全文获取类型
收费全文 | 151148篇 |
免费 | 12373篇 |
国内免费 | 6180篇 |
专业分类
电工技术 | 8707篇 |
技术理论 | 9篇 |
综合类 | 9617篇 |
化学工业 | 25611篇 |
金属工艺 | 8373篇 |
机械仪表 | 9428篇 |
建筑科学 | 12293篇 |
矿业工程 | 4211篇 |
能源动力 | 4303篇 |
轻工业 | 9732篇 |
水利工程 | 2556篇 |
石油天然气 | 9525篇 |
武器工业 | 1070篇 |
无线电 | 17477篇 |
一般工业技术 | 18412篇 |
冶金工业 | 7248篇 |
原子能技术 | 1648篇 |
自动化技术 | 19481篇 |
出版年
2024年 | 444篇 |
2023年 | 2398篇 |
2022年 | 3699篇 |
2021年 | 5849篇 |
2020年 | 4539篇 |
2019年 | 3802篇 |
2018年 | 4128篇 |
2017年 | 4844篇 |
2016年 | 4174篇 |
2015年 | 5852篇 |
2014年 | 7230篇 |
2013年 | 8784篇 |
2012年 | 9412篇 |
2011年 | 10215篇 |
2010年 | 9035篇 |
2009年 | 8541篇 |
2008年 | 8320篇 |
2007年 | 7960篇 |
2006年 | 8266篇 |
2005年 | 7188篇 |
2004年 | 4918篇 |
2003年 | 4268篇 |
2002年 | 4043篇 |
2001年 | 3637篇 |
2000年 | 3802篇 |
1999年 | 4171篇 |
1998年 | 3564篇 |
1997年 | 3049篇 |
1996年 | 2873篇 |
1995年 | 2396篇 |
1994年 | 1967篇 |
1993年 | 1393篇 |
1992年 | 1168篇 |
1991年 | 898篇 |
1990年 | 673篇 |
1989年 | 589篇 |
1988年 | 471篇 |
1987年 | 329篇 |
1986年 | 216篇 |
1985年 | 143篇 |
1984年 | 110篇 |
1983年 | 61篇 |
1982年 | 93篇 |
1981年 | 60篇 |
1980年 | 46篇 |
1979年 | 21篇 |
1978年 | 6篇 |
1977年 | 7篇 |
1976年 | 7篇 |
1970年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Sergey Bombin Mitchell LeFebvre Jennifer Sherwood Yaolin Xu Yuping Bao Katrina M. Ramonell 《International journal of molecular sciences》2015,16(10):24174-24193
Increasing use of iron oxide nanoparticles in medicine and environmental remediation has led to concerns regarding exposure of these nanoparticles to the public. However, limited studies are available to evaluate their effects on the environment, in particular on plants and food crops. Here, we investigated the effects of positive (PC) and negative (NC) charged iron oxide (Fe2O3) nanoparticles (IONPs) on the physiology and reproductive capacity of Arabidopsis thaliana at concentrations of 3 and 25 mg/L. The 3 mg/L treated plants did not show evident effects on seeding and root length. However, the 25 mg/L treatment resulted in reduced seedling (positive-20% and negative-3.6%) and root (positive-48% and negative-negligible) length. Interestingly, treatment with polyethylenimine (PEI; IONP-PC coating) also resulted in reduced root length (39%) but no change was observed with polyacrylic acid (PAA; IONP-NC coating) treatment alone. However, treatment with IONPs at 3 mg/L did lead to an almost 5% increase in aborted pollen, a 2%–6% reduction in pollen viability and up to an 11% reduction in seed yield depending on the number of treatments. Interestingly, the treated plants did not show any observable phenotypic changes in overall size or general plant structure, indicating that environmental nanoparticle contamination could go dangerously unnoticed. 相似文献
62.
Lü Qing Xu Bin Yu Yang Zhan Wei Zhao Yu Zheng Jun Ji Jian 《Bulletin of Engineering Geology and the Environment》2021,80(8):6513-6525
Bulletin of Engineering Geology and the Environment - Many uncertainties exist in pile-stabilized slopes which make their design substantially complicated. In this paper, a first-order reliability... 相似文献
63.
64.
王虔虔在上任中建材(合肥)粉体科技装备有限公司(简称粉体公司)总经理之前,和分管部门的所有同事坐在同一间大办公室内。之所以和大家在同一个空间内工作,王虔虔是想更进一步拉近彼此之间的距离,以身作则潜移默化,传承公司文化,建立相互信任的团队。2012年,粉体公司决定向"提供系统解决方案的综合服务商"转变。 相似文献
65.
66.
Lu Xu Baijun Liu Mingyao Zhang Yang Bai Jinming Zhang Jiayin Song 《Polymer Engineering and Science》2020,60(6):1194-1201
A series of methacrylate-acrylonitrile-butadiene-styrene (MABS) resins was prepared using bulk polymerization. The polarity of the continuous phase and the compatibility of two phases were changed by adjusting the methyl methacrylate (MMA) content, choosing values that were close to styrene-butadiene rubber solubility value. The possibility of controlling the microstructure of the MABS resin by changing the polarity of the components and the compatibility of two phases was assessed. The dynamic mechanical analysis shows that the compatibility of two phases varies with the MMA content. The morphological analysis shows that increasing MMA contents results in a gradual decrease in the sub-inclusion structure with a network skeleton of rubber particles, and that all the particles become solid rubber when the MMA content reaches 75%. The sub-inclusion structure reappears but does not have a network skeleton when the MMA content is 90%. The impact strength and morphological analysis indicate that the solid rubber particles and the sub-inclusion structure with a network skeleton provide excellent toughness, while the sub-inclusion structure without a network skeleton does not. In contrast, the transmittance of the ABS resin first increased and then decreased with increasing MMA content. 相似文献
67.
二氧化钛凭借优异的光催化性能,越来越受到人们的广泛关注和重视。以钛酸四丁酯为原料,利用水解-水热-干燥/煅烧工艺制备得到未掺杂TiO2光催化剂和掺钒TiO2光催化剂,利用其对甲基橙溶液的降解率做了比较分析。结果表明,以钛酸四丁酯为原料,采用溶胶-凝胶法制备钒掺杂TiO2光催化剂是可行的。制备V/TiO2产品的最佳工艺条件:钒钛质量比为6∶100、水热温度为160 ℃、水热时间为12 h,120 ℃下干燥14 h。紫外光照射条件下,甲基橙光催化降解效率达到99.10%,降解时间小于45 min。 相似文献
68.
ABSTRACT This study investigates the effects of strain, strain rates, and forming directions (RD-rolling direction, TD-transverse direction, and ND-normal direction) on adiabatic shear, via dynamic impact compression tests using the Split Hopkinson Pressure Bar (SHPB) apparatus. A modified Johnson-Cook (J-C) constitutive model is proposed, which used to analyse the influence of the constitutive parameters on the sensitivity of adiabatic shear, employing a finite element software. The different sensitivities of adiabatic shear under different directions are explained by combining microscopic analysis and results from mechanical responses. The results show that the sensitivity of adiabatic shear can be related to the time of stress collapse in the following trend: ND?>?TD?>?RD; the sensitivities of these constitutive parameters on adiabatic shear are calculated and compared. 相似文献
69.
Rapid synthesis of silver nanowires(Ag NWs) with high quality and a broad processing window is challenging because of the low selectivity of the formation of multiply twinned particles at the nucleation stage for subsequent Ag NWs growth.Herein we report a systematic study of the water-involved heterogeneous nucleation of Ag NWs with high rate(less than 20 min) in a simple and scalable preparation method.Using glycerol as a reducing agent and a solvent with a high boiling point,the reaction is rapidly heated to 210 ℃ in air to synthesize Ag NWs with a very high yield in gram level.It is noted that the addition of a small dose of water plays a key role for obtaining highly pure Ag NWs in high yield,and the optimal water/glycerol ratio is0.25%.After investigating a series of forming factors including reaction temperature and dose of catalysts,the formation kinetics and mechanism of the Ag NWs are proposed.Compared to other preparation methods,our strategy is simple and reproducible.These Ag NWs show a strong Raman enhancement effect for organic molecules on their surface. 相似文献
70.
以氯化铝和氯化铁为原料制备出一系列不同铝铁物质的量比及碱化度的无机高分子混凝剂——聚合氯化铝铁(PAFC),并应用于地表水的混凝处理过程。考察PAFC的混凝效能及产生的絮体特性,进而对其使用条件进行优化并分析混凝机制。结果表明,PAFC为多羟基桥连的铝铁聚合物,水解后发生电中和作用使胶粒脱稳,而后通过羟桥和氧桥联接产生架桥和卷扫沉淀作用,混凝效果优异。PAFC的pH适用范围较宽,但铝铁物质的量比对其水解过程影响较大,在铝铁物质的量比为7:1、碱化度为0.5、投加量为10 mg/L时,絮体的粒度及生长速度最大,此时浊度和UV254的去除率分别达84.93%和78.52%。此外,正交实验的结果表明水力条件对PAFC的混凝效能影响显著,其最佳使用条件为:快搅时间为20 s、快搅速度为200 r/min、慢搅时间为15 min、慢搅速度为40 r/min。 相似文献