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   194862篇
  免费   17132篇
  国内免费   12068篇
电工技术   30631篇
技术理论   13篇
综合类   17919篇
化学工业   10600篇
金属工艺   6788篇
机械仪表   16907篇
建筑科学   19259篇
矿业工程   9070篇
能源动力   5398篇
轻工业   8267篇
水利工程   7534篇
石油天然气   6709篇
武器工业   2944篇
无线电   13570篇
一般工业技术   9821篇
冶金工业   8198篇
原子能技术   2096篇
自动化技术   48338篇
  2024年   310篇
  2023年   2141篇
  2022年   3699篇
  2021年   4698篇
  2020年   5475篇
  2019年   4231篇
  2018年   3864篇
  2017年   5547篇
  2016年   6288篇
  2015年   6921篇
  2014年   13654篇
  2013年   11579篇
  2012年   14796篇
  2011年   15471篇
  2010年   11694篇
  2009年   11869篇
  2008年   11799篇
  2007年   14483篇
  2006年   12935篇
  2005年   11182篇
  2004年   9204篇
  2003年   8128篇
  2002年   6452篇
  2001年   5272篇
  2000年   4442篇
  1999年   3533篇
  1998年   2668篇
  1997年   2329篇
  1996年   1847篇
  1995年   1559篇
  1994年   1327篇
  1993年   970篇
  1992年   763篇
  1991年   578篇
  1990年   438篇
  1989年   394篇
  1988年   288篇
  1987年   162篇
  1986年   119篇
  1985年   123篇
  1984年   164篇
  1983年   129篇
  1982年   116篇
  1981年   80篇
  1980年   56篇
  1979年   67篇
  1978年   50篇
  1977年   49篇
  1964年   13篇
  1959年   18篇
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
101.
为了避免和减轻由过大隔震层位移引起的损害,对基础隔震框架结构装设调频液柱阻尼器(tuned liquid column damper,简称TLCD)后混合系统的减振效果进行研究。建立了单层和多层混合控制系统在地震作用下的运动方程,采用TLCD-结构体系转化为调频质量阻尼器(tuned mass damper,简称TMD)-结构体系的等效方法,利用TMD参数优化公式,得到单个TLCD初始设计参数,并采用状态空间方程得到多个TLCD最优设计参数。通过对某8层基础隔震结构进行模拟,证明了该理论设计方法的合理性。该混合结构不仅可以减小隔震层位移和加速度,而且对上部结构位移和加速度反应都能更有效的控制。  相似文献   
102.
针对井下瓦斯抽采中原放水器配气阀安装不规范、双截止阀使用繁琐、工人劳动强度大等现状,研制了具有集成调控装置的放水器,能够实现一个阀门控制所有气路和水路,自主放水和负压排水,从源头上杜绝了瓦斯喷孔和水流溢出等情况,大大降低了职工的劳动强度,实现了井下抽采系统安全可靠运行。  相似文献   
103.
煤矿开采是在地层中进行的,不可避免地受到地质条件的影响。很多煤矿灾害的发生与地质构造有关,因此了解煤矿开采中的地质构造十分有必要。为了了解煤层的地质构造,必须对煤矿地质条件进行测量。分析了煤矿地质测量对安全生产的作用,并提出了一些措施来提升煤矿地质测量的有效性,可以为煤矿地质测量工作人员提供一定的参考。  相似文献   
104.
Structures need to be designed to maintain their stability in the event of a fire. The travelling fire methodology (TFM) defines the thermal boundary condition for structural design of large compartments of fires that do not flashover, considering near field and far field regions. TFM assumes a near field temperature of 1200°C, where the flame is impinging on the ceiling without any extension and gives the temperature of the hot gases in the far field from Alpert correlations. This paper revisits the near field assumptions of the TFM and, for the first time, includes horizontal flame extension under the ceiling, which affects the heating exposure of the structural members thus their load-bearing capacity. It also formulates the thermal boundary condition in terms of heat flux rather than in terms of temperature as it is used in TFM, which allows for a more formal treatment of heat transfer. The Hasemi, Wakamatsu, and Lattimer models of heat flux from flame are investigated for the near field. The methodology is applied to an open-plan generic office compartment with a floor area of 960 m2 and 3.60 m high with concrete and with protected and unprotected steel structural members. The near field length with flame extension (fTFM) is found to be between 1.5 and 6.5 times longer than without flame extension. The duration of the exposure to peak heat flux depends on the flame length, which is 53 min for fTFM compared with 17 min for TFM, in the case of a slow 5% floor area fire. The peak heat flux is from 112 to 236 kW/m2 for the majority of fire sizes using the Wakamatsu model and from 80 to 120 kW/m2 for the Hasemi and Lattimer models, compared with 215 to 228 kW/m2 for TFM. The results show that for all cases, TFM results in higher structural temperatures compared with different fTFM models (600°C for concrete rebar and 800°C for protected steel beam), except for the Wakamatsu model that for small fires, leads to approximately 20% higher temperatures than TFM. These findings mitigate the uncertainty around the TFM near field model and confirm that it is conservative for calculation of the thermal load on structures. This study contributes to the creation of design tools for better structural fire engineering.  相似文献   
105.
秦金辉 《中州煤炭》2020,(12):55-59
针对李雅庄煤矿U型通风工作面上隅角及回风流瓦斯浓度高、瓦斯治理难度大的问题,根据工作面瓦斯来源及在采空区三带的运移储存规律,李雅庄煤矿开展了本煤层抽采工艺优化和裂隙带抽采技术研究。对本煤层钻孔封孔深度、联孔工艺、管路连接方式等进行优化,钻孔抽采浓度由抽采4个月后降低到9%提高到抽采10个月后维持在19%;通过调整裂隙带钻孔布置方式、优化钻孔布孔层位、采取下筛管护孔等技术措施,裂隙带钻场最高瓦斯抽采纯流量达13.6 m3/min,平均瓦斯抽采纯流量达8 m3/min,2个钻场联合抽采瓦斯纯流量在13 m3/min以上;取消了瓦斯措施巷、井下移动泵和上隅角风帘,上隅角和回风流平均瓦斯浓度分别控制在0.5%和0.4%以下,对高瓦斯矿井U型通风工作面瓦斯治理有借鉴意义。  相似文献   
106.
In this paper, we propose an improved torque sensorless speed control method for electric assisted bicycle, this method considers the coordinate conversion. A low-pass filter is designed in disturbance observer to estimate and compensate the variable disturbance during cycling. A DC motor provides assisted power driving, the assistance method is based on the real-time wheel angular velocity and coordinate system transformation. The effect of observer is proved, and the proposed method guarantees stability under disturbances. It is also compared to the existing methods and their performances are illustrated through simulations. The proposed method improves the performance both in rapidity and stability.   相似文献   
107.
In the cyber-physical environment, the clock synchronization algorithm is required to have better expansion for network scale. In this paper, a new measurement model of observability under the equivalent transformation of minimum mean square error (MMSE) is constructed based on basic measurement unit (BMU), which can realize the scaled expansion of MMSE measurement. Based on the state updating equation of absolute clock and the decoupled measurement model of MMSE-like equivalence, which is proposed to calculate the positive definite invariant set by using the theoretical-practical Luenberger observer as the synthetical observer, the local noncooperative optimal control problem is built, and the clock synchronization system driven by the ideal state of local clock can reach the exponential convergence for synchronization performance. Different from the problem of general linear system regulators, the state estimation error and state control error are analyzed in the established affine system based on the set-theory-in-control to achieve the quantification of state deviation caused by noise interference. Based on the BMU for isomorphic state map, the synchronization performance of clock states between multiple sets of representative nodes is evaluated, and the scale of evaluated system can be still expanded. After the synchronization is completed, the state of perturbation system remains in the maximum range of measurement accuracy, and the state of nominal system can be stabilized at the ideal state for local clock and realizes the exponential convergence of the clock synchronization system.   相似文献   
108.
目的:探讨依托泊苷联合卡铂用于复发性髓母细胞瘤患儿的疗效与安全性。方法:选取浙江大学医学院附属儿童医院在2011年1月至2014年6月收治的72例复发性髓母细胞瘤患儿(3~15岁),随机分为CE组和对照组,每组36例,CE组采用依托泊苷+卡铂给药方式化疗;对照组采用经典伊立替康+替莫唑胺+长春新碱方案化疗。比较两组患儿临床疗效、卡诺夫斯基健康状况量表(KPS)评分、儿科生活质量测定量表4.0(PedsQLTM4.0)评分、总生存期(OS)、无事件生存(EFS),记录患儿治疗期间药物不良反应的发生情况。结果:治疗后CE组和对照组完全缓解率(CR)分别为41.67%(15/36)和27.78%(10/36),总缓解率(OR)分别为94.44%(34/36)和77.78%(28/36),差异有统计学意义(P<0.05)。两组患儿治疗前KPS评分及PedsQLTM4.0评分无统计学差异(P>0.05),治疗后CE组和对照组的KPS评分分别为(80±8)和(75±10)分,PedsQLTM4.0评分分别为(89±11)和(84±11)分,差异均有统计学意义(均P<0.05)。截至末次随访时间,CE组有3例失访,对照组有2例失访。截至末次随访时间,CE组和对照组总生存率分别为78.8%(26/33)和55.9%(19/34),差异有统计学意义(P<0.05),无事件生存率分别为72.7%(24/33)和52.9%(18/34),差异无统计学意义(P>0.05)。CE组化疗期间共出现10例3级以上不良反应,发生率为27.78%(10/36),对照组化疗期间共出现9例3级以上不良反应,发生率为25.00%(9/36),差异无统计学意义(P>0.05)。结论:依托泊苷联合卡铂方案能够明显提高患儿临床缓解率,延长患儿总生存率,同时不增加化疗不良反应,但对无事件生存率的影响并不明显。  相似文献   
109.
针对镀液温度变化的非线性和滞后性,设计了采用专家规则的镀液温度实时控制系统。该系统在实时监测的基础上,构建了综合评判镀液温度偏差和镀液温度偏差变化率的专家规则,实现了镀液温度的自适应快速调节。仿真分析结果表明,该系统克服了非线性和滞后性的不良影响,能够实现镀液温度的实时控制。  相似文献   
110.
A Takagi-Sugeno adaptive neuro-fuzzy inference system (TSFIS) model is developed and applied to a dataset of wellhead flow-test data for the Resalat oil field located offshore southern Iran, the objective is to assist in the prediction and control of multi-phase flow rates of oil and gas through the wellhead chokes. For this purpose, 182 test data points (Appendix 1) related to the Resalat field are evaluated. In order to predict production flow rate (QL) expressed as stock-tank barrels per day (STB/D), this dataset includes four selected input variables: upstream pressure (Pwh); wellhead choke sizes (D64); gas to liquid ratio (GLR); and, base solids and water including some water-soluble oil emulsion (BS&W). The test data points evaluated include a wide range of oil flow rate conditions and values for the four input variables recorded. The TSFIS algorithm applied involves five data processing steps: a) pre-processing, b) fuzzification, c) rules base and adaptive neuro-fuzzy inference engine, d) defuzzification, and e) post-processing of the fuzzy model. The developed TSFIS model for the Resalat oil field database predicted oil flow rate to a high degree of accuracy (root mean square error = 247 STB/D, correlation coefficient = 0.9987), which improves substantially on the commonly used empirical algorithms used for such predictions. TSFIS can potentially be applied in wellhead choke fuzzy controllers to stabilize flow in specific wells based on real-time input data records.  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