全文获取类型
收费全文 | 7632篇 |
免费 | 437篇 |
国内免费 | 255篇 |
专业分类
电工技术 | 266篇 |
综合类 | 397篇 |
化学工业 | 969篇 |
金属工艺 | 305篇 |
机械仪表 | 294篇 |
建筑科学 | 377篇 |
矿业工程 | 148篇 |
能源动力 | 209篇 |
轻工业 | 617篇 |
水利工程 | 84篇 |
石油天然气 | 309篇 |
武器工业 | 77篇 |
无线电 | 680篇 |
一般工业技术 | 638篇 |
冶金工业 | 2225篇 |
原子能技术 | 43篇 |
自动化技术 | 686篇 |
出版年
2024年 | 22篇 |
2023年 | 94篇 |
2022年 | 174篇 |
2021年 | 222篇 |
2020年 | 151篇 |
2019年 | 120篇 |
2018年 | 150篇 |
2017年 | 165篇 |
2016年 | 166篇 |
2015年 | 181篇 |
2014年 | 279篇 |
2013年 | 285篇 |
2012年 | 318篇 |
2011年 | 431篇 |
2010年 | 352篇 |
2009年 | 314篇 |
2008年 | 329篇 |
2007年 | 325篇 |
2006年 | 300篇 |
2005年 | 234篇 |
2004年 | 209篇 |
2003年 | 215篇 |
2002年 | 210篇 |
2001年 | 181篇 |
2000年 | 145篇 |
1999年 | 223篇 |
1998年 | 776篇 |
1997年 | 478篇 |
1996年 | 302篇 |
1995年 | 169篇 |
1994年 | 168篇 |
1993年 | 167篇 |
1992年 | 43篇 |
1991年 | 53篇 |
1990年 | 39篇 |
1989年 | 40篇 |
1988年 | 48篇 |
1987年 | 30篇 |
1986年 | 15篇 |
1985年 | 22篇 |
1983年 | 7篇 |
1982年 | 6篇 |
1981年 | 17篇 |
1980年 | 14篇 |
1979年 | 2篇 |
1978年 | 4篇 |
1977年 | 45篇 |
1976年 | 79篇 |
1964年 | 1篇 |
1955年 | 2篇 |
排序方式: 共有8324条查询结果,搜索用时 15 毫秒
41.
DE Anderson XJ Yuan CM Tseng LJ Rubin GM Rosen ML Tod 《Canadian Metallurgical Quarterly》1993,193(3):878-885
Free radicals react with nitrones to form stable nitroxides which can be identified by ESR spectroscopy. Unfortunately, little is known regarding the pharmacological properties of these compounds. In this study, three commonly used nitrones, 5,5-dimethylpyrroline-N-oxide (DMPO), alpha-phenyl-tert-butylnitrone (PBN), and alpha-(4-pyridyl 1-oxide)-N-tert-butylnitrone (POBN), were found to induce relaxation of preconstricted isolated rat pulmonary artery rings. Additional experiments with PBN indicated that vasorelaxation could not be attributed to production of endothelial derived factors, prostaglandins, or free radicals. Patch-clamp techniques revealed reversible calcium channel blockade with PBN at a concentration below that needed to detect free radicals. Calcium channel blockade probably accounts for the vasorelaxation observed in the isolated ring preparations described here, and should be considered when using nitrone spin-traps both in in vivo and clinical studies. 相似文献
42.
BACKGROUND: Computed tomography (CT) and magnetic resonance imaging (MR) are commonly used neuroimaging modalities for patients with signs or symptoms of neuro-ophthalmic disorders. Understanding the technology and clinical uses of these modalities is vital in patient management. METHODS/RESULTS: Basic instrument design and technology are presented together with a discussion of indications and contraindications to the use of these imaging techniques. Case reports are presented to illustrate the usefulness in diagnosis of orbital and neuro-ophthalmic disease. CONCLUSIONS: A basic knowledge of CT and MR helps the optometrist correlate imaging with clinical signs and symptoms of disease. This understanding also results in more effective communication with other health care providers and patients. 相似文献
43.
D Brodaty G Dreyfus C Dubois P De Lentdecker C Barbagelatta PF Bouchet LJ Couderc O Bletry P Honderlick D Guilmet 《Canadian Metallurgical Quarterly》1998,91(12):1525-1529
The authors report a case of giant cell myocarditis leading to rapidly progressive cardiac failure despite immuno-suppressor treatment in a 20 year old woman. The cardiac failure was successfully managed by implantation of a left ventricular assist device and then cardiac transplantation. The problems encountered underline the importance of accurate diagnosis by endomyocardial biopsy before undertaking treatment and the difficulties in the choice of appropriate method of assistance in this indication. Giant cell myocarditis is a rare cause of cardiac failure and should be considered in the differential diagnosis in view of its clinical features and risk of progression. The literature and the therapeutic implications are discussed. 相似文献
44.
WJ Enright DJ Prendiville LJ Spicer PR Stricker AP Moloney TF Mowles RM Campbell 《Canadian Metallurgical Quarterly》1993,71(9):2395-2405
The objective of this study was to determine the effect of long-term administration of a growth hormone (GH)-releasing factor analog (GRFa) and(or) thyrotropin-releasing hormone (TRH) on growth, feed efficiency, carcass characteristics, and blood hormones and metabolites in beef heifers. Crossbred heifers (n = 48; 345.9 +/- 2.8 kg) were divided into four equal groups: control (vehicle), 1 microgram of GRFa (human GRF 1-29 analog).kg BW-1.d-1, 1 microgram of TRH.kg BW-1.d-1, or GRFa + TRH. Daily s.c. injections continued for 86 d. Blood samples were collected from half of the heifers after injection on d 1, 36, and 78. On d 89, all heifers were slaughtered. Treatments did not affect (P > .05) ADG but GRFa + TRH decreased (P < .05) ADFI relative to all other treatments. Feed conversion efficiency tended (P < .10) to be improved in the groups given GRFa alone or TRH alone. Treatment with GRFa and(or) TRH did not affect carcass weight, dressing percentage, conformation score, backfat thickness, or weights of liver, kidneys, pituitary, and ovaries. The GRFa + TRH treatment reduced (P < .05) fat score and increased (P < .05) longissimus muscle area relative to other treatments. The GRFa treatments reduced (P < .05) the weight and fat percentage of the mammary gland and increased (P < .05) heart weight. Treatment with TRH alone failed to stimulate GH on d 1, 36, and 78. Treatment with GRFa alone increased (P < .05) GH above controls on d 36, whereas GRFa + TRH increased (P < .05) GH on d 1, 36, and 78. Treatment with GRFa alone increased (P < .05) IGF-I only on d 1, whereas GRFa + TRH was without effect on all days. Across sampling days, treatments had little effect on blood concentrations of insulin, triiodothyronine, nonesterified fatty acids, urea nitrogen, and glucose. The GRFa alone and GRFa + TRH decreased (P < .05) and TRH alone increased (P < .05) thyroxine concentrations. In conclusion, with the dose and administration regimen used, GRFa and(or) TRH yielded small but positive improvements in animal performance. 相似文献
45.
46.
相转移法制备高纯超细TiO2技术研究 总被引:9,自引:0,他引:9
报道了用相转移法制备高纯超细TiO2的新技术;探讨了Ti(Ⅳ)从有机相转移到水相发生水解反应的机理 ;通过TG-DTA分析以及XRD物相分析对水解产物的组成、热分解机理,晶型转变规律进行了研究,建立了水解产物焙烧的最佳温度。 相似文献
47.
LJ Kleine RV Mulkern CR Guttmann VM Colucci FA Jolesz 《Canadian Metallurgical Quarterly》1995,2(5):365-372
The precise measurement of low numbers of leukocyte below 0.1 WBC/microliter in filtered red cell or platelet suspensions meet both aims: to check the compliance with previously determined requirements and to evaluate the performances of novel filtering material (5 log depletion or more), justified by more and more important clinical use. The reliability of results, obtained with the chosen method, is ensured by applying of validation protocol, including training of technologist, assessment of the analytical range and the detection limit, assessment of precision and accuracy. The flow cytometry (FC) and Nageotte Chamber (NC) method are the both techniques which are currently used in routine Quality Control (QC) and validated by multicenter studies. Recent developments are made for increasing the sensibility of these counting methods, thanks to higher concentration or volume of the sample to be analysed. Among the experimental techniques, requiring more advances before implementing in QC program, quantitative PCR must become essential as reference method for evaluating the efficiency of filtration, in the future. 相似文献
48.
The annual time-series analysis examines the impact of changes in per capita alcohol consumption (NIAAA,AEDS) on changes in community hospital admission rates (AHA) in the United States from 1950 to 1992 (n = 43). Increases in per capita alcohol consumption were expected to increase hospital admission rates contemporaneously and several years thereafter following an exponential risk function. Distributed lag models based on differenced data controlling for changes in: (1) per capita cigarette consumption; (2) private hospital insurance coverage; (3) the drinking age population; (4) per capita disposable personal income; and (5) health care regulatory interventions show a contemporaneous effect of per capita alcohol consumption on hospital admission rates. The time-series analyses imply that between 22-26% of US community hospital admissions are alcohol related. A comparable analysis indicates that per capita alcohol and tobacco expenditures contribute to approximately 28% of US community hospital admissions. The absence of statistically significant lagged effects is inconsistent with an exponentially declining risk functions. However, the contemporaneous effects of per capita alcohol and tobacco consumption suggest that a reduction in smoking and drinking will produce quick reductions in morbidity and hospitalizations. 相似文献
49.
A study of impact toughness of Fe-Cr-X damping alloys 总被引:1,自引:0,他引:1
J. S. Lu X. Liu W. Zheng B. Wu H. Bi G. Wang 《Journal of Materials Engineering and Performance》1994,3(3):409-411
A study was carried out on the impact toughness of Fe- Cr- Х damping alloys. Two measures proved to be effective in improving
impact toughness. One was to lower carbon plus nitrogen content to an ultra- low level. This method is suitable for single-
phase ferrite alloy. The other is to use dual- phase damping alloys. The presence of martensite in Fe- Cr- Х alloys can enhance
impact toughness remarkably, but lower damping capacity drastically. This shows the importance of achieving balance between
mechanical prop-erties and damping capacity by properly controlling martensite volume fraction in dual- phase alloys. 相似文献
50.
B Cullen D Silcock LJ Brown A Gosiewska JC Geesin 《Canadian Metallurgical Quarterly》1997,29(1):241-250
Until recently, research on the pathogenesis of glomerulonephritis has been mainly focused on the characterization of humoral immune responses in the initiation of glomerular injury. However, there is a growing recognition that both cellular and humoral immune responses, in varying proportions, are involved in the pathogenesis of immunologically-mediated glomerulonephritis. T lymphocytes are essential cellular elements of cell-mediated immunity. Both in experimental models of immune-mediated renal disease and in histopathological analyses of human nephropathies, the involvement of T cells has been demonstrated in the immunoregulation of nephritogenic immune responses and in the immune injury in the kidney. T cell activation resulting in either delayed-type hypersensitivity, cytolytic reactions, abnormal expression of major histocompatibility complex (MHC) molecules, or B cell activation can result in glomerulonephritis. These different types of responses are exerted by distinct T cell subsets defined by cell surface markers and cytokine profiles. CD4+ T cells in vivo are functionally heterogeneous with respect to cytokine production and the CD45 isoforms that are found on their surface. Like CD4+ T cells, CD8+ T cells may also be heterogeneous at the level of cytokine production. The roles of CD4+ and CD8+ cells and their cytokine profiles in glomerulonephritis have not been extensively investigated yet, but such studies might improve the understanding of the pathogenesis and possibly lead to new therapeutic approaches of human glomerulonephritis. In this review the role of distinct T lymphocyte subsets in experimental and human glomerulonephritis will be discussed. 相似文献