全文获取类型
收费全文 | 720篇 |
免费 | 57篇 |
专业分类
电工技术 | 5篇 |
化学工业 | 146篇 |
金属工艺 | 3篇 |
机械仪表 | 7篇 |
建筑科学 | 51篇 |
矿业工程 | 3篇 |
能源动力 | 13篇 |
轻工业 | 135篇 |
水利工程 | 5篇 |
石油天然气 | 2篇 |
无线电 | 31篇 |
一般工业技术 | 112篇 |
冶金工业 | 182篇 |
原子能技术 | 1篇 |
自动化技术 | 81篇 |
出版年
2024年 | 1篇 |
2023年 | 3篇 |
2022年 | 7篇 |
2021年 | 26篇 |
2020年 | 11篇 |
2019年 | 15篇 |
2018年 | 16篇 |
2017年 | 28篇 |
2016年 | 24篇 |
2015年 | 26篇 |
2014年 | 22篇 |
2013年 | 46篇 |
2012年 | 49篇 |
2011年 | 69篇 |
2010年 | 45篇 |
2009年 | 29篇 |
2008年 | 53篇 |
2007年 | 38篇 |
2006年 | 46篇 |
2005年 | 24篇 |
2004年 | 28篇 |
2003年 | 27篇 |
2002年 | 23篇 |
2001年 | 13篇 |
2000年 | 12篇 |
1999年 | 15篇 |
1998年 | 14篇 |
1997年 | 15篇 |
1996年 | 6篇 |
1995年 | 9篇 |
1994年 | 5篇 |
1993年 | 6篇 |
1992年 | 6篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 4篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1976年 | 4篇 |
排序方式: 共有777条查询结果,搜索用时 140 毫秒
31.
32.
Silvia Baena‐Ruano Carlos Jiménez‐Ot Inés M. Santos‐Dueñas Jorge E. Jiménez‐Hornero José L. Bonilla‐Venceslada Carmen Álvarez‐Cáliz Isidoro García‐García 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2010,85(7):908-912
BACKGROUND: The acetification process needs an overall study of the variables influencing it in order to establish their optimum values. Based on industrial experience and available literature, including a recently proposed model by the authors, among the variables most strongly influencing the acetification process are the ethanol concentration at the time the reactor is unloaded, the unloaded volume and the loading rate. To ensure economically efficient industrial production of vinegar, and to check the predictions of the aforementioned model, the influence of the final ethanol concentration at unloading time on the mean acetification rate and on productivity has been studied in this work. RESULTS: An increase in the final ethanol concentration from 0.5 to 3.5% (v/v) increased the mean overall acetification rate and acetic acid production by 38 and 26%, respectively. The increase was established mainly during the loading phase. CONCLUSIONS: The final ethanol concentration is a key variable for process optimization. If a high rate is desired then a product containing much unused substrate will be obtained, which may be industrially unacceptable. These results suggest the necessity to investigate other possibilities when high values for yield and productivity must to be achieved. Copyright © 2010 Society of Chemical Industry 相似文献
33.
In Norway, as in many other countries, homeownership is encouraged politically, and a majority of the households become homeowners at some stage in their life cycle. Many households move house when circumstances change, and it is often at this point that they also make their tenure choice. This paper employs a bivariate probit framework to model the transition rate from renting into homeownership. Using a sample of initial renters, subsequent tenure choice is analysed jointly with the stay-move decision. A particularly important question in this context is whether low-income households face differential constraints on entering owner occupation that could be addressed by policy change. The empirical model includes financial characteristics, household characteristics and changes in household characteristics as explanatory variables. Changes in household composition are particularly important in explaining variations in both tenure choice and mobility. Hence, the common practice of estimating housing market behaviour using a panel of intact households potentially obfuscates important determinants of that behaviour. The paper proceeds by using the equivalent of a Chow test to show that a hypothesis of equal coefficients in samples of low- and high-income households is firmly rejected. Thus low-income households do behave differently. Short-term variations in income appear to have little effect on people's capacity to enter owner occupation. However, low-income households are more dependent on past savings for successful entry. This suggests a rather different policy approach if owner occupation is to be expanded. 相似文献
34.
Nyström B Becker-Van Slooten K Bérard A Grandjean D Druart JC Leboulanger C 《Water research》2002,36(8):2020-2028
Irgarol 1051 is a recent herbicidal compound, inhibitor of photosynthesis, used in antifouling paints. This toxic is persistent in aquatic environments, with low abiotic and biotic degradation, highly phytotoxic, and has already been detected in estuaries and coastal areas, with suspected negative impacts on non-target organisms (aquatic plants and algae). We measured the toxicity of Irgarol 1051 to macrophytes and phytoplankton from Lake Geneva (between Switzerland and France) by determining chlorophyll fluorescence yield, and phytoplankton primary production. Long-term toxicity for phytoplankton was estimated in a microcosm study, and growth inhibition tests were performed with isolated algal strains. The concentration of Irgarol 1051 was analysed in the water, and the most polluted site showed a higher level (up to 135 ng/L) than the lowest observed effect concentration for phytoplankton (8-80 ng/L), while the macrophytes appeared to be more tolerant to Irgarol 1051 in short-term tests. The microcosm study showed that phytoplankton structure might be even more sensitive to Irgarol 1051. 相似文献
35.
Skin Texture Modeling 总被引:1,自引:0,他引:1
Cula Oana G. Dana Kristin J. Murphy Frank P. Rao Babar K. 《International Journal of Computer Vision》2005,62(1-2):97-119
36.
Kiehl Kent A.; Bates Alan T.; Laurens Kristin R.; Hare Robert D.; Liddle Peter F. 《Canadian Metallurgical Quarterly》2006,115(3):443
Psychopathy is associated with abnormalities in attention and orienting. However, few studies have examined the neural systems underlying these processes. To address this issue, the authors recorded event-related potentials (ERPs) while 80 incarcerated men, classified as psychopathic or nonpsychopathic via the Hare Psychopathy Checklist-Revised (R. D. Hare, 1991, 2003), completed an auditory oddball task. Consistent with hypotheses, processing of targets elicited larger frontocentral negativities (N550) in psychopaths than in nonpsychopaths. Psychopaths also showed an enlarged N2 and reduced P3 during target detection. Similar ERP modulations have been reported in patients with amygdala and temporal lobe damage. The data are interpreted as supporting the hypothesis that psychopathy may be related to dysfunction of the paralimbic system--a system that includes parts of the temporal and frontal lobes. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
37.
OBJECTIVE: To determine the relationship between matrix metalloproteinases (MMPs), their inhibitors, and the turnover of matrix molecules in articular cartilage from patients with osteoarthritis (OA). METHODS: Synovial fluid samples were collected from the knees of 54 patients with OA. Radiographic evaluations and magnetic resonance imaging were performed on the knees of 34 OA patients to classify the stage of the disease. Biochemical analyses and immunoassays were used to measure the concentrations of MMP-1, MMP-3, tissue inhibitor of metalloproteinases 1 (TIMP-1), TIMP-2, the disaccharide of hyaluronic acid, the proteoglycan glycosaminoglycan disaccharides of chondroitin 4-sulfate (delta di-CS4) and chondroitin 6-sulfate (delta di-CS6), the 846 epitope on chondroitin sulfate of cartilage proteoglycan aggrecan (putative biosynthetic marker), the keratan sulfate (KS) epitope of aggrecan (putative degradation marker), and the C-propeptide of cartilage type II procollagen (CPII) (biosynthetic marker). RESULTS: The concentration of TIMP-1 was directly correlated with the levels of MMP-1 and MMP-3 (both were also correlated with each other), confirming earlier results. There was an inverse correlation between the delta di-CS6:delta di-CS4 ratio and the concentration of MMP-3. The level of delta di-CS6 was correlated with that of the KS epitope, and to a lesser degree, with that of the 846 epitope (the latter was also correlated with the level of delta di-CS4). The concentration of TIMP-1 correlated with that of the 846 epitope, whereas TIMP-2 levels correlated with those of CPII. There were significantly lower concentrations of delta di-CS6, delta di-CS4, the 846 epitope, and CPII in synovial fluid from patients with late-stage OA. CONCLUSION: These observations suggest a link between proteolysis and inhibitor concentrations in OA cartilage. Production of TIMPs appears to be individually linked to the synthesis of specific cartilage molecules. The reduction in the amount of cartilage-matrix structural components suggests that there is a measurable loss of cartilage in the late stages of the disease, as suggested previously. The resultant composition of the cartilage suggests that the loss may primarily involve "resident" molecules originally present in healthy cartilage. 相似文献
38.
We describe here the construction of six deletion mutants and their basic phenotypic analysis in three different backgrounds. The six genes were disrupted in three diploid strains (FY1679, W303 and CEN.PK2) by the long flanking homology (LFH) method (Wach, 1996). Transformants were selected as geneticin (G418)-resistant colonies and correct integration of the kanMX4 cassette was checked by colony PCR. Following sporulation of the heterozygous diploids, tetrads were dissected and scored for segregation of G418-resistance and auxotrophic markers. One of the six ORFs (YNL158w) corresponds to an essential gene which has no homology with other genes present in the databases and has two predicted transmembrane domains. Growth tests performed on different media at 15 degrees C, 30 degrees C or 37 degrees C with haploid deletants of the five non-essential genes revealed no apparent phenotype in any of them. 相似文献
39.
Erik Andreassen Kristin Grstad Ole Jan Myhre Marianne D. Braathen Einar L. Hinrichsen Anne Marie V. Syre Tor Bertel Lvgren 《应用聚合物科学杂志》1995,57(9):1075-1084
Polypropylene fibers produced in a compact-spinning process were studied by differential scanning calorimetry (DSC). With unrestrained fibers, the onset of melting increases with decreasing draw ratio, increasing Mw/Mn, decreasing extrusion temperature, increasing annealing ratio, and increasing draw-down ratio. These trends are discussed in terms of restraints and reorganization. The onset of melting is shifted to lower temperatures as the heating rate increases for all combinations of material and processing parameters, indicating suppressed reorganization. At low draw ratios, the height and width of the endotherm are affected by the spinline stress, and a secondary peak or shoulder is observed on the high temperature side of the main peak. The magnitude of the secondary peak increases with decreasing Mw/Mn, increasing draw ratio, decreasing draw-down ratio, and decreasing heating rate, but its position mainly depends on the heating rate. This indicates that the secondary peak may be due to the melting of structures that have been reorganized during the heating scan. As the draw ratio increases, the melting regime broadens, especially towards lower temperatures, and several maxima emerge on the DSC curve. Reorganization and shrinkage during heating may explain these observations. © 1995 John Wiley & Sons, Inc. 相似文献
40.
Reviewed and critiqued the relevance of the DSM-III-R for school psychological practice. Five misguided assumptions on which the use of the DSM-III-R system is based are presented. These assumptions deal with (1) medical model conceptualization of behavior, (2) reliability, (3) validity, (4) relevance for special education placement, and (5) treatment validity. Based on a critical analysis of each assumption, it was concluded that the DSM-III-R is largely irrelevant for the practice of school psychology. The absence of treatment validity was judged to be the most substantial deficit of the DSM-III-R. An alternative classification system based on a functional analysis of behavior was proposed as being more relevant for assessment, classification, placement, and intervention with students who are behaviorally disordered. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献