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81.
Three series of polyurethane adhesives—polyethyleneadipateurethane (PEAU), polybuthyleneadipateurethane (PBAU), and polyhexyleneadipateurethane (PHAU)—with the same MW and hard/soft segment ratio, based on the three polyesters polyethyleneadipate (PEA), polybuthyleneadipate (PBA), polyhexyleneadipate (PHA), with 4,4′-diphnylmethane diisocyanate (MDI), and butendiol were synthesized by solution polymerization. The crystallinity of these polyesters and polyurethanes (PUs) and the compatibility of blends of PUs with PVC were studied by means of wide-angle x-ray diffraction (WAXD), differential scanning calorimetry (DSC), dynamic thermomechanical analysis (DMA), testing of solubility, and phase contrast microscopy. The results indicated that PBAU/PVC and PHAU/PVC were compatible systems, but PEAU/PVC was incompatible. The adhesive strengths of the three adhesives were quite different from one another, in the order of PBAU ≥ PHAU ? PEAU. The influences of crystallinity and compatibility on adhesion were discussed, and the Diffusion Theory for PU-PVC systems was recommended. © 1995 John Wiley & Sons, Inc. 相似文献
82.
83.
一种适用于降压DC-DC的改进型电流检测电路 总被引:2,自引:0,他引:2
基于电流模式控制能够较好地改善DC-DC的性能,设计一种适用于降压DC-DC的改进型电流检测电路,所提出的电流检测电路提高了电流感应的速度和精度。通过对电路的理论分析与设计,采用SMIC 0.18μm CMOS工艺模型,利用Cadence工具对电路进行仿真验证,所提出的电流检测电路在负载电流为50 mA~500 mA时都能够达到96%的效率以及小于40 ns的建立时间。在开关频率为2 MHz时,输入电压范围为2.5 V~4.2 V,所需电感值为4.7μH,电容值为10μF,输出电压纹波小于18 mV。 相似文献
84.
Although some of the important consequences of flow-induced entanglement loss in entangled polymer rheology have recently been recognized, this specific molecular mechanism has rarely been investigated quantitatively based on experiments or molecular theories. For the first time, the amount of entanglement loss of a short entangled linear polymer (i.e., seven entanglements per chain at equilibrium) during fast-flow deformation is directly tracked in the stochastic simulation of an existing reptation model. The primary finding is that significant entanglement loss is observed in both fast elongation and fast shearing, and, contrary to some earlier conjectures, is particularly pronounced in elongational flow when polymer chain stretching formally commences. Furthermore, according to the current simulation in which three different CCR (Convective Constraint Release) schemes are considered, entanglement loss appears to have very prominent effects on the elongational rheology of an entangled linear polymer – an observation that had rarely been recognized or considered before. On the other hand, the currently explored features of flow-induced entanglement loss are tentatively linked to a wide variety of peculiar empirical properties of temporarily entangled polymer liquids. In particular, we are thus able to provide a consistent molecular explanation of the fairly well-known phenomenological effects of polydispersity and long-chain branching leading to a pronounced strain-hardening phenomenon, in view of two newly proposed effects of heterogeneous relaxations in preventing, directly or indirectly, fast entanglement loss during flows. 相似文献
85.
Jui‐Ming Yeh Chi‐Lun Chen Tai‐Hung Kuo Wen‐Fen Su Hsi‐Ya Huang Der‐Jang Liaw Hsin‐Yi Lu Chi‐Fong Liu Yuan‐Hsiang Yu 《应用聚合物科学杂志》2004,92(2):1072-1079
A series of polymer–clay nanocomposite (PCN) materials consisting of 1,4‐bis(4‐aminophenoxy)‐2‐tert‐butylbenzene–4,4′‐oxydiphthalic anhydride (BATB–ODPA) polyimide (PI) and layered montmorillonite (MMT) clay were successfully prepared by an in situ polymerization reaction through thermal imidization up to 300°C. The synthesized PCN materials were subsequently characterized by Fourier‐Transform infrared (FTIR) spectroscopy, wide‐angle powder X‐ray diffraction (XRD) and transmission electron microscopy (TEM). The effects of material composition on thermal stability, mechanical strength, molecular permeability and optical clarity of bulk PI and PCN materials in the form of membranes were studied by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), molecular permeability analysis (GPA) and ultraviolet‐visible (UV/VIS) transmission spectra, respectively. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1072–1079, 2004 相似文献
86.
压力流化床燃烧技术近二十年来在世界上得到很大发展。煤的湿法给料系统具有比干法输送系统更简单,运行调节更可靠等优点。煤水混合物可泵送的水分在25%左右,煤的粒度一般为0~6mm,表现为非牛顿的假塑性流体特性,通过级配来达到一定的稳定性和良好输送性能,且流动阻力低,不用添加剂即可实现泵送,它的应用使压力流化床的燃烧制备和输送系统成本大大降低。 相似文献
87.
Experimental studies of particle deposition from liquid suspensions of monodispersed particles flowing past single spherical collectors were carried out and compared with theoretical results based on trajectory calculations. The experimental observations indicate the significant effect of particle flocculation and thus suggest the importance of sedimentation as a collection mechanism. The agreement between the theoretical results and the experimental data is good when the surface force interactions are favorable for collection. However, when the electrokinetic repulsion dominates in the neighborhood of the collector, the rate of collection drops rapidly, although not to zero as predicted by theory. 相似文献
88.
89.
在掘进和采煤的过程中,巷道围岩的受力情况复杂多变,因此,巷道离层位移和围岩压力的实时监测是保证巷道正常工作的一个重要因素。设计了一种基于FBG传感器网络的煤矿巷道在线监测系统。该系统实现井下700 m数据采集,井上分析处理,可提供时序趋势变化、结构分布变化和阈值报警等功能。根据朱仙庄煤矿巷道的特点,系统安装4只FBG位移传感器、4只FBG土压力传感器和4只FBG温度传感器,对巷道掘进区域的离层位移、围岩压力和温度变化进行在线监测。监测结果表明:系统对离层位移、围岩压力和巷道温度变化反映灵敏,能够有效保证巷道掘进的正常进行,且为后续巷道施工提供数据支持和理论依据。 相似文献
90.
S2/TDE85复合材料耐自然库存与加速湿热老化的性能研究 总被引:5,自引:0,他引:5
本文对高强2号玻璃纤维(S2)增强环氧(TDE85-MCD体系)基复合材料单向板经自然库存与加速湿热老化后力学性能的变化进行了研究。研究结果表明,温度和湿度的作用会使单向板的拉伸、弯曲、剪切性能有所降低;温度越高、湿度越大,力学性能变化越大;可用加速湿热试验值来表征自然库存条件下的试验值。 相似文献