全文获取类型
收费全文 | 7792篇 |
免费 | 31篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 13篇 |
综合类 | 1篇 |
化学工业 | 152篇 |
金属工艺 | 16篇 |
机械仪表 | 22篇 |
建筑科学 | 25篇 |
矿业工程 | 1篇 |
能源动力 | 19篇 |
轻工业 | 161篇 |
水利工程 | 4篇 |
石油天然气 | 6篇 |
无线电 | 143篇 |
一般工业技术 | 114篇 |
冶金工业 | 7033篇 |
原子能技术 | 11篇 |
自动化技术 | 103篇 |
出版年
2021年 | 11篇 |
2020年 | 6篇 |
2019年 | 5篇 |
2018年 | 11篇 |
2017年 | 18篇 |
2016年 | 13篇 |
2015年 | 16篇 |
2014年 | 18篇 |
2013年 | 23篇 |
2012年 | 32篇 |
2011年 | 50篇 |
2010年 | 43篇 |
2009年 | 30篇 |
2008年 | 34篇 |
2007年 | 37篇 |
2006年 | 44篇 |
2005年 | 25篇 |
2004年 | 31篇 |
2003年 | 38篇 |
2002年 | 15篇 |
2001年 | 12篇 |
2000年 | 23篇 |
1999年 | 238篇 |
1998年 | 2397篇 |
1997年 | 1340篇 |
1996年 | 855篇 |
1995年 | 445篇 |
1994年 | 356篇 |
1993年 | 457篇 |
1992年 | 53篇 |
1991年 | 61篇 |
1990年 | 70篇 |
1989年 | 60篇 |
1988年 | 64篇 |
1987年 | 71篇 |
1986年 | 66篇 |
1985年 | 48篇 |
1984年 | 9篇 |
1983年 | 22篇 |
1982年 | 32篇 |
1981年 | 43篇 |
1980年 | 72篇 |
1979年 | 12篇 |
1978年 | 20篇 |
1977年 | 149篇 |
1976年 | 296篇 |
1975年 | 16篇 |
1973年 | 7篇 |
1972年 | 4篇 |
1955年 | 4篇 |
排序方式: 共有7824条查询结果,搜索用时 0 毫秒
61.
62.
The author describes a patient who has a successful coronary artery bypass. Six weeks later, after a physical examination of the chest, she had unbearable sharp, stabbing pain around the incision which was not responding to nerve blocks, analgesics, nonsteroidal anti inflammatory agents, and epidural blocks. The pain was responsive to mexilitine and disappeared after three weeks of treatment. 相似文献
63.
Traffic accidents are a well-known public health problem worldwide. In Mexico research into risk factors for motor involving vehicles accidents and their consequences has recently been taken into account. The relevant literature does not normally describe the methodological aspects involved in the collection of primary data, since most studies have used secondary data the good quality and validity of which are assumed. The paper presented seeks to discuss and share with researchers in this field, some of the methodological aspects to be considered in the attempt to recreate the scene of the accident and obtain information approximating to reality. The measurements in situ of, such traffic accident variables as injury, use of seat belt, speed and alcohol intake are discussed. 相似文献
64.
R Gutiérrez del Pozo MJ Ricart Brulles MC Bacque L Fernández-Cruz R Talbot-Wright P Carretero González 《Canadian Metallurgical Quarterly》1997,21(10):950-955
OBJECTIVE: Retrospective study of urological complications in our series of reno-pancreatic transplants. MATERIAL AND METHODS: Between February 1983 and May 1994 our group has conducted 93 RPT, 80 of which, mean age 36 +/- 6 years (24-54 years), are studied in this paper: 57 male and 23 female with an average time in dialysis of 20 +/- 15 months (0-84 months) and diabetes evolution of 21 +/- 5 years (11-37 years). RESULTS: Actuarial annual survival of patient, renal graft and pancreatic graft has been 85%, 79% and 74% respectively. Haematuria: 25% incidence, with graft pancreatitis etiology in 16 cases, rejection in 8 and urinary fistula in 6. Urinary infection: 85% incidence, symptomatic in 23 patients (29%) and asymptomatic in the remaining cases. Dysuria, urethritis and urethral stenosis: 14 patients, all male, most with both conditions associated. Reconversion of pancreatic exocrine secretion by intestinal route was performed in 7 patients. Urinary fistula: secondary to surgery in 9 cases and rejection in 4. Etiology of one case remained unknown. In 4 cases it was resolved with conservative treatment, and with surgical correction in 8. One patient required pancreatic transplantectomy and one patient died of AMI. CONCLUSIONS: Urological complication in RPT account for a significant morbidity, urinary fistula being the one with greater repercussion on the patient and pancreatic graft survival. 相似文献
65.
MT Massie MJ Rohrer JA Leppo BS Cutler 《Canadian Metallurgical Quarterly》1997,25(6):975-82; discussion 982-3
PURPOSE: Because dipyridamole thallium (DT) scanning is a useful predictor of perioperative cardiac events, a positive results of a DT scan is frequently the basis for performing more invasive cardiac evaluation and for consideration for performing coronary revascularization procedures before performing peripheral vascular surgery. The rationale for this approach has been that the treatment of anatomically significant coronary artery disease would lower the risk of performing a subsequent vascular operation. However, the benefit of performing aggressive diagnostic and therapeutic cardiac procedures in such patients remains unproved. To examine this issue, data from patients who underwent coronary angiography because of thallium redistribution were compared with data from matched control subjects who underwent peripheral vascular operations without further cardiac evaluation. METHODS: The medical records of 70 consecutive patients who underwent coronary angiography because of the presence of two or more segments of redistribution on DT scan were reviewed and compared with 70 other patients matched with respect to age, gender, peripheral vascular operation, and number of segments of redistribution on DT scan who did not undergo additional cardiac evaluation. RESULTS: DT scans were performed on 934 preoperative peripheral vascular surgery patients to help in the assessment of operative risk. Ischemic responses, defined as two or more segments of redistribution, were observed in 297. Of these, 70 underwent cardiac catheterization and 25 underwent coronary revascularization procedures. Adverse outcomes affected 46% of the coronary angiography group and 44% of the control group (p = NS). Patients who underwent coronary angiography and were considered for myocardial revascularization had fewer cardiac events with a subsequent vascular operation than did the control subjects. However, any possible benefit from invasive cardiac evaluation was offset by the three deaths and two myocardial infarctions (MIs) that complicated the cardiac evaluation. There was no significant difference between the angiography group and the matched control subjects with respect to perioperative nonfatal MI (13% vs 9%), fatal MI (4% vs 3%), late nonfatal MI (16% vs 19%), or late cardiac death (10% vs 13%). In long-term follow-up, MIs occurred later in patients who underwent coronary angiography than the control subjects (p = 0.049), but this difference was not associated with an improvement in the overall survival rate. CONCLUSIONS: The risks of extended cardiac evaluation and treatment did not produce any improvement in either the perioperative or the long-term survival rate. For most vascular surgery patients who have a positive result of a DT scan, coronary angiography does not provide any additional useful information. 相似文献
66.
AF Minnick MJ Roberts WB Young RM Kleinpell RJ Marcantonio 《Canadian Metallurgical Quarterly》1997,35(4):399-409
OBJECTIVES: Market forces make it essential to know what policies and actions influence patients' reports of hospital services. No studies have examined the role of patient characteristics, labor quality and staff characteristics, nonlabor resources, managerial practices, and employee attitudes within a single investigation. METHODS: The authors collected, simultaneously, data about labor, management and service processes, nonlabor resources, and employee attitudes on 117 nonintensive medical-surgical inpatient units in 17 hospitals selected from a pool of 69 institutions within a metropolitan area by a stratified random sample. Of the 2,595 patients who agreed to participate, 2,051 (79%) completed telephone interviews regarding their experiences with physical care, education, and pain management services within 26 days of hospital discharge. RESULTS: A significant amount of variation in patients' service reports was explained (adjusted R2 = 0.41 physical care, 0.35 pain management, 0.44 education). Although the predictors varied for each service report, patient characteristics, especially those related to personal resources, had a large explanatory role. A labor assignment pattern that could explain why earlier studies found labor quality and staff characteristics to have only a weak role in the prediction of patients' service reports was noted. CONCLUSIONS: The results related to patient characteristics may indicate opportunities to improve care by confronting service design strategies that erroneously rely on a homogeneous patient population. Measurement challenges identified by this study must be addressed to determine the role of labor quantity and staff characteristics. 相似文献
67.
S Merino A Aguilar JM Tomás R Bonet MJ Martinez D Simón-Pujol F Congregado 《Canadian Metallurgical Quarterly》1997,22(5):315-320
1. We investigated the effect of exercise on plasma adrenomedullin, atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) concentrations and studied the relationship between these peptides and haemodynamic parameters in nine patients with old myocardial infarction (MI) and in eight normal subjects. 2. The exercise protocol consisted of two fixed work loads (40 and 80 W) for 4 min each and venous blood samples were taken at rest, during each exercise stage and after exercise while monitoring the mean arterial pressure (MAP) and heart rate (HR). In MI, pulmonary arterial pressure (PAP), pulmonary capillary wedge pressure (PCWP), left ventricular end-diastolic pressure (LVEDP) and cardiac output (CO) were measured throughout exercise. 3. Adrenomedullin levels did not significantly increase with exercise. Adrenomedullin levels correlated with PAP and PCWP at rest (P < 0.05). Atrial natriuretic peptide levels correlated with PAP, PCWP and LVEDP throughout exercise (P < 0.05) but, on multiple regression analysis, PCWP correlated only with ANP (P < 0.01). Brain natriuretic peptide levels correlated with LVEDP throughout exercise (P < 0.01) and its increment correlated closely with basal BNP levels at rest (P < 0.01). 4. These results suggest that adrenomedullin does not respond to the acute haemodynamic changes of exercise, whereas ANP responds to it and PCWP is the major stimulus factor. Brain natriuretic peptide responds to exercise in proportion to the basal synthesis of BNP in patients with left ventricular dysfunction and LVEDP may play a role in increasing BNP during exercise. 相似文献
68.
J. L. Olsen 《Journal of Low Temperature Physics》1985,61(1-2):17-43
Standing waves of second sound in superfluid helium deform the free helium surface. Schlieren observations on cylindrical cavities with vertical axis give the wave patterns predicted by Sorbello. Calculations and experiments show that the deformation is stationary, with only a very small time-dependent component. At low second-sound levels the wave amplitude is proportional to intensity. At higher levels the relation of wave height to second-sound intensity becomes nonlinear and when a critical value is reached, the waves break. Their height then increases abruptly, and the dominant wave number doubles. 相似文献
69.
70.
BA Rybicki MJ Maliarik M Major J Popovich MC Iannuzzi 《Canadian Metallurgical Quarterly》1997,18(4):707-717
Hereditary susceptibility to sarcoidosis is suggested by ethnic preponderance, familial clustering, and multigenerational involvement. The genetics of sarcoidosis cannot be adequately addressed in small samples of patients; a large-scale study with stratification for patient phenotypic differences is necessary. A study that uses both genetic marker and environmental data would be able to control for and examine different causative mechanisms. Until such a well-designed, comprehensive study is carried out, we are left with interesting patterns of disease in families and uncertain allelic associations. 相似文献