全文获取类型
收费全文 | 13265篇 |
免费 | 979篇 |
国内免费 | 23篇 |
专业分类
电工技术 | 145篇 |
综合类 | 8篇 |
化学工业 | 3191篇 |
金属工艺 | 217篇 |
机械仪表 | 375篇 |
建筑科学 | 548篇 |
矿业工程 | 34篇 |
能源动力 | 480篇 |
轻工业 | 2896篇 |
水利工程 | 146篇 |
石油天然气 | 74篇 |
武器工业 | 2篇 |
无线电 | 728篇 |
一般工业技术 | 2314篇 |
冶金工业 | 855篇 |
原子能技术 | 84篇 |
自动化技术 | 2170篇 |
出版年
2024年 | 27篇 |
2023年 | 136篇 |
2022年 | 276篇 |
2021年 | 527篇 |
2020年 | 401篇 |
2019年 | 419篇 |
2018年 | 577篇 |
2017年 | 619篇 |
2016年 | 617篇 |
2015年 | 442篇 |
2014年 | 578篇 |
2013年 | 1192篇 |
2012年 | 899篇 |
2011年 | 982篇 |
2010年 | 729篇 |
2009年 | 737篇 |
2008年 | 691篇 |
2007年 | 628篇 |
2006年 | 514篇 |
2005年 | 316篇 |
2004年 | 298篇 |
2003年 | 289篇 |
2002年 | 273篇 |
2001年 | 204篇 |
2000年 | 187篇 |
1999年 | 166篇 |
1998年 | 337篇 |
1997年 | 246篇 |
1996年 | 163篇 |
1995年 | 130篇 |
1994年 | 88篇 |
1993年 | 73篇 |
1992年 | 44篇 |
1991年 | 35篇 |
1990年 | 34篇 |
1989年 | 31篇 |
1988年 | 29篇 |
1987年 | 16篇 |
1986年 | 27篇 |
1985年 | 27篇 |
1984年 | 39篇 |
1983年 | 39篇 |
1982年 | 25篇 |
1981年 | 22篇 |
1980年 | 25篇 |
1979年 | 17篇 |
1978年 | 14篇 |
1977年 | 15篇 |
1976年 | 27篇 |
1973年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 656 毫秒
951.
González-Castaño Francisco J. García-Palomares Ubaldo M. 《Telecommunication Systems》2001,17(4):435-454
This paper describes a new model for routing in survivable ATM networks and a new parallel projection algorithm for solving the corresponding optimization problem. The proposed algorithm has application in general linear programming (LP). Numerical results for medium size networks are presented and discussed. 相似文献
952.
Calaf RE Peña J Paytubi S Blount BC Posada de la Paz M Gelpi E Abian J 《Analytical chemistry》2001,73(16):3828-3837
In 1981, an unknown disease appeared in Spain, the Spanish Toxic Oil Syndrome. Nowadays and despite all efforts, the etiological agent is still unknown. Early studies showed a link between this illness and the consumption of denatured rapeseed oil fraudulently processed and marketed as edible oil. Two families of aniline derivatives present in these oils (fatty acid anilides and acylated phenyl amino propanediol derivatives or PAPs) were found to be good chemical markers of toxic oils. In this work, a new method has been developed to analyze these aniline derivatives in oil samples by HPLC-MS and HPLC-MS/MS with an API source. For their quantification, three different internal standards were used, one for anilides and two for PAPs. Quantification limits were 8 ppm for anilides and 0.2 ppm for PAPs. Anilides and PAPs were found in marker-positive samples at levels up to 50,000 and 330 ppm, respectively. The relative abundance of the different fatty acid anilides and PAPs correlates with the fatty acid composition of the oils. More than 2,600 different samples were analyzed by this method in the most exhaustive screening of suspected toxic oils carried out to date. 相似文献
953.
Reference levels in radiodiagnostics are a requirement stated by the Council Directive 97/43/EURATOM. Reference levels are also relevant for interventional procedures, in accordance with this Directive, which claims special attention to quality assurance programmes, including quality control and patient dose evaluations for special practices such as interventional radiology, to assess the convenience of corrective action depending on the measured doses. The present paper addresses a method of establishing reference levels in interventional radiology, in the framework of optimisation, discussing the ways of putting forward values with a degree of tolerance, to allow for procedure complexity, depending on patient pathology. The need for several estimators used together, namely fluoroscopy time, total number of images per procedure and dose-area product, is also emphasised, proposing a further skin dose estimate in case of risk of deterministic effects. Finally, a brief summary of principles is given for the correct management of reference levels in interventional radiology. 相似文献
954.
Hernández A Martín A Villanueva I Amor I Butragueño JL;Spanish National Dose Registry 《Radiation protection dosimetry》2001,96(1-3):277-280
The Spanish National Dose Registry (BDN) is the Nuclear Safety Council's (CSN) national database of occupational exposure to radiation. Each month BDN receives records of individual external doses from approved dosimetry services. The dose records include information regarding the occupational activities of exposed workers. The dose information and the statistical analysis prepared by the BDN are a useful tool for effective operational protection of occupationally exposed workers and a support for the CSN in the development and application of the ALARA principle. The Spanish radiation passbook was introduced in 1990 and since then CSN, as regulatory authority, has required that all outside workers entering controlled areas should have radiation passbooks. Nowadays, CSN has implemented improvements in the Spanish radiation passbooks, taking into account previous experience and Directive 96/29/EURATOM. 相似文献
955.
Sánchez AH Rejano L Montaño A de Castro A 《International journal of food microbiology》2001,67(1-2):115-122
Inoculation at alkaline pH (above 9) of lye-treated green olives with starter cultures of Lactobacillus pentosus CECT 5138 was studied. Despite an initial loss of viability in the order of 1-2 log cycles on average, depending mainly on time of application, cultures grew and initiated an accelerated fermentation process. Inoculation reduced the population of Enterobacteriaceae, and thereby potential spoilage, and produced a quicker acidification of brines and decrease of pH, when compared with control uninoculated batches. Results obtained throughout three consecutive seasons demonstrated that utilization at high pH of starter cultures of lactobacilli is feasible, provided that the inoculum size takes into account the initial low survival. 相似文献
956.
Seseña S Sánchez-Hurtado I González Viñas MA Palop L 《International journal of food microbiology》2001,67(3):197-205
Trial fermentations were performed using three experimental starter cultures with a view to selecting the most appropriate starter for use in the manufacture of Almagro eggplants. The lactic acid bacterial strains used in the starters had previously been isolated from spontaneous fermentations. The combined action of the obligate heterofermentative species Lactobacillus brevis and the facultative heterofermentative species L. plantarum yielded Almagro eggplants with sensory properties preferred by panelists. Conversely, another obligate heterofermentative species, namely, L. fermentum, present in certain starter formulations tested, appeared to encounter difficulty growing during fermentation and exerted little influence on the sensory characteristics of the eggplants produced. 相似文献
957.
Ochratoxin A (OA)-producing fungi were identified in coffee at different stages of maturation. The toxin was quantified in coffee during terrace drying and in coffee stored in barns. By direct plating, a high level of contamination (100%) was found in the coffee beans studied, with the genus Aspergillus representing 33.2%, of which Aspergillus ochraceus and Aspergillus niger represented 10.3 and 22.9%, respectively, of the strains isolated from the coffee beans. The capacity to produce ochratoxin was determined in 155 strains of A. ochraceus and A. niger using both the agar plug method and extraction with chloroform, giving positive results for 88.1% of the A. ochraceus strains and 11.5% of the A. niger strains. Analysis for OA in the terrace and barn coffee samples showed that, independent of cultivar, year harvested, or production region, all except one of the samples analyzed showed mycotoxin levels below the limit suggested by the European Common Market (8 microg/kg), thus indicating that the problem is restricted and due to severe faults in harvesting and storage practices. 相似文献
958.
Breast-feeding is the optimal mode of feeding for the normal full-term infant. Human milk composition knowledge has been basis for recommended dietary allowances for infants. Few studies about human milk carbohydrates have been done until the last decade. However, carbohydrates provide approximately 40-50% of the total energy content of breast milk. Quantitatively oligosaccharides are the third largest solute in human milk after lactose and fat. Each individual oligosaccharide is based on a variable combination of glucose, galactose, sialic acid, fucose and N-acetylglucosamine with many and varied linkages between them, thus accounting for the enormous number of different oligosaccharides in human milk. The oligosaccharides content in human milk varies with the duration of lactation, diurnally and with the genetic makeup of the mother. At present, a great interest in the roles of human milk oligosaccharides is raising. They act as a the soluble fibre in breast milk and their structure is available to act as competitive ligands protecting the breast-fed infant from pathogens and act as well as prebiotic. They may also act as source of sialic acid and galactose, essential for brain development. This is why today there is an increasing health and industrial interest in human milk oligosaccharides content, with the main purpose of incorporating them as new ingredients in infant nutrition. 相似文献
959.
Effect of Nb Doping on (Sr,Ba)TiO3 (BST) Ceramic Samples 总被引:3,自引:0,他引:3
S. García R. Font J. Portelles R.J. Quiñones J. Heiras J.M. Siqueiros 《Journal of Electroceramics》2001,6(2):101-108
The effect of doping the Sr0.3Ba0.7Ti(1–5y/4)Nb
y
O3 ceramic with different concentration of Nb is studied by scanning electron microscopy (SEM), X-ray diffraction and thermoelectric analysis. It is observed that the grain size decreases as the Nb concentration increases. The critical temperature T
c has a linear decrease at a rate of 19°C/mol% of Nb. The temperature dependence of the dielectric permittivity presents strongly broadened curves, which suggest a non Curie-Weiss behavior near the transition temperature. The diffuse phase transition coefficient () was also determined and its value leads to the conclusion that the degree of disorder in the system increases with the presence of the Nb cation. 相似文献
960.
The buffy-headed marmoset (Callithrix flaviceps) is apparently the only predispersal herbivore of the seeds of Siparuna guianensis at the Caratinga Biological Station in southeastern Brazil. Both the fruit receptacles and the frutioles (seeds) of S. guianensis are relatively rich in nutrients such as carbohydrates, proteins, and lipids, but the receptacles contain high concentrations of benzylisoquinoline alkaloids. The latter presumably act as a qualitative chemical defense, impeding the access of potential predators to the alkaloid-poor frutioles. However, on ripening, the receptacle splits open, exposing the frutioles, which enables C. flaviceps to avoid the plant's chemical defenses effectively. Taking care to avoid contact with the receptacle, the marmosets pluck out the frutioles and ingest the seeds. Qualitative and quantitative changes (in particular a significant reduction in daily ranging) in the marmosets' behavior during the period when S. guianensis frutioles were accessible indicate that this was a preferred plant resource. This is the first record of the consumption of S. guianensis seeds by callitrichine monkeys (which are not known to be systematic seed eaters), despite the fact that both are widely distributed in the Neotropics. It is thus possible that the behavioral strategy observed here is a unique phenomenon resulting from a specific combination of factors, including the abundance of S. guianensis within the study area. The lack of other records may nevertheless be a result of insufficient sampling effort, in which case, the feeding strategies of callitrichines may have an important influence on the reproductive biology of S. guianensis in many areas. 相似文献