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   1079篇
  免费   15篇
  国内免费   6篇
电工技术   35篇
综合类   2篇
化学工业   153篇
金属工艺   26篇
机械仪表   20篇
建筑科学   15篇
能源动力   13篇
轻工业   48篇
水利工程   10篇
无线电   191篇
一般工业技术   180篇
冶金工业   324篇
原子能技术   13篇
自动化技术   70篇
  2021年   12篇
  2020年   5篇
  2019年   10篇
  2018年   8篇
  2017年   10篇
  2016年   10篇
  2015年   12篇
  2014年   19篇
  2013年   33篇
  2012年   20篇
  2011年   32篇
  2010年   27篇
  2009年   25篇
  2008年   32篇
  2007年   30篇
  2006年   33篇
  2005年   20篇
  2004年   15篇
  2003年   20篇
  2002年   29篇
  2001年   28篇
  2000年   31篇
  1999年   31篇
  1998年   115篇
  1997年   82篇
  1996年   65篇
  1995年   38篇
  1994年   33篇
  1993年   35篇
  1992年   21篇
  1991年   19篇
  1990年   23篇
  1989年   11篇
  1988年   15篇
  1987年   20篇
  1986年   16篇
  1985年   17篇
  1984年   9篇
  1983年   8篇
  1982年   14篇
  1981年   10篇
  1980年   3篇
  1979年   3篇
  1978年   5篇
  1977年   15篇
  1976年   18篇
  1974年   3篇
  1973年   2篇
  1970年   2篇
  1967年   3篇
排序方式: 共有1100条查询结果,搜索用时 31 毫秒
1.
Chronic infections are considered one of the most severe problems in skin wounds, and bacteria are present in over 90% of chronic wounds. Pseudomonas aeruginosa is frequently isolated from chronic wounds and is thought to be a cause of delayed wound healing. Invariant natural killer T (iNKT) cells, unique lymphocytes with a potent regulatory ability in various inflammatory responses, accelerate the wound healing process. In the present study, we investigated the contribution of iNKT cells in the host defense against P. aeruginosa inoculation at the wound sites. We analyzed the re-epithelialization, bacterial load, accumulation of leukocytes, and production of cytokines and antimicrobial peptides. In iNKT cell–deficient (Jα18KO) mice, re-epithelialization was significantly decreased, and the number of live colonies was significantly increased, when compared with those in wild-type (WT) mice on day 7. IL-17A, and IL-22 production was significantly lower in Jα18KO mice than in WT mice on day 5. Furthermore, the administration of α-galactosylceramide (α-GalCer), a specific activator of iNKT cells, led to enhanced host protection, as shown by reduced bacterial load, and to increased production of IL-22, IL-23, and S100A9 compared that of with WT mice. These results suggest that iNKT cells promote P. aeruginosa clearance during skin wound healing.  相似文献   
2.
Recently, renewable energy has been attracting attention as a result of global warming and the depletion of fossil fuels. Photovoltaic (PV) systems have spread rapidly around the world because they generate electric power quietly and can be installed in many places. The output power generated in a PV system fluctuates with changes in solar irradiance and panel temperature. The reverse flow of surplus power in output spikes may have a negative effect on electric power quality, such as on the frequency and voltage in a power system. A residential distributed generation (DG) system composed of a fuel cell (FC) unit, an electrolyzer (EL) unit, and a PV system has been proposed in order to resolve these problems. In order to operate this system without interruption, the hydrogen storage volume must be managed. This paper proposes a novel hydrogen management method for a residential DG system with PV cells and hydrogen‐storage type FCs. The hydrogen storage volume is maintained at the preset frequency by operating the FC unit and the EL unit. Models of the PV, FC, and EL were constructed for a simulation. In the simulation, we showed that the proposed management method is viable for a residential DG system with PV cells and hydrogen‐storage FCs.  相似文献   
3.
Wireless Personal Communications - Studying computer programming requires not only an understanding of theories and concepts, but also coding pragmatism. Success in studying or conducting such a...  相似文献   
4.
The ability of Clostridium butyricum RAK25832 to use casamino acids as a nitrogen source was investigated. Strain RAK25832 showed the capacity to utilize different types of carbon sources. With glucose as a carbon source (10 g/L), the preferred final concentration of casamino acids was 26.67 g/L, with a cumulative hydrogen production, production rate, and yield of 2505 mL H2/L, 160 mL/h, and 1.81 mol H2/mol glucose, respectively. Eighteen metal elements were screened to identify the most important metals for biohydrogen production, and four elements were optimized. The optimal medium composition was MgCl2·6H2O (0.1 g/L), K2HPO4·3H2O (6.67 g/L), NaHCO3 (2.6 g/L), and FeCl2·4H2O (0.002 g/L). Vitamin supplementation of the medium showed no significant effect on hydrogen production. Under the optimized conditions, cumulative hydrogen production reached 3074 mL H2/L. This is the first study to demonstrate the use of casamino acids as a nitrogen source by C. butyricum.  相似文献   
5.
Obesity-related metabolic abnormalities, including adipokine imbalance and chronic inflammation, are involved in liver carcinogenesis. Chemerin, a novel adipokine, plays a critical role in adipogenesis, energy metabolism, and inflammation. We evaluated the impact of serum chemerin levels on liver functional reserves in hepatocellular carcinoma (HCC) patients and on the recurrence and prognosis of HCC. This study included 44 patients with any stage of HCC who underwent curative treatment at Gifu Municipal Hospital (Gifu, Japan) between 2006 and 2007. Recurrence-free survival and overall survival were estimated using the Kaplan-Meier method. Serum albumin levels (Pearson’s correlation coefficient; r = 0.3110, p = 0.0399), platelet counts (r = 0.4159, p = 0.0050), and prothrombin times (r = 0.3775, p = 0.0115) were significantly correlated with serum chemerin levels in patients with HCC, and they were inversely correlated with Child-Pugh scores (r = −0.3732, p = 0.0126), serum alanine aminotransferase levels (r = −0.3864, p = 0.0105), and total bilirubin levels (r = −0.4023, p = 0.0068). Among these variables, a multiple comparison test identified that platelet counts and total bilirubin levels were associated with serum chemerin levels (p < 0.0083). No significant correlation was found between serum chemerin levels and recurrence-free survival (p = 0.3691) or overall survival (p = 0.7916). In HCC patients, serum chemerin concentrations were correlated with liver functional reserves and platelet counts, but not with recurrence or prognosis.  相似文献   
6.
Leucine-rich repeat kinase 2 (LRRK2) is a major causative gene of late-onset familial Parkinson’s disease (PD). The suppression of kinase activity is believed to confer neuroprotection, as most pathogenic variants of LRRK2 associated with PD exhibit increased kinase activity. We herein report a novel LRRK2 variant—p.G2294R—located in the WD40 domain, detected through targeted gene-panel screening in a patient with familial PD. The proband showed late-onset Parkinsonism with dysautonomia and a good response to levodopa, without cognitive decline or psychosis. Cultured cell experiments revealed that p.G2294R is highly destabilized at the protein level. The LRRK2 p.G2294R protein expression was upregulated in the patient’s peripheral blood lymphocytes. However, macrophages differentiated from the same peripheral blood showed decreased LRRK2 protein levels. Moreover, our experiment indicated reduced phagocytic activity in the pathogenic yeasts and α-synuclein fibrils. This PD case presents an example wherein the decrease in LRRK2 activity did not act in a neuroprotective manner. Further investigations are needed in order to elucidate the relationship between LRRK2 expression in the central nervous system and the pathogenesis caused by altered LRRK2 activity.  相似文献   
7.
A continuous‐time plant with a discretized continuous‐time controller does not yield stability if the sampling rate is lower than some certain level. Thus far, high‐performance electronic control has made use of expensive hardware needed to implement discretized continuous‐time controllers; low‐cost hardware generally does not have a sufficiently high sampling rate. This technical note presents results comparing performance indexes with and without intersample behavior, and provides some answers to the question of how a low‐specification device can control a plant effectively. We consider a machine simulating wafer handling robots, which is an electromechanical system driven by a direct drive motor, at a semiconductor factory. We illustrate the controller design for the robot with and without intersample behavior, and present simulations and experimental results using these controllers. Taking intersample behavior into account proves to be effective in improving control performance and makes it possible to choose a relatively long sampling period. Controller design in terms of the performance index with intersample behavior makes it possible to deal with situations in which a sufficiently short sampling period may not be employed, and freedom of controller design may be widened, especially regarding the choice of the sampling period.  相似文献   
8.
Thermoelectric materials have received much attention recently from the viewpoint of global environmental issues and effective utilization of energy resources. Especially those effective at relatively low temperature, such as below 100°C, which are usually abandoned without use, have become noteworthy recently. From this point of view, organic thermoelectric materials are most attractive, because they could be prepared at low cost and applied in various locations due to their flexibility. We have investigated the thermoelectric properties of organic conducting polymers such as polyaniline, polypyrrole, and polyphenylenevinylene, and succeeded in increasing the thermoelectric performance by selecting dopants, stretching conducting films, etc. Recently we have focused on new systems of organic–inorganic hybrid thermoelectric materials. Herein we present the preparation of a novel system of hybrids of polyaniline and bismuth(III) telluride nanoparticles, starting from bismuth(III) chloride and tetrachlorotellurium by using polyvinylpyrrolidone as a protecting reagent, as well as their thermoelectric properties. The hybrids prepared by this particular method showed much higher thermoelectric performance than the starting organic conducting polymer.  相似文献   
9.
Two‐pole large generators are extensively used in power utilities. Growing demand for electric power in recent years has led to substantial increases in the capacity of generators. In line with this trend, our company has manufactured two‐pole turbine generators in the 900,000‐kVA to 1,200,000‐kVA classes. As the capacity of generators becomes larger, equivalent circuits are increasingly expected to improve their precision in estimating operation characteristics. The Park model has been widely used as an equivalent circuit model. The Park model with quadrature axis transient reactance $x_{q}^{\prime}$ is claimed to be useful for accurately estimating the load rejection characteristics of turbine generators. However, it is difficult to measure $x_{q}^{\prime}$, few studies based on measured data have appeared. As one of the few examples, we have conducted a measured data on a 500,000‐kVA‐class generator. Recently, the authors obtained test data on $x_{q}^{\prime}$ of a 900,000‐kVA‐class generator. In this study, based on these data, we studied the effect of $x_{q}^{\prime}$ using the finite element method and a transient analysis program (EMTP‐ATP). © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 177(3): 17–27, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21099  相似文献   
10.
To avoid the risk of long-term storage of secrets on a portable device, an online credential system supports the roaming user in retrieving securely at various locations his private key and other material to generate anonymous signatures. The protocol proposed here allows a roaming mobile user to access anonymously services such as whistle blowing and net-counselling. Our approach: (1) allows a mobile user, remembering a short password, to anonymously and securely retrieve the credentials necessary for his anonymous communication without assuming a pre-established anonymous channel to the credential server or establishing an anonymous channel using the time-consuming existing rerouting techniques; (2) provides authenticated anonymous access to privacy-related services without rerouting the packets; (3) helps combatting the abuse of anonymity for performing illegal activities (e.g. redistribution of copy-righted contents, illegal drug trading and so on).  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