全文获取类型
收费全文 | 4233篇 |
免费 | 595篇 |
国内免费 | 437篇 |
专业分类
电工技术 | 176篇 |
技术理论 | 1篇 |
综合类 | 505篇 |
化学工业 | 517篇 |
金属工艺 | 89篇 |
机械仪表 | 313篇 |
建筑科学 | 288篇 |
矿业工程 | 185篇 |
能源动力 | 54篇 |
轻工业 | 84篇 |
水利工程 | 58篇 |
石油天然气 | 87篇 |
武器工业 | 30篇 |
无线电 | 421篇 |
一般工业技术 | 223篇 |
冶金工业 | 81篇 |
原子能技术 | 7篇 |
自动化技术 | 2146篇 |
出版年
2024年 | 9篇 |
2023年 | 36篇 |
2022年 | 83篇 |
2021年 | 162篇 |
2020年 | 139篇 |
2019年 | 106篇 |
2018年 | 97篇 |
2017年 | 108篇 |
2016年 | 172篇 |
2015年 | 144篇 |
2014年 | 250篇 |
2013年 | 208篇 |
2012年 | 300篇 |
2011年 | 328篇 |
2010年 | 284篇 |
2009年 | 318篇 |
2008年 | 345篇 |
2007年 | 379篇 |
2006年 | 298篇 |
2005年 | 254篇 |
2004年 | 230篇 |
2003年 | 217篇 |
2002年 | 174篇 |
2001年 | 120篇 |
2000年 | 136篇 |
1999年 | 81篇 |
1998年 | 54篇 |
1997年 | 36篇 |
1996年 | 39篇 |
1995年 | 36篇 |
1994年 | 19篇 |
1993年 | 21篇 |
1992年 | 21篇 |
1991年 | 11篇 |
1990年 | 7篇 |
1989年 | 7篇 |
1988年 | 7篇 |
1987年 | 4篇 |
1986年 | 11篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1975年 | 3篇 |
1963年 | 1篇 |
排序方式: 共有5265条查询结果,搜索用时 703 毫秒
21.
Before 12 months of age, infants have difficulties coordinating and sequencing their movements to retrieve an object concealed in a box. This study examined (a) whether young infants can discover effective retrieval solutions and consolidate movement coordination earlier if exposed regularly to such a task and (b) whether different environments, indexed by box transparency, would impact the rate of learning and time of discovery of these solutions. Infants (N=12) were presented with an object retrieval task every week from 6 1/2 months of age until they were able to retrieve the toy from the box using coordinated two-handed patterns for 3 weeks. To reach that criterion, infants tested with an opaque box took 2 1/2 months and infants tested with a semitransparent box took 1 1/2 months. Both groups outperformed age-matched controls who received a one-time exposure to the task. Repeated exposure to the task and vision of the toy significantly enhanced this process of solution discovery. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
22.
A. Ardeshir Goshtasby Author Vitae 《Computer aided design》2003,35(5):487-494
Formulations for parametric circles and spheres in terms of rational Gaussian (RaG) curves and surfaces are introduced. With the proposed formulations, a full circle is generated by interpolating a closed RaG curve to the vertices of an equilateral triangle, and a full sphere is generated by interpolating a closed RaG surface to the vertices of an octahedron with equilateral triangular faces. Generation of circles and spheres in this manner is very intuitive and easy to remember as the weights are all 1 and the nodes are all unique and uniformly spaced. 相似文献
23.
24.
椭圆光孔上的Fraunhofer衍射图样 总被引:1,自引:0,他引:1
将椭圆域变换成圆域,从而借助于圆孔衍射问题的处理方法,给出了椭圆孔上的Fraunhofer衍射图样的数学描述。 相似文献
25.
东海陆架盆地西湖凹陷油气发现历程回顾 总被引:4,自引:0,他引:4
东海陆架盆地的油气发现开始于1980年,并主要集中于西湖凹陷。从1980年至1995年是东海油气勘探成果辉煌的15年,期间共发现了平湖、春晓、天外天、宝云亭、武云亭、孔雀亭、断桥、残雪等8个油气田及一大批含油气构造。 相似文献
26.
凸轮机构推程、回程运动角的最佳匹配及其求解方法 总被引:4,自引:1,他引:3
在推程、回程运动角之和 Φ0 +Φ′0 =C(定值 )的情况下 ,必存在某一对推程、回程运动角的最佳匹配 Opti-m um{ Φ0 ,Φ′0 } ;当选用该最佳匹配时 ,对心式直动从动杆盘形凸轮基圆半径 r0 取得最小值 r0 min。本文在揭示出上述事实的基础上 ,研究解决了当选取最佳匹配 Optim um{ Φ0 ,Φ′0 }时 ,按许用压力角 [α]条件求解对心式直动从动杆盘形凸轮基圆半径最小值 r0 min的解析法。 相似文献
27.
Since Samuel's work on checkers over thirty years ago, much effort has been devoted to learning evaluation functions. However, all such methods are sensitive to the feature set chosen to represent the examples. If the features do not capture aspects of the examples significant for problem solving, the learned evaluation function may be inaccurate or inconsistent. Typically, good feature sets are carefully handcrafted and a great deal of time and effort goes into refining and tuning them. This paper presents an automatic knowledge-based method for generating features for evaluation functions. The feature set is developed iteratively: features are generated, then evaluated, and this information is used to develop new features in turn. Both the contribution of a feature and its computational expense are considered in determining whether and how to develop it further.
This method has been applied to two problem-solving domains: the Othello board game and the domain of telecommunications network management. Empirical results show that the method is able to generate many known features and several novel features and to improve concept accuracy in both domains. 相似文献
This method has been applied to two problem-solving domains: the Othello board game and the domain of telecommunications network management. Empirical results show that the method is able to generate many known features and several novel features and to improve concept accuracy in both domains. 相似文献
28.
This article reports the results of a study of domain-independent function finding based on a collection of several hundred real scientific data sets. Prior studies have introduced the controversial idea of discovering functional relationships of interest to scientists directly from the data they collect. The evidence presented here supports the view that this is sometimes possible, but it also suggests how often purely data-driven discovery is not possible and how much more difficult it may be than has often been assumed. Experience with sampled examples of real scientific data suggests as well that emphasis on search in prior studies may have been misplaced. For the function-finding problems studied here, scientists typically propose only a handful of different functional relationships. The difficulty is not in searching through a large space of relationships but in evaluating a few common ones to determine if they are likely to be of scientific interest. 相似文献
29.
文章提出了一种利用无线传感器网络无线信号接收强度(RSSI)和移动锚节点轨迹来获得待定节点位置的算法。该算法在有多个可移动锚节点的情况下,定位将会更加高效。在定位阶段,通过RSSI测得锚节点到待定节点的距离,并利用三个以上移动锚节点的坐标(包括三个)来求解圆的方程,计算出待定节点的位置。 相似文献
30.
A current development trend in research on intelligent systems is to optimize a general intelligent prediction system into an individuation intelligent prediction system that is applied in specialized fields. Protein structure prediction is a challenging international issue. In this paper, we propose a new intelligent prediction system model, designed as a multi-layer compound pyramid model, for predicting secondary protein structure. The model comprises four independent intelligent interfaces and several knowledge discovery methods. The model penetrates throughout the domain knowledge, with the effective attributes chosen by Causal Cellular Automata. Furthermore, a high pure structure database is constructed for training. On the RS126 dataset, the overall state per-residue accuracy, Q3, reached 83.99%, while on the CB513 dataset, Q3 reached 85.58%. Meanwhile, on the CASP8 sequences, the results are superior to those produced by other methods, such as Psipred, Jpred, APSSP2 and BehairPred. These results confirm that our method has a strong generalization ability, and that it provides a model for the construction of other intelligent systems. 相似文献