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   3879篇
  免费   148篇
  国内免费   1篇
电工技术   29篇
化学工业   837篇
金属工艺   31篇
机械仪表   59篇
建筑科学   133篇
矿业工程   10篇
能源动力   53篇
轻工业   790篇
水利工程   43篇
石油天然气   9篇
无线电   166篇
一般工业技术   374篇
冶金工业   1154篇
原子能技术   4篇
自动化技术   336篇
  2023年   26篇
  2022年   103篇
  2021年   112篇
  2020年   90篇
  2019年   70篇
  2018年   80篇
  2017年   83篇
  2016年   87篇
  2015年   77篇
  2014年   99篇
  2013年   230篇
  2012年   170篇
  2011年   198篇
  2010年   157篇
  2009年   169篇
  2008年   157篇
  2007年   164篇
  2006年   133篇
  2005年   133篇
  2004年   117篇
  2003年   108篇
  2002年   88篇
  2001年   61篇
  2000年   62篇
  1999年   57篇
  1998年   126篇
  1997年   94篇
  1996年   83篇
  1995年   60篇
  1994年   58篇
  1993年   50篇
  1992年   55篇
  1991年   24篇
  1990年   46篇
  1989年   58篇
  1988年   37篇
  1987年   50篇
  1986年   44篇
  1985年   40篇
  1984年   33篇
  1983年   20篇
  1982年   47篇
  1981年   24篇
  1980年   31篇
  1979年   17篇
  1978年   28篇
  1977年   19篇
  1976年   16篇
  1975年   17篇
  1973年   14篇
排序方式: 共有4028条查询结果,搜索用时 15 毫秒
51.
Logic languages based on the theory of rational, possibly infinite, trees have much appeal in that rational trees allow for faster unification (due to the safe omission of the occurs-check) and increased expressivity (cyclic terms can provide very efficient representations of grammars and other useful objects). Unfortunately, the use of infinite rational trees has problems. For instance, many of the built-in and library predicates are ill-defined for such trees and need to be supplemented by run-time checks whose cost may be significant. Moreover, some widely used program analysis and manipulation techniques are correct only for those parts of programs working over finite trees. It is thus important to obtain, automatically, a knowledge of the program variables (the finite variables) that, at the program points of interest, will always be bound to finite terms. For these reasons, we propose here a new data-flow analysis, based on abstract interpretation, that captures such information. We present a parametric domain where a simple component for recording finite variables is coupled, in the style of the open product construction of Cortesi et al., with a generic domain (the parameter of the construction) providing sharing information. The sharing domain is abstractly specified so as to guarantee the correctness of the combined domain and the generality of the approach. This finite-tree analysis domain is further enhanced by coupling it with a domain of Boolean functions, called finite-tree dependencies, that precisely captures how the finiteness of some variables influences the finiteness of other variables. We also summarize our experimental results showing how finite-tree analysis, enhanced with finite-tree dependencies, is a practical means of obtaining precise finiteness information.  相似文献   
52.
This paper deals with the influence of the testing equipment on impact load measurements. A previously developed method of analysis and processing of the experimental data based on a refined analogical model of the impact event and inverse problem techniques is used. This method makes it possible to obtain the mechanical response of the material, notwithstanding the disturbance of the dynamic effects associated to the test. Results from tests carried out both on falling weight and swing pendulum instrumented testing machines are compared. It is shown that this method can give an accurate estimation of the actual bending force in impact testing independent of the testing equipment.  相似文献   
53.
The corpus callosum has been proposed to contribute to attention by modulating resource allocation between the hemispheres and filtering interhemispheric signal transmission (M. T. Banich, 1998). The resource allocation hypothesis predicts that interhemispheric interactions become more advantageous with increasing resource demands. The selective filtering hypothesis predicts that interhemispheric interactions become less advantageous as filtering requirements increase. The authors tested both predictions by comparing within- and across-hemisphere letter matching under dual-task (Experiment 1) and selective attention conditions (Experiment 2). Task-specific resource demands (i.e., letter processing load) alter the bihemispheric advantage, but the general demand imposed by an unrelated secondary task does not. Filtering requirements influenced the advantage from interhemispheric interactions, providing new evidence for the role of the corpus callosum in selective attention. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
54.
The authors examined associations among parental and child adjustment, child syncope, somatic, and school problems. Participants were children (N = 56) ages 7-18 years with syncope. Measures included syncope severity, parental distress, and children's internalizing symptoms. For children diagnosed negative for neurocardiogenic syncope (NCS), their fathers' and their own psychological symptoms were positively associated with the severity of syncope, whereas their mothers' functioning was negatively associated with the severity of syncope. Also, for the negative NCS group, fathers' psychological functioning was associated with children's nonsyncope somatic complaints but not with their school problems. For the positive NCS group, few significant father-child associations were found, but several significant positive associations were revealed between mothers' psychological symptoms and their children's syncope as well as somatic and school problems. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
55.
The discovery of conjunctive causes--factors that act in concert to produce or prevent an effect--has been explained by purely covariational theories. Such theories assume that concomitant variations in observable events directly license causal inferences, without postulating the existence of unobservable causal relations. This article discusses problems with these theories, proposes a causal-power theory that overcomes the problems, and reports empirical evidence favoring the new theory. Unlike earlier models, the new theory derives (a) the conditions under which covariation implies conjunctive causation and (b) functions relating observable events to unobservable conjunctive causal strength. This psychological theory, which concerns simple cases involving 2 binary candidate causes and a binary effect, raises questions about normative statistics for testing causal hypotheses regarding categorical data resulting from discrete variables. (PsycINFO Database Record (c) 2011 APA, all rights reserved)  相似文献   
56.
Industrial control applications are usually developed in two phases: control design and real-time system implementation. In the control design stage a regulator is obtained and later it is translated into an algorithm in the implementation phase. Traditionally, these two phases have been developed in separate ways. Recently, some works have pointed out the necessity of the integration of the control design and its implementation. One of these works reduce the delay variance of control tasks (defined as the control action interval (CAI) and data acquisition interval (DAI) parameters) splitting every task into three parts. The CAI reduction method highly reduces the delay variance and improves the control performance. This work shows how to evaluate these delays under static and dynamic scheduling policies. A new task model is proposed in order to reduce the CAI and DAI parameters, which implies an improvement in the control performance. The new task model will be implemented in a real process, and the experimental measurements will show how, effectively, the control performance is highly improved with the methods presented in this paper.  相似文献   
57.
The use of medical services is a function of several interacting psychological and social variables as well as a function of physical malfunction. The clinical significance of addressing patients' psychosocial issues has only occasionally been considered. However, the shift in health care economics toward health care maintenance is responsible for the increased interest in interventions in the domain of behavioral medicine and health psychology. Evidence is reviewed for 6 mechanistic pathways by which behavioral interventions can maximize clinical care and result in significant economic benefits. The rationale for further integration of behavioral and biomedicine interventions is also reviewed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
58.
A comparison of two different styles of operator position in a trencher were compared using biomechanical principles and a field survey. A major postural difference between the two styles is the amount of time spent by the operators looking to the rear of their seated position. This was confirmed by a simple experiment. The style of position used in the skid steer type of trencher, facing the working tool, was found to be significantly better than the traditional fore-aft tractor style configuration.  相似文献   
59.
Immunotherapy has brought hope to the fight against glioblastoma, but its efficacy remains unclear. We present the case of CST, a 25-year-old female patient with a large right-hemisphere glioblastoma treated with a dendritic–tumor cell fusion vaccine. CST showed a near-complete tumor response, with a marked improvement in her functional status and simultaneous increases in tumor-specific CD8+ and CD4+ T cells. Two months before recurrence, the frequency of tumor-specific T cells decreased, while that of IL-17 and CD4+ T cells increased. CST passed away 15 months after enrollment. In this illustrative case, the tumor-specific CD4+ T-cell numbers and phenotype behaved as treatment efficacy biomarkers, highlighting the key role of the latter in glioblastoma immunotherapy.  相似文献   
60.
Hypobaric hypoxia is a condition that occurs at high altitudes (>2500 m) where the partial pressure of gases, particularly oxygen (PO2), decreases. This condition triggers several physiological and molecular responses. One of the principal responses is pulmonary vascular contraction, which seeks to optimize gas exchange under this condition, known as hypoxic pulmonary vasoconstriction (HPV); however, when this physiological response is exacerbated, it contributes to the development of high-altitude pulmonary hypertension (HAPH). Increased levels of zinc (Zn2+) and oxidative stress (known as the “ROS hypothesis”) have been demonstrated in the vasoconstriction process. Therefore, the aim of this review is to determine the relationship between molecular pathways associated with altered Zn2+ levels and oxidative stress in HPV in hypobaric hypoxic conditions. The results indicate an increased level of Zn2+, which is related to increasing mitochondrial ROS (mtROS), alterations in nitric oxide (NO), metallothionein (MT), zinc-regulated, iron-regulated transporter-like protein (ZIP), and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase-induced protein kinase C epsilon (PKCε) activation in the development of HPV. In conclusion, there is an association between elevated Zn2+ levels and oxidative stress in HPV under different models of hypoxia, which contribute to understanding the molecular mechanism involved in HPV to prevent the development of HAPH.  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