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   17172篇
  免费   487篇
  国内免费   206篇
电工技术   267篇
技术理论   6篇
综合类   563篇
化学工业   2700篇
金属工艺   375篇
机械仪表   519篇
建筑科学   2112篇
矿业工程   460篇
能源动力   2191篇
轻工业   777篇
水利工程   3223篇
石油天然气   1066篇
武器工业   16篇
无线电   229篇
一般工业技术   980篇
冶金工业   1221篇
原子能技术   253篇
自动化技术   907篇
  2024年   14篇
  2023年   247篇
  2022年   448篇
  2021年   449篇
  2020年   410篇
  2019年   380篇
  2018年   346篇
  2017年   420篇
  2016年   384篇
  2015年   447篇
  2014年   773篇
  2013年   1043篇
  2012年   806篇
  2011年   1249篇
  2010年   967篇
  2009年   1145篇
  2008年   946篇
  2007年   1044篇
  2006年   911篇
  2005年   851篇
  2004年   697篇
  2003年   631篇
  2002年   510篇
  2001年   407篇
  2000年   380篇
  1999年   381篇
  1998年   290篇
  1997年   241篇
  1996年   205篇
  1995年   198篇
  1994年   148篇
  1993年   89篇
  1992年   97篇
  1991年   60篇
  1990年   42篇
  1989年   48篇
  1988年   34篇
  1987年   38篇
  1986年   24篇
  1985年   22篇
  1984年   11篇
  1983年   8篇
  1982年   12篇
  1981年   3篇
  1980年   6篇
  1979年   2篇
  1977年   1篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
In the chemical industry large amounts of saline wastewater occur. Its disposal into rivers is a considerable burden to the ecosystem. To strive for a circular economy and enable a viable raw material recycling, energy-efficient concentration processes are requisite. High-pressure reverse osmosis meets this criterion, but its industrial application demands suitable membrane elements that withstand the exceptional operation conditions and provide sufficient performance. Hence, new requirements regarding the design of spiral-wound elements arise. To identify those, specific performance-limiting effects need a better understanding.  相似文献   
2.
A numerical model is developed for surface crack propagation in brittle ceramic coatings, aiming at the intrinsic failure of rare-earth silicate environmental barrier coating systems (EBCs) under combustion conditions in advanced gas turbines. The main features of progressive degradation of EBCs in such conditions are captured, including selective silica vaporization in the top coat due to exposure to water vapor, diffusion path-dependent bond coat oxidation, as well as crack propagation during cyclic thermal loading. In light of these features, user-defined subroutines are implemented in finite element analysis, where surface crack growth is simulated by node separation. Numerical results are validated by existing experimental data, in terms of monosilicate layer thickening, thermal oxide growth, and fracture behaviors. The experimentally observed quasi-linear oxidation in the early stage is also elucidated. Furthermore, it is suggested that surface crack undergoes rapid propagation in the late stage of extended thermal cycling in water vapor and leads to catastrophic failure, driven by both thermal mismatch and oxide growth stresses. The latter is identified as the dominant mechanism of penetration. Based on detailed analyses of failure mechanisms, the optimization strategy of EBCs composition is proposed, balancing the trade-off between mechanical compliance and erosion resistance.  相似文献   
3.
In both developing and industrialized/developed countries, various hazardous/toxic environmental pollutants are entering water bodies from organic and inorganic compounds (heavy metals and specifically dyes). The global population is growing whereas the accessibility of clean, potable and safe drinking water is decreasing, leading to world deterioration in human health and limitation of agricultural and/or economic development. Treatment of water/wastewater (mainly industrial water) via catalytic reduction/degradation of environmental pollutants is extremely critical and is a major concern/issue for public health. Light and/or laser ablation induced photocatalytic processes have attracted much attention during recent years for water treatment due to their good (photo)catalytic efficiencies in the reduction/degradation of organic/inorganic pollutants. Pulsed laser ablation (PLA) is a rather novel catalyst fabrication approach for the generation of nanostructures with special morphologies (nanoparticles (NPs), nanocrystals, nanocomposites, nanowires, etc.) and different compositions (metals, alloys, oxides, core-shell, etc.). Laser ablation in liquid (LAL) is generally considered a quickly growing approach for the synthesis and modification of nanomaterials for practical applications in diverse fields. LAL-synthesized nanomaterials have been identified as attractive nanocatalysts or valuable photocatalysts in (photo)catalytic reduction/degradation reactions. In this review, the laser ablation/irradiation strategies based on LAL are systematically described and the applications of LAL synthesized metal/metal oxide nanocatalysts with highly controlled nanostructures in the degradation/reduction of organic/inorganic water pollutants are highlighted along with their degradation/reduction mechanisms.  相似文献   
4.
Unexpected variations in spring characteristics could affect the performance of discharge control valves. In this study, a novel experimental procedure was used to quantify the effects of the spring's elasticity coefficient and unloaded spring length on water delivery by the discharge control valve. Based on an average sensitivity index reflecting the performance of a given structure, the hydraulic behavior of the discharge control valve was quantified. The results indicate that the valve was sensitive to the unloaded spring length, especially when it was slightly smaller than its nominal value. The discharge control valve performance was affected no more than about 16% by ± 4% variation in spring elasticity. In general, spring elasticity variations affect the valve of the smaller design discharge more than that designed for a higher discharge value. The outcome of this study should help design and fabricate discharge control valves to enhance their performance.  相似文献   
5.
邢台市召马地表水厂是南水北调中线工程的配套项目,总工程规模为35×104m3/d,其中一期规模为15×104m3/d,预留二期规模为20×104m3/d,包括新建地表水厂及相应配水管网。水源取自丹江口水库,水质优良,净水采用机械混合池→小网格反应池→双层平流沉淀池→Ⅴ型滤池常规处理+臭氧活性炭滤池深度处理组合工艺,出厂水采用二氧化氯与紫外线多级屏障消毒,确保供水水质安全。实际运行效果表明,各设备设施均运转稳定,水厂出水水质优于《生活饮用水卫生标准》(GB 5749—2006)的要求。工程总投资为70 442万元,经营成本为0.76元/m3(不包括南水北调水资源费)。  相似文献   
6.
针对沁水煤田沟底煤矿开采的3号煤层受顶板砂岩裂隙水、底板灰岩岩溶裂隙承压水威胁的实际情况,运用地质学、水文地质学理论方法,对矿井充水条件进行了系统分析,对井田带压区域进行了分区,对主要水害提出了相应的防治水技术措施。  相似文献   
7.
This article presents the calibration of a compact prover using the weighing method. An evaluation of measurement uncertainty of the prover calibration has been developed using the GUM and Monte Carlo methodologies. A water draw kit was utilized to direct the liquid flow from the compact prover to a water container in order to weigh the transferred water mass on a balance. This amount of mass was used as reference for the calculation of the prover base volume. A modeling of the flow rate into the water draw kit as a function of time was conceived. This modeling was applied for calculating the error in the liquid volume of the water container due to the switching of two solenoid valves of the water draw kit. A mathematical model of the prover base volume has been developed. This model is non-linear and the two largest sources of uncertainty are related to the balance calibration certificate that together account for 31.84% of the uncertainty budget. This work showed that the GUM approach was validated by Monte Carlo method in the calculation of the measurement uncertainty of the calibration of a compact prover. The absolute differences of the respective endpoints of the coverage intervals of these two methods are less than 0.00023% of estimate of the prover base volume whose value is 151.427 dm³. This result was obtained for a coverage probability of 95% and 106 Monte Carlo iterations. The density of the calibration water and its uncertainty have been calculated through an innovative approach.  相似文献   
8.
为避免或减小隧洞穿越富水破碎岩体发生突涌水、塌方等造成的危害,提出了基于地质分析、隧道地震预报(TSP)法与超前钻探结合的综合超前预报体系。首先通过地质分析对不良地质进行评估,之后利用TSP法对前方不良地质体进行定位,确认有不良地质构造存在,最后利用超前钻探进行预报。滇中引水工程富水破碎洞段的两个工程实例表明,此预报技术可准确地预测不良地质段以及涌水段位置和规模大小,可帮助工程技术人员及时地制定相对应的预警措施和处理对策,从而减少施工过程中突泥、涌水、塌方等地质灾害出现的概率,保证隧洞安全施工。  相似文献   
9.
丹江口水库兴利效益影响因素分析   总被引:1,自引:0,他引:1  
丹江口大坝加高后,作为南水北调中线工程水源地,其供水等兴利功能地位更为突出,而汉江上游降雨量的减少及梯级水库的调蓄,大大降低了丹江口水库的可调用水资源量。为充分发挥水库的兴利效益,通过对不同频率的来水进行调节计算,从供水满足率、年均发电量、年均弃水量3个方面计算分析起调水位、来水不确定性和汛限水位对丹江口水库兴利效益的影响。结果表明:①起调水位对来水频率>90%的枯水年供水效益影响较大,由150 m提高至160 m,水库供水满足率可由44.38%提高至93.42%;对来水频率<75.7%的年份其影响主要体现在发电上,起调水位越高,年均发电量越高,年均弃水量越小,起调水位由150 m提高至170 m至少可增加发电量10亿kW·h;②来水频率越大,水库供水满足率、年均发电量均越小;水库弃水和供水短缺在来水较丰时同时存在;③丹江口水库夏季汛限水位对水库兴利效益的影响比秋季汛限水位更显著;对至少有2 a为枯水年的3 a调节周期,汛限水位对弃水量的影响最明显;④兴利效益的主要影响因素为起调水位,除水库遭遇连续枯水年外,丹江口水库兴利起调水位为162 m,可满足不同水平年的供水需求。  相似文献   
10.
In the present study, a membrane-based air-to-air planar humidifier (MAPH) with baffle-blocked flow channels and a common MAPH are fabricated, tested and compared. These MAPHs are well thermal insulated from their surroundings. Polyoxymethylene (POM) plates with some unique properties such as large tensile and flexural strength, high chemical resistance and high stiffness are used to create channels at dry and humid sides of MAPHs. The obtained findings revealed that the higher heat and water transfer rates and smaller dew point approach temperature (DPAT) in entire tested flow rates occurs in baffle-blocked MAPH. To evaluate the MAPH performance with considering the pressure drop, a dimensionless parameter, performance evaluation criteria (PEC), is introduced. At flow rates less than 1 m3/h, PEC is less than 1, indicating a decline in MAPH performance with considering the pressure drop. In baffle-blocked MAPH using water trap in the inlet of dry side leads to the performance deterioration. Additionally, the increased relative humidity (RH) of humid side inlet causes an increase in DPAT, consequently, the performance deterioration.  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