全文获取类型
收费全文 | 217484篇 |
免费 | 31013篇 |
国内免费 | 21610篇 |
专业分类
电工技术 | 25547篇 |
技术理论 | 17篇 |
综合类 | 27544篇 |
化学工业 | 13620篇 |
金属工艺 | 5931篇 |
机械仪表 | 14113篇 |
建筑科学 | 16302篇 |
矿业工程 | 6600篇 |
能源动力 | 7739篇 |
轻工业 | 5316篇 |
水利工程 | 10027篇 |
石油天然气 | 8654篇 |
武器工业 | 2870篇 |
无线电 | 29556篇 |
一般工业技术 | 14671篇 |
冶金工业 | 5618篇 |
原子能技术 | 1548篇 |
自动化技术 | 74434篇 |
出版年
2024年 | 674篇 |
2023年 | 3756篇 |
2022年 | 7272篇 |
2021年 | 8404篇 |
2020年 | 8766篇 |
2019年 | 6964篇 |
2018年 | 6272篇 |
2017年 | 7665篇 |
2016年 | 8619篇 |
2015年 | 9423篇 |
2014年 | 13998篇 |
2013年 | 13727篇 |
2012年 | 16387篇 |
2011年 | 17420篇 |
2010年 | 13612篇 |
2009年 | 14233篇 |
2008年 | 14533篇 |
2007年 | 16350篇 |
2006年 | 13973篇 |
2005年 | 12338篇 |
2004年 | 10105篇 |
2003年 | 8896篇 |
2002年 | 7005篇 |
2001年 | 5855篇 |
2000年 | 4825篇 |
1999年 | 3791篇 |
1998年 | 2939篇 |
1997年 | 2407篇 |
1996年 | 2155篇 |
1995年 | 1831篇 |
1994年 | 1465篇 |
1993年 | 1012篇 |
1992年 | 789篇 |
1991年 | 591篇 |
1990年 | 469篇 |
1989年 | 398篇 |
1988年 | 252篇 |
1987年 | 147篇 |
1986年 | 126篇 |
1985年 | 126篇 |
1984年 | 122篇 |
1983年 | 66篇 |
1982年 | 90篇 |
1981年 | 42篇 |
1980年 | 51篇 |
1979年 | 55篇 |
1978年 | 17篇 |
1974年 | 10篇 |
1959年 | 21篇 |
1951年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Due to the severe outdoor PM2.5 pollution in China, many people have installed air-cleaning systems in homes. To make the systems run automatically and intelligently, we developed a recurrent neural network (RNN) that uses historical data to predict the future indoor PM2.5 concentration. The RNN architecture includes an autoencoder and a recurrent part. We used data measured in an apartment over the course of an entire year to train and test the RNN. The data include indoor/outdoor PM2.5 concentration, environmental parameters and time of day. By comparing three different input strategies, we found that a strategy employing historical PM2.5 and time of day as inputs performed best. With this strategy, the model can be applied to predict the relatively stable trend of indoor PM2.5 concentration in advance. When the input length is 2 h and the prediction horizon is 30 min, the median prediction error is 8.3 µg/m3 for the whole test set. For times with indoor PM2.5 concentrations between (20,50] µg/m3 and (50,100] µg/m3, the median prediction error is 8.3 and 9.2 µg/m3, respectively. The low prediction error between the ground-truth and predicted values shows that the RNN can predict indoor PM2.5 concentrations with satisfactory performance. 相似文献
102.
将幸福河概念与长江三角洲区域一体化发展战略相结合,基于自然、人类社会、人水关系3个系统构建了包含24个指标的长三角幸福河层次评价指标体系;引入需求层次理论,以基础Ⅰ层次、基础Ⅱ层次、提升Ⅰ层次、提升Ⅱ层次、幸福层次5个层次作为幸福河的层次评价等级,运用熵权物元模型,建立了长三角幸福河层次评价模型,并对2018年长三角三省一市幸福河层次等级进行了评价。结果表明,三省一市均处于转化中的中间状态,其中江苏省向提升Ⅰ层次转化,浙江省、安徽省向提升Ⅱ层次转化,上海市向幸福层次转化,说明区域整体幸福河层次处于较高水平,但稳定性较差。 相似文献
103.
Shuangjiang Feng Shuxue Wang Yuanfei Lv Lei He Qiurong Li Tao Zhang 《Polymer International》2019,68(3):494-502
Hydrogels have been widely used as mild biomaterials due to their bio‐affinity, high drug loading capability and controllable release profiles. However, hydrogel‐based carriers are greatly limited for the delivery of hydrophobic payloads due to the lack of hydrophobic binding sites. Herein, nano‐liposome micelles were embedded in semi‐interpenetrating poly[(N‐isopropylacrylamide)‐co‐chitosan] (PNIPAAm‐co‐CS) and poly[(N‐isopropylacrylamide)‐co‐(sodium alginate)] (PNIPAAm‐co‐SA) hydrogels which were responsive to both temperature and pH, thereby establishing tunable nanocomposite hydrogel delivery systems. Nano‐micelles formed via the self‐assembly of phospholipid could serve as the link between hydrophobic drug and hydrophilic hydrogel due to their special amphiphilic structure. The results of transmission and scanning electron microscopies and infrared spectroscopy showed that the porous hydrogels were successfully fabricated and the liposomes encapsulated with baicalein could be well contained in the network. In addition, the experimental results of response release in vitro revealed that the smart hydrogels showed different degree of sensitiveness under different pH and temperature stimuli. The results of the study demonstrate that combining PNIPAAm‐co‐SA and PNIPAAm‐co‐CS hydrogels with liposomes encapsulated with hydrophobic drugs is a feasible method for hydrophobic drug delivery and have potential application prospects in the medical field. © 2018 Society of Chemical Industry 相似文献
104.
A multiphase dc‐dc converter is effective for miniaturization and achieving high‐power density in a switching power supply. However, its mathematical modeling becomes complex as the phase number of the circuit increases. This study proposes a new modeling method to derive a reduced‐order method in a simple manner. The frequency characteristics of the reduced‐order model are fit to those of the original mathematical model of the multiphase dc‐dc converter. Therefore, the efficacy of the proposed method is validated. 相似文献
105.
To efficiently link the continuum mechanics for rocks with the structural statistics of rock masses,a theoretical and methodological system called the statistical mechanics of rock masses(SMRM)was developed in the past three decades.In SMRM,equivalent continuum models of stressestrain relationship,strength and failure probability for jointed rock masses were established,which were based on the geometric probability models characterising the rock mass structure.This follows the statistical physics,the continuum mechanics,the fracture mechanics and the weakest link hypothesis.A general constitutive model and complete stressestrain models under compressive and shear conditions were also developed as the derivatives of the SMRM theory.An SMRM calculation system was then developed to provide fast and precise solutions for parameter estimations of rock masses,such as full-direction rock quality designation(RQD),elastic modulus,Coulomb compressive strength,rock mass quality rating,and Poisson’s ratio and shear strength.The constitutive equations involved in SMRM were integrated into a FLAC3D based numerical module to apply for engineering rock masses.It is also capable of analysing the complete deformation of rock masses and active reinforcement of engineering rock masses.Examples of engineering applications of SMRM were presented,including a rock mass at QBT hydropower station in northwestern China,a dam slope of Zongo II hydropower station in D.R.Congo,an open-pit mine in Dexing,China,an underground powerhouse of Jinping I hydropower station in southwestern China,and a typical circular tunnel in Lanzhou-Chongqing railway,China.These applications verified the reliability of the SMRM and demonstrated its applicability to broad engineering issues associated with jointed rock masses. 相似文献
106.
Miroslav Kárný Marko Ruman 《International Journal of Adaptive Control and Signal Processing》2021,35(5):660-675
Any knowledge extraction relies (possibly implicitly) on a hypothesis about the modelled-data dependence. The extracted knowledge ultimately serves to a decision-making (DM). DM always faces uncertainty and this makes probabilistic modelling adequate. The inspected black-box modeling deals with “universal” approximators of the relevant probabilistic model. Finite mixtures with components in the exponential family are often exploited. Their attractiveness stems from their flexibility, the cluster interpretability of components and the existence of algorithms for processing high-dimensional data streams. They are even used in dynamic cases with mutually dependent data records while regression and auto-regression mixture components serve to the dependence modeling. These dynamic models, however, mostly assume data-independent component weights, that is, memoryless transitions between dynamic mixture components. Such mixtures are not universal approximators of dynamic probabilistic models. Formally, this follows from the fact that the set of finite probabilistic mixtures is not closed with respect to the conditioning, which is the key estimation and predictive operation. The paper overcomes this drawback by using ratios of finite mixtures as universally approximating dynamic parametric models. The paper motivates them, elaborates their approximate Bayesian recursive estimation and reveals their application potential. 相似文献
107.
108.
109.
Jun Yang Jing Na Guanbin Gao 《International Journal of Adaptive Control and Signal Processing》2019,33(12):1868-1884
This paper provides a modified model reference adaptive control (MRAC) scheme to achieve better transient control performance for systems with unknown unmatched dynamics, where an adaptive law with guaranteed convergence is introduced. We first revisit the standard MRAC system and analyze the tracking error bound by using L2‐norm and Cauchy‐Schwartz inequality. Based on this analysis, we suggest a feasible way to compensate the undesired transient dynamics induced by the gradient descent–based adaptive laws subject to sluggish convergence or even parameter drift. Then, a modified adaptive law with an alternative leakage term containing the parameter estimation error is developed. With this adaptive law, the convergence of both the estimation error and tracking error can be proved simultaneously. This enhanced convergence property can contribute to deriving smoother control signal and improved control response. Moreover, this paper provides a simple and numerically feasible approach to online verify the well‐known persistent excitation condition by testing the positive definiteness of an introduced auxiliary matrix. Comparative simulations based on a benchmark 3‐DOF helicopter model are given to validate the effectiveness of the proposed MRAC approach and show the improved performance over several other MRAC schemes. 相似文献
110.
Jiming Xu Howard M. Heys 《International Journal of Circuit Theory and Applications》2019,47(6):971-990
Side-channel attacks have shown to be efficient tools in breaking cryptographic hardware. Many conventional algorithms have been proposed to perform side-channel attacks exploiting the dynamic power leakage. In recent years, with the development of processing technology, static power has emerged as a new potential source for side-channel leakage. Both types of power leakage have their advantages and disadvantages. In this work, we propose to use the deep neural network technique to combine the benefits of both static and dynamic power. This approach replaces the classifier in template attacks with our proposed long short-term memory network schemes. Hence, instead of deriving a specific probability density model for one particular type of power leakage, we gain the ability of combining different leakage sources using a structural algorithm. In this paper, we propose three schemes to combine the static and dynamic power leakage. The performance of these schemes is compared using simulated test circuits designed with a 45-nm library. 相似文献