全文获取类型
收费全文 | 3462篇 |
免费 | 10篇 |
专业分类
电工技术 | 31篇 |
化学工业 | 83篇 |
金属工艺 | 12篇 |
机械仪表 | 11篇 |
建筑科学 | 29篇 |
能源动力 | 15篇 |
轻工业 | 40篇 |
水利工程 | 1篇 |
石油天然气 | 1篇 |
无线电 | 135篇 |
一般工业技术 | 103篇 |
冶金工业 | 2849篇 |
原子能技术 | 6篇 |
自动化技术 | 156篇 |
出版年
2022年 | 7篇 |
2019年 | 5篇 |
2017年 | 5篇 |
2016年 | 9篇 |
2015年 | 5篇 |
2014年 | 8篇 |
2013年 | 19篇 |
2012年 | 28篇 |
2011年 | 26篇 |
2010年 | 14篇 |
2009年 | 17篇 |
2008年 | 30篇 |
2007年 | 31篇 |
2006年 | 24篇 |
2005年 | 26篇 |
2004年 | 23篇 |
2003年 | 36篇 |
2002年 | 25篇 |
2001年 | 19篇 |
2000年 | 18篇 |
1999年 | 98篇 |
1998年 | 855篇 |
1997年 | 483篇 |
1996年 | 327篇 |
1995年 | 173篇 |
1994年 | 168篇 |
1993年 | 160篇 |
1992年 | 36篇 |
1991年 | 42篇 |
1990年 | 32篇 |
1989年 | 59篇 |
1988年 | 52篇 |
1987年 | 43篇 |
1986年 | 39篇 |
1985年 | 43篇 |
1984年 | 12篇 |
1983年 | 16篇 |
1982年 | 27篇 |
1981年 | 26篇 |
1980年 | 46篇 |
1979年 | 6篇 |
1978年 | 9篇 |
1977年 | 92篇 |
1976年 | 176篇 |
1975年 | 14篇 |
1974年 | 14篇 |
1972年 | 5篇 |
1970年 | 5篇 |
1968年 | 4篇 |
1967年 | 4篇 |
排序方式: 共有3472条查询结果,搜索用时 15 毫秒
991.
Heterotopic gastric mucosa may occur throughout the gastrointestinal tract, including the upper esophagus. The capability of this ectopic mucosa to secrete acid has been suggested in different reports. We report for the first time a case of heterotopic gastric mucosa in the upper esophagus complicated by a stricture with secretion of acid demonstrated by prolonged ambulatory pH monitoring. Lansoprazole, 30 mg twice daily, produced symptom resolution, and repeat ambulatory pH showed complete acid suppression in the proximal esophagus. 相似文献
992.
D Lister AJ Evans HC Burrell RW Blamey AR Wilson SE Pinder IO Ellis CW Elston J Kollias 《Canadian Metallurgical Quarterly》1998,53(7):490-492
INTRODUCTION: Recent reports have suggested that breast ultrasound (US) is of value in distinguishing malignant from benign processes. The aim of this study was to establish the accuracy of US in detecting invasive malignancy in clinically benign, discrete, symptomatic breast lumps. METHODS: The US appearances of 205 clinically benign breast masses were documented prospectively and prior to mammography by one radiologist (AJE). The US appearances were then correlated with the fine needle aspiration (FNA), core biopsy and surgical findings and compared with the mammographic findings. RESULTS: The US findings were normal 72 (35%), simple cyst 63 (31%), solid benign 51 (25%), solid indeterminate 15 (7%) and solid malignant four (2%). Ultrasound characterized 13 (93%) of the 14 patients found to have invasive carcinoma as indeterminate or malignant. No patients with normal or simple cyst US findings had invasive malignancy. Ultrasound had significantly better accuracy (97% vs 87%, P < 0.02) sensitivity (93% vs 57%, P < 0.05) and negative predictive value (99% vs 92%, P < 0.002) than mammography in the detection of invasive carcinoma when indeterminate and malignant imaging findings were taken as positive. CONCLUSION: US is a useful adjunct to FNA/core biopsy in confirming the nature of symptomatic, clinically benign breast masses and is superior to mammography in this clinical setting. 相似文献
993.
994.
The electron paramagnetic resonance (EPR) low-temperature spectra of high spin ferric myoglobin samples in different solvent composition have been analyzed in terms of a distribution of the energy differences delta 1 and delta 2 for the iron low-lying electronic states. The widths of these distributions, which are found to be dependent on the solvent composition, have been correlated to the presence of a frozen ensemble of conformational substrates. A dedicated analysis based on the angular overlap method (AOM) has allowed us to work out a quantitative relationship between the delta 1 and delta 2 distributions and the spread of the iron-heme displacement; this being a structural parameter relevant for the biological functionality of the protein. The observed dependence of the iron-heme displacement distribution on the solvent composition is discussed. 相似文献
995.
KJ Greenlund K Liu AR Dyer CI Kiefe GL Burke C Yunis 《Canadian Metallurgical Quarterly》1996,86(4):480-485
OBJECTIVES: Associations of parental education, parental body size, and offspring's education with body mass index and 7-year change in body mass index were examined among participants in the Coronary Artery Risk Development in Young Adults (CARDIA) study. METHODS: CARDIA is a study of coronary artery disease risk factors in 5115 Black and White persons aged 18 to 30 at baseline. Analyses of covariance were carried out with body mass index and change in body mass index as the dependent variables, and with parental education, parental body size, and participant education as the major independent variables. RESULTS: Father's body size was positively associated with participant's baseline body mass index among Black men, White men, and White women. Mother's body size was positively associated with baseline body mass index among all race-sex groups, and with change in body mass index among White women. Father's education was inversely associated with baseline body mass index among Black men and White women, and with change among White women. CONCLUSIONS: Parental education may influence body mass index and changes in young adulthood, especially among White women. Such associations may be both genetic and environmental and may be important for obesity prevention efforts. 相似文献
996.
A simple method using ion-pair high-performance liquid chromatography was established for the rapid and precise simultaneous determination of honokiol (3', 5-di-2-propenyl-1, 1'-biphenyl-2,4'-diol) and magnolol (5,5'-di-2-propenyl-1,1'-biphenyl-2,2'-diol) in oriental pharmaceutical decoctions containing Magnolia bark. An ODS column and a mixture of water involving 10 mM tetra-n-amylammonium bromide (TAA) and acetonitrile (4:6) as a mobile phase were used for the separation. Honokiol and magnolol were eluted without interference of other co-existing components within 12 min. 相似文献
997.
998.
AH Kral JK Watters AR Lifson JR Carlson M Stanley 《Canadian Metallurgical Quarterly》1995,10(3):381-385
Standard HIV-1 testing relies on the enzyme immunoassay (EIA) for detecting antibodies specific to HIV-1. This technique may misclassify persons as HIV-1-negative in instances where testing follows infection but precedes development of antibody to HIV-1. To evaluate the occurrence of HIV infection in the absence of positive antibody, polymerase chain reaction (PCR) for viral DNA in the blood has been applied. Research comparing these two testing techniques has generally focused on populations of homosexual and bisexual men. This study compares PCR and antibody testing of 337 injecting drug users recruited from street settings in San Francisco. Of 286 HIV-1 antibody-negative samples, 3 (1.0%) were PCR-positive. Of 49 HIV-1 antibody-positive samples, 1 (2.0%) was PCR-negative. Two samples were antibody-indeterminate and PCR-negative. This yielded an overall concordance of 331/335 (98.8%), excluding the indeterminate results. These results suggest that current antibody methodology is adequate. However, misclassification among recently infected individuals may occur, which is of concern in high-incidence groups. 相似文献
999.
1000.