全文获取类型
收费全文 | 20263篇 |
免费 | 2405篇 |
国内免费 | 1589篇 |
专业分类
电工技术 | 1551篇 |
综合类 | 2529篇 |
化学工业 | 1102篇 |
金属工艺 | 1334篇 |
机械仪表 | 1742篇 |
建筑科学 | 1990篇 |
矿业工程 | 588篇 |
能源动力 | 619篇 |
轻工业 | 718篇 |
水利工程 | 619篇 |
石油天然气 | 1349篇 |
武器工业 | 186篇 |
无线电 | 3154篇 |
一般工业技术 | 1756篇 |
冶金工业 | 658篇 |
原子能技术 | 237篇 |
自动化技术 | 4125篇 |
出版年
2024年 | 59篇 |
2023年 | 214篇 |
2022年 | 428篇 |
2021年 | 545篇 |
2020年 | 640篇 |
2019年 | 549篇 |
2018年 | 514篇 |
2017年 | 764篇 |
2016年 | 768篇 |
2015年 | 839篇 |
2014年 | 1264篇 |
2013年 | 1286篇 |
2012年 | 1526篇 |
2011年 | 1583篇 |
2010年 | 1247篇 |
2009年 | 1319篇 |
2008年 | 1268篇 |
2007年 | 1495篇 |
2006年 | 1345篇 |
2005年 | 1091篇 |
2004年 | 892篇 |
2003年 | 757篇 |
2002年 | 638篇 |
2001年 | 557篇 |
2000年 | 475篇 |
1999年 | 379篇 |
1998年 | 296篇 |
1997年 | 254篇 |
1996年 | 274篇 |
1995年 | 233篇 |
1994年 | 171篇 |
1993年 | 123篇 |
1992年 | 101篇 |
1991年 | 82篇 |
1990年 | 63篇 |
1989年 | 55篇 |
1988年 | 52篇 |
1987年 | 26篇 |
1986年 | 17篇 |
1985年 | 12篇 |
1984年 | 13篇 |
1983年 | 11篇 |
1982年 | 8篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 8篇 |
1978年 | 2篇 |
1959年 | 2篇 |
1956年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
Data fitting with B-splines is a challenging problem in reverse engineering for CAD/CAM, virtual reality, data visualization, and many other fields. It is well-known that the fitting improves greatly if knots are considered as free variables. This leads, however, to a very difficult multimodal and multivariate continuous nonlinear optimization problem, the so-called knot adjustment problem. In this context, the present paper introduces an adapted elitist clonal selection algorithm for automatic knot adjustment of B-spline curves. Given a set of noisy data points, our method determines the number and location of knots automatically in order to obtain an extremely accurate fitting of data. In addition, our method minimizes the number of parameters required for this task. Our approach performs very well and in a fully automatic way even for the cases of underlying functions requiring identical multiple knots, such as functions with discontinuities and cusps. To evaluate its performance, it has been applied to three challenging test functions, and results have been compared with those from other alternative methods based on AIS and genetic algorithms. Our experimental results show that our proposal outperforms previous approaches in terms of accuracy and flexibility. Some other issues such as the parameter tuning, the complexity of the algorithm, and the CPU runtime are also discussed. 相似文献
2.
针对现有混合入侵检测模型仅定性选取特征而导致检测精度较低的问题,同时为了充分结合误用检测模型和异常检测模型的优势,提出一种采用信息增益率的混合入侵检测模型.首先,利用信息增益率定量地选择特征子集,最大程度地保留样本信息;其次,采用余弦时变粒子群算法确定支持向量机参数构建误用检测模型,使其更好地平衡粒子在全局和局部的搜索能力,然后,选取灰狼算法确定单类支持向量机参数构建异常检测模型,以此来提高对最优参数的搜索效率和精细程度,综合提高混合入侵检测模型对攻击的检测效果;最后,通过两种数据集进行仿真实验,验证了所提混合入侵检测模型具有较好的检测性能. 相似文献
3.
《Planning》2019,(6)
减少手术创伤始终是快速康复的决定性因素,这一点在目前的加速康复外科研究尤其是复杂手术,如妇科肿瘤手术中尚未得到充分重视。尊重学习曲线、全面规划手术方案、总结失利经验、开展前瞻性研究是解决此问题的主要方案。本文着重讨论妇科肿瘤手术创伤对术后加速康复的影响及可能的改进措施。 相似文献
4.
《Energy Policy》2015
The low price of lead-acid, the most popular battery, is often used in setting cost targets for emerging energy storage technologies. Future cost reductions in lead acid batteries could increase investment and time scales needed for emerging storage technologies to reach cost-parity. In this paper the first documented model of cost reductions for lead-acid batteries is developed. Regression to a standard experience curve using 1989–2012 data yield a poor fit, with R2 values of 0.17 for small batteries and 0.05 for larger systems. To address this problem, battery costs are separated into material and residual costs, and experience curves developed for residual costs. Depending on the year, residual costs account for 41–86% of total battery cost. Using running-time averages to address volatility in material costs, a 4-year time average experience curve for residual costs yield much higher R2, 0.78 for small and 0.74 for large lead-acid batteries. The learning rate for residual costs in lead-acid batteries is 20%, a discovery with policy implications. Neglecting to consider cost reductions in lead-acid batteries could result in failure of energy storage start-ups and public policy programs. Generalizing this result, learning in incumbent technologies must be understood to assess the potential of emerging ones. 相似文献
5.
6.
7.
8.
The aim of this paper is to give a general quantitative requirement which the loop gain must satisfy in order to stabilize a given unstable (possibly nonlinear and time-varying) plant, namely that the gain must exceed one. 相似文献
9.
10.