全文获取类型
收费全文 | 3334篇 |
免费 | 11篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 20篇 |
综合类 | 2篇 |
化学工业 | 104篇 |
金属工艺 | 34篇 |
机械仪表 | 64篇 |
建筑科学 | 24篇 |
矿业工程 | 9篇 |
能源动力 | 3篇 |
轻工业 | 56篇 |
水利工程 | 35篇 |
石油天然气 | 42篇 |
武器工业 | 1篇 |
无线电 | 102篇 |
一般工业技术 | 214篇 |
冶金工业 | 2457篇 |
原子能技术 | 157篇 |
自动化技术 | 23篇 |
出版年
2021年 | 11篇 |
2020年 | 14篇 |
2019年 | 16篇 |
2018年 | 36篇 |
2017年 | 50篇 |
2016年 | 33篇 |
2015年 | 11篇 |
2014年 | 25篇 |
2013年 | 38篇 |
2012年 | 25篇 |
2011年 | 45篇 |
2010年 | 33篇 |
2009年 | 27篇 |
2008年 | 36篇 |
2007年 | 25篇 |
2006年 | 28篇 |
2005年 | 18篇 |
2004年 | 13篇 |
2003年 | 20篇 |
2002年 | 17篇 |
2001年 | 27篇 |
2000年 | 15篇 |
1999年 | 83篇 |
1998年 | 743篇 |
1997年 | 407篇 |
1996年 | 286篇 |
1995年 | 177篇 |
1994年 | 119篇 |
1993年 | 166篇 |
1992年 | 26篇 |
1991年 | 35篇 |
1990年 | 41篇 |
1989年 | 44篇 |
1988年 | 46篇 |
1987年 | 25篇 |
1986年 | 28篇 |
1985年 | 22篇 |
1984年 | 11篇 |
1982年 | 19篇 |
1981年 | 23篇 |
1980年 | 35篇 |
1979年 | 14篇 |
1978年 | 16篇 |
1977年 | 86篇 |
1976年 | 198篇 |
1973年 | 11篇 |
1972年 | 13篇 |
1970年 | 11篇 |
1969年 | 11篇 |
1967年 | 10篇 |
排序方式: 共有3347条查询结果,搜索用时 203 毫秒
51.
Activation of auditory cortex during silent lipreading 总被引:1,自引:0,他引:1
GA Calvert ET Bullmore MJ Brammer R Campbell SC Williams PK McGuire PW Woodruff SD Iversen AS David 《Canadian Metallurgical Quarterly》1997,276(5312):593-596
Watching a speaker's lips during face-to-face conversation (lipreading) markedly improves speech perception, particularly in noisy conditions. With functional magnetic resonance imaging it was found that these linguistic visual cues are sufficient to activate auditory cortex in normal hearing individuals in the absence of auditory speech sounds. Two further experiments suggest that these auditory cortical areas are not engaged when an individual is viewing nonlinguistic facial movements but appear to be activated by silent meaningless speechlike movements (pseudospeech). This supports psycholinguistic evidence that seen speech influences the perception of heard speech at a prelexical stage. 相似文献
52.
WE Farrell DJ Simpson JE Bicknell AJ Talbot AS Bates RN Clayton 《Canadian Metallurgical Quarterly》1997,57(13):2703-2709
We have screened 57 cases of primary, nonfunctional, pituitary adenomas for loss of heterozygosity of markers on chromosome 9p. Using a panel of 11 microsatellite markers, we found hemizygous deletion with at least one of the markers in 18 tumors (31.5%). The frequency of loss was similar in both noninvasive (8 of 26; 31%) and invasive tumors (10 of 31; 32%), suggesting that loss on this chromosome might be an early event in pituitary tumorigenesis. Two discrete areas of loss were punctuated by a region of retention of heterozygosity between the markers D9S171 and IFNA, indicative of homozygous deletion. However, multiplex PCR analysis (MTS1 and MTS2) and the presence of a 3' untranslated region polymorphism in MTS1 suggested that neither of these tumor suppressor genes was homozygously deleted. In 6 of the 18 tumors showing LOH, sufficient DNA was also available for Southern blot analysis and, in all cases, showed retention of MTS1. Cell mixing experiments of tumor cell DNA homozygously deleted for MTS1 with DNA in which neither copy of the gene was deleted only gave rise to a signal at contamination levels greater than 30% and could discriminate homozygous and hemizygous loss. These studies support the recent findings that mechanisms other than hemi- and homozygous deletion are most likely responsible for the loss of MTS1 gene product in pituitary tumors (M. Woloschak et al., Cancer Res., 56: 2493-2486, 1996.). These data show that losses on either side of 9p21-22, both or either of which may be deleted, are involved in pituitary tumorigenesis and provide evidence for distinct suppressor gene loci, in addition to MTS1, on chromosome 9p. 相似文献
53.
OBJECTIVE: To evaluate the relationship between morphologic findings seen on high-resolution computed tomography (HRCT) of the lung and regional lung perfusion depicted on single photon-emission computed tomography (SPECT) pulmonary perfusion imaging in patients with cystic fibrosis. MATERIALS AND METHODS: Ten HRCT and 10 technetium-99 m macroaggregated albumin SPECT pulmonary perfusion imaging studies were performed on eight young adult patients who were considered to be clinically well and have mild to moderate cystic fibrosis. HRCT scans of the chest were evaluated using a CT scoring system which included grading of bronchiectasis, peribronchial thickening, hyperlucency, bullae, collapse/consolidation, and mucus plugging. Each lung was divided into six anatomic zones which were independently scored. A lung perfusion score (between 0 and 100), reflecting the percentage of compromised lung, was estimated for each zone. Axial lung perfusion SPECT images were matched anatomically to HRCT images. Lung function was considered compromised when the counts per pixel were less than 25 % of the count level seen in an area of the same patient's lung which was judged to be normal. RESULTS: There was a statistically significant relationship (P = 0.0001) between HRCT total scores and SPECT lung perfusion scores as well as between hyperlucency scores by HRCT and the SPECT lung perfusion scores. However, the HRCT score was a poor predictor of the lung perfusion score in zones with intermediate HRCT scores, which constituted 106 of 120 zones. CONCLUSION: Morphologic changes depicted by HRCT correlate with decreased lung pefusion on SPECT. However, HRCT changes accurately predict regional lung function only in the most normal and severely diseased lung zones. 相似文献
54.
55.
ShSh Eliava IuM Filatov OB Sazonova AIu Lubnin IN Rudnev AS Khe?reddin 《Canadian Metallurgical Quarterly》1996,41(4):3-6
Internal carotid aneurysms in the ophthalmic area presents a challenge in cerebrovascular neurosurgery. The study was undertaken to provide evidence for the application of intravascular aspiration during direct surgical interventions and to outline their variants used at the N. N. Burdenko Institute of Neurosurgery. The study included 4 (3 females and 1 male) patients with large and giant internal carotid aneurysms of parasphenoidal site who were treated at the Institute. Clipping of the aneurysmal neck was made by employing intravascular blood aspiration from the aneurysm. The technique proved to be effective in proximal monitoring the carotid artery at surgery. It substantially reduced aneurysmal blood flow and wall tension, thus favouring aneurysmal dissection to make clipping. 相似文献
56.
57.
An anonymous questionnaire inquiry performed among 324 school teachers in the Randers area with the purpose of elucidating teachers' knowledge about asthma is presented. To a series of statements about asthma, the teachers should answer yes, no or don't know. A limited knowledge about asthma in children was found. The knowledge about medicamental treatment was particularly limited. Only 57 per cent knew that wheezing after physical exertion is a strong indicator of asthma. Only five per cent had received proper instruction. This latter group had a significantly better knowledge of medical treatment (p < 0.0001-0.05). It is recommended that instruction in children's diseases, especially asthma should be reintroduced in teachers' training colleges. 相似文献
58.
An overview of the most important older and newer results regarding the relationship between violent and criminal behavior on the one hand and schizophrenic illness on the other hand is presented. Four different methods are available to study this relationship: (i) study of the prevalence of mental illness in criminal/violent populations; (ii) study of criminality/violence rate in samples of psychiatric patients; (iii) study of criminality/violence in community samples comparing mental patients with non-patient community residents; and (iv) study of criminality/violence in birth cohorts prospectively. All these methods have been used; but samples composed of schizophrenic patients exclusively were only exceptionally studied. The results indicate that there is a modest but significant relationship between schizophrenia and violence and crime which persists even after controlling for demographic and socio-economic variables. The probability of schizophrenic patients to be criminal or violent depends on the acuity of their illness and is increased by their use of psychoactive substances. Generally, however, violent and criminal acts directly attributable to mental illness account only for a very small proportion of such acts in the society. 相似文献
59.
A. F. Ginevskii A. S. Dmitriev D. A. Ovechkin 《Journal of Engineering Physics and Thermophysics》1991,60(4):501-505
Stability has been examined for an ordered chain of monodisperse droplets under vacuum, which interact one with another via the evaporating molecules.Translated from Inzhenerno-fizicheskii Zhurnal, Vol. 60, No. 4, pp. 656–660, April, 1991. 相似文献
60.
BR Crane AS Arvai DK Ghosh C Wu ED Getzoff DJ Stuehr JA Tainer 《Canadian Metallurgical Quarterly》1998,279(5359):2121-2126
Crystal structures of the murine cytokine-inducible nitric oxide synthase oxygenase dimer with active-center water molecules, the substrate L-arginine (L-Arg), or product analog thiocitrulline reveal how dimerization, cofactor tetrahydrobiopterin, and L-Arg binding complete the catalytic center for synthesis of the essential biological signal and cytotoxin nitric oxide. Pterin binding refolds the central interface region, recruits new structural elements, creates a 30 angstrom deep active-center channel, and causes a 35 degrees helical tilt to expose a heme edge and the adjacent residue tryptophan-366 for likely reductase domain interactions and caveolin inhibition. Heme propionate interactions with pterin and L-Arg suggest that pterin has electronic influences on heme-bound oxygen. L-Arginine binds to glutamic acid-371 and stacks with heme in an otherwise hydrophobic pocket to aid activation of heme-bound oxygen by direct proton donation and thereby differentiate the two chemical steps of nitric oxide synthesis. 相似文献