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   882篇
  免费   77篇
电工技术   17篇
化学工业   251篇
金属工艺   6篇
机械仪表   22篇
建筑科学   15篇
能源动力   35篇
轻工业   168篇
水利工程   4篇
石油天然气   8篇
无线电   90篇
一般工业技术   99篇
冶金工业   106篇
原子能技术   2篇
自动化技术   136篇
  2024年   1篇
  2023年   13篇
  2022年   18篇
  2021年   52篇
  2020年   22篇
  2019年   28篇
  2018年   24篇
  2017年   25篇
  2016年   31篇
  2015年   31篇
  2014年   44篇
  2013年   69篇
  2012年   57篇
  2011年   58篇
  2010年   44篇
  2009年   40篇
  2008年   30篇
  2007年   52篇
  2006年   32篇
  2005年   25篇
  2004年   30篇
  2003年   26篇
  2002年   18篇
  2001年   11篇
  2000年   13篇
  1999年   16篇
  1998年   27篇
  1997年   29篇
  1996年   18篇
  1995年   11篇
  1994年   11篇
  1993年   6篇
  1992年   3篇
  1991年   4篇
  1990年   3篇
  1989年   2篇
  1988年   5篇
  1987年   2篇
  1986年   2篇
  1985年   5篇
  1984年   1篇
  1979年   3篇
  1977年   1篇
  1976年   3篇
  1975年   1篇
  1974年   5篇
  1973年   2篇
  1972年   2篇
  1971年   2篇
  1969年   1篇
排序方式: 共有959条查询结果,搜索用时 31 毫秒
91.
An integrated approach to quality of service for content delivery using Web services includes quality definitions, user contracts, and fault monitoring.  相似文献   
92.
Basic information theory is used to analyse the amount of confidential information which may be leaked by programs written in a very simple imperative language. In particular, a detailed analysis is given of the possible leakage due to equality tests and if statements. The analysis is presented as a set of syntax-directed inference rules and can readily be automated.  相似文献   
93.
ABSTRACT This paper empirically examines parameter sensitivity to choice set specification in the context of shopping destination choice, using supermarket choice data from Gainesville, Horida. We estimate parameters of the widely applied multinomial logit (MNL) discrete choice mode) multiple times. Each estimation uses, for all observations, a single randomly selected subset of the universal choice set. The distribution of parameter estimates is examined for specific market segments and choice subset sizes. The results indicate that the parameters of the model can be quite sensitive to the selection of the choice set used in the calibration. However, this sensitivity is not even across all parameters and there are some interesting variations. Distance deterrence and chain image parameters, for example, exhibit much more stability than parameters for store size and store competition. Li addition, model parameters show encouraging stability with relatively small choice sets of seven to ten stores.  相似文献   
94.
We propose a new Raman pump module that effectively reduces four-wave-mixing (FWM) nonlinear interaction among longitudinal pump modes and wavelength-division-multiplexed (WDM) signals in co-pumped distributed Raman amplifiers based on nonzero dispersion-shifted fibers (NZ-DSFs). Theory and experiments confirm that the proposed pump module structure, based on polarization- and wavelength-multiplexed Fabry-Perot lasers, allows distributed amplification with high co-propagating on-off Raman gain, providing a key technology for all-Raman-based dense-WDM ultralong-haul transmission.  相似文献   
95.
This paper deals with a new method improving the static test for analogue-to-digital converters. The method is based on a histogram procedure using as test signals small-amplitude triangular waves superimposed on suitable constant offset values. The histogram is built over the converter fullscale by varying the offset step by step systematically. A small amplitude and a reduced time slope in comparison to the converter range and slew rate, respectively, lead to static test conditions. This procedure allows inexpensive function generators to be used and the test duration to be dramatically reduced. Experimental results of tests aimed at validating, characterizing, and comparing the proposed method on two different converter architectures are presented.  相似文献   
96.
In a deadline-ordered service discipline, packets are assigned transmission deadlines and eligibility times and are transmitted in increasing order of deadlines. Different deadline-ordered service disciplines are distinguished by how they calculate deadlines and eligibility times. One of the more difficult analytical problems one faces when designing a new deadline-ordered service discipline is to prove that one can bound the end of transmission times of packets relative to their assigned deadlines, which we call schedulability. We show that, no matter how one calculates deadlines, there is a simple schedulability condition for deadline-ordered service disciplines. This schedulability condition is necessary and sufficient for preemptive deadline-ordered service disciplines, and for a server that allows the presence of nonreal-time packets (i.e., packets with no deadlines), it is also necessary and sufficient for nonpreemptive deadline-ordered service disciplines. We also address the schedulability problem for service disciplines in general, and show the optimality of deadline-ordered service disciplines. To demonstrate how our results simplify schedulability determination, we use them to prove the known schedulability conditions of VirtualClock, Packet-by-Packet Generalized Processor Sharing (PGPS), Stop-and-Go, and Delay-Earliest-Due-Date (Delay-EDD), and to provide a new result, the necessary schedulability condition of VirtualClock  相似文献   
97.
A membrane is commonly regarded as a barrier capable of being selectively permeated by some components of a mixture or, at least, of changing the composition of a fluid stream that flows through it due to a certain driving force (a pressure, concentration, or electric potential gradient). Permselectivity is thus considered as the most distinctive property of a membrane.  相似文献   
98.
A special interest, both in scientific publications and in the mass media, is recently emerged about the use of hormone replacement therapy (HRT) in post-menopausal women. Beside, in fact, the specific indication for the relief of menopausal symptoms, hypotheses are debated about a possible role of HRT in the reduction of risk of osteoporosis and cardiovascular diseases, and in the increased risk of breast cancer. This situation emphasizes the need for assessing the benefit/risk profile for HRT in order to ensure that strategies of proven clinical effectiveness, based on large randomized clinical trials, will be adopted in the population.  相似文献   
99.
Chronic inflammation is widely diffuse in maintenance hemodialysis (MHD) patients and is associated with poor survival. Hemodiafiltration with endogenous reinfusion (HFR) is a dialysis technique, highly biocompatible, able to adsorb proinflammatory cytokines and to decrease amino acids and antioxidants loss. These features could be helpful in MHD patients affected by idiopathic chronic inflammation, but this issue remains to be elucidated. We performed a multicenter longitudinal study to assess the effect of the switching from bicarbonate HD to HFR in patients with serum C‐reactive Protein (CRP) > 5 mg/L coupled with albumin <4.0 g/dL in the last 6 months. We enrolled 24/176 (14%) patients, of which 20 patients were assessed at 4 months and 18 completed the study. We excluded 11 patients with evident causes of inflammation. At baseline, serum levels of CRP (18.7[7.0–39.4] mg/L) and albumin (3.5[3.3–3.7] g/dL) were significantly correlated (r = ?0.49; P = 0.028). The effect on CRP and albumin was almost evident in the first 4 months and remained stable until to eighth month. A strict correlation (R = ?0.49; 0.040) between percentage change of CRP (?35%) and albumin (+14%) after 8 months of HFR. These effects were associated with the reduction of IL‐6, IL‐1β, and TNF‐α and the increment of pre‐albumin and leptin, whereas the serum levels of Branched Chain Amino Acid (BCAA) remained unchanged. In MHD patients affected by idiopathic chronic inflammation the switching from BHD to HFR is associated with improvement of inflammation. Whether these favorable effects may modify the outcomes of these high‐risk patients needs to be confirmed by studies ad hoc.  相似文献   
100.
BACKGROUND: Salad crops of the Brassicaceae family, such as Diplotaxis tenuifolia and Eruca vesicaria, commonly referred to as ‘rocket salads’, have attracted considerable interest as culinary vegetables because of their strong flavour and their content of putative health‐promoting compounds. Among such compounds, glucosinolates and phenolics are well‐known phytochemicals with an important role also in determining the characteristic flavour of these species. In this study, to identify potentially high‐value rocket salads, 37 cultivated types were examined for sensory characters and their relations with glucosinolate and phenolic contents, which ranged from 0.76 to 3.03 g kg?1 dry weight (DW) and from 4.68 to 31.39 g kg?1 DW, respectively. RESULTS: The perception of bitter taste was significantly affected by specific glucosinolates, namely progoitrin/epiprogoitrin and dimeric glucosativin. Aroma intensity was negatively related to glucoalyssin content, whereas pungency was significantly related to total glucosinolate content. Kaempferol‐3‐(2‐sinapoyl‐glucoside)‐4′‐glucoside was positively and significantly related to all flavour trait perceptions. Aroma intensity, pungency, crunchiness and juiciness were positively related to typical rocket salad flavour perception through a prominent direct effect. CONCLUSION: Aroma intensity, pungency, crunchiness and juiciness were strong determinants of overall rocket salad flavour perception. Visual traits also characterised sensory components. Bitterness, usually considered a negative flavour trait, was moderately perceived in the examined material, without negatively affecting typical flavour perception. In the range of the examined material, glucosinolate content did not contrast with typical flavour, demonstrating that good taste and putative health‐promoting properties may coexist. Copyright © 2011 Society of Chemical Industry  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