全文获取类型
收费全文 | 1537篇 |
免费 | 10篇 |
专业分类
电工技术 | 10篇 |
综合类 | 1篇 |
化学工业 | 69篇 |
金属工艺 | 5篇 |
机械仪表 | 8篇 |
建筑科学 | 20篇 |
矿业工程 | 2篇 |
能源动力 | 1篇 |
轻工业 | 97篇 |
水利工程 | 3篇 |
石油天然气 | 2篇 |
无线电 | 30篇 |
一般工业技术 | 55篇 |
冶金工业 | 1221篇 |
自动化技术 | 23篇 |
出版年
2022年 | 3篇 |
2020年 | 2篇 |
2019年 | 8篇 |
2018年 | 2篇 |
2017年 | 3篇 |
2016年 | 10篇 |
2015年 | 5篇 |
2014年 | 8篇 |
2013年 | 19篇 |
2012年 | 11篇 |
2011年 | 10篇 |
2010年 | 9篇 |
2009年 | 5篇 |
2008年 | 5篇 |
2007年 | 9篇 |
2006年 | 9篇 |
2005年 | 5篇 |
2004年 | 5篇 |
2003年 | 10篇 |
2002年 | 5篇 |
2001年 | 6篇 |
2000年 | 6篇 |
1999年 | 48篇 |
1998年 | 339篇 |
1997年 | 197篇 |
1996年 | 137篇 |
1995年 | 100篇 |
1994年 | 70篇 |
1993年 | 77篇 |
1992年 | 12篇 |
1991年 | 17篇 |
1990年 | 28篇 |
1989年 | 17篇 |
1988年 | 23篇 |
1987年 | 26篇 |
1986年 | 15篇 |
1985年 | 27篇 |
1984年 | 4篇 |
1983年 | 21篇 |
1982年 | 20篇 |
1981年 | 17篇 |
1980年 | 20篇 |
1979年 | 7篇 |
1978年 | 10篇 |
1977年 | 48篇 |
1976年 | 84篇 |
1975年 | 9篇 |
1974年 | 4篇 |
1973年 | 3篇 |
1930年 | 2篇 |
排序方式: 共有1547条查询结果,搜索用时 31 毫秒
81.
The PQ-interval was measured while resting supine before exercise testing, in the erect position on the bicycle before starting exercise, and resting supine after exercise in 68 men 6--8 weeks after acute myocardial infarction. During a 6-year follow-up period the death was non-sudden (greater than 1 hour) in 25 of these patients. In this group the PQ-time was significantly shorter (p less than 0.001) during somatomotor activation on the bicycle before exercise than resting supine. The same directional change (p less than 0.01) was seen in the sudden death (less than 1 hour) group (N = 21), but not in the patients who survived. PQ-time at supine rest before exercise testing, however, was significantly shorter (p less than 0.02) in surviving patients than in the non-sudden death group. The possible mechanisms of these, and of previously reported changes in the R-wave amplitudes and QT-times, are discussed. 相似文献
82.
The aim of this study was to determine the effect of sitting and standing postures on the repeatability of a stadiometer designed to detect small variations in spinal length. Two groups of ten healthy subjects, with no previous or known history of back problems, participated in this study. One group was measured in the standing posture, while the other group was measured in a sitting posture. All subjects gave informed consent to participate in this study. Subjects had a set of landmarks defining the spinal contour marked on their backs and then stood in the stadiometer for three series of ten measurements to be performed. At the end of each measurement, the subjects were requested to move away from and then be repositioned in the stadiometer. Subjects improved the repeatability across the measurement series. At the end of the second measurement series, all subjects presented mean standard deviations of 0.43 +/- 0.08 mm (range 0.30-0.50 mm) in the standing posture. In the sitting posture, deviations of less than 0.05 mm were obtained only at the end of the third measurement series (0.48 +/- 0.08 mm; range 0.34-0.62 mm), suggesting that this posture required three measurement series before repeatable measurements could be assured rather than two in the standing posture. 相似文献
83.
84.
JF Watchko MJ Daood GC Sieck JJ LaBella BT Ameredes AP Koretsky B Wieringa 《Canadian Metallurgical Quarterly》1997,82(5):1416-1423
Creatine kinase (CK) is an enzyme central to cellular high-energy phosphate metabolism in muscle. To characterize the physiological role of CK in respiratory muscle during dynamic contractions, we compared the force-velocity relationships, power, and work output characteristics of the diaphragm (Dia) from mice with combined myofibrillar and sarcomeric mitochondrial CK deficiency (CK[-/-]) with CK-sufficient controls (Ctl). Maximum velocity of shortening was significantly lower in CK[-/-] Dia (14.1 +/- 0.9 Lo/s, where Lo is optimal fiber length) compared with Ctl Dia (17.5 +/- 1.1 Lo/s) (P < 0.01). Maximum power was obtained at 0.4-0.5 tetanic force in both groups; absolute maximum power (2,293 +/- 138 W/m2) and work (201 +/- 9 J/m2) were lower in CK[-/-] Dia compared with Ctl Dia (2,744 +/- 146 W/m2 and 284 +/- 26 J/m2, respectively) (P < 0.05). The ability of CK[-/-] Dia to sustain shortening during repetitive isotonic activation (75 Hz, 330-ms duration repeated each second at 0.4 tetanic force load) was markedly impaired, with CK[-/-] Dia power and work declining to zero by 37 +/- 4 s, compared with 61 +/- 5 s in Ctl Dia. We conclude that combined myofibrillar and sarcomeric mitochondrial CK deficiency profoundly impairs Dia power and work output, underscoring the functional importance of CK during dynamic contractions in skeletal muscle. 相似文献
85.
86.
87.
It is a common practice in computer vision and image processing to convolve rectangular constant coefficient windows with digital images to perform local smoothing and derivative estimation for edge detection and other purposes. If all data points in each image window belong to the same statistical population, this practice is reasonable and fast. But, as is well known, constant coefficient window operators produce incorrect results if more than one statistical population is present within a window, for example, if a gray-level or gradient discontinuity is present. This paper shows one way to apply the theory of robust statistics to the data smoothing and derivative estimation problem. A robust window operator is demonstrated that preserves gray-level and gradient discontinuities in digital images as it smooths and estimates derivatives. 相似文献
88.
Suckling and feeding are central to the child's health and development. In addition, feeding provides a context for early parent–child interaction. Despite the centrality of feeding to the child's development, it has been largely neglected by developmental psychologists as an area of study. To interest the developmental researcher in the acquisition of food acceptance patterns, this article provides a rationale for the significance of the study of early feeding and delineates major questions and issues that require investigation. (PsycINFO Database Record (c) 2011 APA, all rights reserved) 相似文献
89.
90.
S Birch 《Canadian Metallurgical Quarterly》1997,3(4):315-321
Total body water (TBW) was measured by deuterium oxide dilution (D2O) and predicted by bioelectric impedance analysis (BIA) (Deurenberg, Schouten, Andreoli and De Lorenzo 1993) in 21 subjects with Schistosoma mansoni infection and 17 healthy controls of similar age (32.8 +/- 13.7 years, n=38). Patients were selected to have no visible fluid retention and no cardiac or renal abnormalities. Body hydration (TBW per kg of body weight) was significantly higher in patients with schistosomiasis than in controls (62.9 +/- 3.6 vs 57.4 +/- 4.3%, p < 0.0005). A significant correlation was found between albumin levels and TBW% on the pooled sample (n=38; r=0.660, p < 0.0001). This relationship was not influenced by the presence of disease, as determined by ANCOVA. Values of TBW predicted by BIA were highly correlated and not significantly different (p=n.s., ANOVA) from those measured by D2O in both controls and patients (r=0.854, p < 0.001, SEE = 2.3 1, CV=5.9% and r=0.848, p < 0.001, SEE=4.0 1, CV=9.3%, respectively). The bias (TBW by BIA - TBW by D2O) was of 0.9 +/- 3.7 in controls and of -1.3 +/- 4.2 1 in patients. This bias was significantly correlated to TBW% in patients (r=0.575, p < 0.05) but not in controls (p=n.s.). It is concluded that subjects with schistosomiasis show an apparent subclinical increase in body hydration which could affect the prediction of TBW from BIA. 相似文献