全文获取类型
收费全文 | 5730篇 |
免费 | 81篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 40篇 |
综合类 | 6篇 |
化学工业 | 835篇 |
金属工艺 | 90篇 |
机械仪表 | 84篇 |
建筑科学 | 156篇 |
矿业工程 | 11篇 |
能源动力 | 88篇 |
轻工业 | 309篇 |
水利工程 | 27篇 |
石油天然气 | 16篇 |
武器工业 | 2篇 |
无线电 | 345篇 |
一般工业技术 | 600篇 |
冶金工业 | 2575篇 |
原子能技术 | 41篇 |
自动化技术 | 591篇 |
出版年
2022年 | 25篇 |
2021年 | 42篇 |
2020年 | 32篇 |
2019年 | 38篇 |
2018年 | 63篇 |
2017年 | 46篇 |
2016年 | 56篇 |
2015年 | 45篇 |
2014年 | 100篇 |
2013年 | 217篇 |
2012年 | 133篇 |
2011年 | 189篇 |
2010年 | 122篇 |
2009年 | 135篇 |
2008年 | 180篇 |
2007年 | 145篇 |
2006年 | 141篇 |
2005年 | 132篇 |
2004年 | 105篇 |
2003年 | 101篇 |
2002年 | 105篇 |
2001年 | 64篇 |
2000年 | 74篇 |
1999年 | 123篇 |
1998年 | 757篇 |
1997年 | 434篇 |
1996年 | 291篇 |
1995年 | 190篇 |
1994年 | 143篇 |
1993年 | 165篇 |
1992年 | 65篇 |
1991年 | 77篇 |
1990年 | 69篇 |
1989年 | 52篇 |
1988年 | 60篇 |
1987年 | 64篇 |
1986年 | 87篇 |
1985年 | 68篇 |
1984年 | 46篇 |
1983年 | 49篇 |
1982年 | 49篇 |
1981年 | 67篇 |
1980年 | 57篇 |
1979年 | 44篇 |
1978年 | 44篇 |
1977年 | 95篇 |
1976年 | 144篇 |
1975年 | 34篇 |
1972年 | 24篇 |
1971年 | 24篇 |
排序方式: 共有5816条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
J Brake TJ Walsh CE Benton JN Petitte R Meijerhof G Pe?alva 《Canadian Metallurgical Quarterly》1997,76(1):144-151
The relative importance of fat and lean tissue mass in determining bone mineral mass among postmenopausal women was examined in this 1-year longitudinal study. Fifty postmenopausal Caucasian women entered the study; 45 of them completed a 1-year follow-up. Dual-energy X-ray absorptiometry was employed for measuring total and regional bone mineral density (BMD) and bone mineral content (BMC), fat tissue mass (FTM), lean tissue mass (LTM), and body weight. Results from linear regression analysis using the cross-sectional data (n = 50) of the study indicated that LTM explained a larger percentage of variation in bone mineral mass than did FTM. FTM and LTM were found to be moderately correlated (r = 0.55); when FTM was entered in the same predicting regression models, LTM was a significant predictor (p < 0.05) of the total and regional BMC, but not BMD. The percent FTM (and inversely %LTM) was correlated with BMD and BMC, but significant correlation was primarily found only for total body BMD (or BMC). Weight was the best predictor of total body BMD and BMC. Longitudinally (n = 45), annual changes in both FTM and weight were significantly associated with annual changes in regional BMD after adjustment for initial bone mineral values (p < 0.05). We conclude that bone mineral mass is more closely related to LTM than to FTM, while annual changes in regional BMD are more closely correlated with changes in FTM in healthy postmenopausal women. Meanwhile, increased body weight is significantly associated with increased bone mineral mass. 相似文献
5.
C Montixi C Langlet AM Bernard J Thimonier C Dubois MA Wurbel JP Chauvin M Pierres HT He 《Canadian Metallurgical Quarterly》1998,17(18):5334-5348
T-cell receptors (TCRs) upon binding to peptide-MHC ligands transduce signals in T lymphocytes. Tyrosine phosphorylations in the cytoplasmic domains of the CD3 (gammadeltaepsilon) and zeta subunits of the TCR complex by Src family kinases initiate the signaling cascades via docking and activation of ZAP-70 kinase and other signaling components. We examined the role of the low-density detergent-insoluble membranes (DIMs) in TCR signaling. Using mouse thymocytes as a model, we characterized the structural organization of DIMs in detail. We then demonstrated that TCR engagement triggered an immediate increase in the amount of TCR/CD3 present in DIMs, which directly involves the engaged receptor complexes. TCR/CD3 recruitment is accompanied by the accumulation of a series of prominent tyrosine-phosphorylated substrates and by an increase of the Lck activity in DIMs. Upon TCR stimulation, the DIM-associated receptor complexes are highly enriched in the hyperphosphorylated p23 zeta chains, contain most of the TCR/CD3-associated, phosphorylation-activated ZAP-70 kinases and seem to integrate into higher order, multiple tyrosine-phosphorylated substrate-containing protein complexes. The TCR/CD3 recruitment was found to depend on the activity of Src family kinases. We thus provide the first demonstration of recuitment of TCR/CD3 to DIMs upon receptor stimulation and propose it as a mechanism whereby TCR engagement is coupled to downstream signaling cascades. 相似文献
6.
Jean-Michel L. Bernard 《电信纪事》1994,49(11-12):673-683
The time-scattering of an electromagnetic wave by a wedge-shaped region in a lossy medium, both with frequency dependent electric characteristics, is analyzed for plane wave and line source illuminations. New exact analytical expressions, satisfying explicitely the causality and allowing useful physical decompositions of the field, are obtained in these cases, using the particularities of the harmonic response in Sommerfeld-Maliuzhinets integral, especially original properties of the spectral function attached to it. 相似文献
7.
DC Reynolds CE Leak KK Bajaj CE Stutz RL Jones KR Evans PW Yu WM Theis 《Canadian Metallurgical Quarterly》1989,40(9):6210-6217
8.
9.
10.
Pure cardiolipins (1,3-diphosphatidylglycerol) were prepared from mitochondria of heart, liver and kidney from 21-day-old
male Wistar rats and submitted toNaja naja venom phospholipase A2 (EC 3.1.1.4) action. Incubation conditions were controlled carefully, and a complete hydrolysis of cardiolipin to lysocardiolipin
{di [1 (1″) acylsn-glycero-3-phosphoryl] 1′, 3′-sn-glycerol} and fatty acids from positions 2 (2″) was obtained in less than two hr practically without side reactions. Cardiolipins
from the three organs contained low levels of saturated fatty acids; stearic acid accounted for 0.4–0.7% and palmitic acid
for 1.4–3.5% of total fatty acids. These percentages apparently depended on the organ. In all three cases, linoleic acid was
the major component, but its percentage varied from 62–78% of total fatty acids. Acyl chains linked to positions 1 (1″) of
all three cardiolipin preparations exhibited a similar pattern; they were composed of linoleic acid for 85–89%. This fatty
acid also was the main component esterified at position 2 (2″), but its percentage was much more variable: from 39.8% in heart
to 51.2% in kidney and 67.8% in liver mitochondria. The remaining acids comprised octadecenoic and polyunsaturated fatty acids
with more than 18 carbon atoms in different proportions. As opposed to other phospholipids,cis-vaccenic acid, and not oleic acid, was the main octadecenoic acid present in cardiolipins.
Octadecenoic acids were nine- to 10-fold more concentrated at positions 2 (2″) than at positions 1 (1″). The percentage ofcis-vaccenic acid was four- to five-fold higher than that of oleic acid at positions 2 (2″), whereas oleic acid dominated at
positions 1 (1″). From results presented in this study and selected literature data, it may be concluded that fatty acids
are asymmetrically distributed in cardiolipins of different origins, with linoleic acid showing a definite preference for
position 1 (1″). 相似文献