全文获取类型
收费全文 | 2135篇 |
免费 | 8篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 5篇 |
化学工业 | 14篇 |
金属工艺 | 2篇 |
机械仪表 | 4篇 |
建筑科学 | 10篇 |
能源动力 | 10篇 |
轻工业 | 46篇 |
水利工程 | 2篇 |
石油天然气 | 2篇 |
无线电 | 18篇 |
一般工业技术 | 41篇 |
冶金工业 | 1943篇 |
原子能技术 | 1篇 |
自动化技术 | 46篇 |
出版年
2021年 | 2篇 |
2019年 | 4篇 |
2018年 | 2篇 |
2017年 | 2篇 |
2016年 | 3篇 |
2015年 | 3篇 |
2014年 | 6篇 |
2013年 | 6篇 |
2012年 | 11篇 |
2011年 | 12篇 |
2010年 | 7篇 |
2009年 | 8篇 |
2008年 | 8篇 |
2007年 | 12篇 |
2006年 | 13篇 |
2005年 | 10篇 |
2004年 | 11篇 |
2003年 | 15篇 |
2002年 | 14篇 |
2001年 | 10篇 |
2000年 | 11篇 |
1999年 | 60篇 |
1998年 | 579篇 |
1997年 | 331篇 |
1996年 | 225篇 |
1995年 | 106篇 |
1994年 | 114篇 |
1993年 | 128篇 |
1992年 | 19篇 |
1991年 | 22篇 |
1990年 | 28篇 |
1989年 | 25篇 |
1988年 | 21篇 |
1987年 | 16篇 |
1986年 | 20篇 |
1985年 | 16篇 |
1984年 | 5篇 |
1983年 | 6篇 |
1982年 | 11篇 |
1981年 | 15篇 |
1980年 | 13篇 |
1978年 | 7篇 |
1977年 | 65篇 |
1976年 | 126篇 |
1975年 | 7篇 |
1974年 | 1篇 |
1972年 | 2篇 |
1967年 | 1篇 |
1966年 | 1篇 |
1955年 | 3篇 |
排序方式: 共有2144条查询结果,搜索用时 15 毫秒
91.
This study quantified Escherichia coli (EC) and enterococci (ENT) in beach waters and dominant source materials, correlated these with ambient conditions, and determined selected EC genotypes and ENT phenotypes. Bathing-water ENT criteria were exceeded more frequently than EC criteria, providing conflicting interpretations of water quality. Dominant sources of EC and ENT were bird feces (10(8)/d/bird), storm drains (10(7)/d), and river water (10(11)/d); beach sands, shallow groundwater and detritus were additional sources. Beach-water EC genotypes and ENT phenotypes formed clusters with those from all source types, reflecting diffuse inputs. Some ENT isolates had phenotypes similar to those of human pathogens and/or exhibited high-level resistance to human-use antibiotics. EC and ENT concentrations were influenced by collection time and wind direction. There was a 48-72-h lag between rainfall and elevated EC concentrations at three southern shoreline beaches, but no such lag at western and eastern shoreline beaches, reflecting the influence of beach orientation with respect to cyclic (3-5 d) summer weather patterns. In addition to local contamination sources and processes, conceptual or predictive models of Great Lakes beach water quality should consider regional weather patterns, lake hydrodynamics, and the influence of monitoring method variables (time of day, frequency). 相似文献
92.
In the absence of reliable live animal tests for the presence of BSE in cattle, a number of measures have been applied to exclude specified risk materials (SRM) from the human food chain. However, concerns remain that current practices in the stunning and slaughter of cattle may disseminate central nervous system (CNS) tissue to meat and meat contact surfaces. The objective of this study was to establish the particular risks of CNS tissue dissemination associated with captive bolt stunning and carcass splitting. The study applied enzyme linked immunosorbent assays (ELISAs) in the detection and quantification of two CNS proteins, syntaxin 1b and GFAP. The study observed extensive dispersal of both CNS proteins onto equipment, beef hide and personnel. These results demonstrate that despite the rigorous application of current SRM control policies, normal slaughter practices continue to present significant opportunities for CNS material including BSE prion present in the CNS of any sub-clinically infected cattle to contaminate meat entering the human food chain. 相似文献
93.
Whereas there exists a vast literature investigating consumer satisfaction ratings of various behavioral interventions, the majority of these studies have been limited to analogue conditions, which may compromise utility and generalization. Additionally, most research has failed to explore multiple-source, multiple-setting data in the investigation of treatment acceptability. This study investigated parent, teacher, and child treatment acceptability ratings derived from field-based conjoint behavioral consultation cases. Data indicate that overall, 67 parents (aged 23-54 yrs), 67 teachers (aged 22-57 yrs), and 67 children (aged 5-15 yrs) rated conjoint behavioral consultation-based behavioral interventions as very to highly acceptable. For parents, interventions with a reductive component were rated as more acceptable than interventions using both positive and negative components; no significant differences were found among teacher and child group ratings. For teachers, there was a positive relationship between (a) intervention complexity and treatment acceptability ratings and (b) problem severity ratings and treatment acceptability ratings... (PsycINFO Database Record (c) 2011 APA, all rights reserved) 相似文献
94.
95.
STUDY DESIGN: The canal space of burst-fractured, human cervical spine specimens was monitored to determine the extent to which spinal position affected post-injury occlusion. OBJECTIVE: To test the null hypothesis that there is no difference in spinal canal occlusion as a function of spinal positioning for a burst-fractured cervical spine model. SUMMARY OF BACKGROUND DATA: Although previous studies have documented the effect of spinal positioning on canal geometry in intact cadaver spines, to the authors' knowledge, none has examined this relationship specifically in a burst fracture model. METHODS: Eight human cervical spine specimens (levels C1 to T3) were fractured by axial impact, and the resulting burst injuries were documented using post-injury radiographs and computed tomography scans. Canal occlusion was measured using a custom transducer in which water was circulated through a section of flexible tygon tubing that was passed through the spinal canal. Any impingement on the tubing produced a rise in fluid pressure that was monitored with a pressure transducer. Each spine was positioned in flexion, extension, lateral (and off-axis) bending, axial rotation, traction, and compression, while canal occlusion and angular position were monitored. Occlusion values for each position were compared with measurements taken with the spine in neutral position. RESULTS: Compared with neutral position, compression, extension, and extension combined with lateral bending significantly increased canal occlusion, whereas flexion decreased the extent of occlusion. In extension, the observed mechanism of occlusion was ligamentum flavum bulge caused by ligament laxity resulting from reduced vertebral body height. CONCLUSIONS: Increased compression of the spinal cord after injury may lead to more extensive neurologic loss. This study demonstrated that placing a burst-fractured cervical spine into either extension or compression significantly increased canal occlusion as compared with occlusion in a neutral position. 相似文献
96.
In separate clinical trials, two preparations of recombinant interferon (IFN)-beta, IFN beta-1a and IFN beta-1b, reduced exacerbation rates in relapsing-remitting multiple sclerosis (RR-MS). Further, IFN beta-1a slows the progression of disability in patients with RR-MS. Although they are effective in the treatment of MS, use of these drugs is associated with both class-specific and agent-specific side effects. Class-specific side effects include fever, chills, myalgias, arthralgias, and other flulike symptoms beginning 2 to 6 hours after injection and resolving within 24 hours of injection. Transient worsening of preexisting MS symptoms also occurs infrequently. Agent-specific side effects include injection-site reactions with IFN beta-1b. Simple management strategies can be used to minimize these reactions, including patient education; tailoring the dose and time of administration of IFN-beta; and prescribing appropriate combinations of acetaminophen, non-steroidal anti-inflammatory drugs, and steroids. Although side effects tend to diminish with treatment, successful management allows long-term administration of these drugs to achieve a reduction in disease activity and commensurate improvement in outcomes. 相似文献
97.
98.
The pattern of changes in human bone remodeling produced by raloxifene (60 mg/day) was compared to that of estrogen (given as hormone replacement therapy) in 33 early postmenopausal women randomly assigned to raloxifene, estrogen, or no treatment. Remodeling was measured using calcium tracer kinetic methods employed under a constant diet and full metabolic balance conditions. Studies were performed at baseline and, to detect both early and late remodeling changes, at 4 and 31 weeks of treatment. Both raloxifene and estrogen produced a significant positive calcium balance shift at each treatment measurement point: +74 and +60 mg/day at 4 weeks, and +60 and +91 mg/day at 31 weeks for raloxifene and estrogen, respectively. Externally, this balance change was due to a highly significant fall in the urinary calcium level and marginal improvement in calcium absorption efficiency. Internally, bone resorption was significantly reduced at both measurement points: -64 and -60 mg/day at 4 weeks, and -82 and -162 mg/day at 31 weeks for raloxifene and estrogen, respectively. Bone formation was not significantly affected by either agent at 4 weeks; at 31 weeks, formation was reduced by estrogen, but not by raloxifene. Thus, at 4 weeks, the general pattern of remodeling change was identical for the two agents. At 31 weeks, remodeling suppression was greater for estrogen than for raloxifene; however, remodeling balance was the same for the two agents. We conclude that raloxifene and estrogen affect the bone remodeling apparatus similarly, and that raloxifene, therefore, is acting on bone as an estrogen agonist. 相似文献
99.
100.
The problem of restenosis in blood vessels after balloon angioplasty could not be overcome by the use of metallic stents as had been anticipated. With respect to restenosis, clinical and experimental results now focus the attention on the risk that stents could initiate or potentiate vascular lesions, especially by inhomogenous stent expansion. Here the stent design seems to dominante depending on the use of well rounded structural stent-elements with appropriate surfaces and a material deposition which is compatible with a homogeneous stent expansion. With respect to hemocompatibility the surface quality of the stents is of great importance, too. Coating of surfaces of metallic stents for the enhancement of hemocompatibility might create new risks of blood vessel damages and requires a careful consideration of the co-expansional behaviour of the metallic substrate and the coating material. With these problems in mind the surface coated stent Tensum 3 of the Biotronik company was investigated. 相似文献