全文获取类型
收费全文 | 2251篇 |
免费 | 54篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 13篇 |
综合类 | 1篇 |
化学工业 | 138篇 |
金属工艺 | 19篇 |
机械仪表 | 57篇 |
建筑科学 | 38篇 |
矿业工程 | 7篇 |
能源动力 | 20篇 |
轻工业 | 83篇 |
水利工程 | 6篇 |
无线电 | 99篇 |
一般工业技术 | 184篇 |
冶金工业 | 1535篇 |
原子能技术 | 2篇 |
自动化技术 | 106篇 |
出版年
2023年 | 6篇 |
2022年 | 5篇 |
2021年 | 30篇 |
2020年 | 13篇 |
2019年 | 11篇 |
2018年 | 16篇 |
2017年 | 22篇 |
2016年 | 21篇 |
2015年 | 24篇 |
2014年 | 36篇 |
2013年 | 56篇 |
2012年 | 54篇 |
2011年 | 72篇 |
2010年 | 43篇 |
2009年 | 53篇 |
2008年 | 31篇 |
2007年 | 40篇 |
2006年 | 30篇 |
2005年 | 21篇 |
2004年 | 29篇 |
2003年 | 30篇 |
2002年 | 13篇 |
2001年 | 14篇 |
2000年 | 10篇 |
1999年 | 64篇 |
1998年 | 468篇 |
1997年 | 251篇 |
1996年 | 187篇 |
1995年 | 132篇 |
1994年 | 84篇 |
1993年 | 89篇 |
1992年 | 10篇 |
1991年 | 19篇 |
1990年 | 28篇 |
1989年 | 34篇 |
1988年 | 32篇 |
1987年 | 19篇 |
1986年 | 13篇 |
1985年 | 12篇 |
1983年 | 3篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1980年 | 15篇 |
1979年 | 3篇 |
1978年 | 5篇 |
1977年 | 44篇 |
1976年 | 85篇 |
1975年 | 4篇 |
1973年 | 3篇 |
1890年 | 4篇 |
排序方式: 共有2308条查询结果,搜索用时 281 毫秒
1.
Woo‐Seok Cheong 《ETRI Journal》2003,25(6):503-509
Selective epitaxial growth (SEG) of silicon has attracted considerable attention for its good electrical properties and advantages in building microstructures in high‐density devices. However, SEG problems, such as an unclear process window, selectivity loss, and nonuniformity have often made application difficult. In our study, we derived processing diagrams for SEG from thermodynamics on gas‐phase reactions so that we could predict the SEG process zone for low pressure chemical vapor deposition. In addition, with the help of both the concept of the effective supersaturation ratio and three kinds of E‐beam patterns, we evaluated and controlled selectivity loss and nonuniformity in SEG, which is affected by the loading effect. To optimize the SEG process, we propose two practical methods: One deals with cleaning the wafer, and the other involves inserting dummy active patterns into the wide insulator to prevent the silicon from nucleating. 相似文献
2.
Norton NBD 200 silicon nitride ceramics were implanted with sodium to a dose of 7.0×1015cm-2 at 72 keV (1 at% peak sodium content at 100 nm). The sodium-implanted samples were further implanted with aluminium to 7.3×1015cm-2 at 87 keV (1 at% peak aluminium content at 100 nm). The implanted and unimplanted samples were oxidized in 1 atm dry oxygen
at 1100 and 1300°C for 2–6 h. Profilometry and scanning electron microscopy measurements indicated that sodium implantation
led to up to a two-fold increase in the oxidation rate of silicon nitride. The sodium effect was effectively neutralized when
aluminium was co-implanted. The opposite effects of sodium and aluminium on the oxidation resistance of silicon nitride can
be attributed to their different roles in modifying the structure and properties of the oxide formed.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
3.
AG Niessen JG Bollemeijer RJ de Keizer PH de Meijer 《Canadian Metallurgical Quarterly》1994,138(15):770-775
OBJECTIVE: To assess how often the aetiology is established in patients with uveitis, what systemic disease are found and what is the contribution of the internist to the diagnostic process. DESIGN: Retrospective study. SETTING: University Hospital Leiden, the Netherlands. METHOD: From January 1987 to April 1992, 342 patients presented with uveitis. All patients underwent a standard ophthalmological examination. Referral to an internist and individualised laboratory screening followed in patients with recurrent, chronic, bilateral or panuveitis. Recorded were: ophthalmological data, results of laboratory screening, results of analysis by the internist, final diagnosis and presence of systemic disease. RESULTS: 149 (44%) patients were examined by the internist, 18 (5.2%) were seen by another specialist. In 169 (49%) patients a specific diagnosis was made. 74 (22%) had a systemic disease, 74 a primary ocular disease. In 28 (8%) a systemic disease was presumed (5% were HLA-B27 positive, 3% had abnormal laboratory results); 5 (1%) patients had endophthalmitis as a complication of a septic process. CONCLUSION: In approximately 1/3 of the patients with uveitis a systemic disease was found. Examination by the internist tailored to the individual patient is essential in the evaluation of uveitis patients. 相似文献
4.
5.
MD Goldberg JR Canvin P Freestone C Andersen D Laoudj PH Williams IB Holland V Norris 《Canadian Metallurgical Quarterly》1997,79(6):315-322
In the bacterium Escherichia coli, H-NS-(H1, H1a) is a heat-stable protein with a molecular mass of 15.5 kDa involved in nucleoid organisation and gene regulation linked to certain signal transduction pathways. We have shown that, following addition of preparations of everted inner membrane vesicles, heat-stable cleavage products of approximately 10 kDa of H-NS are formed in vitro from newly synthesised, radio-labelled H-NS and from purified H-NS. The 15.5 kDa protein and its cleavage products were also recovered from a minicell system. These results raised the possibility that cleavage of H-NS is physiologically significant. However, the cleavage of H-NS observed appears to occur during cell breakage and to depend on the method of protein extraction and the presence of the outer membrane protease, OmpT. Nevertheless, the results indicate that H-NS may contain at least two separate domains with cleavage occurring between these domains at a preferred OmpT site. Failure to take account of H-NS cleavage in sample preparation and analysis can lead to serious underestimation of H-NS levels. 相似文献
6.
Rh/Lil/SnR4 is an effective catalyst system for the conversion of methyl formate to acetic acid under carbon monoxide pressure. The effects
of solvent and initial CO partial pressure on the turnover rate of the reaction were investigated. The possibility of replacing
some of the iodide promoters by tin compounds has been probed. 相似文献
7.
Acute and chronic antidepressant drug treatments respectively decrease and increase the aggressive behaviour of resident rats during encounters with unfamiliar conspecifics. We have now examined the effect of the 5-hydroxytryptamine1A receptor antagonist, WAY-100635, on fluoxetine-, paroxetine- or venlafaxine-induced changes in aggression. WAY-100635 (0.1 mg/kg), which did not modify behaviour when given alone, potentiated the venlafaxine (5.54 mg/kg)-induced reduction in aggression after acute treatment and, during chronic treatment, accelerated the fluoxetine (0.34 mg/kg/day)-induced increase in aggression, from day 5 to day 2. A similar change in time course was seen with paroxetine (0.33 mg/kg/day), although the increase in aggression was smaller. Venlafaxine (5.54 mg/kg/day, alone or co-administered with WAY-100635) increased aggression by day 2. During chronic treatment, therefore, venlafaxine, at the dose used, had a more rapid onset of action than either fluoxetine or paroxetine, whereas the fluoxetine- and paroxetine-, but not the venlafaxine-, induced increase in aggression was accelerated by WAY-100635. These studies further support the hypothesis that selective blockade of the 5-hydroxytryptamine1A receptor augments the effects of antidepressant drugs in an animal model predictive of antidepressant activity, presumably by concomitant blockade of the somatodendritic 5-hydroxytryptamine1A autoreceptor-mediated negative feedback system of serotonergic neurones. 相似文献
8.
9.
Temporal order and functional analysis of mutations within the Fli-1 and p53 genes during the erythroleukemias induced by F-MuLV 总被引:1,自引:0,他引:1
JC Howard S Yousefi G Cheong A Bernstein Y Ben-David 《Canadian Metallurgical Quarterly》1993,8(10):2721-2729
The erythroleukemias induced by Friend murine leukemia virus (F-MuLV) result from the accumulation of a number of genetic changes, including activation of the Fli-1 proto-oncogene and inactivation of the p53 tumor suppressor gene. We have determined the temporal order of mutation of the genes involved in this multistage malignancy, by serial in vivo transplantation of F-MuLV induced primary erythroleukemias into syngenic Balb/c mice. These primary tumors are capable of growing when transplanted into syngenic mice, but die after several days of in vitro culture. From the transplanted tumors grown in syngenic mice, erythropoietin-dependent cell lines were established in culture that are clonally related to cells in the primary tumors. We show that retroviral insertional activation of the Fli-1 ets family member is the first detectable genetic event in F-MuLV induced primary erythroleukemias. Mutations in the p53 gene were observed in the Epo-dependent cell lines but not in the transplanted erythroleukemias used to establish these cell lines in culture. These data suggest that activation of Fli-1 plays an important role in the early stages of F-MuLV-induced leukemia, perhaps by altering the self-renewal probabilities of erythroid progenitor cells and that p53 mutations immortalize these cells, enabling them to grow in vitro in the presence of Epo. 相似文献
10.
Wilhelm Conrad Roentgen's discovery of the X-ray one century ago has been ranked in importance with the discovery and development of anesthesia and the discovery of microorganisms and their role in disease. Roentgen's scientific devotion and the persistence of C. Edmund Kells, who took Roentgen's discovery and applied it to dentistry, had a great impact on how dentists practice today. 相似文献