全文获取类型
收费全文 | 22366篇 |
免费 | 1870篇 |
国内免费 | 1208篇 |
专业分类
电工技术 | 1403篇 |
综合类 | 1729篇 |
化学工业 | 2460篇 |
金属工艺 | 1983篇 |
机械仪表 | 1973篇 |
建筑科学 | 2120篇 |
矿业工程 | 1414篇 |
能源动力 | 939篇 |
轻工业 | 1265篇 |
水利工程 | 652篇 |
石油天然气 | 955篇 |
武器工业 | 250篇 |
无线电 | 1388篇 |
一般工业技术 | 2980篇 |
冶金工业 | 1112篇 |
原子能技术 | 237篇 |
自动化技术 | 2584篇 |
出版年
2024年 | 90篇 |
2023年 | 344篇 |
2022年 | 589篇 |
2021年 | 670篇 |
2020年 | 722篇 |
2019年 | 609篇 |
2018年 | 621篇 |
2017年 | 776篇 |
2016年 | 874篇 |
2015年 | 896篇 |
2014年 | 1356篇 |
2013年 | 1453篇 |
2012年 | 1514篇 |
2011年 | 1807篇 |
2010年 | 1378篇 |
2009年 | 1324篇 |
2008年 | 1168篇 |
2007年 | 1455篇 |
2006年 | 1221篇 |
2005年 | 1025篇 |
2004年 | 905篇 |
2003年 | 751篇 |
2002年 | 630篇 |
2001年 | 482篇 |
2000年 | 472篇 |
1999年 | 447篇 |
1998年 | 320篇 |
1997年 | 323篇 |
1996年 | 233篇 |
1995年 | 187篇 |
1994年 | 183篇 |
1993年 | 114篇 |
1992年 | 95篇 |
1991年 | 73篇 |
1990年 | 72篇 |
1989年 | 55篇 |
1988年 | 45篇 |
1987年 | 24篇 |
1986年 | 26篇 |
1985年 | 20篇 |
1984年 | 20篇 |
1983年 | 19篇 |
1982年 | 19篇 |
1981年 | 8篇 |
1980年 | 10篇 |
1979年 | 2篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
141.
Particle swarm optimization (PSO) is an evolutionary metaheuristic inspired by the flocking behaviour of birds, which has successfully been used to solve several kinds of problems, although there are few studies aimed at solving discrete optimization problems. One disadvantage of PSO is the risk of a premature search convergence. To prevent this, we propose to introduce diversity into a discrete PSO by adding a random velocity. The degree of the introduced diversity is not static (i.e. preset before running PSO) but instead changes dynamically according to the heterogeneity of the population (i.e. if the search has converged or not). We solve the response time variability problem (RTVP) to test these two new ideas. The RTVP is an NP-hard combinatorial scheduling problem that has recently appeared in the literature. It occurs whenever products, clients or jobs need to be sequenced in such a way that the variability in the time between the instants at which they receive the necessary resources is minimized. The most efficient algorithm for solving non-small instances of the RTVP published to date is a classical PSO algorithm, referred to by the authors as PSO-M1F. In this paper, we propose 10 discrete PSO algorithms for solving the RTVP: one based on the ideas described above (PSO -c3dyn) and nine based on strategies proposed in the literature and adapted for solving a discrete optimization problem such as the RTVP. We compare all 11 PSO algorithms and the computational experiment shows that, on average, the best results obtained are due to our proposal of dynamic control mechanism for introducing diversity. 相似文献
142.
Precision investment casting process planning has been tackled in the past according to experience. Recently, casting simulation software is being increasingly used to predict product quality by implementing ‘what-if’ scenarios. Input parameters include relatively simple factors such as mould temperature, melting temperature, casting material. They also include factors whose influence is more complex to quantify, such number and location of feeding points, diameter and length of inflow channels, angle of channel with respect to the main sprue axis. Simulation results cannot help the engineer for workpieces other than the one simulated. In this paper a series of feedforward artificial neural network (ANN) models is presented aiming at such generalisation. To achieve this, a large number of software simulation runs were conducted for a number of different small parts, with varying runner geometry and casting conditions. The parameters characterising part geometry have been chosen to be surface area and volume-to-area ratio. The different ANN models predictive capabilities are reflected to the respective training and generalisation errors. A user-friendly interface has been conducted for model execution in a complete application, whose main virtue is expandability. 相似文献
143.
A genetic algorithm-based artificial neural network model for the optimization of machining processes 总被引:5,自引:2,他引:3
Artificial intelligent tools like genetic algorithm, artificial neural network (ANN) and fuzzy logic are found to be extremely
useful in modeling reliable processes in the field of computer integrated manufacturing (for example, selecting optimal parameters
during process planning, design and implementing the adaptive control systems). When knowledge about the relationship among
the various parameters of manufacturing are found to be lacking, ANNs are used as process models, because they can handle
strong nonlinearities, a large number of parameters and missing information. When the dependencies between parameters become
noninvertible, the input and output configurations used in ANN strongly influence the accuracy. However, running of a neural
network is found to be time consuming. If genetic algorithm-based ANNs are used to construct models, it can provide more accurate
results in less time. This article proposes a genetic algorithm-based ANN model for the turning process in manufacturing Industry.
This model is found to be a time-saving model that satisfies all the accuracy requirements. 相似文献
144.
145.
针对具有不同动力学节点和不同拓扑结构的两个复杂网络,研究其广义同步问题,并考虑具有耦合时滞和参数未知的情况.基于Babalat引理,并利用Lyapunov稳定性方法,获得广义同步判据,设计有效的自适应控制器,实现混沌系统参数已知和参数未知两种情况下的广义同步.仿真验证了算法的有效性. 相似文献
146.
协同过滤推荐算法是电子商务推荐系统中应用最成功的推荐技术之一,而影响协同过滤推荐算法准确率的关键因素是用户相似性度量方法。针对传统相似性度量方法没有考虑共同评分项数量对推荐质量的影响,将用户之间的共同评分项数量作为相似性计算的一个重要指标,从而得到一种改进的相似性度量方法。但这仍然不能解决数据稀疏带来的推荐质量下降的问题,鉴于此,在上述改进的基础上,提出了利用复杂网络中的结构相似性来度量用户之间相似性的方法,使计算结果更具实际意义和准确性。实验表明,通过这些改进能够有效避免传统方法带来的弊端,提高系统的推荐质量。 相似文献
147.
148.
传统的灰色GM(1,1)预测模型是针对近似齐次指数序列建立的预测模型。为了拓广灰色预测模型的适用范围,建立了近似非齐次指数序列的灰色DNGM(1,1)预测模型。研究了这种灰色预测模型的性质,证明了这种模型都具有线性不变性,也能够完全拟合非齐次指数序列。考虑到初值条件对灰色模型的影响,对该模型进行了参数优化。数据仿真和实例分析表明,灰色DNGM(1,1)预测模型具有较高的预测精度。 相似文献
149.
三角形迷宫流道滴灌灌水器结构参数及水力特性研究 总被引:1,自引:0,他引:1
以滴灌灌水器三角形迷宫流道结构为研究单元,利用均匀设计方法,结合计算流体动力学软件Fluent6.2对流道内部流体的流动进行了数值模拟,通过多元回归计算,获得流道各结构参数与流量系数和流态指数的量化关系。分析这一量化关系表明,流道转角与流量成负相关,与流态指数成正相关;流道宽与流量成正相关,与流态指数成负相关;齿高与流量成负相关,与流态指数成正相关。同时分析了灌水器内部流道的水力性能和流场特性,为三角形迷宫流道滴灌灌水器的研发提供了相应的理论依据。 相似文献
150.
Meiling Liu Xiangnan Liu Menxin Wu Lufeng Li Lina Xiu 《Computers & Geosciences》2011,37(10):1642-1652
A generalized dynamic fuzzy neural network (GDFNN) was created to estimate heavy metal concentrations in rice by integrating spectral indices and environmental parameters. Hyperspectral data, environmental parameters, and heavy metal content were collected from field experiments with different levels of heavy metal pollution (Cu and Cd). Input variables used in the GDFNN model were derived from 10 variables acquired by gray relational analysis. The assessment models for Cd and Cu concentration employed five and six input variables, respectively. The results showed that the GDFNN for estimating Cu and Cd concentrations in rice performed well at prediction with a compact network structure using the training, validation, and testing sets (for Cu, fuzzy rules=9, R2 greater than 0.75, and RMSE less than 2.5; for Cd, fuzzy rules=9, R2 greater than 0.75, and RMSE less than 1.0). The final GDFNN model was then compared with a back-propagation (BP) neural network model, adaptive-network-based fuzzy interference systems (ANFIS), and a regression model. The accuracies of GDFNN model prediction were usually slightly better than those of the other three models. This demonstrates that the GDFNN model is more suitable for predicting heavy metal concentrations in rice. 相似文献