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   1397篇
  免费   27篇
  国内免费   3篇
电工技术   8篇
综合类   7篇
化学工业   137篇
金属工艺   5篇
机械仪表   25篇
建筑科学   41篇
矿业工程   1篇
能源动力   15篇
轻工业   170篇
水利工程   13篇
石油天然气   3篇
无线电   80篇
一般工业技术   140篇
冶金工业   690篇
原子能技术   15篇
自动化技术   77篇
  2021年   10篇
  2020年   13篇
  2019年   13篇
  2018年   14篇
  2017年   16篇
  2016年   7篇
  2015年   12篇
  2014年   18篇
  2013年   41篇
  2012年   46篇
  2011年   39篇
  2010年   34篇
  2009年   36篇
  2008年   47篇
  2007年   44篇
  2006年   28篇
  2005年   32篇
  2004年   24篇
  2003年   23篇
  2002年   20篇
  2001年   21篇
  2000年   23篇
  1999年   27篇
  1998年   212篇
  1997年   115篇
  1996年   69篇
  1995年   47篇
  1994年   48篇
  1993年   49篇
  1992年   10篇
  1991年   19篇
  1990年   15篇
  1989年   19篇
  1988年   13篇
  1987年   17篇
  1986年   15篇
  1985年   23篇
  1984年   11篇
  1983年   10篇
  1982年   7篇
  1981年   6篇
  1980年   6篇
  1979年   9篇
  1978年   6篇
  1977年   18篇
  1976年   41篇
  1975年   9篇
  1974年   7篇
  1973年   6篇
  1970年   6篇
排序方式: 共有1427条查询结果,搜索用时 15 毫秒
1.
BACKGROUND: Myocardial reperfusion is believed to be associated with free radical injury. However, indexes of oxidative stress in vivo have been limited by their poor specificity and sensitivity. Isoprostanes are stable products of arachidonic acid formed in a nonenzymatic, free radical-catalyzed manner. We have developed a sensitive and specific assay for one of these compounds, 8-epi prostaglandin (PG) F2 alpha. METHODS AND RESULTS: To address its utility as an index of oxidative stress during coronary reperfusion, we measured urinary levels by gas chromatography/mass spectrometry in a canine model of coronary thrombolysis, in patients with acute myocardial infarction treated with thrombolytic therapy, and in patients after elective coronary artery bypass surgery. Urinary 8-epi PGF2 alpha was unchanged after circumflex artery occlusion in a canine model of coronary thrombolysis (n = 13; 437.2 +/- 56.4 versus 432.7 +/- 55.2 pmol/mmol creatinine) but increased significantly (P < .05) immediately after reperfusion (553.8 +/- 64.7 pmol/mmol). Urinary levels were increased (P < .001) in patients (n = 12) with acute myocardial infarction given lytic therapy (265.8 +/- 40.8 pmol/mmol) compared with age-matched control subjects (n = 20; 91.5 +/- 11.8 pmol/mmol) and patients with stable coronary disease (n = 20; 95.7 +/- 6.3 pmol/mmol). Preoperative levels rose from 113.2 +/- 11.8 to 248.2 +/- 86.3 pmol/mmol at 30 minutes into revascularization to 332.2 +/- 82.6 pmol/mmol by 15 minutes after global myocardial reperfusion (P < .05) and dropped to 181.2 +/- 50.4 pmol/mmol at 30 minutes and 120.2 +/- 9.9 pmol/mmol at 24 hours after bypass surgery (n = 5). Corresponding changes in spin adduct formation, found with electron paramagnetic resonance, were noted in 2 patients. CONCLUSIONS: These data support the hypothesis that free radical generation occurs during myocardial reperfusion. Measurement of isoprostane production may serve as a noninvasive index of oxidative stress.  相似文献   
2.
T cell cytokines play an important role in mediating airway inflammation in asthma. The predominance of a Th2 cytokine profile, particularly interleukin (IL)-4 and IL-5, is associated with the pathogenesis and course of asthma. The aim of this study was to test the hypothesis that a stressful life event alters the pattern of cytokine release in asthmatic individuals. Thirteen healthy controls and 21 asthmatic adolescents gave blood samples three times over a semester: midsemester, during the week of final examinations, and 2-3 weeks after examinations. Interferon-gamma (IFN-gamma), IL-2, IL-4, and IL-5 were measured from supernatants of cells stimulated with PHA/PMA for 24 h. Cells from asthmatic subjects released significantly more IL-5 during the examination and postexamination periods, whereas cells from healthy controls released significantly more IL-2 during the midsemester and examination periods, thereby indicating a bias for a Th2-like pattern in asthmatics and a Th1-like pattern in healthy controls. IL-4 and IL-5 production showed a marked decrease during and after examinations in healthy controls, whereas this decline was absent in asthmatics. The ratios of IFN-gamma:IL-4 and IFN-gamma:IL-5 also revealed significant changes in the profile of cytokine release across the semester. These results indicate differential cytokine responses in asthmatics that may become pronounced during periods of cellular activation.  相似文献   
3.
This paper examines Total Quality Management (TQM) as defined by Dr. W. Edwards Deming including Deming's fourteen points and explains how the United States' Department of Defense (DOD) defines TQM and why TQM is necessary. It also covers how the DOD is planning on implementing TQM and the policy that has been established as guidance in the implementation process.  相似文献   
4.
BACKGROUND: Laparoscopic Nissen fundoplication is an effective procedure for the treatment of gastro-oesophageal reflux disease (GORD), but the underlying motility mechanisms that explain the success of this operation remain unclear. METHODS: Twenty patients with a history of GORD underwent stationary oesophageal manometry and prolonged ambulatory pH monitoring, both before and 3 months after fundoplication. RESULTS: Eighteen patients were completely cured of reflux symptoms and stopped all antireflux medication after operation. After fundoplication there was a significant increase (P < 0.01) in median resting lower oesophageal sphincter (LOS) pressure and length. Median residual LOS pressure during swallow-induced LOS relaxation also increased significantly after operation (P < 0.01). The number of reflux episodes decreased from a median of 48 to 3 after fundoplication (P < 0.01). The time at pH less than 4 decreased from 5.7 to 0 per cent in the supine position (P < 0.01), and from 9.8 to 0.2 per cent while upright (P < 0.001). CONCLUSION: Early subjective results at 3 months following laparoscopic antireflux surgery show improved symptoms. One of the mechanisms underlying the antireflux action of fundoplication is an increase in median residual LOS pressure at the gastro-oesophageal junction. This may be a purely mechanical effect of the fundic wrap extrinsic to the LOS.  相似文献   
5.
Infants with congenital diaphragmatic hernia (DH) and profound pulmonary hypoplasia are currently unsalvageable. The authors previously demonstrated that tracheal ligation (TL) accelerates fetal lung growth and reverses the pulmonary hypoplasia of fetal nephrectomy. The purpose of this study was to determine if the pulmonary hypoplasia of experimental DH could be similarly reversed and, if so, whether the resulting lungs would show better function than those of their DH counterparts. Eighteen fetal lambs were divided into three experimental groups of six animals each. In group 1, DH was created at 90 days' gestation. In group 2, DH was created at 90 days' gestation and TL performed during the same operation. Group 3 consisted of sham-operated controls. These animals were delivered near full-term, and their lungs analyzed by standard morphometric techniques. Ten additional fetal lambs were divided into two experimental groups of five animals each. In group 4, DH was created at 90 days' gestation. In group 5, DH was created at 90 days' gestation and TL performed 20 days later, at 110 days' gestation. These animals were pressure-ventilated via tracheostomy over a 2-hour period in which PaO2, PaCO2, and compliance were measured. Intratracheal pressure (ITP) was measured at the time of delivery in all groups. Upon retrieval, DH animals had abdominal viscera in the chest and small lungs; in contrast, DH/TL animals had the herniated viscera reduced from the chest by enlarged lungs. DH/TL lungs showed markedly increased growth, with significant increases in lung volume:body weight ratio (LV:BW; P = .0001), alveolar surface area (ALV.SA; P = .0001), and alveolar number (ALV#) (P = .0001) when compared with those of the DH or control group. This growth was associated with a normal maturation pattern based on histological appearance, normal airspace fraction, and normal alveolar numerical density. ITP in the DH/TL group was increased when compared with that of DH and control animals (P = .0001). Total lung DNA and protein were both elevated in the DH/TL animals (P = .0001). However, the DNA:protein ratio remained normal, suggesting lung growth had occurred through cell proliferation, not by hypertrophy. When ventilated over a range of settings, DH/TL lungs were more compliant (P = .0001) and achieved higher PaO2s (P < .003) and lower PaCO2s (P = .0001) than their DH counterparts. From these data, the authors conclude: (1) Experimental fetal DH produces hypoplastic lungs that are not capable of adequate gas exchange with conventional ventilation.(ABSTRACT TRUNCATED AT 400 WORDS)  相似文献   
6.
The EU Concerted Action Workshop on 11q23 Abnormalities in Hematological Malignancies collected 550 patients with abnormalities involving 11q23. Of these, 53 patients had a translocation involving chromosome 11, breakpoint q23, and chromosome 19, breakpoint p13. Karyogram review enabled each patient to be further defined as t(11;19)(q23;p13.1) (21 patients) or t(11;19)(q23;p13.3) (32 patients). There was a marked difference between the type of banding and the translocation identified: t(11;19)(q23;p13.1) was detected predominantly by R-banding, whereas t(11;19)(q23;p13.3) was detected almost solely by G-banding. Additional change was extremely rare in patients with t(11;19)(q23;p13.1) but occurred in nearly half of the patients with t(11;19)(q23;p13.3). Patients with t(11;19)(q23;p13.1) all had leukemia of a myeloid lineage, mostly acute myeloid leukemia (AML), and were predominantly adult. In contrast patients with t(11;19)(q23;p13.3) had malignancies of both myeloid and lymphoid lineage and were mainly infants less than 1 year old. The survival of both groups of patients was generally poor, over 50% of t(11;19)(q23;p13.1) patients died within 2 years of diagnosis and the median survival of acute lymphoblastic leukemia (ALL) patients with t(11;19)(q23;p13.3) was 17.6 months.  相似文献   
7.
The emergence of new tourism‐related land uses within historic port cities has brought a range of physical, economic and social benefits. However, there are often associated tensions between the need for economic development and the need to maintain the unique heritage resource that may be a large part of the attraction for visitors. The case of Malta's Cottonera Project—for the waterfront of part of the historic ‘Grand Harbour’—throws these tensions into sharp relief; indeed, the controversy generated by the proposal led to a successful vote of no confidence in the Maltese government. The case illustrates the problematic role of the spatial planning system in seeking to mediate between interests with opposing aims in historic port cities, and the need to apply principles of sustainable regeneration.  相似文献   
8.
The goal of the present studies was to construct and validate a short form of the 50-item Smoking Consequences Questionnaire (SCQ; T. H. Brandon & T. B. Baker, 1991), a measure of smoking outcome expectancies. In Study 1, a 21-item short form (S-SCQ) was derived from a sample of 107 young adults previously treated for substance abuse. In Study 2, the measure was cross-validated on 125 adolescents in treatment for substance abuse. Confirmatory factor analyses revealed good model fit and factorial invariance for the 4 S-SCQ subscales across both samples. Validation analyses on each sample found that subscale scores generally correlated significantly with smoking-related variables. The present studies provide initial evidence for the utility of the S-SCQ when used with young adults and adolescents. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
9.
Cyclosporine was introduced in 1981 as an immunosuppressive agent in renal transplantation. Its use was soon extended to the treatment of various glomerular disorders. In light of its known immunomodulating effects, the use of cyclosporine has been most prominent in those glomerular diseases thought to have an immune basis. The most careful studies of cyclosporine in glomerular diseases have been performed in the pediatric population with idiopathic nephrotic syndrome (i.e., minimal change disease and focal segmental glomerulosclerosis), although data are accumulating regarding efficacy and safety in adults with idiopathic nephrotic syndrome. In patients who are steroid-dependent, cyclosporine therapy can induce complete or partial remission in a significant proportion of cases; success rates in patients with steroid-resistant nephrotic syndrome are less encouraging. Treatment with cyclosporine allows for dose reduction or elimination of corticosteroids, and the consequent salutary effect on growth in the child and glucose and bone metabolism in all patients. Studies that suggest a potential benefit of cyclosporine in recurrent nephrotic syndrome in renal allografts and in other glomerular diseases are also discussed.  相似文献   
10.
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