全文获取类型
收费全文 | 1771篇 |
免费 | 76篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 13篇 |
综合类 | 1篇 |
化学工业 | 301篇 |
金属工艺 | 42篇 |
机械仪表 | 23篇 |
建筑科学 | 62篇 |
矿业工程 | 9篇 |
能源动力 | 46篇 |
轻工业 | 137篇 |
水利工程 | 15篇 |
石油天然气 | 7篇 |
无线电 | 159篇 |
一般工业技术 | 363篇 |
冶金工业 | 430篇 |
原子能技术 | 15篇 |
自动化技术 | 226篇 |
出版年
2023年 | 12篇 |
2022年 | 15篇 |
2021年 | 36篇 |
2020年 | 35篇 |
2019年 | 41篇 |
2018年 | 48篇 |
2017年 | 44篇 |
2016年 | 40篇 |
2015年 | 30篇 |
2014年 | 48篇 |
2013年 | 87篇 |
2012年 | 81篇 |
2011年 | 115篇 |
2010年 | 86篇 |
2009年 | 58篇 |
2008年 | 101篇 |
2007年 | 75篇 |
2006年 | 69篇 |
2005年 | 72篇 |
2004年 | 56篇 |
2003年 | 65篇 |
2002年 | 45篇 |
2001年 | 26篇 |
2000年 | 33篇 |
1999年 | 33篇 |
1998年 | 25篇 |
1997年 | 34篇 |
1996年 | 35篇 |
1995年 | 26篇 |
1994年 | 29篇 |
1993年 | 20篇 |
1992年 | 19篇 |
1991年 | 11篇 |
1990年 | 22篇 |
1989年 | 22篇 |
1988年 | 18篇 |
1987年 | 14篇 |
1986年 | 9篇 |
1985年 | 17篇 |
1984年 | 13篇 |
1983年 | 25篇 |
1982年 | 12篇 |
1981年 | 13篇 |
1980年 | 9篇 |
1979年 | 26篇 |
1978年 | 16篇 |
1977年 | 17篇 |
1976年 | 9篇 |
1973年 | 8篇 |
1972年 | 8篇 |
排序方式: 共有1849条查询结果,搜索用时 15 毫秒
11.
The Role of Network Topologies in the Optical Core of IP-over-WDM Networks with Static Wavelength Routing 总被引:3,自引:0,他引:3
Freire Mário M. Rodrigues Joel J.P.C. Coelho Rui M.F. 《Telecommunication Systems》2003,24(2-4):111-122
In this paper, we present a performance analysis of network topologies for the optical core of IP-over-WDM networks with static wavelength routing. The performance analysis is focused on regular degree four topologies, and, for comparison purposes, degree three topologies are also considered. It is shown that the increase of the nodal degree from three (degree three topology with smallest diameter) to four (degree four topology with smallest diameter) improves the network performance if a larger number of wavelengths per link is available. However, the influence of wavelength interchange on the nodal degree gain is small. The performance of regular degree four topologies with smallest diameter is also compared with the performance of mesh–torus topologies (which are also degree four topologies), and it is shown that the blocking probability of degree four topologies with smallest diameter is about two orders of magnitude lower than the blocking probability of mesh–torus topologies. It is also presented a performance comparison of WDM-based networks with nodal degrees ranging from two to five and it is shown that the increase of the nodal degree from two to three leads to high nodal degree gains, while de increase of the nodal degree from four to five leads to low nodal degree gains. These results show that degree three and degree four topologies are very attractive for use in the optical core of IP-over-WDM networks. 相似文献
12.
Stakeholder involvement is essential to the development of a total maximum daily load (TMDL) and its implementation plan. A tool, beyond a simulation model, is needed to support the decision making process that requires negotiation and compromise among stakeholders. The decision support system (DSS) described herein has a TMDL module to calculate various combinations of point and nonpoint loads that can meet the water quality criteria. Its Consensus module allows stakeholders to formulate, evaluate, modify, and vote for alternatives. The DSS displays bar charts for pollution loads from various subwatersheds and attributes the nonpoint loads to land uses. The water quality consequence of the pollution loads is output in maps, which shows sections meeting criteria in green and those not in red. The DSS requires a front end effort of site specific adaptation and model calibration. An Internet-based stakeholder process was developed to allow more concerned citizens to participate in management decisions. 相似文献
13.
14.
15.
The rat's willingness to ingest glucose after an initial intraoral intake test was probed by beginning a 2nd intraoral intake test at variable durations (1–220 min). In Exp 1, after an initial meal of 12.5% glucose solution averaging 26.9?±?1.7 ml, the size of the 2nd (probe) meal of the same stimulus increased linearly from 4.0?±?0.9 ml after a 1-min delay to 15.4?±?2.7 ml after a 120-min delay. In Exp 2, intraoral intake of a more concentrated (37.5%) glucose solution rose more slowly as a function of delay from 2.4?±?2.7 ml to 4.9?±?0.6 ml. For each glucose concentration, the linear recovery function and a slope that depends on stimulus concentration are consistent with a role for gastric emptying during the delay in intake recovery. In Exp 3, rats ingested 12.5% or 37.5% glucose to satiety in an initial test and received, after a variable delay, either the same or the other concentration as the probe stimulus. The same volumes were ingested at each delay whether the glucose concentration of the probe stimulus was the same or was switched from that presented in the initial test. This result shows that the taste and caloric properties of the probe stimulus played no role in determining how much of it would be ingested… (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
16.
Jones Enrico E.; Ghannam Jess; Nigg Joel T.; Dyer Jennifer F. 《Canadian Metallurgical Quarterly》1993,61(3):381
Articulates a paradigm for single-case research in psychotherapy. A patient diagnosed as having major depressive disorder was seen in an intensive, twice-weekly psychodynamic psychotherapy for 2.5 years. Each session was videotaped, and assessments of patient change were obtained at regular intervals. A time-series analysis was used to model fluctuations in the therapy process to take into account time and the effect of previous events on subsequent changes, thereby preserving the context-determined meaning for therapist and patient actions. A bidirectional analysis of causal effects shows that the influence processes between therapist and patient are mutual and reciprocal and suggests that the effect of the patient on the therapist and on the process has not been made sufficiently explicit in previous models of process and change. The potential of intensive single-case designs for uncovering causal effects in psychotherapy is demonstrated. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
17.
Chun-Ren Chen Joel L. Zatz Eugene Reilly 《Drug development and industrial pharmacy》1993,19(11):1265-1282
This potential for ion-pairing between dyclonine, a local anesthetic, and pharmaceutical dyes commonly used in liquid pharmaceutical formulations was examined. Occurrence of ion-pairing at a pH of 3 was confirmed by shift of the absorption maximum of all five sulfonate-containing dyes, and by measurements of octanol/water partition coefficient and surface tension. There was also an increase in the uptake of dyclonine by phosphatidylcholine liposomes in the presence of a dye (tartrazine) at pH 3 but not at pH 7, where the uncharged anesthetic is dominant. 相似文献
18.
19.
According to D. E. Broadbent's (1958) selective filter theory, people do not process unattended stimuli beyond the analysis of basic physical properties. This theory was later rejected on the basis of numerous findings that people identify irrelevant (and supposedly unattended) stimuli. A careful review of this evidence, however, reveals strong reasons to doubt that these irrelevant stimuli were in fact unattended. This review exposed a clear need for new experiments with tight control over the locus of attention. The authors present 5 such experiments using a priming paradigm. When steps were taken to ensure that irrelevant stimuli were not attended, these stimuli produced no priming effects. Hence, the authors found no evidence that unattended stimuli can be identified. The results support a modern version of Broadbent's selective theory, updated to reflect recent research advances. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
20.