全文获取类型
收费全文 | 3476篇 |
免费 | 8篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 2篇 |
综合类 | 3篇 |
化学工业 | 23篇 |
金属工艺 | 3篇 |
机械仪表 | 3篇 |
建筑科学 | 9篇 |
矿业工程 | 1篇 |
能源动力 | 3篇 |
轻工业 | 10篇 |
石油天然气 | 1篇 |
武器工业 | 2篇 |
无线电 | 10篇 |
一般工业技术 | 18篇 |
冶金工业 | 3380篇 |
自动化技术 | 17篇 |
出版年
2022年 | 2篇 |
2021年 | 1篇 |
2020年 | 1篇 |
2017年 | 2篇 |
2016年 | 2篇 |
2014年 | 1篇 |
2013年 | 6篇 |
2012年 | 1篇 |
2011年 | 27篇 |
2010年 | 5篇 |
2009年 | 2篇 |
2008年 | 2篇 |
2006年 | 4篇 |
2005年 | 5篇 |
2004年 | 5篇 |
2003年 | 10篇 |
2002年 | 5篇 |
2000年 | 3篇 |
1999年 | 118篇 |
1998年 | 1126篇 |
1997年 | 655篇 |
1996年 | 389篇 |
1995年 | 196篇 |
1994年 | 179篇 |
1993年 | 228篇 |
1992年 | 13篇 |
1991年 | 28篇 |
1990年 | 27篇 |
1989年 | 41篇 |
1988年 | 33篇 |
1987年 | 33篇 |
1986年 | 16篇 |
1985年 | 26篇 |
1984年 | 1篇 |
1983年 | 7篇 |
1982年 | 18篇 |
1981年 | 13篇 |
1980年 | 26篇 |
1979年 | 2篇 |
1978年 | 10篇 |
1977年 | 76篇 |
1976年 | 136篇 |
1971年 | 1篇 |
1955年 | 3篇 |
排序方式: 共有3485条查询结果,搜索用时 15 毫秒
41.
42.
A test designed to separate those undergoing thoracic surgery without complications and those with complications must be both highly specific and sensitive. Clearly, the difference between patients at opposite ends of the population curves is easy to identify. Spirometry can be helpful for screening, although it is not a very discriminating test. If patients fall in the overlap region between the populations, however, it is impossible to discern the risks with any certainty using low-yield tests. A test with higher sensitivity, specificity, and predictive values is necessary to ascertain such marginal differences. With this kind of analysis at hand, preoperative testing can be divided into three predictive value groups. Calculating the predictive value of each preoperative test can provide a comparative measure of usefulness of discriminative power (Table 1). In this way, spirometry, blood gas analysis, and stair climbing tolerance are shown to be poor predictors of outcome. An intermediate predictive value can be achieved using diffusion capacity, exercise-induced decreases in O2 saturation, and exercise PVR. High predictive value can be accomplished with combination indexes (PPP, possibly PRQ), measurement of VO2 at 40 watts of exercise, or VO2max. Logic dictates a step-wise preoperative evaluation using prediction value analysis (Fig.4). A flow decision chart for the preoperative evaluation of patients for pulmonary resection begins with exercise oximetry, spirometry, and blood gas analysis as general screening tests to separate those patients at minimal or no risks for complications from those patients that require further evaluation. Functional indexes (PPP, PRQ) or exercise testing can aid further in the selection of those patients in whom a nonsurgical option should be considered. Flow decision chart for the preoperative evaluation of patients for pulmonary resection should continue to evolve as new information about outcome studies is gathered. Examination of outcome data will provide us with reduction of the size of the nonoperable population, so that we can deny only those patients who truly pose a prohibitive risk. 相似文献
43.
44.
The different chi-square statistics reported in the many-faceted Rasch model analysis are presented and interpreted. In addition, other chi-square summary values are computed and presented for interpretation of facets. The chi-square values are useful for determining: (1) the significance of a facet in the Rasch model; (2) the significant contribution of facet main and interaction effects; (3) differences among facet elements; and (4) identifying the specific facet interaction adjustments to the subjects' calibrated logit ability measure. 相似文献
45.
PH Kilmarx AA Zaidi JC Thomas AK Nakashima ME St Louis ML Flock TA Peterman 《Canadian Metallurgical Quarterly》1997,87(12):1937-1943
OBJECTIVES: Syphilis in the United States is focally distributed, with high incidence rates in the South and in metropolitan areas nationwide. In this study an ecological analysis, using the county as the unit of analysis, was performed to generate hypotheses about community-level determinants of syphilis rates. METHODS: Bivariate rank correlations and multivariate, backward stepwise elimination linear regressions were performed. Mean annual incidence of primary- and secondary-stage syphilis in a county was the dependent variable, and county sociodemographic characteristics (from census data) were the independent variables. RESULTS: In the multivariate regression model, sociodemographic characteristics accounted for 71% of the variation in syphilis rates among counties. With other factors accounted for, the most highly correlated characteristics were percentage non-Hispanic Black population, county location in the South, percentage of the population that was urban, percentage Hispanic population, and percentage of births to women younger than 20 years. CONCLUSIONS: Most of the variation in syphilis rates among counties is accounted for by sociodemographic characteristics. Identification and remediation of modifiable health determinants for which these factors are markers are needed to improve the health status of these populations. 相似文献
46.
Pre-clerking of all patients undergoing elective general surgical operations was introduced at our hospital in an attempt to reduce an unacceptably high operation cancellation rate. A prospective audit has been performed on the effect of this policy on the cancellation rate. Before the introduction of pre-clerking there was a marked seasonal variation in the number of patients who failed to attend for surgery, which could be explained by absence on holiday. This seasonal variation disappeared after the start of pre-clerking clinics, but there has been no reduction in the number of cancellations for medical reasons. 相似文献
47.
KI el-Noueam V Giuliano ME Schweitzer BJ O''Hara 《Canadian Metallurgical Quarterly》1997,21(5):796-799
A 62-year-old female who had a complaint of palpitation was diagnosed as bicuspid aortic stenosis and left single coronary artery by the echocardiographic examination, cardiac catheterization study and coronary artery angiography. Aortic valve replacement was performed and the patient was discharged 22 days after surgery with good post-operative course. Preoperative coronary artery angiography was important in the case of aortic valvular disease. 相似文献
48.
R Kath K H?ffken C Otte K Metz ME Scheulen F Hülskamp S Seeber 《Canadian Metallurgical Quarterly》1993,4(7):585-590
Patients with non-cardiac chest pain (NCCP) (n = 387) and cardiac chest pain (CCP) (n = 93) were compared with community controls (n = 81), using a symptom questionnaire that assessed the presence of irritable bowel syndrome (IBS), functional dyspepsia, and oesophageal dysfunction and chest pain characteristics. A significantly (p < 0.05) increased prevalence of symptoms compatible with IBS occurred in NCCP patients when compared with those with CCP and with controls. Dysphagia was more frequent in both those with non-cardiac and cardiac chest pain than in controls; this was not apparent, however, when patients with concomitant IBS were excluded. The presence of oesophageal or gastrointestinal symptoms did not enable discrimination with regard to the chest pain characteristics. We conclude that unselected referred patients with documented NCCP are more likely to have IBS and that the presence of oesophageal symptoms such as dysphagia may merely reflect the spectrum of the 'irritable gut'. 相似文献
49.
50.
ME Salive 《Canadian Metallurgical Quarterly》1994,159(2):83-86
A male patient presented with complaints of fever, cough with expectoration, burning micturition and 5-6 semisolid motions per day for the past 6 days. Skiagram chest (PA view) revealed lung abscess in the left mid zone. There was no improvement, symptomatically and radiologically, after an empirical course of antibiotics (IV ampicillin and gentamycin). Sputum, urine and stool cultures grew salmonella group E organisms sensitive only to cefotaxime. The patient was treated with IV cefotaxime and responded well clinically, radiologically and bacteriologically. 相似文献