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   458篇
  免费   13篇
  国内免费   2篇
电工技术   6篇
综合类   1篇
化学工业   60篇
金属工艺   7篇
机械仪表   11篇
建筑科学   14篇
能源动力   28篇
轻工业   46篇
水利工程   5篇
石油天然气   3篇
武器工业   1篇
无线电   51篇
一般工业技术   107篇
冶金工业   60篇
原子能技术   5篇
自动化技术   68篇
  2023年   2篇
  2022年   14篇
  2021年   11篇
  2020年   9篇
  2019年   10篇
  2018年   5篇
  2017年   7篇
  2016年   14篇
  2015年   6篇
  2014年   19篇
  2013年   17篇
  2012年   24篇
  2011年   27篇
  2010年   16篇
  2009年   20篇
  2008年   26篇
  2007年   28篇
  2006年   25篇
  2005年   20篇
  2004年   18篇
  2003年   14篇
  2002年   13篇
  2001年   8篇
  2000年   5篇
  1999年   11篇
  1998年   12篇
  1997年   13篇
  1996年   7篇
  1995年   13篇
  1994年   2篇
  1993年   9篇
  1992年   3篇
  1991年   2篇
  1990年   3篇
  1989年   3篇
  1988年   2篇
  1987年   2篇
  1986年   3篇
  1985年   6篇
  1983年   2篇
  1982年   2篇
  1980年   1篇
  1979年   2篇
  1978年   1篇
  1977年   3篇
  1976年   5篇
  1975年   3篇
  1973年   1篇
  1972年   1篇
  1968年   1篇
排序方式: 共有473条查询结果,搜索用时 15 毫秒
61.
Metallic cobalt nanoparticles were synthesized by hydrogen reduction method. Particles were coated in situ with carbon by adding ethene to reaction flow. Particles were characterized by transmission electron microscopy, energy dispersive X-ray emission, X-ray diffraction, X-ray fluorescence and BET method. The observed cobalt particle size distributions in different cobalt batches produced with unvarying reaction parameters was reproducible: The mean diameter of primary cobalt particle varied only 5% from the mean value of 76 nm in different batches. Increased carbon precursor concentration decreased mean diameter of cobalt particles to 17 nm. The produced nanoparticles were used as filler material in 0–3 type metalpolymer composites. Composite samples with varying filler loading were fabricated with mixing extrusion and injection moulding techniques. The magnetic properties of the fabricated composites were measured up to 1 GHz. In order to analyse the particle distribution in composite matrix and its effect on magnetic properties the microstructure was studied.  相似文献   
62.
63.
Cardiovascular abnormality-mediated retinal ischemia causes severe visual impairment. Retinal ischemia is involved in enormous pathological processes including oxidative stress, reactive gliosis, and retinal functional deficits. Thus, maintaining retinal function by modulating those pathological processes may prevent or protect against vision loss. Over the decades, nicotinamide mononucleotide (NMN), a crucial nicotinamide adenine dinucleotide (NAD+) intermediate, has been nominated as a promising therapeutic target in retinal diseases. Nonetheless, a protective effect of NMN has not been examined in cardiovascular diseases-induced retinal ischemia. In our study, we aimed to investigate its promising effect of NMN in the ischemic retina of a murine model of carotid artery occlusion. After surgical unilateral common carotid artery occlusion (UCCAO) in adult male C57BL/6 mice, NMN (500 mg/kg/day) was intraperitoneally injected to mice every day until the end of experiments. Electroretinography and biomolecular assays were utilized to measure ocular functional and further molecular alterations in the retina. We found that UCCAO-induced retinal dysfunction was suppressed, pathological gliosis was reduced, retinal NAD+ levels were preserved, and the expression of an antioxidant molecule (nuclear factor erythroid-2-related factor 2; Nrf2) was upregulated by consecutive administration of NMN. Our present outcomes first suggest a promising NMN therapy for the suppression of cardiovascular diseases-mediated retinal ischemic dysfunction.  相似文献   
64.
Carriers of GBA1 gene variants have a significant risk of developing Parkinson’s disease (PD). A cohort study of GBA carriers between 40–75 years of age was initiated to study the presence of prodromal PD features. Participants underwent non-invasive tests to assess different domains of PD. Ninety-eight unrelated GBA carriers were enrolled (43 males) at a median age (range) of 51 (40–74) years; 71 carried the N370S variant (c.1226A > G) and 25 had a positive family history of PD. The Montreal Cognitive Assessment (MoCA) was the most frequently abnormal (23.7%, 95% CI 15.7–33.4%), followed by the ultrasound hyperechogenicity (22%, 95% CI 14–32%), Unified Parkinson’s Disease Rating Scale part III (UPDRS-III) (17.2%, 95% CI 10.2–26.4%), smell assessment (12.4%, 95% CI 6.6–20.6%) and abnormalities in sleep questionnaires (11%, 95% CI 5.7–19.4%). Significant correlations were found between tests from different domains. To define the risk for PD, we assessed the bottom 10th percentile of each prodromal test, defining this level as “abnormal”. Then we calculated the percentage of “abnormal” tests for each subject; the median (range) was 4.55 (0–43.5%). Twenty-two subjects had more than 15% “abnormal” tests. The limitations of the study included ascertainment bias of individuals with GBA-related PD in relatives, some incomplete data due to technical issues, and a lack of well-characterized normal value ranges in some tests. We plan to enroll additional participants and conduct longitudinal follow-up assessments to build a model for identifying individuals at risk for PD and investigate interventions aiming to delay the onset or perhaps to prevent full-blown PD.  相似文献   
65.
Oxidative processes in meat lead to meat quality deterioration. Meat has endogenous antioxidants and prooxidants, but information on factors influencing the activity of antioxidant enzymes in meat is limited. Lipolytic and proteolytic enzymes are involved in important aspects of meat quality. Our objective was to find differences between five different genotypes on the activity of antioxidant, lipolytic and proteolytic enzymes in meat. Forty Psoas major muscles of females of five different pig genotypes were used, Pietrain, Landrace, Large-White, lberian, and lberian×Duroc. Pre slaughter conditions were similar for all the genotypes. After slaughter, muscles were vacuum packed and frozen at -20?°C until required. Differences between genotypes were found for the activity of catalase and SOD, while GSH-Px showed no differences. The highest differences between breeds were found for the lberian breed where catalase had the highest activity. Catalase activity also showed differences between the white pigs, with large values for LR and lower activities in P. There were no differences in neutral lipase activities between the different genotypes while acid lipase and phospholipase showed significant differences. The activities of cathepsin B and H were significantly lower for Iberian pigs compared with other breeds except LR, while the ratio of cathepsin B+L/cathepsin B was higher in Iberian. The differences between genotypes found in enzyme activities suggest some genetic effects on the antioxidant, lipolytic and proteolitytic activity of pork meat.  相似文献   
66.
I. D. Yalom's (1995) hypothesis that group therapy cohesiveness is the precursor to the development of group-derived collective self-esteem (CSE), hope for the self (HS), and psychological well-being (personal self-esteem and depression) was tested. Participants were 102 university counseling center group therapy clients from process (n = 54) and theme (n = 48) groups. Path analyses supported Yalom's theory that cohesiveness is the primary group factor and that it directly related to curative group factors such as CSE and HS. Additional path analyses showed that the relationship between group therapy CSE and personal self-esteem was moderated by HS, such that a significant relationship between CSE and personal self-esteem was no longer found once HS was entered into the model. Implications of these findings for research and practice are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
67.
Transient electromagnetic fields are produced when breakers, disconnectors, and switches of various types are operated under varying load conditions. For analysis purposes, a discharge current pulse is assumed during switching operations, which can act as a dipole antenna. The transient electromagnetic fields of this antenna can be calculated for near-and far-field conditions.  相似文献   
68.
Designers and creative artists use computer graphics and image processing effects on stall photographs in application areas such as advertising entertainment broadcasting and the arts Most of the effects available in research arid commercial work are two-dimensional in nature, for example image processing filters [blur, edge enhancement) and creative effects (tilings, reflections) There is almost no usage of information taken from the 3-D world in which the objects appearing an the image are located. In this paper we present a novel method for creating 3-D effects on photographs or in general on any image created by rendering a 3-D world The artist interacts with the image using a set of intuitive direct manipulation interface objects These objects let the user define a 3-D model, display at, and manipulate it in a 3-D space which is correlated with that of the input image. The generated model can be an arbitrarily complex 3-D polyhedron Any texture, including texture taken from the input photograph, can be mapped into any of its faces arid used for special effects We discuss and show examples for effects such as copy and paste, motion blur, model editing and deformations lighting effects, and shadows.  相似文献   
69.
Components of cellular stress responses can be identified by correlating changes in stress tolerance with gain or loss of function of defined genes. Previous work has shown that yeast cells deficient in Ppz1 protein phosphatase or overexpressing Hal3p, a novel regulatory protein of unknown function, exhibit increased resistance to sodium and lithium, whereas cells lacking Hal3p display increased sensitivity. These effects are largely a result of changes in expression of ENA1, encoding the major cation extrusion pump of yeast cells. Disruption or overexpression of HAL3 (also known as SIS2) has no effect on salt tolerance in the absence of PPZ1, suggesting that Hal3p might function upstream of Ppz1p in a novel signal transduction pathway. Hal3p is recovered from crude yeast homogenates by using immobilized, bacterially expressed Ppz1p fused to glutathione S-transferase, and it also copurifies with affinity-purified glutathione S-transferase-Ppz1p from yeast extracts. In both cases, the interaction is stronger when only the carboxyl-terminal catalytic phosphatase domain of Ppz1p is expressed. In vitro experiments reveal that the protein phosphatase activity of Ppz1p is inhibited by Hal3p. Overexpression of Hal3p suppresses the reduced growth rate because of the overexpression of Ppz1p and aggravates the lytic phenotype of a slt2/mpk1 mitogen-activated protein kinase mutant (thus mimicking the deletion of PPZ1). Therefore, Hal3p might modulate diverse physiological functions of the Ppz1 phosphatase, such as salt stress tolerance and cell cycle progression, by acting as a inhibitory subunit.  相似文献   
70.
The polarizability of gyrotropic spheres is studied in this short article. Gyrotropic media are anisotropic in two respects: the symmetric part of the permittivity dyadic is uniaxial, and furthermore, there is also antisymmetric part in the permittivity. The polarizability is also dyadic with its components depending on the relations of the permittivity components of the material.  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