全文获取类型
收费全文 | 4992篇 |
免费 | 144篇 |
国内免费 | 9篇 |
专业分类
电工技术 | 46篇 |
综合类 | 10篇 |
化学工业 | 838篇 |
金属工艺 | 67篇 |
机械仪表 | 102篇 |
建筑科学 | 222篇 |
矿业工程 | 41篇 |
能源动力 | 146篇 |
轻工业 | 536篇 |
水利工程 | 38篇 |
石油天然气 | 8篇 |
无线电 | 466篇 |
一般工业技术 | 702篇 |
冶金工业 | 1109篇 |
原子能技术 | 28篇 |
自动化技术 | 786篇 |
出版年
2023年 | 24篇 |
2022年 | 41篇 |
2021年 | 62篇 |
2020年 | 76篇 |
2019年 | 63篇 |
2018年 | 87篇 |
2017年 | 99篇 |
2016年 | 100篇 |
2015年 | 90篇 |
2014年 | 106篇 |
2013年 | 287篇 |
2012年 | 176篇 |
2011年 | 215篇 |
2010年 | 201篇 |
2009年 | 193篇 |
2008年 | 222篇 |
2007年 | 228篇 |
2006年 | 184篇 |
2005年 | 141篇 |
2004年 | 132篇 |
2003年 | 153篇 |
2002年 | 113篇 |
2001年 | 85篇 |
2000年 | 101篇 |
1999年 | 104篇 |
1998年 | 359篇 |
1997年 | 204篇 |
1996年 | 154篇 |
1995年 | 102篇 |
1994年 | 89篇 |
1993年 | 84篇 |
1992年 | 39篇 |
1991年 | 50篇 |
1990年 | 37篇 |
1989年 | 47篇 |
1988年 | 59篇 |
1987年 | 39篇 |
1986年 | 37篇 |
1985年 | 49篇 |
1984年 | 35篇 |
1983年 | 39篇 |
1982年 | 32篇 |
1981年 | 53篇 |
1980年 | 26篇 |
1979年 | 26篇 |
1978年 | 17篇 |
1977年 | 43篇 |
1976年 | 58篇 |
1973年 | 24篇 |
1972年 | 15篇 |
排序方式: 共有5145条查询结果,搜索用时 0 毫秒
1.
2.
K Giesen T Hummel A Stollewerk S Harrison A Travers C Kl?mbt 《Canadian Metallurgical Quarterly》1997,124(12):2307-2316
Two classes of glial cells are found in the embryonic Drosophila CNS, midline glial cells and lateral glial cells. Midline glial development is triggered by EGF-receptor signalling, whereas lateral glial development is controlled by the gcm gene. Subsequent glial cell differentiation depends partly on the pointed gene. Here we describe a novel component required for all CNS glia development. The tramtrack gene encodes two zinc-finger proteins, one of which, ttkp69, is expressed in all non-neuronal CNS cells. We show that ttkp69 is downstream of gcm and can repress neuronal differentiation. Double mutant analysis and coexpression experiments indicate that glial cell differentiation may depend on a dual process, requiring the activation of glial differentiation by pointed and the concomitant repression of neuronal development by tramtrack. 相似文献
3.
4.
Less may not be more,but it still counts: The state of social capital in Yeoville,Johannesburg 总被引:2,自引:2,他引:0
Kirsten Harrison 《Urban Forum》2002,13(1):67-84
5.
During large scale wildfires, suppression activities are carried out under the direction of an Incident Management Team (IMT). The aim of the research was to increase understanding of decision processes potentially related to IMT effectiveness. An IMT comprises four major functions: Command, Operations, Planning, and Logistics. Four methodologies were used to study IMT processes: computer simulation experiments; analyses of wildfire reports; interviews with IMT members; and cognitive ethnographic studies of IMTs. Three processes were important determinants of IMT effectiveness: information management and cognitive overload; matching component function goals to overall goals; and team metacognition to detect and counter task‐disruptive developments. These processes appear to be complex multi‐person analogues of individual Incident Command processes identified previously. The findings have implications for issues such as: creating IMTs; training IMTs; managing IMTs; and providing decision support to IMTs. 相似文献
6.
There are some foods that contain mutagenic or carcinogenic agents, some of which occur naturally and others that may be formed during preparation or cooking. Several foods such as legumes, also contain natural antimutagens and/or anticarcinogens. Lupine is one such legume that contains high amounts of protein (40%) and oils (14%). About 90 species of lupine have been reported throughout Mexico. However, the use of this crop as a source of food has been limited by the presence of antinutritional agents such as phenolic compounds (PC), carbohydrates (CH) and quinolizidinic alkaloids (Qas). It has also been suggested that consuming these compounds can affect human health and may even reduce the risk of disease. The objective of this work was to determine the effect of PC, CH and Qas, isolated and quantified from Lupinus campestris on the mutagenicity of 1-nitropyrene (1-NP) as a model mutagen and we used the Salmonella typhimurium tester strain YG1024 by the Kado microsuspension method. The results indicate that L. campestris seeds have 11 mg (+)catechin equivalent g(-1) seed coat; 120.3 mg g(-1) seeds and 2.13 mg g(-1) seeds of PC, CH and Qas, respectively. 1-NP mutagenicity was inhibited by 86% for PC, 76% for CH and 75% for Qas at concentrations of 200, 512 and 13.6 microg/tube, respectively. 相似文献
7.
Ricardo Beristain‐Cardoso Anne‐Claire Texier Reyes Sierra‐Álvarez Jim A Field Elías Razo‐Flores Jorge Gómez 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(9):1197-1203
BACKGROUND: Simultaneous removal of sulfur, nitrogen and carbon compounds from wastewaters is a commercially important biological process. The objective was to evaluate the influence of the CH3COO?/NO3? molar ratio on the sulfide oxidation process using an inverse fluidized bed reactor (IFBR). RESULTS: Three molar ratios of CH3COO?/NO3? (0.85, 0.72 and 0.62) with a constant S2?/NO3? molar ratio of 0.13 were evaluated. At a CH3COO?/NO3? molar ratio of 0.85, the nitrate, acetate and sulfide removal efficiencies were approximately 100%. The N2 yield (g N2 g?1 NO3?‐N consumed) was 0.81. Acetate was mineralized, resulting in a yield of 0.65 g inorganic‐C g?1 CH3COO?‐C consumed. Sulfide was partially oxidized to S0, and 71% of the S2? consumed was recovered as elemental sulfur by a settler installed in the IFBR. At a CH3COO?/NO3? molar ratio of 0.72, the efficiencies of nitrate, acetate and sulfide consumption were of 100%, with N2 and inorganic‐C yields of 0.84 and 0.69, respectively. The sulfide was recovered as sulfate instead of S0, with a yield of 0.92 g SO42?‐S g?1 S2? consumed. CONCLUSIONS: The CH3COO?/NO3? molar ratio was shown to be an important parameter that can be used to control the fate of sulfide oxidation to either S0 or sulfate. In this study, the potential of denitrification for the simultaneous removal of organic matter, sulfide and nitrate from wastewaters was demonstrated, obtaining CO2, S0 and N2 as the major end products. Copyright © 2008 Society of Chemical Industry 相似文献
8.
A physically based hysteresis theory incorporating a domain size that depends on the Weiss effective field explains the observed ranges of reversible and irreversible magnetization in the initial-magnetization curve and exterior loop of ferromagnetic materials. The theory applies to materials exhibiting both normal and wasp-waisted exterior loops and agrees well with measured data. It also provides close linkages between magnetization at the quantum scale, domain properties at the mesoscopic scale, and measurements at the macroscopic scale. 相似文献
9.
10.