these films have a regular local porous structure, the structural regularity has not been used practically yet because of difficulties in its control on macroscopic scales. Here, we demonstrate the preparation of mesoporous silica films whose porous structure can be described as a single crystal, that is, a long-range order of cage-like pores is maintained over centimetre scales. These films have a three-dimensional hexagonal (space group P6(3)/mmc) porous structure, and the in-plane arrangement of the pores is strictly controlled by a polymeric substrate surface that has been treated by rubbing. This new class of single-crystalline films with mesoscopic periodic structure is a significant breakthrough in bottom-up nanotechnology, and could lead to novel devices, for example, optics in a soft X-ray region, and quantum electronics. 相似文献
98.
Hisamoto H Shimizu Y Uchiyama K Tokeshi M Kikutani Y Hibara A Kitamori T 《Analytical chemistry》2003,75(2):350-354
Here we report a design and synthesis of a chemically functional polymer membrane by an interfacial polycondensation reaction and multilayer flow inside a microchannel. Single and parallel dual-membrane structures are successfully prepared by using organic/aqueous two-layer flow and organic/aqueous/organic three-layer flow inside the microchannel followed by an interfacial polycondensation reaction. By using the inner-channel membrane, permeation of ammonia species through the inner-channel membrane is successfully achieved. Furthermore, horseradish peroxidase is immobilized on one side of the membrane surface to integrate the chemical transform function onto the inner-channel membrane. Here substrate permeation through the membrane and subsequent chemical transformation at the membrane surface are realized. The polymer membrane prepared inside the microchannel has an important role in ensuring stable contact of different phases such as gas/liquid or liquid/ liquid and the permeation of chemical species through the membrane. Furthermore, membrane surface modification chemistry allows chemical transformation of permeated chemical species. These methods are expected to lead to development of complicated and sophisticated chemical systems involving membrane permeation and chemical reactions. 相似文献
99.
Hiromi?YoshidaEmail author Kyoko?Matsuda Yuki?Hirakawa Yoshiyuki?Mizushina 《Journal of the American Oil Chemists' Society》2003,80(7):665-674
To clarify the effects of microwave roasting on the distribution of tocopherols and FA of phospholipids within soybeans, whole
soybeans (Glycine max) were treated by microwave and further evaluted as compared to a raw sample. Tocopherol homologs, measured using HPLC, and
phospholipid profiles, quantified with GC, were determined in the seed coat, the embryonic axis, and selections of cotyledons
separated from three cultivars. The tocopherols were predominantly detected in the axis, followed by the cotyledons, and then
very little in the coat. As much as 25% of the individual tocopherols originally present in the coat were lost at 12 min of
roasting, whereas <25% was lost in the cotyledons and the axis after 20 min of roasting. The greatest rate of phospholipid
loss (P<0.05) was observed in PE, followed by PC and PI, and their changing patterns were more pronounced in the coat than in the
cotyledons or the axis. Thus, tocopherol content and phospholipid profiles change with microwave roasting according to tissue. 相似文献
100.
Gordonia amarae is the cause of foaming activated sludge. In this study, the mechanism of foam formation by G. amarae SC1 was investigated. A liquid culture of SC1 cells generated a stable foam when shaken reciprocally. This foam formation was dependent on the presence of both bacterial cells and culture supernatant. A high-molecular-weight fraction (Mw>10000) of the supernatant was capable of emulsifying n-hexadecane in addition to exhibiting foaming activity, indicating that it contains a surface-active substance(s). The bacterial cells showed a high affinity to hexadecane. This hydrophobic cell surface property might be involved in the attachment of cells to air bubbles to generate a stable foam. The results demonstrated the participation of cells and the extracellular biosurfactant in the formation and stabilization of foam in G. amarae SC1 culture. 相似文献