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171.
根据等精度频率测量原理,分析了测量精度与频率测量闸门时间和预置门时间的关系,提出了一种改进型等精度频率测量的方法。该方法的主要思想是利用VHDL语言设计的测频计数模块不需要根据被测信号的频率大小而不断改变预置门信号的宽度,只需要固定给出100mS的预置门信号即可。单片机根据频率计数模块的计数结果进行相应运算得出频率值。经仿真和测试,在输入前级加放大整形电路和高速分频电路可以实现幅度从0.1V~10V,频率从0.1HZ~2.7GHZ的信号的全程测量。 相似文献
172.
多速率混合系统的符号化可达性分析 总被引:2,自引:0,他引:2
针对目前还没有专门的数据结构处理多速率混合系统的符号化可达性问题,定义了多速率区域来表示和处理多速率自动机的无穷状态空间,从而把多速率混合系统的符号化可达性分析等价地转化成多速率区域上的3种操作,即并操作、变量重赋值操作和控制状态上的时间流逝操作.从理论上证明了多速率区域在这3种操作上的封闭性,同时定义了矩阵数据结构不同上限矩阵(DCM),并用其存储多速率区域,这样就得到了一种专门处理多速率混合系统符号化可达性分析的数据结构.理论上证得,DCM可以大大降低可达性分析算法的复杂度. 相似文献
173.
Water isotope variations in the snow pack and summer precipitation at July 1 Glacier, Qilian Mountains in northwest China 总被引:8,自引:0,他引:8
ZHOU ShiQiao NAKAWO Masayoshi SAKAI Akiko MATSUDA Yoshihiro DUAN KeQin PU JianChen 《科学通报(英文版)》2007,52(21):2963-2972
This paper presents the stable isotope data of the snow pack and summer precipitation collected at the July 1 Glacier, Qilian Mountains in northwest China and analyses their relationships with meteorologi- cal factors. On an event scale, there is no temperature effect on the δ 18O values in the summer pre- cipitation, whereas the amount effect is shown to be clear. By tracing the moisture transport history and comparing the precipitation with its isotopic composition, it is shown that this amount effect not only reflects the change in moisture trajectory, which is related to the monsoon activities, but is also associated with the cooling degree of vapor in the cloud, the evaporation of falling raindrops and the isotopic exchange between the falling drops and the atmospheric vapor. As very little precipitation occurs in winter, the snow pack profile mainly represents the precipitation in the other three seasons. There are low precipitation δ 18O ratios in summer and high ratios in spring and autumn. The Meteoric Water Line (MLW) for the summer precipitation is δ D = 7.6 δ 18O 13.3, which is similar to that at Delingha, located in the south rim of the Qilian Mountains. The MWL for the snow pack is δ D = 10.4 δ 18O 41.4, showing a large slope and intercept. The deuterium excess (d) of the snow pack is positively correlated with δ 18O, indicating that both d and δ 18O decrease from spring to summer and increase from early autumn to early spring. This then results in the high slope and intercept of the MWL. Sea- sonal fluctuations of d in the snow pack indicate the change of moisture source and trajectory. During spring and autumn, the moisture originates from continental recycling or rapid evaporation over rela- tively warm water bodies like Black, Caspian and Aral Seas when the dry westerly air masses pass over them, hence very high d values in precipitation are formed. During summer, the monsoon is responsi- ble for the low d values. This indicates that the monsoon can reach the western part of the Qilian Mountains. 相似文献
174.
Reconfiguration planning is recognized as an important factor for reducing the cost of manufacturing reconfigurable products, and the associated main task is to generate a set of optimal or near-optimal reconfiguration sequences using some effect algorithms. A method is developed to generate a Petri net as the reconfiguration tree to represent two-state-transit of product, which solved the representation problem of reconfiguring interfaces replacement. Relating with this method, two heuristic algorithms are proposed to generate task sequences which considering economics to search reconfiguration paths effectively. At last, an objective evaluation is applied to compare these two heuristic algorithms to other ones. The developed reconfiguration task planning heuristic algorithms can generate better strategies and plans for reconfiguration. The research finds are exemplified with struts reconfiguration of reconfigurable parallel kinematics machine (RPKM). 相似文献
175.
Modeling Mixed Traffic Flow at Crosswalks in Micro-Simulations Using Cellular Automata 总被引:1,自引:0,他引:1
The cellular automata (CA) micro-simulation model was used to describe the behavior of the mixed traffic flows at crosswalks where the pedestrians compete with the vehicles to cross the roadway. The focus of this paper is the behavior of pedestrians and the influence of pedestrians’ behavior on the vehicle flow, pedestrian flows, and the vehicle waiting time. The proportion of pedestrians who do not obey traffic laws, the group effect, and expected waiting time of pedestrians, regarded as the most important pedestrian characteristics, are taken into consideration in the analysis. Simulation results show the ability of the micro-simulation to capture the most important features of mixed traffic flow. 相似文献
176.
杆体可回收锚杆锚固性能分析 总被引:1,自引:0,他引:1
塑料锚头、金属可回收杆体,在锚固端能够提供足够大的胀锚力。在完成支护任务后,杆体可回收复用以降低支护材料成本。为了分析其锚固作用,应用ANSYS软件,对其锚固性能进行了数值计算。分析结果说明,该锚杆具有恒阻让压特性,能够有效支护围岩。 相似文献
177.
178.
神经外科手术中动脉与呼气末二氧化碳分压差稳定性的观察 总被引:2,自引:0,他引:2
观察神经外科手术过程中动脉和呼气末二氧化碳分压差值(Pa-ETCO2)的稳定性。对30例幕上肿瘤行择期肿瘤切除术的患者,于硬脑膜打开后,给予安氟醚1.1~1.5MAC,将动脉内压维持在每小时10±0.67kPa。分别于麻醉前、气管插管后5min、开颅后5min、术中降压1h和术终抽取动脉血行血气分析。对开颅超过3h的14例患者,则于3h后再抽取1次动脉血样,同时记录呼气末二氧化碳分压(PETCO2)。在手术过程中PaCO2平均值为4.21±0.77kPa,PETCO2平均值为3.86±0.66kPa,Pa-ETCO2平均值为0.33±0.66kPa,PaCO2与PETCO2显著相关(P<0.01)。PaCO2、PETCO2和Pa-ETCO2不同时间点之间无显著性差异。如能在麻醉后及早确定Pa-CO2与PETCO2差值,术中监测PETCO2仍有一定价值 相似文献
179.
本文对激光驱动气相合成超细微粉的反应条件与反应过程的关系作了讨论和分析,探讨了提高生成率的途径。 相似文献
180.
阐述了房地产业发展状况及郑州行业背景,对郑州市房地产发展进行了客观、全面的评价,分析了郑州市房地产预警的重要意义,针对存在的一些问题提出了郑州市房地产预警的相关政策建议。 相似文献