全文获取类型
收费全文 | 5002篇 |
免费 | 103篇 |
国内免费 | 17篇 |
专业分类
电工技术 | 228篇 |
综合类 | 4篇 |
化学工业 | 905篇 |
金属工艺 | 126篇 |
机械仪表 | 138篇 |
建筑科学 | 59篇 |
矿业工程 | 1篇 |
能源动力 | 172篇 |
轻工业 | 250篇 |
水利工程 | 24篇 |
石油天然气 | 4篇 |
无线电 | 563篇 |
一般工业技术 | 764篇 |
冶金工业 | 1365篇 |
原子能技术 | 166篇 |
自动化技术 | 353篇 |
出版年
2023年 | 23篇 |
2022年 | 17篇 |
2021年 | 103篇 |
2020年 | 48篇 |
2019年 | 48篇 |
2018年 | 62篇 |
2017年 | 64篇 |
2016年 | 79篇 |
2015年 | 64篇 |
2014年 | 101篇 |
2013年 | 227篇 |
2012年 | 148篇 |
2011年 | 211篇 |
2010年 | 141篇 |
2009年 | 164篇 |
2008年 | 208篇 |
2007年 | 151篇 |
2006年 | 163篇 |
2005年 | 136篇 |
2004年 | 122篇 |
2003年 | 132篇 |
2002年 | 111篇 |
2001年 | 101篇 |
2000年 | 101篇 |
1999年 | 137篇 |
1998年 | 540篇 |
1997年 | 318篇 |
1996年 | 224篇 |
1995年 | 146篇 |
1994年 | 124篇 |
1993年 | 129篇 |
1992年 | 45篇 |
1991年 | 53篇 |
1990年 | 39篇 |
1989年 | 43篇 |
1988年 | 42篇 |
1987年 | 40篇 |
1986年 | 54篇 |
1985年 | 35篇 |
1984年 | 50篇 |
1983年 | 39篇 |
1982年 | 48篇 |
1981年 | 42篇 |
1980年 | 39篇 |
1979年 | 17篇 |
1978年 | 35篇 |
1977年 | 34篇 |
1976年 | 61篇 |
1975年 | 10篇 |
1973年 | 8篇 |
排序方式: 共有5122条查询结果,搜索用时 171 毫秒
41.
Hideaki Katayama Tsutomu Tawa Shinzaburo Ito Masahide Yamamoto Yoshio Wada 《Polymer Bulletin》1992,29(3-4):365-367
Summary The effect of side chain length on intramolecular triplet energy migration of naphthalene containing polymers was investigated by a delayed fluorescence (DF) spectroscopy for the solid solution of the polymers. The degree of triplet energy migration depends strongly on whether the chromophores are directly attached to the main chain or not. 相似文献
42.
Poly(L-ornithine)s having various azo-contents in the side chains were synthesized by the water-soluble carbodiimide procedure. The photochemical properties of the polypeptides poly[Nδ-p-(phenylazo)benzoyl-L-ornithine] (PPABLO) containing 3–77 mol% azobenzene were investigated by absorption and circular dichroism spectroscopy in hexafluoro-2-propanol (HFIP) or water, and in HFIP-water or methanol-water solvent mixtures. The photochromism of the dichroic bands of the PPABLOs containing 20–77 mol% azobenzene in the visible and ultraviolet wavelength regions was found to be mostly reversible as a function of irradiation time at different wavelengths due to the photostationary state (above 80% trans-cis photoisomerization) of the azo aromatic moieties. The PPABLO containing 3.2 mol% azobenzene in water exhibited conformational changes from random coil to helix by the addition of methanol or sodium dodecyl sulphate (SDS). The photo-induced conformational change was observed in HFIP-water-SDS solvent mixtures, while no conformational change was seen in water and HFIP-water solvent mixtures. 相似文献
43.
44.
M Nagata H Tanioka H Mibu M Hikida M Akiba I Yamamoto 《Canadian Metallurgical Quarterly》1993,9(1):59-68
The effect of ascorbic acid 2-O-alpha-glucoside (AA-2G) on hydrocortisone (HC)-induced lens opacity in developing chick embryo was examined and compared with those of ascorbic acid (AsA) and ascorbic acid 2-phosphate (AA-2P). The opacity was dose-dependently inhibited by a single administration of 10 or 20 mumol/egg of AA-2G and by three repeated administrations of 1, 3 or 10 mumol/egg of AA-2G. AA-2G was the most effective among the three compounds. Glucose did not enhance the preventive effect of AsA against HC-induced opacity, and neither dehydro ascorbic acid nor glucose also prevented HC-induced cataract. In the histological study, we observed many small vacuoles in the nuclear region of the opaque lens treated with HC. AA-2G inhibited the formation of such vacuoles, an effect closely correlated with the prevention of cataract formation. 相似文献
45.
S Maruyama T Kurosaki K Sada Y Yamanashi T Yamamoto H Yamamura 《Canadian Metallurgical Quarterly》1996,271(12):6631-6635
Human leukemic cell line K562 is induced to differentiate into the megakaryocytic lineage by stimulation with 12-O-tetradecanoylphorbol-13-acetate (TPA). We demonstrate here that TPA stimulation increases tyrosine phosphorylation of an 80-kDa protein at an early stage of megakaryocytic differentiation and that this 80-kDa protein is identical with cortactin. Since tyrosine kinase Syk was activated by TPA stimulation, we examined the possibility that cortactin is a potential substrate of Syk in K562 cells. TPA-induced tyrosine phosphorylation of cortactin was decreased profoundly by overexpression of dominant-negative Syk. Furthermore, cortactin was associated with Syk even before TPA stimulation. Since cortactin was previously referred as an 80/85-kilodalton pp60src substrate, we examined the association between Src and cortactin, whereas its association could not be detected. These data suggest that Syk phosphorylates cortactin in K562 cells upon TPA treatment. 相似文献
46.
47.
48.
T Kaji Y Fujiwara M Hoshino C Yamamoto M Sakamoto H Kozuka 《Canadian Metallurgical Quarterly》1995,95(1-3):87-92
We investigated the effect of lead nitrate (0.5, 1.0, 2.0 or 5.0 microM) on the proliferation of cultured bovine aortic endothelial cells. After exposure to lead, the number of cells and the incorporation of [3H]thymidine into the acid-insoluble fraction of the cells were reduced in parallel in a concentration-dependent manner. Histologically, lead treatment resulted in a decrease in the cell number accompanied by a change in the cell shape from polygonal to spindle; however, no degenerative change was observed except in 5.0 microM lead-treated cells. Furthermore, stimulation of [3H]thymidine incorporation by either basic or acidic fibroblast growth factor was significantly reduced by lead. However, the leakage of lactate dehydrogenase into the medium from the cells, a marker of nonspecific cell damage, was not changed by lead. From these results, it was revealed that lead inhibits the proliferation of cultured vascular endothelial cells without nonspecific cell damage. Although lead does not destroy the monolayer of endothelial cells, the metal may exhibit its noxious effect in the repair process of the vascular endothelium. 相似文献
49.
Melt crystallization of isotactic polypropylene (iPP), containing crystallites of N,N′-dicyclohexyl-2,6-naphthalenedicarboxamide (DCNDCA) as a nucleating agent of the the β-phase iPP crystal, is carried out under a magnetic field (6 T) to obtain the alignment of the iPP crystal induced by magnetic alignment of DCNDCA. In a previous paper, DCNDCA was reported to undergo magnetic alignment in a liquid suspension. The obtained iPP sample exhibits alignment of the β-phase crystal with the c-axis aligned perpendicular to the magnetic field. The comparison of this alignment of iPP with the reported magnetic alignment of DCNDCA indicates that the β-phase crystal grows epitaxially on the DCNDCA crystal. The (330)β plane of the iPP crystal lies on the bc-plane of the DCNDCA crystal in which the direction of the c-axis of the iPP coincides with the direction of the b-axis of the DCNDCA crystal. 相似文献
50.