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991.
用微波谐振腔技术测定任意形状生物体的湿度 总被引:4,自引:0,他引:4
短形诸振腔,工作于TE(105)和TE(107)模式,中心频率分别为4.55和5.80GHz;当大小和湿度不同的生物体(黄豆或玉米粒)置于谐振腔中心时,谐振频率和品质因数发生变化。对频偏(ΔF)和传输因子(ΔT)的测量,发现它们与颗粒的含水量及干燥质量之间有重要的统计相关关系,可以用这两个测量的腔参量来表示湿度。通过“曲线拟合法”进一步获得简单的湿度近似表达式,且与颗粒的形状无关。应用这些谐振腔测量技术,测定形状近似球形的黄豆粒的7~16%范围内的湿度,其不确定性小于1%,可信度达95%以上。对于大小悬殊,形状很不均匀的玉米粒,把它们固定在腔中央、相对于腔内最大电场矢量互差90度的两个位置上,对ΔF和ΔT分别作两次测量,发现它们的平均值实际上与形状无关。这样,上述方法也能确定任意形状的玉米颗粒的湿度,不确定性仅为1%左右。 相似文献
992.
993.
It has been reported that application of tensile axial stress can simultaneously increase quality factor and resonant frequency for micromechanical resonators. In this study, we formulate an analytical model for evaluating thermoelastic damping in micromechanical resonators based on the thermal energy method, in which thermal conductions in both thickness direction and axial direction are considered. An explicit expression for thermoelastic damping in the form of infinite series has been obtained. The proposed analytical model is further validated by finite element analysis. Results of the present study demonstrate that the 2D model needs to be adopted in order to accurately evaluate thermoelastic damping of micromechanical resonators with axial pretension. In addition, the 2D model proposed in the present study eliminates the inherent inconsistency entailed in the 1D model. 相似文献
994.
995.
研制了一种采用氮化硅/二氧化硅/氮化硅复合膜作为支持薄膜的高Q薄膜体声波谐振器.当采用单层氮化硅膜或二氧化硅膜作为谐振器的支持薄膜时,由于残余应力的作用,释放完的薄膜往往会出现褶皱的现象,极大地降低了薄膜体声波谐振器的Q值;上述复合膜结构有效地解决了这个问题.采用直流磁控溅射法制备了氧化锌压电薄膜,X射线衍射结果表明制备的氧化锌薄膜具有很好的c轴择优取向,意味着氧化锌薄膜具有较好的压电性.S参数测试结果表明该薄膜体声波谐振器在0.4~2.6GHz的频率范围内具有3个明显的谐振模式,计算了这些谐振模式的串联谐振频率、并联谐振频率、有效机电耦合系数和Q值.在这3个模式中,第3个谐波模式的工作频率约为2.4GHz,具有最高的Q值(约为500),可用来制备2.4GHz的低相噪射频振荡源. 相似文献
996.
Compact Interlaced Dual Circularly Polarized Sequentially Rotated Dielectric-Resonator Antenna Array
Yazeed Qasaymeh 《计算机、材料和连续体(英文)》2022,72(3):4631-4643
In this study, a compact 2 × 2 interlaced sequentially rotated dual-polarized dielectric-resonator antenna array is proposed for 5.8 GHz applications. The array is composed of a novel unit elements that are made of rectangular dielectric resonator (RDR) coupled to an eye slot for generating the orthogonal modes, and to acquire circular polarization (CP) radiation. For the purpose of miniaturization and achieving dual polarized resonance, the array is fed by two interlaced ports and each port excites two radiating elements. The first port feeds horizontal elements to obtain left hand circular polarization (LHCP). The second port feeds vertical elements to obtain right hand circular polarization (RHCP). A quarter-wave length transformer is employed to reduce the attenuation and consequently increase the array gain performance. The 35 × 35 mm2 () gains were 8.4 and 8.2 dBi for port 1 and port 2, respectively, with port isolations of −33.51 dB. The design achieves a voltage standing-wave ratio (VSWR) < −10 dB and an axial ratio (AR) ˂ − 3 dB bandwidth of 2.48% (5.766 to 5.911 GHz) for LHCP at port 1 and a VSWR < −10 dB and AR ˂ −3 dB bandwidth of 2.28% (5.788 to 5.922 GHz) for RHCP at port 2. The findings of the proposed design validate its use for ISM band applications. 相似文献
997.
998.
The paper contains a practical perspective on regenerative machine tool chatter. Chatter is a well known phenomenon, occurrence of which is undesired in manufacturing. Aggressive machining conditions, in the sense of removing more metal rapidly, usually cause chatter. In most cases, these conditions can be determined a priori to the operation. A chatter stability study and its reasoning based on root locus plot analysis of time delayed systems is presented as a new and practical perspective in the field. At the junction of root locus and chatter concepts an area of particular interest to the authors arises: a new method for active vibration suppression, the Delayed Resonator. It is an active vibration absorber tuning of which is achieved utilizing a simple time delayed feedback. The cross linking between the Delayed Resonator study and the subject matter, machine tool chatter, is exciting to share. This is the primary motivation in pursuing this study. One of the highlights of the work appears at the phenomenon called Dual Frequency Delayed Resonator. This feature has been conjectured in the literature using the well known “stability lobes”, but never discussed with detail. 相似文献
999.
固体装配型薄膜体声波谐振器(FBAR)机械强度好,尺寸小,可在硅片上三维立体集成,灵敏度大,在未来的通信设备制作高带通滤波器和物联网传感器中展现出广泛的应用前景。通过射频磁控溅射系统制备了以掺镁ZnO(MgxZn1-xO)作为压电层的固体装配型薄膜体声波谐振器,研究了掺镁ZnO对薄膜体声波谐振器谐振性能的影响。利用场发射扫描电镜(FESEM)对FBAR的结构进行了微观表征。比较了不同掺镁ZnO靶材对于晶向和谐振性能的影响。通过优化条件,制备出了性能优越的FBAR,其谐振频率在1.8~2.4GHz,品质因数(Q)可达800,回波损耗可达-30dB。 相似文献
1000.