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991.
992.
龚中字 《自动化与仪器仪表》2007,(1):63-65,81
介绍采用MSP430微功耗微处理构成的智能补偿电路及软件。该电路接受涡街流量变送器输出的脉冲fi,根据频率fi一线性度E曲线,软件采用多点线性内查补偿运算出与流量成正比的频率fic,为确保频率fic的转换精度,微处理器的定时器接受双时钟源,输出占空比为50%PWM方波,从而提高变送器的线性度及准确度。 相似文献
993.
Development and analysis of a 12-year daily 1-km forest fire dataset across North America from NOAA/AVHRR data 总被引:1,自引:0,他引:1
Ruiliang Pu Zhanqing Li Peng Gong Robert Fraser Shobha Kondragunta 《Remote sensing of environment》2007,108(2):198-208
Fires in boreal and temperate forests play a significant role in the global carbon cycle. While forest fires in North America (NA) have been surveyed extensively by U.S. and Canadian forest services, most fire records are limited to seasonal statistics without information on temporal evolution and spatial expansion. Such dynamic information is crucial for modeling fire emissions. Using the daily Advanced Very High Resolution Radiometer (AVHRR) data archived from 1989 to 2000, an extensive and consistent fire product was developed across the entire NA forest regions on a daily basis at 1-km resolution. The product was generated following data calibration, geo-referencing, and the application of an active fire detection algorithm and a burned area mapping algorithm. The spatial-temporal variation of forest fire in NA is analyzed in terms of (1) annual and monthly patterns of fire occurrences in different eco-domains, (2) the influence of topographic factors (elevation zones, aspect classes, and slope classes), and (3) major forest types and eco-regions in NA. It was found that 1) among the 12 years analyzed, 1989 and 1995 were the most severe fire years in NA; 2) the majority of burning occurred during June-July and in low elevation zones (< 500 m) with gentle slopes (< 10°), except in the dry eco-domain where more fires occurred in higher elevation zones (> 2000 m); 3) most fires occurred in the polar eco-domain, sub-arctic eco-division, and in the taiga ( boreal forests), forest-tundras and open woodlands eco-provinces in the boreal forests of Canada. The tendency for multiple burns to occur increases with elevation and slope until about 2500 m elevation and 24° slope, and decreases therefore. In comparison with ground observations, the omission and commission errors are on the order of 20%. 相似文献
994.
The majority of existing tracking algorithms are based on the maximum a posteriori solution of a probabilistic framework using a Hidden Markov Model, where the distribution of the object state at the current time instance is estimated based on current and previous observations. However, this approach is prone to errors caused by distractions such as occlusions, background clutters and multi-object confusions. In this paper, we propose a multiple object tracking algorithm that seeks the optimal state sequence that maximizes the joint multi-object state-observation probability. We call this algorithm trajectory tracking since it estimates the state sequence or “trajectory” instead of the current state. The algorithm is capable of tracking unknown time-varying number of multiple objects. We also introduce a novel observation model which is composed of the original image, the foreground mask given by background subtraction and the object detection map generated by an object detector. The image provides the object appearance information. The foreground mask enables the likelihood computation to consider the multi-object configuration in its entirety. The detection map consists of pixel-wise object detection scores, which drives the tracking algorithm to perform joint inference on both the number of objects and their configurations efficiently. The proposed algorithm has been implemented and tested extensively in a complete CCTV video surveillance system to monitor entries and detect tailgating and piggy-backing violations at access points for over six months. The system achieved 98.3% precision in event classification. The violation detection rate is 90.4% and the detection precision is 85.2%. The results clearly demonstrate the advantages of the proposed detection based trajectory tracking framework. 相似文献
995.
996.
Nickel catalysts supported on CeO2-ZrO2-CeO2,ZrO2-Al2O3 and Al2O3 were prepared and characterized by means of X-ray diffraction(XRD),BET areas,H2 temperature-programmed reduction(H2-TPR),and X-ray photoelectron spectroscopy(XPS).Through the test of catalytic partial oxidation of methane(CPOM),Ni/CeO2-ZrO2-Al2O3 displayed the highest activity,which resulted from its largest BET area and best NiO dispersion.Furthermore,Ni/CeO2-ZrO2-Al2O3 maintained a long-time stability in CPOM,which was attributed to its best coking resistance among all the prepared catalysts. 相似文献
997.
Wang Jianli Cao Hongyan Zhong Junbo Gong Maochu Yan Shenghui Liu Zhimin Shen Mei Chen Yaoqiang 《中国稀土学报(英文版)》2007,25(1)
This article showed that the catalytic activity of MnOx/γ-Al2O3/Ce0.5Zr0.5O2 monolithic catalyst toward the catalytic combustion of ethanol in a fixed bed reactor could be greatly improved by doping three metal oxides into Ce0.5Zr0.5O2. The catalytic activity of MnOx/γ-Al2O3/Ce0.45Zr0.45M0.1Ox (M=Y, La, Mn) is better than that of MnOx/γ-Al2O3/Ce0.5Zr0.5O2. The order of activity of the catalysts is as follows: MnOx/γ-Al2O3/Ce0.45Zr0.45Y0.1Ox>MnOx/γ-Al2O3/Ce0.45Zr0.45La0.1Ox>MnOx/γ-Al2O3/Ce0.45Zr0.45Mn0.1Ox>MnOx/γ-Al2O3/Ce0.5Zr0.5O2. The influence of the loading amount of manganese oxide in enhancing the catalytic activity of MnOx/γ-Al2O3/Ce0.45Zr0.45Y0.1Ox was investigated. The results showed that when MnO2 loading amount was 10%(mass fraction), the MnOx/Al2O3/Ce0.45Zr0.45Y0.1Ox catalyst recorded the highest activity. 相似文献
998.
The response of a beam-column frame to impulsive ground shock, such as those induced by an underground explosion, has characteristics of both impact and natural earthquake responses. The critical effects may be governed by the dynamic response of individual elements as continuous mass systems, while to a certain extent the global vibration (as of lumped-mass systems) may also be involved. To incorporate both dynamic features, the present study proposes a combined continua and lumped parameter (CCLP) model, which consists of the basic beam-column element with distributed stiffness and mass, along with concentrated mass-springs at element ends to form the reduced dynamic system. To take into account of the shear deformation and rotary inertia which become important in the impulsive response, the governing equations are formulated based on the Timoshenko beam theory. The nonlinearities are described through three mechanisms, namely the distributed nonlinear flexural and diagonal shear behavior, and the direct sliding shear at the member ends. A generic restoring force model is adopted to describe the hysteretic behavior. Comparison with a scaled model test demonstrates that the CCLP model is capable of representing the primary dynamic features in a frame structure under impulsive ground shock. Extended parametric studies indicate that, with increase of the ground shock frequency, the failure tends to become shear dominant. For ground shocks of frequency at 20–30?Hz and above, the failure in a reinforced concrete column will require a peak ground velocity (PGV) on the order of 3?m/s, whereas failure in a beam would occur at PGV of about 1.5?m/s. 相似文献
999.
1000.
以六甲基亚胺为模板剂,静态水热晶化法合成了MCM-56分子筛,通过X-射线衍射、N2等温吸附等方法对样品进行表征.当硅铝比低于20时易生成MCM-49和丝光沸石,加入少量碱能提高分子筛的相对结晶度,最佳合成温度为135~150 ℃,时间分别为3天.考察了MCM-56对苯和长链烯烃烷基化反应的催化活性,并与MCM-22进行了对比.实验表明,在最佳反应温度120 ℃时,烯烃的转化率为29.35%,烷基苯(LAB)的选择性为98.22%,MCM-56的催化活性明显低于MCM-22. 相似文献