全文获取类型
收费全文 | 830篇 |
免费 | 0篇 |
国内免费 | 1篇 |
专业分类
化学工业 | 6篇 |
石油天然气 | 2篇 |
无线电 | 1篇 |
一般工业技术 | 1篇 |
冶金工业 | 820篇 |
自动化技术 | 1篇 |
出版年
2011年 | 2篇 |
2005年 | 1篇 |
2003年 | 4篇 |
1999年 | 26篇 |
1998年 | 253篇 |
1997年 | 155篇 |
1996年 | 99篇 |
1995年 | 37篇 |
1994年 | 44篇 |
1993年 | 55篇 |
1992年 | 3篇 |
1991年 | 6篇 |
1990年 | 1篇 |
1989年 | 4篇 |
1988年 | 7篇 |
1987年 | 4篇 |
1986年 | 5篇 |
1985年 | 10篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 12篇 |
1978年 | 3篇 |
1977年 | 26篇 |
1976年 | 64篇 |
1975年 | 2篇 |
1959年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有831条查询结果,搜索用时 875 毫秒
51.
52.
Two simple chromenes with anti-JH activity have been isolated and identified from the bedding plant Ageratum houstoianum. By contact and fumigation these compounds induce precocious metamorphosis and sterilization in several hemipteran species of insects. Certain holometabolous species are sterilized, forced into diapause, or both. Each of these biological actions is equivalent to removal of the corpora allata, which produce the JH's, and is reversible by treatment with exogenous JH. Thus, the action of these compounds is to stop the production or depress the titer of the JH's. To our knowledge, this is the first discovery of anti-JH, and we hope it will guide the way to the emergence of a fourth generation of safe and insect-specific pesticides. 相似文献
53.
54.
PURPOSE: To determine whether a hooked appearance of the soft palate can be seen in awake patients with snoring with or without obstructive sleep apnea syndrome (OSAS) on cephalometric radiographs and computed tomographic (CT) scans. MATERIALS AND METHODS: One hundred thirty-one patients with snoring underwent cephalometric radiography, with which the posterior airway space, soft palate length and width, and distance between the hyoid bone and mandibular plane were measured, and/or pharyngeal CT, with which the luminal areas of the airway at the naso-, oro-, and hypopharyngeal levels were measured. RESULTS: Of the 131 patients, 96 had OSAS, and 35 had snoring. Nine of 96 patients with OSAS had soft palate hooking on awake pharyngeal CT or cephalometric images. No patient with snoring alone had hooking. Patients with hooking had a larger posterior airway space than did patients with OSAS without hooking (P = .05), and an enlarged (> or = 15-mm) posterior airway space was more frequent in patients with hooking (eight of nine patients) than in those without hooking (34 of 87) (P < .01). Oropharyngeal and hypopharyngeal areas were significantly larger in patients with hooking than in patients without hooking or in patients with snoring (P < or = .04). CONCLUSION: Cephalometric radiography and CT can demonstrate hooking of the soft palate in awake patients. This finding indicates a high risk for OSAS. 相似文献
55.
JM Wallace SJ Ferguson P Loane M Kell S Millar WS Gillmore 《Canadian Metallurgical Quarterly》1997,54(2):85-87
Out of the total number at 200 suspected cases of otomycoses consisting of 40 malnourished and 160 apparently healthy children examined in this study between the months of July and August in Edo State, 64 Cases (32%) were identified to be of fungal aetiology on the basis of positive culture and careful microscopic examination. The state at protein energy malnourishment was deterwined using physicians' comments in their case files. The fungal agents isolated were Aspergillus niger 28 (43.8%); A. fumigatus 4 (25%); Fusarium solari 4 (6.3%); Candida albicans 8 (12.5%); and Hendersonula teruloidea types torn B 5 (6.3%). Of these isolates, A. niger having an solation rate of (43.8%) was found to be the most predominant fungal species associated with otomycosis. 相似文献
56.
Chemical communication in scarab beetles (Coleoptera: Scarabaeidae) is achieved with a wide variety of pheromones, but one typical structure is the gamma-lactone having a long unsaturated hydrocarbon chain. Several species utilize (R, Z)-5-(-)-(oct-1-enyl)-oxacyclopentan-2-one (buibuilactone), (R, Z)-5-(-)-(dec-1-enyl)-oxacyclopentan-2-one and (S, Z)-5-(+)-(dec-1-enyl)-oxacyclopentan-2-one [(R)-japonilure and (S)-japonilure]. Using deuterated precursors, we have demonstrated that these compounds are biosynthesized from fatty acids. (9, 10-d4)-Palmitic acid, (9,10-d4)-stearic acid, (9,10-d2)-palmitoleic acid, (9,10-d2)-oleic acid, (9,10-d2)-8-hydroxypalmitoleic acid and (9,10-d2)-8-hydroxyoleic acid were readily incorporated by female Anomala cuprea into the pheromone molecules, while (Z)-(5, 6-d2)-5-dodecenoic acid and (Z)-(5,6-d2)-5-tetradecenoic acid were not. Therefore, the reaction pathway starts from saturated fatty acids, involves their desaturation, followed by 8-hydroxylation, chain shortening and cyclization. The products obtained from racemic (9,10-d2)-8-hydroxypalmitoleic acid and (9,10-d2)-8-hydroxyoleic acid were also racemic, implying that the steps following hydroxylation were not stereospecific. Perdeuterated palmitic acid was applied to disclose the mechanism of the unique hydroxylation reaction. Retention of all deuterium atoms implied that this reaction was a direct process mediated by a specific fatty acid hydroxylase, and preceding desaturation or epoxidation was not involved. 相似文献
57.
VS Kashyap WS Moore WJ Quinones-Baldrich 《Canadian Metallurgical Quarterly》1999,29(1):90-6; discussion 97-9
OBJECTIVE: The development of carotid atherosclerosis after neck irradiation is well documented. There has been concern about the safety and durability of carotid artery repair through a radiated field. The objective of this report is to describe the immediate and long-term results of a series of cases collected in a 13-year interval. METHODS: From 1984 to 1997, 24 patients underwent 26 carotid artery operations. All the patients had undergone prior radiation therapy at a mean interval of 17 years, with an average radiation dose of 6300 rad. Severe scarring of the skin or radiation fibrosis were present in two thirds of the patients, with 4 patients having permanent tracheostomies. The indications for carotid surgery included cerebral or monocular transient ischemic attack (58%), asymptomatic high-grade stenosis (27%), prior stroke (12%), and tumor invasion of the carotid artery (4%). General anesthesia was used with selective shunting on the basis of carotid artery back pressure or electroencephalography monitoring. Patch angioplasty closure was used in 79% of the patients. The operations included standard carotid endarterectomy (n = 20), external carotid endarterectomy (n = 2), carotid patch angioplasty alone (n = 2), aortocarotid bypass grafting (n = 1), and carotid interposition grafting (n = 1). Four patients required skin grafting or myocutaneous flaps. RESULTS: No deaths or strokes occurred within 30 days of the operations. Six patients had transient cranial nerve palsy, and two had wound infections. The patients were followed from 1 to 156 months, with six patients being followed for longer than 18 months. No strokes were seen at late follow-up examination. Duplex scan examination documented one occlusion, in a patient with primary closure, and two restenoses, one of which necessitated reoperation. The remainder of the grafts were widely patent. CONCLUSIONS: Carotid surgery after neck irradiation is safe and durable. The long-term patency rates and the protection against subsequent neurologic events are similar to the results obtained in the absence of radiation therapy. Problems of wound healing were not found in this series. 相似文献
58.
59.
The purpose of this study was to examine differences in postprandial hypertriglyceridemia (PP-HTG) and low density lipoprotein (LDL) subfraction distribution among groups of men and women with different fitness levels. Fifty-four men and women (ages 30-53 yr) were recruited based on their previous two-year activity level: sedentary (S), recreational exercisers (R), and endurance trained (T). After a 24-h dietary preparation, blood was collected, and LDL subfractions were separated and analyzed for cholesterol (C) and apoprotein B100. Plasma triglyceride (TG) concentration was assessed before and at 2, 4, 6, and 8 h after fat meal. PP-HTG was significantly higher for the S group compared with the two activity groups. LDL3-C and LDL3-apoprotein B100 were significantly higher for the S group compared with the T group and for men compared with women. These findings suggest that both recreational and competitive aerobic training are associated with a lower TG response after a fatty meal. However, higher volume aerobic training may be necessary to reduce the number of dense LDL molecules and their cholesterol content. 相似文献
60.
J Qing VM Maher H Tran WS Argraves RW Dunstan JJ McCormick 《Canadian Metallurgical Quarterly》1997,15(18):2159-2168
Using differential display, we identified an mRNA that is markedly down-regulated in cell line 6A/SB1, derived from a fibrosarcoma formed in an athymic mouse following injection of carcinogen-transformed MSU-1.1 cells. The nontumorigenic parental cell strain, MSU-1.1, expresses high levels of this mRNA. Sequencing of the corresponding cDNA fragment revealed that it corresponded to an expressed sequence tag, which ultimately led to its identification as the fibulin-1D gene. Fibulin-1 is a cysteine-rich, calcium-binding extracellular matrix and plasma protein, which has four isoforms, A-D, derived from alternative splicing. Northern and Western blotting analysis of 16 cell lines established from tumors formed in athymic mice by MSU-1.1-derived cell strains independently transformed in culture showed that 44% exhibited low level or lack of expression of fibulin-1D mRNA and protein. In a similar analysis of 15 malignant cell lines derived from patients, 80% showed low level or no expression. To study the role of fibulin-1D in transformation, we transfected 6A/SB1 cells and a human fibrosarcoma-derived cell line (SHAC) with a fibulin-1D cDNA expression construct. Transfectants displaying high levels of fibulin-1D were isolated and characterized. Elevated expression of fibulin-1D led to reduced ability to form colonies in soft agar and reduced invasive potential as tested in a matrigel in vitro invasion assay. Furthermore, expression of fibulin-1D resulted in a markedly extended latency in tumor formation in athymic mice. These results indicate that low expression of fibulin-1D plays a role in tumor formation and invasion. 相似文献