全文获取类型
收费全文 | 927篇 |
免费 | 0篇 |
专业分类
化学工业 | 1篇 |
建筑科学 | 3篇 |
石油天然气 | 1篇 |
冶金工业 | 921篇 |
自动化技术 | 1篇 |
出版年
2012年 | 1篇 |
2011年 | 1篇 |
2010年 | 1篇 |
2003年 | 2篇 |
2000年 | 1篇 |
1999年 | 22篇 |
1998年 | 244篇 |
1997年 | 154篇 |
1996年 | 96篇 |
1995年 | 56篇 |
1994年 | 52篇 |
1993年 | 53篇 |
1992年 | 3篇 |
1991年 | 24篇 |
1990年 | 10篇 |
1989年 | 18篇 |
1988年 | 12篇 |
1987年 | 10篇 |
1986年 | 11篇 |
1985年 | 14篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1981年 | 8篇 |
1980年 | 11篇 |
1978年 | 4篇 |
1977年 | 28篇 |
1976年 | 82篇 |
1975年 | 3篇 |
排序方式: 共有927条查询结果,搜索用时 15 毫秒
101.
102.
103.
The objective of the present experiment was to study genetic variation within and among well-defined Japanese quail lines by DNA fingerprinting. The Japanese quail lines included a randombred control line (R1) and lines developed from R1 by divergent selection over 30 generations for 4-wk BW (HW, LW) and total plasma phosphorus (TPP) (HP, LP), a measure of yolk precursor in the blood. In addition, two sublines (HW-HP, HW-LP) of HW, developed in the ninth generation, were included in the analysis. Males of the sublines were selected for increased 4-wk BW whereas females were selected for increased (HW-HP) or decreased (HW-LP) TPP. Sixteen individual DNA samples per line were digested with HaeIII restriction enzyme and hybridized with Jeffreys' 33.6 probe. The DNA fingerprints were analyzed with computer programs designed to measure band sharing (BS). Within lines, BS ranged from 0.384 to 0.525. The BS within the R1 line was less than that of all selected lines, except for the HP and LP lines, indicating that, in general, selection had increased genetic homogeneity within the selected lines. Between lines, BS was less than within lines and the R1 line had the highest average level of BS (0.278) with the other lines. The BS between lines for the selected lines ranged from 0.230 to 0.308 with an average of 0.265. In the comparison of the R1 line with the selected lines, it appeared that selection for increased TPP or decreased BW may have influenced BS levels. The relationships of the HW line with its sublines (HW-HP and HW-LP) were not accurately predicted by the DNA fingerprinting technique used. All lines were separated, as indicated by the genetic distance between lines. 相似文献
104.
OBJECTIVE: Evaluate wound healing of incisions created by the scalpel, electrocautery, CO2 laser, and potassium titanyl phosphate (KTP) laser in the upper aerodigestive tract in an animal model. STUDY DESIGN: Prospective randomized study in an animal model. METHODS: Postoperative oral intake, histologic depth of injury, and tensile mechanical strength were measured in rat tongues after creating incisions using a scalpel, electrocautery, CO2 laser, and KTP laser. An unpaired, two-tailed Student's t-test was used to compare results between the experimental groups. RESULTS: Oral intake, indirectly assessed by postoperative weight loss, by the third postoperative day was significantly decreased in the electrocautery (P = 0.004), CO2 laser (P = 0.001), and KTP laser (P = 0.0001) groups as compared with the scalpel group. The depth of the wound healing, as assessed by histologic examination, was successively greater for the scalpel (75 +/- 13 microm), electrocautery (110 +/- 10 microm), CO2 laser (145 +/- 10 microm), and KTP laser (195 +/- 23 microm) groups. However, this difference was only statistically significant for the CO2 laser (P = 0.006) and KTP laser (P = 0.01) groups relative to the scalpel group. Wounds created by the KTP laser had the lowest strength (76.5 +/- 6.9 kPa) as compared with the CO2 laser (156 +/- 28.4 kPa), electrocautery (153 +/- 15.7 kPa), and scalpel groups (249 +/- 61.8 kPa). This difference was only statistically significant for the KTP laser group (P = 0.02) when compared with the scalpel group. CONCLUSIONS: Wounds created in the upper aerodigestive tract of rats by scalpels result in the least postoperative weight loss, tissue destruction, and decrease in tensile strength, whereas wounds created by the KTP laser demonstrated a significantly greater postoperative weight loss, depth of wounding, and decrease in tensile strength. 相似文献
105.
The development of an antigen presentation system based on the plum pox potyvirus (PPV) is here described. The amino-terminal part of PPV capsid protein was chosen as the site for expression of foreign antigenic peptides. Modifications in this site were engineered to avoid the capability of natural transmission by aphids of this PPV vector. As a first practical attempt, different forms of an antigenic peptide (single and tandem repetition) from the VP2 capsid protein of canine parvovirus (CPV) were expressed. Both chimeras are able to infect Nicotiana clevelandii plants with similar characteristics to wild-type virus and remain genetically stable after several plant passages. The antigenicity of purified chimeric virions was demonstrated, proving the suitability of this system for diagnostic purposes. Moreover, mice and rabbits immunized with chimeric virions developed CPV-specific antibodies, which showed neutralizing activity. 相似文献
106.
WL Hutton DG Fuller WB Snyder RL Fellman WH Swanson 《Canadian Metallurgical Quarterly》1996,103(12):2152-8; discussion 2158-9
PURPOSE: The purpose of the study is to report the problem of a temporal visual field defect occurring after macular hole surgery. METHODS: The authors reviewed the records of 13 patients found to have visual field defects after vitrectomy for macular holes. Fluorescein angiograms (13 patients), optic nerve photographs (13 patients), focal electroretinograms (3 patients), and nerve fiber analyses (8 patients) were performed in patients with visual field defects. RESULTS: An absolute, temporal, usually inferior field defect was noted in 13 patients. In eight patients, the defect was detected because of specific reports or retrospective field examination results. Five patients examined in a prospective manner were found to have field defects. No history of abnormal intraocular pressure or direct trauma to the optic nerve or retinal vessels was identified. Four patients showed optic nerve pallor and three had an anomalous-appearing disc. Focal electroretinograms were of similar amplitude in the involved retina compared to corresponding areas in the healthy fellow eye. Nerve fiber analysis showed a reduction in nerve fiber layer thickness correlating to the visual field defect in those eight patients in which this test was used. CONCLUSION: A significant temporal field defect may occur in patients after otherwise uncomplicated surgery for macular holes. The cause is unclear; however, reductions in nerve fiber layer thickness from the superior and nasal peripapillary area suggest that acute surgical release of the posterior hyaloid and the use of long-acting intraocular gas may in certain patients result in visual field defects. 相似文献
107.
BACKGROUND: Although radiotherapy is an integral part of managing certain types of hematologic malignancies, its effect on the reproductive system are well established. We report a case of successful pregnancy in a patient who received high-dose whole-body irradiation (WBI) (1,575 cGy) as part of her treatment for acute myeloid leukemia (AML). CASE: A 26-year-old woman received high-dose cyclophosphamide accompanied by high-dose (1,575 cGy) WBI as part of her treatment for AML when she was 23 years of age. The patient received oral contraceptives before, during and after treatment. After WBI, the patient developed ovarian failure and amenorrhea, which was confirmed by hormonal evaluation. The amenorrhea persisted for one year. No recurrence of AML was found. The patient was placed on hormone replacement therapy (HRT) because of vasomotor changes. An unexpected pregnancy occurred 14 months later; HRT was discontinued. The patient delivered a normal female infant at 38 weeks of gestation. The infant was followed for eight months; her development appeared to be normal. CONCLUSION: In this case report, it is unclear whether pregnancy resulted from active folliculogenesis remote from radiation therapy or from possible ovarian protection rendered by the use of oral contraceptives. The benefit of oral contraceptives in protecting the ovary from radiation injury is unknown and remains an area for future research. 相似文献
108.
As part of a programme for the implementation of a Smoking Control Policy in our hospital, an open study, without randomization, of 65 hospital workers, who wanted to give up smoking, was carried out. The characteristics of smoking in each subject were recorded. The Fagerstrom Questionnaire was used to measure the degree of dependence on nicotine. The treatment consisted of the daily use of 16 h nicotine patches for 12 weeks. During the first 4 weeks, the patches contained 15 mg of nicotine, for the second 4 weeks, 10 mg, and for the last 4 weeks 5 mg (per patch and day). Five visits were scheduled during the 26 week study period: at the start of the study and after 4, 8, 12 and 26 weeks. The abstinence was checked by measuring carbon monoxide in end-expiratory air. The success rate was 31% after 12 weeks, and decreased to 29% after 26 weeks. In conclusion, the nicotine patches appeared safe and effective in this study. 相似文献
109.
110.