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   173篇
  免费   8篇
电工技术   1篇
化学工业   57篇
金属工艺   2篇
机械仪表   6篇
能源动力   7篇
轻工业   21篇
水利工程   3篇
无线电   20篇
一般工业技术   25篇
冶金工业   27篇
自动化技术   12篇
  2023年   2篇
  2022年   1篇
  2021年   11篇
  2020年   3篇
  2019年   2篇
  2018年   5篇
  2017年   7篇
  2016年   2篇
  2015年   3篇
  2014年   4篇
  2013年   7篇
  2012年   8篇
  2011年   8篇
  2010年   7篇
  2009年   11篇
  2008年   11篇
  2007年   6篇
  2006年   3篇
  2005年   4篇
  2004年   4篇
  2003年   10篇
  2002年   9篇
  2001年   2篇
  2000年   4篇
  1999年   5篇
  1998年   8篇
  1997年   4篇
  1996年   7篇
  1995年   3篇
  1993年   3篇
  1991年   1篇
  1990年   1篇
  1987年   1篇
  1985年   1篇
  1984年   1篇
  1982年   1篇
  1980年   1篇
  1979年   1篇
  1978年   3篇
  1977年   1篇
  1976年   2篇
  1974年   1篇
  1971年   1篇
  1967年   1篇
排序方式: 共有181条查询结果,搜索用时 31 毫秒
31.
Androgen-dependent urinary constituents from males hasten reproductive maturation (the Vandenbergh effect) and disrupt peri-implantation pregnancy (the Bruce effect) in nearby females. Each of these effects can be mimicked in socially isolated females by direct administration of exogenous oestrogens. The current experiments were designed to determine the role of males' urinary 17β-oestradiol (E(2)) in their capacities to induce these effects. A preliminary experiment showed that both males on a phyto-oestrogen-rich soy-based diet and those on a phyto-oestrogen-free diet could induce both effects. For subsequent experiments, males were castrated and treated with either oil vehicle or E(2). Enzyme immunoassay was conducted on non-invasively collected urine samples from these males. Concentrations of urinary testosterone were subnormal in both conditions, but urinary E(2) was restored to the normal range for intact males in castrates given E(2). Urinary creatinine was also quantified as a measure of hydration and was significantly reduced in males treated with E(2). Castration diminished the capacity of males to promote growth of the immature uterus and also their capacity to disrupt blastocyst implantation in inseminated females. Injections of E(2) to castrated males restored both capacities. These data converge with other studies indicating that E(2) is the main constituent of male urine responsible for induction of both the Vandenbergh and the Bruce effects.  相似文献   
32.
Cobalt tetramethoxyphenyl porphyrin (CoTMPP) adsorbed on a high area carbon support (Vulcan XC72-R) and heat-treated at 900 °C under inert atmosphere was studied as electrocatalyst for the reduction of O2 to H2O2 in acid medium. Experiments performed on rotating ring-disc electrode (RRDE) and gas diffusion electrode (GDE) show that the catalyst performance depends on the cobalt loading, going through a maximum at 0.2 wt. % Co. For higher cobalt loadings, a growing part of oxygen is reduced into water, decreasing therefore the selectivity of the catalyst. These results are interpreted in terms of a further reduction of H2O2 on Co-based catalytic sites before leaving the catalytic layer. For a GDE polarized at −150 mV vs. saturated calomel electrode (SCE) and loaded with 0.9 μg cm−2 of 0.2 wt. % Co-based catalyst, a H2O2 production rate of 300 μmol h−1 cm−2 was obtained which is five times higher than the H2O2 production rate measured with Vulcan. In these conditions, the selectivity of the Co-based catalyst for H2O2 production is 92%. The good agreement observed between RRDE and GDE results confirms the relevance of using RRDE experiment for screening these non-precious metal catalysts for further GDE applications.  相似文献   
33.
The main purpose of this study is to characterize the relative noise given out by a diesel engine, around the Top Dead Centre (TDC) by quantifying the proportions of “mechanical noise” originating mainly from piston-slap on the one hand and ‘thermal noise” originating from combustion on the other hand. Two different approaches are described here to solve this problem.In the first part of the paper, the cylinder pressure is measured and used as a reference in order to reconstruct the thermal noise. Next, we propose a method based on applying a cyclic Wiener filter to the measured cylinder pressure in order to separate the noises of mechanical and thermal origins. The final result is to reduce the engine resulting noise.The second part of the paper is devoted to blind source separation (BSS) methods applied on signals issued from accelerometers placed on one of the cylinders. It develops a BSS method based on a convolutive model of non-stationary mixtures and introduces a new method based on the joint diagonalization of time varying spectral matrices of the observations. Both methods are then applied to real data and the estimated sources are finally validated by several physical arguments.  相似文献   
34.
This paper focuses on the formation control of several mobile robots in off‐road conditions. A control strategy based on bidirectional referencing is proposed, where each robot combines a velocity control w.r.t. the immediate preceding neighbor with a control w.r.t. the immediate following neighbor. Two virtual leaders, respectively, at the head and at the tail of the fleet, are propelling the fleet at the desired velocity. The fleet stability is investigated using Lyapunov techniques, pending on combination coefficients. The stability is theoretically proven for constant coefficients as weights of the respective velocity controls and tested through simulations and full‐scale experiments. It is shown that this control strategy permits us to reduce the error propagation problem often encountered in formation control, while limiting the communication problems of the global strategies. As a result, a stable formation control architecture is defined, which requires each vehicle to be refereed only to two other robots. This limited communication need is particularly interesting for agricultural operations. The proposed approach is implemented in this paper on agricultural tractors.  相似文献   
35.
Art painting diagnostic is commonly performed using electromagnetic waves at wavelengths from terahertz to X-ray. These former techniques are essential in conservation and art history research, but they could be also very useful for restoring artwork. While most studies use time domain imaging technique, in this study, a painting has been investigated using both time domain imaging (TDI) and frequency-modulated continuous wave (FMCW) system in the millimeter frequency range. By applying these systems to a painting of the eighteenth century, we detect and analyze the structure of some defects. This study underlines the differences between FMCW and TDI. We present the advantages and disadvantages of each technique on a real artwork.  相似文献   
36.
Esterification of the fatty acids contained in waste cooking oil with glycerol, a reaction involving immiscible and viscous reactants, was achieved in two pilot‐scale continuous pulsed reactors: the oscillatory baffled reactor and the helix reactor. In both reactors, with or without baffles, the reaction reaches its thermodynamic equilibrium at lower temperatures, shorter residence times and with higher selectivities than those reported in the literature. This equilibrium is then shifted by an increase in the excess of glycerol, or by removing water from the reactive media by an intermediary decantation or by the use of dodecylbenzene sulfonic acid, a surfactant catalyst. Further investigations would be required to increase the conversions without decreasing the selectivities, by increasing the initial amount of free fatty acids.  相似文献   
37.
Tool-life and wear mechanisms of CBN tools in machining of Inconel 718   总被引:2,自引:0,他引:2  
The demand for increasing productivity when machining heat resistant alloys has resulted in the use of new tool materials such as cubic boron nitride (CBN) or ceramics. However, CBN tools are mostly used by the automotive industry in hard turning, and the wear of those tools is not sufficiently known in aerospace materials. In addition, the grade of these tools is not optimized for superalloys due to these being a small part of the market, although expanding (at 20% a year). So this investigation has been conducted to show which grade is optimal and what the wear mechanisms are during finishing operations of Inconel 718. It is shown that a low CBN content with a ceramic binder and small grains gives the best results. The wear mechanisms on the rake and flank faces were investigated. Through SEM observations and chemical analysis of the tested inserts, it is shown that the dominant wear mechanisms are adhesion and diffusion due to chemical affinity between elements from workpiece and insert.  相似文献   
38.
Patients with active SLE often have an ongoing production of IFN-alpha. We therefore searched for an endogenous IFN-alpha-inducing factor (IIF) in SLE patients and found that their sera frequently induced production of IFN-alpha in cultures of peripheral blood mononuclear cells (PBMC) from healthy blood donors, especially when the PBMC were costimulated with the cytokines IFN-alpha2b and granulocyte-macrophage colony-stimulating factor (GM-CSF). The phenotype of the IFN-alpha-producing cells (IPC) as determined by flow cytometry corresponded to that of the natural IPC, resembling immature dendritic cells. The IIF activity in SLE sera was sometimes as high as that of a virus and was present especially in patients with active disease and with measurable IFN-alpha levels in serum. The IIF had an apparent molecular weight of 300-1000 kD and appeared to consist of both immunoglobulin and DNA, possibly being immune complexes. This endogenous IFN-alpha inducer may be of pathogenic significance, since a reported occasional adverse effect of IFN-alpha therapy in patients with non-autoimmune disorders is development of anti-dsDNA antibodies and SLE.  相似文献   
39.
This study has two goals. The first is to provide more information on the asymmetrical and negative link between psychological disengagement mechanisms and self-esteem level. The second is to pursue the investigation of the protective effect of psychological disengagement via the evaluation of another facet of self-esteem that is, its stability. This study conducted amongst 152 policemen confirms that disengagement allows individuals to secure their self-esteem stability. Results militate in favour of the occupation's social status to explain the variable association between disengagement and self-esteem level. In the discussion, we raise the veil on the hidden face of the protective effect of disengagement. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
40.
Breast cancer (BC) is the most predominant type of cancer among women. The aim of this study is to find new biomarkers that can help in early detection of BC, especially for those who are too young to be screened using mammography as per guidelines. Using microRNA microarray, we previously showed dysregulation of 74 microRNAs in tumors from early BC patients as compared with normal adjacent tissues, which we were interested in studying in blood circulation. In this study, we investigated the expression of 12 microRNA (miR-21/miR-155/miR-23a/miR-130a/miR-145/miR-425-5p/miR-139-5p/miR-451/miR-195/miR-125b/miR-100, and miR-182) in the plasma of 41 newly diagnosed Lebanese BC patients with early invasive ductal carcinoma as compared with 32 healthy controls. Total RNA was extracted from plasma, and expression levels of miRNA of interest were measured using RT-qPCR followed by statistical analysis; miR-21, miR-155, miR-23a, miR-130a, miR-145, miR-425-5p, and miR-139-5p were significantly upregulated and miR-451 was significantly downregulated, in the plasma of BC patients as compared with healthy controls. The positively correlated miR-23a, miR-21, and miR-130a had a high diagnostic accuracy (86%). Importantly, the combination of miR-145/miR-425-5p/miR-139-5p/miR-130a scored the highest diagnostic accuracy of 95% with AUC = 0.97 (sensitivity 97% and specificity 91%). MicroRNAs are promising non-invasive diagnostic biomarkers for early-stage BC with the panel of miR-145/miR-425-5p/miR-139-5p/miR-130a having the highest diagnostic accuracy.  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