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801.
Direct numerical simulation (DNS) has been carried out to investigate the effect of weak rarefaction on turbulent gas flow
and heat transfer characteristics in microchannel. The Reynolds number based on the friction velocity and the channel half
width is 150. Grid number is 64 × 128 × 64. Fractional time-step method is employed for the unsteady Navier–Stokes equations,
and the governing equations are discretized with finite difference method. Statistical quantities such as turbulent intensity,
Reynolds shear stress, turbulent heat flux and temperature variance are obtained under various Knudsen number from 0 to 0.05.
The results show that rarefaction can influence the turbulent flow and heat transfer statistics. The streamwise mean velocity
and temperature increase with increase of Kn number. In the near-wall-region rarefaction can increase the turbulent intensities and temperature variance. The effects
of rarefaction on Reynolds shear stress and wall-normal heat flux are presented. The instantaneous velocity fluctuations in
the vicinity of the wall are visualized and the influence of Kn number on the flow structure is discussed. 相似文献
802.
Test strategies for cost-sensitive decision trees 总被引:2,自引:0,他引:2
Ling C.X. Sheng V.S. Yang Q. 《Knowledge and Data Engineering, IEEE Transactions on》2006,18(8):1055-1067
In medical diagnosis, doctors must often determine what medical tests (e.g., X-ray and blood tests) should be ordered for a patient to minimize the total cost of medical tests and misdiagnosis. In this paper, we design cost-sensitive machine learning algorithms to model this learning and diagnosis process. Medical tests are like attributes in machine learning whose values may be obtained at a cost (attribute cost), and misdiagnoses are like misclassifications which may also incur a cost (misclassification cost). We first propose a lazy decision tree learning algorithm that minimizes the sum of attribute costs and misclassification costs. Then, we design several novel "test strategies" that can request to obtain values of unknown attributes at a cost (similar to doctors' ordering of medical tests at a cost) in order to minimize the total cost for test examples (new patients). These test strategies correspond to different situations in real-world diagnoses. We empirically evaluate these test strategies, and show that they are effective and outperform previous methods. Our results can be readily applied to real-world diagnosis tasks. A case study on heart disease is given throughout the paper. 相似文献
803.
804.
Bacterial populations meet the challenges of dynamic spatially heterogeneous environments with fluctuating biotic and abiotic
factors in a number of ways. The motivation for the work presented here has been to transfer ideas from bacterial adaptability
and evolvability to computational problem solving. Following a brief comment on some examples of the ways bacteria solve problems,
a bacterially-inspired computational architecture for simulating aspects of problem solving is described. We then examine
three case studies. The first, a study of the mutational impact of a remediation to toxic (fitness-reducing) material, highlights
how a sufficiently pre-engineered adaptive system can solve a difficult problem quite easily. The second study looks at why
it is difficult to evolve complex problem solving behaviours and how artificial selection mechanisms coupled with pre-engineering
the system can help. Specifically, this refers to quorum sensing and tactic behaviours. A further study looked at ways in
which a quorum sensing analogue could help computational agents find multiple peaks in a landscape. The paper concludes with
a discussion of an investigation of bacteria that had both quorum sensing and tactic capabilities. 相似文献
805.
Excitation pulse shape effects in drop test simulation of the actuator arm of a hard disk drive 总被引:1,自引:0,他引:1
B. J. Shi S. Wang D. W. Shu J. Luo H. Meng Q. Y. Ng R. Zambri 《Microsystem Technologies》2006,12(4):299-305
For a head actuator assembly (HAA) of a hard disk drive, the deflection of the tip of the arm relative to the pivot can be
used as an indicator of its response to shock. To study the pulse shape effects in a shock analysis, the actuator arm of an
HAA subjected to different acceleration pulse shapes, such as half-sine, triangular and dual-quadratic, was simulated by using
a dynamic finite element package. It has been found that, for the three acceleration pulses, the peak displacements have opposite
behaviors for 0.1- and 1-ms pulse widths. The above phenomena have been explained in terms of a power spectrum analysis. It
has been found that the relative magnitude of the peak displacement of the actuator arm is mainly determined by the power
magnitude of the acceleration pulse at the resonant frequency. A simple mathematical theory was developed to predict the location
of a cross-over interval which divides the power spectrum curve into two major regions where opposite behaviors are observed.
The theoretical pulse width is correlated with a pulse width based on a threshold value as normally used in experiments.
B.J. Shi: On leave from School of Mechanical and Electronic Engineering, Shandong Institute of Architecture and Engineering,
Jinan 250014, China 相似文献
806.
Plale B. Gannon D. Brotzge J. Droegemeier K. Kurose J. Mclaughlin D. Wilhelmson R. Graves S. Ramamurthy M. Clark R.D. Yalda S. Reed D.A. Joseph E. Chandrasekar V. 《Computer》2006,39(11):56-64
Two closely linked projects aim to dramatically improve storm forecasting speed and accuracy. CASA is creating a distributed, collaborative, adaptive sensor network of low-power, high-resolution radars that respond to user needs. LEAD offers dynamic workflow orchestration and data management in a Web services framework designed to support on-demand, real-time, dynamically adaptive systems 相似文献
807.
The ordered weighted averaging (OWA) operator was introduced by Yager. 1 The fundamental aspect of the OWA operator is a reordering step in which the input arguments are rearranged in descending order. In this article, we propose two new classes of aggregation operators called ordered weighted geometric averaging (OWGA) operators and study some desired properties of these operators. Some methods for obtaining the associated weighting parameters are discussed, and the relationship between the OWA and DOWGA operators is also investigated. © 2002 Wiley Periodicals, Inc. 相似文献
808.
809.
Development of a robotic device for facilitating learning by children who have severe disabilities 总被引:2,自引:0,他引:2
Cook A.M. Meng M.Q.-H. Gu J.J. Howery K. 《IEEE transactions on neural systems and rehabilitation engineering》2002,10(3):178-187
This paper presents technical aspects of a robot manipulator developed to facilitate learning by young children who are generally unable to grasp objects or speak. The severity of these physical disabilities also limits assessment of their cognitive and language skills and abilities. The CRS robot manipulator was adapted for use by children who have disabilities. Our emphasis is on the technical control aspects of the development of an interface and communication environment between the child and the robot arm. The system is designed so that each child has user control and control procedures that are individually adapted. Control interfaces include large push buttons, keyboards, laser pointer, and head-controlled switches. Preliminary results have shown that young children who have severe disabilities can use the robotic arm system to complete functional play-related tasks. Developed software allows the child to accomplish a series of multistep tasks by activating one or more single switches. Through a single switch press the child can replay a series of preprogrammed movements that have a development sequence. Children using this system engaged in three-step sequential activities and were highly responsive to the robotic tasks. This was in marked contrast to other interventions using toys and computer games. 相似文献
810.
The PID relay auto-tuner of Astrom–Hagglund is one of the simplest and most robust auto-tuning techniques for process controllers and has been successfully applied to industry for more than 15 years. This tuner is based on an approximate estimation of the critical point on the process frequency response from relay oscillations. Many developments have recently been reported to extend its applications. It turns out that more and accurate information on process dynamics can be obtained from the same relay test with the help of new identification techniques, and used to tune PID controllers better. Extensions are also made to tune model-based advanced controllers and multivariable controllers. The present paper reviews these developments and shows the state-of art in relay auto-tuning of process controllers. 相似文献