全文获取类型
收费全文 | 10128篇 |
免费 | 285篇 |
国内免费 | 14篇 |
专业分类
电工技术 | 113篇 |
综合类 | 8篇 |
化学工业 | 1792篇 |
金属工艺 | 117篇 |
机械仪表 | 228篇 |
建筑科学 | 394篇 |
矿业工程 | 52篇 |
能源动力 | 216篇 |
轻工业 | 743篇 |
水利工程 | 122篇 |
石油天然气 | 18篇 |
无线电 | 729篇 |
一般工业技术 | 1573篇 |
冶金工业 | 2751篇 |
原子能技术 | 82篇 |
自动化技术 | 1489篇 |
出版年
2023年 | 50篇 |
2022年 | 75篇 |
2021年 | 138篇 |
2020年 | 92篇 |
2019年 | 116篇 |
2018年 | 179篇 |
2017年 | 154篇 |
2016年 | 153篇 |
2015年 | 145篇 |
2014年 | 229篇 |
2013年 | 575篇 |
2012年 | 401篇 |
2011年 | 504篇 |
2010年 | 371篇 |
2009年 | 341篇 |
2008年 | 465篇 |
2007年 | 451篇 |
2006年 | 386篇 |
2005年 | 371篇 |
2004年 | 321篇 |
2003年 | 283篇 |
2002年 | 286篇 |
2001年 | 207篇 |
2000年 | 172篇 |
1999年 | 213篇 |
1998年 | 416篇 |
1997年 | 295篇 |
1996年 | 259篇 |
1995年 | 236篇 |
1994年 | 215篇 |
1993年 | 185篇 |
1992年 | 172篇 |
1991年 | 97篇 |
1990年 | 163篇 |
1989年 | 132篇 |
1988年 | 124篇 |
1987年 | 141篇 |
1986年 | 111篇 |
1985年 | 125篇 |
1984年 | 102篇 |
1983年 | 105篇 |
1982年 | 90篇 |
1981年 | 87篇 |
1980年 | 84篇 |
1979年 | 80篇 |
1978年 | 61篇 |
1977年 | 91篇 |
1976年 | 85篇 |
1975年 | 57篇 |
1974年 | 41篇 |
排序方式: 共有10000条查询结果,搜索用时 390 毫秒
51.
A. J. Slifka T. Hall E. S. Boltz 《Journal of research of the National Institute of Standards and Technology》2003,108(2):151-156
A simple measurement system is described for evaluating damage to graphite-epoxy panels, such as those used in high-performance aircraft. The system uses a heating laser and infrared imaging system to measure thermal performance. Thermal conductivity or diffusivity is a sensitive indicator of damage in materials, allowing this thermal measurement to show various degrees of damage in graphite-epoxy composites. Our measurements track well with heat-flux damage to graphite epoxy panels. This measurement system, including analysis software, could easily be used in the field, such as on the deck of an aircraft carrier or at remote air strips. 相似文献
52.
Tokar David M.; Withrow Jason R.; Hall Rosalie J.; Moradi Bonnie 《Canadian Metallurgical Quarterly》2003,50(1):3
Structural equation modeling was used to test theoretically based models in which psychological separation and attachment security variables were related to career indecision and those relations were mediated through vocational self-concept crystallization. In contrast to previous studies, which have found either weak or no support for a relation between separation or attachment security variables and career indecision, results based on a sample of 350 college students indicated that some components of separation and attachment security did relate to career indecision in a theoretically supportable direction. Results also revealed that regardless of whether global or component career indecision measures were used, separation and attachment security effects on indecision were at least partially mediated through vocational self-concept crystallization. The strongest mediated relations were observed for the effects of attachment anxiety and maternal separation. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
53.
Yoon Carolyn; Feinberg Fred; Hu Ping; Gutchess Angela Hall; Hedden Trey; Chen Hiu-Ying Mary; Jing Qicheng; Cui Yao; Park Denise C. 《Canadian Metallurgical Quarterly》2004,19(3):379
Understanding how aging influences cognition across different cultures has been hindered by a lack of standardized, cross-referenced verbal stimuli. This study introduces a database of such item-level stimuli for both younger and older adults, in China and the United States, and makes 3 distinct contributions. First, the authors specify which item categories generalize across age and/or cultural groups, rigorously quantifying differences among them. Second, they introduce novel, powerful methods to measure between-group differences in freely generated ranked data, the rank-ordered logit model and Hellinger Affinity. Finally, a broad archive of tested, cross-linguistic stimuli is now freely available to researchers: data, similarity measures, and all stimulus materials for 105 categories and 4 culture-by-age groups, comprising over 10,000 fully translated unique item responses. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
54.
A series of novel poly(hydroxy ethers) have been prepared via polymerization of the diglycidyl ethers of bisphenol-A ( 4 ), 4,4 ′-tribromotetramethylbiphenol ( 6a ), and 4,4 ′-tetrabromotetramethylbiphenol ( 6b ) with a variety of rigid diols in an effort to systematically modify structural features of the phenoxy repeat unit in order to control the torsional mobility of polymer backbones and produce materials with softening temperatures higher than are typical for the class. The resulting poly(hydroxy ethers) displyed glass transition temperatures ranging from 109 to 242°C. There of the polymers were characterized with respect to tensile and impact properties and were compared to the polymer sythesized from bisphenol-A ( 1 ) and bisphenol-A diglycidyl ether ( 4 ). 相似文献
55.
We have studied the short term C mineralization of six wastes from important food industries, one sludge from a biogas plant and three composts. All the wastes were characterized chemically and fractionated according to the Van Soest method. The fresh wastes were incubated under controlled environment conditions to determine the C mineralization rate. Based on first order mineralization kinetics, we calculated the hypothetical amount of stable C in the wastes as the amount of C that would not be mineralized within one year under field conditions. The percentage of stable organic C in the organic matter was in general much larger in the composts than in the other wastes, but when expressed on dry matter, the non-composted wastes had comparable or larger amounts of stable organic C than the composts and have a considerable potential for supplying organic matter to soils, and hence for C sequestration. The amount of stable organic C could best be predicted by the total N content of the wastes (R
a
2 = 0.855), whereas the results of the fractionation had very little predictive power, probably due to problems related to the high ash content of some of the wastes. An index that combined stable organic C and N and P content in the wastes was calculated to assess possible limitations for applying these wastes in agriculture. Under current nutrient legislation in Western Europe, a number of these wastes will only be usable in small amounts, but these and other food industry wastes could still prove to be valuable soil amendments in nutrient poor situations, for increasing soil organic C content and supplying nutrients. 相似文献
56.
Gamebirds provide a considerable incentive to plant and manage new woodlands. The supplementary income thus generated can improve their overall value. Other studies suggest that Short Rotation Coppice (SRC) crops may provide an attractive habitat for some gamebird species and could increase the value of the crop. To investigate this, the use by pheasants and partridge of different types of SRC at one site was assessed.
A method using sand quadrats to record gamebird footprints and hence relative use was developed. Pheasant footprints were recorded more frequently in the quadrats alongside the willow coppice, whereas partridge footprints occurred more frequently alongside the poplar coppice. Footprint analysis offers a reliable method of investigating how gamebirds use different types of SRC within small areas. The results are considered in terms of the placement of short rotation coppice plantations in the landscape to improve their ecological design. 相似文献
57.
J Randerson L Cawkwell A Jack JA Child F Lewis N Hall P Johnson P Evans S Barrans GJ Morgan 《Canadian Metallurgical Quarterly》1996,93(1):160-162
Fluorescent polymerase chain reaction (PCR) was used to assay 12 microsatellite markers (APC x 2, DCC, P53 x 2, RB1, NM23, WT1, D6S260, D6S262, D6S281 and TNFa) to look for evidence of microsatellite instability in 40 cases of follicle centre cell lymphoma (FCC). Evidence of novel alleles seen in the tumour tissue but not the normal uninvolved tissue was seen in seven cases (17%). In only two of these cases (5%) was more than one locus involved but in these cases multiple affected loci were seen (4/12 and 7/12 respectively). The detection of microsatellite instability indicates a DNA repair defect such as that which would be predicted to occur in cells with mutated mismatch repair genes, a novel finding in FCC lymphoma. 相似文献
58.
ME Farago P Kavanagh R Blanks J Kelly G Kazantzis I Thornton PR Simpson JM Cook HT Delves GE Hall 《Canadian Metallurgical Quarterly》1998,123(3):451-454
Increasing Pt concentrations from vehicle catalysts have been reported from a number of countries. Analysis of Pt and Pd in soils and road dusts taken from areas of high and low traffic flows in SE England show concentrations of Pt in the range < 0.30-40.1 ng g-1 and Pd in the range < 2.1-57.9 ng g-1. Higher concentrations of Pt are associated with high traffic densities. Samples taken from streets of lower traffic flows were found to contain the lower concentrations of the ranges. Pilot studies of Pt concentrations in blood and urine using ICP-MS have been carried out. Platinum concentrations in whole blood were: precious metal workers, 780-2170, mean 1263 pmol l-1 (0.152-0.423, mean 0.246 microgram l-1); motorway maintenance workers, 645-810, mean 744 pmol l-1 (0.126-0.158, mean 0.145 microgram l-1); Imperial College staff, 590-713, mean 660 pmol l-1 (0.115-0.139, mean 0.129 microgram l-1). Platinum concentrations in urine in pmol Pt per mmol creatinine were: precious metal workers, 122-682, mean 273 [0.21-1.18, mean 0.47 microgram Pt (g creatinine)-1]; motorway maintenance workers, 13-78, mean 33.7 [0.022-0.135, mean 0.058 microgram Pt (g creatinine)-1]; Imperial College staff, 28-130, mean 65.6 [0.048-0.224, mean 0.113 microgram Pt (g creatinine)-1]. Detection limits were 0.03 microgram l-1 for both blood and urine. The possible health effects of increasing Pt in the environment are discussed. Platinum provides an excellent example of the significance of speciation in metal toxicity. Platinum allergy is confined to a small group of charged compounds that contain reactive ligand systems, the most effective of which are chloride ligand systems. Metallic Pt is considered to be biologically inert and non allergenic and since the emitted Pt is probably in the metallic or oxide form, the sensitising potential is probably very low. Platinum from road dusts, however, can be solubilised, and enter waters, sediments, soils and the food chain. There is at present no evidence for any adverse health effects from Pt in the general environment, particularly allergic reactions. 相似文献
59.
FV Elmslie AJ Vivian H Gardiner C Hall AP Mowat RM Winter 《Canadian Metallurgical Quarterly》1995,32(4):264-268
Alagille syndrome (AGS) is one of the major forms of chronic liver disease in childhood with severe morbidity and a mortality of 10 to 20%. It is characterised by cholestasis of variable severity with paucity of interlobular bile ducts and anomalies of the cardiovascular system, skeleton, eyes, and face. Previous studies suggest a wide variation in the expression of the disease and a high incidence of new mutations. To determine more accurately the rate of new mutations and to develop criteria for detecting the disorder in parents we systematically investigated parents in 14 families with an affected child. Clinical examination was supplemented by liver function tests, echocardiography, radiographic examination of the spine and forearm, ophthalmological assessment, and chromosome analysis. Six parents had typical anomalies in two or more systems pointing to the presence of autosomal dominant inheritance. Systematic screening of parents for the features defined in this study should improve the accuracy of genetic counselling. 相似文献
60.
J Barrette R Bellwied P Braun-Munzinger WE Cleland T Cormier G Dadusc G David J Dee O Dietzsch M Fatyga SV Greene JV Germani JR Hall TK Hemmick N Herrmann RW Hogue B Hong K Jayananda D Kraus BS Kumar R Lacasse D Lissauer WJ Llope TW Ludlam R Majka SK Mark JT Mitchell M Muthuswamy E O'Brien C Pruneau FS Rotondo da Silva NC J Simon-Gillo U Sonnadara J Stachel H Takai EM Takagui TG Throwe L Waters C Winter D Wolfe CL Woody N Xu Y Zhang Z Zhang C Zou 《Canadian Metallurgical Quarterly》1995,52(5):2679-2683