全文获取类型
收费全文 | 51378篇 |
免费 | 4266篇 |
国内免费 | 972篇 |
专业分类
电工技术 | 1338篇 |
综合类 | 1616篇 |
化学工业 | 10791篇 |
金属工艺 | 1464篇 |
机械仪表 | 1640篇 |
建筑科学 | 2291篇 |
矿业工程 | 475篇 |
能源动力 | 1293篇 |
轻工业 | 9145篇 |
水利工程 | 830篇 |
石油天然气 | 861篇 |
武器工业 | 137篇 |
无线电 | 3228篇 |
一般工业技术 | 7063篇 |
冶金工业 | 6230篇 |
原子能技术 | 294篇 |
自动化技术 | 7920篇 |
出版年
2024年 | 166篇 |
2023年 | 617篇 |
2022年 | 1244篇 |
2021年 | 1877篇 |
2020年 | 1529篇 |
2019年 | 1411篇 |
2018年 | 1966篇 |
2017年 | 2011篇 |
2016年 | 2021篇 |
2015年 | 2059篇 |
2014年 | 2602篇 |
2013年 | 4137篇 |
2012年 | 3863篇 |
2011年 | 3935篇 |
2010年 | 3201篇 |
2009年 | 2990篇 |
2008年 | 2898篇 |
2007年 | 2672篇 |
2006年 | 1989篇 |
2005年 | 1555篇 |
2004年 | 1210篇 |
2003年 | 1005篇 |
2002年 | 855篇 |
2001年 | 625篇 |
2000年 | 514篇 |
1999年 | 509篇 |
1998年 | 2054篇 |
1997年 | 1330篇 |
1996年 | 842篇 |
1995年 | 480篇 |
1994年 | 370篇 |
1993年 | 377篇 |
1992年 | 133篇 |
1991年 | 110篇 |
1990年 | 99篇 |
1989年 | 84篇 |
1988年 | 106篇 |
1987年 | 102篇 |
1986年 | 80篇 |
1985年 | 99篇 |
1984年 | 72篇 |
1983年 | 47篇 |
1982年 | 48篇 |
1981年 | 74篇 |
1980年 | 69篇 |
1978年 | 35篇 |
1977年 | 109篇 |
1976年 | 221篇 |
1975年 | 35篇 |
1973年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 17 毫秒
151.
B Acea Nebril J Aguirrezabalaga González F Fraguela Mari?a L Taboada Filgueira D Freire Rodríguez C Gómez Freijoso 《Canadian Metallurgical Quarterly》1997,21(7):705-707
Gut involvement in bladder tumours is low, even exceptional in the presence of surface, low-grade neoplasia. The authors explain their experience in the diagnosis and management of a patient treated endoscopically for a vesical surface tumour which subsequently exhibited peritoneal and gut metastatic seeding. The various mechanisms for gut dissemination of vesical neoplasias and the repercussion of their endoscopic management are discussed. 相似文献
152.
Subsequent to the implementation of a severity marker stamp in case notes, an audit was performed in 86 admissions with acute asthma to a specialist centre over a 12 month period. Compared to previous audit the documentation of severity markers was significantly better (PEFR: 52% vs 83% p = 0.001, Respiratory rate: 44% vs 81% p = 0.001, ABG: 72% vs 80% p = 0.04, air entry: 58% vs 86% p = 0.001, speech: 27% vs 86% p = 0.001, exhaustion: 4% vs 86% p = 0.001). In contrast to the previous audit where no patient received FiO2 > 0.35, 66% of the cases in the repeat audit received FiO2 0.60 (p = 0.001). The mean duration of admission was five days and showed highest partial correlation (r = 0.6) to the time in hours for the pulse to fall to 80/min. Multiple linear regression showed that this was the only variable best predicting the duration of admission (R2 = 0.3). Admission pulse rate (p = 0.04) and serum K+ (p = 0.04) best discriminated between patients admitted for over and under five days. Logistic regression identified only the admission pulse as significant in calculating the odds of the patient staying in the hospital for > 5 days. 相似文献
153.
Craniometric data from the three extinct tribes that inhabited Tierra del Fuego (Selk'nam, Yámana, and Kawéskar) were gathered following Howell's measurement technique. We studied 180 skulls preserved at thirteen different institutions. Analysis of variance (ANOVA) between groups showed that morphological similarities among Fueguian groups are far more important than some differences between marine (Yámana and Kawéskar) and terrestrial (Selk'nam) groups. A principal component analysis (PCA) generated from the correlation matrix shows that Fueguians fall as outliers with respect to the typical Mongoloid morphology. In addition, a UPGMA tree generated from a squared Euclidean distance matrix indicates that Fueguian groups have a morphological pattern that is very distinct from that of other present-day Amerindian groups, with the exception of the Eskimos. One of the variables that contributes substantially to the differentiation of Eskimos and Fueguians is the nasal height. This suggests that nasal morphology in both groups could be a response to adaptive pressures related to the cold environment. However, other morphological particularities of Fueguian skulls, such as craniofacial robustness and variables of craniofacial width, can be attributed to a large masticatory stress. As a whole, the morphological features of Fueguian groups can be regarded as a general adaptive response to a very harsh environment, along with the retention of some plesiomorphic features. Assuming that the initial entry in Tierra de Fuego took place around 10,000 years BP, before the disappearance of the last land bridges in the Magellan Straits, then this adaptation might have arisen in a relatively short period, hastened by the extreme environmental conditions. 相似文献
154.
II Kalachev AN Baídus' OA Ivanova EA Ganina IA Boldyrev EA Svetoch 《Canadian Metallurgical Quarterly》1997,(6):32-37
Unlike the glanders agent, the superficial structures of the melioidosis agent were demonstrated to be responsible for marked was immunosuppressive activity. Some antigenic fractions suppressing the blast transformation of lymphocytes, reducing the count of T helpers and profoundly potentiating the infection in vivo were isolated from P. pseudomallei cells. The immunogenic and immunosuppressive activities of both agents' superficial structures were studied by high performance chromatography. Antigenic complexes that were able to protect immunized laboratory animals against fatal infections and to prevent bacterial carriage due to the activation of T cells and to the bacterial activity of macrophages were identified. A composition comprising several immunogens was found to provide an additive protective action against both causative agents. Therefore, the composition may be considered to be a prototype of a molecular antipseudomonadic vaccine. 相似文献
155.
156.
157.
LA Pérula de Torres J Martínez de la Iglesia J Espejo Espejo MV Rubio Cuadrado I Enciso Berge FJ Fonseca del Pozo JM Aranda Lara 《Canadian Metallurgical Quarterly》1997,20(8):425-434
OBJECTIVE: To describe the health status of a population over 60 years and to study their relationship with several socio-demographic variables. DESIGN: A cross-sectional study, population based. SETTINGS: A community. PARTICIPANTS: A randomized sample of 1,103 non institutionalized people over 60 years living in the city of Cordoba (Spain). MEASUREMENTS AND MAIN RESULTS: By mean of a personal interview at home we used the OARS-MFAQ-VE questionnaire. Low self-rated health was associated with the age, to be female sex, a low cultural background, and a low income. Only 5.2% of the study people do not suffered any illness and 56% state that their health problems are major problems for doing their current activities. 4.9% declared to have some degree of physical incapacity. 3.7% of elderly population has an important cognitive deficit. CONCLUSIONS: The majority of elderly people has good health. Age is related with a poor health. Women have more health problems than men. 相似文献
158.
A cryptic multidrug resistance (MDR) system in Stenotrophomonas maltophilia, the expression of which is selectable by tetracycline, is described. Tetracycline resistance was the consequence of active efflux of the antibiotic, and it was associated with resistance to quinolones and chloramphenicol, but not to aminoglycosides or beta-lactam antibiotics. MDR is linked to the expression of an outer membrane protein (OMP54) both in a model system and in multidrug-resistant clinical isolates. 相似文献
159.
JA Carballido Rodríguez 《Canadian Metallurgical Quarterly》1997,21(7):641-643
A case of a large dentigerous cyst containing a canine tooth in the maxillary antrum is presented. This case is of interest due because of its extensiveness and the presence of a canine tooth in the roof of the maxillary sinus. In addition, this caused a right-sided epiphora. Enucleation of the cyst containing the ectopic tooth was made. 相似文献
160.
A Serrano Pascual C Merino Hernáez R Ochoa Mejías A Escolano Chamois J Golbano Ablanque I Otero Tejero M Sanz Redondo F Román Ruiz 《Canadian Metallurgical Quarterly》1997,21(6):631-635
BACKGROUND AND AIMS OF THE STUDY: Surgical treatment of functional tricuspid regurgitation associated with advanced valvular disease remains controversial, mainly due to the difficulty in choosing between valve replacement or reconstructive surgery. Failure to correct tricuspid regurgitation during valvular surgery carries a poor prognosis, as reoperation may represent a significant risk to the patient. Thus correct tricuspid valve surgery is vital to achieve improved early and long-term clinical results. METHODS: A total of 142 patients underwent concomitant tricuspid annuloplasty with mitral valve replacement and their clinical outcome was assessed. RESULTS: Overall hospital mortality rate was 11.3%. Seven patients died during follow up. The overall actuarial survival rate for 10 years was 74.1 +/- 14.2%. Postoperatively, 75.8% of the patients had no residual tricuspid insufficiency, while 24.2% had first- or second-degree tricuspid insufficiency and were treated medically. All patients were in NHYA functional class I or II postoperatively. CONCLUSION: Clinically, it is important to assess the severity of functional tricuspid insufficiency before and/or during the operation. Bicuspidalization annuloplasty for functional tricuspid insufficiency has provided good results, with a low incidence of reoperation and significant clinical improvement. The technique could be used in most patients with functional tricuspid regurgitation. 相似文献