全文获取类型
收费全文 | 539篇 |
免费 | 13篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 7篇 |
化学工业 | 115篇 |
金属工艺 | 21篇 |
机械仪表 | 16篇 |
建筑科学 | 3篇 |
能源动力 | 17篇 |
轻工业 | 57篇 |
水利工程 | 2篇 |
无线电 | 45篇 |
一般工业技术 | 73篇 |
冶金工业 | 154篇 |
原子能技术 | 15篇 |
自动化技术 | 28篇 |
出版年
2023年 | 3篇 |
2022年 | 5篇 |
2021年 | 8篇 |
2019年 | 4篇 |
2018年 | 13篇 |
2017年 | 2篇 |
2016年 | 13篇 |
2015年 | 8篇 |
2014年 | 11篇 |
2013年 | 17篇 |
2012年 | 25篇 |
2011年 | 29篇 |
2010年 | 17篇 |
2009年 | 21篇 |
2008年 | 23篇 |
2007年 | 14篇 |
2006年 | 15篇 |
2005年 | 15篇 |
2004年 | 15篇 |
2003年 | 13篇 |
2002年 | 10篇 |
2001年 | 14篇 |
2000年 | 8篇 |
1999年 | 9篇 |
1998年 | 49篇 |
1997年 | 32篇 |
1996年 | 21篇 |
1995年 | 21篇 |
1994年 | 16篇 |
1993年 | 8篇 |
1992年 | 9篇 |
1991年 | 5篇 |
1990年 | 10篇 |
1989年 | 4篇 |
1988年 | 7篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1983年 | 10篇 |
1982年 | 4篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 4篇 |
1976年 | 7篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1972年 | 2篇 |
排序方式: 共有553条查询结果,搜索用时 15 毫秒
1.
The void fraction in a three-component randomly packed bed was calculated from the authors' model, and the calculated values were compared with published experimental data for spherical and irregularly shaped particles and with results from computer simulations. Results from the model were in good agreement with simulated and published experimental data. 相似文献
2.
N Nishioka T Kawabata KH Minagawa M Nakamura A Oshima Y Mochizuki 《Canadian Metallurgical Quarterly》1996,43(6):434-445
The purpose of this study was to evaluate the short-term effect of a smoking prevention program for Japanese elementary school-children in the fifth and sixth grades. The program was developed with concepts found in the Know Your Body Program and the conclusions of a National Cancer Institute-convened Expert Advisory Panel, and focused on teaching about the short-term effects of smoking and on resistance to social pressures to smoke. The study was conducted with a quasi-experimental design. An intervention group (52 boys and 54 girls) received three sessions for both the fifth grade in 1992 and the sixth grade in 1993. Moreover, the intervention group received a pre-test before the first session and a post-test after the third session in each grade. A comparison group (102 boys and 91 girls) received the same tests at the same time as the intervention group, but did not receive any program on smoking prevention. The short-term effect of the program were evaluated using the results of the pre-test in the fifth grade and of the post-test in the sixth grade in both groups. The results were as follows: 1) Remarkable short-term effects of the intervention were seen in respect to awareness of the importance of not smoking in girls, and also in the knowledge of the short-term effects of smoking in both sexes. 2) The intervention was not effective with respect to intention to smoke at the age of 20 and self-efficacy of refusing to smoke in both sexes. 3) The short-term effects were not clear in the smoking behavior in both sexes because the rates of ever smokers and of monthly smokers were almost the same for two years between the intervention group and the comparison group. 4) The smoking behaviors of children, their parents and their best friends had little influence on the results of the post-test in the sixth grade. 相似文献
3.
4.
G Wallon G Kryger ST Lovett T Oshima D Ringe GA Petsko 《Canadian Metallurgical Quarterly》1997,266(5):1016-1031
The basis of protein stability has been investigated by the structural comparison of themophilic enzymes with their mesophilic counterparts. A number of characteristics have been found that can contribute to the stabilization of thermophilic proteins, but no one is uniquely capable of imparting thermostability. The crystal structure of 3-isopropylmalate dehydrogenase (IPMDH) from the mesophiles Escherichia coli and Salmonella typhimurium have been determined by the method of molecular replacement using the known structure of the homologous Thermus thermophilus enzyme. The structure of the E. coli enzyme was refined at a resolution of 2.1 A to an R-factor of 17.3%, that of the S. typhimurium enzyme at 1.7 A resolution to an R-factor of 19.8%. The three structures were compared to elucidate the basis of the higher thermostability of the T. thermophilus enzyme. A mutant that created a cavity in the hydrophobic core of the thermophilic enzyme was designed to investigate the importance of packing density for thermostability. The structure of this mutant was analyzed. The main stabilizing features in the thermophilic enzyme are an increased number of salt bridges, additional hydrogen bonds, a proportionately larger and more hydrophobic subunit interface, shortened N and C termini and a larger number of proline residues. The mutation in the hydrophobic core of T. thermophilus IPMDH resulted in a cavity of 32 A3, but no significant effect on the activity and thermostability of the mutant was observed. 相似文献
5.
Sachi Oshima Shunichi Asai Naohiko Seki Chikashi Minemura Takashi Kinoshita Yusuke Goto Naoko Kikkawa Shogo Moriya Atsushi Kasamatsu Toyoyuki Hanazawa Katsuhiro Uzawa 《International journal of molecular sciences》2021,22(12)
We identified the microRNA (miRNA) expression signature of head and neck squamous cell carcinoma (HNSCC) tissues by RNA sequencing, in which 168 miRNAs were significantly upregulated, including both strands of the miR-31 duplex (miR-31-5p and miR-31-3p). The aims of this study were to identify networks of tumor suppressor genes regulated by miR-31-5p and miR-31-3p in HNSCC cells. Our functional assays showed that inhibition of miR-31-5p and miR-31-3p attenuated cancer cell malignant phenotypes (cell proliferation, migration, and invasion), suggesting that they had oncogenic potential in HNSCC cells. Our in silico analysis revealed 146 genes regulated by miR-31 in HNSCC cells. Among these targets, the low expression of seven genes (miR-31-5p targets: CACNB2 and IL34; miR-31-3p targets: CGNL1, CNTN3, GAS7, HOPX, and PBX1) was closely associated with poor prognosis in HNSCC. According to multivariate Cox regression analyses, the expression levels of five of those genes (CACNB2: p = 0.0189; IL34: p = 0.0425; CGNL1: p = 0.0014; CNTN3: p = 0.0304; and GAS7: p = 0.0412) were independent prognostic factors in patients with HNSCC. Our miRNA signature and miRNA-based approach will provide new insights into the molecular pathogenesis of HNSCC. 相似文献
6.
Continuous emulsion polymerizations of vinyl acetate were conducted at 50°C in a single continuous Couette–Taylor vortex flow reactor (CCTVFR) using sodium lauryl sulfate as emulsifier and potassium persulfate as initiator. The polymerization can be carried out very smoothly and stably, but the steady‐state monomer conversion attained in a CCTVFR is not as high as that in a plug flow reactor (PFR), but only slightly higher than that in a continuous stirred tank reactor (CSTR), even if the Taylor number is adjusted to an optimum value. Also, the effects of operating variables, such as the emulsifier, initiator, and monomer concentrations in the feed and the mean residence time on the kinetic behaviors were almost the same as those observed in a CSTR. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2755–2762, 2002 相似文献
7.
Motoi Takahashi Toshiyuki Mori Fei Ye Ajayan Vinu Hidehiko Kobayashi John Drennan 《Journal of the American Ceramic Society》2007,90(4):1291-1294
A Pt on nano-sized CeO2 particles that in turn are supported on carbon black (CB) was synthesized using the co-impregnation method. This potential anode material for fuel cell applications was synthesized in a stepwise process. The pure CeO2 was synthesized using an ammonium carbonate precipitation method, and the Pt particles dispersed on the CeO2 in such a way that a uniform dispersion with the CB was obtained (Pt–CeO2 /CB). The electrochemical activity of the methanol (CH3 OH) oxidation reaction on the Pt–CeO2 /CB was investigated using cyclic voltammetry and chronoamperometry experimentation. The onset potential of CH3 OH oxidation reaction on the Pt–CeO2 /CB anode was shifted to a lower potential as compared with that on commercially available Pt–Ru/carbon (C) alloy anode. In addition, the activation energy of the Pt–CeO2 /CB anode was much lower than that of the Pt–Ru/C alloy anode. Moreover, the current density of the Pt–CeO2 /CB anode was much higher than that of the Pt–Ru/C alloy anode at temperatures between 28° and 60°C. These results suggest that the anode performance of the Pt–CeO2 /CB anode at the operating temperature of typical fuel cells (80°C) is superior to that of the more usual Pt–Ru/C alloy anode. Importantly, the rare metal, Ru, is not required in the present anode material and the amount of Pt required is also significantly reduced. As a consequence, we report a promising candidate Pt–CeO2 /CB composite anode for application in the development of direct methanol fuel cells. 相似文献
8.
The coenzyme specificity of 3isopropylmalate dehydrogenasefrom an extreme thermophile, Thermus thermophilus HB8, was changedfrom NAD to NADP by sitedirected mutagenesis Based onsequence comparison of 3isopropylmalate dehydrogenasesfrom various organisms with NAD and NADPdependentisocitrate dehydrogenases, Ser226, Ser253 and De279 of 3isopropylmalatedehydrogenase were suggested as determining the coenzymespecificity. These residues were replaced with the correspondingresidues of NADPdependent isocitrate dehydrogenases;Arg, Gly and Tyr respectively. The singlemutated enzymes,S226R and I279Y, enhanced the activities towards NADP 10and 3fold respectively, whereas S253G reduced the activity.Among the multiplemutated enzymes, the doublemutatedS226R/I279Y increased the catalytic efficiency against NADP( fold) and shifted the specificity for NAD towards NADP mostsignificantly ( 173fold). 相似文献
9.
Tran Huu Nam Ken Goto Kahori Oshima E.V.A. Premalal Yoshinobu Shimamura Yoku Inoue 《Advanced Composite Materials》2016,25(1):73-86
A solid-state drawing and winding process was done to create thin aligned carbon nanotube (CNT) sheets from CNT arrays. However, waviness and poor packing of CNTs in the sheets are two main weaknesses restricting their reinforcing efficiency in composites. This report proposes a simple press-drawing technique to reduce wavy CNTs and to enhance dense packing of CNTs in the sheets. Non-pressed and pressed CNT/epoxy composites were developed using prepreg processing with a vacuum-assisted system. Effects of pressing on the mechanical properties of the aligned CNT sheets and CNT/epoxy composites were examined. Pressing with distributed loads of 147, 221, and 294 N/m showed a substantial increase in the tensile strength and the elastic modulus of the aligned CNT sheets and their composites. The CNT sheets under a press load of 221 N/m exhibited the best mechanical properties found in this study. With a press load of 221 N/m, the pressed CNT sheet and its composite, respectively, enhanced the tensile strength by 139.1 and 141.9%, and the elastic modulus by 489 and 77.6% when compared with non-pressed ones. The pressed CNT/epoxy composites achieved high tensile strength (526.2 MPa) and elastic modulus (100.2 GPa). Results show that press-drawing is an important step to produce superior CNT sheets for development of high-performance CNT composites. 相似文献
10.
In order to elucidate the natural history of early gastric cancer, we followed up non-concurrently certain patients who had been diagnosed endoscopically as having "early' gastric cancer and who had histological evidence of cancer by biopsy, but on whom surgical resection had been delayed or had not been conducted. At the Center for Adult Diseases, Osaka, 56 cases were eligible for this study. Out of these, 27 cases progressed to advanced cancer and 16 remained at the early stage during the follow-up period (6-88 months, mean: 29 months). The remaining 13 cases had had neither surgical resection nor examinations. The survivorship function for the duration of "early" gastric cancer was estimated by the life-table method of Kaplan and Meier. The median of the duration was estimated as 37 months. The 5-year survival rate of the 34 cases on whom surgical resection had not been conducted was estimated as 64.5%. These results suggest that early diagnosis and early treatment may lead to a reduction of mortality from stomach cancer. 相似文献