首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   249154篇
  免费   23249篇
  国内免费   15416篇
电工技术   40758篇
技术理论   20篇
综合类   21829篇
化学工业   19489篇
金属工艺   9313篇
机械仪表   18954篇
建筑科学   25042篇
矿业工程   9235篇
能源动力   17705篇
轻工业   7354篇
水利工程   7127篇
石油天然气   7939篇
武器工业   3262篇
无线电   18438篇
一般工业技术   15645篇
冶金工业   11708篇
原子能技术   2454篇
自动化技术   51547篇
  2024年   902篇
  2023年   3531篇
  2022年   5715篇
  2021年   6940篇
  2020年   7815篇
  2019年   6485篇
  2018年   5609篇
  2017年   7643篇
  2016年   8590篇
  2015年   9133篇
  2014年   16822篇
  2013年   14972篇
  2012年   18271篇
  2011年   19883篇
  2010年   15062篇
  2009年   15370篇
  2008年   14843篇
  2007年   17757篇
  2006年   15397篇
  2005年   13152篇
  2004年   10928篇
  2003年   9567篇
  2002年   7833篇
  2001年   6585篇
  2000年   5653篇
  1999年   4513篇
  1998年   3484篇
  1997年   3003篇
  1996年   2455篇
  1995年   1953篇
  1994年   1671篇
  1993年   1247篇
  1992年   984篇
  1991年   776篇
  1990年   600篇
  1989年   515篇
  1988年   383篇
  1987年   248篇
  1986年   181篇
  1985年   203篇
  1984年   242篇
  1983年   169篇
  1982年   183篇
  1981年   109篇
  1980年   97篇
  1979年   87篇
  1978年   61篇
  1977年   56篇
  1959年   17篇
  1951年   24篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
While exercise training (ET) is an efficient strategy to manage obesity, it is recommended with a dietary plan to maximize the antiobesity functions owing to a compensational increase in energy intake. Capsiate is a notable bioactive compound for managing obesity owing to its capacity to increase energy expenditure. We aimed to examine whether the antiobesity effects of ET can be further enhanced by capsiate intake (CI) and determine its effects on resting energy expenditure and metabolic molecules. Mice were randomly divided into four groups (n = 8 per group) and fed high-fat diet. Mild-intensity treadmill ET was conducted five times/week; capsiate (10 mg/kg) was orally administered daily. After 8 weeks, resting metabolic rate and metabolic molecules were analyzed. ET with CI additively reduced the abdominal fat rate by 18% and solely upregulated beta-3-adrenoceptors in adipose tissue (p = 0.013) but did not affect the metabolic molecules in skeletal muscles. Surprisingly, CI without ET significantly increased the abdominal fat rate (p = 0.001) and reduced energy expenditure by 9%. Therefore, capsiate could be a candidate compound for maximizing the antiobesity effects of ET by upregulating beta-3-adrenoceptors in adipose tissue, but CI without ET may not be beneficial in managing obesity.  相似文献   
82.
刘越  周平 《信息与控制》2022,51(1):54-68
马尔可夫跳变线性系统(MJLS)是一种具有多个模态的随机系统,系统在各个模态之间的跳变转移由一组马尔可夫链来决定。MJLS模型因其在表示过程中可以产生突变而更能精确的描述实际工程应用中的系统。近年来,MJLS的最优控制问题成为了研究的热点,动态规划、极大值原理以及线性矩阵不等式等成为了解决此类问题的主流方法。本文对MJLS最优控制领域的研究现状进行了综述。分别对一般情况下、带有噪声的情况下、带有时滞的情况下以及某些特定情况下的MLJS最优控制问题的国内外研究现状进行论述。最后进行了总结并提出MJLS最优控制领域未来值得关注的研究方向。  相似文献   
83.
在钻井过程中,常常钻遇不同宽度的井下地层裂缝。钻遇裂缝时容易发生钻井液漏失现象,甚至发生钻井液失返现象,严重影响了安全、高效钻井。目前裂缝封堵的方法常存在封堵成功率不高、堵漏承压能力低的问题,其中一个重要的原因是对井下地层的裂缝宽度等特征认识不清。基于地层裂缝产生的岩石力学机理,确定影响裂缝宽度关键的6个力学和工程因素,并利用神经网络计算的非线性、大数据特点建立了井下地层裂缝宽度的分析模型,模型包含输入层、输出层和3个隐藏层。通过该模型诊断井下裂缝宽度,提高了计算精度,平均误差仅为2.09%,最大误差为5.88%,解决钻井现场仅凭经验判断裂缝误差较大和依靠成像测井成本较高的问题。同时根据神经网络模型诊断得到的裂缝宽度优化堵漏材料的粒径配比,提高了裂缝内的架桥封堵强度和架桥的稳定性,封堵层的承压能力达到12.8 MPa,反向承压能力达到4.5 MPa。现场堵漏试验最高憋压10 MPa,经过封堵作业后大排量循环不漏,达到了裂缝性地层高效堵漏的目的,堵漏一次成功。   相似文献   
84.
85.
Bromine-based flow batteries (Br-FBs) are considered one of the most promising energy storage systems due to their features of high energy density and low cost. However, they generally suffer from uncontrolled diffusion of corrosive bromine particularly at high temperatures. That is because the interaction between polybromide anions and the commonly used complexing agent (N–methyl–N–ethyl–pyrrolidinium bromide [MEP]) decreases with increasing temperatures, which causes serious self-discharge and capacity fade. Herein, a novel bromine complexing agent, 1–ethyl–2–methyl–pyridinium bromide (BCA), is introduced in Br-FBs to solve the above problems. It is proven that BCA can combine with polybromide anions very well even at a high temperature of 60 °C. Moreover, the BCA contributes to decreasing the electrochemical polarization of Br/Br2 couple, which in turn improves their power density. As a result, a zinc–bromine flow battery with BCA as the complexing agent can achieve a high energy efficiency of 84% at 40 mA cm−2, even at high temperature of 60 °C and it can stably run for more than 400 cycles without obvious performance decay. This paper provides an effective complexing agent to enable a wide temperature range Br-FB.  相似文献   
86.
《Ceramics International》2021,47(20):28338-28347
Transition metal oxides have been explored in supercapacitor applications owing to their safety, low cost, high specific capacitance and high electrochemical activity. Among all transition metal oxides, zinc oxide based materials show remarkable response for designing the supercapacitors with high electrochemical activity. Here in, Mn doped ZnO (Zn1-xMnxO3 with x = 0, 0.25, 0.50, 0.75 and 1) was synthesized by a facile hydrothermal method. Doping of Mn into the ZnO increased the surface area and decease the charge transfer resistance for the Zn0.5Mn0.5O3. All the synthesized materials were characterized by x-ray diffraction (XRD), scanning electron microscopy SEM), BET, electrochemical tests and other various analytical techniques to confirm the structural, morphological, textural and suprcapacitive properties. The synthesized material Zn0.5Mn0.5O3 having the porous nanoribons structure with BET surface area (2490 cm2/g). The electrochemical studies showed significantly enhanced response toward pseudocapacitive nature. The synthesized material exhibited the excellent specific capacitance (515F/g), specific energy (28.61 Wh/kg) and specific power (1000 W/kg) at current density of 2 mA/g. Such impressive and superior properties make the MnZnO3 material as promising candidate for new generation supercapacitor applications.  相似文献   
87.
This paper proposes an event-triggered distributed receding horizon control (DRHC) approach for the formation and tracking problems of homogeneous multi-agent systems. For each agent, an event-triggering condition, based on assumed predictive information of the neighbours, is derived from stability analysis. Considering the uncertain deviation between the assumed and true predictive information, we design a time-varying compatibility constraint for the individual optimization problem. In the event-triggered DRHC algorithm, each agent solves the optimization problem and communicates with its neighbours only when the event-triggering condition is satisfied, so the communication and computation burden are reduced. Moreover, guarantees for the recursive feasibility and asymptotic stability of the overall system are proved. A simulation example is provided to illustrate effectiveness of the proposed approach.  相似文献   
88.
Li7La3Zr2O12-based garnet-type solid electrolytes are promising candidates for use in all-solid-state lithium batteries (ASSLBs). However, their potential in large-scale commercial applications is largely hindered by the time/energy-consuming and lithium-wasting synthetic method which typically needs a long-duration high temperature solid state reaction process. Herein we invent a fast preparation route that involves a short-period thermal reaction (1100 °C for 10 min) in laboratory muffle furnaces following by conventional hot pressing technique to get almost fully dense (Al, Ga, Ta, Nb)-doped garnet-type electrolytes with high phase purity (>99.9 %). The large and compact grains, low porosity and high phase purities of garnet ceramic electrolytes synthesized in this study ensure superior electrochemical performance. Particularly, Ga-doped cubic Li7La3Zr2O12 shows extremely low Ea values (0.17?0.18 eV) and record-high lithium ionic conductivities (>2 × 10?3 S cm-1 at 25 °C).  相似文献   
89.
This paper mainly focuses on the development of pressure tracking control logic of electro-hydraulic actuators for vehicle application. This is done to improve and ensure the performance of a precise lower-level controller for evolving modern shift control logic. The required performance is obtained by hysteresis model-based feed-forward control and additional feedback control. The hysteresis and the time delay, which adversely affect pressure control, are well known nonlinear behaviors in electro-hydraulic actuators. In order to cope with the hysteresis, a novel hysteresis model is proposed based on a physical phenomenon. A mathematical model based on a characteristic curve obtained in preliminary experiments is presented using only one tuning parameter, and this model can be inverted easily to construct a feed-forward controller. In addition, a feedback controller is designed considering the stability margin of a time delay system. The feedback control inputs ensure compensation of the feed-forward errors caused by model error and uncertainty. The proposed controller is designed to lower computational cost considering applicability for production vehicles. As a result, the developed pressure controller is applied to a transmission control unit of a production vehicle and verified experimentally for various driving scenarios.  相似文献   
90.
In this article, adaptive compensation designs are developed for nonlinear systems with uncertainties from the system functions and persistent actuator failures of characterizations that (i) some unknown system inputs are stuck at some unknown fixed or varying values at unknown time instants and (ii) the failure pattern always switches from one to another and the switching does not stop. Such a controlled plant is described by an uncertain time-varying nonlinear system, and some robust adaptive feedback linearization based failure compensation results are studied for closed-loop system stabilization and bounded output tracking for some specific conditions. To improve the tracking performance in the presence of persistent actuator failures, a new adaptive control scheme is developed, using the failure indicator function which contains the failure pattern and failure time in the formulation. Detailed stability and tracking performance are shown. Simulation results are shown to verify the effectiveness of the proposed adaptive actuator failure compensation method.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号