全文获取类型
收费全文 | 8171篇 |
免费 | 568篇 |
国内免费 | 9篇 |
专业分类
电工技术 | 65篇 |
综合类 | 7篇 |
化学工业 | 1713篇 |
金属工艺 | 109篇 |
机械仪表 | 179篇 |
建筑科学 | 309篇 |
矿业工程 | 21篇 |
能源动力 | 211篇 |
轻工业 | 1767篇 |
水利工程 | 100篇 |
石油天然气 | 35篇 |
无线电 | 383篇 |
一般工业技术 | 1168篇 |
冶金工业 | 1330篇 |
原子能技术 | 33篇 |
自动化技术 | 1318篇 |
出版年
2024年 | 19篇 |
2023年 | 87篇 |
2022年 | 143篇 |
2021年 | 232篇 |
2020年 | 209篇 |
2019年 | 234篇 |
2018年 | 337篇 |
2017年 | 317篇 |
2016年 | 338篇 |
2015年 | 269篇 |
2014年 | 363篇 |
2013年 | 657篇 |
2012年 | 550篇 |
2011年 | 561篇 |
2010年 | 415篇 |
2009年 | 396篇 |
2008年 | 384篇 |
2007年 | 359篇 |
2006年 | 274篇 |
2005年 | 217篇 |
2004年 | 189篇 |
2003年 | 167篇 |
2002年 | 147篇 |
2001年 | 119篇 |
2000年 | 80篇 |
1999年 | 91篇 |
1998年 | 529篇 |
1997年 | 286篇 |
1996年 | 200篇 |
1995年 | 115篇 |
1994年 | 83篇 |
1993年 | 84篇 |
1992年 | 34篇 |
1991年 | 24篇 |
1990年 | 17篇 |
1989年 | 23篇 |
1988年 | 18篇 |
1987年 | 22篇 |
1986年 | 19篇 |
1985年 | 24篇 |
1984年 | 13篇 |
1983年 | 11篇 |
1982年 | 8篇 |
1981年 | 16篇 |
1980年 | 11篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1977年 | 14篇 |
1976年 | 20篇 |
1975年 | 5篇 |
排序方式: 共有8748条查询结果,搜索用时 15 毫秒
991.
Trends in Hydrological Parameters of a Southern Brazilian Watershed and its Relation to Human Induced Changes 总被引:4,自引:1,他引:4
Moraes Jorge M. Pellegrino Giampaolo Q. Ballester Maria V. Martinelli Luiz A. Victoria Reynaldo L. Krusche Alex V. 《Water Resources Management》1998,12(4):295-311
The Piracicaba river basin is a subtropical watershed located in the southeastern region of Brazil. With an area of 12 400 km2, the basin is a typical example of new landscape resulting from development in tropical and sub-tropical regions: establishment of intensive industrial and agricultural processes were followed by significant population growth and water management. This scenario has led to significant increase in water demand and decrease in water quality. The main objective of this study is the detection of changes in the patterns of flow and precipitation in the basin, and its possible relation to man-induced changes. Statistical analyses were performed on records of precipitation, evapotranspiration and streamflow, from 1947 to 1991. Precipitation and evapotranspiration totals showed significant increasing trends for the entire basin. From eight streamflow gauge stations, half showed significant decreasing trend. The most probable cause of such trends is the export of water from the basin to the metropolitan region of São Paulo city. 相似文献
992.
Palomares Iván Martínez-Cámara Eugenio Montes Rosana García-Moral Pablo Chiachio Manuel Chiachio Juan Alonso Sergio Melero Francisco J. Molina Daniel Fernández Bárbara Moral Cristina Marchena Rosario de Vargas Javier Pérez Herrera Francisco 《Applied Intelligence》2021,51(9):6497-6527
Applied Intelligence - The17 Sustainable Development Goals (SDGs) established by the United Nations Agenda 2030 constitute a global blueprint agenda and instrument for peace and prosperity... 相似文献
993.
Non-enzymatic browning predictions in reduced-moisture foods stored over one year at “ambient” temperature, were made using, (a) realistic environmental daily (and seasonal) temperature fluctuations, and (b) a constant mean temperature. Daily temperature records taken every 6 h from January 1st to December 31st (1460 temperature data) in four selected cities from Argentina, were used.
The predicted amount of browning over one year storage was different depending whether the annual mean temperature (Tam), the monthly mean temperature (Tmm) or the daily temperature fluctuations (Tdf) were used for the predictions. Predicted browning over one year was generally higher when realistic storage conditions (i.e., daily/seasonal temperature fluctuations) rather than mean values (annual or monthly), were used instead. 相似文献
994.
Moliner Carolina; Martínez-Tur Vicente; Peiró José M.; Ramos José; Cropanzano Russell 《Canadian Metallurgical Quarterly》2005,12(2):99
Relationships between organizational justice and well-being are traditionally investigated at the individual level. This article extends previous efforts by testing such relationships at the work-unit level. Three corridors of influence were examined. First, the level (work units' average scores) of justice is related to the level of burnout. Second, justice climate strength (level of agreement among work-unit members) moderates the predictability of the level of burnout. Third, justice strength is related to burnout strength. The authors interviewed 324 contact employees from 108 work units in 59 service organizations. Findings showed the predominance of interactional justice over distributive and procedural justice in all 3 corridors. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
995.
F Martín J Pintor JM Rovira C Ripoll MT Miras-Portugal B Soria 《Canadian Metallurgical Quarterly》1998,12(14):1499-1506
In pancreatic beta-cells, stimulatory glucose concentrations increase cytosolic diadenosine polyphosphates ([ApnA]i) to concentrations sufficient to block ATP-sensitive K+ (KATP) channels. High-performance liquid chromatography and patch clamp techniques were used to study the metabolic pathways by which pancreatic beta-cells synthesize ApnA and the mechanism through which ApnA inhibit KATP channels. ApnA show a glucose- and time-dependent cytosolic concentration increase parallel, though 30- to 50-fold higher, to changes observed in adenine nucleotides. Other fuel secretagogues, leucine and 2-ketoisocaproate, raise [ApnA]i as efficiently as 22 mM glucose. Blockade of glycolysis or Krebs cycle decreases glucose-induced [ApnA]i. No significant increase in cytosolic ApnA concentrations is induced by nonnutrient secretagogues or nonmetabolizable nutrient secretagogues. Inorganic pyrophosphatase inhibition with sodium fluoride blocks 22 mM glucose-induced [ApnA]i increase. ApnA inhibition of KATP channel resembles that of ATP in efficacy, but shows clear functional differences. Unlike ATP, Ap4A does not restore channel activity after rundown. Furthermore, these compounds do not compete with each other for the same site. These features suggest a prominent role for Ap4A in beta-cell function, comparable to ATP. We conclude that nutrient metabolism through pyrophosphatase activation is necessary to induce ApnA synthesis, which in turn constitutes a new, ATP-independent, metabolic regulator of KATP channel activity. 相似文献
996.
A Segovia Martínez C Pérez Fuentes J Torío Durántez MC García Tirado 《Canadian Metallurgical Quarterly》1998,22(9):562-569
OBJECTIVES: To find the social, demographic and family characteristics, the psychological malaise and reasons for consultation of normal and hyper-attenders at a primary care practice. DESIGN: Crossover study with a control. SETTING: Primary care. PATIENTS: 127 hyper-attenders (they attended the practice as often as, or more often than, the mean number of visits, stratified by sex and age) and 120 normal attenders chosen by stratified random sampling. INTERVENTIONS: Questionnaire with characterisation data, family demography, psychological malaise (Goldberg general health questionnaire) and reasons for consultation. RESULTS: To be considered a hyper-attender, the number of attendances per year ranged from > or = 8 (in 15 to 44-year olds) to > or = 20 (in men over 65). Hyper-attenders were about 12% of almost all groups, except in men between 45 and 64 and women over 64, in whom it was around 18%. We found no relevant differences between normal and hyper-attenders as to demography or perception of family function. In almost 60% of hyper-attenders and 34% of normal attenders (p < 0.001), psychological malaise was detected. CONCLUSIONS: If the definition of hyper-attenders is stratified by age and sex, their social and demographic characteristics are very different from in other studies, even though there are a similar number of them. However, these demographic and/or family characteristics are similar in normal and hyper-attenders. 相似文献
997.
W Martínez-López EM Boccardo GA Folle V Porro G Obe 《Canadian Metallurgical Quarterly》1998,150(5):585-592
BACKGROUND: We recently demonstrated that arachidonic:linoleic acid ratio of erythrocytes of essential hypertension patients is greater than normal. OBJECTIVE: To investigate fatty acid composition, capability for adhesion to biological substrate and expression of beta2 integrins of leucocytes obtained from peripheral blood and skin window exudate of essential hypertension patients. DESIGN: Neutrophil activation state was evaluated by reproducing the various conditions occurring in vivo during the life of the cell (i.e. under the 'resting' condition, such as in peripheral blood, and 'primed' condition, such as after transmigration through the endothelium and after administration of specific chemo-attractants). Because both peripheral blood and skin window leucocytes of the subjects were obtained on the same day, we could be sure that there had been no dietary influences on changes in levels of fatty acid. Thus, the observed changes should reliably reflect the metabolic rate of utilization of fatty acids coupled to the activation and migration of cells. RESULTS: Leucocytes from essential hypertension patients were richer in arachidonic acid than were the corresponding cells from normotensive subjects; this difference was also evident for functionally activated skin window leucocytes, in spite of there having been a greater loss of poly-unsaturated fatty acids and arachidonic acid after migration. Moreover, a greater than normal arachidonic acid:linoleic acid ratio was shown for the first time to apply for leucocytes of essential hypertension patients, so extending our previous findings on the erythrocytes. Leucocytes from essential hypertension patients, collected both from peripheral blood and from skin window exudate, proved far more adhesive than the corresponding cells from age-matched and sex-matched controls, but this was not associated with a quantitative hyperexpression of beta2 integrins. CONCLUSIONS: The results suggest that an increase in availability of arachidonic acid in leucocytes could be a further expression of the generalized disturbance of fatty acid levels associated with essential hypertension and that a condition of hyperadhesion of neutrophils could occur spontaneously in vivo during the course of hypertension. 相似文献
998.
T Martínez Y Escamilla M Gutiérrez M Bodoque B Scola MF Vega 《Canadian Metallurgical Quarterly》1996,47(2):125-128
Listeria innocua NCTC 11289 was grown aerobically in continuous culture in defined media at 30 degrees C. Both acetate and lactate were produced, the proportion of acetate decreased with increasing dilution rate. Enzymatic analysis showed lactate dehydrogenase was activated 10-fold by fructose-1, 6-bisphosphate. The presence of phosphate acetyltransferase and acetate kinase but not pyruvate oxidase was detected, suggesting the sequential action of phosphate acetyltransferase and acetate kinase to produce acetate from acetyl CoA via acetylphosphate. 相似文献
999.
Initial reports on antiproteinuric effect of pefloxacine in small groups of patients with minimal-change nephropathy (MCN) and focal and segmental glomerulosclerosis (FSGS) have not been confirmed in other papers. To assess its antiproteinuric effect in experimental animals we administered pefloxacine to rats with adriamycin nephropathy showing morphological changes resembling human minimal-change disease or focal segmental glomerulosclerosis, and clinically with full-blown nephrotic syndrome. Pefloxacine treatment was at least partially effective in preventing further increase of proteinuria in rats with adriamycin nephropathy. The mechanism of this effect remains unclear and deserves further studies concentrating on the glomerular cytokine network and glomerular production of reactive oxygen species. 相似文献
1000.