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   11539篇
  免费   1406篇
  国内免费   862篇
电工技术   538篇
综合类   1068篇
化学工业   1262篇
金属工艺   217篇
机械仪表   541篇
建筑科学   330篇
矿业工程   96篇
能源动力   231篇
轻工业   293篇
水利工程   252篇
石油天然气   235篇
武器工业   186篇
无线电   3130篇
一般工业技术   1854篇
冶金工业   121篇
原子能技术   445篇
自动化技术   3008篇
  2024年   10篇
  2023年   145篇
  2022年   141篇
  2021年   255篇
  2020年   272篇
  2019年   280篇
  2018年   215篇
  2017年   343篇
  2016年   351篇
  2015年   366篇
  2014年   564篇
  2013年   703篇
  2012年   699篇
  2011年   831篇
  2010年   640篇
  2009年   760篇
  2008年   685篇
  2007年   823篇
  2006年   708篇
  2005年   674篇
  2004年   543篇
  2003年   519篇
  2002年   435篇
  2001年   343篇
  2000年   320篇
  1999年   277篇
  1998年   235篇
  1997年   242篇
  1996年   217篇
  1995年   192篇
  1994年   186篇
  1993年   153篇
  1992年   110篇
  1991年   114篇
  1990年   69篇
  1989年   75篇
  1988年   48篇
  1987年   29篇
  1986年   17篇
  1985年   49篇
  1984年   42篇
  1983年   28篇
  1982年   45篇
  1981年   9篇
  1980年   10篇
  1979年   4篇
  1978年   3篇
  1976年   8篇
  1974年   6篇
  1959年   3篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
为了提高智能化光纤复合架空线路态势感知的实时性,将人工神经网络方法应用于光纤沿线应变解调,确定了神经网络的结构。编程实现了基于洛伦兹模型的最小二乘谱拟合方法和神经网络方法,采用不同信噪比和布里渊频移的布里渊谱训练神经网络,将它们应用于某光纤复合架空线路沿线光纤应变的测量,从不同角度比较了两种方法的计算结果。计算结果表明,神经网络方法能有效获得光纤沿线的布里渊频移进而获得应变,具有与谱拟合方法相似的准确性,但应变解调时间仅约为谱拟合方法的1/20000。研究结果为提高智能光纤复合架空线路态势感知的实时性提供了参考。  相似文献   
2.
目的 建立磁固相萃取技术结合表面增强拉曼散射(surface enhanced Raman scattering, SERS)法快速检测葡萄汁中的三唑磷。方法 以Fe3O4为磁芯,三醛基间苯三酚(trihydroxy-benzene tricarbaldehyde, Tp)和联苯胺(benzidine, BD)为配体合成共价有机框架(covalent organic framework,COF)包裹的磁性纳米材料Fe3O4@COF (TpBD)。以Fe3O4@COF (TpBD)为吸附材料,通过π-π相互作用和氢键作用吸附样品溶液中的三唑磷,实现复杂基质中三唑磷的分离和富集。以金纳米颗粒为SERS增强基底,结合便携式拉曼光谱仪建立一种三唑磷的快速检测和定量分析方法。结果 利用1000、1409和1596 cm-1拉曼位移处的SERS信号强度计算的三唑磷检出限分别为2.97、3.57和3.44 nmol/L,相关系数分别为0.9647、0.9677和0.9579。利用该方法检测葡萄汁中三唑磷的回收率为67.56%~86.80%,相对标准偏差为0.99%~1.68%。结论 本研究建立的磁固相萃取结合SERS方法在三唑磷的快速检测和定量分析中表现出了良好的灵敏度、准确性和稳定性,具有应用于果汁中三唑磷快速检测的潜力。  相似文献   
3.
本文充分发挥中子对磁灵敏、穿透力强等技术优势,利用加载磁场小角中子散射实验技术研究核电站实际服役14年的阀杆17 4PH不锈钢样品。结果表明,与不加磁场时相比,加载磁场条件下二维散射图谱呈明显各向异性,在散射矢量垂直于磁场方向上散射强度显著增强。利用多分散球模型对数据进行拟合,结合原子探针实验结果分析得出,衬度的增加降低了Cu析出物周围元素分布不均匀对散射的相对贡献,从而有助于更加准确地获得Cu纳米析出物的尺寸。  相似文献   
4.
中子引起的轻核反应是核数据研究的重要内容。当前我国核数据库中氘核中子反应截面的计算结果局限于采用s 波可分离势,且入射能量在20 MeV以下。需要发展三体核反应的法捷耶夫方程理论方法,采用超出s 波的核子 核子相互作用,从而对更高能量范围内氘核全套中子反应截面做出准确的描述。本文介绍了利用法捷耶夫方程计算n+d三核子反应体系的弹性散射微分截面、破裂反应、破裂反应出射中子和质子的双微分截面的理论框架及数值计算结果,同时计算了弹性散射总截面和破裂反应总截面的激发函数。计算结果与实验数据及CENDL 32、ENDF/B Ⅷ.0、JENDL 5、JEFF 33等数据库中的评价数据符合较好。  相似文献   
5.
费金磊  林剑 《光学仪器》2022,44(4):49-56
相干反斯托克斯拉曼散射(CARS)是一种受激拉曼现象,在显微成像时,存在非共振背景,会导致光谱产生峰位偏移和谱线变形。本文利用飞秒激光作为光源,通过光栅滤波系统产生窄带泵浦光,飞秒激光激发光子晶体光纤产生超连续谱作为斯托克斯光,两束光被调制为圆偏振光后同时激发样品产生CARS光谱。通过模拟计算说明圆偏振光可以有效去除各向异性材料CARS光谱中的非共振背景,从而使CARS光谱具有和自发拉曼相似的谱线形状。聚苯乙烯微球和液晶样品的CARS光谱实验结果与模拟计算基本相符,说明圆偏振是一种有效去除CARS光谱非共振背景的方法。  相似文献   
6.
Among various carbon materials, diamond stands out due to excellent physical and chemical properties. In this work, we designed Dia@SiO2@Ag composites combining diamond micropowder and Ag nanoparticles by a simple chemical method and obtained stable substrate for surface enhanced Raman scattering (SERS) owing to its high surface-to-volume ratio, low density, as well as close bond between diamond and Ag. As-prepared Dia@SiO2@Ag presented high activity to detect crystal violet and rhodamine 6G molecules, which was demonstrated by significantly enhanced SERS spectra and high enhancement factor values (108-109). Moreover, Dia@SiO2@Ag also showed desired sensitivity, which was investigated by detection limit. Therefore, our study provided more theoretical support and broadened the functional applications of diamond, particularly in Raman detection.  相似文献   
7.
In this paper, we investigate multiphase flow monitoring inside metallic pipes by qualitative microwave imaging, where foreign objects inside the liquid flow are monitored to eliminate contamination. The motivation stems from the fact that conventional tomographic approaches of microwave imaging are inherently not suitable for real-time flow monitoring due to their computational requirements as these techniques aim to retrieve the dielectric permittivity profile inside the pipeline. In this context, we envision that the factorization method of qualitative inverse scattering theory, which is a shape retrieval algorithm from scattered field measurements, provides a better alternative for flow monitoring. To demonstrate the feasibility of such an approach, we first reformulate the factorization method by considering dyadic Green’s functions inside a cuboid cavity with perfectly conducting walls. Later, the formulation is simplified for a specific microwave measurement configuration to accelerate the reconstructions for real-time flow monitoring. Finally, flow monitoring is realized as a differential imaging procedure where foreign objects are detected by using differences of multi-static scattering parameters that are measured consecutively. The simulation studies performed for food and petroleum flows reveal the capabilities of the technique as a viable solution for different industrial flows.  相似文献   
8.
Rift Valley fever virus (RVFV) is a mosquito-transmitted virus from the Bunyaviridae family that causes high rates of mortality and morbidity in humans and ruminant animals. Previous studies indicated that DEAD-box helicase 17 (DDX17) restricts RVFV replication by recognizing two primary non-coding RNAs in the S-segment of the genome: the intergenic region (IGR) and 5′ non-coding region (NCR). However, we lack molecular insights into the direct binding of DDX17 with RVFV non-coding RNAs and information on the unwinding of both non-coding RNAs by DDX17. Therefore, we performed an extensive biophysical analysis of the DDX17 helicase domain (DDX17135–555) and RVFV non-coding RNAs, IGR and 5’ NCR. The homogeneity studies using analytical ultracentrifugation indicated that DDX17135–555, IGR, and 5’ NCR are pure. Next, we performed small-angle X-ray scattering (SAXS) experiments, which suggested that DDX17 and both RNAs are homogenous as well. SAXS analysis also demonstrated that DDX17 is globular to an extent, whereas the RNAs adopt an extended conformation in solution. Subsequently, microscale thermophoresis (MST) experiments were performed to investigate the direct binding of DDX17 to the non-coding RNAs. The MST experiments demonstrated that DDX17 binds with the IGR and 5’ NCR with a dissociation constant of 5.77 ± 0.15 µM and 9.85 ± 0.11 µM, respectively. As DDX17135–555 is an RNA helicase, we next determined if it could unwind IGR and NCR. We developed a helicase assay using MST and fluorescently-labeled oligos, which suggested DDX17135–555 can unwind both RNAs. Overall, our study provides direct evidence of DDX17135–555 interacting with and unwinding RVFV non-coding regions.  相似文献   
9.
The skin’s barrier ability is an essential function for terrestrial survival, which is controlled by intercellular lipids within the stratum corneum (SC) layer. In this barrier, free fatty acids (FFAs) are an important lipid class. As seen in inflammatory skin diseases, when the lipid chain length is reduced, a reduction in the barrier’s performance is observed. In this study, we have investigated the contributing effects of various FFA chain lengths on the lamellar phase, lateral packing. The repeat distance of the lamellar phase increased with FFA chain length (C20–C28), while shorter FFAs (C16 to C18) had the opposite behaviour. While the lateral packing was affected, the orthorhombic to hexagonal to fluid phase transitions were not affected by the FFA chain length. Porcine SC lipid composition mimicking model was then used to investigate the proportional effect of shorter FFA C16, up to 50% content of the total FFA mixture. At this level, no difference in the overall lamellar phases and lateral packing was observed, while a significant increase in the water permeability was detected. Our results demonstrate a FFA C16 threshold that must be exceeded before the structure and barrier function of the long periodicity phase (LPP) is affected. These results are important to understand the lipid behaviour in this unique LPP structure as well as for the understanding, treatment, and development of inflammatory skin conditions.  相似文献   
10.
报道了一种采用同轴静电纺丝法制备的表面增强Raman散射(SERS)活性衬底,用于微量环境污染物的快速检测。采用醋酸纤维素(CA)/丙酮-二甲基乙酰胺溶液作为前驱液分散银纳米立方体,利用丙酮促进银颗粒适度团聚,采用同轴静电纺丝法制备了大面积银立方体/CA纳米纤维。由于团聚态银纳米立方体之间的等离子体耦合作用,复合薄膜具有优异的SERS活性,是单分散态的银立方体/CA纳米纤维SERS灵敏度的4倍,实现了0.1nmol/L的对巯基苯胺以及10nmol/L的甲基对硫磷农药的SERS检测,SERS信号强度偏差小于12%。  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