首页 | 官方网站   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   392篇
  免费   22篇
工业技术   414篇
  2023年   7篇
  2022年   3篇
  2021年   7篇
  2020年   7篇
  2019年   9篇
  2018年   9篇
  2017年   11篇
  2016年   7篇
  2015年   8篇
  2014年   15篇
  2013年   16篇
  2012年   18篇
  2011年   20篇
  2010年   21篇
  2009年   14篇
  2008年   19篇
  2007年   12篇
  2006年   14篇
  2005年   13篇
  2004年   13篇
  2003年   9篇
  2002年   6篇
  2001年   6篇
  2000年   5篇
  1999年   4篇
  1998年   16篇
  1997年   9篇
  1996年   6篇
  1995年   4篇
  1994年   5篇
  1993年   4篇
  1991年   5篇
  1989年   3篇
  1985年   3篇
  1979年   5篇
  1978年   4篇
  1977年   2篇
  1976年   6篇
  1975年   9篇
  1974年   5篇
  1973年   3篇
  1972年   2篇
  1970年   3篇
  1968年   2篇
  1966年   5篇
  1940年   3篇
  1938年   4篇
  1928年   2篇
  1915年   2篇
  1911年   2篇
排序方式: 共有414条查询结果,搜索用时 806 毫秒
1.
Anaerobic co-digestion of organic wastes from households, slaughterhouses and meat processing industries was optimised in a half technical scale plant. The plant was operated for 130 days using two different substrates under organic loading rates of 10 and 12 kgCOD.m(-3).d(-1). Since the substrates were rich in fat and protein components (TKN: 12 g.kg(-1) the treatment was challenging. The process was monitored on-line and in the laboratory. It was demonstrated that an intensive and stable co-digestion of partly hydrolysed organic waste and protein rich slaughterhouse waste can be achieved in the balance of inconsistent pH and buffering NH4-N. In the first experimental period the reduction of the substrate COD was almost complete in an overall stable process (COD reduction >82%). In the second period methane productivity increased, but certain intermediate products accumulated constantly. Process design options for a second digestion phase for advanced degradation were investigated. Potential causes for slow and reduced propionic and valeric acid degradation were assessed. Recommendations for full-scale process implementation can be made from the experimental results reported. The highly loaded and stable codigestion of these substrates may be a good technical and economic treatment alternative.  相似文献   
2.
1前言及历史背景 为避免钢水造成燃烧或破碎引起对人体的可能伤害,必须对连铸平台的平面布置进行分析.  相似文献   
3.
Between July 1993 and December 1994 five term infants of mothers with Graves' disease were hospitalised at the Frühgeburtenstation of the Univ.-Frauenklinik Graz. Four Mothers had elevated TSH-receptor-antibody (TRAb)--levels during pregnancy, one had normalised TRAb-titers. In one case hyperthyroidism was first diagnosed during pregnancy. Three newborns had elevated TRAb-titers; in one of them thyrotoxicosis was diagnosed clinically and biochemically at the second day of life, one newborn had mild hyperthyroidism with tachycardia at the end of the first week of life and one newborn was asymptomatic by immediately initiated therapy. The two other newborns had normal thyroid hormone and antibody levels and no symptoms or signs of hyperthyroidism. The cases are reported and discussed in detail and our overall approach to diagnosis and treatment of neonatal hyperthyroidism in case of maternal Graves' disease will be given.  相似文献   
4.
BACKGROUND: This study evaluated the perceptions of patients with breast cancer of their medical interactions with providers. The determinants and psychological consequences of communication problems also were examined. METHODS: Ninety-seven patients with Stage I or II breast cancer completed a set of validated questionnaires before initiating postoperative therapy. Data on psychological distress were collected at baseline and 3-month follow-up, and multivariate models were fit to explain the relationship between pretreatment communication problems and subsequent psychological distress. Data on clinical variables were abstracted from medical records. RESULTS: A substantial proportion of patients (84%) reported difficulties communicating with the medical team. Communication problems were more common among patients who were less optimistic about their disease and had less assertive coping styles. Patient-reported communication problems were associated with increased anxiety, depression anger, and confusion at the 3-month follow-up. The association between communication problems and mood disturbance remained significant, although small, after adjusting for baseline mood disturbance, demographic, clinical, and coping style variables. CONCLUSION: Interventions that enhance communication between patients with breast cancer and their providers may improve patients' psychological adjustment to treatment. Conversely, interventions that lower distress and modify coping style may enhance communication.  相似文献   
5.
This paper deals dynamically with the question of how recruitment to terror organizations is influenced by counter-terror operations. This is done within an optimal control model, where the key state is the (relative) number of terrorists and the key controls are two types of counter-terror tactics, one (“water”) that does not and one (“fire”) that does provoke recruitment of new terrorists. The model is nonlinear and does not admit analytical solutions, but an efficient numerical implementation of Pontryagin's minimum principle allows for solution with base case parameters and considerable sensitivity analysis. Generally, this model yields two different steady states, one where the terror organization is nearly eradicated and one with a high number of terrorists. Whereas water strategies are used at almost any time, it can be optimal not to use fire strategies if the number of terrorists is below a certain threshold.  相似文献   
6.
7.
At the core of luminescence color and lifetime tuning of rare earth doped upconverting nanoparticles (UCNPs), is the understanding of the impact of the particle architecture for commonly used sensitizer (S) and activator (A) ions. In this respect, a series of core@shell NaYF4 UCNPs doped with Yb3+ and Ho3+ ions are presented here, where the same dopant concentrations are distributed in different particle architectures following the scheme: YbHo core and YbHo@…, …@YbHo, Yb@Ho, Ho@Yb, YbHo@Yb, and Yb@YbHo core–shell NPs. As revealed by quantitative steady‐state and time‐resolved luminescence studies, the relative spatial distribution of the A and S ions in the UCNPs and their protection from surface quenching has a critical impact on their luminescence characteristics. Although the increased amount of Yb3+ ions boosts UCNP performance by amplifying the absorption, the Yb3+ ions can also efficiently dissipate the energy stored in the material through energy migration to the surface, thereby reducing the overall energy transfer efficiency to the activator ions. The results provide yet another proof that UC phosphor chemistry combined with materials engineering through intentional core@shell structures may help to fine‐tune the luminescence features of UCNPs for their specific future applications in biosensing, bioimaging, photovoltaics, and display technologies.  相似文献   
8.
9.
We study a family of problems, called Maximum Solution (Max Sol), where the objective is to maximise a linear goal function over the feasible integer assignments to a set of variables subject to a set of constraints. When the domain is Boolean (i.e. restricted to {0,1}), the maximum solution problem is identical to the well-studied Max Ones problem, and the complexity and approximability is completely understood for all restrictions on the underlying constraints. We continue this line of research by considering the Max Sol problem for relations defined by regular signed logic over finite subsets of the natural numbers; the complexity of the corresponding decision problem has recently been classified by Creignou et al. (Theory Comput. Syst. 42(2):239–255, 2008). We give sufficient conditions for when such problems are polynomial-time solvable and we prove that they are APX-hard otherwise. Similar dichotomies are also obtained for variants of the Max Sol problem.  相似文献   
10.
A comparison is made between synchronous motors and induction motors with regard to industrial power system stability. Representation of motor loads in stability studies is reviewed. The specific system studied is an infinite bus supplying a combination induction and synchronous motor load through a transmission line and transformer. The system is subjected to a fault at the transformer and critical values of fault clearing time are computer calculated for ratios of synchronous motor load to induction motor load from zero to unity. The effect of variation of motor parameters on clearing times is discussed.  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-23

京公网安备 11010802026262号