全文获取类型
收费全文 | 8291篇 |
免费 | 325篇 |
国内免费 | 48篇 |
专业分类
电工技术 | 79篇 |
综合类 | 21篇 |
化学工业 | 1652篇 |
金属工艺 | 126篇 |
机械仪表 | 228篇 |
建筑科学 | 158篇 |
矿业工程 | 5篇 |
能源动力 | 377篇 |
轻工业 | 582篇 |
水利工程 | 86篇 |
石油天然气 | 36篇 |
无线电 | 559篇 |
一般工业技术 | 1074篇 |
冶金工业 | 2678篇 |
原子能技术 | 85篇 |
自动化技术 | 918篇 |
出版年
2024年 | 23篇 |
2023年 | 114篇 |
2022年 | 327篇 |
2021年 | 403篇 |
2020年 | 305篇 |
2019年 | 331篇 |
2018年 | 360篇 |
2017年 | 301篇 |
2016年 | 327篇 |
2015年 | 195篇 |
2014年 | 324篇 |
2013年 | 548篇 |
2012年 | 311篇 |
2011年 | 318篇 |
2010年 | 279篇 |
2009年 | 248篇 |
2008年 | 168篇 |
2007年 | 147篇 |
2006年 | 133篇 |
2005年 | 98篇 |
2004年 | 76篇 |
2003年 | 80篇 |
2002年 | 58篇 |
2001年 | 46篇 |
2000年 | 38篇 |
1999年 | 98篇 |
1998年 | 870篇 |
1997年 | 483篇 |
1996年 | 327篇 |
1995年 | 211篇 |
1994年 | 135篇 |
1993年 | 183篇 |
1992年 | 44篇 |
1991年 | 45篇 |
1990年 | 45篇 |
1989年 | 44篇 |
1988年 | 34篇 |
1987年 | 56篇 |
1986年 | 53篇 |
1985年 | 38篇 |
1984年 | 30篇 |
1983年 | 32篇 |
1982年 | 28篇 |
1981年 | 16篇 |
1980年 | 33篇 |
1979年 | 14篇 |
1978年 | 15篇 |
1977年 | 63篇 |
1976年 | 167篇 |
1975年 | 11篇 |
排序方式: 共有8664条查询结果,搜索用时 15 毫秒
11.
12.
The present study was designed to determine if spinal calcium channels, calmodulin, and calcium/calmodulin-dependent protein kinase II were involved in the production of antinociception induced by cold water swimming stress (CWSS). The effects of intrathecal (i.t.) injection of nimodipine, omega-conotoxin GVIA, calmidazolium, or (S)-5-isoquinolinesulfonic acid, 4-[2-[(5-isoquinolinyl-sulfonyl)methylamino]-3-oxo-3-(4-phenyl-1-piperaz inyl)-propyl]phenyl ester (KN-62) on CWSS-induced antinociception were studied in ICR mice. The antinociception was assessed by the tail-flick test. CWSS produced inhibition of the tail-flick response. Various doses of nimodipine (10-40 ng), omega-conotoxin GVIA (5-40 ng), calmidazolium (10-40 ng), or KN-62 (5-40 ng) injected i.t. alone did not show any antinociceptive effect in the tail-flick test. I.t. pretreatment with omega-conotoxin GVIA, calmidazolium, or KN-62 dose dependently attenuated the CWSS-induced inhibition of the tail-flick response. However, i.t. pretreatment with nimodipine did not affect the inhibition of the tail-flick response induced by CWSS. Our results suggest that spinal N-type calcium channel, calmodulin and calcium/calmodulin-dependent protein kinase II may be involved in the production of antinociception induced by CWSS. On the other hand, CWSS-induced antinociception appears not to be mediated via the spinal L-type calcium channel. 相似文献
13.
14.
15.
AL Lindstrom SL Erlandsen JH Kersey CA Pennell 《Canadian Metallurgical Quarterly》1997,90(6):2323-2334
Vascular leak syndrome (VLS) is the dose-limiting toxicity observed in clinical trials of immunotoxins containing ricin toxin A chain (RTA). RTA itself is thought to cause VLS by damaging vascular endothelial cells, but the exact mechanism remains unclear. This is partially due to the paucity of appropriate models. To study VLS, we developed an in vitro model in which human umbilical vein-derived endothelial cells were first grown to confluence on microporous supports and then cultured under low pressure in the presence or absence of RTA. Endothelial cell barrier function was assessed by measuring the volume of fluid that passed through each monolayer per unit time. We found that RTA significantly increased monolayer permeability at times and concentrations consistent with the onset of VLS in patients treated with RTA-based immunotoxins. Scanning electron microscopy showed that intercellular gaps formed in endothelial monolayers exposed to RTA. Intercellular gap formation followed endothelial cell death caused by the enzymatic activity of RTA. We conclude that RTA is directly toxic to endothelial cells in vitro and speculate that this contributes to VLS in vivo. 相似文献
16.
SD Shiian SV Kha?dukov AL Pukhal''ski? AP Toptygina NV Bovin 《Canadian Metallurgical Quarterly》1996,41(2):24-29
The interaction of human peripheral blood leukocytes with alpha 1-acid glycoprotein (AGP), its glycoforms as well as neoglyco-conjugates representing carbohydrate chains of AGP or its fragments was studied by flow cytometry. It was shown that the main target cells for AGP as well as for conjugates of its carbohydrate chains with polyacrylamide (PAA) are monocytes and polymorphonuclear leukocytes but not lymphocytes. The interaction of AGP with monocytes and granulocytes are mediated by its carbohydrate chains: the binding of AGP with cells was inhibited by AGP, AGP oligosaccharides as well as conjugates of oligosaccharides and its fragments with PAA. The data obtained show the existence of monocyte (and granulocyte) receptors which interact with complex type sialooligosaccharides of AGP. 相似文献
17.
Helen N. Asemota Max A. Wellington Adewale A. Odutuga Mohammed H. Ahmad 《Journal of the science of food and agriculture》1992,60(3):309-312
The effect of short-term storage on the protein, phosphorus and phenolic content as well as peroxidase and o-diphenolase activities of cut, harvested Jamaican yam (Dioscorea sp) tubers (D rotundata. D alata and D cayenensis) was studied. There was an initial increase in the total phenolic content up to the third week of storage followed by a gradual decrease to the sixth week. Phenolic content was found to be highest in D cayenensis followed by D rotundata and D alata. The activities of peroxidase (EC 1. 11. 1. 7) and o-diphenolase (EC 1. 10.3.1) increased steadily up to the third week of storage and thereafter decreased to the fifth week. The intensity and rapidity of browning in tubers when cut, correlated very closely with the tuber o-diphenolase and phenolic content levels while the onset of rotting correlated with the peroxidase activity levels in the species studied. 相似文献
18.
VM Coiro AL Segre A Di Nola M Paci A Grottesi G Veglia A Ballio 《Canadian Metallurgical Quarterly》1998,257(2):449-456
Pseudomycin A is a cyclic lipodepsinonapeptide phytotoxin produced by a strain of the plant pathogenic bacterium Pseudomonas syringae. Like other members of this family of bacterial metabolites, it is characterised by a fatty acylated cyclic peptide with mixed chirality and lactonic closure. Several biological activities of Pseudomycin A are lower than those found for some of its congeners, a difference which might depend on the diverse number and distribution of charged residues in the peptide moiety. Hence, it was of interest to investigate its conformation in solution. After the complete interpretation of the two-dimensional NMR spectra, NOE data were obtained and the structure was determined by computer simulations, applying distance geometry and molecular dynamics procedures. The conformation of the large ring of Pseudomycin A in solution includes three rigid structural regions interrupted by three short flexible regions that act as hinges. The overall three-dimensional structure of the cyclic moiety is similar to that of previously studied bioactive lipodepsinonapeptides produced by other pseudomonads. 相似文献
19.
The interaction of different metal oxides such as Co3O4, NiO, Al2O3, Cr2O3, Fe2O3 and SiO2 with Na2SO4 at a temperature of 1100 and 1200 K in flowing oxygen has been studied. The thermogravimetric studies for each system were
carried out as a function of Na2SO4 in the mixture. The presence of different constituents in the reaction products were identified by X-ray diffraction analysis
and the morphologies of the reaction products were characterized using metallography and scanning electron microscopy (SEM).
The formation of products was also investigated by thermodynamic computation of free energies of the reactions and the study
of relevant equilibrium phase diagrams. The soluble species in the aqueous solutions of the reaction products were determined
quantitatively using atomic absorption spectrophotometry.
The high temperature interaction products usually contain a 3-phase structure namely, Na2O·M2O
x
, M2O
x
and metal sulphide and/or metal sulphate. The formation of Na2O·M2O
x
depends upon the solid state solubility of metal oxide in the molten salt at high temperatures. Under limited solubility
conditions Na2O·M2O
x
is invariably formed, but as soon as this condition is relaxed the oxide. M2O
x
, precipitates and forms a separate phase. 相似文献
20.