全文获取类型
收费全文 | 3004篇 |
免费 | 109篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 27篇 |
综合类 | 3篇 |
化学工业 | 444篇 |
金属工艺 | 28篇 |
机械仪表 | 75篇 |
建筑科学 | 140篇 |
矿业工程 | 1篇 |
能源动力 | 37篇 |
轻工业 | 430篇 |
水利工程 | 33篇 |
石油天然气 | 4篇 |
无线电 | 205篇 |
一般工业技术 | 463篇 |
冶金工业 | 898篇 |
原子能技术 | 8篇 |
自动化技术 | 320篇 |
出版年
2023年 | 24篇 |
2022年 | 45篇 |
2021年 | 82篇 |
2020年 | 52篇 |
2019年 | 63篇 |
2018年 | 53篇 |
2017年 | 56篇 |
2016年 | 54篇 |
2015年 | 63篇 |
2014年 | 74篇 |
2013年 | 122篇 |
2012年 | 110篇 |
2011年 | 157篇 |
2010年 | 121篇 |
2009年 | 122篇 |
2008年 | 155篇 |
2007年 | 168篇 |
2006年 | 135篇 |
2005年 | 126篇 |
2004年 | 103篇 |
2003年 | 95篇 |
2002年 | 72篇 |
2001年 | 43篇 |
2000年 | 46篇 |
1999年 | 51篇 |
1998年 | 139篇 |
1997年 | 93篇 |
1996年 | 99篇 |
1995年 | 49篇 |
1994年 | 63篇 |
1993年 | 46篇 |
1992年 | 29篇 |
1991年 | 15篇 |
1990年 | 31篇 |
1989年 | 27篇 |
1988年 | 15篇 |
1987年 | 27篇 |
1986年 | 29篇 |
1985年 | 24篇 |
1984年 | 20篇 |
1983年 | 22篇 |
1982年 | 17篇 |
1981年 | 15篇 |
1980年 | 21篇 |
1979年 | 13篇 |
1978年 | 12篇 |
1977年 | 16篇 |
1976年 | 33篇 |
1974年 | 15篇 |
1973年 | 14篇 |
排序方式: 共有3116条查询结果,搜索用时 30 毫秒
981.
Renner R 《Environmental science & technology》2004,38(20):384A-385A
982.
Renner R 《Environmental science & technology》2004,38(14):262A-263A
983.
A process is described in which toxic aromatic compounds are converted by toluene dioxygenase and in turn toluene cis-dihydrodiol dehydrogenase to catechols which are further polymerized by peroxidase-catalyzed oxidation producing polycatechols. Three approaches for obtaining catechols were employed: (1) addition of halogenated aromatics to P. putida F1, resulting in the accumulation of halogenated catechols; (2) inhibition of catechol 2,3-dioxygenase of P. putida F1 by known aromatic and aliphatic inhibitors; and (3) overexpression of toluene dioxygenase and toluene cis-dihydrodiol dehydrogenase genes in E. coli JM109. The process is suitable for producing novel catechols that upon oxidation may yield polymers with unique properties, presenting a tool for producing tailor-made biopolymers. Formation of 3-chlorocatechol from chlorobenzene, 3,4-dichlorocatechol from 1,2-dichlorobenzene, and catechol from benzene and their subsequent oxidation and polymerization was demonstrated. Oxidation of catechol yielded polymers with molecular weights of up to 4000 Daltons. Their apparently high water solubility eliminates the need for water-miscible solvents. In aqueous solution oxidation of catechols was rapid, yet the presence of 20%, 30%, and 40% ethanol, resulted in a rate decrease of 31%, 95%, and 93%, respectively. The advantage is that significantly less peroxidase is required for performing the reactions if miscible solvents are not employed. Furthermore, water-soluble polymers may be desirable for many applications. 相似文献
984.
Galloway TS Brown RJ Browne MA Dissanayake A Lowe D Jones MB Depledge MH 《Environmental science & technology》2004,38(6):1723-1731
Incorporation of ecologically relevant biomarkers into routine environmental management programs has been advocated as a pragmatic means of linking environmental degradation with its causes. Here, suites of biomarkers, devised to measure molecular damage, developmental abnormality and physiological impairment, were combined with chemical analysis to determine exposure to and the effects of pollution at sites within Southampton Water (UK). Test species included a filter feeder, a grazer, and an omnivore to determine the sensitivity of organisms occupying different trophic levels. Linear regression confirmed a significant association between incidence of intersex in Littorina littorea and tributyltin (TBT) concentrations (R2 = 0.954) and between PAH metabolites in Carcinus maenas urine and PAHs in sediments (R2 = 0.754). Principal component analysis revealed a gradient of detrimental impact to biota from the head to the mouth of the estuary, coincident with high sediment concentrations of heavy metals, PAHs, and biocides. Multidimensional scaling identified C. maenas as the organism most sensitive to contamination. Carboxylesterase activity, metallothionein and total haemolymph protein were the most discriminating biomarkers among sites. This holistic approach to environmental assessment is encouraged as it helps to identify the integrated impact of chemical contamination on organisms and to provide a realistic measure of environmental quality. 相似文献
985.
L. Tuck M. Sayer M. Mackenzie J. Hadermann D. Dunfield A. Pietak J. W. Reid A. D. Stratilatov 《Journal of Materials Science》2006,41(13):4273-4284
Silicon stabilized tricalcium phosphate (Si-TCP) is formed, among other phases, as a result of sintering hydroxyapatite (HA)
in the presence of silica (SiO2) at >800°C. Calcium phosphate films sintered at 1000°C on quartz substrates are examined with and without additional SiO2 added to the starting precipitate. Data from transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy
(XPS) separate the undoped film morphology into a surface layer with a monoclinic crystal structure P21/a characteristic of α or Si-tricalcium phosphate and grain size in the range 100–1000 nm and a substrate layer with a crystal structure which is
predominantly apatitic P63/m and grain size in the range 30–100 nm. The silicon content is greatest in the substrate layer. The addition of SiO2 to the film material during fabrication induces a more uniform grain size of 10–110 nm and a higher Si content. The structural
and phase evolution of these films suggests the nucleation of α-TCP by the local formation of Si-TCP at a SiO2-hydroxyapatite interface. The results are consistent with X-ray diffraction studies and are explained by a model of nucleation
and growth developed for bulk powders. 相似文献
986.
Markham Rebecca G.; Toth Gabriella; Lickliter Robert 《Canadian Metallurgical Quarterly》2006,120(6):1315
Neonatal studies suggest elevated arousal can negatively influence perceptual and cognitive processes during early development. The authors explored this issue during the prenatal period by pharmacologically elevating physiological arousal in bobwhite quail (Colinus virginianus) embryos during exposure to a maternal call, then assessing preference for the familiar call following hatching. Embryos receiving norepinephrine showed a prenatal elevation in heart rate and failed to demonstrate a preference for the familiar call following hatching. Embryos not receiving norepinephrine showed no elevation in heart rate and demonstrated a preference for the familiar call. These results indicate elevated arousal can interfere with perceptual learning during the prenatal period and provide additional evidence for an optimal window of arousal necessary to foster species-typical perceptual functioning during early development. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
987.
Stein L. A. R.; Colby Suzanne M.; Barnett Nancy P.; Monti Peter M.; Golembeske Charles; Lebeau-Craven Rebecca; Miranda Robert 《Canadian Metallurgical Quarterly》2006,3(1):25
The purpose of this study was to determine whether motivational interviewing (MI), compared with an attention control condition (relaxation training [RT]) enhances substance abuse treatment engagement in incarcerated adolescents. At the start of incarceration, adolescents were randomly assigned to individually administered MI or RT. Subsequently, therapists and adolescents (N = 130) rated degree of adolescent participation in the facility's standard care group-based treatments targeting crime and substance use. All adolescents received the facility standard care treatment after their individual MI or RT session. MI statistically significantly mitigated negative substance abuse treatment engagement. Other indicators of treatment engagement were in the expected direction; however, effect sizes were small and nonsignificant. These findings are significant, given concerns regarding the deleterious effects of treating delinquent adolescents in groups and the potential for adolescents to reinforce each other's negative behavior, which in turn may lead to escalated substance use and other delinquent behaviors after release. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
988.
Hale James B.; Fiorello Catherine A.; Kavanagh Jack A.; Hoeppner Jo-Ann B.; Gaither Rebecca A. 《Canadian Metallurgical Quarterly》2001,16(1):31
The Wechsler Intelligence Scale for Children-Third Edition (WISC-III) provides a Full Scale Intelligence Quotient (FSIQ), four factor standard scores, and subtest scale scores. In contrast with previous findings, this study of 174 children (aged 6–16 yrs) meeting criteria for learning disabilities revealed that the WISC-III factors accounted for a large portion of achievement variance during hierarchical regression analyses, yet FSIQ added little predictive power. A commonality analysis of FSIQ indicated that it is largely comprised of unique, not shared, factor variance. Analyzing the WISC-III subtests from a fluid-crystallized (Gf-Gc) intelligence theoretical framework, academic achievement commonality analyses revealed complex relationships among the predictors, with crystallized, quantitative, and short-term memory factors accounting for the most achievement variance, regardless of academic domain. Results suggest that simple rejection of factor or subtest scores based on hierarchical regression techniques is unwarranted and that systematic exploration of nomothetic and idiographic patterns of performance is recommended for practitioners. (PsycINFO Database Record (c) 2011 APA, all rights reserved) 相似文献
989.
Silicon imagers with integrated motion-detection circuitry have been developed and tested for the past 15 years. Many previous circuits estimate motion by identifying and tracking spatial or temporal features. These approaches are prone to failure at low SNR conditions, where feature detection becomes unreliable. An alternate approach to motion detection is an intensity-based spatiotemporal correlation algorithm, such as the one proposed by Hassenstein and Reichardt in 1956 to explain aspects of insect vision. We implemented a Reichardt motion sensor with integrated photodetectors in a standard CMOS process. Our circuit operates at sub-microwatt power levels, the lowest reported for any motion sensor. We measure the effects of device mismatch on these parallel, analog circuits to show they are suitable for constructing 2-D VLSI arrays. Traditional correlation-based sensors suffer from strong contrast dependence. We introduce a circuit architecture that lessens this dependence. We also demonstrate robust performance of our sensor to complex stimuli in the presence of spatial and temporal noise. 相似文献
990.
Julie-Anne Fenger Gregory T. Sigurdson Rebecca J. Robbins Thomas M. Collins M. Mnica Giusti Olivier Dangles 《International journal of molecular sciences》2021,22(9)
Red cabbage (RC) and purple sweet potato (PSP) are naturally rich in acylated cyanidin glycosides that can bind metal ions and develop intramolecular π-stacking interactions between the cyanidin chromophore and the phenolic acyl residues. In this work, a large set of RC and PSP anthocyanins was investigated for its coloring properties in the presence of iron and aluminum ions. Although relatively modest, the structural differences between RC and PSP anthocyanins, i.e., the acylation site at the external glucose of the sophorosyl moiety (C2-OH for RC vs. C6-OH for PSP) and the presence of coordinating acyl groups (caffeoyl) in PSP anthocyanins only, made a large difference in the color expressed by their metal complexes. For instance, the Al3+-induced bathochromic shifts for RC anthocyanins reached ca. 50 nm at pH 6 and pH 7, vs. at best ca. 20 nm for PSP anthocyanins. With Fe2+ (quickly oxidized to Fe3+ in the complexes), the bathochromic shifts for RC anthocyanins were higher, i.e., up to ca. 90 nm at pH 7 and 110 nm at pH 5.7. A kinetic analysis at different metal/ligand molar ratios combined with an investigation by high-resolution mass spectrometry suggested the formation of metal–anthocyanin complexes of 1:1, 1:2, and 1:3 stoichiometries. Contrary to predictions based on steric hindrance, acylation by noncoordinating acyl residues favored metal binding and resulted in complexes having much higher molar absorption coefficients. Moreover, the competition between metal binding and water addition to the free ligands (leading to colorless forms) was less severe, although very dependent on the acylation site(s). Overall, anthocyanins from purple sweet potato, and even more from red cabbage, have a strong potential for development as food colorants expressing red to blue hues depending on pH and metal ion. 相似文献