全文获取类型
收费全文 | 16535篇 |
免费 | 1752篇 |
国内免费 | 1135篇 |
专业分类
电工技术 | 1081篇 |
综合类 | 2128篇 |
化学工业 | 1051篇 |
金属工艺 | 1348篇 |
机械仪表 | 1639篇 |
建筑科学 | 2027篇 |
矿业工程 | 568篇 |
能源动力 | 531篇 |
轻工业 | 598篇 |
水利工程 | 610篇 |
石油天然气 | 1326篇 |
武器工业 | 131篇 |
无线电 | 1007篇 |
一般工业技术 | 1533篇 |
冶金工业 | 603篇 |
原子能技术 | 196篇 |
自动化技术 | 3045篇 |
出版年
2024年 | 39篇 |
2023年 | 154篇 |
2022年 | 325篇 |
2021年 | 420篇 |
2020年 | 463篇 |
2019年 | 403篇 |
2018年 | 380篇 |
2017年 | 571篇 |
2016年 | 576篇 |
2015年 | 668篇 |
2014年 | 1010篇 |
2013年 | 982篇 |
2012年 | 1235篇 |
2011年 | 1314篇 |
2010年 | 1009篇 |
2009年 | 1081篇 |
2008年 | 1006篇 |
2007年 | 1222篇 |
2006年 | 1118篇 |
2005年 | 909篇 |
2004年 | 725篇 |
2003年 | 628篇 |
2002年 | 517篇 |
2001年 | 441篇 |
2000年 | 387篇 |
1999年 | 320篇 |
1998年 | 254篇 |
1997年 | 199篇 |
1996年 | 224篇 |
1995年 | 205篇 |
1994年 | 149篇 |
1993年 | 98篇 |
1992年 | 85篇 |
1991年 | 65篇 |
1990年 | 49篇 |
1989年 | 53篇 |
1988年 | 41篇 |
1987年 | 25篇 |
1986年 | 15篇 |
1985年 | 10篇 |
1984年 | 13篇 |
1983年 | 7篇 |
1982年 | 8篇 |
1980年 | 3篇 |
1979年 | 9篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1959年 | 1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 15 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.
《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
3.
《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
4.
This article presents a method that can be applied to molten AA-6101 alloy to improve electrical properties of the aluminium part of the optical ground wire (OPGW) used in overhead transmission lines to protect phase conductors from lightning strike and to transmit signals and data. AA-6101 alloy in casting of the log as 6 m length and 178 mm diameter for extrusion has been inoculated by AlB2 to decrease detrimental effects of Cr, Ti, V, and Zr on the conductivity of the material. After inoculation, improved billets were extruded as 9.5 mm diameter feedstock. Required wires drawn from the feedstock according to the construction types of OPGW to be tested were exposed to aging at 175°C, 6 h (T-8). Upon completion of the back-twist and performing-type stranding process, resistance, and short-circuit current capacity and breaking load of the OPGW 88/44 constructions with other metal combinations have been examined and tested to show improvement. Results are summarized in tables and graphically. 相似文献
5.
用矩阵光学理论计算了由主振荡器和功率放大器组成的种子注入光腔。主振荡器光腔是由曲率半径R1=-250mm,R2=5000mm,相距L=2375mm的球面镜组成的正支非稳腔;功率非稳腔是由曲率半径R3=400mm,R4=5600mm,相距S=3000mm的球面镜构成的负支非稳腔。理论计算表明,该种子注入光腔可输出光束发散角约几十微弧的激光,可满足铜蒸气激光器主振荡器功率放大器(MOPA)的技术要求。 相似文献
6.
7.
8.
9.
结合工程实例,介绍了在物性条件和地质条件复杂地区利用面波勘探技术解决软岩地区第四系覆盖层及其岩埋深的勘探方法。 相似文献
10.
Ching-Liang Su 《Journal of Intelligent and Robotic Systems》2006,45(1):1-14
This research uses the object extracting technique to extract the index, middle and ring fingers from the hand images. The algorithm developed in this research can find the precise locations of the different fingers' fingertips and the finger-to-finger-valleys. After finding the positions of the fingertips and finger-valleys, the index, middle and ring fingers can be extracted from the hand images by using morphological technique. The extracted index, middle and ring fingers contain many useful geometry features. One can use these features to do the person's identification. The orientations of the index, middle and ring fingers are found in this research. Image rotating, image shifting, and image interpolating techniques are used to align different persons' index, middle and ring fingers. Image subtraction is used to exam the difference of two index, middle and ring finger images. In this research so far only use the index, middle and the ring fingers as the features to identify different persons.
★This work was supported by National Science Council under grant NSC 93-2213-E-212-011. 相似文献