全文获取类型
收费全文 | 3408篇 |
免费 | 31篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 14篇 |
综合类 | 1篇 |
化学工业 | 245篇 |
金属工艺 | 40篇 |
机械仪表 | 36篇 |
建筑科学 | 41篇 |
能源动力 | 28篇 |
轻工业 | 94篇 |
水利工程 | 16篇 |
石油天然气 | 6篇 |
无线电 | 112篇 |
一般工业技术 | 154篇 |
冶金工业 | 2529篇 |
原子能技术 | 11篇 |
自动化技术 | 113篇 |
出版年
2022年 | 9篇 |
2021年 | 11篇 |
2020年 | 14篇 |
2019年 | 7篇 |
2018年 | 10篇 |
2017年 | 12篇 |
2016年 | 14篇 |
2015年 | 12篇 |
2014年 | 29篇 |
2013年 | 73篇 |
2012年 | 35篇 |
2011年 | 58篇 |
2010年 | 55篇 |
2009年 | 38篇 |
2008年 | 40篇 |
2007年 | 50篇 |
2006年 | 38篇 |
2005年 | 39篇 |
2004年 | 24篇 |
2003年 | 32篇 |
2002年 | 28篇 |
2001年 | 27篇 |
2000年 | 25篇 |
1999年 | 122篇 |
1998年 | 822篇 |
1997年 | 441篇 |
1996年 | 280篇 |
1995年 | 173篇 |
1994年 | 144篇 |
1993年 | 154篇 |
1992年 | 23篇 |
1991年 | 24篇 |
1990年 | 22篇 |
1989年 | 33篇 |
1988年 | 29篇 |
1987年 | 37篇 |
1986年 | 33篇 |
1985年 | 34篇 |
1984年 | 16篇 |
1983年 | 21篇 |
1982年 | 22篇 |
1981年 | 22篇 |
1980年 | 27篇 |
1979年 | 9篇 |
1978年 | 12篇 |
1977年 | 77篇 |
1976年 | 113篇 |
1975年 | 15篇 |
1974年 | 7篇 |
1973年 | 9篇 |
排序方式: 共有3440条查询结果,搜索用时 0 毫秒
51.
Plasma and blood lead concentrations, lead absorption, and lead excretion in nonhuman primates 总被引:2,自引:0,他引:2
EJ O''Flaherty MJ Inskip AP Yagminas CA Franklin 《Canadian Metallurgical Quarterly》1996,138(1):121-130
The effects of pH, temperature, block of energy production, calcium/calmodulin, protein phosphorylation, and cytoskeleton-disrupting agents (cytochalasin D, nocodazole) on the integrity of the membrane skeleton were studied in polarized MDCK cells. The intracellular distributions of alpha-fodrin, actin, and ankyrin were monitored by immunofluorescence microscopy. The membrane skeleton, once assembled, seemed to be quite stable; the only factors releasing alpha-fodrin from the lateral walls were the acidification of the cytoplasm and the depletion of extracellular calcium ions. Upon cellular acidification, some actin was also released from its normal location along the lateral walls and was seen in colocalization with alpha-fodrin in the cytoplasm, whereas ankyrin remained associated with the lateral walls. No accumulation of plasma membrane lipids was observed in the cytoplasm of acidified cells, as visualized by TMA-DPH. These results suggest that the linkages between the fodrin-actin complex and its membrane association sites are broken upon acidification. The pH-induced change in alpha-fodrin localization was reversible upon restoring the normal pH. Reassembly of the membrane skeleton, however, required temperatures above +20 degrees C, normal energy production, proper cell-cell contacts, and polymerized actin. Release of alpha-fodrin from the lateral walls to the cytoplasm was also observed upon depletion of extracellular calcium ions. This change was accompanied by the disruption of cell-cell contacts, supporting the role of proper cell-cell contacts in the maintenance of the membrane skeleton polarity. These results suggest that local alterations of the cytoplasmic pH and calcium ion concentration may be important in regulating the integrity of the membrane skeleton. 相似文献
52.
53.
54.
This study examined the effects of instructional match and content overlap on students' ability to generalize from passage reading instruction. Four students with mild disabilities served as participants. Using a multielement design, students were instructed with passages at two levels of text difficulty (instructionally matched vs. instructionally mismatched), and generalization was assessed with passages at two levels of similarity to those instructed (low vs. high content overlap). Results indicated that students' oral reading accuracy and fluency showed the greatest degree of generalization when instructional materials were matched to the students' skill level and assessment materials were similar to those used during instruction. Moreover, these results were maintained at 1-month follow-up. The implications of these findings for classroom reading instruction and the assessment of students' reading skills are discussed. 相似文献
55.
GJ Wetscher G Perdikis DH Kretchmar RG Stinson D Bagchi EJ Redmond TE Adrian RA Hinder 《Canadian Metallurgical Quarterly》1995,40(6):1297-1305
Free radical-mediated esophagitis was studied during duodenogastroesophageal reflux (mixed reflux) or acid reflux in rats. The influence of reflux on esophageal glutathione levels was also examined. Mixed reflux caused more gross mucosal injury than acid reflux. Gross mucosal injury occurred in the mid-esophagus. Total glutathione (GSH) in the esophageal mucosa of control rats was highest in the distal esophagus. The time course of esophageal GSH in rats treated by mixed reflux showed a significant decrease 4 hr after initiation of reflux, followed by a significant increase from the 12th hour on. Mucosal GSH was increased in both reflux groups after 24 hr but significantly more so in the mixed than in the acid reflux group. The free radical scavenger superoxide dismutase (SOD) prevented esophagitis and was associated with decreased GSH levels. GSH depletion by buthionine sulfoximine (BSO) prevented esophagitis and stimulated SOD production in the esophageal mucosa. It is concluded that gastroesophageal reflux is associated with oxidative stress in the esophageal mucosa. The lower GSH levels in the mid-esophagus may predispose to damage in this area. Duodenogastroesophageal reflux causes more damage than pure acid reflux. Oxidative stress leads to GSH depletion of the esophageal mucosa in the first few hours following damage but then stimulates GSH production. GSH depletion by BSO does not worsen esophagitis since it increases the esophageal SOD concentration. 相似文献
56.
57.
GR Swanwick RF Coen BA Lawlor D O'Mahony JB Walsh D Coakley 《Canadian Metallurgical Quarterly》1996,8(3):413-424
Despite new developments in the concept of vascular dementia, the Hachinski Ischemic Score (HIS) and its modified versions continue to be widely used in the clinical differentiation of Alzheimer's disease (AD) and ischemic vascular dementia (IVD). The sensitivity of the HIS and two modified versions in the diagnosis of AD, IVD, and single infarcts in a large, geriatric population with mild cognitive impairment (N = 100) was evaluated. Sensitivity for identification of AD was greater than 90% but was less than 70% for IVD. Over one third of patients with one or more infarcts on computed tomographic brain scans and 63% of mixed cases were classified as having probable AD. It is concluded that ischemic scores may be useful at predicting prevalence rates if individual case accuracy is ignored. Despite being sensitive to identifying AD, ischemic scores are insensitive to both cerebral infarction and IVD and cannot reliably exclude IVD. Finally, patients with mixed dementia should not be expected to have intermediate scores. 相似文献
58.
EJ Raubenheimer JM Brown DB Rama MJ Dreyer PD Smith J Dauth 《Canadian Metallurgical Quarterly》1998,43(8):641-647
OBJECTIVES: The purpose of the present study was to compare the inclination of the occlusal plane with occlusal guidance as a contributing factor to masticatory movement. METHODS: Masticatory movements of 41 young adults were measured using a 3-D mandibular movement analysing system. The inclination of the occlusal plane was measured in the sagittal plane using a 3-D digitizer. The contribution of the occlusal guidance and the inclination of the occlusal plane to the direction of the masticatory path of closure was evaluated at various closing levels. RESULTS: The masticatory path of closure outside the intercuspal range was influenced mainly by the inclination of the occlusal plane, and the masticatory path of closure near the intercuspal range was only influenced by occlusal guidance. The so-called gliding type masticatory pattern was observed predominantly in subjects with a posteriorly inclined occlusal plane. In contrast, a chopping type masticatory pattern was observed predominantly in subjects with an anteriorly inclined occlusal plane. CONCLUSIONS: The contribution of the inclination of the occlusal plane to masticatory movement was greater than that of occlusal guidance throughout the closing phase except near the intercuspal range. 相似文献
59.
JR Council EJ Smith J Kaster-Bundgaard BA Gladue 《Canadian Metallurgical Quarterly》1997,39(4):258-265
We surveyed hypnosis researchers and Institutional Review Boards (IRBs) with regard to the ethical evaluation of research protocols. Researchers and IRB administrators were independently surveyed within the same institutions. Both objective and free response items were used to address substantive issues such as deception and at-risk populations, as well as practical matters such as paperwork. Parallel questions allowed a point-counterpoint between researchers and IRBs. Overall, the results suggest that IRBs do not treat hypnosis research differently than other types of research. We end with recommendations for facilitating interactions between hypnosis researchers and their IRBs. 相似文献
60.
BACKGROUND: Early diagnosis and treatment of intra-abdominal pathology in critically ill intensive care unit (ICU) patients remains a clinical challenge. The objective of this study is to assess the feasibility of portable, bedside diagnostic laparoscopy (DL) in the ICU for patients suspected of intra-abdominal pathology, and to contrast its accuracy with diagnostic peritoneal lavage (DPL). METHODS: All adult ICU patients for whom a general surgery consultation was requested were eligible. Patients with a recent laparotomy or obvious peritonitis were excluded. All procedures were performed in the ICU. RESULTS: Over a consecutive 16-month period, 12 patients underwent DPL/DL. Ages ranged from 28 to 88 (mean, 72) years. Causative findings were disclosed by DL in five patients, (42%) including intestinal ischemia in two. Perforated diverticulitis, thickened terminal ileum, and nonpurulent peritonitis were found in one patient each. All patients with findings by DL had a positive DPL (WBC > 200 cells/mm3), and one negative laparoscopy was positive by lavage. The average length of time to perform DPL was 14 min, and to complete DL 19 min. One patient underwent laparotomy based on DPL/DL and survived along with three others with negative DPL/DL. Eight patients died (67%), four from their surgically untreated intra-abdominal pathology. One patient sustained a procedure-related complication of bradycardia and high ventilatory airway pressures. Peak airway pressures increased an average of 8 mmHg and were significantly higher (p < 0. 001) than pre-DL pressures without any significant change in end-tidal CO2 or pCO2. There were no statistically significant hemodynamic changes based on mean arterial pressure (MAP), central venous pressure (CVP), or pulmonary artery diastolic pressure (PADP). CONCLUSIONS: Bedside laparoscopy can be performed rapidly and safely in the ICU. In predicting the need for laparotomy, DL was more accurate than DPL. 相似文献