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   3315篇
  免费   8篇
  国内免费   2篇
电工技术   3篇
化学工业   58篇
金属工艺   2篇
机械仪表   4篇
建筑科学   3篇
能源动力   2篇
轻工业   33篇
水利工程   3篇
石油天然气   1篇
无线电   12篇
一般工业技术   24篇
冶金工业   3156篇
原子能技术   2篇
自动化技术   22篇
  2022年   3篇
  2021年   3篇
  2020年   2篇
  2018年   5篇
  2017年   2篇
  2016年   3篇
  2015年   3篇
  2014年   3篇
  2013年   7篇
  2012年   4篇
  2011年   4篇
  2010年   7篇
  2009年   5篇
  2008年   3篇
  2007年   11篇
  2006年   10篇
  2005年   11篇
  2004年   9篇
  2003年   10篇
  2002年   7篇
  2001年   2篇
  2000年   6篇
  1999年   116篇
  1998年   1029篇
  1997年   604篇
  1996年   379篇
  1995年   181篇
  1994年   189篇
  1993年   189篇
  1992年   24篇
  1991年   13篇
  1990年   20篇
  1989年   25篇
  1988年   28篇
  1987年   19篇
  1986年   16篇
  1985年   20篇
  1984年   4篇
  1983年   8篇
  1982年   23篇
  1981年   19篇
  1980年   26篇
  1979年   3篇
  1978年   7篇
  1977年   90篇
  1976年   164篇
  1975年   6篇
  1973年   1篇
  1965年   2篇
排序方式: 共有3325条查询结果,搜索用时 31 毫秒
991.
Epstein-Barr virus (EBV)-associated lymphoproliferative disease (EBV-LPD) is a frequently fatal complication of organ transplantation and human immunodeficiency virus (HIV) infection. We have studied the safety and efficacy of adoptively transferred, gene-marked virus-specific cytotoxic T lymphocytes (CTLs) as prophylaxis and treatment of EBV-LPD in recipients of T-cell-depleted allogeneic bone marrow. In 42 patients treated prophylactically, no toxicity was experienced. None of these patients developed EBV-LPD, in contrast with eight of 53 (15%) patients who did not receive prophylactic CTL. Three patients who had not received CTL developed aggressive disease and received CTL as treatment. Gene-marked CTL homed to tumor sites and selective accumulation of marker gene was detected in tumor tissues. Tumors regressed completely in two patients, but the third died of respiratory failure. Infused CTLs persisted for up to 3 years in vivo, they rapidly reconstituted EBV-specific immune responses to levels seen in normal individuals, and they reduced high viral titers by two to three logs. We are now using autologous EBV-specific CTL to treat patients with relapsed EBV-positive Hodgkin's disease and we are developing methods for the generation of antigen-specific lines. This approach could be applied to patients with HIV who develop EBV-LPD, using CTL derived early in the course of HIV infection.  相似文献   
992.
The current treatment of haemophiliacs consists of injection of concentrates of blood clotting factors VIII (haemophilia A) and IX (haemophilia B). The inconvenience of the multiple injections needed, and the risk of transmission of infectious agents (HIV, hepatitis) prompted the development of alternative therapies. Gene therapy aims at introducing functional factor VIII and IX genes into the body cells of patients in order to make these cells produce the desired clotting factors. There are two strategies for gene therapy: (a) in the laboratory cells of the patient may be provided with the desired gene, followed by reintroduction of the cells that now produce factor VIII, into the patient (ex vivo strategy); (b) vectors with the desired genes may be injected into the patient in order to induce the modification (in vivo strategy) For both routes, the formal proof-of-principle has been acquired recently in animal experiments: cells modified by factor VIII or IX genes will produce adequate concentrations of the clotting products in plasma and will correct the bleeding tendency. Before the clinical evaluation and widespread application of the technology can be considered many technical problems have to be solved.  相似文献   
993.
994.
Intra-articular calcaneal fractures are associated with significant long-term morbidity, and considerable controversy exists regarding the optimum method of treating them. The contact characteristics in the intact subtalar joint were determined at known loads and for different positions of the ankle and subtalar joint, using pressure-sensitive film (Super Low; Fuji, Itochu Canada Ltd, Montreal, Quebec). We measured the contact area to joint area ratio (pressure > 5 kg force/cm2 [kgf/cm2]) which normalizes for differences in joint size and the ratio of high pressure zone (>20 kgf/cm2) as a reflection of overall increase in joint pressure. Three simulated fracture patterns were then created and stabilized with either 1 or 2 mm of articular incongruity. Eight specimens were prepared with a primary fracture line through the posterior facet, eight with a joint depression-type fracture, and six with a central joint depression fracture. A measure of 1 to 2 mm of incongruity in the posterior facet for all three fracture patterns produced significant unloading of the depressed fragment, with a redistribution of the overall pattern of pressure distribution to parts of the facet that were previously unloaded.  相似文献   
995.
OBJECTIVES: To examine associations between medical and functional variables and at-fault car crashes in a cohort of older drivers. DESIGN: A case-control study. SETTING: A tertiary care medical center. PARTICIPANTS: Older drivers (ages 55-90 years) residing in Jefferson County, Alabama (n = 174). Cases were drivers who had at least one at-fault crash in the previous 6 years; controls were crash-free during the same period. MEASUREMENTS: Self-reported medical conditions, reported and observed functional measures, and urinary drug screens. The occurrence of one or more at-fault car crashes in the 6 years preceding the 1991 assessment date represented the outcome measure. RESULTS: Ninety-nine older drivers experienced between one and seven at-fault vehicle crashes during the period 1985 through 1991, whereas 75 drivers did not. Logistic regression models indicated that the following variables were independently associated with crash involvement: A 40% or greater reduction in the useful field of view (OR = 6.1; 95% CI, 2.9 to 12.7; P < 0.001), black race (OR = 6.6; 95% CI, 1.7 to 26.2; P = .007), a history of falling in the previous 2 years (OR = 2.6; CI, 1.1 to 6.1; P = .025), and not taking a beta-blocking drug (OR = 4.3; CI, 1.2 to 15.0; P = .023). CONCLUSIONS: Functional assessments, such as a comprehensive test of visual processing, a falls history, and a review of current medications may be of greater relevance than specific medical conditions in the identification of older at-risk drivers. If prospective studies determine that falling and crashing share risk factors, a unified approach to the prevention of these mobility disorders could result. The finding of an independent association of black race with at-fault crashing is in need of further clarification because of the low representation of black drivers in this sample.  相似文献   
996.
Mortality data for B6CF1 mice exposed to 60Co gamma rays for the duration of life were used to make quantitative predictions of age-specific mortality observed in comparably exposed beagles. Simple Kaplan-Meier survival curves for the beagles and their 95% confidence intervals were computed for each dose-rate group observed. A dose-response equation was estimated from the mortality data for mice using a proportional hazard model. The dose-response model for mice was then used to generate predicted survivorship curves at dose rates that would recreate the dose burdens observed in the beagle at comparable points within the life span of the two organisms. When these predicted survivorship curves were scaled to adjust for species differences in the life span of control animals, the predictions for the mouse fell within the confidence intervals observed for the beagle. The successful interspecies extrapolation of age-specific mortality risks for species as different as the mouse and dog enhances both the value of studies involving laboratory animals and the potential relevance of the animal studies to the prediction of health effects in humans.  相似文献   
997.
998.
BACKGROUND: Gingival hyperplasia (GH) is a common side effect of cyclosporine . Azithromycin (Zithromax; AZI) is a macrolide antibiotic reported in case studies to reduce cyclosporine-induced gingival hyperplasia (CIGH) in renal transplant recipients (RTR). METHODS: The efficacy of AZI to treat CIGH in RTR was examined in a double-blind, randomized crossover trial. Patients (n=17) with CIGH were randomized to receive AZI and a matching placebo in alternate order for 5 days, separated by a 2-week washout period. Follow-up visits were conducted at week 6 and week 12. Changes in GH were evaluated by measuring the clinical gingival sulcus depths, tooth length, and the length of the interdental papillae to the cementum-enamel junction of two teeth in each of the four quadrants. RESULTS: Significant improvements were observed in all three types of periodontal measurements, representing reductions of gingival tissue above the medial aspect of the tooth, of the gingival sulcus depth, and of the length of the interdental papillae. Patients reported an improvement in gum bleeding. AZI was well tolerated, and 67% of the patients reported that the treatment was at least somewhat useful. CONCLUSIONS: AZI should be considered for RTR with CIGH.  相似文献   
999.
Nonsteroidal anti-inflammatory drugs reduce the incidence and mortality of colorectal carcinoma. Their chemopreventive effects appear to be due to inhibition of cyclooxygenase (COX)-2. Here, we have studied the relationship between the COX-2 mRNA levels and pathological characteristics in 43 primary colorectal carcinomas. COX-2 levels were significantly higher in tumors with larger sizes and in those with deeper invasions but were not correlated with whether the patients had metastasis or not. These results suggest that larger carcinomas produce more COX-2 to support their own growth and that COX-2 inhibitors may be effective agents of carcinoma growth suppression.  相似文献   
1000.
Unlike simple cold storage, machine preservation allows dynamic assessment and manipulation of the donor organ before transplantation. The effects of four pharmacologic agents added to the perfusate during machine preservation of expanded criteria donor (ECD) kidneys were prospectively compared to 1) describe their influence on perfusion parameters and 2) determine their influence on early graft outcome. Between 1 January 1995 and 1 October 1997, 125 consecutive ECD kidneys were preserved in the authors' laboratory. A definition of ECD was assigned to kidneys requiring pretransplant biopsy. The ECD kidneys were randomized to receive prostaglandin E1 (PGE1), trifluoperazine (TFP), verapamil (VER), mannitol (MAN), or no intervention (control) during machine preservation. All kidneys were preserved by continuous hypothermic pulsatile perfusion (CHPP) using Belzer II solution, and perfusion parameters were measured every 2 hours during pulsatile perfusion. The addition of PGE1 to the perfusate increased renal flow and decreased renal resistance. Moreover, the PGE1 treated group was associated with improved early graft function when compared with all other groups. The addition of VER, TFP, and MAN influenced neither the perfusion characteristics nor the incidence of early graft function. Treatment with PGE1 during machine preservation enhances hydrostatic perfusion parameters (renal flow and renal resistance) and reduces the incidence of delayed graft function in ECD kidneys.  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