全文获取类型
收费全文 | 3119篇 |
免费 | 21篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 23篇 |
综合类 | 1篇 |
化学工业 | 115篇 |
金属工艺 | 46篇 |
机械仪表 | 8篇 |
建筑科学 | 67篇 |
矿业工程 | 4篇 |
能源动力 | 34篇 |
轻工业 | 107篇 |
水利工程 | 8篇 |
石油天然气 | 21篇 |
无线电 | 109篇 |
一般工业技术 | 223篇 |
冶金工业 | 2172篇 |
原子能技术 | 11篇 |
自动化技术 | 192篇 |
出版年
2022年 | 9篇 |
2021年 | 13篇 |
2020年 | 8篇 |
2019年 | 11篇 |
2018年 | 13篇 |
2017年 | 16篇 |
2016年 | 19篇 |
2015年 | 18篇 |
2014年 | 23篇 |
2013年 | 62篇 |
2012年 | 28篇 |
2011年 | 40篇 |
2010年 | 33篇 |
2009年 | 32篇 |
2008年 | 41篇 |
2007年 | 50篇 |
2006年 | 41篇 |
2005年 | 40篇 |
2004年 | 52篇 |
2003年 | 48篇 |
2002年 | 42篇 |
2001年 | 48篇 |
2000年 | 31篇 |
1999年 | 83篇 |
1998年 | 643篇 |
1997年 | 352篇 |
1996年 | 276篇 |
1995年 | 149篇 |
1994年 | 123篇 |
1993年 | 129篇 |
1992年 | 35篇 |
1991年 | 47篇 |
1990年 | 49篇 |
1989年 | 48篇 |
1988年 | 61篇 |
1987年 | 37篇 |
1986年 | 43篇 |
1985年 | 37篇 |
1984年 | 19篇 |
1983年 | 15篇 |
1982年 | 18篇 |
1981年 | 23篇 |
1980年 | 18篇 |
1979年 | 9篇 |
1978年 | 10篇 |
1977年 | 52篇 |
1976年 | 96篇 |
1975年 | 9篇 |
1973年 | 8篇 |
1966年 | 5篇 |
排序方式: 共有3141条查询结果,搜索用时 9 毫秒
151.
152.
Aging differentially affects receptor function. In the present electrophysiological study we compared neuronal responsiveness to locally applied dopamine D1 and D2 receptor agonist in the striatum of female Fischer 344 rats aged 3 and 26-27 months. In a subgroup of the old rats, the nigrostriatal dopamine bundle was destroyed unilaterally with 6-hydroxydopamine (6-OHDA) to assess receptor plasticity in response to denervation. Spontaneous firing rate of striatal neurons was higher in aged compared to young rats. Higher doses of the D1 agonist SKF 38393 or the D2 agonist quinpirole were required to elicit a 50% change in firing rate in aged compared to young rats. No difference with SKF 38393 or quinpirole was detected between 6-OHDA denervated and control (nonlesioned) striatum in aged rats. Supersensitivity to D2 agonists has been reported following 6-OHDA lesions in young rats. These observations suggest that D2 receptors in aged rat striatum might not be as plastic as in younger rats. 相似文献
153.
P Sharma K Reddy N Franki V Sanwal R Sankaran TS Ahuja N Gibbons J Mattana PC Singhal 《Canadian Metallurgical Quarterly》1996,50(5):1604-1611
Hyperlipidemia has been demonstrated to contribute to hypercellularity of the mesangium in experimental animal models of glomerulosclerosis. We studied whether it also has the potential to convert a hypercellular mesangium into a hypocellular one by inducing mesangial cell (MC) apoptosis. Low density lipoprotein (LDL) enhanced (P < 0.001) mouse mesangial cell (MMC) proliferation at lower concentrations (control, 10.3 +/- 0.3 vs. LDL 100 micrograms/ml, 24.2 +/- 0.3 x 10(4) cells/ml) but augmented (P < 0.001) apoptosis at higher concentrations (control, 5.6 +/- 0.5% vs. LDL, 500 micrograms/ml 26.2 +/- 3.4% apoptotic cells/field). Oxidized (OX) LDL enhanced MMC apoptosis in concentrations of 50 to 200 micrograms/dl. There was a direct relationship between MMC apoptosis and oxidation of LDL as judged by measuring thiobarbituric acid reactive species (TBARS). Since superoxide dismutase (SOD) attenuated (P < 0.001) LDL-induced MMC apoptosis, it seems to be mediated through the generation of free radicals by mesangial cells (control, 4.3 +/- 1.5%; LDL, 200 micrograms/ml, 19.4 +/- 0.5%; LDL + SOD, 8.1 +/- 1.3% apoptotic cells/field). LDL also induced a similar effect on human mesangial cells. These studies were further confirmed by DNA fragment assays and ELISA for programmed cell death. LDL treated cells also showed enhanced mRNA expression for RSG-2, a marker for active cell death. These in vitro results provide a basis for the speculation that LDL has the potential to cause an initial hypercellular and subsequent hypocellular mesangium in the course of the development of glomerulosclerosis. 相似文献
154.
The role of microtubules in determining the mechanical rigidity of neutrophils was assessed. Neutrophils were treated with colchicine to disrupt microtubules, or with paclitaxel to promote formation of microtubules. Paclitaxel caused an increase in the number of microtubules in the cells as assessed by immunofluorescence, but it had no effect on the presence or organization of actin filaments or on cellular mechanical properties. Colchicine at concentrations <1.0 microM caused disruption of microtubular structures, but had little effect on either F-actin or on cellular mechanical properties. Higher concentrations of colchicine disrupted microtubular structure, but also caused increased actin polymerization and increases in cell rigidity. Treatment with 10 microM colchicine increased F-actin content by 17%, the characteristic cellular viscosity by 30%, the dependence of viscosity on shear rate by 10%, and the cortical tension by 18%. At 100 microM colchicine the corresponding increases were F-actin, 25%; characteristic viscosity, 50%; dependence of viscosity on shear rate, 20%; and cortical tension, 21%. These results indicate that microtubules have little influence on the mechanical properties of neutrophils, and that increases in cellular rigidity caused by high concentrations of colchicine are due to a secondary effect that triggers actin polymerization. This study supports the conclusion that actin filaments are the primary structural determinants of neutrophil mechanical properties. 相似文献
155.
The arrangement of 18-S rRNA and 28-S rRNA within their 40-S common precursor molecule (pre-rRNA) of Xenopus laevis was investigated by electron microscopic analysis of secondary structure of nascent pre-rRNA chains of oocytes, and by 5'-end analysis of 18-S rRNA and 28-S rRNA hybridized to the EcoRI fragment of rDNA cloned as plasmid pCD42. Secondary structure mapping of phenol-extracted RNA from nucleolar cores revealed complete pre-rRNA chains or molecules at various stages of processing and pre-rRNA molecules apparently lacking one end. In this latter group, which was regarded as representing nascent chains, more than 90% of the molecules had no 28-S rRNA REGION. This shows that the 28-S rRNA sequence is transcribed after the 18-S rRNA region and hence must be located nearer to the 3' end of the pre-rRNA molecule. For 5' end-group determination [3H]uridine-labelled 18-S rRNA and 28-S rRNA were hybridized, as fragments of about 200 nucleotides, to the plasmid pCD42 containing coding sequences for four-fifths of the 18-S rRNA sequence, the external transcribed spacer, the non-transcribed spacer and a tenth of the 28-S rRNA sequence. The RNA was recovered from the hybrids and analyzed for uridine 3',5'-bisphosphate (pUp) after alkaline hydrolysis. The pUp content of the hybridized 18-S rRNA fragments was 20-fold higher than in those of 28-S rRNA, THUS DEMONSTRATING THAT THE 5' END OF THE 18-S rRNA is located next to the external spacer region. From these results it is concluded that the 18-S rRNA is located close to the 5' end of the 40-S pre-rRNA molecule. 相似文献
156.
M. J. Playne Anna C. Stirling P. McDonald 《Journal of the science of food and agriculture》1967,18(1):19-20
The organic acid composition of aseptically-grown timothy grass (Phleum pratense) was examined. Changes in organic acids of the grass during incubation in small test tubes with and without the addition of lactic acid bacteria were studied. Malic acid, a major acid of the grass, was broken down during incubation mainly by the activity of bacterial enzymes. The amount of succinic acid was increased by the action of both plant and bacterial enzymes. Citric acid was not detected in the aseptically-grown timothy grass but two unidentified acids formed a major part of the total organic acid fraction. 相似文献
157.
Collins Karen W.; Dansereau Donald F.; Garland John C.; Holley Charles D.; McDonald Barbara A. 《Canadian Metallurgical Quarterly》1981,73(1):122
Evaluated 3 strategies for controlling concentration during academic tasks. 82 undergraduates served as Ss. One strategy, self-initiated relaxation (SIR), required Ss to employ a combination of relaxation techniques to set and maintain constructive study and test-taking states. The 2nd strategy, self-coaching (SC), was an extension of the positive self-talk techniques developed by D. Meichenbaum (1972). Ss were taught to coach (talk) themselves into constructive states and to maintain these states during studying and test taking. Finally, a 3rd strategy that combined SIR and SC was created. Results indicate that the 3rd strategy, SIR plus SC, significantly facilitated some aspects of academic performance in comparison to a no-treatment control group. (18 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
158.
A 6-week-old breast-fed infant had obstructive jaundice and hepatomegaly. When a dry-cleaning solvent, tetrachloroethylene, was detected in the mother's milk and blood, breast-feeding was discontinued. Rapid clinical and biochemical improvement followed. The child grew normally and had normal liver function during 2 years of follow-up. 相似文献
159.
160.