首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   109篇
  免费   5篇
化学工业   32篇
金属工艺   4篇
建筑科学   4篇
矿业工程   1篇
轻工业   16篇
无线电   7篇
一般工业技术   17篇
冶金工业   25篇
原子能技术   1篇
自动化技术   7篇
  2023年   5篇
  2022年   9篇
  2021年   10篇
  2020年   1篇
  2019年   4篇
  2018年   6篇
  2017年   5篇
  2016年   4篇
  2015年   3篇
  2014年   1篇
  2013年   5篇
  2012年   7篇
  2011年   6篇
  2010年   6篇
  2009年   5篇
  2008年   1篇
  2007年   3篇
  2006年   3篇
  2004年   2篇
  2003年   2篇
  2002年   3篇
  2001年   2篇
  2000年   2篇
  1999年   1篇
  1998年   1篇
  1997年   2篇
  1996年   2篇
  1990年   1篇
  1988年   1篇
  1987年   1篇
  1984年   2篇
  1983年   1篇
  1982年   2篇
  1981年   1篇
  1975年   3篇
  1974年   1篇
排序方式: 共有114条查询结果,搜索用时 15 毫秒
21.
Presents a new multiple-effects model that emphasizes subtle behavioral alteration as an early sign of toxicity and as evidence that a particular chemical agent may produce long-term impairment in susceptible individuals. The permeability of the placenta to a variety of chemical agents and the special sensitivity of the fetus to some of these agents draws attention to prenatal exposure and the need for prospective longitudinal studies of affective, social, and cognitive development in exposed individuals. The multiple-effects model provides a role for the psychologist in teratological diagnosis and research since the measurement of behavioral variation has developed primarily in psychology. Limitations inherent in both experimental animal research and correlational human studies of toxic effects make it necessary for these methodologies to be used in a complementary fashion. The implications of behavioral teratology for the study of human development and the design of protective social policies are discussed. (45 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
22.
BACKGROUND: Numerous studies have demonstrated that in vitro controlled enzymatic hydrolysis of fish and shellfish proteins leads to bioactive peptides. Ultrafiltration (UF) and/or nanofiltration (NF) can be used to refine hydrolysates and also to fractionate them in order to obtain a peptide population enriched in selected sizes. This study was designed to highlight the impact of controlled UF and NF on the stability of biological activities of an industrial fish protein hydrolysate (FPH) and to understand whether fractionation could improve its content in bioactive peptides. RESULTS: The starting fish protein hydrolysate exhibited a balanced amino acid composition, a reproducible molecular weight (MW) profile, and a low sodium chloride content, allowing the study of its biological activity. Successive fractionation on UF and NF membranes allowed concentration of peptides of selected sizes, without, however, carrying out sharp separations, some MW classes being found in several fractions. Peptides containing Pro, Hyp, Asp and Glu were concentrated in the UF and NF retentates compared to the unfractionated hydrolysate and UF permeate, respectively. Gastrin/cholecystokinin‐like peptides were present in the starting FPH, UF and NF fractions, but fractionation did not increase their concentration. In contrast, quantification of calcitonin gene‐related peptide (CGRP)‐like peptides demonstrated an increase in CGRP‐like activities in the UF permeate, relative to the starting FPH. The starting hydrolysate also showed a potent antioxidant and radical scavenging activity, and a moderate angiotensin‐converting enzyme (ACE)‐1 inhibitory activity, which were not increased by UF and NF fractionation. CONCLUSION: Fractionation of an FPH using membrane separation, with a molecular weight cut‐off adapted to the peptide composition, may provide an effective means to concentrate CGRP‐like peptides and peptides enriched in selected amino acids. The peptide size distribution observed after UF and NF fractionation demonstrates that it is misleading to characterize the fractions obtained by membrane filtration according to the MW cut‐off of the membrane only, as is currently done in the literature. Copyright © 2010 Society of Chemical Industry  相似文献   
23.
The present study examines pyruvate kinase-conjugated antibodies for potential use in ELISA applications. The conjugates had an acceptable stability, and the coupling inflicted only minor impairment on the kinase activity. To mimic the setup of an immunoassay under development, a test antigen (BSA) was attached to polystyrene nanoparticles. This arrangement was found to be suitable as solid support for presentation of antigens in sensitive bioluminescence assays. The nanoparticles were well characterized in terms of protein surface load and were used to establish the number of conjugate complexes needed to generate a detectable signal. Under the biochemical conditions employed here, the detection limit of the pyruvate kinase conjugate lies in the femtomole range.  相似文献   
24.
25.
Nanostructured Cu(x)Zn(1-x)Al(2)O(4) with a Cu:Zn ratio of ?:? has been prepared by a microwave-assisted hydrothermal synthesis at 150 °C and used as a precursor for Cu/ZnO/Al(2)O(3)-based catalysts. The spinel nanoparticles exhibit an average size of approximately 5 nm and a high specific surface area (above 250 m(2) g(-1)). Cu nanoparticles of an average size of 3.3 nm can be formed by reduction of the spinel precursor in hydrogen and the accessible metallic Cu(0) surface area of the reduced catalyst was 8 m(2) g(-1). The catalytic performance of the material in CO(2) hydrogenation and methanol steam reforming was compared with conventionally prepared Cu/ZnO/Al(2)O(3) reference catalysts. The observed lower performance of the spinel-based samples is attributed to a lack of synergetic interaction of the Cu nanoparticles with ZnO due to the incorporation of Zn(2+) in the stable spinel lattice. Despite its lower performance, however, the nanostructured nature of the spinel catalyst was stable after thermal treatment up to 500 °C in contrast to other Cu-based catalysts. Furthermore, a large fraction of the re-oxidized copper migrates back into the spinel upon calcination of the reduced catalyst, thereby enabling a regeneration of sintered catalysts after prolonged usage at high temperatures. Similarly prepared samples with Ga instead of Al exhibit a more crystalline catalyst with a spinel particle size around 20 nm. The slightly decreased Cu(0) surface area of 3.2 m(2) g(-1) due to less copper incorporation is not a significant drawback for the methanol steam reforming.  相似文献   
26.
The chemical and microstructural properties of nanosized TiO2, obtained by sol—gel procedure, were investigated. The samples were characterized by analytical electron microscopy combining electron diffraction, high resolution electron microscopy and atomic force microscopy. These methods were supported by X-ray diffraction and thermal analysis. The chemical and structural properties, as well as the size of grains, depended on the temperature of TiO2 preparation. In the temperature range between 293 and 820 K the TiO2 grains consisted of anatase, as the dominant phase, and brookite. High resolution electron microscopy showed that the sample heated at 573 K had grain sizes from 2 to 10 nm, the average being (5 ± 1) nm, and the pore sizes from 4.5 to 12 nm. The sample heated at820 K revealed larger grain sizes, from 7 to 12 nm, the average being (9 ± 1) nm, and the pore sizes from 6 to 10 nm. These values were confirmed by X-ray diffraction broadening.  相似文献   
27.
Abstract. This paper examines the score or Lagrange multiplier statistic for testing the adequacy of a fitted autoregressive moving-average model and gives a simple closed-form expression for this test statistic. Some singularities arising as the order of the alternative model is increased are examined.  相似文献   
28.
The antioxidant activity (free radical scavenging ability and lipid oxidation inhibitory activity) and the activity in cell culture [influence on HT-29 human colon cancer cell viability and nuclear factor kappa B (NF-κB) activation] of natural fruit juices from red grape, strawberry, cherry and sour cherry were investigated in vitro. Analysis of polyphenolic composition of fruit juices showed the dominant presence of anthocyanins (cyanidin-3-glucoside, cyanidin-3-rutinoside, peonidin-3-rutinoside, pelargonidin-3-glucoside), anthocyanidins (procyanidins B1, B2 and B3), flavonoids (glucosides of myricetin, quercetin and kaempferol), and phenolic acids (neochlorogenic acid, chlorogenic acid, ellagic acid, p-coumaroylquinic acid) in juices. DPPH test and β-carotene bleaching method indicated that grape, strawberry, cherry and sour cherry natural juices (at the concentration of 2.5%) showed very strong free radical scavenging (75–92%) and antioxidant activity (71–94%). In addition, at the concentration of 0.01% they showed complete inhibition of copper-induced oxidation of human LDL (low density lipoprotein). In contrast, selected fruit juices did not show cytotoxic effects on HT-29 cells and NF-κB inhibitory activity (at the concentrations of 0.5 and 2%). Results of this study showed no correlation between the antioxidant activity of natural fruit juices from red grape, strawberry, cherry and sour cherry and their effect on HT-29 cell viability and NF-κB inhibitory activity.  相似文献   
29.
Metallurgical and Materials Transactions A - The microstructure response of laser-powder bed fusion (L-PBF)-processed ferritic stainless steel (AISI 441) during post-heat treatments is studied in...  相似文献   
30.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号