全文获取类型
收费全文 | 334826篇 |
免费 | 5959篇 |
国内免费 | 1660篇 |
专业分类
电工技术 | 7372篇 |
综合类 | 2166篇 |
化学工业 | 51549篇 |
金属工艺 | 11363篇 |
机械仪表 | 9903篇 |
建筑科学 | 9343篇 |
矿业工程 | 1294篇 |
能源动力 | 9174篇 |
轻工业 | 35119篇 |
水利工程 | 3058篇 |
石油天然气 | 4406篇 |
武器工业 | 144篇 |
无线电 | 41701篇 |
一般工业技术 | 61298篇 |
冶金工业 | 58026篇 |
原子能技术 | 5662篇 |
自动化技术 | 30867篇 |
出版年
2022年 | 2282篇 |
2021年 | 3370篇 |
2020年 | 2499篇 |
2019年 | 2850篇 |
2018年 | 4439篇 |
2017年 | 4379篇 |
2016年 | 4395篇 |
2015年 | 3734篇 |
2014年 | 5960篇 |
2013年 | 16174篇 |
2012年 | 9467篇 |
2011年 | 12394篇 |
2010年 | 9819篇 |
2009年 | 10937篇 |
2008年 | 11307篇 |
2007年 | 11160篇 |
2006年 | 9727篇 |
2005年 | 8814篇 |
2004年 | 8392篇 |
2003年 | 7944篇 |
2002年 | 7724篇 |
2001年 | 7812篇 |
2000年 | 7420篇 |
1999年 | 7722篇 |
1998年 | 17981篇 |
1997年 | 13081篇 |
1996年 | 10262篇 |
1995年 | 7982篇 |
1994年 | 7282篇 |
1993年 | 6982篇 |
1992年 | 5325篇 |
1991年 | 5098篇 |
1990年 | 4963篇 |
1989年 | 4815篇 |
1988年 | 4695篇 |
1987年 | 3911篇 |
1986年 | 4031篇 |
1985年 | 4739篇 |
1984年 | 4292篇 |
1983年 | 4031篇 |
1982年 | 3610篇 |
1981年 | 3774篇 |
1980年 | 3469篇 |
1979年 | 3422篇 |
1978年 | 3231篇 |
1977年 | 3825篇 |
1976年 | 4877篇 |
1975年 | 2782篇 |
1974年 | 2661篇 |
1973年 | 2677篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
993.
Epidemiological studies have linked dietary fiber to the prevention of human colorectal cancer and suggest that short chain fatty acids such as butyric acid, which is produced by fermentation of dietary fiber in the large intestine, may be an important mediator of the protective effects of fiber. We investigated the role of Bcl-2 deregulation on the sensitivity of colorectal carcinoma cells to undergo butyrate-induced apoptosis. Here we report an inverse relationship between the levels of Bcl-2 and the sensitivity of colorectal carcinoma cell lines to undergo apoptosis in response to butyrate. Overexpression of Bcl-2 in colorectal carcinoma DiFi cells resulted in suppression of butyrate-induced apoptosis and enhanced cell survival in response to butyrate. Butyrate-induced apoptosis was accompanied by inhibition of expression of a 30 kDa protein (p30, immunorecognized by anti-Bcl-2 mAb) and this cellular effect of butyrate was inhibited by Bcl-2 overexpression. These findings suggest that deregulation of Bcl-2 in human colorectal carcinoma cells confers resistance to induction of apoptosis by butyrate, a dietary micronutrient. 相似文献
994.
995.
Six measures of divergent thinking were administered to 825 men ranging in age from 17 to 101 over the period from 1959 to 1972; repeat administrations were given to a subset of 278 men after a 6-year interval. Cross-sectional analyses showed curvilinear trends, with an increase in scores for men under 40 and a decline thereafter. Repeated measures analyses on subjects initially aged 33 to 74 generally replicated this finding, whereas cross-sequential analyses suggested a decline for all cohorts tested at a later time. Additional analyses suggested that not all of the decline could be attributed to reduced speed of response production. These longitudinal findings confirm earlier cross-sectional reports of decline in divergent thinking abilities with age. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
996.
When domestic wastewater was treated with different onsite applications of buried sand filters and sequencing batch reactors, good organic matter removal was common and effluent BOD7 concentrations from 5 to 20 mg/l were easily achievable. For total nitrogen, effluent concentrations were usually between 20 and 80 mg/l. Good phosphorus removal, even using special adsorption or precipitation materials, was difficult to achieve and large variations occurred. The median effluent concentration of total phosphorus in the most successful sand filter application was less than 0.1 mg/l and other sand filters and SBRs had the median concentrations varying from 1.7 to 6.7 mg/l. These results are based on one year in situ monitoring of 2 conventional buried sand filters, 6 sand filter applications with special phosphorus adsorbing media within the filter bed, 5 sand filters with separate tertiary phosphorus filtration and 11 small SBRs of three different types. The study was carried out in southern Finland during 2003-05. The whole project included monitoring of more than 60 plants of 20 different treatment types or methods, used in normal conditions to treat domestic wastewater. Evaluation of the different systems was made by comparing the measured effluent concentrations. In addition the effluent concentrations were compared to the discharge limits calculated according to the new Finnish regulation. 相似文献
997.
The electrolytical methanogenic/methanotrophic coupling (eMaMoC) process was tested in a laboratory-scale single-stage reactor for the treatment of tetrachloroethene (PCE)-contaminated waters. A water electrolysis cell was placed directly in the effluent recirculation loop for the supply of both O2 and H2 to the system: H2 serving as the electron donor for both carbonate reduction into CH4 and reductive dechlorination. The concurrent presence of O2 and CH4 could be used by the methanotrophs for co-metabolically oxidising the chlorinated intermediates left over by the anaerobic transformation of PCE. At a PCE inlet of 33-52 microM and a hydraulic residence time (HRT) of 5.6 days, PCE reductive dechlorination to dichloroethene (DCE) was over 95% with a maximum DCE mineralisation of 83%. Fluorescence in situ hybridisation with 16S rRNA probes related to type I and type II methanotrophic bacteria were utilised to localise the methanotrophic communities in the anaerobic/aerobic granules. It evidenced that with operational time, along with increasing oxygenation rate, methanotrophic communities were specifically colonising onto the outermost layer of the anaerobic/aerobic granule. 相似文献
998.
999.
1000.
LiSoR (liquid metal–solid metal reaction) loop is a unique facility which was designed to investigate simultaneously the influence of flowing lead bismuth eutectic (LBE), static stress and irradiation by protons onto steel that might be used as structural material in a future ADS (accelerator driven system) reactor. LiSoR is worldwide the first LBE loop that is under operation while it is irradiated at the same time.Up to now five LiSoR test sections have been irradiated. In this paper the experience on LiSoR no. 3 is presented including irradiation experiment and dissembling of the test section and EDM wire cutting of the samples. Additionally the results obtained by SEM and EDX analyses on LiSoR specimen and on beam window are shown whereby the most interesting outcome is the finding of an oxide layer, which was clearly identified by X-ray mapping. This layer is located directly in the irradiated area having a total thickness less than 1 μm. Additionally solidified LBE was detected on some areas of the samples but no wetting of the steel or penetration of LBE into the steel matrix was observed. No enrichment or dissolution of steel elements such as Fe and Cr could be detected on the surface near area. The steel surface is still smooth without any indications of corrosion attack. 相似文献