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排序方式: 共有852条查询结果,搜索用时 31 毫秒
1.
Tanu Sharma Sanjeev Aggarwal Shyam Kumar V. K. Mittal P. C. Kalsi V. K. Manchanda 《Journal of Materials Science》2007,42(4):1127-1130
The UV-Visible absorption spectra of virgin and gamma irradiated (20–800 kGy) CR-39 polymer have been deduced by using Shimadzu
Double beam Double Monochromator UV-Visible Spectrophotometer (UV-2550). The existence of the peaks, their shifting and broadening
as a result of gamma irradiation has been discussed. Finally the indirect and direct band gap in virgin and gamma irradiated
CR-39 has been determined. The values of indirect band gap have been found to be lower than the corresponding values of direct
band gap. 相似文献
2.
Ultrasound backscattered signals for object detection could be too weak to be perceived when superposed to strong reflection signals, and could also be complicated either in time or frequency domain. These peculiarities raise a challenge for signal processing methods. In this paper four signal processing methods were studied to detect objects in containers. Root mean squares (RMS) method was better in object detection but needed to combine other methods to increase detection success rate. Variance, center frequency pressure ratio (CFPR) and backscattered amplitude integral (BAI) methods have similar overall detection ratings. The optimal signal size, to increase the detection ability, corresponded approximately to the length of reverberation signals before it was dissipated. 相似文献
3.
We consider a system comprising a finite number of nodes, with infinite packet buffers, that use unslotted ALOHA with Code
Division Multiple Access (CDMA) to share a channel for transmitting packetised data. We propose a simple model for packet
transmission and retransmission at each node, and show that saturation throughput in this model yields a sufficient condition
for the stability of the packet buffers; we interpret this as the capacity of the access method. We calculate and compare
the capacities of CDMA‐ALOHA (with and without code sharing) and TDMA‐ALOHA; we also consider carrier sensing and collision
detection versions of these protocols. In each case, saturation throughput can be obtained via analysis of a continuous time
Markov chain. Our results show how saturation throughput degrades with code‐sharing. Finally, we also present some simulation
results for mean packet delay. Our work is motivated by optical CDMA in which “chips” can be optically generated, and hence
the achievable chip rate can exceed the achievable TDMA bit rate which is limited by electronics. Code sharing may be useful
in the optical CDMA context as it reduces the number of optical correlators at the receivers. Our throughput results help
to quantify by how much the CDMA chip rate should exceed the TDMA bit rate so that CDMA‐ALOHA yields better capacity than
TDMA‐ALOHA.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
4.
Changes in the NHS have supported the idea of targeting health services to those in greatest need. This has meant that health visitors are increasingly having to identify 'vulnerable' families in need of increased health visiting intervention. This paper reports on a qualitative study undertaken in order to explore the ways in which health visitors plan and organize their work in relation to the concept of vulnerability. Focus groups and semi-structured interviews were carried out with health visitors from two separate geographical areas, one an inner city area and the other suburban, in order to explore the criteria by which health visitors define vulnerability and decide to increase their levels of intervention to particular families. It was found that vulnerability was extremely difficult to define but that the health visitors used criteria which were appropriate to the particular localities in which they worked to identify vulnerable families and to increase their levels of intervention to those families. Health visitors were targeting their services within a framework of a basic minimum service to all and were assessing the health needs of individuals or families rather than planning their work on the basis of community or practice profiles. 相似文献
5.
Four murine monoclonal antibodies (mAbs) designated as C9E8, A10, G12, and G8 which recognized both Serpulina hyodysenteriae and S. innocens were produced and characterized. The mAbs reacted with whole cell antigens in ELISA, indirect immunofluorescence and immunoblot assays. The mAbs did not show any cross reactivity in rapid dot ELISA or immunoblot assay with Leptospira icterohemorrhagiae, Campylobacter jejuni and Escherichia coli. Treatment of whole cell suspension with proteinase K and sodium periodate indicated that the reacting epitopes of the mAbs were protein in nature. The genus-specific antigens were identified as heat-stable proteins with molecular weight in the range of 26 to 45 kDa. Immunofluorescence and immunogold labelling studies showed that the antibody-binding epitopes were exposed on the outer-surface of the spirochaetal cell wall. The mAbs inhibited growth of reference strains of both S. hyodysenteriae and S. innocens in vitro but failed to cause agglutination. The detection of spirochaetal forms directly in fecal smears or paraffin-embeded tissue sections from experimentally infected pigs indicated that such mAbs were potentially useful for the diagnosis of swine spirochaetosis. This is the first report of mAbs identifying and characterizing common antigens of porcine Serpulina. 相似文献
6.
N Mittal N Gupta S Saksena N Goyal U Roy AK Rastogi 《Canadian Metallurgical Quarterly》1998,63(20):1823-1834
The prevalent drugs for treatment of kala azar viz. sodium stibogluconate (SSG) and pentamidine cause severe toxic side effects and acute immunosuppression in the treated individuals. Picroliv, a standardized mixture of iridoid glycosides, prepared from the alcoholic extract of the root and rhizome of Picrorhiza kurroa has shown strong hepatoprotective activity against several models of hepatotoxicity. Therefore, the present study was undertaken with an objective to study the effects of Picroliv (12.5 mg/kg x 7 days oral) alone and in combination with SSG on parasitemia, lipid peroxidation and hepatic marker enzymes of golden hamsters during Leishmania donovani infection. The results indicated a marked hepatoprotective effect of Picroliv in terms of biochemical markers, and a significant antileishmanial activity implying that it can be utilized as an adjunct to chemotherapy or in combination therapy of kala azar along with sodium stibogluconate, thus enhancing the efficacy of antileishmanials. 相似文献
7.
One strategy for alleviating excess latency (delay) in the Internet is the caching of web content at multiple locations. This
reduces the number of hops necessary to reach the desired content. This strategy is used for web content such as html pages,
images, streaming video, and Internet radio. The network of servers which store this content, and the collections of objects
stored on each server, is called a content distribution network (CDN). In order to optimally design a CDN, given a network
topology with available server storage capacity at various points in the network, one must decide which object collections
to place on each server in order to achieve performance or cost objectives. The placements must be within the storage limits
of the servers and must reflect the request patterns for each collection of objects to be cached. Researchers have suggested
formulations for the CDN problem which address performance by minimizing latency (the average number of hops is a commonly
accepted measure of latency) from client to content, or formulations that focus on minimizing cost of storage and/or bandwidth.
In this research, we develop a model which allows for the simultaneous treatment of performance and cost, present examples
to illustrate the application of the model and perform a detailed designed experiment to gain insights into cost/hops tradeoff
for a variety of network parameters. 相似文献
8.
Efficient compression and network adaptive video coding for distributed video surveillance 总被引:1,自引:1,他引:0
The availability of cheap network based video cameras and the prevalence of wireless networks has lead to a major thrust towards
deployment of large scale Distributed Video Surveillance (DVS) systems. This has opened up an important area of research to
deal with the issues involved in DVS system for efficient collection and transmission of large scale video streams from the
cameras at the guarded sites, to the end users in possibly constrained network conditions. In this paper, we propose a framework
based on content-based video classification and scalable compression scheme to provide a robust bandwidth efficient video
transmission for DVS. The scheme builds on a Discrete Wavelet Transform (DWT) based Color-Set Partitioning for Hierarchical
Trees (CSPIHT) coding to obtain a scalable bitstream. Wavelet domain segmentation and compression assists in development of
a DVS architecture. The architecture includes a novel module for dynamic allocation of Network bandwidth based on the current
available resources and constraints. Different frame constituents are optimally coded based on their relative significance,
perceptual quality, and available estimate of network bandwidth. Experimental result over different video sequences and simulations
for Network conditions demonstrate the efficient performance of the approach. 相似文献
9.
This paper presents OS-Guard(On-Site Guard), a novel on-site signature based framework for multimedia surveillance data management. One of the major concerns in widespread
deployment of multimedia surveillance systems is the enormous amount of data collected from multiple media streams that need
to be communicated, observed and stored for crime alerts and forensic analysis. This necessitates investigating efficient
data management techniques to solve this problem. This work aims to tackle this problem, motivated by the following observation,
more data does not mean more information. OS-Guard is a novel framework that attempts to collect informative data and filter out non-informative data on-site, thus
taking a step towards solving the data management problem. In the framework, both audio and video cues are utilized by extracting
features from the incoming data stream and the resultant real valued feature data is binarized for efficient storage and processing.
A feature selection process based on association rule mining selects discriminant features. A short representative sample
of the whole database is generated using a novel reservoir sampling algorithm that is stored onsite and used with an support
vector machine to classify an important event. Initial experiments for a Bank ATM monitoring scenario demonstrates promising
results. 相似文献
10.
The paper addresses the adaptive behaviour of parallel fuzzy proportional plus fuzzy integral plus fuzzy derivative (FP+FI+FD) controller. The parallel FP+FI+FD controller is actually a non-linear adaptive controller whose gain changes continuously with output of the process under control. Two non-stationary processes, whose characteristics change with time, are considered for simulation study. Simulation is performed using software LabVIEW TM . The set-point tracking response of parallel FP+FI+FD is compared with conventional parallel proportional plus integral plus derivative (PID) controller, tuned with the Ziegler-Nichols (Z-N) tuning technique. Simulation results show that conventional PID controller fails to track the set-point and becomes unstable as the process changes its characteristic with time. But the parallel FP+FI+FD controller shows considerably much better set-point tracking response and does not deviate from steady state. Also, a huge spike is observed in the output of PID controller as the reference set-point and process parameters are changed, while the FP+FI+FD controller gives spike free control signal. 相似文献