全文获取类型
收费全文 | 5719篇 |
免费 | 158篇 |
国内免费 | 89篇 |
专业分类
电工技术 | 76篇 |
综合类 | 125篇 |
化学工业 | 444篇 |
金属工艺 | 153篇 |
机械仪表 | 121篇 |
建筑科学 | 302篇 |
矿业工程 | 33篇 |
能源动力 | 82篇 |
轻工业 | 332篇 |
水利工程 | 42篇 |
石油天然气 | 61篇 |
武器工业 | 24篇 |
无线电 | 329篇 |
一般工业技术 | 559篇 |
冶金工业 | 2986篇 |
原子能技术 | 42篇 |
自动化技术 | 255篇 |
出版年
2023年 | 18篇 |
2022年 | 56篇 |
2021年 | 67篇 |
2020年 | 59篇 |
2019年 | 68篇 |
2018年 | 64篇 |
2017年 | 68篇 |
2016年 | 62篇 |
2015年 | 61篇 |
2014年 | 73篇 |
2013年 | 152篇 |
2012年 | 144篇 |
2011年 | 167篇 |
2010年 | 127篇 |
2009年 | 146篇 |
2008年 | 136篇 |
2007年 | 146篇 |
2006年 | 145篇 |
2005年 | 115篇 |
2004年 | 113篇 |
2003年 | 103篇 |
2002年 | 82篇 |
2001年 | 59篇 |
2000年 | 68篇 |
1999年 | 153篇 |
1998年 | 875篇 |
1997年 | 548篇 |
1996年 | 345篇 |
1995年 | 229篇 |
1994年 | 184篇 |
1993年 | 236篇 |
1992年 | 51篇 |
1991年 | 59篇 |
1990年 | 55篇 |
1989年 | 62篇 |
1988年 | 54篇 |
1987年 | 47篇 |
1986年 | 45篇 |
1985年 | 47篇 |
1984年 | 32篇 |
1983年 | 25篇 |
1982年 | 45篇 |
1981年 | 43篇 |
1980年 | 38篇 |
1979年 | 27篇 |
1978年 | 32篇 |
1977年 | 102篇 |
1976年 | 191篇 |
1975年 | 19篇 |
1974年 | 19篇 |
排序方式: 共有5966条查询结果,搜索用时 31 毫秒
31.
32.
Although the good appearance and biocompatibility of dental porcelains, failures are still of considerable concern because of the limited properties to all ceramic system. Physical properties that might be considered ideal include high strength, resistance to abrasion, and resistance to the hostile oral environment. Porcelain has been considered by many of its physical characteristic are similar to those of enamel. In 1983 a new modality of treatment, the etched porcelain restoration was introduced by Simonsen and Calamia. Numerous investigations have shown the strength of the etched porcelain bonded to composite resin and also the clinical success of this porcelain to be used as laminated veneers and etched inlays and onlays. 相似文献
33.
Oxidized low density lipoprotein (LDL) may play a significant role in atherosclerosis. We have investigated the effect of pH on the oxidation of LDL by iron or copper. When LDL was oxidized by iron in the presence of cysteine in either Hanks' balanced salt solution (HBSS) or Ham's F-10 medium, an acidic pH greatly decreased the lag period and increased the rate of formation of hydroperoxides and thiobarbituric acid-reactive substances (TBARS), and increased its uptake by macrophages. There was a dose-dependent increase of LDL oxidation at acidic pH in the presence of increasing concentrations of cysteine. When LDL was oxidized by copper in HBSS, an acidic pH increased the lag phase before the rapid formation of conjugated dienes, hydroperoxides, and TBARS, but increased its uptake by macrophages. Similar results were obtained using Ham's F-10 medium. Cysteine (100 microM) inhibited the modification of LDL by copper in HBSS at both pH 7.4 and 5.5 As atherosclerotic lesions may be acidic, these observations may help to explain why LDL oxidation occurs locally at these sites. 相似文献
34.
35.
36.
AA Ovchinnikov VE Tsvettsikh BA Berdichevski? VN Lykov VR Suktanbaev AV Murychev 《Canadian Metallurgical Quarterly》1996,20(4):7-9
Through TCD test, observation on the blood flow dynamics change before and after treatment with 31 cases of the child cerebral atrophy was made. It is found that scalp therapy is able to speed up the blood flow of part artery, especially increase the even blood flow speed of MCA, ACA obviously (P < 0.05), which preliminary shows the mechanism of scalp therapy for child cerebral atrophy mean while. It is found that scalp therapy also has the function to restrain epilepsy. 相似文献
37.
45 persons (aged 19–74 yrs) referred for neuropsychological evaluation were administered both the Symbol Digit Modalities Test (SDMT) and the Digit Symbol (DS) subtest of the Wechsler Adult Intelligence Scale (WAIS). SDMT and DS scores correlated very highly (r?=?.91). Relative to the tests' normative populations, however, the SDMT yielded scores for individual Ss that were the equivalent of 4–5 WAIS age-scaled points lower than obtained DS age-scaled scores. Results indicate that SDMT and DS scores cannot be presumed to be directly interchangeable in clinical use and suggest a general need for caution when interpreting interest patterns across measures normed on different populations. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
38.
BA Lawrence J Polse A DePina MM Allen NH Kolodny 《Canadian Metallurgical Quarterly》1997,34(5):280-283
The identity of a number of phosphorus-containing metabolites present in Synechocystis sp. PCC 6308 has been confirmed by 31P NMR spectroscopy. The presence of D-ribulose 1,5-bisphosphate (RuBP); DL-glyceraldehyde 3-phosphate (GlyP); D(-)3-phosphoglyceric acid (3PGA); D-ribulose 5-phosphate (Ru5P);6-phosphogluconic acid (6PGA); phosphoenolpyruvate (PEP); inorganic phosphate (Pi); uridine diphosphoglucose (UDPG); ADP and ATP were demonstrated by the pH dependence of their 31P NMR chemical shifts in spectra of perchloric acid cell extracts. Intracellular pH of cells was determined to be 7.5-7.7. 相似文献
39.
BA Stankiewicz JC Hutchins R Thomson DE Briggs RP Evershed 《Canadian Metallurgical Quarterly》1997,11(17):1884-1890
Flash pyrolysis-gas chromatography/mass spectrometry (py-GC/MS) was used to assess the quality and mechanism of protein preservation in the tissue of Iron Age bog bodies from Lindow, UK, and south-eastern Drenthe, The Netherlands. Abundant pyrolysis products of the fresh skin tissue, including 2,5-diketopiperazines of Pro-Gly, Pro-Ala, Pro-Val, Pro-Pro and Hyp, were readily assigned to specific amino acid or dipeptide moieties. Comparison of the pyrolysates of the bog-body tissues with that of modern samples revealed qualitative similarities suggesting good preservation of the collagen and non-collagenous proteins in the ancient tissues. Examination of the pyrolysates of samples of fresh calf skin, which had been treated with various vegetable tanning agents, clearly revealed markers of non-hydrolysable tannins including 1,2-benzenediol, 1,3-benzenediol and 1,2,3-benzenetriol, although chromatographic quality inevitably diminished with increasing functionalization of the compounds. Such markers were not detected in the pyrolysates of the bog-body tissues. Instead 4-isopropenylphenol, a characteristic pyrolysis product of Sphagnum moss, was detected in both solvent-extracted and base-treated samples of tissue. The presence of 4-isopropenylphenol in the pyrolysates of the bog-body tissues provides evidence that their preservation involves reactions of amino acids with sphagnum acid, and possibly other agents derived from the peat. The study constitutes the first chemical characterization of the pyrolysis products of modern and ancient collagen. 相似文献
40.
The thermal degradation of ITO Schottky contacts on GaAs has been studied. The rectifying contacts show rapid degradation with heating and could have serious implications for optoelectronic devices that operate at elevated temperatures.<> 相似文献