全文获取类型
收费全文 | 262114篇 |
免费 | 4317篇 |
国内免费 | 1819篇 |
专业分类
电工技术 | 5426篇 |
技术理论 | 5篇 |
综合类 | 1168篇 |
化学工业 | 42258篇 |
金属工艺 | 11296篇 |
机械仪表 | 7770篇 |
建筑科学 | 6628篇 |
矿业工程 | 1667篇 |
能源动力 | 5602篇 |
轻工业 | 25899篇 |
水利工程 | 2897篇 |
石油天然气 | 6004篇 |
武器工业 | 243篇 |
无线电 | 27839篇 |
一般工业技术 | 49349篇 |
冶金工业 | 47363篇 |
原子能技术 | 5642篇 |
自动化技术 | 21194篇 |
出版年
2021年 | 2482篇 |
2019年 | 2124篇 |
2018年 | 3459篇 |
2017年 | 3425篇 |
2016年 | 3754篇 |
2015年 | 2875篇 |
2014年 | 4606篇 |
2013年 | 11388篇 |
2012年 | 7719篇 |
2011年 | 10718篇 |
2010年 | 8152篇 |
2009年 | 8710篇 |
2008年 | 9516篇 |
2007年 | 9600篇 |
2006年 | 8446篇 |
2005年 | 7404篇 |
2004年 | 6663篇 |
2003年 | 6207篇 |
2002年 | 6216篇 |
2001年 | 6331篇 |
2000年 | 5918篇 |
1999年 | 5883篇 |
1998年 | 12888篇 |
1997年 | 9547篇 |
1996年 | 7294篇 |
1995年 | 5530篇 |
1994年 | 5089篇 |
1993年 | 4959篇 |
1992年 | 3953篇 |
1991年 | 3757篇 |
1990年 | 3829篇 |
1989年 | 3775篇 |
1988年 | 3537篇 |
1987年 | 3021篇 |
1986年 | 3054篇 |
1985年 | 3414篇 |
1984年 | 3328篇 |
1983年 | 3075篇 |
1982年 | 2700篇 |
1981年 | 2907篇 |
1980年 | 2655篇 |
1979年 | 2842篇 |
1978年 | 2742篇 |
1977年 | 2846篇 |
1976年 | 3713篇 |
1975年 | 2459篇 |
1974年 | 2292篇 |
1973年 | 2323篇 |
1972年 | 1984篇 |
1971年 | 1788篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
High‐intensity sweeteners in espresso coffee: ideal and equivalent sweetness and time–intensity analysis 下载免费PDF全文
Bruna M. Azevedo Flávio L. Schmidt Helena M. A. Bolini 《International Journal of Food Science & Technology》2015,50(6):1374-1381
The efficient substitution of sucrose by a sweetener in beverages requires the application of some sensory techniques. First, one must determine the concentrations of the sweeteners under study, equivalent in sweetness to the ideal sucrose concentration. In addition, it is fundamental to determine which is most similar to sucrose. The objectives of this study were to determine the ideal sweetness for espresso coffee and the equivalent concentrations in sweetness of different sweeteners, as well as characterise the time–intensity profile of each sweetener in relation to sweetness. The sweeteners evaluated were sucralose, aspartame, neotame, a cyclamate/saccharin mixture (2:1) and stevia. The sucrose concentration considered ideal by consumers was 12.5% (w/v), and the equivalent concentrations of the sweeteners were 0.0159% for sucralose, 0.0549% for aspartame, 0.0016% for neotame, 0.0359% for the cyclamate/saccharin mixture and 0.0998% for stevia. The time–intensity analysis indicated that possibly the sweeteners neotame, aspartame and sucralose would be the best substitutes for sucrose. 相似文献
33.
L. S. Belevskii N. V. Koptseva I. V. Belevskaya Yu. Yu. Efimova 《Russian Metallurgy (Metally)》2015,2015(9):753-758
The microstructure and properties of the functional coatings formed by impact friction processing of product surfaces with a flexible tool are studied. It is established that the processing produces a hard nanostructured surface layer with fragments up to 0.13 µm in size, as it is achieved by severe plastic deformation. 相似文献
34.
35.
Precil Diego M. M. Neves Fernanda M. Freitas Christiane A. Kojima Beatriz L. Carmello Rodrigo Bazan Pasqual Barretti Luis C. Martin 《Hemodialysis international. International Symposium on Home Hemodialysis》2015,19(1):143-145
Antibiotics are potentially a cause of neurotoxicity in dialysis patients, the most common are the beta‐lactams as ceftazidime and cefepime, and few cases have been reported after piperacillin/tazobactam use. This report presents a case of a hypertensive and diabetic 67‐year‐old woman in regular hemodialysis, which previously had a stroke. She was hospitalized presenting pneumonia, which was initially treated with cefepime. Two days after treatment, she presented dysarthria, left hemiparesis, ataxia, and IX and X cranial nerves paresis. Computed tomography showed no acute lesions and cefepime neurotoxicity was hypothesized, and the antibiotic was replaced by piperacillin/tazobactam. The neurologic signs disappeared; however, 4 days after with piperacillin/tazobactam treatment, the neurological manifestations returned. A new computed tomography showed no new lesions, and the second antibiotic regimen withdrawn. After two hemodialysis sessions, the patient completely recovered from neurological manifestations. The patient presented sequentially neurotoxicity caused by two beta‐lactams antibiotics. This report meant to alert clinicians that these antibiotics have dangerous neurological effects in chronic kidney disease patients. 相似文献
36.
Temperature history can have a significant effect on the strength of water-saturated chalk.In this study,hydrostatic stress cycles are applied to understand the mechanical response of chalk samples exposed to temperature cycling between each stress cycle,compared to the samples tested at a constant temperature.The total accumulated strain during a stress cycle and the irreversible strain are reported.Chalk samples from Kansas(USA)and Mons(Belgium),with different degrees of induration(i.e.amount of contact cementation),were used.The samples were saturated with equilibrated water(polar)and nonpolar Isopar H oil to quantify water weakening.All samples tested during 10 stress cycles with varying temperature(i.e.temperature cycled in between each stress cycle)accumulated more strain than those tested at constant temperatures.All the stress cycles were performed at 30℃.The two chalk types behaved similarly when saturated with Isopar H oil,but differently when saturated with water.When saturated with water,the stronger Kansas chalk accumulated more total strain and more irreversible strain within each stress cycle than the weaker Mons chalk. 相似文献
37.
38.
A new constitutive equation of thermoelasticity for crystals is presented based on the interatomic potential and solid mechanics at finite temperature. Using the new constitutive equation, the calculations for crystal copper and graphene are carried out under different loading paths at different temperatures. The calculated results are in good agreement with those of the previous thermoelasticity constitutive equation based on quantum mechanics, which clearly indicates that our new constitutive equation of thermoelasticity is correct. A lot of comparisons also show that the present theory is more concise and efficient than the previous thermal stress theory in the practical application. 相似文献
39.
H Daims F Maixner S Lücker K Stoecker K Hace M Wagner 《Water science and technology》2006,54(1):21-27
Nitrite-oxidizing bacteria of the genus Nitrospira are key nitrifiers in wastewater treatment plants. Pure cultures of these organisms are unavailable, but cultivation-independent molecular methods make it possible to detect Nitrospira-like bacteria in environmental samples and to investigate their ecophysiology. Comprehensive screening of natural and engineered habitats and of public databases for 16S rRNA sequences of Nitrospira-like bacteria revealed a surprisingly high biodiversity in the genus Nitrospira, which comprises at least four phylogenetic sublineages. All Nitrospira-like bacteria detected in wastewater treatment plants belonged to the sublineages I and II. Subsequently, the population dynamics of different Nitrospira-like bacteria were monitored, by quantitative fluorescence in situ hybridization with rRNA-targeted probes, confocal laser scanning microscopy and digital image analysis, during incubation of nitrifying activated sludge in media containing different nitrite concentrations. These experiments showed that Nitrospira-like bacteria, which were affiliated with the phylogenetic sublineages I or II of the genus Nitrospira, responded differently to nitrite concentration shifts. Previously unknown properties of Nitrospira-like bacteria were discovered in the course of an environmental genomics project. Implications of the obtained results for fundamental understanding of the microbial ecology of nitrite oxidizers as well as for future improvement of nutrient removal in wastewater treatment plants are discussed. 相似文献
40.
Y S Cao C M Ang K S Raajeevan A K Kiran K C Lai S W Ng I Zulkifli Y L Wah 《Water science and technology》2006,54(8):237-246
This paper analyses the performance of the anaerobic selector (A/O process) in a full-scale activated sludge process receiving mostly industrial sewage discharge (> 60%) in Singapore. In addition to the sludge settleability, enhanced biological phosphorus removal (EBPR) was studied. The sludge volume index (SVI) reduced from 200 to 80 ml g(-1) and foaming was suppressed significantly, indicating the effectiveness of the anaerobic selector in improving sludge settleability. The phosphorus removal efficiency was 66%, and 7.5 mg HAc-COD was consumed per mg PO4(3-) -P removed. In the anaerobic compartment, 31% of the SCOD and 73% of the acetic acid in the settled sewage were removed with PO4(3-) -P release of 14.1 mg PO4(3-)-P l(-1). The linear correlation between PO4(3-) -P release in the anaerobic compartment and PO4(3-) -P uptake in the aerobic compartment indicates that there is about 0.8 mg PO4(3-) -P release in the anaerobic compartment per mg PO34(3-) -P uptake in the aerobic compartment. The fates of volatile fatty acids (VFAs) and its short chain acids (SCAs) in the process were studied and discussed. 相似文献