全文获取类型
收费全文 | 6307篇 |
免费 | 111篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 35篇 |
综合类 | 1篇 |
化学工业 | 284篇 |
金属工艺 | 17篇 |
机械仪表 | 40篇 |
建筑科学 | 72篇 |
矿业工程 | 3篇 |
能源动力 | 34篇 |
轻工业 | 130篇 |
水利工程 | 15篇 |
石油天然气 | 7篇 |
无线电 | 308篇 |
一般工业技术 | 397篇 |
冶金工业 | 4762篇 |
原子能技术 | 24篇 |
自动化技术 | 293篇 |
出版年
2022年 | 13篇 |
2021年 | 21篇 |
2020年 | 26篇 |
2019年 | 28篇 |
2018年 | 36篇 |
2017年 | 27篇 |
2016年 | 28篇 |
2015年 | 47篇 |
2014年 | 38篇 |
2013年 | 126篇 |
2012年 | 50篇 |
2011年 | 77篇 |
2010年 | 56篇 |
2009年 | 42篇 |
2008年 | 73篇 |
2007年 | 58篇 |
2006年 | 58篇 |
2005年 | 55篇 |
2004年 | 58篇 |
2003年 | 55篇 |
2002年 | 51篇 |
2001年 | 36篇 |
2000年 | 47篇 |
1999年 | 183篇 |
1998年 | 1479篇 |
1997年 | 825篇 |
1996年 | 527篇 |
1995年 | 317篇 |
1994年 | 243篇 |
1993年 | 306篇 |
1992年 | 78篇 |
1991年 | 70篇 |
1990年 | 83篇 |
1989年 | 98篇 |
1988年 | 79篇 |
1987年 | 86篇 |
1986年 | 72篇 |
1985年 | 82篇 |
1984年 | 23篇 |
1983年 | 45篇 |
1982年 | 36篇 |
1981年 | 54篇 |
1980年 | 52篇 |
1978年 | 23篇 |
1977年 | 137篇 |
1976年 | 241篇 |
1975年 | 21篇 |
1974年 | 12篇 |
1972年 | 14篇 |
1970年 | 14篇 |
排序方式: 共有6422条查询结果,搜索用时 31 毫秒
101.
Since the beginning of the twentieth century, different methods to control the quality of analyses have been in use. The advent of modern analytical instruments has prompted the need for such controls. In a modern clinical chemistry laboratory, quality control is an important tool to maintain the high predictive value of the methods in use. In this article the most important aspects of quality control are outlined. For further study, I recommend the references listed at the end of this article. 相似文献
102.
This paper describes the use of a nonphotolithographic technique-microcontact printing-to fabricate a concentric cylindrical microtransformer having an outer diameter of ~350 μm. For frequencies of up to 20 kHz, this microtransformer has a high coupling coefficient (>0.9). At higher frequencies, properties of the ferromagnetic material used in the construction of the microtransformer limit performance 相似文献
103.
104.
105.
Extracellular amyloid beta-peptide (A beta) deposition is a pathological feature of Alzheimer's disease and the aging brain. Intracellular A beta accumulation is observed in the human muscle disease, inclusion body myositis. A beta has been reported to be toxic to neurons through disruption of normal calcium homeostasis. The pathogenic role of A beta in inclusion body myositis is not as clear. Elevation of intracellular calcium following application of calcium ionophore increases the generation of A beta from its precursor protein (betaAPP). A receptor-based mechanism for the increase in A beta production has not been reported to our knowledge. Here, we use caffeine to stimulate ryanodine receptor (RYR)-regulated intracellular calcium release channels and show that internal calcium stores also participate in the genesis of A beta. In cultured HEK293 cells transfected with betaAPP cDNA, caffeine (5-10 mM) significantly increased the release of A beta fourfold compared with control. These actions of caffeine were saturable, modulated by ryanodine, and inhibited by the RYR antagonists ruthenium red and procaine. The calcium reuptake inhibitors thapsigargin and cyclopiazonic acid potentiated caffeine-stimulated A beta release. NH4Cl and monensin, agents that alter acidic gradients in intracellular vesicles, abolished both the caffeine and ionophore effects. Immunocytochemical studies showed some correspondence between the distribution patterns of RYR and cellular betaAPP immunoreactivities. The relevance of these findings to Alzheimer's disease and inclusion body myositis is discussed. 相似文献
106.
107.
JD Swales 《Canadian Metallurgical Quarterly》1993,306(6869):42-44
The postgraduate hospitals of London grew up in the nineteenth century and offered a unique national specialist service. Since then specialist services have developed in undergraduate hospitals throughout Britain as well as in London, but the postgraduate hospitals have nevertheless preserved their high levels of staffing. Although numbers of medical posts in the provinces have grown, this has not been by redistribution of London posts but merely differential growth. The fact identified by Tomlinson--that Londoners are not receiving the most appropriate clinical care--is in fact the strongest argument for changing postgraduate medical education. Such education needs to be rooted first in clinical care, though Tomlinson underestimates the importance to education of such care being sited in a shared environment with strong scientific activity. 相似文献
108.
109.
Meat tenderness and the calpain proteolytic system in longissimus muscle of young bulls and steers 总被引:1,自引:0,他引:1
JB Morgan TL Wheeler M Koohmaraie JW Savell JD Crouse 《Canadian Metallurgical Quarterly》1993,71(6):1471-1476
The objectives of this study were to examine the effects of castration on the calpain proteinase system (mu-calpain, m-calpain, and calpastatin) activities and meat tenderness. Six each, MARC III bulls and steers were slaughtered at approximately 12 mo of age. Longissimus muscle samples were obtained for determining myofibril fragmentation index, Warner-Bratzler shear force, and sensory panel evaluation at 1, 7, and 14 d postmortem, and mu- and m-calpain and calpastatin activities at 24 h postmortem. Bulls produced leaner carcasses with lower (P < .05) quality grades than did steers. Meat from bulls had higher (P < .05) shear force values than meat from steers; however, sensory panelists were unable (P > .05) to detect differences in tenderness or other sensory traits between bulls and steers. Activities of mu- and m-calpain were not affected (P > .05) by castration; however, calpastatin was higher (P < .05) in muscles from the bull carcasses. Lower (P < .05) myofibril fragmentation index values indicate that less proteolysis occurred in muscle from bulls than in muscle from steers during the first 7 d postmortem. Greater calpastatin 24-h activity may be associated with the increased shear force of meat from bulls. 相似文献
110.
JD Belcher RC Ellison WE Shepard C Bigelow LS Webber JH Wilmore GS Parcel DM Zucker RV Luepker 《Canadian Metallurgical Quarterly》1993,22(2):143-153
Male and female isometric strength curves for elbow fixation, shoulder flexion, and wrist supination-pronation are obtained during systematic variation in arm configuration. The shape of a given moment-angle curve is found to be a function of the orientations of joints kinematically coupled to the primary joint. It is also found that female elbow strength curves are shifted toward flexion with respect to male elbow-strength curves, suggesting that the in situ rest length of upper-limb muscles relative to joint angle may be longer for males than for females. Experimental results were contrasted with simulation results obtained using a three-dimensional musculoskeletal model which estimates the relationships between initial joint orientations, muscle tension-length behavior, and joint moments. In most of the cases, simulation results complimented experimental data and provided insights into likely in situ muscle rest lengths and moments arms, especially for the multiarticular biceps brachii muscle. Where inconsistencies exist between simulated and experimental data, subtle biomechanical complexities within the forearm and the shoulder girdle complex are identified that require future investigation. 相似文献