全文获取类型
收费全文 | 4100篇 |
免费 | 20篇 |
国内免费 | 12篇 |
专业分类
电工技术 | 13篇 |
综合类 | 15篇 |
化学工业 | 64篇 |
金属工艺 | 16篇 |
机械仪表 | 22篇 |
建筑科学 | 22篇 |
矿业工程 | 15篇 |
能源动力 | 4篇 |
轻工业 | 56篇 |
水利工程 | 5篇 |
石油天然气 | 11篇 |
武器工业 | 1篇 |
无线电 | 34篇 |
一般工业技术 | 61篇 |
冶金工业 | 3740篇 |
原子能技术 | 11篇 |
自动化技术 | 42篇 |
出版年
2022年 | 8篇 |
2021年 | 17篇 |
2020年 | 10篇 |
2019年 | 14篇 |
2018年 | 9篇 |
2017年 | 11篇 |
2016年 | 9篇 |
2015年 | 14篇 |
2014年 | 13篇 |
2013年 | 24篇 |
2012年 | 15篇 |
2011年 | 24篇 |
2010年 | 24篇 |
2009年 | 15篇 |
2008年 | 21篇 |
2007年 | 17篇 |
2006年 | 14篇 |
2005年 | 28篇 |
2004年 | 16篇 |
2003年 | 9篇 |
2002年 | 14篇 |
2001年 | 5篇 |
2000年 | 5篇 |
1999年 | 112篇 |
1998年 | 1222篇 |
1997年 | 712篇 |
1996年 | 414篇 |
1995年 | 251篇 |
1994年 | 196篇 |
1993年 | 211篇 |
1992年 | 40篇 |
1991年 | 28篇 |
1990年 | 42篇 |
1989年 | 37篇 |
1988年 | 47篇 |
1987年 | 39篇 |
1986年 | 39篇 |
1985年 | 39篇 |
1983年 | 4篇 |
1982年 | 14篇 |
1981年 | 21篇 |
1980年 | 29篇 |
1978年 | 16篇 |
1977年 | 85篇 |
1976年 | 157篇 |
1975年 | 12篇 |
1974年 | 4篇 |
1973年 | 3篇 |
1969年 | 4篇 |
1955年 | 3篇 |
排序方式: 共有4132条查询结果,搜索用时 0 毫秒
71.
72.
Detailed active site configuration of a new crystal form of methanol dehydrogenase from Methylophilus W3A1 at 1.9 A resolution 总被引:1,自引:0,他引:1
ZX Xia YN He WW Dai SA White GD Boyd FS Mathews 《Canadian Metallurgical Quarterly》1999,38(4):1214-1220
The three-dimensional structure of a new crystal form of methanol dehydrogenase from Methylophilus W3A1 has been obtained in the presence of substrate using data recorded at a synchrotron. The structure of this approximately 140 kDa heterotetramer, refined at 1. 9 A resolution, reveals the detailed configuration of its redox cofactor, pyrroloquinoline quinone (PQQ). C4, one of the oxygen-bearing atoms of this orthoquinone is in a planar configuration while C5, which bears the other quinone oxygen, is tetrahedral, suggesting that the PQQ is in the semiquinone redox state. The substrate binding site has been identified close to PQQ and to the side chain of Asp297, the putative active site base. The proximity of the hydroxyl of methanol to C5 of PQQ compared to the greater separation of the substrate methyl group from C5 supports the addition-elimination reaction mechanism involving a hemiketal intermediate. 相似文献
73.
MJ Koebbe JA Golden G Bennett RH Finnell SA Mackler 《Canadian Metallurgical Quarterly》1999,59(1):12-19
PURPOSE: To estimate the impact of visual impairment in older Australians on the use of community support services. METHODS: In the Blue Mountains Eye Study, 3654 people aged 49 or older were examined- 82.4% of eligible residents in an area west of Sydney, Australia. Presenting and best-corrected visual acuities were measured using a LogMAR chart. Subjects were categorized as having visual impairment if their better eye read 40 or fewer letters (20/40 or worse). Interview data included marital and other socioeconomic status measures, living status (alone or with spouse or other person), use of community support services, reliance on regular help from nonspouse family members or friends, and perceived ability to go out alone. RESULTS: After adjusting for age, gender, education, living status, walking disability, and health-related factors, for each one-line (five-letter) decrease in best-corrected visual acuity, there was a corresponding increase in reliance on community support services (odds ratio [OR], 1.17; 95% confidence interval, [CI] 1.07-1.28) or combined community and family support (OR 1.22; 95% CI, 1.12-1.32). Visually impaired persons were three times as likely to use regular support services provided by the municipality (OR 3.1; 95% CI, 1.8-5.1). A similar increased reliance on regular help from community, nonspouse family members, or friends was found. Visually impaired persons were also much more likely to state that they thought they were unable to go out alone (OR 6.2; 95% CI, 2.6-14.3). The findings were similar when presenting visual acuity was used to define visual impairment or after subjects with walking disabilities were excluded. Visual impairment seemed to have a greater effect on use of community support services in women than in men. CONCLUSIONS: After adjustment was made for confounding factors, visual impairment was found to affect significantly and negatively the independence of elderly people, particularly older women. Presenting visual acuity closely approximated best-corrected visual acuity in its impact on the use of community support services. 相似文献
74.
Enteric coated dexchlorpheniramine maleate (DCPA) tablets and pellets with varying coating thickness were subjected to several in vitro tests after irradiation by thermal neutrons in a flux of 1. 1 x 10(13) n cm-2 s-1 for 2, 4 or 15 min. The appearance of the tablet formulation changed extensively after exposure of the tablets to pile radiation. The irradiation caused the film to loosen from the surface of the core, indicating the generation of gases during the irradiation process. Already after irradiating the tablets for 2 min the disintegration and dissolution behaviour were significantly changed. The extent of tablet damage increased with increasing time of exposure and increasing thickness of the coating. Compared with the tablet formulation, the cores could resist a larger amount of irradiation since dissolution behaviour of the cores was only affected after 15 min of irradiation. This indicates that the irradiation procedure initially affects the coating of the formulation. Although the dissolution behaviour of the pellet formulations changed significantly after the irradiation procedure, the changes were too small to be attributed exclusively to radiation damage. 相似文献
75.
OBJECTIVES: To determine whether biopsy-detectable transition zone tumors are more common in black than in white men with suspected Stage T1c and T2 prostate cancer. METHODS: We performed a prospective study of transition zone prostate biopsy (TZ biopsy) in 1 78 black and 261 white men who had not undergone previous prostate biopsy and in 61 black and 65 white men who had undergone one benign sextant peripheral zone prostate biopsy (PZ biopsy). RESULTS: The mean age of the 239 black and 326 white study patients was 68.6+/-7.4 and 67.2+/-7.2 years, respectively (P = 0.02), the mean prostate-specific antigen (PSA) was 8.4+/-7.4 and 6.4+/-5.4 ng/mL, respectively (P = 0.003), and the mean PSA density was 0.20+/-0.23 and 0.16+/-0.16 ng/mL/mL, respectively (P = 0.006). Overall, cancer was diagnosed by TZ biopsy only in 7 black men (3%) and in no white men (0%) (P = 0.003). However, cancer detection with a TZ biopsy only was not significantly different in the black and white men when controlled for age, PSA, or PSA density (P>0.90). A TZ biopsy only detected cancer in 1% of patients who had not undergone prior PZ biopsy and in 2% of patients who had undergone prior PZ biopsy. Of the seven cancers detected with TZ biopsy, six (86%) had a Gleason score of 2 to 6. CONCLUSIONS: Prostate cancer detection with a TZ biopsy only is not common and when controlled for confounding variables is the same in black and white men. The preferential use of TZ biopsies in black men is not warranted, and the low diagnostic yield argues against routine use of the biopsy technique in men of either race. 相似文献
76.
MH Skiadopoulos S Surman JM Tatem M Paschalis SL Wu SA Udem AP Durbin PL Collins BR Murphy 《Canadian Metallurgical Quarterly》1999,73(2):1374-1381
77.
78.
79.
80.
Programming and Computer Software - In recent years, the field of image inpainting has developed rapidly, learning based approaches show impressive results in the task of filling missing parts in... 相似文献