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   2427篇
  免费   90篇
  国内免费   1篇
电工技术   28篇
化学工业   517篇
金属工艺   80篇
机械仪表   38篇
建筑科学   134篇
矿业工程   28篇
能源动力   54篇
轻工业   222篇
水利工程   16篇
石油天然气   4篇
无线电   142篇
一般工业技术   394篇
冶金工业   491篇
原子能技术   40篇
自动化技术   330篇
  2021年   20篇
  2020年   24篇
  2019年   30篇
  2018年   34篇
  2017年   42篇
  2016年   41篇
  2015年   49篇
  2014年   62篇
  2013年   189篇
  2012年   88篇
  2011年   113篇
  2010年   98篇
  2009年   78篇
  2008年   103篇
  2007年   96篇
  2006年   100篇
  2005年   77篇
  2004年   92篇
  2003年   86篇
  2002年   56篇
  2001年   39篇
  2000年   38篇
  1999年   40篇
  1998年   43篇
  1997年   36篇
  1996年   38篇
  1995年   23篇
  1994年   29篇
  1993年   41篇
  1992年   35篇
  1991年   20篇
  1990年   20篇
  1989年   19篇
  1988年   26篇
  1987年   23篇
  1986年   25篇
  1985年   34篇
  1984年   35篇
  1983年   25篇
  1982年   20篇
  1981年   32篇
  1980年   20篇
  1979年   20篇
  1978年   25篇
  1977年   32篇
  1976年   30篇
  1975年   22篇
  1974年   25篇
  1972年   18篇
  1967年   14篇
排序方式: 共有2518条查询结果,搜索用时 60 毫秒
1.
Soybean oil hydrogenation alters the linolenic acid molecule to prevent the oil from becoming rancid, however, health reports have indicated trans-fat caused by hydrogenation, is not generally regarded as safe. Typical soybeans contain approximately 80 g kg−1 to 120 g kg−1 linolenic acid and 240 g kg−1 of oleic acid. In an effort to accommodate the need for high-quality oil, the United Soybean Board introduced an industry standard for a high oleic acid greater than 750 g kg−1 and linolenic acid less than 30 g kg−1 oil. By combing mutations in the soybean plant at four loci, FAD2-1A and FAD2-1B, oleate desaturase genes and FAD3A and FAD3C, linoleate desaturase genes, and seed oil will not require hydrogenation to prevent oxidation and produce high-quality oil. In 2017 and 2018, a study comparing four near-isogenic lines across multiple Tennessee locations was performed to identify agronomic traits associated with mutations in FAD3A and FAD3C loci, while holding FAD2-1A and FAD2-1B constant in the mutant (high oleic) state. Soybean lines were assessed for yield and oil quality based on mutations at FAD2-1 and FAD3 loci. Variations of wild-type and mutant genotypes were compared at FAD3A and FAD3C loci. Analysis using a generalized linear mixed model in SAS 9.4, indicated no yield drag or other negative agronomic traits associated with the high oleic and low linolenic acid genotype. All four mutations of fad2-1A, fad2-1B, fad3A, and fad3C were determined as necessary to produce a soybean with the new industry standard (>750 g kg−1 oleic and <30 g kg−1 linolenic acid) in a maturity group-IV-Late cultivar for Tennessee growers.  相似文献   
2.
JOM - A machine vision sensor was developed for predicting deviations from the optimum amount of pitch in anode formulations using paste texture analysis. It could help operators mitigate the...  相似文献   
3.
Boundary colors are observed when light from a scene is dispersed by a prism or diffraction grating. We discovered that patterns with repeating black and white stripes can produce repeating bands of boundary colors with two hues. These hues are virtually constant as measured by chromaticity or CIELAB. We found seven cases of this kind using a new appearance model for boundary colors. The model correctly predicts that green and magenta bands recur as stripe widths and dispersion strength vary. The first green/magenta case in the sequence traces out an accurate ellipse in XYZ color space. Green and magenta bands are prominent in supernumerary rainbows and interference rings, and we explain why that might be the case. The explanation is based on an interesting property of the visible spectrum. In addition to the green/magenta cases, the other cases are orange/cyan, yellowish‐green/purple, and yellow/violet. The success of the boundary color appearance model implies that bands are perceived as if the wavelength responses of the cones were essentially independent, which contradicts the actual behavior of cones. © 2014 Wiley Periodicals, Inc. Col Res Appl, 40, 135–146, 2015  相似文献   
4.
5.
The versatility of porphyrins as optoelectronic or catalytic units makes them attractive elements for inclusion in functional materials. Polymers that include porphyrins have been created with a wide variety of structures and used in a wide range of applications. This review covers recent developments in the synthesis, characterization and applications of polymeric materials in which porphyrins are key components of the repeat units, including the rapidly growing area of metal–organic frameworks and related covalent organic frameworks. © 2015 Society of Chemical Industry  相似文献   
6.
ABSTRACT

Northwest Arkansas planning policies, like a number of communities across the country, have identified goals working toward more sustainable, livable, and subsequently denser development patterns. However, the understanding of residents’ perceptions of such living arrangements is limited. This study provides a more nuanced understanding of Northwest Arkansas residents’ spatial preferences through a survey of residents’ preferences for private amenities and their trade-off with various spatial densities and patterns in support of sustainability. Results of the survey indicate a preference for, and experience with, single-family residential living arrangements and amenities, with the preponderance (80%) of survey respondents currently living in single-family housing. There is a preference for low-density neighborhoods even if it means sacrificing other amenities. This study is in alignment with previous research suggesting that people may learn to prefer where they live. Additionally, while the majority of survey respondents indicated a preference for communal greenspaces, renters are more likely to prefer communal greenspaces when compared to homeowners. This study indicates that attached, multi-family development and renter development in Northwest Arkansas should consider the provision of communal green spaces, walkable access to transit, and walkable access to services as desired amenities for those residents.  相似文献   
7.
Soybean [Glycine max (L.) Merr.] oil with high oleic acid (>75%) has increased oxidative stability and health benefits that are valuable for food, fuel, and industrial products. It has been determined that two naturally occurring mutations in genes FAD2-1A and FAD2-1B can combine to produce high oleic soybeans. The objective of this study was to test the effect of these mutant alleles on seed yield and oil and protein concentration. Molecular markers assisted in the creation of a population of 48 BC3F2:4 lines (93.75% expected genome commonality). Each line was classified into one of four genotypic groups where both FAD2-1A and FAD2-1B genes were either homozygous wild type or mutant, respectively. Twelve lines for each genotypic group were evaluated in three replications at six locations across Tennessee. There was no seed yield difference between the high oleic genotypic group and the other groups (P < 0.05). On the other hand, there were differences in fatty acid profiles and oil and protein concentrations. In combination, the mutant FAD2-1A and FAD2-1B alleles produced a mean of 803.1 g kg−1 oleic acid. This is, on average, approximately 500 g kg−1 more oleic acid compared to soybean lines with only one mutant FAD2-1 allele. The high oleic double mutant group had more total oil (228.0 g kg−1) and protein (401.0 g kg−1) compared to all other genotypic groups (P < 0.05). Overall, this specific combination of mutant FAD2-1A and FAD2-1B alleles appears to generate conventional high oleic soybeans without a yield drag.  相似文献   
8.
Rapid 3D positioning and modeling in construction can be used to more effectively plan, visualize, and communicate operations before execution. It can also help to optimize equipment operations, significantly improve safety, and enhance a remote operator's spatial perception of the workspace. A new framework for rapid local area sensing and 3D modeling for better planning and control of construction equipment operation is described and demonstrated. By combining human-assisted graphical workspace modeling with pre-stored Computer-Aided Design (CAD) models and simple sensors (such as single-axis laser rangefinders and remote video cameras), modeling time can be significantly reduced while potentially increasing modeling accuracy.  相似文献   
9.
Pilot studies investigated the fates of color, dissolved organic carbon (DOC), and biodegradable organic matter (BOM) by the tandem of ozone plus biofiltration for treating a source water having significant color (50 cu) and DOC (3.2 mg/l). Transferred ozone doses were from 1.0 to 1.8 g O3/g C. Rapid biofilters used sand, anthracite, or granular activated carbon as media with empty-bed contact time (EBCT) up to 9 min. The pilot studies demonstrated that ozonation plus biofiltration removed most color and substantial DOC, and increasing the transferred ozone dose enhanced the removals. For the highest ozone dose, removals were as high as 90% for color and 38% for DOC. While most of the color removal took place during ozonation, most DOC removal occurred in the biofilters, particularly when the ozone dose was high. Compared to sand and anthracite biofilters, the GAC biofilter gave the best performance for color and DOC removal, but some of this enhanced performance was caused by adsorption, since the GAC was virgin at the beginning of the pilot studies. Backwashing events had no noticeable impact of the performance of the biofilters. The Transient-State, Multiple-Species Biofilm Model (TSMSBM) was used to interpret the experimental results. Model simulations show that soluble microbial products, which comprised a significant part of the effluent BOM, offset the removal of original BOM, a factor that kept the removal of DOC relatively constant over the range of EBCTs of 3.5-9 min. Although improved biofilm retention, represented by a small detachment rate, allowed more total biofilm accumulation and greater removal of original BOM, it also caused more release of soluble microbial products and the build up of inert biomass in the biofilm. Backwashing had little impact on biofilter performance, because it did not remove more than 25% of the biofilm under any condition simulated.  相似文献   
10.
'Natural' treatment systems such as wetlands and reed beds have been proposed as sustainable means of reducing fluxes of faecal indicator organisms (FIOs) to recreational and shellfish harvesting waters. This is because FIO fluxes to coastal waters from both point (effluent) and diffuse (catchment) sources can cause non-compliance with microbiological standards for bathing and shellfish harvesting waters. The Water Framework Directive requires competent authorities in the member states to manage both point and diffuse sources of FIOs in an integrated manner to achieve compliance with 'good' water quality as defined in a series of daughter Directives. This study was undertaken to investigate the relative sources of FIOs to the popular bathing waters around Clacton, UK. In this predominantly arable (mainly cereal cropping) farming area, the principal land use predictor, explaining 76% of the variance in geometric mean presumptive Escherichia coli concentration at sub-catchment outlets during the bathing season, was the proportion of built-up (i.e. urbanised) land in each sub-catchment. This new finding contrasts with earlier studies in livestock farming regions where the proportion of improved grassland has proven to be the strongest predictor of microbial concentration. Also novel in this investigation, a flood defence wall has been built creating a wetland area which discharges every tidal cycle. The wetland produces over 97% reduction in the flux and concentrations of FIOs to the marine recreational waters. Also, FIO concentrations in water draining through the wetland to the sea were similar to concentrations measured in six UK sewage treatment plant effluents subject to secondary (biological) treatment followed by UV disinfection.  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