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   1614篇
  免费   1篇
化学工业   7篇
建筑科学   1篇
轻工业   4篇
一般工业技术   8篇
冶金工业   1592篇
自动化技术   3篇
  2020年   1篇
  2019年   1篇
  2018年   1篇
  2010年   1篇
  2009年   1篇
  2006年   1篇
  2005年   1篇
  2004年   1篇
  2003年   3篇
  2002年   2篇
  2000年   1篇
  1999年   48篇
  1998年   484篇
  1997年   266篇
  1996年   201篇
  1995年   94篇
  1994年   78篇
  1993年   98篇
  1992年   15篇
  1991年   21篇
  1990年   22篇
  1989年   23篇
  1988年   22篇
  1987年   43篇
  1986年   24篇
  1985年   28篇
  1984年   2篇
  1983年   3篇
  1982年   9篇
  1981年   10篇
  1980年   9篇
  1978年   1篇
  1977年   31篇
  1976年   68篇
  1955年   1篇
排序方式: 共有1615条查询结果,搜索用时 15 毫秒
171.
The advantages of the laparoscopic mode of access for hysterectomy include shorter recovery time and less pain and scarring. The laparoscopic component of the hysterectomy is usually combined with a vaginal component. The relative proportions of the procedure, performed laparoscopically and vaginally, vary considerably between surgeons. The main problem associated with the laparoscopic approach is to ensure adequate hemostasis while avoiding damage to the urinary tract. A variety of differing techniques have been developed in attempts to ensure the safe and efficient removal of the uterus laparoscopically.  相似文献   
172.
173.
OBJECTIVE: To assess the frequency of transient bacteremia among women undergoing transabdominal and transcervical chorionic villus sampling (CVS). METHODS: One hundred fourteen women undergoing CVS consented to participate in a university review board-approved study protocol. Exclusion criteria included known cardiac valve anomaly or replacement (or other prosthetic) and antibiotic use within the preceding 21 days. Blood cultures (aerobic and anaerobic) were drawn by a single operator on all patients, before CVS and within 15 minutes after completing CVS. Either the catheter tip or needle tip aspirate from each procedure was also sent for culture. RESULTS: Post-procedure bacteremia was detected in two (1.8%) of the patients undergoing CVS. These two patients both had their procedures performed transcervically, resulting in a 4.1% (two of 49) bacteremia rate after transcervical CVS, compared to none (zero of 65) in the transabdominal group (P = .36). The incidence of positive cultures from sampling instruments was also higher in the transcervical group (16.3 versus 0%; P = .003), but did not result in comparable rates of bacteremia among patients with positive instrument cultures. CONCLUSIONS: In this study, CVS was associated with a low rate of bacteremia, regardless of the procedure route. Recommendations for antibiotic prophylaxis in women with abnormal cardiac valves should parallel those for spontaneous vaginal delivery and other comparable genitourinary procedures.  相似文献   
174.
Mortality was determined in 519 patients with delirium who were seen in psychiatric consultation in two general hospitals. Among 419 patients with simple delirium (DSM-III: 293.00) in-hospital mortality was 26%. As compared to average hospital patients the age adjusted in-hospital excess mortality ratio varied from 6.2 for patients with malignancies to 2.1 for patients with motor system disease. After hospital discharge the 5-yr cumulative mortality was 51%. As compared to the general population excess mortality was noted in most, but not in all diagnostic subgroups. The age and sex adjusted excess mortality ratio varied from 14.1 for malignancies to 1.3 for motor system disease. The figures underline a general notion that delirium may be an indicator of disorders of grave prognosis, but mortality appears to depend more on the medical condition than on the presence of delirium.  相似文献   
175.
Duodenum-preserving resection of the head of the pancreas was developed 25 years ago by Beger. This procedure is indicated in patients suffering from chronic pain in combination with inflammation of the head of the pancreas, common bile duct obstruction, pancreatic duct obstruction and/or obstruction of the retropancreatic vessels. At the Inselspital in Berne, 74 patients underwent this operation between 1993 and 1996. The median length of the operation was 380 min, with the need for transfusion in a median of 0 units (0-6). There was no postoperative mortality. Total postoperative morbidity was 13%. One patient needed relaparotomy on day 17 for small bowel obstruction. Median length of hospital stay was 11 days. Postoperatively, two patients developed diabetes. Duodenum-preserving resection of the head of the pancreas represents an organ-preserving principle of surgery. This procedure treats the complications of chronic pancreatitis and provides long-term pain relief in more than 80% of patients.  相似文献   
176.
All leaders in health care today are charged with the responsibility of transforming present practices into new and different ones that are needed for the future. The structural side of transforming is ultimately easier than the human side. However, the most frequent failures come from not concentrating sufficiently on the behavioral side of the change. Structural and psychological change must occur simultaneously and embrace each other for best results.  相似文献   
177.
BACKGROUND: Recent studies suggest that dyslipidaemia accelerates the progression of diabetic nephropathy, but the various pathomechanisms underlying such abnormalities are not completely delineated. METHODS: We isolated, radiolabelled, and characterized very-low-density lipoproteins (VLDL) and low-density lipoproteins (LDL) from eight diabetic patients with moderate impairment of renal function and dyslipidaemia and studied their interaction with LDL receptors in human glomerular epithelial cells. RESULTS: While diabetic VLDL showed no compositional changes, LDL particles contained a higher proportion of triglycerides at the expense of cholesterol in comparison with healthy controls. Despite differences in composition, both VLDL and LDL from patients exhibited reduced receptor affinity and cellular uptake capacity by glomerular epithelial cells. Since LDL composition was altered intracellular cholesterol homeostasis was investigated. Due to reduced cholesterol content and lower uptake capacity, diabetic LDL were less effective in suppressing intracellular sterol synthesis and in activating acylcholesterol acyltransferase than LDL from controls. Electrophoretic mobility of apoB from diabetic patients was enhanced as compared to controls, most probably due to the higher degree of glycation (17 + 1.7 versus 11 + 1%, P < 0.05) but not to oxidation (TBARS 0.5 + 0.2 versus 0.2 + 0.1 mumol/1). Oxidized LDL was not taken up in significant amounts, indicating no scavenger receptor activity in glomerular epithelial cells. CONCLUSION: The receptor-specific uptake of diabetic VLDL and LDL by glomerular epithelial cells is impaired. Compositional changes of the LDL particle and glycation of the protein moiety may contribute to altered glomerular uptake. However, glycation of the protein moiety may be superior to compositional changes. Because glomerular structures like mesangial matrix and endothelial cells are known for preferential binding of modified lipoproteins, further studies are required to elucidate their potential role in the progression of diabetic glomerulosclerosis.  相似文献   
178.
179.
BACKGROUND: Lignin degradation leads to the formation of a broad spectrum of aromatic molecules that can be used by various fungal micro-organisms as their sole source of carbon. When grown on phenolic compounds, Penicillium simplicissimum induces the strong impression of a flavin-containing vanillyl-alcohol oxidase (VAO). The enzyme catalyses the oxidation of a vast array of substrates, ranging from aromatic amines to 4-alkyphenols. VAO is a member of a novel class of widely distributed oxidoreductases, which use flavin adenine dinucleotide (FAD) as a cofactor covalently bound to the protein. We have carried out the determination of the structure of VAO in order to shed light on the most interesting features of these novel oxidoreductases, such as the functional significance of covalent flavinylation and the mechanism of catalysis. RESULTS: The crystal structure of VAO has been determined in the native state and in complexes with four inhibitors. The enzyme is an octamer with 42 symmetry; the inhibitors bind in a hydrophobic, elongated cavity on the si side of the flavin molecule. Three residues, Tyr108, Tyr503 and Arg504 form an anion-binding subsite, which stabilises the phenolate form of the substrate. The structure of VAO complexed with the inhibitor 4-(1-heptenyl)phenol shows that the catalytic cavity is completely filled by the inhibitor, explaining why alkylphenols bearing aliphatic substituents longer than seven carbon atoms do not bind to the enzyme. CONCLUSIONS: The shape of the active-site cavity controls substrate specificity by providing a 'size exclusion mechanism'. Inside the cavity, the substrate aromatic ring is positioned at an angle of 18 degrees to the flavin ring. This arrangement is ideally suited for a hydride transfer reaction, which is further facilitated by substrate deprotonation. Burying the substrate beneath the protein surface is a recurrent strategy, common to many flavoenzymes that effect substrate oxidation or reduction via hydride transfer.  相似文献   
180.
A method is described for the densitometric determination of the p-hydroxybenzoic esters and p-hydroxybenzoic acid in mixtures or in drugs. This method is compared with the one used in high performance liquid chromatography (HPLC). The calibration curves were linear in interval 0.250-3.60 mumol ml-1 per 200 nl per spot. The limit of detection and the relative standard deviation (RSD) are higher than in HPLC (RSD is 6% in HPTLC. 3% in HPLC; limit of detection about 40 pmol in HPTLC and 25 pmol in HPLC) but HPTLC quantitative determination of parabens in drugs is faster.  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