全文获取类型
收费全文 | 2625篇 |
免费 | 1篇 |
国内免费 | 1篇 |
专业分类
化学工业 | 4篇 |
轻工业 | 4篇 |
水利工程 | 1篇 |
一般工业技术 | 3篇 |
冶金工业 | 2612篇 |
自动化技术 | 3篇 |
出版年
2021年 | 1篇 |
2019年 | 2篇 |
2015年 | 1篇 |
2008年 | 1篇 |
2007年 | 1篇 |
2006年 | 1篇 |
2004年 | 1篇 |
2003年 | 3篇 |
1999年 | 75篇 |
1998年 | 874篇 |
1997年 | 501篇 |
1996年 | 256篇 |
1995年 | 166篇 |
1994年 | 151篇 |
1993年 | 164篇 |
1992年 | 10篇 |
1991年 | 19篇 |
1990年 | 19篇 |
1989年 | 33篇 |
1988年 | 29篇 |
1987年 | 21篇 |
1986年 | 21篇 |
1985年 | 22篇 |
1983年 | 5篇 |
1982年 | 12篇 |
1981年 | 16篇 |
1980年 | 22篇 |
1978年 | 3篇 |
1977年 | 55篇 |
1976年 | 137篇 |
1975年 | 2篇 |
1955年 | 2篇 |
1954年 | 1篇 |
排序方式: 共有2627条查询结果,搜索用时 31 毫秒
191.
192.
193.
BACKGROUND: Subvalvular preservation is necessary to maintain left ventricular function, but accidental retention of infected tissue could cause postoperative endocarditis. METHODS: We examined 71 consecutive patients who underwent operation for mitral endocarditis. Endocarditis was uncontrolled and active in 24 patients, partially treated (unfinished antibiotic course) in 17, and healed in 30. RESULTS: Valves were repaired in 17% versus 59% versus 63% and replaced with subvalvular preservation in 25% versus 6% versus 3% of the uncontrolled active, partially treated, and healed groups, respectively. Thirty-day mortality was 29% versus 0% versus 3.3% (p=0.003), total mortality was 46% versus 18% versus 17% (p=0.035), and complications-related mortality was 38% versus 11% versus 13% (p=0.054), respectively. There was a trend toward lower complications-related mortality with subvalvular preservation than without. Postoperative endocarditis occurred in 3 of 30 patients without and 1 of 41 patients with subvalvular preservation. CONCLUSIONS: Postoperative mortality in uncontrolled active mitral endocarditis remains high, but results are good with partially treated or healed endocarditis. Subvalvular preservation improves outcome, does not increase postoperative endocarditis rates, and should be performed whenever feasible. 相似文献
194.
LM McDowell A Schmidt ER Cohen DR Studelska J Schaefer 《Canadian Metallurgical Quarterly》1996,256(1):160-171
The 46 kDa enzyme 5-enolpyruvylshikimate-3-phosphate (EPSP) synthase catalyzes the condensation of shikimate-3-phosphate (S3P) and phosphoenolpyruvate to form EPSP. The reaction is inhibited by N-(phosphonomethyl)-glycine (Glp), which in the presence of S3P, binds to EPSP synthase to form a stable ternary complex. As part of a solid-state NMR characterization of this structure, 15N labels were introduced selectively into the lysine, arginine and histidine residues of EPSP synthase and distances to a 13C label in Glp and to the 31P in S3P and Glp were measured by rotational-echo double-resonance NMR. Three lysine and four arginine residues are in the proximity of the phosphate group of S3P and the carboxyl and phosphonate groups of Glp. A single histidine residue is in the vicinity of the binding site (closer to Glp than to S3P) but is more distant than the lysine and arginine residues. 相似文献
195.
MO Bahtiyar E Seli E Oral LM Senturk TG Zreik A Arici 《Canadian Metallurgical Quarterly》1998,13(12):3492-3495
The peritoneal environment in endometriosis is known to have growth-promoting effects on endometrial cells. To investigate whether follicular fluid, a contributor to the peritoneal fluid, stimulates endometrial cell proliferation, we incubated endometrial stromal cells in culture with various dilutions of follicular fluid obtained from women with or without endometriosis undergoing oocyte retrieval for in-vitro fertilization. Cell proliferation assays were performed using follicular fluid from 28 women (without endometriosis, n = 13; with endometriosis, n = 15) in eight different endometrial stromal cell culture set-ups. Cell proliferation was assessed by a colorimetric method. Maximum cell proliferation was detected when endometrial cells were incubated with 50% dilution of follicular fluid for 48 h. Follicular fluid from women with endometriosis induced significantly higher cell proliferation than follicular fluid from women without endometriosis (P < 0.05). Our findings indicate that follicular fluid contents may contribute to the growth-promoting factors in the peritoneal fluid of women with endometriosis. 相似文献
196.
JL Mankowski DL Carter JP Spelman ML Nealen KR Maughan LM Kirstein PJ Didier RJ Adams M Murphey-Corb MC Zink 《Canadian Metallurgical Quarterly》1998,153(4):1123-1130
We investigated the effects of dietary factors on the pH and the ammonia emission from slurry of growing-finishing pigs. Sixteen male hybrid pigs (80 to 90 kg BW) were allotted to one of four diets based on barley-wheat, tapioca, barley-tapioca, and sugar beet pulp. Diets were formulated to have similar NE and CP contents and a similar lysine:NE ratio. Diets differed in nonstarch polysaccharide content (NSP) and dietary electrolyte balance (dEB). Urine and feces were daily collected quantitatively in metabolism cages and mixed as a slurry at the end of the collection period. After mixing, the pH and the ammonia emission from the slurry were measured daily in a laboratory setup for 7 d at 20 degrees C. The type of diet affected the pH of the slurry and the ammonia emission (P < .001). The pH of the slurry from pigs fed the sugar beet pulp-based diet was .8 unit lower and ammonia emission was 52 to 53% lower than that of the other three diets. The low dEB and high NPS sugar beet pulp-based diet increased the VFA concentration and reduced the pH and ammonia emission from the slurry. We conclude that dietary NSP and dEB influence the pH and ammonia emission from slurry of growing-finishing pigs. 相似文献
197.
Susceptibility to atrial fibrillation: a study in an ovine model of pacing-induced early heart failure 总被引:1,自引:0,他引:1
JM Power GA Beacom CA Alferness J Raman M Wijffels SJ Farish LM Burrell AM Tonkin 《Canadian Metallurgical Quarterly》1998,9(4):423-435
INTRODUCTION: The development of susceptibility to atrial fibrillation (AF) is a common consequence of many forms of cardiovascular disease, especially heart failure. In this study we used a sheep model of pacing-induced stable early heart failure to describe, quantify, and relate the level of susceptibility to AF to changes in structural and electrophysiologic parameters. METHODS AND RESULTS: Epicardial electrodes were implanted on the atria and right ventricles of nine sheep. The AF threshold, atrial vulnerability period, atrial effective refractory period (ERP), and interatrial conduction time were examined during control and over a 6-week period of ventricular pacing at 190 beats/min. Left atrial (LA) area and left ventricular (LV) fractional shortening were monitored using echocardiography. There were significant increases in LA susceptibility to AF (P < 0.0003), LA area (P < 0.0002), and LA ERP400 (P < 0.0002). Rate of increase in LA area was related positively to AF susceptibility (P = 0.02) and inversely to LA ERP400 (P = 0.002). LV fractional shortening decreased to approximately 50% of control value (P < 0.00001). No changes were observed in right atrial electrophysiology. CONCLUSION: In this study, susceptibility (the ability of an extrastimulus to induce AF) was rigorously measured within a predetermined format. Significant relationships were found to exist between susceptibility, certain of the observed changes in atrial electrophysiology and structure. 相似文献
198.
NR Asad LM Asad AB Silva I Felzenszwalb AC Leit?o 《Canadian Metallurgical Quarterly》1998,407(3):253-259
Despite a large body of evidence showing the beneficial effects of successful treatment of anemia with recombinant human erythropoietin (EPO) in patients with end-stage renal disease, controversy remains as to whether EPO treatment of anemia can improve the nutritional status in patients on maintenance hemodialysis. This prompted us to conduct a prospective study in 41 hemodialysis patients with basal hemoglobin less than 9 g/dl. The dose of EPO was increased for 12 weeks to achieve the target hemoglobin concentration of 10 g/dl and then titrated in the following 12 weeks to maintain the target value. Nutritional status was assessed at baseline and after 6 months of follow-up, using the global protein-calorie malnutrition (PCM) index proposed by Bilbrey and Cohen. A low global PCM score indicates better nutrition. The results showed that hemoglobin values significantly increased from 8.7 +/- 0.8 g/dl at baseline to 10.7 +/- 0.5 g/dl in the 6th month (p < 0.001). No significant changes were observed in the normalized protein catabolic rate and Kt/V during the study period. Global PCM scores improved from 30.0 +/- 7.5 to 23.6 +/- 3.1 (p < 0.001) and paralleled the correction of anemia by EPO treatment. The data were consistent with a major improvement in the nutritional markers of relative body weight, triceps skinfold, midarm circumference, midarm muscle circumference, serum albumin, serum transferrin and total lymphocyte count in the 6th month as compared to baseline. The percentages of mild and moderate-severe PCM at baseline were 32 and 58%, respectively. These percentages were significantly reduced during the 6th month to 20 and 30%, respectively (p = 0.0004). In summary, correction of renal anemia with EPO improves the nutritional status in hemodialysis patients. A postulated mechanism is that EPO may exhibit anabolic effects, with a better utilization of ingested protein. 相似文献
199.
Male Sprague-Dawley rats received either radiofrequency lesions of the lateral internal medullary lamina (IML) or ibotenic acid lesions of the lateral intralaminar nuclei (ILN) and midline nuclei (MLN) or sham treatment. Neither lesion group was impaired in the retention of 3 object pair discriminations acquired before surgery nor in the acquisition of a new object pair after surgery. Rats with ILN, but not IML, lesions were impaired in acquiring an initial and 5 subsequent hidden platform locations in a water maze task. These results suggest that damage to both ILN and MLN are needed to produce spatial learning deficits and that extensive damage to the IML or ILN has no detectable effects on retrograde or anterograde memory of object discriminations. 相似文献
200.
Y Takahashi CD Bucana Y Akagi W Liu KR Cleary M Mai LM Ellis 《Canadian Metallurgical Quarterly》1998,4(2):429-434
Most patients with primary IgA nephropathy (IgAN) have a significantly higher memory repertoire of IgA1-producing B lymphocytes in their bone marrow together with high plasma levels of IgA1. The connection between the mucosal immune system and the bone marrow compartment is probably based on traffic of either antigen-presenting cells (APC) or antigen-specific lymphocytes. Cytokines play an important role in the proliferation and differentiation of lymphoid cells. In order to mimic the in vivo situation as much as possible, we assessed cytokine production profiles ex vivo in 23 IgAN patients and matched controls, using lipopolysaccharide (LPS)- or phytohaemagglutinin (PHA)-stimulated whole blood (WB) cultures. Interferon-gamma (IFN-gamma), IL-2, IL-6, IL-10 and tumour necrosis factor-alpha (TNF-alpha) production in culture supernatants were determined by cytokine-specific ELISAs. Compared with controls, PHA-stimulated cultures resulted in significantly higher IL-10 (P<0.001), IL-2 (P<0.005) and IFN-gamma (P<0.001) levels in IgAN patients, but no significant differences in TNF-alpha or IL-6 levels were found. In LPS-stimulated cultures, the only significant difference (P<0.001) between the two groups was the increased IL-10 production in IgAN patients. The enhanced cytokine production in stimulated WB cultures suggests altered monocyte-related T cell responses in patients with IgAN. Increased IL-10 production may eventually result in an increased number of IgA-producing B lymphocytes in the bone marrow. In addition, high levels of endogenous IL-10 may down-regulate the effector functions of monocytes, or possibly APC in general, and consequently the IgA response at the mucosal level. 相似文献