全文获取类型
收费全文 | 62848篇 |
免费 | 8072篇 |
国内免费 | 6037篇 |
专业分类
电工技术 | 5210篇 |
技术理论 | 9篇 |
综合类 | 6744篇 |
化学工业 | 1913篇 |
金属工艺 | 996篇 |
机械仪表 | 3795篇 |
建筑科学 | 2971篇 |
矿业工程 | 2642篇 |
能源动力 | 885篇 |
轻工业 | 1054篇 |
水利工程 | 1711篇 |
石油天然气 | 3128篇 |
武器工业 | 822篇 |
无线电 | 9092篇 |
一般工业技术 | 3217篇 |
冶金工业 | 1411篇 |
原子能技术 | 761篇 |
自动化技术 | 30596篇 |
出版年
2024年 | 292篇 |
2023年 | 866篇 |
2022年 | 1866篇 |
2021年 | 2308篇 |
2020年 | 2369篇 |
2019年 | 1849篇 |
2018年 | 1655篇 |
2017年 | 2071篇 |
2016年 | 2344篇 |
2015年 | 2700篇 |
2014年 | 4316篇 |
2013年 | 3849篇 |
2012年 | 4692篇 |
2011年 | 4985篇 |
2010年 | 3851篇 |
2009年 | 3784篇 |
2008年 | 4237篇 |
2007年 | 4795篇 |
2006年 | 4101篇 |
2005年 | 3651篇 |
2004年 | 3154篇 |
2003年 | 2677篇 |
2002年 | 2092篇 |
2001年 | 1612篇 |
2000年 | 1375篇 |
1999年 | 1008篇 |
1998年 | 791篇 |
1997年 | 645篇 |
1996年 | 555篇 |
1995年 | 475篇 |
1994年 | 383篇 |
1993年 | 268篇 |
1992年 | 192篇 |
1991年 | 188篇 |
1990年 | 138篇 |
1989年 | 124篇 |
1988年 | 90篇 |
1987年 | 68篇 |
1986年 | 59篇 |
1985年 | 86篇 |
1984年 | 59篇 |
1983年 | 72篇 |
1982年 | 60篇 |
1981年 | 38篇 |
1980年 | 20篇 |
1979年 | 34篇 |
1978年 | 12篇 |
1977年 | 20篇 |
1976年 | 13篇 |
1959年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
181.
网格曲面中孔洞的光滑填充算法研究 总被引:14,自引:0,他引:14
三角网格模型是几何描述的一种重要形式,有着广泛的应用。但三角网络模型常常会存在孔洞缺陷。这些孔洞的存在一方面影响视觉效果,另一方面会影响许多后续的操作,如快速原型制造、有限元分析等,因此有必要对这些孔洞进行修补。目前绝大多数孔洞填充算法是将网格模型中的孔洞提取成空间多边形,并对孔洞多边形进行三角化。这种处理方法的主要缺陷是没有考虑网格曲面在孔洞附近的几何形态,因而填充部分不能与整个曲面光滑地融为一体。笔者提出了一种三角网格曲面中孔洞的光滑填充算法。该算法根据孔洞周围网格曲面的几何信息来增加孔洞内部的采样点,然后再对增加的采样点进行三角化,较好地解决了填充部分与整体曲面光滑连接的问题。 相似文献
182.
183.
金永杰 《核电子学与探测技术》1989,9(1):10-17
本文所提出的投影域重建——再投影迭代算法可以恢复不完整的扇形束投影数据,从而实现从有限的投影数据重建图象。这种算法把滤波——反投影图象重建过程和再投影的过程纳入一个公式,仅在投影域上估算未知的投影数据,因此避免了重建过程和反投影过程中的插值运算,改善了收敛性,提高了计算精度,缩短了运算时间。模拟实验表明:即使有70%的投影数据丢失,经过两次迭代就能以令人满意的精度恢复丢失的投影数据。 相似文献
184.
185.
This paper introduces and evaluates a new class of knowledge model, the recursive Bayesian multinet (RBMN), which encodes the joint probability distribution of a given database. RBMNs extend Bayesian networks (BNs) as well as partitional clustering systems. Briefly, a RBMN is a decision tree with component BNs at the leaves. A RBMN is learnt using a greedy, heuristic approach akin to that used by many supervised decision tree learners, but where BNs are learnt at leaves using constructive induction. A key idea is to treat expected data as real data. This allows us to complete the database and to take advantage of a closed form for the marginal likelihood of the expected complete data that factorizes into separate marginal likelihoods for each family (a node and its parents). Our approach is evaluated on synthetic and real-world databases. 相似文献
186.
Experimentally determined p,V,T data are reported for toluene, trichloromethane, dichloromethane, acetonitrile, aniline, and n-dodecane at 278, 288, 298, 313, and 323 K, except for dichloromethane, for which the highest temperature was 298 K. At each temperature, measurements were done at pressures up to about 280 MPa or (for aniline and n-dodecane) at a lower pressure slightly below the freezing pressure at the temperature of measurement. Values of the isobaric expansivity isothermal compressibility and (for toluene, trichloromethane, dichloromethane, and acetonitrile) internal pressure, derived from the p,V,T data, are presented. 相似文献
187.
从微观评价核数据库出发 ,计算给出了快堆谱的伪裂变产物数据 ,包括一群的截面数据和多群的全套中子数据 ,裂变核有2 3 5U和2 3 9Pu。截面数据有全截面、弹性散射、非弹散射、(n ,γ)、(n ,2n)截面 ,多群全套中子数据还包括次级中子角分布和能谱。数据以ENDF B -6格式给出 ,同时还分析讨论了数据误差和可靠性 ,数据可用于实际的快堆计算 相似文献
188.
Transport problems typically involve at least two types of constraints, on income and on time. Therefore, the indirect utility
function depends either on the income available after having subtracted the cost of the discrete alternative and on the free
time left after having worked and travelled by each competing option. In the typical linear-in-the-attributes and in-the-parameters
specification, that represents the first grade approximation of the indirect utility function, the effect of income and time
constraints cancel out and only the cost and time of the alternatives matter in the comparison between them. From a microeconomic
point of view this is equivalent to assume that income and time effects could be disregarded; which is not always the case.
To account for these effects the utility function should include second order attributes; however, in non-linear utility functions
it may not be easy to distinguish among several effects that could be relevant: direct preferences for good and leisure, and
simple interactions between attributes other than income and time effects. This paper analyses these effects from a theoretical
point of view focusing on the possible confounding problem in detecting income and time effects. We use a dataset collected
for a modal choice context and containing both revealed and stated preference data, and estimate several NL models examining
the effect of the different second-order terms on detecting income and time effects. We compared specifications including
square cost and time attributes, interactions between time and cost, cost divided by the income available to be spent on free
time, and time multiplied by free time. Our results confirm the strong effect of direct preferences for goods and leisure
time on choice, and the potential confounding effect between quadratic attributes and other non-linear omitted terms. Finally,
we also found that care should be taken in highlighting income and time effects using mixed data sources, since confounding
effects can occur when non-linearities are accounted for in both data sets. 相似文献
189.
190.
This paper presents Bayes estimators for the reliability measures of the individual components in a multi-component systems in the presence of masked system life test data. The life time distributions of the system components are assumed to be geometric with different parameters. Two-sided Bayesian probability intervals of the parameters are also derived. Numerical simulation study is given in order to: (i) explain how one can apply the theoretical results obtained, (ii) study the influence of the sample size and masking level on the accuracy of point estimates. 相似文献