全文获取类型
收费全文 | 1682篇 |
免费 | 111篇 |
国内免费 | 85篇 |
专业分类
电工技术 | 106篇 |
综合类 | 116篇 |
化学工业 | 181篇 |
金属工艺 | 68篇 |
机械仪表 | 105篇 |
建筑科学 | 82篇 |
矿业工程 | 37篇 |
能源动力 | 23篇 |
轻工业 | 110篇 |
水利工程 | 39篇 |
石油天然气 | 245篇 |
武器工业 | 18篇 |
无线电 | 145篇 |
一般工业技术 | 88篇 |
冶金工业 | 292篇 |
原子能技术 | 14篇 |
自动化技术 | 209篇 |
出版年
2024年 | 7篇 |
2023年 | 14篇 |
2022年 | 35篇 |
2021年 | 51篇 |
2020年 | 32篇 |
2019年 | 29篇 |
2018年 | 36篇 |
2017年 | 41篇 |
2016年 | 36篇 |
2015年 | 51篇 |
2014年 | 80篇 |
2013年 | 62篇 |
2012年 | 87篇 |
2011年 | 101篇 |
2010年 | 112篇 |
2009年 | 120篇 |
2008年 | 118篇 |
2007年 | 94篇 |
2006年 | 88篇 |
2005年 | 82篇 |
2004年 | 45篇 |
2003年 | 21篇 |
2002年 | 19篇 |
2001年 | 22篇 |
2000年 | 42篇 |
1999年 | 74篇 |
1998年 | 148篇 |
1997年 | 112篇 |
1996年 | 36篇 |
1995年 | 14篇 |
1994年 | 12篇 |
1993年 | 14篇 |
1992年 | 2篇 |
1990年 | 1篇 |
1986年 | 1篇 |
1982年 | 1篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1978年 | 2篇 |
1977年 | 7篇 |
1976年 | 22篇 |
排序方式: 共有1878条查询结果,搜索用时 0 毫秒
11.
PURPOSE: To compare admission data and academic performances of medical students younger and older than 25, and to qualify older students' experiences and perceptions in medical school. METHOD: The authors reviewed 1988-1991 data for applications to the McGill University Faculty of Medicine. Data included GPAs and MCAT scores, as well as ratings for reference letters, autobiographical statements, and interviews. For those same years, the authors measured students' academic performances in the preclinical and clinical years. The authors compared the data by students' age: "younger" students, aged 17 to 24; and "older" students, aged 25 and above. All enrolled students took the Derogatis Stress Profile, and the older students participated in focus groups. RESULTS: The older applicants had lower GPAs and MCAT scores, but higher interview and reference letter ratings. For older accepted students, basic science course scores were lower than those of younger students, but clinical scores did not differ significantly between the groups. The two groups had similar stress levels, although older students tested lower in driven behavior, relaxation potential, attitude posture, and hostility. In focus groups, the older students spoke of learning style differences, loss of social support, and loss of professional identity. CONCLUSION: Different scores in admission criteria suggest that McGill uses different standards to select older medical students. Older students admitted under different criteria, however, do just as well as do younger students by their clinical years. A broad-based study of admission criteria and outcomes for the older student population is warranted. 相似文献
12.
神经网络已经在模式识别、自动控制及数据挖掘等领域取得了广泛的应用,但学习方法的速度不能满足实际需求。传统的误差反向传播方法(BP)主要是基于梯度下降的思想,需要多次迭代;网络的所有参数都需要在训练过程中迭代确定,因此算法的计算量和搜索空间很大。ELM(Extreme Learning Machine,ELM)是一次学习思想使得学习速度提高很多,避免了多次迭代和局部最小值,具有良好的泛化性能、鲁棒性与可控性。但对于不同的数据集和不同的应用领域,无论ELM是用于数据分类或是回归,ELM算法本身还是存在问题,所以本文对已有方法深入对比分析,并指出极速学习方法未来的发展方向。 相似文献
13.
14.
15.
16.
17.
18.
Infections due to Lancefield group F and related Streptococci (S. milleri, S. anginosus) 总被引:1,自引:0,他引:1
DM Shlaes PI Lerner E Wolinsky KV Gopalakrishna 《Canadian Metallurgical Quarterly》1981,60(3):197-207
We can no longer accept classification of streptococci solely on the basis of hemolytic reactions or Lancefield agglutinations. While the "viridans" streptococci cannot be serologically differentiated, physiological separation of the species offers a satisfactory method of classifying human isolates. We review the microbiology of Lancefield group F and related streptococci (S. milleri, S. anginosus), emphasizing microbial ecology and current taxonomic considerations. A series of 28 patients infected with these organisms is presented. There was a striking male predominance in the series (6:1) as well as an obvious association with underlying diseases and/or antecedent trauma. The most remarkable feature of these pathogens is their predilection for abscess formation, confirming their overdue recognition as the most common "viridans" streptococcus recovered from abscesses within internal organs. We observed purulent disease of the nervous and skeletal systems, oral cavity, lung and pleural space, abdomen and subcutaneous tissues. Microbial synergy (i.e. polymicrobic infection) was not a requisite for abscess formation. Four of the five deaths in this series occurred in patients 60 years of age of older. Some degree of variability in antimicrobial susceptibility was noted, so speciation alone may not always provide sufficient information on which to base a therapeutic decision. 相似文献
19.
利用双端信号输出的塑料闪烁体与灵敏度高、时间响应快的硅光电倍增管构成塑料闪烁体探测器探头,并与后端的数字化转换器等电子学系统搭建成塑料闪烁体探测器系统。为了研究不同数据处理方法对真事件探测效率和能量分辨率的优化,分别使用标准γ源60Co和137Cs对塑料闪烁体探测器系统进行测试。研究了关联事件的符合时间窗对探测器真事件探测效率的影响,分析了波形的积分长度与脉冲信号甄别(Pulse Shape Discrimination,PSD)开窗法对能谱能量分辨率的改进。结果表明,在关联事件的符合时间窗为15 ns时,真事件探测效率最佳,当波形积分长度为80 ns时,通过PSD开窗后能量分辨率由原来的53.38%优化为42.21%。 相似文献
20.
群机器人仿真系统是一个能够对群机器人系统的体系结构、协调控制和学习算法等进行实验的数字仿真系统。分析了各仿真对象的物理特性及其实现难点,给出了仿真系统的软件架构和对象建模,描述了各仿真功能的具体实现。利用本仿真系统进行的实验结果表明此系统达到了比较理想的效果,具有良好的分布式运行能力和方便的实时交互能力,为群机器人系统的研究提供了一个有效的平台。 相似文献