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   464篇
  免费   33篇
电工技术   7篇
综合类   1篇
化学工业   76篇
金属工艺   12篇
机械仪表   7篇
建筑科学   6篇
矿业工程   1篇
能源动力   10篇
轻工业   29篇
水利工程   1篇
无线电   45篇
一般工业技术   73篇
冶金工业   89篇
原子能技术   7篇
自动化技术   133篇
  2023年   6篇
  2022年   10篇
  2021年   13篇
  2020年   18篇
  2019年   9篇
  2018年   20篇
  2017年   11篇
  2016年   25篇
  2015年   12篇
  2014年   24篇
  2013年   32篇
  2012年   26篇
  2011年   28篇
  2010年   21篇
  2009年   19篇
  2008年   19篇
  2007年   15篇
  2006年   13篇
  2005年   12篇
  2004年   11篇
  2003年   11篇
  2002年   4篇
  2001年   6篇
  2000年   5篇
  1999年   9篇
  1998年   24篇
  1997年   22篇
  1996年   9篇
  1995年   10篇
  1994年   5篇
  1993年   6篇
  1992年   2篇
  1991年   2篇
  1988年   2篇
  1985年   3篇
  1984年   1篇
  1982年   1篇
  1981年   1篇
  1980年   2篇
  1979年   1篇
  1978年   3篇
  1977年   3篇
  1976年   8篇
  1975年   4篇
  1974年   2篇
  1973年   1篇
  1972年   1篇
  1971年   1篇
  1970年   1篇
  1968年   2篇
排序方式: 共有497条查询结果,搜索用时 15 毫秒
51.
In this paper, a method based on an integral formulation with an excitation term is presented. The particularities of this approach lie in the utilization of entire domain trial functions and in the characterization of the coupling effect due to the excitation mechanism. The trial functions are taken as the TE-TM modes of a waveguide whose cross section corresponds to the shape of the discontinuity. The trial functions are computed and stored in the memory, then the study of complex planar structures becomes easy. A complete study is proposed, including the analysis of the coupling mechanism due to the source interaction and the characterization of higher order modes influence. This work is followed by two applications: a multiaxial discontinuity (bend discontinuity) in microstrip and in CPW. The computed results have been compared with data furnished by the literature. A good accuracy has been obtained  相似文献   
52.
The limit of penetration of a given coal-tar pitch into two cokes during mixing of the coke and liquid tar has been studied. It was shown that tar penetration is limited by compression of gas occluded in pores. Mercury porosimetry of cokes and pyrolysed coke-tar mixtures as well as micrographs of cokes impregnated with tar allow one to estimate the limiting pore diameter of tar penetration into coke at ca. 6 μm for the system considered.  相似文献   
53.
54.
Asked a total of 84 children and adults in 4 age groups (means = 5.11, 7.8, 9.8, 11.5, and 24.4 yrs) to match, by the method of adjustment, the lengths of 2 horizontal lines staggered so as to form 2 sides of a parallelogram under 2 main conditions (variable over the standard or standard over the variable) and a control condition (variable and standard in prolongation). Results show that the variable was generally overestimated, this overestimation did not differ significantly from 1 condition to another, and this overestimation decreased significantly with age. Results suggest that this systematic error would not be attributed to the top positioning but rather to the movement of the variable, which would be a source of overestimation by drawing the relative frequency of S's perceptive centrations. The decrement of the error with age could be explained by the development of perceptual activity, allowing a more balanced centration on the standard and the variable. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
55.
Multiple endocrine neoplasias (MEN) are familial diseases characterized by endocrine neoplasms and transmitted in an autosomal dominant manner. In MEN type 1, the major lesions affect parathyroid glands, pancreatic islet cells and anterior pituitary. The MEN-1 gene has been mapped to chromosome 11q13 and a set of DNA-polymorphic markers localized close to this region provides a useful tool for presymptomatic diagnosis in MEN-1 families. MEN type 2 refers to the inherited forms of medullary thyroid carcinoma (MTC) associated or not with pheochromocytoma and hyperparathyroidism. In MEN-2, germinal mutations of the C-RET proto-oncogene which is localized on chromosome 10q11 have been found in the three clinical and allelic forms of the syndrome respectively, MEN-2 type A, B and familial isolated MTC. Mutations of C-RET are found in more than 90% of MEN-2 patients and genetic screening leads to accurate risk evaluation in families and consequently a preventive treatment of MTC and adrenal neoplasms. Recent discoveries on MEN syndromes and related familial endocrine disorders have a major clinical impact and allow a better understanding of the physiological pathways involved in familial as well as in sporadic endocrine tumor pathogenesis.  相似文献   
56.
The levels of resistance to pristinamycin (Pt) and to its major constituents, pristinamycin IIA and IB (PIIA and PIB, respectively; classified as streptogramins A and B, respectively) were determined for 126 staphylococcal isolates. The results suggest tentative susceptibility breakpoints of < or = 2, < or = 8, and < or = 0.5 microgram/ml for PIIA, PIB, and Pt, respectively. Fifty-six isolates that were inhibited by > or = 4 micrograms of PIIA per ml were investigated for the presence of staphylococcal genes encoding resistance to PIIA (vga, vat, and vatB) and PIB (vgb). None of these genes was found in the 4 isolates inhibited by 4 micrograms of PIIA per ml or in 4 of the other 52 isolates tested. The remaining 48 isolates harbored plasmids carrying vatB and vga or combinations of genes (vga-vat-vgb or vga-vat). The absence of any known PIIA resistance gene from the four Staphylococcus aureus isolates inhibited by > or = 8 micrograms of PIIA per ml suggests that there is at least one PIIA resistance mechanism in staphylococci that has not yet been characterized.  相似文献   
57.
58.
The motion of a SECM tip above a substrate generates a flow of the surrounding fluid. Finite element calculations show that this flow is a simple linear-shear flow (Couette flow) for small tip-substrate separations and deviates from Couette's law at larger ones. The effect of fluid flow on the tip current response was determined numerically. Different mass-transfer regimes are observed depending on the insulating or conducting nature of the substrate, the tip speed (or fluid velocity), and the tip-substrate separation. Those observations are tested experimentally, and good agreement is obtained between numerical and experimental results.  相似文献   
59.
Administered 2 tasks bearing on the perception and concept of relative velocity to 7-, 9-, 11-, and 13-yr-old children (24 at each age level). The perceptual task presented an illusion created by the movement of a target on a moving background, while the conceptual task was a modified version of Piaget's technique. In each task the 2 movements involved were either in the same (MS) or in the opposite direction. It was found that the illusion appeared earlier than the corresponding concept under the MS condition. The possibility of a retroactive effect of the concept on the percept is suggested. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
60.
In a study of the relation between foot pain and disability, a cross-sectional analysis was performed using baseline data (1992-1995) from the Women's Health and Aging Study, a population-based study of 1,002 disabled women aged 65 years and older living in Baltimore, Maryland. Chronic and severe foot pain, defined as pain lasting 1 month or longer in the previous year, plus pain in the previous month rated severe (7-10 on a scale of 0 to 10), was reported by 14% of the women. Severe foot pain was more common in women who were younger (aged 65-74 years), obese, or had hand or knee osteoarthritis. Walking speed and five repeated chair stands were slower in women with foot pain. After adjustment for age, body mass index, race, education, self-rated health, smoking status, comorbidities, and number of other pain sites, severe foot pain was independently associated with increased risk for walking difficulty (adjusted odds ratio = 1.69, 95% confidence interval 1.10-2.59) and disability in activities of daily living (adjusted odds ratio = 1.91, 95% confidence interval 1.21-3.01). These findings suggest that severe foot pain may play a key role in disability in older women. Further studies are warranted to confirm these results longitudinally and to determine whether interventions to alleviate foot pain could reduce or prevent disability in older women.  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