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   131篇
  免费   4篇
电工技术   8篇
综合类   1篇
化学工业   25篇
金属工艺   3篇
机械仪表   2篇
建筑科学   15篇
能源动力   7篇
轻工业   17篇
水利工程   2篇
无线电   9篇
一般工业技术   23篇
冶金工业   15篇
原子能技术   5篇
自动化技术   3篇
  2023年   1篇
  2022年   4篇
  2021年   4篇
  2020年   1篇
  2019年   3篇
  2018年   2篇
  2017年   1篇
  2016年   1篇
  2015年   2篇
  2014年   3篇
  2013年   10篇
  2012年   7篇
  2011年   6篇
  2010年   6篇
  2009年   6篇
  2008年   4篇
  2007年   11篇
  2006年   5篇
  2005年   6篇
  2004年   3篇
  2003年   5篇
  2001年   1篇
  2000年   2篇
  1999年   1篇
  1998年   5篇
  1997年   8篇
  1996年   2篇
  1995年   3篇
  1994年   2篇
  1993年   1篇
  1992年   1篇
  1991年   3篇
  1990年   1篇
  1989年   1篇
  1988年   2篇
  1986年   1篇
  1985年   4篇
  1984年   1篇
  1983年   2篇
  1980年   1篇
  1976年   2篇
排序方式: 共有135条查询结果,搜索用时 15 毫秒
61.
Reactions of cycloheptane and cyclooctane were performed over the superacid of sulfated zirconia in liquid phase at 50 °C a main product was methylcyclohexane from cycloheptane through a protonated bicyclo[4.1.0]heptane and ethylcyclohexane from cyclooctane via a protonated bicyclo[4.2.0]octane. Cyclodecane was dehydrogenated into decalines; cyclododecane was converted into many products, more than 30 species.  相似文献   
62.
The recommendations presented here are designed to support easier communication of NMR data and NMR structures of proteins and nucleic acids through unified nomenclature and reporting standards. Much of this document pertains to the reporting of data in journal articles; however, in the interest of the future development of structural biology, it is desirable that the bulk of the reported information be stored in computer-accessible form and be freely accessible to the scientific community in standardized formats for data exchange. These recommendations stem from an IUPAC-IUBMB-IUPAB inter-union venture with the direct involvement of ICSU and CODATA. The Task Group has reviewed previous formal recommendations and has extended them in the light of more recent developments in the field of biomolecular NMR spectroscopy. Drafts of the recommendations presented here have been examined critically by more than 50 specialists in the field and have gone through two rounds of extensive modification to incorporate suggestions and criticisms.  相似文献   
63.
This article proposes a logical support tool for maintenance management decision making. This tool is called the Graphical Analysis for Maintenance Management (GAMM), a method to visualize and analyze equipment dependability data in a graphical form. The method helps for a quick and clear analysis and interpretation of equipment maintenance (corrective and preventive) and operational stoppages. Then, opportunities can be identified to improve both operations and maintenance management (short–medium term) and potential investments (medium–long term). The method allows an easy visualization of parameters, such as the number of corrective actions between preventive maintenance, the accumulation of failures in short periods of time, and the duration of maintenance activities and sequence of stops of short duration. In addition, this tool allows identifying, a priori, anomalous behavior of equipment, whether derived from its own function, maintenance activities, misuse, or even equipment designs errors. In this method, we used a nonparametric estimator of the reliability function as a basis for the analysis. This estimator takes into account equipment historical data (total or partial) and can provide valuable insights to the analyst even with few available data. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   
64.
We report the results of a nationwide survey of commonly used human and veterinary antibiotics (7 sulfonamides, trimethoprim, and 4 macrolides) in 37 Japanese rivers. Concentrations of the sum of the 12 target antibiotics ranged from undetectable to 626 ng/L, with a median of 7.3 ng/L for the 37 rivers. Antibiotics concentrations were higher in urban rivers than in rural rivers and were correlated with those of molecular markers of sewage (crotamiton and carbamazepine). Macrolides were dominant over sulfonamides in urban rivers. Sulfonamides, especially sulfamethazine (used in animals), were dominant in a few rivers in whose catchment animal husbandry is active. However, these signals of veterinary antibiotics were overwhelmed by those of human antibiotics in lower reaches of most rivers. The analysis of the antibiotics in all 88 samples showed that the target antibiotics in Japanese rivers are derived mainly from urban sewage, even though larger amounts of antibiotics are used in livestock. Most of the livestock waste-derived antibiotics are unlikely to be readily discharged to surface waters.  相似文献   
65.
We examined the utility of 13 pharmaceuticals and personal care products (PPCPs) as molecular markers of sewage contamination in riverine, groundwater, and coastal environments. The PPCPs were crotamiton, ibuprofen, naproxen, ketoprofen, fenoprofen, mefenamic acid, thymol, triclosan, propyphenazone, carbamazepine, diethyltoluamide, ethenzamide, and caffeine. Measurements in 37 Japanese rivers showed positive correlations of riverine flux of crotamiton (r2 = 0.85), carbamazepine (r2 = 0.84), ibuprofen (r2 = 0.73), and mefenamic acid (r2 = 0.67) with the population in the catchments. In three surveys in the Tamagawa estuary, crotamiton, carbamazepine, and mefenamic acid behaved conservatively across seasons within a salinity range of 0.4-29 per thousand, suggesting their utility as molecular markers in coastal environments. Removal of ketoprofen and naproxen in the estuary was ascribed to photodegradation. Ibuprofen and thymol were removed from estuarine waters in summer by microbial degradation. Triclosan was removed by a combination of microbial degradation, photodegradation, and adsorption. These results were consistent with those of river water incubated for 8 d at 25 degrees C in the dark in order to examine the effects of biodegradation and photodegradation. Crotamiton was detected in groundwater from the Tokyo metropolitan area (12 out of 14 samples), suggesting wastewater leakage from decrepit sewers. Carbamazepine, ketoprofen, and ibuprofen (5/14), caffeine (4/14), and diethyltoluamide (3/14) were also detected in the groundwater, whereas the other carboxylic and phenolic PPCPs were not detected and were thought to be removed during their passage through soil. All the data demonstrated the utility of crotamiton and carbamazepine as conservative markers in freshwater and coastal environments. We recommend combining these conservative markers with labile PPCPs to detect inputs of poorly treated sewage.  相似文献   
66.
Although photonics presents the fastest and most energy-efficient method of data transfer,magnetism still offers the cheapest and most natural way to store data.The ultrafast and energy-efficient optical control of magnetism is presently a missing technological link that prevents us from reaching the next evolution in information processing.The discovery of all-optical magnetization reversal in GdFeCo with the help of 100fs laser pulses has further aroused intense interest in this compelling problem.Although the applicability of this approach to high-speed data processing depends vitally on the maximum repetition rate of the switching,the latter remains virtually unknown.Here we experimentally unveil the ultimate frequency of repetitive all-optical magnetization reversal through time-resolved studies of the dual-shot magnetization dynamics in Gd27 Fe63.87 C09.T3.Varying the intensities of the shots and the shotto-shot separation,we reveal the conditions for ultrafast writing and the fastest possible restoration of magnetic bits.It is shown that although magnetic writing launched by the first shot is completed after 100 ps,a reliable rewriting of the bit by the second shot requires separating the shots by at least 300 ps.Using two shots partially overlapping in space and minimally separated by 300 ps,we demonstrate an approach for GHz magnetic writing that can be scaled down to sizes below the diffraction limit.  相似文献   
67.
Ufmylation is a posttranslational modification in which the modifier UFM1 is attached to target proteins. This conjugation requires the concerted work of three enzymes named UBA5, UFC1, and UFL1. Initially, UBA5 activates UFM1 in a process that ends with UFM1 attached to UBA5’s active site Cys. Then, in a trans-thiolation reaction, UFM1 is transferred from UBA5 to UFC1, forming a thioester bond with the latter. Finally, with the help of UFL1, UFM1 is transferred to the final destination—a lysine residue on a target protein. Therefore, not surprisingly, deletion of one of these enzymes abrogates the conjugation process. However, how overexpression of these enzymes affects this process is not yet clear. Here we found, unexpectedly, that overexpression of UBA5, but not UFC1, damages the ability of cells to migrate, in a similar way to cells lacking UBA5 or UFC1. At the mechanistic level, we found that overexpression of UBA5 reverses the trans-thiolation reaction, thereby leading to a back transfer of UFM1 from UFC1 to UBA5. This, as seen in cells lacking UBA5, reduces the level of charged UFC1 and therefore harms the conjugation process. In contrast, co-expression of UBA5 with UFM1 abolishes this effect, suggesting that the reverse transfer of UFM1 from UFC1 to UBA5 depends on the level of free UFM1. Overall, our results propose that the cellular expression level of the UFM1 conjugation enzymes has to be tightly regulated to ensure the proper directionality of UFM1 transfer.  相似文献   
68.
The mammalian secondary palate is formed through complex developmental processes: growth, elevation, and fusion. Although it is known that the palatal elevation pattern changes along the anterior–posterior axis, it is unclear what molecules are expressed and whether their locations change before and after elevation. We examined the expression regions of molecules associated with palatal shelf elevation (Pax9, Osr2, and Tgfβ3) and tissue deformation (F-actin, E-cadherin, and Ki67) using immunohistochemistry and RT–PCR in mouse embryos at E13.5 (before elevation) and E14.5 (after elevation). Pax9 was expressed at significantly higher levels in the lingual/nasal region in the anterior and middle parts, as well as in the buccal/oral region in the posterior part at E13.5. At E14.5, Pax9 was expressed at significantly higher levels in both the lingual/nasal and buccal/oral regions in the anterior and middle parts and the buccal/oral regions in the posterior part. Osr2 was expressed at significantly higher levels in the buccal/oral region in all parts at E13.5 and was more strongly expressed at E13.5 than at E14.5 in all regions. No spatiotemporal changes were found in the other molecules. These results suggested that Pax9 and Osr2 are critical molecules leading to differences in the elevation pattern in palatogenesis.  相似文献   
69.
70.
Complete and rapid peptide and glycopeptide mapping of a mouse monoclonal immunoglobulin (IgG2b) were carried out by liquid chromatography/electrospray ionization ion trap-mass spectrometry/mass spectrometry (LC/ ESI IT-MS/MS). It was possible to obtain spectra of a minor glycopeptide at a quantity as low as 1.8 pmol. Reduced and carboxymethylated mouse antidansyl monoclonal IgG2b (RCM-IgG2b) was digested with lysyl-endopeptidase. Proteolytic peptides were subjected to capillary HPLC separation followed by analysis with an ion trap mass spectrometer. The complete amino acid sequence of the IgG2b was characterized by using LC/ ESI IT-MS/MS. The structures of 12 different types of O-linked oligosaccharides attached to Thr-221AH in the hinge region and those of three major types of N-linked oligosaccharides attached to Asn-297H have been characterized.  相似文献   
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