全文获取类型
收费全文 | 639408篇 |
免费 | 8157篇 |
国内免费 | 1914篇 |
专业分类
电工技术 | 11550篇 |
综合类 | 491篇 |
化学工业 | 98122篇 |
金属工艺 | 23782篇 |
机械仪表 | 18578篇 |
建筑科学 | 16895篇 |
矿业工程 | 2602篇 |
能源动力 | 16290篇 |
轻工业 | 61523篇 |
水利工程 | 5956篇 |
石油天然气 | 8706篇 |
武器工业 | 29篇 |
无线电 | 77553篇 |
一般工业技术 | 121203篇 |
冶金工业 | 118420篇 |
原子能技术 | 11899篇 |
自动化技术 | 55880篇 |
出版年
2021年 | 4406篇 |
2019年 | 4074篇 |
2018年 | 6911篇 |
2017年 | 6970篇 |
2016年 | 7444篇 |
2015年 | 5481篇 |
2014年 | 9079篇 |
2013年 | 28656篇 |
2012年 | 15407篇 |
2011年 | 21773篇 |
2010年 | 17134篇 |
2009年 | 19550篇 |
2008年 | 20613篇 |
2007年 | 20758篇 |
2006年 | 18573篇 |
2005年 | 17296篇 |
2004年 | 16561篇 |
2003年 | 16152篇 |
2002年 | 15821篇 |
2001年 | 15830篇 |
2000年 | 14810篇 |
1999年 | 15355篇 |
1998年 | 35623篇 |
1997年 | 26191篇 |
1996年 | 20540篇 |
1995年 | 15938篇 |
1994年 | 14279篇 |
1993年 | 13827篇 |
1992年 | 10496篇 |
1991年 | 10187篇 |
1990年 | 9719篇 |
1989年 | 9500篇 |
1988年 | 9197篇 |
1987年 | 7787篇 |
1986年 | 7749篇 |
1985年 | 9236篇 |
1984年 | 8785篇 |
1983年 | 7787篇 |
1982年 | 7320篇 |
1981年 | 7407篇 |
1980年 | 7037篇 |
1979年 | 6878篇 |
1978年 | 6673篇 |
1977年 | 7899篇 |
1976年 | 10410篇 |
1975年 | 5807篇 |
1974年 | 5551篇 |
1973年 | 5461篇 |
1972年 | 4636篇 |
1971年 | 4173篇 |
排序方式: 共有10000条查询结果,搜索用时 19 毫秒
991.
A random sample of patients (n = 43) had been investigated to detect any difference in response of bright light therapy in lithium-treated inpatients (n = 18) suffering from depression. Only 27% of the lithium-based inpatients respond to bright light therapy, but 73% of patients respond who were not treated with lithium. We conclude that lithium therapy reduces the chance of achieving t remission of depression by bright light therapy. 相似文献
992.
BACKGROUND: Systemic osteoporosis is a common and pathogenetically heterogenous complication in rheumatoid arthritis. Various factors such as disease activity, dosage and duration of glucocorticoid treatment and immobilization are involved in pathogenesis of osteoporosis in rheumatoid arthritis. INFLAMMATION AND BONE METABOLISM: Proinflammatory cytokines secreted by immunocompetent cells have a role in the regulation of the activity of osteoblasts and osteoclasts. The effects of these proinflammatory cytokines include the inhibition of bone formation and an increase in bone resorption. Interleukin-6 and nitric oxide induced in osteoblasts by proinflammatory cytokines are likely to be important mediators between these cytokines and the function of osteoblasts and osteoclasts. Furthermore, disease activity dependent changes in the secretion of glucocorticoids and in vitamin D metabolism may be involved in the pathogenesis of osteoporosis in this disease. Alteration of bone remodeling associated with immobilization is an important factor of systemic bone loss in rheumatoid arthritis. CONCLUSION: The inflammatory process in rheumatoid arthritis may cause penarticular and systemic bone loss by various cytokine and hormone mediated mechanisms. Concluding from these pathogenetic mechanisms, bisphosphonates and active vitamin D metabolites are likely to be effective therapeutic options in osteoporosis associated with rheumatoid arthritis. 相似文献
993.
JN Vauthey RJ Tomczak T Helmberger P Gertsch C Forsmark J Caridi A Reed MR Langham GY Lauwers P Goffette J Lerut 《Canadian Metallurgical Quarterly》1997,113(4):1390-1401
BACKGROUND & AIMS: Arterioportal fistulas (APFs) are rare vascular disorders of the mesenteric circulation. The aim of this study was to determine the etiology, anatomical location, and main symptom at presentation of APFs, and analyze the various modes of treatment. METHODS: The etiology, clinical presentation, radiographs, and treatment of 12 patients with APFs are reported in detail, and another 76 cases published since 1980 are reviewed. RESULTS: APFs result from trauma (n = 25, 28%), iatrogenic procedures (n = 14, 16%), congenital vascular malformations (n = 13, 15%), tumor (n = 13, 15%), aneurysm (n = 12, 14%), and other causes (n = 11, 12%). The origin of APFs is the hepatic artery in the majority of patients (n = 56, 65%). The main symptoms at presentation are lower or upper gastrointestinal bleeding (n = 29, 33%), ascites (n = 23, 26%), heart failure (n = 4.5%), or diarrhea (n = 4.5%). Radiological intervention provides definitive treatment in 42% (n = 33) of patients, whereas the remainder are treated by surgery alone (n = 27, 31%) or a combination of radiological intervention and surgery (n = 8, 9%). CONCLUSIONS: APFs result in a protean syndrome variously combining portal hypertension and other hemodynamic imbalances (heart failure, intestinal ischemia). Single or multiple interventional radiological procedures using arterial and/or venous approaches allow definitive treatment of most APFs. With increasing technological advances, it is anticipated that surgery will only be indicated in rare instances after failure of radiological intervention(s). 相似文献
994.
The finite-element method is used to model the elastic-plastic indentation response of a flat extensive specimen for the case
of a spherical indenter. The work highlights several interesting finite-element modelling techniques and provides insight
into the physical processes involved in elastic-plastic indentation of certain structural ceramics. Full details of the stress
distribution are given and compared with the results of elastic formulae. This work has particular application to the modelling
of physical phenomena of deformation in ceramic materials in machining, wear, bearings and hardness testing.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
995.
A chromosomally integrated Bradyrhizobium japonicum hoxA mutant is unable to oxidize hydrogen in free-living conditions. Derepressing conditions that induce hydrogenase activity in free-living, wild-type B. japonicum cells cannot induce expression of the hydrogenase structural genes in the hoxA mutant. The DNA-binding capacity of HoxA at the hup promoter region was studied by means of gel retardation. Both heterotrophically growing cells and cells induced to express hydrogenase activity contain a protein that specifically binds to the hup promoter region. Crude protein extracts isolated from a B. japonicum hoxA mutant do not contain this binding compound. The HoxA protein was overexpressed in E. coli and isolated in the form of a maltose-binding protein (MBP)-HoxA fusion. The MBP-HoxA hybrid protein specifically bound to a 50 bp region of the hupSL promoter known to be important for regulation of hupSL expression. 相似文献
996.
MineSet aids knowledge discovery and supports decision making based on relational data. It uses visualization and data mining to arrive at interesting results. Providing diverse visualization tools lets users choose the most appropriate method for a given problem. The client-server architecture performs most of the computationally intensive tasks on a server, while the processed results return to the client for visualization. The paper discusses MineSet database visualization and data mining visualization 相似文献
997.
J Weber P Majer J Litera J Urban M Soucek J Vondrásek J Konvalinka P Novek J Sedlácek P Strop HG Kr?usslich I Pichová 《Canadian Metallurgical Quarterly》1997,341(1):62-69
The results of investigation of haptoglobin (Hp) types in 596 donor blood samples in some towns of Ukraine (Dnepropetrovsk, Kharkov, Odessa, Kiev, Uzhgorod, Zhitomir) are presented. Three normal Hp types (Hp1-1, Hp2-1 and Hp2-2) have been found. The reliable interpopulation differences in the Hp types frequency were not found. On the whole the Hp types frequency in the type Hp1-1 comprised 12.7%. In the type Hp2-1-48.1% and in the type Hp2-2-36.5%. The frequency of the gene Hp1 is 0.38. The frequency of the Hp types and of the gene Hpl in Ukraine is similar to that in population of Eastern Europe and European Part of Russia. 相似文献
998.
S. Vaynman R. S. Guico M. E. Fine S. J. Manganello 《Metallurgical and Materials Transactions A》1997,28(5):1274-1276
999.
Wernicke encephalopathy is considered a complication of dialytic therapy, but there are few reports of this complication. We report a 57 years old man and a 45 years old woman, with grade IV renal failure, who after acute peritoneodialysis and chronic hemodialysis respectively, had a confusional syndrome that responded to the administration of thiamine. CT scans in both patients discarded abnormal blood collections or new cerebrovascular episodes. The man bad two previous cerebrovascular episodes, a severe anemia that was corrected, angina and an episode of arrhythmia during the dialytic procedure previous to the confusional episode. The woman had an acute uremic syndrome and a concomitant urinary tract infection during the confusional episode. Wernicke encephalopathy must be suspected in patients in dialysis with confusional episodes. 相似文献
1000.
INTRODUCTION: Cystic fibrosis is a recessive genetic systemic exocrinopathy caused by a variety of mutations in the cystic fibrosis transmembrane conductance regulator gene (CFTR). The disease is characterized by alterations of the secretions, which become thickened and viscous. Both the paranasal sinuses and the lung parenchyma are involved in all cases. The aim of this study was to assess a correlation between the rhinosinusal and lung parenchyma changes in cystic fibrosis patients. MATERIAL AND METHODS: Eighteen patients (11 men and 7 women, age range: 8 to 22 years) were examined with chest HRCT and sinonasal low dose CT. Lung symptoms were found in all patients; 13 of them, also affected with rhinosinusal symptoms, had been examined with ENT and nasal endoscopy. The other 5 patients, without rhinosinusal symptoms and previously examined with ENT, were evaluated as control group. Chest CT was performed with the high-resolution technique, 2 mm slice thickness and 10 mm table feed. Rhinosinusal CT was performed with the low dose technique, acquiring contiguous 2-4 mm thickness coronal sections. The CT patterns were analyzed by two radiologists and scored as slight, medium and diffuse involvement of both districts. RESULTS: No statistically significant correlation between lung and sinonasal damage was found in our study. Parenchymal lung involvement appeared more severe than sinonasal involvement in 14/18 patients. The retention of secretions in the paranasal sinuses, even if limited, was demonstrated in all symptomatic and asymptomatic patients. CONCLUSIONS: The absence of correlation between pulmonary and sinonasal damage and more generally, the different severity of cystic fibrosis can be caused by different allele mutations of the cystic fibrosis transmembrane conductance regulator gene, the most frequent of which is Delta F-508. 相似文献