全文获取类型
收费全文 | 47895篇 |
免费 | 8139篇 |
国内免费 | 5454篇 |
专业分类
电工技术 | 3805篇 |
综合类 | 5707篇 |
化学工业 | 2759篇 |
金属工艺 | 2234篇 |
机械仪表 | 3150篇 |
建筑科学 | 3068篇 |
矿业工程 | 986篇 |
能源动力 | 695篇 |
轻工业 | 1022篇 |
水利工程 | 625篇 |
石油天然气 | 1584篇 |
武器工业 | 712篇 |
无线电 | 8353篇 |
一般工业技术 | 3324篇 |
冶金工业 | 3818篇 |
原子能技术 | 235篇 |
自动化技术 | 19411篇 |
出版年
2024年 | 170篇 |
2023年 | 961篇 |
2022年 | 1893篇 |
2021年 | 1886篇 |
2020年 | 2052篇 |
2019年 | 1732篇 |
2018年 | 1470篇 |
2017年 | 1923篇 |
2016年 | 2118篇 |
2015年 | 2230篇 |
2014年 | 3131篇 |
2013年 | 3172篇 |
2012年 | 3813篇 |
2011年 | 4003篇 |
2010年 | 3221篇 |
2009年 | 3156篇 |
2008年 | 3065篇 |
2007年 | 3571篇 |
2006年 | 2925篇 |
2005年 | 2483篇 |
2004年 | 1983篇 |
2003年 | 1762篇 |
2002年 | 1482篇 |
2001年 | 1292篇 |
2000年 | 1098篇 |
1999年 | 933篇 |
1998年 | 717篇 |
1997年 | 628篇 |
1996年 | 474篇 |
1995年 | 427篇 |
1994年 | 349篇 |
1993年 | 231篇 |
1992年 | 234篇 |
1991年 | 164篇 |
1990年 | 148篇 |
1989年 | 110篇 |
1988年 | 62篇 |
1987年 | 48篇 |
1986年 | 42篇 |
1985年 | 51篇 |
1984年 | 58篇 |
1983年 | 32篇 |
1982年 | 45篇 |
1981年 | 38篇 |
1980年 | 25篇 |
1979年 | 17篇 |
1978年 | 14篇 |
1977年 | 18篇 |
1959年 | 3篇 |
1951年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Nilesh P. Vanikar Shantipal S. Ohol Saeede Goldar 《International Journal of Cast Metals Research》2018,31(4):249-259
Bottom pour ladles with stopper rod systems are commonly used in the metal casting industry. However, stopper rod bottom-pouring systems have not yet been developed for the lower thermal masses of alloys typically used in the investment casting industry. Large thermal masses used with bottom pour systems are typically limited for ladles larger than 700 kg and to certain alloys with higher fluidity and longer solidification time like cast iron, aluminum alloys etc. In this study, bottom pour ladle designs and low thermal mass refractory systems have been developed and evaluated in production investment foundry trials with 300 kg pouring ladle. The ladles system and pouring practices used will be described along with the results from the pouring trials for SS304 that represents typical alloys used in Investment casting industries. Optimization of the variables used in an experimentation using Genetic algorithm is also explained. 相似文献
72.
针对齿轮故障特征微弱,在强背景噪声下难以有效提取的问题,提出了一种改进奇异谱分解(ISSD)结合奇异值分解(SVD)的齿轮故障特征提取方法。针对奇异谱分解(SSD)算法中模态参数需凭经验选取的缺陷,基于散布熵优化算法对SSD算法进行了改进,在得到既定的一组奇异谱分量的基础上,根据峭度值最大准则筛选出了最佳奇异谱分量并进行了SVD处理,采用奇异值能量标准谱自适应地确定了信号重构阶数以还原信号和提高降噪效果。最后对信号进行包络解调以提取齿轮故障特征,将所提方法运用到仿真信号和齿轮实测信号中,并同传统包络谱、SSD包络谱以及经验模态分解结合SVD(EMD-SVD)方法进行了对比分析,结果表明,所提方法的降噪和特征提取效果更佳,能够更加有效地实现齿轮故障的判别。 相似文献
73.
74.
ABSTRACTFeature selection is an important task to improve the classifier’s accuracy and to decrease the problem size. A number of methodologies have been presented for feature selection problems using metaheuristic algorithms. In this paper, an improved self-adaptive inertia weight particle swarm optimisation with local search and combined with C4.5 classifiers for feature selection algorithm is proposed. In this proposed algorithm, the gradient base local search with its capacity of helping to explore the feature space and an improved self-adaptive inertia weight particle swarm optimisation with its ability to converge a best global solution in the search space. Experimental results have verified that the SIW-APSO-LS performed well compared with other state of art feature selection techniques on a suit of 16 standard data sets. 相似文献
75.
The swirl gripper is an electrically activated noncontact handling device that uses swirling airflow to generate a lifting force. This force can be used to pick up a workpiece placed underneath the swirl gripper without any contact. It is applicable, for example, on a semiconductor wafer production line, where contact must be avoided during the handling and moving of a workpiece to minimize damage. When a workpiece levitates underneath a swirl gripper, the gap height between them is critical for safe handling. Therefore, in this study, we develop a theoretical model of the swirl gripper, based on which a method to estimate the levitation gap height by detecting pressure at two points is proposed. Experiments indicate that the estimated gap height can track changes in actual gap height accurately in real time, when the gap height is relatively small and the inertia of airflow in the gap is negligible. In addition, the force between the gripper and workpiece can also be estimated using the detected pressure. As a result, a desired relationship between the force and gap height can be achieved by adjusting the rotating speed of the fan according to the real-time estimated force and gap height using a microcontroller. The control system was experimentally verified using a desired linear relationship. Because the stiffness of the force decreases with increasing gap height for a constant gripper fan rotating speed, the linear relationship between the force and gap height, which means a constant stiffness, is expected to enhance handling stability of workpieces. 相似文献
76.
Abdelmoty M. Ahmed Reda Abo Alez Gamal Tharwat Muhammad Taha B. Belgacem Ahmad M. J. Al Moustafa 《成像科学杂志》2020,68(1):11-23
ABSTRACTArabic sign language (ArSL) is method of communication between deaf communities in Arab countries; therefore, the development of systemsthat can recognize the gestures provides a means for the Deaf to easily integrate into society. In this research we implemented a computational structurefor an intelligent interpreter that automatically recognizes the isolated dynamic gestures. The proposed system recognizes and translates gesturesperformed with one or both hands. It comprises five subsystems, building dataset, video processing, feature extraction, mapping between ArSL and Arabictext, and text generation. To apply the system, 100-signs of ArSL was used, which was applied on 1500 video files. It's were divided into five classes:alphabet, numbers, "prepositions, pronouns and question words", Arabic life expressions, and "nouns and verbs". The evaluation indicated that thesystem automatically recognizes and translates isolated dynamic ArSL gestures by highly accurate manner. The results showed that the system accuracy is 95.8%. 相似文献
77.
ABSTRACTThis paper proposes the multiple-hypotheses image segmentation and feed-forward neural network classifier for food recognition to improve the performance. Initially, the food or meal image is given as input. Then, the segmentation is applied to identify the regions, where a particular food item is located using salient region detection, multi-scale segmentation, and fast rejection. Then, the features of every food item are extracted by the global feature and local feature extraction. After the features are obtained, the classification is performed for each segmented region using a feed-forward neural network model. Finally, the calorie value is computed with the aid of (i) food volume and (ii) calorie and nutrition measure based on mass value. The experimental results and performance evaluation are validated. The outcome of the proposed method attains 0.947 for Macro Average Accuracy (MAA) and 0.959 for Standard Accuracy (SA), which provides better classification performance. 相似文献
78.
Amer Ibrahim Al-Omari Ibrahim M. Almanjahie Amal S. Hassan Heba F. Nagy 《计算机、材料和连续体(英文)》2020,64(2):835-857
In reliability analysis, the stress-strength model is often used to describe the life of
a component which has a random strength (X) and is subjected to a random stress (Y). In this
paper, we considered the problem of estimating the reliability R=P [Y<X] when the
distributions of both stress and strength are independent and follow exponentiated Pareto
distribution. The maximum likelihood estimator of the stress strength reliability is calculated
under simple random sample, ranked set sampling and median ranked set sampling methods.
Four different reliability estimators under median ranked set sampling are derived. Two
estimators are obtained when both strength and stress have an odd or an even set size. The
two other estimators are obtained when the strength has an odd size and the stress has an
even set size and vice versa. The performances of the suggested estimators are compared
with their competitors under simple random sample via a simulation study. The simulation
study revealed that the stress strength reliability estimates based on ranked set sampling and
median ranked set sampling are more efficient than their competitors via simple random
sample. In general, the stress strength reliability estimates based on median ranked set
sampling are smaller than the corresponding estimates under ranked set sampling and simple
random sample methods. 相似文献
79.
In this article, a new generalization of the inverse Lindley distribution is
introduced based on Marshall-Olkin family of distributions. We call the new distribution,
the generalized Marshall-Olkin inverse Lindley distribution which offers more flexibility
for modeling lifetime data. The new distribution includes the inverse Lindley and the
Marshall-Olkin inverse Lindley as special distributions. Essential properties of the
generalized Marshall-Olkin inverse Lindley distribution are discussed and investigated
including, quantile function, ordinary moments, incomplete moments, moments of
residual and stochastic ordering. Maximum likelihood method of estimation is considered
under complete, Type-I censoring and Type-II censoring. Maximum likelihood estimators
as well as approximate confidence intervals of the population parameters are discussed.
A comprehensive simulation study is done to assess the performance of estimates based
on their biases and mean square errors. The notability of the generalized Marshall-Olkin
inverse Lindley model is clarified by means of two real data sets. The results showed the
fact that the generalized Marshall-Olkin inverse Lindley model can produce better fits
than power Lindley, extended Lindley, alpha power transmuted Lindley, alpha power
extended exponential and Lindley distributions. 相似文献
80.
Massive Open Online Course (MOOC) has become a popular way of online
learning used across the world by millions of people. Meanwhile, a vast amount of
information has been collected from the MOOC learners and institutions. Based on the
educational data, a lot of researches have been investigated for the prediction of the
MOOC learner’s final grade. However, there are still two problems in this research field.
The first problem is how to select the most proper features to improve the prediction
accuracy, and the second problem is how to use or modify the data mining algorithms for
a better analysis of the MOOC data. In order to solve these two problems, an improved
random forests method is proposed in this paper. First, a hybrid indicator is defined to
measure the importance of the features, and a rule is further established for the feature
selection; then, a Clustering-Synthetic Minority Over-sampling Technique (SMOTE) is
embedded into the traditional random forests algorithm to solve the class imbalance
problem. In experiment part, we verify the performance of the proposed method by using
the Canvas Network Person-Course (CNPC) dataset. Furthermore, four well-known
prediction methods have been applied for comparison, where the superiority of our
method has been proved. 相似文献