全文获取类型
收费全文 | 3658篇 |
免费 | 55篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 48篇 |
化学工业 | 500篇 |
金属工艺 | 82篇 |
机械仪表 | 135篇 |
建筑科学 | 200篇 |
矿业工程 | 4篇 |
能源动力 | 75篇 |
轻工业 | 276篇 |
水利工程 | 23篇 |
石油天然气 | 12篇 |
无线电 | 329篇 |
一般工业技术 | 571篇 |
冶金工业 | 1129篇 |
原子能技术 | 27篇 |
自动化技术 | 306篇 |
出版年
2021年 | 31篇 |
2020年 | 24篇 |
2019年 | 38篇 |
2018年 | 42篇 |
2017年 | 40篇 |
2016年 | 46篇 |
2015年 | 51篇 |
2014年 | 55篇 |
2013年 | 137篇 |
2012年 | 92篇 |
2011年 | 139篇 |
2010年 | 100篇 |
2009年 | 95篇 |
2008年 | 109篇 |
2007年 | 117篇 |
2006年 | 102篇 |
2005年 | 107篇 |
2004年 | 80篇 |
2003年 | 73篇 |
2002年 | 98篇 |
2001年 | 66篇 |
2000年 | 72篇 |
1999年 | 90篇 |
1998年 | 273篇 |
1997年 | 174篇 |
1996年 | 129篇 |
1995年 | 92篇 |
1994年 | 97篇 |
1993年 | 97篇 |
1992年 | 48篇 |
1991年 | 44篇 |
1990年 | 45篇 |
1989年 | 60篇 |
1988年 | 57篇 |
1987年 | 53篇 |
1986年 | 55篇 |
1985年 | 37篇 |
1984年 | 49篇 |
1983年 | 39篇 |
1982年 | 31篇 |
1981年 | 42篇 |
1980年 | 40篇 |
1979年 | 37篇 |
1978年 | 32篇 |
1977年 | 48篇 |
1976年 | 68篇 |
1975年 | 37篇 |
1974年 | 29篇 |
1973年 | 35篇 |
1972年 | 23篇 |
排序方式: 共有3717条查询结果,搜索用时 15 毫秒
1.
G Davies 《Canadian Metallurgical Quarterly》1993,34(2):103-121
This paper describes an efficient computer method for generating three-dimensional (3-D) ultrasonic speckle patterns for sector scans of an annular array with dynamic focusing in both transmit and receive. Assuming random scatterers in an attenuating medium, the system synthesizes the waveform for each scan line using echo data received at all annular elements of the transducer when short pulses are transmitted by one annulus after another. The amount of echo data needed to synthesize one waveform is tremendously reduced by reducing the 3-D distributions of scatterers to line distributions and by representing scatterers on a small line segment by a single equivalent scatterer taking into account the two-way travel time differences. Furthermore, by a judicious 3-D arrangement of the scatterer lines and scan lines, it is possible to synthesize the waveform for a new scan line with negligible computation overhead. The waveforms of the scan lines are detected to obtain a B-mode image or speckle patterns. The patterns obtained on several differently-oriented image planes showed a good statistical agreement with experimentally obtained patterns. 相似文献
2.
This social research project investigated community receptivity to using rainwater and greywater as alternative domestic water sources. It was focused in the Ku-ring-gai local government area in northern Sydney, and involved a household questionnaire followed by community leader interviews and resident focus groups. Trends, such as a prolonged drought and increasing population, compound the current crisis and concern facing Sydney's available water supply. Substitution of domestic potable water has been promoted as part of the solution. The research results revealed that community receptivity was highest for external uses, such as watering gardens and flushing toilets, and progressively decreased with increasing personal contact. Receptivity to greywater reuse fell more rapidly with the community believing there was a higher health risk associated with its use. Gender and cultural background were revealed as significant variables and give insight into the design of strategies to target these demographic groups. This evidence provides a reliable stocktake of current receptivity revealing that the community has good awareness and positive association with water reuse for many household activities. This now needs to be harnessed through programs targeted at developing skills, resources and motivation for new water reuse practices and technologies across diverse social groupings. 相似文献
3.
The author considers the shifts produced by mode filters on curved boundaries and contours. It is shown that these are similar to those produced by mean and median filters, the cases of linear intensity variations and of step edges being somewhat different and at opposite extremes of a continuum. Thus, shifts are intrinsic to basic neighbourhood averaging techniques, and can be avoided only by specially designed operators 相似文献
4.
A dyeing profile for a range of reactive dyes suitable for application to cellulosic knitwear is defined. Such a profile shows good level-dyeing, reproducibility and fastness properties together with potential for simplified dyeing processes. 相似文献
5.
Thompson Robert J.; Gil Karen M.; Keith Barbara R.; Gustafson Kathryn E.; George Linda K.; Kinney Thomas R. 《Canadian Metallurgical Quarterly》1994,62(4):856
Rates of poor psychological adjustment of children with sickle cell disease remained relatively constant over initial and follow-up assessment points. 50 children (aged 7–12 yrs) and their mothers completed the initial protocol. 30 children completed the follow-up plus 5 additional children and their mothers. These Ss were aged 7–24 yrs at follow-up. With initial levels of adjustment controlled, children's strategies for coping with pain accounted for a significant increment in child-reported symptoms and mother-reported internalizing behavior problems at follow-up beyond the contribution of illness and demographic parameters and follow-up interval. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
6.
SW Qian JK Burmester PD Sun A Huang DJ Ohlsen L Suardet KC Flanders D Davies AB Roberts MB Sporn 《Canadian Metallurgical Quarterly》1994,33(40):12298-12304
Transforming growth factor-beta (TGF-beta) is a potent regulator of cell growth and differentiation. On the basis of the crystal structure of TGF-beta 2, we have designed and synthesized two mutant TGF-beta s, TGF-beta 1 (71 Trp) and TGF-beta 1 (delta 69-73). Although both of these molecules inhibited the growth of Mv1Lu mink lung epithelial cells and LS1034 colorectal cancer cells, which are affected equally by TGF-beta 1 and TGF-beta 2, TGF-beta 1 (delta 69-73) was much less potent than TGF-beta 1 or TGF-beta 1 (71 Trp) at inhibiting the growth of LS513 colorectal cancer cells which are growth-inhibited by TGF-beta 1 but not TGF-beta 2. Both TGF-beta 1 (71 Trp) and TGF-beta 1 (delta 69-73) increased levels of mRNAs for fibronectin and plasminogen activator inhibitor with Mv1Lu cells, whereas only TGF-beta 1 (71 Trp) and not TGF-beta 1 (delta 69-73) up-regulated the mRNA level of carcinoembryonic antigen in LS513 cells. The expression level of carcinoembryonic antigen mRNA in LS1034 cells was not altered by either wild-type or mutant TGF-beta s. Receptor labeling experiments demonstrated that TGF-beta 1 (71 Trp) bound with high affinity to the cell-surface receptors of Mv1Lu, LS1034, and LS513 cells while TGF-beta 1 (delta 69-73) bound effectively to the receptors of Mv1Lu and LS1034 cells but much less to the receptors on LS513 cells.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
7.
Relations of social goal pursuit to (1) social acceptance by teachers and peers, (2) prosocial and irresponsible classroom behavior, and (3) perceived support from teachers and peers were examined. Ss were 475 6th and 7th graders. Students' pursuit of academic prosocial goals (to help classmates with academic problems) was related positively to peer acceptance. Pursuit of academic responsibility goals (adhering to classroom rules) was related negatively to peer acceptance but positively to teacher acceptance. These findings reflected in part, significant relations between social goal pursuit and displays of social behavior. Perceived support from teachers and peers was also related positively to social goal pursuit, although findings differed as a function of type and source of support. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
8.
Ockene Judith K.; Kristeller Jean; Pbert Lori; Hebert James R.; Luippold Rose; Goldberg Robert J.; Landon Joan; Kalan Kathryn 《Canadian Metallurgical Quarterly》1994,13(3):278
Patterns of smoking cessation using 6- and 12-mo follow-up data are reported for 1,261 primary care patients randomized to 3 physician-delivered smoking interventions: advice only (AO), counseling (CI), and counseling plus availability of nicotine-containing gum (CI?+?NCG). One-week point-prevalence cessation rates at 12 mo did not differ among the interventions: AO (15.2%), CI (12.9%) and CI?+?NCG (16.7%). However, maintained cessation rates (abstinent at both 6 and 12 mo) increased with intervention intensity: AO (6.0%), CI (7.8%), and CI?+?NCG (10.0%): Test of trend χ–2?=?5.06, p?=?.02. CI?+?NCG was significantly higher than AO (p?=?.02). The findings support the following conclusions: Brief physician delivered intervention with availability of nicotine-containing gum can have a beneficial long-term effect on smoking cessation, and cohort data as well as point-prevalence rates are important when assessing the long-term impact of lifestyle interventions. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
9.
SD Walter SE Birnie LD Marrett SM Taylor D Reynolds J Davies JJ Drake M Hayes 《Canadian Metallurgical Quarterly》1994,84(3):367-376
OBJECTIVES: Our objectives were (1) to describe an analysis of the spatial pattern of cancer incidence in Ontario and (2) to discuss the quality of data in the Ontario Cancer Registry with respect to the accuracy of local cancer rates. METHODS: Cancer incidence rates were calculated for 22 cancer sites in 49 counties of Ontario during 1976 to 1986. Capture-recapture methods were used to estimate completeness of case registration, and completeness of residence information was also assessed. Spatial autocorrelation was used in measuring the geographic pattern of incidence rates. Comparisons were also made between sexes and with earlier data from 1966 to 1975. RESULTS: The quality of the geographic data in the registry appeared good, and corrections for incomplete or inaccurate registration had little impact. About one third of the sex-site combinations showed some evidence of spatial patterning in the cancer rate. Particularly strong regional variation was noted for cancers of the stomach, lung, uterus, and prostate. CONCLUSIONS: The analysis revealed a number of cancers with significant spatial patterning of risk. Further work is needed to relate the cancer data to other information on potential life-style and environmental factors. 相似文献
10.
Despite differences in the structures of aldoses and ascorbic acid, ASA, the non-enzymic browning of the latter involves intermediates similar to those found in Maillard browning. The kinetics of the sulphite-inhibited browning of ASA suggest that, under anaerobic conditions, the rate of reaction of sulphite species, S(IV), is of first order with respect to S(IV). The possibility that S(IV) could catalyse the hydrolysis of the lactone ring of ASA is considered by reference to D-glucono-delta-lactone. Evidence is presented to suggest that, under aerobic conditions, autoxidation of ASA leads to the oxidation of S(IV). The composition of melanoidins from ASA-glycine mixtures is compared with that from arabinose-glycine; the former contain 2 x 5 times more ASA-derived residues per glycine molecule than arabinose-derived residues per glycine molecule in the latter. The implications of these findings to the mechanism of ASA browning are discussed. 相似文献