全文获取类型
收费全文 | 1982篇 |
免费 | 28篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 4篇 |
综合类 | 1篇 |
化学工业 | 205篇 |
金属工艺 | 33篇 |
机械仪表 | 29篇 |
建筑科学 | 29篇 |
能源动力 | 33篇 |
轻工业 | 103篇 |
水利工程 | 6篇 |
石油天然气 | 6篇 |
无线电 | 90篇 |
一般工业技术 | 252篇 |
冶金工业 | 1113篇 |
原子能技术 | 9篇 |
自动化技术 | 98篇 |
出版年
2021年 | 11篇 |
2020年 | 8篇 |
2019年 | 11篇 |
2018年 | 21篇 |
2017年 | 12篇 |
2016年 | 18篇 |
2015年 | 21篇 |
2014年 | 18篇 |
2013年 | 74篇 |
2012年 | 29篇 |
2011年 | 33篇 |
2010年 | 27篇 |
2009年 | 24篇 |
2008年 | 40篇 |
2007年 | 42篇 |
2006年 | 36篇 |
2005年 | 27篇 |
2004年 | 26篇 |
2003年 | 33篇 |
2002年 | 36篇 |
2001年 | 34篇 |
2000年 | 15篇 |
1999年 | 46篇 |
1998年 | 320篇 |
1997年 | 175篇 |
1996年 | 134篇 |
1995年 | 70篇 |
1994年 | 62篇 |
1993年 | 67篇 |
1992年 | 21篇 |
1991年 | 32篇 |
1990年 | 24篇 |
1989年 | 29篇 |
1988年 | 30篇 |
1987年 | 30篇 |
1986年 | 29篇 |
1985年 | 27篇 |
1983年 | 12篇 |
1982年 | 15篇 |
1981年 | 19篇 |
1980年 | 18篇 |
1979年 | 13篇 |
1978年 | 16篇 |
1977年 | 40篇 |
1976年 | 81篇 |
1975年 | 19篇 |
1973年 | 8篇 |
1972年 | 8篇 |
1971年 | 8篇 |
1970年 | 7篇 |
排序方式: 共有2011条查询结果,搜索用时 15 毫秒
101.
102.
103.
X Fang NL Weintraub CD Rios DA Chappell RM Zwacka JF Engelhardt LW Oberley T Yan DD Heistad AA Spector 《Canadian Metallurgical Quarterly》1998,82(12):1289-1297
Oxidation of LDL in the subendothelial space has been proposed to play a key role in atherosclerosis. Endothelial cells produce superoxide anions (O2.-) and oxidize LDL in vitro; however, the role of O2.- in endothelial cell-induced LDL oxidation is unclear. Incubation of human LDL (200 microg/mL) with bovine aortic endothelial cells (BAECs) for 18 hours resulted in a 4-fold increase in LDL oxidation compared with cell-free incubation (22.5+/-1.1 versus 6.3+/-0.2 [mean+/-SEM] nmol malondialdehyde/mg LDL protein, respectively; P<0.05). Under similar conditions, incubation of LDL with porcine aortic endothelial cells resulted in a 5-fold increase in LDL oxidation. Inclusion of exogenous copper/zinc superoxide dismutase (Cu/ZnSOD, 100 microg/mL) in the medium reduced BAEC-induced LDL oxidation by 79%. To determine whether the intracellular SOD content can have a similar protective effect, BAECs were infected with adenoviral vectors containing cDNA for human Cu/ZnSOD (AdCu/ZnSOD) or manganese SOD (AdMnSOD). Adenoviral infection increased the content and activity of either Cu/ZnSOD or MnSOD in the cells and reduced cellular O2.- release by two thirds. When cells infected with AdCu/ZnSOD or AdMnSOD were incubated with LDL, formation of malondialdehyde was decreased by 77% and 32%, respectively. Two other indices of LDL oxidation, formation of conjugated dienes and increased LDL electrophoretic mobility, were similarly reduced by SOD transduction. These data suggest that production of O2.- contributes to endothelial cell-induced oxidation of LDL in vitro. Furthermore, adenovirus-mediated transfer of cDNA for human SOD, particularly Cu/ZnSOD, effectively reduces oxidation of LDL by endothelial cells. 相似文献
104.
HD Mercer LD Rollins GG Carter RP Gural DW Bourne LW Dittert 《Canadian Metallurgical Quarterly》1977,66(8):1198-1200
Fifteen Aberdeen Angus steers, 295-364 kg, were dosed with either 4.4 or 11 mg of oxytetracycline hydrochloride/kg im. The antimicrobial activity of the serum was determined periodically, and the resulting data were treated statistically to determine the sources of variation. Variance in serum levels of oxytetracycline activity was attributed to dose, time of bleeding, order of dosing, animal, and assay. The total variance component was proportionately greater for the 11-mg/kg dose than for the 4.4-mg/kg dose. Animal variance increased with the higher dose level of oxytetracycline. The influence of dose on serum level was tested by applying a t test to the mean serum levels and their standard deviations at each bleeding time. The 4.4- and 11-mg/kg serum levels were significantly different (p less than 0.01) at all bleeding times. The 4.4-mg/kg serum levels mutliplied by 2.5 were not significantly different (p less than 0.05) from the 11-mg/kg serum levels at all bleeding times. 相似文献
105.
A group of 15 midtrimester gravid patients underwent intracervical laminaria tent insertion prior to repeated intramuscular injections of 250mu g of prostaglandin 15 (S) 15-methyl F2 alpha at two-hour intervals for elective termination of pregnancy. This group was compared with a previously reported group of 80 patients who had received identical treatment without laminaria insertion. A significant reduction in mean abortion time and an increased 24-hour abortion rate were observed with the addition of laminaria. There was a proportionate decrease in gastrointestinal side effects as well as a reduced need for analgesia in the laminaria group with no complications attributable to the laminaria insertion. 相似文献
106.
Only one molecular weight species of DNA polymerase was found in different developmental stages of the eukaryotic microorganism Dictyostelium discoideum. The molecular weight of this DNA polymerase is estimated to be about 127 000 by sucrose gradient centrifugation. The enzyme is present in all stages of growth and development, including dormant spores. All DNA polymerase activity is lost upon incubation of the crude extract with N-ethylmaleimide. The reaction properties, molecular weight and N-ethylmaleimide sensitivity of the D. discoideum DNA polymerase are similar to those of the DNA polymerase-alpha from mammalian sources. 相似文献
107.
Nancy R. Mann 《Engineering Fracture Mechanics》1976,8(1):123-130
A two-parameter Weibull model for failure time is assumed. An easily implemented method is developed for calculating, from information obtained from a possibly censored life test, an approximate warranty period before which the th failure occurs in a production lot of given size with some small specified probability. The precision of the approximation is investigated and a numerical example applied to failure data is given.The procedure developed can also be used for obtaining lower prediction limits for ultimate strengths of composite structures in production lots of specified size and for certain models other than the Weibull. 相似文献
108.
The cycle time distribution (CTD) within closed, continuously circulating systems is defined and related to the residence time distributions of flow regions which make up such systems. Examples of the application of the CTD are noted and experimental methods for determining CTDs for various systems are summarized. 相似文献
109.
110.