全文获取类型
收费全文 | 2619篇 |
免费 | 50篇 |
国内免费 | 10篇 |
专业分类
电工技术 | 19篇 |
化学工业 | 287篇 |
金属工艺 | 45篇 |
机械仪表 | 91篇 |
建筑科学 | 49篇 |
矿业工程 | 4篇 |
能源动力 | 60篇 |
轻工业 | 65篇 |
水利工程 | 5篇 |
石油天然气 | 10篇 |
无线电 | 215篇 |
一般工业技术 | 397篇 |
冶金工业 | 1162篇 |
原子能技术 | 60篇 |
自动化技术 | 210篇 |
出版年
2023年 | 18篇 |
2022年 | 31篇 |
2021年 | 37篇 |
2020年 | 34篇 |
2019年 | 29篇 |
2018年 | 33篇 |
2017年 | 30篇 |
2016年 | 36篇 |
2015年 | 24篇 |
2014年 | 48篇 |
2013年 | 104篇 |
2012年 | 60篇 |
2011年 | 92篇 |
2010年 | 88篇 |
2009年 | 70篇 |
2008年 | 73篇 |
2007年 | 64篇 |
2006年 | 59篇 |
2005年 | 36篇 |
2004年 | 38篇 |
2003年 | 42篇 |
2002年 | 34篇 |
2001年 | 27篇 |
2000年 | 29篇 |
1999年 | 43篇 |
1998年 | 320篇 |
1997年 | 156篇 |
1996年 | 158篇 |
1995年 | 99篇 |
1994年 | 84篇 |
1993年 | 68篇 |
1992年 | 26篇 |
1991年 | 51篇 |
1990年 | 41篇 |
1989年 | 40篇 |
1988年 | 33篇 |
1987年 | 35篇 |
1986年 | 29篇 |
1985年 | 35篇 |
1984年 | 26篇 |
1983年 | 20篇 |
1982年 | 31篇 |
1981年 | 26篇 |
1980年 | 21篇 |
1979年 | 17篇 |
1978年 | 16篇 |
1977年 | 43篇 |
1976年 | 81篇 |
1975年 | 8篇 |
1973年 | 9篇 |
排序方式: 共有2679条查询结果,搜索用时 31 毫秒
11.
12.
We performed simultaneous fasting and fed antroduodenal manometry and EGG in 25 children with functional bowel disorders. Three patients (12%) had an uninterpretable EGG. The manometric studies showed severe neuropathy in six patients; milder neuropathic changes in five patients; postprandial hypomotility in one patient; myopathy in four patients, and normal motility in the remaining six patients. The percentage of tachygastria time (frequency > 3.5 cycles/min) was higher in the patiens with mild (44.1 +/- 15.8%) and severe (48 +/- 19.1%) neuropathy than in the patients with myopathy (20 +/- 16.2%, P < 0.05) or with normal motility (23 +/- 13.3%, P < 0.05). There was a considerable overlap in the percentage of tachygastria and total arrhythmia time among the different study groups. The ratio of post- to preprandial power was significantly higher (2.5 +/- 0.07) in children with normal motility than in the other patients groups. Every child with total arrhythmia time < 35% and a ratio of post- to preprandial power > 2.4 had normal manometry. In summary, EGG differentiated groups of children with normal manometry from others with neuropathic or myopathic changes, but in a minority of patients the study was not interpretable and there was overlap in EGG results between children with normal and abnormal manometry. 相似文献
13.
SV Filippov MD Rekhter RS Polishchuk SV Gurkin SN Voronov VI Cherviakov AA Mironov 《Canadian Metallurgical Quarterly》1993,35(9):62-65
It has been shown that changes in the orientation of arterial smooth muscle cells during a constant longitudinal stretching of the artery in vivo are not similar in different sections of the stretching zone. Cells in the proximal and distal sections keep their orientation but this orientation differs from that of smooth muscle cells in the control arteries. Cells in the central part of the stretching region lose their definite orientation to settle randomly. 相似文献
14.
15.
Segregation of germ granules in living Caenorhabditis elegans embryos: cell-type-specific mechanisms for cytoplasmic localisation 总被引:1,自引:0,他引:1
Extrinsic allergic alveolitis and pulmonary sarcoidosis are granulomatous diseases of the lung for which clinical presentation and anatomic site of granuloma formation differ. Extrinsic allergic alveolitis is caused by inhaled antigens, whereas the nature and source of the inciting antigen in sarcoidosis is unknown. To test the hypothesis that the route via which antigen is introduced to the lung contributes to the clinicopathological presentation of pulmonary granulomatous disease, rats immunized with intravenous (i.v.) Corynebacterium parvum were challenged after 2 weeks with either intratracheal (i.t.) or i.v. C. parvum. The granulomatous inflammation elicited by i.t. challenge predominantly involved alveolar spaces and histologically simulated extrinsic allergic alveolitis. In contrast, the inflammation induced by i.v. challenge was characterized by granulomatous angiitis and interstitial inflammation simulating sarcoidosis. Elevations of leukocyte counts and TNF levels in bronchoalveolar fluid, which reflect inflammation in the intra-alveolar compartment, were much more pronounced after i.t. than after i.v. challenge. Tumor necrosis factor, interleukin-6, CC chemokine, CXC chemokine, and adhesion molecule mRNA and protein expression occurred in each model. In conclusion, i.t. or i.v. challenge with C. parvum in sensitized rats caused pulmonary granulomatous inflammation that was histologically similar to human extrinsic allergic alveolitis and sarcoidosis, respectively. Although the soluble and cellular mediators of granulomatous inflammation were qualitatively similar in both disease models, the differing anatomic source of the same antigenic challenge was responsible for differing clinicopathological presentations. 相似文献
16.
17.
18.
19.
M. K. Karthikeyan R. K. Gupta V. Rajesh B. R. Ghosh P. P. Sinha 《Journal of Failure Analysis and Prevention》2007,7(6):429-433
17-4 PH stainless steel is used as internal drive shaft material in liquid engine pumps. One of the drive shafts failed during
operation. The shaft pieces were in contact for short duration after failure, which has resulted in abrasion of fractured
surfaces. Samples from the location of failure were taken, and investigation of the failure was carried out using optical
and scanning electron microscopy. The microstructural analysis of the material and fractographic analysis of the fractured
surface show that the failure was caused by excessive torsion. 相似文献
20.
New modulation formats are presented that increase the transmission rate over that of conventional systems, without degrading the bit error rate (BER) and with minimal bandwidth variation. A time-varying function called an "extra phase variation function" (EPVF) is added to the discrete phase of conventional modulation formats such as M-PSK and QAM to transmit additional data bits. A receiver configuration is presented that allows the decoding of information represented by the discrete and extra phases. It is shown that in an additive white Gaussian noise (AWGN) channel, the BER performance of the bits carried by the discrete phase and the extra phase in the modified format improves over the BER of conventional modulation formats. 相似文献