全文获取类型
收费全文 | 40626篇 |
免费 | 4092篇 |
国内免费 | 2429篇 |
专业分类
电工技术 | 3659篇 |
技术理论 | 6篇 |
综合类 | 4490篇 |
化学工业 | 5081篇 |
金属工艺 | 1796篇 |
机械仪表 | 3267篇 |
建筑科学 | 3362篇 |
矿业工程 | 1468篇 |
能源动力 | 1162篇 |
轻工业 | 2111篇 |
水利工程 | 1102篇 |
石油天然气 | 2238篇 |
武器工业 | 646篇 |
无线电 | 3373篇 |
一般工业技术 | 5408篇 |
冶金工业 | 1087篇 |
原子能技术 | 442篇 |
自动化技术 | 6449篇 |
出版年
2024年 | 216篇 |
2023年 | 602篇 |
2022年 | 1303篇 |
2021年 | 1367篇 |
2020年 | 1242篇 |
2019年 | 1066篇 |
2018年 | 986篇 |
2017年 | 1349篇 |
2016年 | 1466篇 |
2015年 | 1520篇 |
2014年 | 2421篇 |
2013年 | 2701篇 |
2012年 | 2963篇 |
2011年 | 2740篇 |
2010年 | 2244篇 |
2009年 | 2430篇 |
2008年 | 2234篇 |
2007年 | 2512篇 |
2006年 | 2223篇 |
2005年 | 1885篇 |
2004年 | 1576篇 |
2003年 | 1342篇 |
2002年 | 1132篇 |
2001年 | 939篇 |
2000年 | 825篇 |
1999年 | 682篇 |
1998年 | 528篇 |
1997年 | 466篇 |
1996年 | 1402篇 |
1995年 | 809篇 |
1994年 | 621篇 |
1993年 | 195篇 |
1992年 | 210篇 |
1991年 | 178篇 |
1990年 | 142篇 |
1989年 | 105篇 |
1988年 | 90篇 |
1987年 | 53篇 |
1986年 | 45篇 |
1985年 | 46篇 |
1984年 | 72篇 |
1983年 | 34篇 |
1982年 | 37篇 |
1981年 | 39篇 |
1980年 | 28篇 |
1979年 | 21篇 |
1978年 | 22篇 |
1977年 | 18篇 |
1976年 | 5篇 |
1959年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
The ensemble learning paradigm has proved to be relevant to solving most challenging industrial problems. Despite its successful application especially in the Bioinformatics, the petroleum industry has not benefited enough from the promises of this machine learning technology. The petroleum industry, with its persistent quest for high-performance predictive models, is in great need of this new learning methodology. A marginal improvement in the prediction indices of petroleum reservoir properties could have huge positive impact on the success of exploration, drilling and the overall reservoir management portfolio. Support vector machines (SVM) is one of the promising machine learning tools that have performed excellently well in most prediction problems. However, its performance is a function of the prudent choice of its tuning parameters most especially the regularization parameter, C. Reports have shown that this parameter has significant impact on the performance of SVM. Understandably, no specific value has been recommended for it. This paper proposes a stacked generalization ensemble model of SVM that incorporates different expert opinions on the optimal values of this parameter in the prediction of porosity and permeability of petroleum reservoirs using datasets from diverse geological formations. The performance of the proposed SVM ensemble was compared to that of conventional SVM technique, another SVM implemented with the bagging method, and Random Forest technique. The results showed that the proposed ensemble model, in most cases, outperformed the others with the highest correlation coefficient, and the lowest mean and absolute errors. The study indicated that there is a great potential for ensemble learning in petroleum reservoir characterization to improve the accuracy of reservoir properties predictions for more successful explorations and increased production of petroleum resources. The results also confirmed that ensemble models perform better than the conventional SVM implementation. 相似文献
3.
Multifunctional 3D Patternable Drug‐Embedded Nanocarrier‐Based Interfaces to Enhance Signal Recording and Reduce Neuron Degeneration in Neural Implantation 下载免费PDF全文
4.
Fresh and frozen-thawed (F-T) pork meats were classified by Vis–NIR hyperspectral imaging. Eight optimal wavelengths (624, 673, 460, 588, 583, 448, 552 and 609 nm) were selected by successive projections algorithm (SPA). The first three principal components (PCs) obtained by principal component analysis (PCA) accounted for over 99.98% of variance. Gray-level-gradient co-occurrence matrix (GLGCM) was applied to extract 45 textural features from the PC images. The correct classification rate (CCR) was employed to evaluate the performance of the partial least squares-discriminate analysis (PLS-DA) models, by using (A) the reflected spectra at full wavelengths and (B) those at the optimal wavelengths, (C) the extracted textures based on the PC images, and (D) the fused variables combining spectra at the optimal wavelengths and textures. The results showed that the best CCR of 97.73% was achieved by applying (D), confirming the high potential of textures for fresh and F-T meat discrimination. 相似文献
5.
This article presents a new approach for solving the Optimal Control Problem (OCP) of linear time-delay systems with a quadratic cost functional. The proposed method can also be used for designing optimal control time-delay systems with disturbance. In this study, the Variational Iteration Method (VIM) is employed to convert the original Time-Delay Optimal Control Problem (TDOCP) into a sequence of nonhomogeneous linear two-point boundary value problems (TPBVPs). The optimal control law obtained consists of an accurate linear feedback term and a nonlinear compensation term which is the limit of an adjoint vector sequence. The feedback term is determined by solving Riccati matrix differential equation. By using the finite-step iteration of a nonlinear compensation sequence, we can obtain a suboptimal control law. Finally, Illustrative examples are included to demonstrate the validity and applicability of the technique. 相似文献
6.
宁东供水工程供水水泵共有卧式和立式离心泵2种方案可供选择,也是工程论证时争论的焦点,经综合比较及主机设备的国际招标,最终确定了奥地利安德里兹公司的卧式双吸中开式离心泵为宁东供水工程的供水水泵。 相似文献
7.
8.
9.
Barbara M. Johnston Peter R. Johnston 《International journal for numerical methods in engineering》2003,56(4):589-607
Accurate numerical evaluation of integrals arising in the boundary element method is fundamental to achieving useful results via this solution technique. In this paper, a number of techniques are considered to evaluate the weakly singular integrals which arise in the solution of Laplace's equation in three dimensions and Poisson's equation in two dimensions. Both are two‐dimensional weakly singular integrals and are evaluated using (in a product fashion) methods which have recently been used for evaluating one‐dimensional weakly singular integrals arising in the boundary element method. The methods used are based on various polynomial transformations of conventional Gaussian quadrature points where the transformation polynomial has zero Jacobian at the singular point. Methods which split the region of integration into sub‐regions are considered as well as non‐splitting methods. In particular, the newly introduced and highly accurate generalized composite subtraction of singularity and non‐linear transformation approach (GSSNT) is applied to various two‐dimensional weakly singular integrals. A study of the different methods reveals complex relationships between transformation orders, position of the singular point, integration kernel and basis function. It is concluded that the GSSNT method gives the best overall results for the two‐dimensional weakly singular integrals studied. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
10.
电信企业信息化的实质就是赋予电信企业精细化的企业资源整合能力,本以此认识为出发点,通过定义基本的信息化业务元素,需求参数和基本信息处理机制,构建出带有行业共性的电信企业信息化统一模型,该模型针对目前电信企业信息化中常见的和潜在的问题提供了有效的解决措施。 相似文献