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91.
Absolute figure measurements with a liquid-flat reference 总被引:2,自引:0,他引:2
We describe a variation of the liquid-flat technique fordetermining the absolute flatness of a 240-mm-diameter optical surfaceto an accuracy better than 1/100lambda in both its horizontal(three-point support) and vertical orientations. Using theappropriate mathematics to calculate the surface deformation of a diskdue to gravity, we achieved verification of the method by comparingmeasurements carried out on a pair of optical flats and a liquidreference surface. 相似文献
92.
Industry has become aware of the problem of severe generator damage due to stator ground faults. It has been suggested that, to prevent this damage, the practices employed for neutral grounding should be changed. This paper provides an analytical perspective on this problem and suggests that the real issue is the manner in which the neutral of the generator itself is grounded 相似文献
93.
Powell I 《Applied optics》1996,35(31):6190-6194
A design study was undertaken on an infrared, 3-5-μm, panoramic optical system for a particular monitoring application. The different types of systems investigated covered the conventional fish-eye lens system, a panoramic block arrangement, and a new type of configuration based on a panoramic shell. Examples of these systems are included, and their advantages and disadvantages are discussed. 相似文献
94.
T. Takada J. D. Mackenzie M. Yamane K. Kang N. Peyghambarian R. J. Reeves E. T. Knobbe R. C. Powell 《Journal of Materials Science》1996,31(2):423-430
Non-linear optical properties of CdS quantum dots embedded in the sol-gel derived Na2O-B2O3-SiO2x3 glass matrix have been studied using nanosecond degenerate four-wave mixing (DFWM), pump-probe experiments, and time-resolved subpicosecond DFWM measurements. The concentration of CdS microcrystallites was varied from 1.4 to 10.2 wt% while the particle size was controlled to be in the range of 3–6 nm in diameter so that the confinement effects can be realized. The third-order susceptibility, 3, was determined to be of the order of 10–7-10–6 e.s.u. near the resonant wavelength between 450 and 470 nm by the nanosecond DFWM and pump-probe experiments, and of the order of 10–11-10–10 e.s.u. at the off-resonant wavelength, 580 nm, by a time-resolved DFWM measurement with 400 fs laser pulse. The decay time changed from 0.5 to 50 picoseconds as a function of the size, size distribution and number density of CdS microcrystallites in the glasses. Photodarkening reduced the optical non-linearity of the melt-quenched samples by a factor of 20, while it had no appreciable effect on that of the sol-gel derived samples.[/p] 相似文献
95.
In this paper, we present Rambo, an algorithm for emulating a read/write distributed shared memory in a dynamic, rapidly changing environment. Rambo provides a highly reliable, highly available service, even as participants join, leave, and fail. In fact, the entire set
of participants may change during an execution, as the initial devices depart and are replaced by a new set of devices. Even
so, Rambo ensures that data stored in the distributed shared memory remains available and consistent. There are two basic techniques
used by Rambo to tolerate dynamic changes. Over short intervals of time, replication suffices to provide fault-tolerance. While some devices
may fail and leave, the data remains available at other replicas. Over longer intervals of time, Rambo copes with changing participants via reconfiguration, which incorporates newly joined devices while excluding devices that have departed or failed. The main novelty of Rambo lies in the combination of an efficient reconfiguration mechanism with a quorum-based replication strategy for read/write
shared memory. The Rambo algorithm can tolerate a wide variety of aberrant behavior, including lost and delayed messages, participants with unsynchronized
clocks, and, more generally, arbitrary asynchrony. Despite such behavior, Rambo guarantees that its data is stored consistency. We analyze the performance of Rambo during periods when the system is relatively well-behaved: messages are delivered in a timely fashion, reconfiguration is
not too frequent, etc. We show that in these circumstances, read and write operations are efficient, completing in at most
eight message delays. 相似文献
96.
Maxine M. Denniston Nancy D. Brener Laura Kann Danice K. Eaton Timothy McManus Tonja M. Kyle Alice M. Roberts Katherine H. Flint James G. Ross 《Computers in human behavior》2010
The Youth Risk Behavior Surveillance System (YRBSS) monitors priority health-risk behaviors among US high school students. To better understand the ramifications of changing the YRBSS from paper-and-pencil to Web administration, in 2008 the Centers for Disease Control and Prevention conducted a study comparing these two modes of administration. Eighty-five schools in 15 states agreed to participate in the study. Within each participating school, four classrooms of students in grades 9 or 10 were randomly assigned to complete the Youth Risk Behavior Survey questionnaire in one of four conditions (in-class paper-and-pencil, in-class Web without programmed skip patterns, in-class Web with programmed skip patterns, and “on your own” Web without programmed skip patterns). Findings included less missing data for the paper-and-pencil condition (1.5% vs. 5.3%, 4.4%, 6.4%; p < .001), less perceived privacy and anonymity among respondents for the in-class Web conditions, and a lower response rate for the “on your own” Web condition than for in-class administration by either mode (28.0% vs. 91.2%, 90.1%, 91.4%; p < .001). Although Web administration might be useful for some surveys, these findings do not favor the use of a Web survey for the YRBSS. 相似文献
97.
This paper addresses the non-preemptive single machine scheduling problem to minimize total tardiness. We are interested in
the online version of this problem, where orders arrive at the system at random times. Jobs have to be scheduled without knowledge
of what jobs will come afterwards. The processing times and the due dates become known when the order is placed. The order
release date occurs only at the beginning of periodic intervals. A customized approximate dynamic programming method is introduced
for this problem. The authors also present numerical experiments that assess the reliability of the new approach and show
that it performs better than a myopic policy. 相似文献
98.
This paper describes the inter-rater and intra-rater reliability, and the concurrent validity of an observational instrument, the Keyboard Personal Computer Style instrument (K-PeCS), which assesses stereotypical postures and movements associated with computer keyboard use. Three trained raters independently rated the video clips of 45 computer keyboard users to ascertain inter-rater reliability, and then re-rated a sub-sample of 15 video clips to ascertain intra-rater reliability. Concurrent validity was assessed by comparing the ratings obtained using the K-PeCS to scores developed from a 3D motion analysis system. The overall K-PeCS had excellent reliability [inter-rater: intra-class correlation coefficients (ICC)=.90; intra-rater: ICC=.92]. Most individual items on the K-PeCS had from good to excellent reliability, although six items fell below ICC=.75. Those K-PeCS items that were assessed for concurrent validity compared favorably to the motion analysis data for all but two items. These results suggest that most items on the K-PeCS can be used to reliably document computer keyboarding style. 相似文献
99.
Shaowen Wang Yan Liu Nancy Wilkins-Diehr Stuart Martin 《Computers & Geosciences》2009,35(12):2283-2294
Cyberinfrastructure science and engineering gateways have become an important modality to connect science and engineering communities and cyberinfrastructure. The use of cyberinfrastructure through gateways is fundamental to the advancement of science and engineering. However, learning science gateway technologies and developing science gateways remain a significant challenge, given that science gateway technologies are still actively evolving and often include a number of sophisticated components. A geosciences gateway must be designed to accommodate legacy methods that geoscientists use in conventional computational tools. The research described in this paper establishes an open-source toolkit—SimpleGrid for learning and developing science gateways based on a service-oriented architecture using a component-based approach that allows flexible separation and integration of the components between geocomputation applications and cyberinfrastructure. The design and implementation of SimpleGrid is based on the National Science Foundation TeraGrid—a key element of the U.S. and world cyberinfrastructure. This paper illustrates our experience of using SimpleGrid and a spatial interpolation method in a tutorial to teach TeraGrid science gateways. 相似文献
100.
Qin Liu Nancy R. Cook Anna Bergstrm Chung-Cheng Hsieh 《Computational statistics & data analysis》2009,53(12):4157-4167
To estimate a summarized dose–response relation across different exposure levels from epidemiologic data, meta-analysis often needs to take into account heterogeneity across studies beyond the variation associated with fixed effects. We extended a generalized-least-squares method and a multivariate maximum likelihood method to estimate the summarized nonlinear dose–response relation taking into account random effects. These methods are readily suited to fitting and testing models with covariates and curvilinear dose–response relations. 相似文献