全文获取类型
收费全文 | 3476篇 |
免费 | 7篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 2篇 |
综合类 | 3篇 |
化学工业 | 24篇 |
金属工艺 | 3篇 |
机械仪表 | 2篇 |
建筑科学 | 9篇 |
矿业工程 | 1篇 |
能源动力 | 3篇 |
轻工业 | 10篇 |
石油天然气 | 1篇 |
武器工业 | 2篇 |
无线电 | 10篇 |
一般工业技术 | 10篇 |
冶金工业 | 3384篇 |
自动化技术 | 20篇 |
出版年
2022年 | 2篇 |
2021年 | 1篇 |
2020年 | 1篇 |
2017年 | 2篇 |
2016年 | 2篇 |
2014年 | 1篇 |
2013年 | 6篇 |
2012年 | 1篇 |
2011年 | 27篇 |
2010年 | 6篇 |
2009年 | 3篇 |
2008年 | 3篇 |
2006年 | 1篇 |
2005年 | 4篇 |
2004年 | 5篇 |
2003年 | 9篇 |
2002年 | 3篇 |
2000年 | 4篇 |
1999年 | 119篇 |
1998年 | 1127篇 |
1997年 | 656篇 |
1996年 | 393篇 |
1995年 | 194篇 |
1994年 | 178篇 |
1993年 | 229篇 |
1992年 | 13篇 |
1991年 | 28篇 |
1990年 | 27篇 |
1989年 | 42篇 |
1988年 | 33篇 |
1987年 | 33篇 |
1986年 | 16篇 |
1985年 | 25篇 |
1984年 | 1篇 |
1983年 | 7篇 |
1982年 | 17篇 |
1981年 | 13篇 |
1980年 | 26篇 |
1979年 | 1篇 |
1978年 | 10篇 |
1977年 | 75篇 |
1976年 | 136篇 |
1971年 | 1篇 |
1955年 | 3篇 |
排序方式: 共有3484条查询结果,搜索用时 15 毫秒
991.
Jeffery S. Horsburgh Amber Spackman Jones David K. Stevens David G. Tarboton Nancy O. Mesner 《Environmental Modelling & Software》2010,25(9):1031-1044
Characterizing spatial and temporal variability in the fluxes and stores of water and water borne constituents is important in understanding the mechanisms and flow paths that carry constituents to a stream and through a watershed. High frequency data collected at multiple sites can be used to more effectively quantify spatial and temporal variability in water quality constituent fluxes than through the use of low frequency water quality grab sampling. However, for many constituents (e.g., sediment and phosphorus) in-situ sensor technology does not currently exist for making high frequency measurements of constituent concentrations. In this paper we describe how water quality measures such as turbidity or specific conductance, which can be measured in-situ with high frequency, can be used as surrogates for other water quality constituents that cannot economically be measured with high frequency to provide continuous time series of water quality constituent concentrations and fluxes. We describe the observing infrastructure required to make high frequency estimates of water quality constituent fluxes based on surrogate data at multiple sites within a sensor network supporting an environmental observatory. This includes the supporting sensor, communication, data management, and data storage and processing infrastructure. We then provide a case study implementation in the Little Bear River watershed of northern Utah, USA, where a wireless sensor network has been developed for estimating total phosphorus and total suspended solids fluxes using turbidity as a surrogate. 相似文献
992.
Stress and modal analyses are performed on an ultrasonic vibration system by means of a 3-dimensional finite element computation and dynamic modal analysis code "Algor" The system consists of an edge-cracked specimen linked elastically with one or two amplifying horns which come into resonant longitudinal vibration at 20kHz.Operating principle of the ultrasonic fatigue machines and experimental procedures for ultrasonic fatigue crack growth studies are briefly presented. 相似文献
993.
KJ Haley ME Sunday BR Wiggs HP Kozakewich JJ Reilly SJ Mentzer DJ Sugarbaker CM Doerschuk JM Drazen 《Canadian Metallurgical Quarterly》1998,158(2):565-572
Asthmatic airways are infiltrated with inflammatory cells that release mediators and cytokines into the microenvironment. In this study, we evaluated the distribution of CD45-positive leukocytes and eosinophils in lung tissue from five patients who died with severe asthma compared with five patients with cystic fibrosis. For morphometric analysis, the airway wall was partitioned into an "inner" area (between basement membrane and smooth muscle) and an "outer" area (between smooth muscle and alveolar attachments). Large airways (with a perimeter greater than 3.0 mm) from patients with asthma or cystic fibrosis had a greater density of CD45-positive cells (p < 0.05) and eosinophils (p < 0.001) in the inner airway region compared with the same airway region in small airways. Furthermore, in small airways, asthmatic lungs showed a greater density of CD45-positive cells (p < 0.01) and eosinophils (p < 0.01) in the outer compared with the inner airway wall region. These observations indicate that there are regional variations in inflammatory cell distribution within the airway wall in patients with asthma that are not observed in airways from patients with cystic fibrosis. We speculate that this inflammatory cell density in peripheral airways in severe asthma may relate to the peripheral airway obstruction characteristic of this condition. 相似文献
994.
Classic adamantinoma of the long bones is a rare, low-grade malignant neoplasm arising most often in the tibia and usually in patients during the second to fifth decades. Although adamantinomas have been described in children, the histologic pattern in this age group is different from that seen in adults and resembles osteofibrous dysplasia. The usual pattern of adamantinoma in children has been termed "differentiated adamantinoma" and follows a benign course. We report a case of adamantinoma in the proximal tibia of a 3-year-old patient. The lesion had abundant epithelial component with formation of keratin pearls, a pattern that has been described only in classic adamantinoma occurring in adults. Since differentiated adamantinomas are essentially benign and classic adamantinomas are low-grade malignancies, the finding of a classic variant at this young age raised important therapeutic and prognostic issues. 相似文献
995.
Hemocyanins are giant oxygen transport proteins found in many arthropods and molluscs. Freely dissolved in the hemolymph, they are multisubunit proteins that contain many copies of the active site, a copper atom pair that reversibly binds oxygen. Octopus hemocyanin is composed of ten subunits, each of which contain seven oxygen-binding "functional units". The carboxyl-terminal 47 kDa functional unit, Odg, is a proteolytic isolate that binds oxygen reversibly while exhibiting slight Bohr and magnesium ion effects. In this work we present the X-ray structure determination and analysis of Odg at 2.3 A resolution. Odg has two structural domains: a largely alpha-helical copper binding domain, and a five-stranded anti-parallel beta-sandwich with the jelly roll topology found in many viruses. Six histidine residues ligate the copper atoms, one of which is involved in a thioether bridge. The results show that the hemocyanin from the mollusc and that from the arthropod have distinct tertiary folds in addition to the long recognized differences in their quaternary structures. Nonetheless, a comparison of Octopus and horseshoe crab hemocyanin reveals a similar active site, in a striking example of perhaps both convergent and divergent evolution. 相似文献
996.
OBJECTIVES: Autologous fat has been used as a bulking implant material for stress urinary incontinence. There is considerable controversy as to the ultimate fate of the grafted fat. This study was conducted to determine the fate of autogenous fat implanted into the bladder of rats. METHODS: Two groups of adult female rats were studied. In the test animals (group 1, n = 20), mesenteric adipose tissue (1 mL) was harvested and homogenized with an equal weight of sterile saline. Using a 25-gauge needle, 0.5 g of saline-fat mixture was injected into the dorsal bladder neck submucosa. Control animals (group 2, n = 12) were injected with sterile saline only. A subset of animals from each group were killed after 7, 35, 105, and 1 50 days, and the bladder and urethra were fixed. The fixed tissue was examined microscopically and photographed at each follow-up period. RESULTS: Seven days after injection of fat, there was a pronounced acute inflammatory reaction with numerous polymorphonuclear leukocytes and macrophages at the site of fat injection. There was minimal inflammatory reaction at the site of saline injection. By day 35, most of the fat had been eliminated by these phagocytes because of severe acute and chronic inflammation. By day 105, the submucosa tissue of the experimental rats had returned to normal visually and to a flat surface, lacking the appearance of a sizable "bulge" as shown at days 0 and 7. Histopathologic findings were also similar to the control rats. Inflammatory cells were no longer present by day 105. CONCLUSIONS: The implantation of homogenized, autologous fat in the rat urinary bladder submucosa causes acute and chronic inflammation and fat necrosis. The severe phagocytosis at the implant sites eliminates the vast majority of the devitalized implanted fat during the first month. 相似文献
997.
998.
ME Solov''eva VS Akatov VV Leshchenko AA Kudriavtsev 《Canadian Metallurgical Quarterly》1998,8(2):194-199
OBJECT: The goal of this study was to investigate the impact of mild or moderate degrees of degenerative or ischemic encephalopathy on predicting clinical outcome following unilateral posteroventral medial pallidotomy for treatment of advanced Parkinson's disease (PD). METHODS: Thirty-five patients with PD were studied prospectively. The presence and degree of cortical atrophy, ventriculomegaly, deep white matter lesions (DWML), periventricular lucencies (PVL), and the presence of lacunes and status cribriformis (multiple and bilateral enlarged Virchow-Robin spaces) were determined by magnetic resonance (MR) imaging before the patients underwent stereotactic pallidotomy performed according to a standard protocol. Clinical outcome was measured using a standard battery of tests including application of the Unified Parkinson's Disease Rating Scale (UPDRS). The preoperative MR imaging features were correlated with UPDRS subscores such as motor "off' score, the activities of daily living (ADL) off score, the off subscore for bradykinesia, the percentage of "on" time dyskinesias, and a global outcome rating. The MR findings were also correlated with the occurrence of side effects. Global outcome was rated as markedly improved in 22 patients (63%) and as moderately improved in 12 patients (34%) 6 months postoperatively. At the 1-year follow-up examination, global outcome in 31 patients was rated as markedly improved in 14 patients (45%), as moderately improved in another 14 (45%), as slightly improved in two (6%), and as worse in one patient (3%). The mean UPDRS motor off score changed from 58.7 preoperatively to 33.2 at 6 months and 33.4 at 1 year (p < 0.0001), the ADL off score from 31.8 to 18.2 at 6 months and 18.6 at 1 year (p < 0.0001), the off score from contralateral bradykinesia from 11.6 to 5.6 at 6 months and 4.1 at 1 year (p < 0.0001), and the percentage of awake time with dyskinesias from 37.4 to 17.4% at 6 months and 21.1% at 1 year (p < 0.0001). The presence of mild or moderate degrees of cortical atrophy, PVL, and DWML had no effect on clinical outcome. Patients with status cribriformis and those with lacunes tended to show comparatively less improvement in the UPDRS ADL off score (p = 0.014 and p = 0.016, respectively) at 6 months. This tendency was also present in patients with status cribriformis 1 year postoperatively (p = 0.046). Patients with both status cribriformis and lacunes had a higher incidence of transient altered mental status immediately postoperatively (p = 0.05). CONCLUSIONS: Mild-to-moderate degrees of cortical atrophy, ventriculomegaly, and ischemic encephalopathy do not predispose patients to less favorable outcomes following unilateral pallidotomy. Patients with both status cribriformis and lacunes have a higher risk of transient side effects; however, with regard to clinical outcome, these patients should not be denied surgical treatment. 相似文献
999.
K Schulze-Osthoff D Ferrari M Los S Wesselborg ME Peter 《Canadian Metallurgical Quarterly》1998,254(3):439-459
How do stimulus size and item number relate to the magnitude and direction of error on center estimation and line cancellation tests? How might this relationship inform theories concerning spatial neglect? These questions were addressed by testing twenty patients with right hemisphere lesions, eleven with left hemisphere lesions and eleven normal control subjects on multiple versions of center estimation and line cancellation tests. Patients who made large errors on these tests also demonstrated an optimal or pivotal stimulus value, i.e., a particular size center estimation test or number of lines on cancellation that either minimized error magnitude relative to other size stimuli (optimal) or marked the boundary between normal and abnormal performance (pivotal). Patients with right hemisphere lesions made increasingly greater errors on the center estimation test as stimuli were both larger and smaller than the optimal value, whereas those with left hemisphere lesions made greater errors as stimuli were smaller than a pivotal value. In normal subjects, the direction of errors on center estimation stimuli shifted from the right of true center to the left as stimuli decreased in size (i.e., the crossover effect). Right hemisphere lesions exaggerated this effect, whereas left hemisphere lesions diminished and possibly reversed the direction of crossover. Error direction did not change as a function of stimulus value on cancellation tests. The demonstration of optimal and pivotal stimulus values indicates that performances on center estimation and cancellation tests in neglect are only relative to the stimuli used. In light of other studies, our findings indicate that patients with spatial neglect grossly overestimate the size of small stimuli and underestimate the size of large stimuli, that crossover represents an "apparent" shift in error direction that actually results from normally occurring errors in size perception, and that the left hemisphere is specialized for one aspect of size estimation, whereas the right performs dual roles. 相似文献
1000.
The effects of practice on the functional anatomy observed in two different tasks, a verbal and a motor task, are reviewed in this paper. In the first, people practiced a verbal production task, generating an appropriate verb in response to a visually presented noun. Both practiced and unpracticed conditions utilized common regions such as visual and motor cortex. However, there was a set of regions that was affected by practice. Practice produced a shift in activity from left frontal, anterior cingulate, and right cerebellar hemisphere to activity in Sylvian-insular cortex. Similar changes were also observed in the second task, a task in a very different domain, namely the tracing of a maze. Some areas were significantly more activated during initial unskilled performance (right premotor and parietal cortex and left cerebellar hemisphere); a different region (medial frontal cortex, "supplementary motor area") showed greater activity during skilled performance conditions. Activations were also found in regions that most likely control movement execution irrespective of skill level (e.g., primary motor cortex was related to velocity of movement). One way of interpreting these results is in a "scaffolding-storage" framework. For unskilled, effortful performance, a scaffolding set of regions is used to cope with novel task demands. Following practice, a different set of regions is used, possibly representing storage of particular associations or capabilities that allow for skilled performance. The specific regions used for scaffolding and storage appear to be task dependent. 相似文献