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   556篇
  免费   31篇
  国内免费   28篇
电工技术   14篇
综合类   35篇
化学工业   99篇
金属工艺   22篇
机械仪表   17篇
建筑科学   6篇
矿业工程   7篇
能源动力   17篇
轻工业   73篇
水利工程   5篇
石油天然气   9篇
无线电   31篇
一般工业技术   97篇
冶金工业   106篇
原子能技术   12篇
自动化技术   65篇
  2024年   5篇
  2023年   9篇
  2022年   19篇
  2021年   31篇
  2020年   23篇
  2019年   17篇
  2018年   17篇
  2017年   10篇
  2016年   25篇
  2015年   18篇
  2014年   17篇
  2013年   32篇
  2012年   27篇
  2011年   26篇
  2010年   30篇
  2009年   23篇
  2008年   28篇
  2007年   21篇
  2006年   33篇
  2005年   24篇
  2004年   21篇
  2003年   30篇
  2002年   24篇
  2001年   20篇
  2000年   13篇
  1999年   5篇
  1998年   7篇
  1997年   6篇
  1996年   12篇
  1995年   6篇
  1994年   4篇
  1993年   3篇
  1992年   2篇
  1991年   3篇
  1990年   1篇
  1989年   7篇
  1988年   2篇
  1987年   1篇
  1986年   3篇
  1985年   4篇
  1982年   1篇
  1981年   1篇
  1980年   1篇
  1976年   1篇
  1974年   1篇
  1965年   1篇
排序方式: 共有615条查询结果,搜索用时 15 毫秒
31.
Natural polysaccharides have shown promising effects on the regulation of immunity in animals. In this study, we examined the immune stimulatory effect of intranasally administered Codium fragile polysaccharides (CFPs) in mice. Intranasal administration of CFPs in C57BL/6 mice induced the upregulation of surface activation marker expression in macrophages and dendritic cells (DCs) in the mediastinal lymph node (mLN) and the production of interleukin-6 (IL-6), IL-12p70, and tumor necrosis factor-α in bronchoalveolar lavage fluid. Moreover, the number of conventional DCs (cDCs) was increased in the mLNs by the upregulation of C-C motif chemokine receptor 7 expression, and subsets of cDCs were also activated following the intranasal administration of CFP. In addition, the intranasal administration of CFPs promoted the activation of natural killer (NK) and T cells in the mLNs, which produce pro-inflammatory cytokines and cytotoxic mediators. Finally, daily administration of CFPs inhibited the infiltration of Lewis lung carcinoma cells into the lungs, and the preventive effect of CFPs on tumor growth required NK and CD8 T cells. Furthermore, CFPs combined with anti-programmed cell death-ligand 1 (PD-L1) antibody (Ab) improved the therapeutic effect of anti-PD-L1 Ab against lung cancer. Therefore, these data demonstrated that the intranasal administration of CFP induced mucosal immunity against lung cancer.  相似文献   
32.
Immersion and intraperitoneal injection are the two most common methods used for the vaccination of fish. Because both methods require that fish are handled and thereby stressed, oral administration of vaccines as feed supplements is desirable. In addition, in terms of revaccination (boosting) of adult fish held in net pens, oral administration of vaccines is probably the only feasible method to obtain proper protection against diseases over long periods of time. Oral vaccination is considered a suitable method for mass immunization of large and stress-sensitive fish populations. Moreover, oral vaccines may preferably induce mucosal immunity, which is especially important to fish. Experimental oral vaccine formulations include both non-encapsulated and encapsulated antigens, viruses and bacteria. To develop an effective oral vaccine, the desired antigens must be protected against the harsh environments in the stomach and gut so they can remain intact when they reach the lower gut/intestine where they normally are absorbed and transported to immune cells. The most commonly used encapsulation method is the use of alginate microspheres that can effectively deliver vaccines to the intestine without degradation. Other encapsulation methods include chitosan encapsulation, poly D,L-lactide-co-glycolic acid and liposome encapsulation. Only a few commercial oral vaccines are available on the market, including those against infectious pancreatic necrosis virus (IPNV), Spring viremia carp virus (SVCV), infectious salmon anaemia virus (ISAV) and Piscirickettsia salmonis. This review highlights recent developments of oral vaccination in teleost fish.  相似文献   
33.
关于推进怒江流域水能资源开发的思考   总被引:1,自引:0,他引:1  
贺恭 《水力发电》2007,33(5):1-3,6
从本世纪初开始,围绕开发水能资源促进怒江流域地区经济社会发展等问题曾引发了一场大讨论。通过讨论,大家一致认为:怒江流域地区的发展不能再继续等待下去,应以切实可行的步伐向前推进。结合工作实践,简要回顾了怒江水能资源开发前期工作情况,畅谈了从怒江开发讨论中得到的有益启发,对现阶段怒江中下游水能资源开发的相关工作提出了若干建议。  相似文献   
34.
搭建红外波段双波长(1940 nm和980 nm)激光诱发痛觉刺激系统,探索基线温度控制、激光吸收导热涂层、致痛区域控制对痛觉刺激效果的影响。利用热电偶测温模块实时监测基线温度控制及涂抹20%氧合血红蛋白溶液时离体猪皮皮肤表面温度的变化;利用滤光片实现致痛区域控制。利用1940 nm激光模块实现了40℃基线温度控制,结合980 nm脉冲激光模块完成了联合痛觉刺激实验;皮肤表面涂抹20%氧合血红蛋白溶液时温降时间(110 ms)远低于空白对照(1.2 s)和风冷散热(341 ms),可提升痛觉信号质量;列举了三种不同尺寸滤光片下的温度场分布情况,证明了致痛区域的可控性。双波长红外激光诱发痛觉系统提出的三种技术对痛觉刺激效果有较好的促进作用,证明了这种痛觉刺激模式的可行性和可信性。  相似文献   
35.
Processes engaged when information is encoded into memory are an important determinant of whether that information will be recovered subsequently. Also influential, however, are processes engaged at the time of retrieval, and these were investigated here by using event-related potentials (ERPs) to measure a specific class of retrieval operations. These operations were revealed by contrasts between ERPs elicited by new (unstudied) test items in distinct tasks, the assumption being that these contrasts index operations that are engaged in service of retrieval and that vary according to the demands of different retrieval tasks. Specific functional accounts of this class of retrieval processing operations assume that they influence the accuracy of memory judgments, and this experiment was designed to test for the first time whether this is in fact the case. Toward this end, participants completed 2 retrieval tasks while ERPs were acquired, and the extent to which processes were engaged differentially across tasks in service of retrieval was operationalized as the magnitude of the differences between the new-item ERPs that were elicited. This measure correlated positively with response accuracy on the tasks, which provides strong evidence that this class of retrieval processing operations benefits the accuracy of memory judgments. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
36.
随着全球过敏人群数量的增加,食物过敏日益受到人们的关注。炎症性肠道疾病(inflammatory bowel disease,IBD)对食物过敏的发生具有重要的免疫学意义。越来越多的研究表明,食物过敏与IBD具有相似的流行病学研究数据、发病机制、临床症状以及治疗方法,并且IBD能够增加患者患食物过敏的几率。本文在阐述食物过敏与IBD发病率和临床症状相似性的基础上,重点讨论食物过敏与IBD的发病机制以及影响两种疾病发生的关联因素,最后概述针对IBD患者未来缓解以及避免食物过敏的方法和应对策略。通过了解食物过敏与IBD的关联性,可为认知IBD患者发生食物过敏的风险因素提供科学依据,并为预防及治疗IBD患者发生食物过敏提供新的研究思路和科学信息。  相似文献   
37.
Two experiments tested the hypothesis that alcohol increases race-biased responding via impairment of self-regulatory cognitive control. Participants consumed either a placebo or alcohol and then made speeded responses to stereotypic trait words presented after White and Black face primes while behavioral and event-related brain potential (ERP) data were recorded. Alcohol did not affect stereotype activation in either experiment. Experiment 2 showed that alcohol significantly impaired the ability to inhibit race-biased responses but did not reliably influence control of counterstereotypic responses. This disinhibition appears driven by impairment of regulative cognitive control, as indexed by amplitude of the negative slow wave ERP component. These findings suggest that controlling racial bias can be a function of effective implementation of basic self-regulatory processes in addition to the motivational processes identified in other research. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
38.
The solution of Markov Decision Processes (MDPs) often relies on special properties of the processes. For two-level MDPs, the difference in the rates of state changes of the upper and lower levels has led to limiting or approximate solutions of such problems. In this paper, we solve a two-level MDP without making any assumption on the rates of state changes of the two levels. We first show that such a two-level MDP is a non-standard one where the optimal actions of different states can be related to each other. Then we give assumptions (conditions) under which such a specially constrained MDP can be solved by policy iteration. We further show that the computational effort can be reduced by decomposing the MDP. A two-level MDP with M upper-level states can be decomposed into one MDP for the upper level and M to M(M-1) MDPs for the lower level, depending on the structure of the two-level MDP. The upper-level MDP is solved by time aggregation, a technique introduced in a recent paper [Cao, X.-R., Ren, Z. Y., Bhatnagar, S., Fu, M., & Marcus, S. (2002). A time aggregation approach to Markov decision processes. Automatica, 38(6), 929-943.], and the lower-level MDPs are solved by embedded Markov chains.  相似文献   
39.
针对中潜伏期听觉诱发脑电的特点,利用信号和噪声的小波变换模极大值在分解尺度上的不同特性来滤除中潜伏期听觉诱发脑电信号中的EEG强噪声成份,重构出真实的中潜伏期听觉诱发脑电信号。通过仿真实验表明:采用小波变换模极大值技术,可以有效地提取信号,为信号特征选取提供可靠的特征分析数据。  相似文献   
40.
以新疆库尔勒土壤模拟溶液为腐蚀介质(0.06 M Cl- 0.009 M SO2-4 0.001 7 M HCO3-),在阴极极化条件下,采用楔型缝隙模型研究了具有剥离涂层缺陷X70钢的缝隙腐蚀.楔型缝隙的一端封闭,另一开口端延伸到溶池(100 mm×100 mm×100 mm)的模拟溶液中.楔型缝隙的尺寸为深100 mm,宽45 mm,开口尺寸0.15~0.45 mm.将6条X70钢电极试样安装到缝隙中用以测定缝口不同距离处的局部电流密度、极化电位并监测试样的腐蚀状况.安装在缝隙上盖测量孔中的H 离子探头用于测量缝内的pH值.采用-0.85,-1.0和-1.15 V(相对于CSE)的阴极极化电位分别对缝口尺寸(δ)为 0.15,0.30和 0.45 mm的楔型缝隙进行阴极极化.试验结果表明,随着极化时间的延长,缝内局部电流密度和极化电位变得更为均匀,随着缝口控电位的降低以及缝口尺寸的增加,缝内的局部电流密度和pH值增加.缝口控电位相同时,从缝口到缝底的pH值先增加,然后达到一个较稳定的状态.缝口控电位越低以及缝口尺寸越大,pH值越易于达到稳定状态,且pH值开始增加的速率越小.  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