全文获取类型
收费全文 | 2519篇 |
免费 | 67篇 |
国内免费 | 34篇 |
专业分类
电工技术 | 53篇 |
综合类 | 38篇 |
化学工业 | 259篇 |
金属工艺 | 46篇 |
机械仪表 | 34篇 |
建筑科学 | 44篇 |
矿业工程 | 8篇 |
能源动力 | 11篇 |
轻工业 | 108篇 |
水利工程 | 27篇 |
石油天然气 | 11篇 |
武器工业 | 7篇 |
无线电 | 41篇 |
一般工业技术 | 156篇 |
冶金工业 | 1668篇 |
原子能技术 | 22篇 |
自动化技术 | 87篇 |
出版年
2023年 | 5篇 |
2022年 | 12篇 |
2021年 | 12篇 |
2020年 | 8篇 |
2019年 | 15篇 |
2018年 | 18篇 |
2017年 | 16篇 |
2016年 | 12篇 |
2015年 | 12篇 |
2014年 | 28篇 |
2013年 | 30篇 |
2012年 | 38篇 |
2011年 | 80篇 |
2010年 | 62篇 |
2009年 | 53篇 |
2008年 | 66篇 |
2007年 | 66篇 |
2006年 | 51篇 |
2005年 | 64篇 |
2004年 | 34篇 |
2003年 | 16篇 |
2002年 | 31篇 |
2001年 | 27篇 |
2000年 | 31篇 |
1999年 | 43篇 |
1998年 | 474篇 |
1997年 | 286篇 |
1996年 | 187篇 |
1995年 | 111篇 |
1994年 | 104篇 |
1993年 | 89篇 |
1992年 | 26篇 |
1991年 | 26篇 |
1990年 | 28篇 |
1989年 | 37篇 |
1988年 | 41篇 |
1987年 | 29篇 |
1986年 | 19篇 |
1985年 | 21篇 |
1984年 | 8篇 |
1983年 | 7篇 |
1982年 | 10篇 |
1981年 | 16篇 |
1980年 | 23篇 |
1979年 | 11篇 |
1978年 | 7篇 |
1977年 | 60篇 |
1976年 | 124篇 |
1975年 | 7篇 |
1974年 | 7篇 |
排序方式: 共有2620条查询结果,搜索用时 0 毫秒
81.
一种新的基于相位调制跟踪的电源并联控制方法 总被引:3,自引:2,他引:3
研究了抗干扰能力强、控制可靠性高的数字化并联控制技术,提出了一种数字均流控制方法一相位调制跟踪法。该方法将每个模块有功功率、无功功率和同步信号通过相位调制的方法变换为相位变化的周期脉冲信号,然后通过锁相同步的方法使所有并联逆变器模块都跟踪相位最超前,即输出功率最大模块的脉冲信号,从而实现功率均分。该方法具有控制信号分辨率高,抗干扰能力强以及稳定性好等优点,提高了系统均流控制精度;同时,自然实现了民主主从控制,具有好的控制冗余性。克服了线路阻抗变化对系统均流精度的影响。实验结果表明,该方法能较好地实现逆变模块的功率均分,模块间输出电流偏差小于1%。 相似文献
82.
Polymer microlayer structures with anisotropic conductivity 总被引:1,自引:0,他引:1
Continuous layer-multiplying coextrusion offers a new approach for processing metal-filled polymers into conducting structures. In this process, filled and unfilled polymers are combined into unique structures with many alternating layers of two or more components. The total number of layers can range from tens to thousands. The ability of microlayering to organize anisotropic particles was used to obtain metal-filled polypropylene tape with highly anisotropic electrical properties. Orientation of metal flakes by microlayering increased the anisotropy in resistivity by two orders of magnitude over compression molding. Isolation of individual filled layers by alternating filled and unfilled layers resulted in materials with many independent conducting pathways. Filled layers with 10% (v/v) copper flakes or 15% (v/v) nickel flakes were conductive only if the filled layers were thick compared to the thickness of the flake particles. When the thickness of the filled layers approached the particle thickness, the conductive properties were lost. This behavior was understood by comparing the three-dimensional arrangement of flakes in thick conductive layers with the two-dimensional particle layout of thin non-conductive layers. 相似文献
83.
84.
Tensile fracture mechanisms in single edge notched injection-moulded specimens of a polycarbonate/ABS 30/70 wt% blend have been studied by fractography. When the tensile force was applied parallel to the injection direction, a herringbone pattern could be observed on the fracture surface, while for the perpendicular case, a reverse herringbone pattern was seen. At the same testing condition, the former was tougher than the latter. Fracture images and two-dimensional temperature profiles in the thickness direction were used to locate the crack initiation sites. Herringbone fracture occurred when the main crack repeatedly interacted with secondary cracks initiated along the centreline. Reverse herringbone fracture was formed in a similar mechanism but secondary cracks initiated near the edge. Anisotropy of the fracture modes was attributed to the processing-induced orientation of the polycarbonate phase near the edge. 相似文献
85.
Although left anterior oblique (LAO) gastric emptying studies appear to be an adequate alternative to geometric mean (GM) measurements in patients with normal gastric anatomy, it is not clear whether they can be used after gastric or duodenal surgery. In this study, dual-phase gastric emptying studies with combined solid-liquid meal were performed in 54 patients who had undergone pancreaticoduodenectomy (Whipple procedure). Gastric emptying was studied with GM, LAO, and anterior (ANT) methods. T1/2 and percent gastric retention at 10, 30, 60, 90, and 120 minutes were calculated. Results from the three methods were compared using correlation analysis and the t test. The t test showed no significant difference in T1/2 and percent retention values between the GM and LAO or ANT views. The solid emptying T1/2 showed a better correlation between GM and LAO values (r = 0.824) than between GM and ANT (r = 0.589). For the liquid T1/2, the reverse was true. Correlation between GM and ANT (r = 0.939) was better than between GM and LAO (r = 0.839); however, both LAO and ANT views correlated well with GM liquid emptying. It is concluded that the LAO view can replace GM gastric emptying methods in postpancreaticoduodenectomy patients for evaluation of both solid and liquid emptying, although the ANT view appears completely adequate for the study of liquid emptying. 相似文献
86.
87.
A new classification algorithm, called VFI5 (for Voting Feature Intervals), is developed and applied to problem of differential diagnosis of erythemato-squamous diseases. The domain contains records of patients with known diagnosis. Given a training set of such records, the VFI5 classifier learns how to differentiate a new case in the domain. VFI5 represents a concept in the form of feature intervals on each feature dimension separately. classification in the VFI5 algorithm is based on a real-valued voting. Each feature equally participates in the voting process and the class that receives the maximum amount of votes is declared to be the predicted class. The performance of the VFI5 classifier is evaluated empirically in terms of classification accuracy and running time. 相似文献
88.
89.
90.
MP Vercauteren HC Coppejans VL Hoffmann V Saldien HA Adriaensen 《Canadian Metallurgical Quarterly》1998,86(5):989-993
In a double-blind, randomized trial, 98 parturients undergoing cesarean section received either hyperbaric or plain bupivacaine 6.6 mg combined with sufentanil 3.3 microg as part of a combined spinal-epidural procedure. To prevent hypotension, 1000 mL of lactated Ringer's solution, 500 mL of hydroxyethyl starch 6%, and ephedrine 5 mg were administered i.v. The height of the block was equal in both groups, but more patients in the plain group had blocks that were either too high or too low (P < 0.01). The number of patients requiring epidural supplementation was equal in both groups. Strict criteria were used to treat hypotension. The overall incidence of systolic blood pressure (<90 mm Hg) was 13%, whereas it was more pronounced in the plain group (21% vs 6% in the hyperbaric group, P < 0.05), which required more ephedrine (P < 0.05) and in which a greater incidence of nausea was noticed (P < 0.05). We conclude that the use of a small dose of intrathecal bupivacaine combined with sufentanil plus our described preloading regimen resulted in a lower incidence of hypotension. Further, we conclude that the use of hyperbaric bupivacaine in this manner provides a more reliable block and a lower incidence of hypotension than plain bupivacaine. Implications: A small dose of hyperbaric bupivacaine 0.5% combined with sufentanil used intrathecally during cesarean section offered a more reliable cephalad spread of the spinal block than the glucose-free combination, which was reflected in a lower incidence of hypotension and nausea. 相似文献