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   2343篇
  免费   4篇
电工技术   3篇
化学工业   21篇
金属工艺   6篇
机械仪表   1篇
建筑科学   5篇
能源动力   1篇
轻工业   17篇
水利工程   2篇
无线电   9篇
一般工业技术   22篇
冶金工业   2253篇
原子能技术   1篇
自动化技术   6篇
  2018年   2篇
  2017年   2篇
  2016年   2篇
  2013年   3篇
  2012年   6篇
  2011年   4篇
  2010年   6篇
  2009年   2篇
  2008年   7篇
  2007年   6篇
  2006年   6篇
  2005年   4篇
  2004年   6篇
  2003年   5篇
  2002年   4篇
  2001年   3篇
  2000年   3篇
  1999年   75篇
  1998年   719篇
  1997年   436篇
  1996年   253篇
  1995年   134篇
  1994年   103篇
  1993年   127篇
  1992年   19篇
  1991年   18篇
  1990年   17篇
  1989年   25篇
  1988年   34篇
  1987年   17篇
  1986年   16篇
  1985年   14篇
  1983年   2篇
  1982年   10篇
  1981年   6篇
  1980年   16篇
  1978年   3篇
  1977年   62篇
  1976年   146篇
  1975年   5篇
  1974年   2篇
  1973年   2篇
  1972年   2篇
  1971年   1篇
  1968年   2篇
  1967年   1篇
  1964年   1篇
  1957年   1篇
  1955年   3篇
  1954年   1篇
排序方式: 共有2347条查询结果,搜索用时 15 毫秒
71.
Patients with idiopathic and symptomatic restless legs syndrome (RLS) suffer from "dyskinesia while awake" or "daytime myoclonus" when at rest preceded by sensory symptoms. In order to characterise the RLS either as reflex movement or as voluntary movement we measured movement-related cortical potentials in 5 idiopathic and 8 uraemic RLS patients. Movements from both legs were polygraphically recorded concomitantly with cortical activity 2000 msec before to 500 msec after onset of EMG activity. These data were compared with a voluntary simulation of each patient's movement pattern and with 5 age-matched controls performing dorsiflexion of the right, left and both feet. Cortical activity preceding daytime myoclonus was absent in RLS patients whereas self-initiated leg movements in patients elicited onset times (1180-1380 msec) and amplitudes of Bereitschaftspotential (readiness potential) not significantly different from readiness potentials in control subjects (P > 0.05). Lack of movement-related potentials in myoclonus and/or dyskinesias during daytime in RLS patients is compatible with an involuntary mechanism of induction and points towards a subcortical or spinal origin of RLS.  相似文献   
72.
Congenital diseases of the equine head   总被引:1,自引:0,他引:1  
Many questions concerning heritability arise when a veterinarian is asked to supervise and treat disease of congenital origin. Genetic counseling, ethics, and legality are often confronted in discussions between animal health professionals and laymen in animal industry. Guidelines have been offered as in the 1984 statement of the Judicial Council of the American Veterinary Medical Association: "Performance of surgical procedures in all species for the purpose of concealing genetic defects in animals to be shown, raced, bred, or sold as breeding animals is unethical. However, should the health or welfare of the individual patient require correction of such genetic defects, it is recommended that the patient be rendered incapable of reproduction." The Australian Veterinary Law, Ethics, Etiquette and Convention declares it fraud to alter a defect for sale purposes and unethical for a veterinarian to perform such treatments. It is permissible to correct defects causing discomfort or inconvenience, but the veterinarian is required to advise appropriate breeding counseling. Genetic counseling has progressed significantly in human medicine. This has been supported by better diagnostic methods for genetic disorders, greater acceptance of preventive measures, and extended screening programs to identify carriers of specific abnormal genes or chromosomal aberrations. Congenital diseases in veterinary medicine are constantly under investigation. The veterinary practitioner must continue to operate with an appreciation of the incomplete understanding of most of these abnormalities and act in accordance with personal ethical judgment and the guidance of the American Veterinary Medical Association when treating the affected individual animal patient.  相似文献   
73.
74.
As the whole context of nursing continues to change radically in the face of unmet societal needs, nothing short of total revolution will suffice. Nurses must take control of nursing practice and be critical of the nation's inadequate "sick-care" system in order to effect sweeping changes in the scope, availability and efficacy of healthcare in the U.S. To do this requires an acknowledgment that true nursing education cannot exist without nursing practice. The transformation of curriculum must center on caring, which characterizes what nurses really do in a medically dominated system focused exclusively on curing.  相似文献   
75.
An unusual clinical variant of porokeratosis (Mibelli's disease) appeared in a patient soon after birth; the lesions were widely distributed mostly on the right half of the body. Spontaneous recurrent ulcerations occurred over certain sites. The right foot was grossly deformed as a result of atrophic scarring after ulcerations. Biopsy specimens of the classical lesion showed cornoid lamella. It is suggested that the term "ulcerative systematized porokeratosis" be used to describe this clinical variant of porokeratosis.  相似文献   
76.
Paired grain, shoot, and soil of 173 individual sample sets of commercially farmed temperate rice, wheat, and barley were surveyed to investigate variation in the assimilation and translocation of arsenic (As). Rice samples were obtained from the Carmargue (France), Do?ana (Spain), Cadiz (Spain), California, and Arkansas. Wheat and barleywere collected from Cornwall and Devon (England) and the east coast of Scotland. Transfer of As from soil to grain was an order of magnitude greater in rice than for wheat and barley, despite lower rates of shoot-to-grain transfer. Rice grain As levels over 0.60 microg g(-1) d. wt were found in rice grown in paddy soil of around only 10 microg g(-1) As, showing that As in paddy soils is problematic with respect to grain As levels. This is due to the high shoot/soil ratio of approximately 0.8 for rice compared to 0.2 and 0.1 for barley and wheat, respectively. The differences in these transfer ratios are probably due to differences in As speciation and dynamics in anaerobic rice soils compared to aerobic soils for barley and wheat. In rice, the export of As from the shoot to the grain appears to be under tight physiological control as the grain/shoot ratio decreases by more than an order of magnitude (from approximately 0.3 to 0.003 mg/kg) and as As levels in the shoots increase from 1 to 20 mg/kg. A down regulation of shoot-to-grain export may occur in wheat and barley, but it was not detected at the shoot As levels found in this survey. Some agricultural soils in southwestern England had levels in excess of 200 microg g(-1) d. wt, although the grain levels for wheat and barley never breached 0.55 microg g(-1) d. wt. These grain levels were achieved in rice in soils with an order of magnitude lower As. Thus the risk posed by As in the human food-chain needs to be considered in the context of anaerobic verses aerobic ecosystems.  相似文献   
77.
OBJECTIVE: The purpose of our study was to review and report the patient selection, techniques, and results of percutaneous drainage of pancreatic abscesses by retrospective review. MATERIALS AND METHODS: Fifty-nine patients (46 men and 13 women) with a mean age of 44 years old had 80 pancreatic abscesses that were drained percutaneously under radiologic guidance (CT, n = 77; sonography, n = 2; and fluoroscopy, n = 1). Abscesses had a wide spectrum of causes, with alcoholic pancreatitis being most common, trauma second most common, and gallstones third. Ten patients had undergone surgery for pancreatic necrosis or abscess. Patients with pancreatic pseudocysts, necrosis, or acute fluid collections were excluded from this study. RESULTS: Of the 59 patients, 51 (86%) were cured with percutaneous drainage and antibiotic therapy. Of the patients who were not cured with percutaneous drainage, seven required surgery and one underwent repeat percutaneous drainage. In the 59 patients, complications included non-life-threatening bleeding in three patients. Ten of 59 patients (17%) had fistulas that spontaneously formed into the gastrointestinal tract. The duration of catheterization ranged from 4 to 119 days, with a mean duration of 33 days. The rate of mortality at 30 days after completion of percutaneous drainage was 8% (5 of 59). CONCLUSION: Percutaneous drainage was an effective therapy for this defined group of patients with pancreatic abscesses. Factors leading to the relatively high success rate described in this study likely included selection of patients; catheters of adequate size, number, and location; careful follow-up with appropriate catheter manipulations; and an integrated, cooperative approach whereby surgeons were willing to permit drainage to effect its benefits, rather than operating prematurely.  相似文献   
78.
Poly(L ‐lactic acid) (PLLA) films containing various concentrations of two natural antioxidants, α‐tocopherol and resveratrol, were fabricated by a melt compounding and compression molding process. The influence of the antioxidants on the optical properties such as color and UV‐visible light transmission was analyzed. The thermal, mechanical, rheological and physical properties of PLLA films with added antioxidants were assessed. PLLA films with added α‐tocopherol and resveratrol showed a yellowish brown color and the lightness was influenced by the presence of the antioxidants. The glass transition and melting temperatures were significantly reduced with the addition of antioxidants while enhanced thermal stability was observed, which could be a benefit and important for processing and production. PLLA films with added antioxidants were slightly more hydrophobic than neat PLLA. The combination effect of plasticizing and enhancement of the elastic modulus with differing concentrations of two antioxidants played a critical role in the mechanical and thermomechanical properties of PLLA films. The melt viscosity of the PLLA films with added antioxidants was substantially higher than that of neat PLLA. The higher melt viscosity and G′(ω) could be an indication of formation of entanglement between PLLA and the two antioxidants. Copyright © 2012 Society of Chemical Industry  相似文献   
79.
Two approaches were undertaken to characterize the arsenic (As) content of Chinese rice. First, a national market basket survey (n = 240) was conducted in provincial capitals, sourcing grain from China's premier rice production areas. Second, to reflect rural diets, paddy rice (n = 195) directly from farmers fields were collected from three regions in Hunan, a key rice producing province located in southern China. Two of the sites were within mining and smeltery districts, and the third was devoid of large-scale metal processing industries. Arsenic levels were determined in all the samples while a subset (n = 33) were characterized for As species, using a new simple and rapid extraction method suitable for use with Hamilton PRP-X100 anion exchange columns and HPLC-ICP-MS. The vast majority (85%) of the market rice grains possessed total As levels < 150 ng g(-1). The rice collected from mine-impacted regions, however, were found to be highly enriched in As, reaching concentrations of up to 624 ng g(-1). Inorganic As (As(i)) was the predominant species detected in all of the speciated grain, with As(i) levels in some samples exceeding 300 ng g(-1). The As(i) concentration in polished and unpolished Chinese rice was successfully predicted from total As levels. The mean baseline concentrations for As(i) in Chinese market rice based on this survey were estimated to be 96 ng g(-1) while levels in mine-impacted areas were higher with ca. 50% of the rice in one region predicted to fail the national standard.  相似文献   
80.
Although several measures of obsessive-compulsive (OC) symptoms exist, most are limited in that they are not consistent with the most recent empirical findings on the nature and dimensional structure of obsessions and compulsions. In the present research, the authors developed and evaluated a measure called the Dimensional Obsessive-Compulsive Scale (DOCS) to address limitations of existing OC symptom measures. The DOCS is a 20-item measure that assesses the four dimensions of OC symptoms most reliably replicated in previous structural research. Factorial validity of the DOCS was supported by exploratory and confirmatory factor analyses of 3 samples, including individuals with OC disorder, those with other anxiety disorders, and nonclinical individuals. Scores on the DOCS displayed good performance on indices of reliability and validity, as well as sensitivity to treatment and diagnostic sensitivity, and hold promise as a measure of OC symptoms in clinical and research settings. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  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