全文获取类型
收费全文 | 24819篇 |
免费 | 2768篇 |
国内免费 | 2807篇 |
专业分类
电工技术 | 1001篇 |
技术理论 | 5篇 |
综合类 | 3336篇 |
化学工业 | 3077篇 |
金属工艺 | 350篇 |
机械仪表 | 328篇 |
建筑科学 | 10510篇 |
矿业工程 | 1508篇 |
能源动力 | 743篇 |
轻工业 | 1246篇 |
水利工程 | 4482篇 |
石油天然气 | 456篇 |
武器工业 | 23篇 |
无线电 | 309篇 |
一般工业技术 | 856篇 |
冶金工业 | 1111篇 |
原子能技术 | 184篇 |
自动化技术 | 869篇 |
出版年
2024年 | 109篇 |
2023年 | 296篇 |
2022年 | 668篇 |
2021年 | 869篇 |
2020年 | 814篇 |
2019年 | 727篇 |
2018年 | 674篇 |
2017年 | 782篇 |
2016年 | 854篇 |
2015年 | 894篇 |
2014年 | 1665篇 |
2013年 | 1343篇 |
2012年 | 1755篇 |
2011年 | 1958篇 |
2010年 | 1599篇 |
2009年 | 1656篇 |
2008年 | 1439篇 |
2007年 | 1912篇 |
2006年 | 1711篇 |
2005年 | 1629篇 |
2004年 | 1359篇 |
2003年 | 1103篇 |
2002年 | 861篇 |
2001年 | 698篇 |
2000年 | 608篇 |
1999年 | 491篇 |
1998年 | 367篇 |
1997年 | 275篇 |
1996年 | 241篇 |
1995年 | 192篇 |
1994年 | 172篇 |
1993年 | 83篇 |
1992年 | 99篇 |
1991年 | 71篇 |
1990年 | 55篇 |
1989年 | 58篇 |
1988年 | 46篇 |
1987年 | 50篇 |
1986年 | 40篇 |
1985年 | 30篇 |
1984年 | 34篇 |
1983年 | 17篇 |
1982年 | 14篇 |
1981年 | 11篇 |
1980年 | 10篇 |
1979年 | 40篇 |
1978年 | 5篇 |
1973年 | 1篇 |
1959年 | 2篇 |
1951年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 19 毫秒
211.
212.
A fully continuous lab scale supercritical fluid extraction system has been designed, built and tested. The system continuously pumps carbon dioxide under supercritical conditions and soil slurry into a counter‐current contacting column. Delhi Loamy Sand, spiked with approximately 10 mg/g of naphthalene, was used as the testing soil. The soil slurry ranged from 0.0028 g dry soil per g slurry to 0.072 g/g. The operating temperature was 43°C and the operating pressure was 7.7 MPa. Near steady state, fully continuous flow was achieved with runs lasting as long as 2 h. All carbon dioxide samples contained measurable quantities of naphthalene and the measured mass transfer coefficients were as high as 4.6×10?4 s?1. 相似文献
213.
214.
通过渗析法和水汽平衡法研究不同温度控制下干密度1.7 g/cm~3压实红粘土持水特性(SWRC:soil water retention characteristics)。试验结果表明:20℃下干密度1.7 g/cm~3压实红粘土进气值约为110 k Pa;试样控制的温度越高,压实红粘土样持水能力越低,土样进气值随着温度升高而减小,且呈线性关系;Van Genuchten(1980年)土水特征模型能很好的描述干密度1.7 g/cm~3压实红粘土持水特性曲线。 相似文献
215.
216.
花岗岩残积土在华南、东南沿海、南岳、新疆等地区广泛分布,前人的研究多集中在结构性及微观特性上,后循环加载、位移演化、土壤密度等因素对筋-土界面的剪切特性及加筋作用效果的影响评估研究较少。从循环试验剪切刚度这一重要参数入手,以加载次数、加载频率值、位移振幅值、土壤重度值为自变量,应用控制变量法,通过设计循环直剪试验,得到加筋花岗岩残积土的剪切应力与剪切位移、垂直位移与剪切位移关系曲线进行观察对比,结果表明:花岗岩残积土土工格栅界面剪切刚度受位移半振幅、土壤干重度影响很大,受加载频率影响很小,循环加载并没有弱化后循环界面剪切强度,剪切位移与位移半振幅呈负相关关系。 相似文献
217.
针对上海地区软土地基特点,利用工业废渣为主要原料配制成新型土体固结材料——土体固结粉。通过室内的无侧限抗压强度及XRD试验得出其固化土的强度性能及加固机理;再通过室外原位搅拌桩施工及芯样试验进行分析,研究了土体固结粉在软土地基加固实际工程中的适用性。 相似文献
218.
219.
Nitrogen transformations occurring in ten soils fertilized with urea were determined during incubation in the laboratory for four weeks. Urea was applied at one rate, but with different placement methods. Urea was applied in solution, as prills with a 1 cm grid spacing and as prills with no spacing. Unfertilized soils and soils amended with KNO3 solution were included as controls.Nitrite accumulated in the majority of soils treated with urea, and the maximum nitrite concentration measured was directly related to initial soil pH. Cumulative gaseous N losses as percentages of applied N were: NH3, 0-59.6; N2, 0-4.9; N2O, 0-9.9; KMnO4-N, 0-1.3; CH3ONO, 0-<0.1. No gaseous N evolution was detected in control treatments. Gaseous N losses were correlated with soil pH (NH3) maximum NO
2
-
concentration (N2, N2O, KMnO4-N) and organic C content (N2, N2O). Fertilizer placement effects were generally not significant and were small in comparison with differences between soils.
Resumo Foram determinadas, durante incubação em laboratório por quatro semanas, as transformações do nitrogênio ocorridas em dez solos fertilizados com uréia. A uréia foi aplicada a um só nivel, mas com diferentes métodos de aplicação: em solução e em grânulos com 1 cm de espaçamento de grade e em grânulos sem espaçamento. Solos não fertilizados e solos corrigidos com solução de KNO3 foram incluidos como controles.O nitrito acumulado na maioria dos solos tratados com uréia e a concentração máxima de nitrito medido foram diretamente relacionados ao pH inicial do solo. As perdas cumulativas de N gasoso tomadas em percentagens de N aplicado foram: NH3, 0-59.6; N2, 0-4.9; N2O; 0-9.9; KMnO4-N, 0-1.3; CH3ONO, 0-<0.1. Não foi detectada liberação de N gasoso nos tratamentos de controle. As perdas de N gasoso foram relacionadas com o pH do solo (NH3), concentração máxima de NO 2 - (N2, N2O, KMnO4-N) e teor de C orgânico (N2, N2O). Efeitos da aplicação de fertilizante não foram de um modo geral significativos e foram pequenos em comparação com as diferenças entre os solos.相似文献
220.
针对熔融石英砂与混合油、溴化钙及蔗糖等孔隙液体制配成的3种透明土试样,开展渗流液体与孔隙液体一致或者不一致两种情况下的常水头渗透试验,测得透明土材料在不同孔隙液体、粒径及相对密实度等情况下的渗透率,以及水在3种透明土试样中的渗透过程;并与福建标准砂相关试验结果进行了对比分析。进而开展透明土试样电渗可视化模型试验,初步探讨孔隙液体、渗透率等因素对电渗过程与机理的影响规律。试验结果表明,透明土试样渗透特性不仅与粒径分布、相对密实度等因素相关,而且与孔隙液体种类相关;混合油、溴化钙溶液制配成的透明土渗透率与天然砂土渗透率最为相近。 相似文献