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   17133篇
  免费   1463篇
  国内免费   21篇
电工技术   162篇
综合类   10篇
化学工业   4509篇
金属工艺   237篇
机械仪表   512篇
建筑科学   780篇
矿业工程   44篇
能源动力   497篇
轻工业   3133篇
水利工程   155篇
石油天然气   56篇
无线电   1223篇
一般工业技术   3051篇
冶金工业   866篇
原子能技术   77篇
自动化技术   3305篇
  2024年   56篇
  2023年   237篇
  2022年   406篇
  2021年   652篇
  2020年   498篇
  2019年   523篇
  2018年   720篇
  2017年   737篇
  2016年   813篇
  2015年   645篇
  2014年   851篇
  2013年   1572篇
  2012年   1416篇
  2011年   1433篇
  2010年   930篇
  2009年   919篇
  2008年   912篇
  2007年   838篇
  2006年   693篇
  2005年   503篇
  2004年   438篇
  2003年   405篇
  2002年   365篇
  2001年   212篇
  2000年   221篇
  1999年   160篇
  1998年   159篇
  1997年   152篇
  1996年   131篇
  1995年   109篇
  1994年   97篇
  1993年   87篇
  1992年   55篇
  1991年   50篇
  1990年   36篇
  1989年   48篇
  1988年   37篇
  1987年   25篇
  1986年   30篇
  1985年   40篇
  1984年   36篇
  1983年   27篇
  1982年   37篇
  1981年   30篇
  1980年   25篇
  1979年   36篇
  1978年   33篇
  1976年   20篇
  1975年   14篇
  1973年   16篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
An assessment was made of the microbiological quality of the final product (different retail cuts), produced by two different retail supermarket groups (A & B). The influence of sanitary conditions on the microbiological quality of the final product was evaluated, and the possible influences on shelf life were determined. Supermarket group A (Sup group A) received carcasses with significantly lower surface counts of micro-organisms than supermarket group B (Sup group B), while the latter had a more efficient overall sanitation programme than supermarket group A. Five cuts were monitored for the presence of total aerobic counts, psychrotrophic counts, lactobacilli, Enterobacteriaceae and numbers of Pseudomonadaceae present. A shelf life study was also executed by repeating these enumerations on the same meat samples after refrigerated storage at 5°C for 2 and 4 days, respectively. It is generally accepted that a good refrigeration or chilling regime will preserve the inherent meat quality, but in this study it was found that neither served as a guarantee of quality. The more stringent hygiene at retail level of Sup group B yielded consistently lower mean counts of the different bacterial groups for all the meat cuts monitored and, thus meat with an extended shelf life. The total count (at 30°C) on meat cuts was the highest, followed by the psychrotrophs, the Pseudomonadaceae the Enterobacteriaeae and the lactobacilli. Minced meat generally had the highest mean aerobic total microbial counts. This count on minced meat might be a suitable indicator for monitoring the overall sanitary condition of a retail premises. The results re-emphasized the multi-factorial complexity of fresh meat quality and shelf life. The microbial quality of the raw material (carcasses), the maintenance of the cold chain, sanitary condition of premises, equipment and personnel surfaces and general management practices are factors that collectively determine the microbiological quality of the product.  相似文献   
142.
The influence of different centralised pre-packaging systems (PVC, modified atmosphere packaging (MAP), 25% CO(2) and 75% O(2), vacuum skin packaging (VSP) and the mother bag concept, 100% CO(2)) on the shelf-life (0, 7, 14 and 21 days at 0°C) of fresh pork was determined using microbiological, colour, odour and acceptability characteristics. All the packaging treatments were equally efficient for the first 4 days of retail display. In the extended shelf-life study (7, 14 and 21 days) the mother bag centralised packaging system gave the most promising shelf-life results (21 days) and was also judged superior in terms of odour. Modified atmosphere packaging (14 days) and VSP (7 days) may be considered as other possible options.  相似文献   
143.
This study attempted to identify the major sources of work-related stress among telephone operators, with special emphasis on computer monitoring and telephone surveillance. A cross-sectional random sample of over 700 telephone operators participated in a questionnaire survey (response rate = 88%). The survey included items designed to measure perceived stress, management practices, specific job stressors and monitoring preferences. Call-time pressure items were most strongly linked to job stress by operators, with 70% reporting that difficulty in serving a customer well and still keeping call-time down contributed to their feelings of stress to a large or very large extent. About 55% of operators reported that telephone monitoring contributed to their feelings of job stress. If given the opportunity, 44% of operators stated they would prefer not to be monitored by telephone at all, while 23% stated they would prefer some monitoring; 33% had no preference. The setting of inappropriate individual-call-time objectives, which may be consistently unachievable for some operators and which create conflict between management demands for quantity and quality and also between workers values concerning quality and productivity demands, appears to be the most stress-inducing aspect of the job. In terms of telephone surveillance, the issues of timeliness and specificity of feedback appear to be less important than call-time pressure.  相似文献   
144.
In finite labelled transition systems the problems of deciding strong bisimilarity, observation equivalence and observation congruence areP-complete under many—oneNC-reducibility. As a consequence, algorithms for automated analysis of finite state systems based on bisimulation seem to be inherently sequential in the following sense: the design of anNC algorithm to solve any of these problems will require an algorithmic breakthrough, which is exceedingly hard to achieve.  相似文献   
145.
146.
In response to K. Danzinger's (see record 1986-00068-001) suggestion that the first use of the term subject in the English-language psychological literature occurred in 1886 in the context of experiments involving the hypnotic state, the present author points out that there are examples of the use of the term in discussions of experiments on thought transference published by the Society for Psychical Research in the 1880's. (8 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
147.
Iranian Polymer Journal - The present work focuses on the assessment of the ability of porcine plasma protein (PPP) to be electrospun satisfactorily to form fibre mats, and their rheological and...  相似文献   
148.
Esophageal cancer (EC) is a life-threatening disease, demanding the discovery of new biomarkers and molecular targets for precision oncology. Aberrantly glycosylated proteins hold tremendous potential towards this objective. In the current study, a series of esophageal squamous cell carcinomas (ESCC) and EC-derived circulating tumor cells (CTCs) were screened by immunoassays for the sialyl-Tn (STn) antigen, a glycan rarely expressed in healthy tissues and widely observed in aggressive gastrointestinal cancers. An ESCC cell model was glycoengineered to express STn and characterized in relation to cell proliferation and invasion in vitro. STn was found to be widely present in ESCC (70% of tumors) and in CTCs in 20% of patients, being associated with general recurrence and reduced survival. Furthermore, STn expression in ESCC cells increased invasion in vitro, while reducing cancer cells proliferation. In parallel, an ESCC mass spectrometry-based proteomics dataset, obtained from the PRIDE database, was comprehensively interrogated for abnormally glycosylated proteins. Data integration with the Target Score, an algorithm developed in-house, pinpointed the glucose transporter type 1 (GLUT1) as a biomarker of poor prognosis. GLUT1-STn glycoproteoforms were latter identified in tumor tissues in patients facing worst prognosis. Furthermore, healthy human tissues analysis suggested that STn glycosylation provided cancer specificity to GLUT1. In conclusion, STn is a biomarker of worst prognosis in EC and GLUT1-STn glycoforms may be used to increase its specificity on the stratification and targeting of aggressive ESCC forms.  相似文献   
149.
In response to cardiac ischemia/reperfusion, proteolysis mediated by extracellular matrix metalloproteinase inducer (EMMPRIN) and its secreted ligand cyclophilin-A (CyPA) significantly contributes to cardiac injury and necrosis. Here, we aimed to investigate if, in addition to the effect on the funny current (I(f)), Ivabradine may also play a role against cardiac necrosis by reducing EMMPRIN/CyPA-mediated cardiac inflammation. In a porcine model of cardiac ischemia/reperfusion (IR), we found that administration of 0.3 mg/kg Ivabradine significantly improved cardiac function and reduced cardiac necrosis by day 7 after IR, detecting a significant increase in cardiac CyPA in the necrotic compared to the risk areas, which was inversely correlated with the levels of circulating CyPA detected in plasma samples from the same subjects. In testing whether Ivabradine may regulate the levels of CyPA, no changes in tissue CyPA were found in healthy pigs treated with 0.3 mg/kg Ivabradine, but interestingly, when analyzing the complex EMMPRIN/CyPA, rather high glycosylated EMMPRIN, which is required for EMMPRIN-mediated matrix metalloproteinase (MMP) activation and increased CyPA bonding to low-glycosylated forms of EMMPRIN were detected by day 7 after IR in pigs treated with Ivabradine. To study the mechanism by which Ivabradine may prevent secretion of CyPA, we first found that Ivabradine was time-dependent in inhibiting co-localization of CyPA with the granule exocytosis marker vesicle-associated membrane protein 1 (VAMP1). However, Ivabradine had no effect on mRNA expression nor in the proteasome and lysosome degradation of CyPA. In conclusion, our results point toward CyPA, its ligand EMMPRIN, and the complex CyPA/EMMPRIN as important targets of Ivabradine in cardiac protection against IR.  相似文献   
150.

Electrocaloric (EC) refrigeration, is accepted as an auspicious method to develop eco-friendly cooling devices. Here, the investigations on the EC response and energy storage performance of heterovalent-doped Ba(Sn, Ti)O3 relaxor ferroelectrics are carried out. Doping of aliovalent Mn or Nb elements into Ti site would regulate both the EC and energy storage behaviors. An enhanced EC temperature change up to 1.31 K, and a maximal recoverable energy storage density of 0.24 J cm??3 with the efficiency as high as 87.11?%, can be observed under 70 kV cm??1 in 0.5?% acceptor-doped Ba(Sn, Ti)O3 ceramics. It is found that the local internal stress, the local charge fluctuation, and the oxygen deficiencies would benefit the electrical behaviors of this system. These results would shed light on the effect of the heterovalent substitution on the electrical properties of lead-free BaTiO3 system and provide a novel and simple route to further improve the EC response and energy storage performance.

  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