首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1817篇
  免费   7篇
电工技术   1篇
化学工业   39篇
金属工艺   2篇
机械仪表   4篇
建筑科学   4篇
矿业工程   1篇
能源动力   3篇
轻工业   21篇
水利工程   1篇
无线电   11篇
一般工业技术   16篇
冶金工业   1677篇
自动化技术   44篇
  2022年   5篇
  2021年   2篇
  2017年   4篇
  2014年   2篇
  2013年   2篇
  2012年   7篇
  2011年   6篇
  2010年   2篇
  2009年   7篇
  2008年   4篇
  2007年   7篇
  2006年   3篇
  2005年   3篇
  2004年   3篇
  2003年   5篇
  2002年   5篇
  2001年   5篇
  2000年   6篇
  1999年   41篇
  1998年   463篇
  1997年   266篇
  1996年   182篇
  1995年   123篇
  1994年   102篇
  1993年   97篇
  1992年   14篇
  1991年   19篇
  1990年   20篇
  1989年   29篇
  1988年   27篇
  1987年   29篇
  1986年   22篇
  1985年   22篇
  1984年   7篇
  1983年   6篇
  1982年   10篇
  1981年   14篇
  1980年   23篇
  1978年   8篇
  1977年   62篇
  1976年   134篇
  1975年   5篇
  1974年   4篇
  1973年   2篇
  1969年   1篇
  1964年   2篇
  1962年   1篇
  1959年   1篇
  1955年   1篇
  1943年   1篇
排序方式: 共有1824条查询结果,搜索用时 15 毫秒
151.
This study was conducted to compare gross efficiency (GE), net efficiency (NE), work efficiency (WE), and delta efficiency (DE) between arm crank and cycle exercise at the same relative intensities. Eight college-aged males underwent two experimental trials presented in a randomized counterbalanced order. During each trial subjects performed three intermittent 7-min exercise bouts separated by 10-min rest intervals on an arm or semirecumbent leg ergometer. The power outputs for the three bouts of arm crank or cycle exercise corresponded to 50, 60, and 70% of the mode-specific VO2peak. GE, NE, and WE were determined as the ratio of Kcal.min-1 equivalent of power output to Kcal.min-1 of total energy expended, energy expended above rest and energy expended above unloaded exercise, respectively. DE was determined as the ratio of the increment of Kcal.min-1 of power output above the previous lower intensity to the increment of kcal.min-1 of total energy expended above the previous lower intensity. GE and NE did not differ between arm crank and cycle exercises. However, WE was lower (P < 0.05) during arm crank than cycle exercise at 50, 60, and 70% VO2peak. DE was also lower (P < 0.05) during arm crank than cycle exercise at delta 50-60 and at delta 60-70% VO2peak. It is concluded metabolic efficiency as determined by work and delta efficiency indices was lower during arm crank compared with cycle exercise at the same relative intensities. These findings add to the understanding of the difference in metabolic efficiency between upper and lower body exercise.  相似文献   
152.
A series of substituted indolylalkoxyiminoalkylcarboxylates were found to be potent leukotriene biosynthesis inhibitors. The structure-activity relationships were investigated. Representative potent inhibitors identified were the quinolyl 3a (A-86885) and pyridyl 3b (A-86886) congeners with in vitro IC50s of 21 and 9 nM and in vivo leukotriene inhibition in the rat with oral ED50s of 0.9 and 1.7 mg/kg, respectively.  相似文献   
153.
The in vitro minimal inhibitory concentrations (MIC) and minimal bactericidal concentration (MBC) of roxithromycin and erythromycin against Actinobacillus actinomycetemcomitans were evaluated. Sixty-seven different A. actinomycetemcomitans isolated from periodontal pockets of 101 subjects with different forms of early-onset and adult periodontitis and three reference strains of A. actinomycetemcomitans (ATCC 29522, ATCC 29523, and NCTC 9710) were included in this study. Erythromycin showed poor in vitro activity against A. actinomycetemcomitans; roxithromycin, on the contrary, exhibited good in vitro activity. Moreover, roxithromycin showed the best in vitro antimicrobial activity against 17 serotype a and 12 serotype c subpopulations of A. actinomycetemcomitans; against 38 serotype b subpopulation of A. actinomycetemcomitans, roxithromycin was consistently active. Roxithromycin exhibited MBC values usually equal to, or one-fold higher than MIC values. All the MBC values of erythromycin were three- to four-fold higher than the respective MIC result. Since roxithromycin is characterized by high concentrations in serum and good penetration and diffusion into gingival tissue, it could be expected to pass into the gingival crevicular fluid at levels sufficiently high to inhibit A. actinomycetemcomitans in vivo. These data indicate that roxithromycin might be a potential candidate for therapeutic trials in patients with A. actinomycetemcomitans-associated periodontitis.  相似文献   
154.
155.
156.
157.
PURPOSE: Posterior lens fragments after phacoemulsification can be a serious complication of cataract surgery. This study is designed to evaluate the clinical features of eyes after pars plana vitrectomy has been performed to remove posteriorly dislocated lens fragments after phacoemulsification. METHODS: The authors performed a retrospective chart review of 126 consecutive eyes of 126 patients with dislocated lens fragments after phacoemulsification, managed with pars plana vitrectomy at Associated Retinal Consultants of Michigan. These eyes were operated on from January 1986 through January 1996. RESULTS: The relation of the intervals between cataract surgery and vitrectomy to various postoperative clinical parameters was studied. Clinical features at presentation included elevated intraocular pressure (IOP over 25 mmHg) in 52.4% of the eyes, uveitis in 69.6%, and corneal edema in 50.8%. Initial visual acuity was 20/400 or worse in 73.8% of the eyes. The mean preoperative visual acuity was 20/278 (median, 20/400), whereas the mean final visual acuity was 20/40 (median, 20/50) after a mean follow-up of 18.9 months. Retinal detachments were found in 20 eyes: 7 before vitrectomy and 13 during or after it. After surgery, 44% of eyes achieved a final visual acuity of 20/40 or better and 90% were 20/400 or better. The distribution of best-corrected final visual acuities among the eyes showed statistically significant differences based on the type of intraocular lens (IOL) used, with posterior chamber IOL greater than anterior chamber IOL, and anterior chamber IOL greater than aphakia. Reasons for a poor visual outcome included persistent corneal edema (four eyes), retinal detachment (two eyes), central retinal vein occlusion (two eyes), age-related macular degeneration (two eyes) glaucoma (one year), and endophthalmitis (one eye). CONCLUSIONS: There were no statistically significant differences between early (< 7 days) and delayed (8 days or more) vitrectomy when increased IOP, corneal edema, choroidal effusions, cystoid macular edema, and visual acuity were analyzed. The use of vitrectomy to remove posteriorly dislocated lens fragments has been shown to be an effective treatment method that significantly reduces the inflammatory response and hastens visual recovery.  相似文献   
158.
In situ hybridization of a biotin-labeled specific dopamine1A (D1A) receptor gene oligonucleotide probe combined with computer-assisted image analyzer was used to directly visualize D1A receptor mRNA and quantify the relative mRNA levels in sections of rat aorta and pulmonary and caudal arteries. Positive D1A receptor mRNA signals were found in rat aorta and pulmonary arteries, while no specific signals could be detected in the caudal artery. D1A receptor mRNA was located mainly within the medial layer of aorta, with intimal distribution in the pulmonary artery. The density of D1A receptor mRNA in different vascular beds demonstrated heterogeneity. D1A receptor mRNA levels in the aorta were much higher than those in the pulmonary artery (p < 0.01). These results demonstrate the existence of D1A receptor mRNA in both aorta and pulmonary beds, although with different distribution and density. The results further support the heterogeneity of the D1A receptor in different vascular beds.  相似文献   
159.
The present study was designed to explore mechanisms of amnesia for meaningful auditory material presented during the sleep onset transition. Thirty undergraduate subjects (17 female, 13 male) were presented with auditory stimuli in an oddball paradigm until sleep onset. Subjects were allowed to accumulate either 30 seconds or 10 minutes of sleep, then awakened and tested on free recall and recognition memory for the meaningful stimuli. After 10 minutes of sleep, but not after 30 seconds of sleep, subjects had profound amnesia on free recall for stimuli presented in the 4-minute window prior to sleep onset. Increased beta electroencephalograph (EEG) power during the sleep period correlated positively with recall of stimuli in the 4-minute presleep window. Event-related potential recordings provided suggestive evidence that subjects continued to process the auditory stimuli to some extent during the sleep onset transition. When allowed to sleep for 10 minutes, subjects evidenced a mixed anterograde and retrograde amnesia for auditory stimuli presented in the 4-minute window prior to sleep onset. The results are discussed in terms of stimulus encoding, consolidation, and retrieval.  相似文献   
160.
BACKGROUND: Diagnostic peritoneal lavage (DPL) is used to diagnose intra-abdominal injury in patients with stab wounds and blunt trauma. Because exploratory celiotomy is routinely performed on patients with gunshot wounds to the abdomen, DPL is rarely employed. However, several studies have questioned routine exploration and have drawn attention to the associated morbidity of negative celiotomy. Diagnostic peritoneal lavage is an easily performed and inexpensive test that may be useful in this situation. OBJECTIVE: To evaluate the performance of DPL in the diagnosis of intra-abdominal injury in hemodynamically stable patients with gunshot wounds to the abdomen. DESIGN: A prospective clinical trial. SETTING: Two urban trauma centers. PATIENTS: Patients with gunshot wounds to the abdomen and a systolic blood pressure of at least 90 mm Hg. INTERVENTIONS: Clinical predication of intra-abdominal injury in the emergency department and DPL performed in the operating room before the initiation of celiotomy. Injuries found during the celiotomy were recorded. MAIN OUTCOME MEASURES: The results of the clinical evaluation and DPL were compared with the findings of the celiotomy. RESULTS: Forty-four patients were enrolled into the study. Intra-abdominal injury was present in 32 (73%) of these patients. The senior surgery resident correctly predicted the presence of intra-abdominal injury in 36 (82%) of the patients (sensitivity = 90.0%, specificity = 58.3%, positive predictive value = 85.3%, negative predictive value = 63.6%, phi = 0.52, P < .01) in the emergency department before DPL and celiotomy were performed. Diagnostic peritoneal lavage correctly identified the presence or absence of intra-abdominal injury in 40 (91%) of the patients (positive predictive value = 96.7%, negative predictive value = 78.6%, phi = 0.79, P < .01). CONCLUSIONS: Clinical judgment is highly accurate in separating patients with tangential gunshot wounds to the abdomen from those with intra-abdominal injury but may miss patients with intra-abdominal hemorrhage. Diagnostic peritoneal lavage is highly predictive of the presence of intra-abdominal injury. The return of gross blood on aspiration or a lavage red blood cell count greater than 10 x 10(9)/L should prompt an urgent celiotomy. Missed injuries are rare and most likely to be bowel perforations. Diagnostic peritoneal lavage is an objective test that may augment clinical judgment in selecting hemodynamically stable patients with potential tangential gunshot wounds for observation and is especially useful in identifying intra-abdominal hemorrhage.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号