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1.
This article presents an overview of smart structures technologies in connection with long-span cable-supported bridges. Considering the broad scope of the smart structures technologies, two subareas, namely, structural health monitoring and structural control technologies, and their applications in long-span cable supported bridges, are identified as the focus of this review. It is believed that by, adopting the smart structures technologies, reliable operation and hazard management of long-span bridges can be achieved much more efficiently and can be made economically feasible, especially for bridges located at sites with high risks of severe natural hazardous events, such as those facing the bridges of the Taiwan Strait Crossing project. The feasibility of and practical issues in implementing the smart structures technologies in the design and construction of long-span cable-supported bridges are also discussed here. Considering the time span of the construction of the Taiwan Strait Crossing, some of the innovative technologies with a high potential for future long-span bridge applications, while still at the stage of exploratory research at the time of writing, are also examined as it is believed these technologies might have become prevalent by the completion time of the Taiwan Strait Crossing project.  相似文献   
2.
本文利用37个CMIP5模式和CESM(Community Earth System Model)包含40个成员的超级集合试验的表面气温预估数据,比较了工业革命前气候参照试验、多项式拟合法和方差分析方法这三种目前在国际上运用较多的方法所估算的表面气温内部变率的异同,分析了内部变率的估算对气候预估中信号萌芽时间(TOE)的影响。结果表明:若采用CMIP5多模式集合,则工业革命前气候参照试验和多项式拟合法都是估算内部变率的合理方法,而方差分析方法则由于包含模式性能自身的影响会夸大内部变率故不推荐使用。内部变率的全球分布呈现出极向强化的现象,中高纬度地区的内部变率幅度远大于热带、副热带地区。内部变率受不同排放情景的影响较小,且随时间无显著变化,但方差分析方法估算的内部变率在热带地区容易受到排放情景的影响。若基于类似CESM这样的单个气候模式的超级集合模拟试验来估算内部变率,三种方法估算的结果相似。不同方法估算的内部变率对TOE的影响主要位于北大西洋拉布拉多海、南大洋威德尔海和罗斯海等邻近海洋深对流区。对于中国区域平均来说,基于CESM超级集合模拟试验,三种方法估算的内部变率与强迫信号之比都小于15%;对CMIP5多模式集合,采用工业革命前气候参照试验和多项式拟合法得到的结果与此接近,但若采用方差分析方法则显著高估内部变率的作用。  相似文献   
3.
The sequencing batch reactor (SBR) process has shown great success in the treatment of industrial wastewater from intermittent discharge factories and for the treatment of domestic wastewater from medium or small towns. As automation technology has developed, many studies have been conducted to determine the optimal conditions for the SBR process. This review outlines the progress and application of control strategies that have been developed for the SBR process and provides a summary and comparison of the advantages and disadvantages of various control strategies, especially fixed‐time control strategies and various real‐time control strategies. Moreover, an analysis and discussion of novel optimal control methods for biologic nutrient removal are provided. Although previous studies in this field have greatly enriched our understanding of SBR systems, it is clear that many unsolved problems remain. Therefore, a summary of unanswered questions regarding control strategies for the SBR process is provided and future research directions are suggested.  相似文献   
4.
Upgrading noncode conforming buildings to mitigate seismic induced damages is important in moderate to high seismic hazard regions. The damage, can be mitigated by using conventional (e.g. FRP wrapping) and emerging (e.g. smart structures) retrofit techniques. A model for the structure to be retrofitted should include relevant performance indicators. This paper proposes a variable stiffness smart structure device known as the Smart Spring to be integrated on building structures to mitigate seismic induced damage. The variable stiffness capability is of importance to structures that exhibit vertical (e.g. soft storey) irregularities and to meet different performance levels under seismic excitation. To demonstrate the utility of the proposed retrofitting technique, a four‐storey steel building is modelled in MATLAB and appropriate performance indicators are chosen. Various return period seismic hazards are generated from past earthquake event records to predict the structure's performance. The performance improvement because of the retrofitting of building structures using the variable stiffness device is presented. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   
5.
Effective force testing (EFT) is one of the force‐based experimental methods used for performance evaluation of structures that incorporate dynamic force control using hydraulic actuators. Although previous studies have shown successful implementations of force control, controllable frequency ranges are limited to low frequencies (10 Hz). This study presents the EFT method using a robust loop shaping force feedback controller that can extend the frequency range up to 25 Hz or even higher. Unlike the conventional PID controllers, loop shaping controllers can provide robustness for a high level of force measurement noise. This study investigates the dynamic properties of hydraulic actuators and the design of a loop shaping controller that compensates for control–structure interaction and suppresses the effect of oil‐column resonance. The designed loop shaping controller was successfully implemented into an EFT setup at the Johns Hopkins University. An experimental investigation of the loop shaping controller was performed under step, random, and earthquake force loadings. Experimental results showed that the loop shaping controller provided excellent force tracking performance and robustness for dynamic force loadings. It was also shown that the loop shaping controller had the gain margin of 9.54 dB at the frequency of 28 Hz. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   
6.
A new method for the simultaneous recovery of U, Th and Pb from ca. 0.5 g calcium carbonate samples for the purpose of U‐(Th)‐Pb geochronometry is presented. The protocol employs ion‐exchange chromatography. Standard anion exchange resin (AG 1‐X8 100–200 mesh) was used as the static phase, and 90% acetic acid was used as the mobile phase to elute the unwanted matrix components; dilute nitric acid was used to elute the U, Th and Pb. Blanks of 1.8 pg Th, 6.4 pg Pb and 8.4 pg U were obtained. The protocol was evaluated by determining the isotopic composition of U‐Th‐Pb separates obtained from an in‐house reference material (prepared from a natural speleothem) by MC‐ICP‐MS. An independently dated speleothem was also reanalysed. Based on these tests, the extraction protocol had an acceptable blank and produced a Pb separate sufficiently free of matrix‐induced instrumental biases to be appropriate for U‐Th‐Pb chronology.  相似文献   
7.
8.
This paper presents a feasibility study of multidegrees‐of‐freedom effective force testing (MDOF‐EFT). The study is intended to facilitate the development of a force feedback controller and investigation of performance as well as robustness of MDOF‐EFT. First, the dynamics of MDOF‐EFT systems are analytically investigated. Analytical transfer functions of the control plant, the valve‐to‐force relations, showed that the plant is dynamically coupled and the natural frequencies of test structures are the transmission zeros of the plant. Using a set of model parameters from a previous study, a case study that includes controller design, numerical simulations and robust stability assessment is performed. A decoupling loop shaping (DLS) controller consisting of a pseudo inverse of the plant and second‐order loop shaping controllers is adopted as the force feedback controller. It is shown that the DLS controller provides a stable control system while successfully decoupling the control loops and compensating the control‐structure interaction. Numerical simulations demonstrate that the DLS controller enables tracking of static and dynamic forces for multiple actuators. Robust stability of MDOF‐EFT with the DLS controller is assessed using Monte Carlo simulation. The stochastic simulation results show that the DLS controller is stable and robust, providing sufficient stability margins for uncertain models with maximum 50% errors in the estimated system parameters. This paper demonstrates that MDOF‐EFT is feasible with the DLS controller and can be implemented in experimental laboratories. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   
9.
Vibration control systems are being used increasingly worldwide to provide enhanced seismic protection for new and retrofitted buildings. This paper presents a new vibration control system on the basis of a seesaw mechanism with viscoelastic dampers. The proposed vibration control system comprises three parts: brace, seesaw member, and viscoelastic dampers. In this system, only tensile force appears in bracing members. Consequently, the brace buckling problem is negligible, which enables the use of steel rods for bracing members. By introducing pre‐tension in rods, long steel rods are applicable as bracing between the seesaw members and the moment frame connections over some stories. Seesaw mechanisms can magnify the damper deformation according to the damper system configuration. In this paper, first, the magnification factor, that is, the ratio of the damper deformation to the story drift, is delivered, which includes the rod deformation. Results of a case study demonstrate that the magnification factor of the proposed system is greater than unity for some cases. Seismic response analysis is conducted for steel moment frames with the proposed vibration control system. Energy dissipation characteristics are examined using the time‐history response results of energy. The maximum story drift angle distributions and time‐history response results of displacement show that the proposed system can reduce the seismic response of the frames effectively. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   
10.
对工程土石方量计算中的等高线法、断面法、方格网法以及基于数字高程模型(DEM)法的基本原理、方法和优缺点进行比较分析,从理论上讨论它们的实用范围、测量条件并进行精度分析,进而找出存在问题并给出结论.  相似文献   
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