全文获取类型
收费全文 | 96985篇 |
免费 | 1827篇 |
国内免费 | 517篇 |
专业分类
电工技术 | 977篇 |
综合类 | 2376篇 |
化学工业 | 14941篇 |
金属工艺 | 5098篇 |
机械仪表 | 3497篇 |
建筑科学 | 2684篇 |
矿业工程 | 582篇 |
能源动力 | 2085篇 |
轻工业 | 4854篇 |
水利工程 | 1412篇 |
石油天然气 | 590篇 |
武器工业 | 4篇 |
无线电 | 10556篇 |
一般工业技术 | 18746篇 |
冶金工业 | 3114篇 |
原子能技术 | 355篇 |
自动化技术 | 27458篇 |
出版年
2024年 | 73篇 |
2023年 | 288篇 |
2022年 | 615篇 |
2021年 | 945篇 |
2020年 | 807篇 |
2019年 | 881篇 |
2018年 | 15153篇 |
2017年 | 13985篇 |
2016年 | 10649篇 |
2015年 | 1101篇 |
2014年 | 1029篇 |
2013年 | 1651篇 |
2012年 | 4028篇 |
2011年 | 10314篇 |
2010年 | 8895篇 |
2009年 | 6127篇 |
2008年 | 7172篇 |
2007年 | 8099篇 |
2006年 | 420篇 |
2005年 | 1396篇 |
2004年 | 1296篇 |
2003年 | 1320篇 |
2002年 | 654篇 |
2001年 | 190篇 |
2000年 | 269篇 |
1999年 | 139篇 |
1998年 | 192篇 |
1997年 | 148篇 |
1996年 | 142篇 |
1995年 | 80篇 |
1994年 | 63篇 |
1993年 | 68篇 |
1992年 | 58篇 |
1991年 | 60篇 |
1990年 | 40篇 |
1989年 | 32篇 |
1988年 | 34篇 |
1986年 | 34篇 |
1968年 | 45篇 |
1967年 | 34篇 |
1966年 | 42篇 |
1965年 | 44篇 |
1963年 | 28篇 |
1960年 | 30篇 |
1959年 | 35篇 |
1958年 | 37篇 |
1957年 | 36篇 |
1956年 | 34篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
BACKGROUND: The incidental discovery of an adrenal mass poses the problem of distinguishing between the frequent benign masses and the infrequent malignant ones that require surgery. Univocal guidelines to approach this problem are unavailable. OBJECTIVE: To perform a survey of the clinical management of incidentally discovered adrenal masses (ie, adrenal incidentalomas). DESIGN: A multicentric retrospective analysis of hospital medical records of adrenal incidentalomas diagnosed during a 5-year period; the medical records were scrutinized for demographic data and clinical details by means of a specifically tailored questionnaire. SETTING: The major surgical and medical centers of Piedmont, a northern Italian region with approximately 4 million inhabitants. The recruitment pattern of these centers was unselected. PATIENTS: The definition of adrenal incidentaloma was limited to patients with a physical examination and a clinical history unindicative of adrenal disease. Exclusion criteria also included hypertension of suspected endocrine origin and a history of neoplasms known to metastasize frequently in the adrenal glands. Two hundred twenty-four medical records were collected, and 210 were analyzed (14 excluded a posteriori). RESULTS: Most patients were in their 50s and 60s, and women were predominantly affected. The frequency of adrenocortical cancer was 13% among patients operated on. The tumor diameter was highly correlated with the risk of cancer; a cutoff at 5 cm had a sensitivity of 93% with a specificity of 64% in discriminating between benign and malignant cortical lesions. CONCLUSIONS: The occurrence of adrenocortical carcinoma among adrenal incidentalomas is not rare. The evaluation of the mass size is a simple and effective method for selecting patients at risk for cancer. The indication for surgery of masses larger than 5 cm, or of masses of any diameter that have suspicious imaging characteristics, limits unnecessary operations and costs. 相似文献
2.
The purpose of this paper is to evaluate two methods of assessing the productivity and quality impact of Computer Aided Software Engineering (CASE) and Fourth Generation Language (4GL) technologies: (1) by the retrospective method; and (2) the cross-sectional method. Both methods involve the use of questionnaire surveys. Developers' perceptions depend on the context in which they are expressed and this includes expectations about the effectiveness of a given software product. Consequently, it is generally not reliable to base inferences about the relative merits of CASE and 4GLs on a cross-sectional comparison of two separate samples of users. The retrospective method that requires each respondent to directly compare different products is shown to be more reliable. However, there may be scope to employ cross-sectional comparisons of the findings from different samples where both sets of respondents use the same reference point for their judgements, and where numerical rather than verbal rating scales are used to measure perceptions. 相似文献
3.
4.
5.
J-M Choe 《欧洲信息系统杂志》2002,11(2):142-158
This study empirically examined the organisational learning effects of the nonfinancial performance information provided by management accounting information systems (MAISs) under advanced manufacturing technology (AMT). In this study, a target costing system and the frequent and quick reporting of information were considered the facilitators of learning. First, we examined the relationships between AMT level and the amount of nonfinancial performance information produced by MAISs. The empirical results showed that there are significant positive relationships between the level of AMT and nonfinancial performance information. With a systems approach, we also proved the impact of the relationships among AMT levels, nonfinancial performance information and learning facilitators on the organisational performance of a firm. The results of our research suggest that under a high level of AMT, for the provision of information to result in an increase of performance through organisational learning, a target costing system must be introduced and a large amount of information should be provided frequently and quickly. The results of this study also showed that although AMT level may be low, fairly well-arranged facilitators and a moderately large amount of information may be necessary for the improvement of performance. In conclusion, effective organisational learning depends on the provision of relevant information as well as efficient learning support mechanisms. 相似文献
6.
7.
8.
9.
10.