全文获取类型
收费全文 | 11334篇 |
免费 | 1541篇 |
国内免费 | 1201篇 |
专业分类
电工技术 | 674篇 |
综合类 | 1056篇 |
化学工业 | 325篇 |
金属工艺 | 171篇 |
机械仪表 | 594篇 |
建筑科学 | 537篇 |
矿业工程 | 375篇 |
能源动力 | 196篇 |
轻工业 | 367篇 |
水利工程 | 131篇 |
石油天然气 | 221篇 |
武器工业 | 154篇 |
无线电 | 1222篇 |
一般工业技术 | 548篇 |
冶金工业 | 104篇 |
原子能技术 | 95篇 |
自动化技术 | 7306篇 |
出版年
2024年 | 31篇 |
2023年 | 131篇 |
2022年 | 258篇 |
2021年 | 285篇 |
2020年 | 335篇 |
2019年 | 287篇 |
2018年 | 296篇 |
2017年 | 334篇 |
2016年 | 421篇 |
2015年 | 445篇 |
2014年 | 732篇 |
2013年 | 688篇 |
2012年 | 894篇 |
2011年 | 970篇 |
2010年 | 737篇 |
2009年 | 898篇 |
2008年 | 905篇 |
2007年 | 975篇 |
2006年 | 790篇 |
2005年 | 729篇 |
2004年 | 531篇 |
2003年 | 454篇 |
2002年 | 357篇 |
2001年 | 239篇 |
2000年 | 222篇 |
1999年 | 185篇 |
1998年 | 137篇 |
1997年 | 130篇 |
1996年 | 103篇 |
1995年 | 98篇 |
1994年 | 71篇 |
1993年 | 56篇 |
1992年 | 58篇 |
1991年 | 30篇 |
1990年 | 30篇 |
1989年 | 25篇 |
1988年 | 10篇 |
1987年 | 13篇 |
1986年 | 13篇 |
1985年 | 17篇 |
1984年 | 18篇 |
1983年 | 21篇 |
1982年 | 17篇 |
1981年 | 14篇 |
1980年 | 18篇 |
1979年 | 12篇 |
1978年 | 8篇 |
1977年 | 12篇 |
1976年 | 13篇 |
1975年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
21.
22.
许禄 《计算机与应用化学》1994,11(2):107-111
进行碳-13NMR波谱模拟的一种常用方法为线性回归,其数学模型则由已知结构所测得的化学位来建立。显然,每一数学模型仅可用于某种相似的化学环境。因此,为了进行化学环境的分类,本文提出权重层次位图法和分子连接性指数法两种方法以进行一些参数的计算,同时采用多元分析手段,如主成分分析和聚类分析,以进行多维空间数据点的显示,所得结果比较满意,从而可为碳-13波谱模拟中回归方程的选择提供理论依据。 相似文献
23.
Bezier曲线树 总被引:2,自引:0,他引:2
王晓东 《计算机辅助设计与图形学学报》1994,6(4):266-270
本文提出Bezier样条曲线树结构用以高效地实现对曲边几何体的各种几何运算。对任意一条Bezier样条曲线,用deCasteljau算法进行分割后,将分割结果用一平衡二叉树来存储。此后,对于该曲线所作的各种几何运算可以一种逼近等级的方式来进行。先以粗糙的逼近来进行计算,必要时增加精密度,从而提高各种运算的效率。 相似文献
24.
25.
DNA序列比对分析中的统计特征方法 总被引:1,自引:0,他引:1
提出了一种新的基于统计的序列特征定义,并以此对进化树进行构建.同时对这一方法进行了分类测试和进化树构建测试,发现所得测试结果与同样是用进化树进行构建的基于两序列比对的传统算法比较,其性能和适用性都有明显改善. 相似文献
26.
27.
28.
The goal of face recognition is to distinguish persons via their facial images. Each person's images form a cluster, and a new image is recognized by assigning it to the correct cluster. Since the images are very high-dimensional, it is necessary to reduce their dimension. Linear discriminant analysis (LDA) has been shown to be effective at dimension reduction while preserving the cluster structure of the data. It is classically defined as an optimization problem involving covariance matrices that represent the scatter within and between clusters. The requirement that one of these matrices be nonsingular restricts its application to datasets in which the dimension of the data does not exceed the sample size. For face recognition, however, the dimension typically exceeds the number of images in the database, resulting in what is referred to as the small sample size problem. Recently, the applicability of LDA has been extended by using the generalized singular value decomposition (GSVD) to circumvent the nonsingularity requirement, thus making LDA directly applicable to face recognition data. Our experiments confirm that LDA/GSVD solves the small sample size problem very effectively as compared with other current methods. 相似文献
29.
Education-driven research in CAD 总被引:1,自引:0,他引:1
We argue for a new research category, named education-driven research (EDR), which fills the gap between traditional field-specific research that is not concerned with educational objectives and research in education that focuses on fundamental teaching and learning principles and possibly on their customization to broad areas (such as mathematics or physics), but not to specific disciplines (such as CAD). The objective of EDR is to simplify the formulation of the underlying theoretical foundations and of specific tools and solutions in a specialized domain, so as to make them easy to understand and internalize. As such, EDR is a difficult and genuine research activity, which requires a deep understanding of the specific field and can rarely be carried out by generalists with primary expertise in broad education principles. We illustrate the concept of EDR with three examples in CAD: (1) the Split and Tweak subdivisions of a polygon and its use for generating curves, surfaces, and animations; (2) the construction of a topological partition of a plane induced by an arbitrary arrangement of edges; and (3) a romantic definition of the minimal and Hausdorff distances. These examples demonstrate the value of using analogies, of introducing evocative terminology, and of synthesizing the simplest fundamental building blocks. The intuitive understanding provided by EDR enables the students (and even the instructor) to better appreciate the limitations of a particular solution and to explore alternatives. In particular, in these examples, EDR has allowed the author to: (1) reduce the cost of evaluating a cubic B-spline curve; (2) develop a new subdivision curve that is better approximated by its control polygon than either a cubic B-spline or an interpolating 4-point subdivision curve; (3) discover how a circuit inclusion tree may be used for identifying the faces in an arrangement; and (4) rectify a common misconception about the computation of the Hausdorff error between triangle meshes. We invite the scientific community to encourage the development of EDR by publishing its results as genuine research contributions in peer-reviewed professional journals. 相似文献
30.
We developed a stream classification system that is based on stream’s susceptibility to algal growth using a two-step approach. The model portrays algal biomass as a result of stream’s response to nutrient concentrations and the response is governed by various stream factors. In the first step, a nutrient-chlorophyll a relationship was developed to characterize nutrient’s effects on algal biomass. Residuals of the relationship were attributed to stream’s susceptibility to algal growth in response to nutrients and referred to as “observed” susceptibility. In the second step, conditions of other contributing factors were used to explain the variation in the residuals and the developed relationship was used to generate “predicted” susceptibility. Existing data compiled from various monitoring projects of Illinois streams and rivers were used to illustrate the approach. Streams were classified into three (high, medium, and low) categories based on their observed and predicted susceptibility values, respectively. With the available data, the model showed a 40-50% success rate for classifying the streams based on three observed and predicted susceptibility categories. Model entropy also was calculated for selecting the best model. The results show the important role of both nutrients and other contributing factors in explaining the variation of algal biomass. The study also suggests ways to fine tune the model and improve its accuracy, which would make the presented model a more viable tool for stream classification for establishing nutrient criteria to prevent surface streams from eutrophication. 相似文献