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   115323篇
  免费   12001篇
  国内免费   6099篇
电工技术   18655篇
技术理论   16篇
综合类   7575篇
化学工业   12156篇
金属工艺   4441篇
机械仪表   5606篇
建筑科学   11836篇
矿业工程   3501篇
能源动力   17051篇
轻工业   7058篇
水利工程   2596篇
石油天然气   3867篇
武器工业   1254篇
无线电   10461篇
一般工业技术   10823篇
冶金工业   4769篇
原子能技术   1646篇
自动化技术   10112篇
  2024年   500篇
  2023年   2406篇
  2022年   3797篇
  2021年   4451篇
  2020年   4645篇
  2019年   4048篇
  2018年   3395篇
  2017年   4095篇
  2016年   4522篇
  2015年   4642篇
  2014年   8061篇
  2013年   7292篇
  2012年   8688篇
  2011年   9451篇
  2010年   7108篇
  2009年   7045篇
  2008年   6309篇
  2007年   7196篇
  2006年   6005篇
  2005年   4851篇
  2004年   4083篇
  2003年   3600篇
  2002年   3010篇
  2001年   2588篇
  2000年   2162篇
  1999年   1763篇
  1998年   1381篇
  1997年   1059篇
  1996年   966篇
  1995年   759篇
  1994年   673篇
  1993年   512篇
  1992年   433篇
  1991年   358篇
  1990年   270篇
  1989年   226篇
  1988年   199篇
  1987年   137篇
  1986年   104篇
  1985年   140篇
  1984年   108篇
  1983年   72篇
  1982年   85篇
  1981年   41篇
  1980年   49篇
  1979年   29篇
  1978年   18篇
  1977年   18篇
  1974年   12篇
  1951年   13篇
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
91.
《Ceramics International》2020,46(9):12921-12927
The further development of clean energy requires the use of more stable and reliable energy storage system. In addition to lithium ion battery power supplies, sodium ion batteries also have prospects for application and development thanks to the low cost and abundant resource. NaTi2(PO4)3 has attracted much attention due to its three-dimensional channels for sodium ion transfer. In order to meliorate sodium storage properties of NaTi2(PO4)3 electrode, a facile strategy of Sn substitution at Ti sites was employed, and a series of electrodes were successfully synthesized through sol-gel route. The electrochemical performances of Sn substituted composites are significantly improved compared with bare NaTi2(PO4)3/C. And it was found that NaSn0.2Ti1.8(PO4)3 (NTP/C-Sn-2) delivers the largest capacity, and it also demonstrates the outstanding cycling performances. NTP/C-Sn-2 has discharge capacity of 131.1 mAh g−1 at 4 A g−1 in rate test and 121.4 mAh g−1 at 1 A g−1 after 1000 cycles in cycling test. The experimental results show that NaTi2(PO4)3/C with Sn substitution with proper content exhibits the great potential in anode for sodium ion batteries, and can further provide reference for next generation electrode materials and battery systems.  相似文献   
92.
The present work reports the realization of an analog fractional‐order phase‐locked loop (FPLL) using a fractional capacitor. The expressions for bandwidth, capture range, and lock range of the FPLL have been derived analytically and then compared with the experimental observations using LM565 IC. It has been observed that bandwidth and capture range can be extended by using FPLL. It has also been found that FPLL can provide faster response and lower phase error at the time of switching compared to its integer‐order counterpart. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   
93.
中联万基水泥有限公司4500t/d熟料生产线采用SCLW4-12×13.4第四代篦冷机,煤磨热风取风口和余热发电AQC热风取风口在篦冷机同一对称位置,煤磨与余热发电系统存在争风现象,开停煤磨对余热发电系统影响较大。通过从废气管道处开孔,加装管道和电动阀,与热风管道汇合通往煤磨沉降室,调整相应阀门开度,可以控制入煤磨烟气温度,这样不但提高了余热发电量,而且提高了煤磨产量,同时也降低了窑头排风机的负荷,降低了熟料生产电耗。  相似文献   
94.
防碰装置是起重机械重要的安全防护装置,其性能质量直接关系到人员和设备安全。常规的防碰装置性能试验方法难以保证试验数据的精度和可靠性。针对防碰装置的工作特点和试验要求,从试验原理、系统结构、运行逻辑等方面入手,设计一套能模拟防碰装置实际运行工况,自动进行性能试验和数据采集处理,精度高、重复性好的试验系统,可以有效提升防碰装置检测能力。  相似文献   
95.
This paper reviews recent studies, that not only includes both experiments and modeling components, but celebrates a close coupling between these techniques, in order to provide insights into the plasticity and failure of polycrystalline metals. Examples are provided of studies across multiple-scales, including, but not limited to, density functional theory combined with atom probe tomography, molecular dynamics combined with in situ transmission electron miscopy, discrete dislocation dynamics combined with nanopillars experiments, crystal plasticity combined with digital image correlation, and crystal plasticity combined with in situ high energy X-ray diffraction. The close synergy between in situ experiments and modeling provides new opportunities for model calibration, verification, and validation, by providing direct means of comparison, thus removing aspects of epistemic uncertainty in the approach. Further, data fusion between in situ experimental and model-based data, along with data driven approaches, provides a paradigm shift for determining the emergent behavior of deformation and failure, which is the foundation that underpins the mechanical behavior of polycrystalline materials.  相似文献   
96.
This study aimed to know the effect of adding pulp in rambutan fruit juice on the characteristics of rambutan juice during storage. Research using the CRD, the treatment were kind of pulp (mandarin and rambutan) and pulp concentration (5%, 7.5%, and 10%). The results showed that the addition of pulp significantly affect the characteristics of rambutan juice (pH, vitamin C, total acid) during storage. Pulpy juice with the most prefered was addition of rambutan pulp as much as 7.5% (w/v) and the addition of citrus pulp as much as 7.5% (w/v) with the score of 3-4 (moderate like - like).  相似文献   
97.
Hyperbaric storage (HS) was evaluated as a new food preservation methodology at room temperature (RT) for beef and pork meat, both minced and in pieces, and compared to refrigeration (RF) storage. The meat samples were stored at 50, 75 and 100 MPa and variable RT up to 60 days. HS at 75 and 100 MPa could not only inhibit microbial growth but also inactivate microorganisms. Regarding physicochemical analyses, an overall equal to better pH maintenance in HS samples was achieved, and similar colour differences between HS and RF were observed. Generally, similarities in moisture content and drip loss between HS (mostly 75 and 100 MPa) and RF were detected (tendency for lower values in the former and higher values in the latter for the higher pressure level). Protein solubility revealed a decrease of sarcoplasmic protein values during storage with a pressure level dependency in some samples.  相似文献   
98.
(1-x)Sr0.7Pb0.15Bi0.1TiO3-xBi4Ti3O12 ((1-x)SPBT-xBIT, x = 0-0.125) bulk ceramics were developed and calcined via the solid-state method, aimed at the application of pulsed power capacitors. The phase structures, temperature stability, hysteresis loop, and discharge properties were systematically investigated. Considering both the temperature stability and dielectric properties, 0.925SPBT-0.075BIT bulk ceramics with a capacitance variation satisfying the X7R specification were developed for pulsed power capacitors. The energy storage density was 0.252 J/cm3, and the ceramics showed high temperature stability at 80 kV/cm. The discharge current waveforms of the 0.925SPBT-0.075BIT ceramics were recorded. A high discharge power density of approximately 1.01 × 108 W/kg with an 8 Ω load resistor and short discharge period of 84 ns were achieved at 50 kV/cm. The good temperature stability properties and high power density show that the 0.925SPBT-0.075BIT ceramics are well suited for pulsed power capacitors with a wide temperature range.  相似文献   
99.
Using mean value theorem for integrals we show that the well-known LCOE definition is incorrect.  相似文献   
100.
Automatic load shedding is the ultimate countermeasure against imbalance in a power system and can effectively help preventing large blackouts. Taking into account a high penetration of renewable energy sources (RES) in the distribution grid, a clear distinction between load and generation at the PCC becomes increasingly more difficult. For that reason an adaptation of frequency relay parameters and their locations of installation are necessary. In Europe this is rest on a multi-step plan based on values such as the yearly peak load. In this paper a novel probabilistic method for automatic load shedding is presented that uses the average values instead of peak values for load shedding. Its applicability is verified by a dynamic power system model that was developed to compare the classical and novel probabilistic load shedding principle. The method is verified using data from a German TSO.  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