全文获取类型
收费全文 | 1033篇 |
免费 | 3篇 |
专业分类
电工技术 | 5篇 |
化学工业 | 4篇 |
金属工艺 | 1篇 |
机械仪表 | 2篇 |
建筑科学 | 7篇 |
能源动力 | 6篇 |
轻工业 | 5篇 |
无线电 | 12篇 |
一般工业技术 | 8篇 |
冶金工业 | 973篇 |
自动化技术 | 13篇 |
出版年
2021年 | 1篇 |
2019年 | 1篇 |
2018年 | 1篇 |
2016年 | 1篇 |
2015年 | 1篇 |
2013年 | 6篇 |
2012年 | 1篇 |
2011年 | 3篇 |
2010年 | 7篇 |
2009年 | 5篇 |
2008年 | 4篇 |
2007年 | 2篇 |
2006年 | 3篇 |
2003年 | 4篇 |
2002年 | 3篇 |
2001年 | 4篇 |
2000年 | 4篇 |
1999年 | 31篇 |
1998年 | 304篇 |
1997年 | 170篇 |
1996年 | 100篇 |
1995年 | 61篇 |
1994年 | 72篇 |
1993年 | 60篇 |
1992年 | 4篇 |
1991年 | 5篇 |
1990年 | 3篇 |
1989年 | 8篇 |
1988年 | 8篇 |
1987年 | 9篇 |
1986年 | 7篇 |
1985年 | 7篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 7篇 |
1980年 | 11篇 |
1979年 | 1篇 |
1978年 | 3篇 |
1977年 | 31篇 |
1976年 | 70篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1970年 | 1篇 |
1966年 | 2篇 |
1954年 | 2篇 |
排序方式: 共有1036条查询结果,搜索用时 16 毫秒
991.
We have devised an advanced computer-controlled system (ADEPT) for the objective evaluation of endoscopic task performance. The system's hardware consists of a dual gimbal mechanism that accepts a variety of 5.0-mm standard endoscopic instruments for manipulation in a precisely mapped and enclosed work space. The target object consists of a sprung base plate incorporating various tasks. It is covered by a sprung perforated transparent top plate that has to be moved and held in the correct position by the operator to gain access to the various tasks. Standard video endoscope equipment provides the visual interface between the operator and the target-instrument field. Different target modules can be used, and the level of task difficulty can be adjusted by varying the manipulation, elevation, and azimuth angles. The system's software is designed to (a) prompt the surgeon with the information necessary to perform the task, (b) collect and collate data on performance during execution of specified tasks, and (c) save the data for future analysis. The system was alpha and beta tested to ensure that all functions operated correctly. 相似文献
992.
993.
994.
G Vescovo R Zennaro M Sandri U Carraro C Leprotti C Ceconi GB Ambrosio L Dalla Libera 《Canadian Metallurgical Quarterly》1998,30(11):2449-2459
Congestive heart failure (CHF) is characterized by a limb skeletal muscle myopathy with shift from the slow aerobic, fatigue resistant fibers, to the fast, anaerobic ones, and muscle bulk loss. Apoptosis (A) has been recently demonstrated to play a role in several cardiovascular diseases. AIM OF THE STUDY: we have investigated the role of A in the skeletal muscle of the hindlimbs in an experimental model of CHF. ANIMALS AND METHODS: CHF was induced in 7 males 80-100 g Sprague-Dawley rats with 30 mg/kg monocrotaline. Five age and diet matched controls were also studied. The time course of A was also studied in additional animals at day 0, 17, 24 and 30 days. RESULTS: At day 27 the electrophoretic analysis of myosin heavy chains (MHCs) demonstrated in the CHF rats the occurrence of a myopathy, with disappearance of slow MHC1 in the Tibialis Anterior (TA), and a significant shift from the slow to the fast isoforms in the soleus and EDL. With in situ DNA nick-end labelling (TUNEL) we found in the TA of CHF animals a significantly higher number of TUNEL positive nuclei (0.43 +/- 0.24 v 0.08 +/- 0.02, P<0.02 and TUNEL positive myonuclei (0.031 +/- 0.012 v 0.0025 +/- 0.005, P<0.02). The time course of A showed a progressive rise in interstitial and myocyte A, accompanied by a drop in fibers cross-sectional area and muscle weight/body weight, that came out to be significant at 30 days. Western blot showed a lower expression of Bcl-2 at 27 days and a further drop at 30 days in the CHF rats. Double staining for TUNEL and antibody against anti-MHC2a and anti MHC2b + 2x showed that A occurs non-selectively in all the myofiber types. BetaANP and Right Ventricle Mass/Volume (RVM/V) correlated significantly with total apoptotic nuclei. CONCLUSIONS: In CHF myofibers A can lead to muscle atrophy. Endothelial cells A may produce an imbalance in myofibres nutrition with relative ischemia that triggers the preferential synthesis of fast anaerobic myosin as an adaptive mechanism or alternatively induce myofibres death. 相似文献
995.
N Prato D Peloso A Franconeri G Tegaldo GB Ravera E Silvestri LE Derchi 《Canadian Metallurgical Quarterly》1998,8(9):1639-1646
The aim of this study was to test whether the anterior tilt of the acromion can be objectively evaluated on lateral radiographs, and whether there is a relation between this anatomical feature and the most common shoulder diseases. Lateral radiographs of 15 dried scapulas were performed in neutral position and with 5 degrees of caudal, cranial, anterior and posterior angulations. Two hundred and forty-three shoulders, both asymptomatic and affected by chronic and post-traumatic impingement, calcific tendinitis and instability, were examined by conventional radiography. The presence of rotator-cuff tears was investigated by sonography. A method was elaborated to obtain reproducible lateral radiographs and to determine the acromial tilt angle. Inter- and intraobserver and inter- and intraoperator variations in measurements were evaluated. Variations in tube angulation produced changes in tilt-angle values on dried scapulas. The average tilt angle for the chronic impingement and the instability groups were significantly different from the post-traumatic, calcific tendinitis and control groups. Rotator-cuff tears were significantly more frequent in the chronic impingement group and related to a more acute tilt angle. The inter- and intraobserver variability coefficients were 0.95 and 0.98, whereas the inter- and intraoperator variability coefficients were 0.94 and 0.96, respectively. Conventional radiography using fluoroscopy for positioning is a well-reproducible method for the evaluation of acromial tilt. There is a significant difference in tilt-angle values between some groups of subjects examined, but the lack of specificity limits the clinical importance of such measurement. 相似文献
996.
Spreading depression (SD) of electroencephalographic activity is a dynamic wave phenomenon in the central nervous system (CNS). The retina, especially the isolated chicken retina, is an excellent constituent of the CNS in which to observe the dynamic behavior of the SD wave fronts, because it changes its optical properties during a SD attack. The waves become visible as milky fronts on a black background. It is still controversial what the basic mechanistic steps of SD are, but certainly SD belongs to the self-organization phenomena occurring in neuronal tissue. In this work, spiral-shaped wave fronts are analyzed using digital video imaging techniques. We report how the inner end of the wave front, the spiral tip, breaks away repeatedly. This separation process is associated with a Z-shaped trajectory (extension approximately 1.2 mm) that is described by the tip over one spiral revolution (period 2.45+/-0.1 min). The Z-shaped trajectory does not remain fixed, but performs a complex motion across the retina with each period. This is the first time, to our knowledge, that established imaging methods have been applied to the study of the two-dimensional features of SD wave propagation and to obtaining quantitative data of their dynamics. Since these methods do not interfere with the tissue, it is possible to observe the intrinsic properties of the phenomenon without any external influence. 相似文献
997.
998.
GB Hunt 《Canadian Metallurgical Quarterly》1995,24(2):172-175
Skin fold advancement flaps can be created from the elbow and flank folds to close large wounds in the pectoral and inguinal regions of cats and dogs, respectively. The attachments of the laterally facing (outer) and medially facing (inner) layers of the skin fold to the adjacent limb are divided to produce a U-shaped pedicle graft attached to the trunk. This mobilizes skin that can be advanced over large wounds involving the ventral chest or abdomen, or both. The use of skin fold advancement flaps enables direct closure of large skin defects without undue tension and without compromising the mobility of the adjacent limb. 相似文献
999.
1000.