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   2313篇
  免费   36篇
  国内免费   2篇
电工技术   20篇
化学工业   260篇
金属工艺   30篇
机械仪表   24篇
建筑科学   48篇
矿业工程   9篇
能源动力   30篇
轻工业   148篇
水利工程   9篇
石油天然气   4篇
无线电   145篇
一般工业技术   212篇
冶金工业   1238篇
原子能技术   10篇
自动化技术   164篇
  2022年   16篇
  2021年   30篇
  2020年   23篇
  2019年   14篇
  2018年   36篇
  2017年   19篇
  2016年   9篇
  2015年   12篇
  2014年   28篇
  2013年   61篇
  2012年   33篇
  2011年   66篇
  2010年   40篇
  2009年   45篇
  2008年   55篇
  2007年   42篇
  2006年   50篇
  2005年   41篇
  2004年   28篇
  2003年   27篇
  2002年   41篇
  2001年   30篇
  2000年   17篇
  1999年   54篇
  1998年   323篇
  1997年   191篇
  1996年   156篇
  1995年   78篇
  1994年   76篇
  1993年   98篇
  1992年   33篇
  1991年   28篇
  1990年   41篇
  1989年   34篇
  1988年   31篇
  1987年   36篇
  1986年   21篇
  1985年   35篇
  1984年   20篇
  1983年   16篇
  1982年   23篇
  1981年   16篇
  1980年   22篇
  1979年   15篇
  1978年   9篇
  1977年   47篇
  1976年   77篇
  1975年   16篇
  1974年   14篇
  1973年   10篇
排序方式: 共有2351条查询结果,搜索用时 10 毫秒
41.
Plant lignans are converted to mammalian forms, enterodiol and enterolactone, in the colon. Enhanced plasma or urinary enterolactone levels have been associated with lowered risk of cardiovascular diseases and breast cancer. Processed rye bran and its fractions were compared to ascertain the fermentation rates of fermentable carbohydrates and the bioconversion of lignans. Rye bran was extruded and treated with a food‐grade xylanase. Part of the xylanase‐treated rye bran was separated into a soluble rye bran extract and an insoluble residue, and a part of the xylanase‐treated rye bran was freeze‐dried without separation. All the samples were digested by pepsin and pancreatin and subsequently fermented with a human faecal inoculum in vitro. The consumption of carbohydrates, the productions of short‐chain fatty acids (SCFA), enterodiol and enterolactone were followed as a function of time. The soluble rye bran extract showed the fastest fermentation rate and the highest extent of fermentation determined as the consumption of neutral sugar residues (arabinose, xylose and glucose), the production of SCFA and the formation of enterodiol and enterolactone. Xylanase treatment enhanced the fermentation rate of extruded rye bran. An even a higher fermentation rate was observed for rye bran extract containing soluble carbohydrates. The amount of enterolactone precursors in rye seemed to be too low for enterolactone formation using an amount of substrate suitable for carbohydrate fermentation. However, xylanase treatment enhanced the availability of plant lignans from rye bran, as enterodiol formation was increased by the use of xylanase. Copyright © 2005 Society of Chemical Industry  相似文献   
42.
Cold-pressed chardonnay, muscadine, ruby red, and concord grape seed oils and their defatted flours were studied for their fatty acid composition, oxidative stability and antioxidant and antiproliferative activities. The phenolic profiles of the seed flours were also measured. The most abundant fatty acid in the oils was linoleic acid, ranging from 66.0 g/100 g of total fatty acids in ruby red seed oil to 75.3 g/100 g of total fatty acids in concord seed oil. The oils were also high in oleic acid and low in saturated fat. Ruby red grape seed oil recorded the highest oxidative stability index of 40 h under the accelerated conditions. Total phenolic content (TPC) was up to 100 times lower in the oils than in the flours. Lutein, zeaxanthin, cryptoxanthin, β-carotene, and α-tocopherol levels were also measured. DPPH radical-scavenging capacity ranged from 0.07 to 2.22 mmol trolox equivalents (TE)/g of oil and 11.8 to 15.0 mmol TE/g of flour. Oxidative stability of menhaden fish oil containing extracts of the seed flours was extended by up to 137%. HPLC analysis was conducted to determine the levels of free soluble, soluble conjugated and insoluble bound phenolics in the seed flours. The phenolic compounds analyzed included catechin, epicatechin, epicatechin gallate, quercetin, gallic acid, and procyanidins B1 and B2. Antiproliferative activity was tested against HT-29 colon cancer cells. All of the seed flours and muscadine seed oil registered significant (P < 0.05) inhibition of cancer cell growth. The results from this study demonstrate the potential of developing value-added uses for these seed oils and flours as dietary sources of natural antioxidants and antiproliferative agents for optimal health.  相似文献   
43.
This study investigated the identity, growth and metabolite production of micro-organisms causing spoilage of Pangasius hypophthalmus fillets packaged in air, vacuum and modified atmospheres (MAP) (MAP 1: 50%CO(2)-50%N(2) and MAP 2: 50%CO(2)-50%O(2)) during storage at 4 °C. Based on the time it took for psychrotrophic total colony counts to exceed 7 log cfu g(-1), the shelf life of the fillets packaged in air, vacuum, MAP 1 and MAP 2 was estimated to be 7, 10, 12 and 14 days respectively. The longest lag phases were observed in the samples packaged in MAP 2 (50%CO(2)-50%O(2)). In the fillets packaged in air and under vacuum, the dominant flora identified by partial 16S rDNA sequencing at the end of the shelf life generally consisted of Gram-negative bacteria mostly belonging to the genera Serratia and Pseudomonas. In contrast, lactic acid bacteria (Carnobacterium maltaromaticum and Carnobacterium divergens) and Brochothrix thermosphacta were identified as the dominant spoilage flora in the samples packaged under the two MAPs investigated. By means of solid-phase microextraction gas chromatography mass spectrometry (SPME GC-MS) analysis, volatile organic compounds in the headspace of the samples at the end of the shelf life were identified for each packaging condition. Based on these results, a selective ion flow tube mass spectrometry (SIFT-MS) method was developed to quantify the production of volatile metabolites during storage of the fillets. The results of these analyses indicated that several compounds contributed to the bacterial spoilage of Pangasius fillets e.g., ethanol, 2,3-butanediol, diacetyl, acetoin, ethyl acetate, acetic acid and sulfur compounds. It also emerged that the production of these compounds was dependent on the packaging condition applied.  相似文献   
44.
The occurrence of nocardial mastitis, mostly in the context of outbreaks, has been reported in many countries. However, there is a paucity of reports regarding detailed characterization of Nocardia cyriacigeorgica from bovine mastitis. Thus, herein we report characteristics, antimicrobial susceptibility patterns, molecular identification, and pathogenicity of N. cyriacigeorgica isolated from an outbreak of clinical mastitis in a dairy herd in northern China. A total of 182 (80.2%) lactating cows had clinical mastitis with severe inflammation and firmness of the udder, reduced milk production, and anorexia, with no apparent clinical response to common antibiotics. Out of 22 mastitic milk samples submitted to our laboratory, 12 N. cyriacigeorgica were isolated and characterized using standard microbiological analysis, 16S rRNA gene sequencing, random amplified polymorphic DNA PCR analysis, biochemical assays, and antibiotic susceptibility testing. Additionally, in vivo experiments were done to determine pathogenicity of these clinical mastitis isolates. All isolates were resistant to ampicillin, amoxicillin-clavulanic acid, ciprofloxacin, minocycline, rifampicin, and aminoglycosides (type VI pattern). Additionally, intramammary inoculation of mice with N. cyriacigeorgica caused chronic inflammatory changes, including hyperemia, edema, and infiltration of lymphocytes and neutrophils, as well as hyperplasia of lymph nodules in mammary glands. Therefore, we concluded that N. cyriacigeorgica was involved in the current outbreak of mastitis. To our best knowledge, this is the first report to characterize N. cyriacigeorgica isolated from cases of bovine mastitis in China.  相似文献   
45.
Green leaf standard, chemical composition and quality of black tea (Camellia sinensis (L) O Kuntze) change with plucking intervals. Long plucking intervals lead to poor leaf standard with a lot of mature leaves and lower theaflavins, the sum of volatile flavour compounds imparting a sweet flowery aroma (group II volatile flavour compounds), caffeine contents and tasters' evaluations of black tea. The sum of volatile flavour compounds imparting inferior, grassy, green flavour (group I volatile flavour compounds) to tea, however, increases with long plucking intervals.  相似文献   
46.
Diminishing returns from increased clock frequencies and instruction‐level parallelism have forced computer architects to adopt architectures that exploit wider parallelism through multiple processor cores. While emerging many‐core architectures have progressed at a remarkable rate, concerns arise regarding the performance and productivity of numerous parallel‐programming tools for application development. Development of parallel applications on many‐core processors often requires developers to familiarize themselves with unique characteristics of a target platform while attempting to maximize performance and maintain correctness of their applications. The family of partitioned global address space (PGAS) programming models comprises the current state of the art in balancing performance and programmability. One such PGAS approach is SHMEM, a lightweight, shared‐memory programming library that has demonstrated high performance and productivity potential for parallel‐computing systems with distributed‐memory architectures. In the paper, we present research, design, and analysis of a new SHMEM infrastructure specifically crafted for low‐level PGAS on modern and emerging many‐core processors featuring dozens of cores and more. Our approach (with a new library known as TSHMEM) is investigated and evaluated atop two generations of Tilera architectures, which are among the most sophisticated and scalable many‐core processors to date, and is intended to enable similar libraries atop other architectures now emerging. In developing TSHMEM, we explore design decisions and their impact on parallel performance for the Tilera TILE‐Gx and TILEPro many‐core architectures, and then evaluate the designs and algorithms within TSHMEM through microbenchmarking and applications studies with other communication libraries. Our results with barrier primitives provided by the Tilera libraries show dissimilar performance between the TILE‐Gx and TILEPro; therefore, TSHMEM's barrier design takes an alternative approach and leverages the on‐chip mesh network to provide consistent low‐latency performance. In addition, our experiments with TSHMEM show that naive collective algorithms consistently outperformed linear distributed collective algorithms when executed in an SMP‐centric environment. In leveraging these insights for the design of TSHMEM, our approach outperforms the OpenSHMEM reference implementation, achieves similar to positive performance over OpenMP and OSHMPI atop MPICH, and supports similar libraries in delivering high‐performance parallel computing to emerging many‐core systems. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   
47.
48.
The anomeric alkylation of D-fructose is efficiently catalyzed by mild acid catalysts. Degradation of fructose is negligible under the conditions applied.  相似文献   
49.
The objective of this study was to establish the relation between the calcium sequestering capacity (SC) of dicarboxy-starch and that of dicarboxy-inulin, and the oxidation degree of these products. An S-type curve is obtained when plotting the SC of oxidized starch versus the degree of oxidation. By contrast the sequestering capacity of dicarboxy-inulin increases linearly with the degree of oxidation. The difference in behaviour of these materials can be attributed to the fact that upon starch oxidation the favourable oxydiacetate structure is obtained only after substantial conversion, whereas in inulin this structure is obtained immediately and is present in each oxidized fructose unit.  相似文献   
50.
Rotationplasty     
Today rotationplasty is well established as an acceptable procedure for limb salvage in patients who have a malignant tumor in the femur or tibia. The main indication is that it is the alternative to amputation. Rotationplasty should further be used in the very young child because of growth-dependent complications that can be expected after tumor resection and any kind of reconstruction. This article covers the classification of the different types of rotationplasties, the operative procedure, prosthetic care, and the functional results.  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