全文获取类型
收费全文 | 263410篇 |
免费 | 75155篇 |
国内免费 | 49390篇 |
专业分类
电工技术 | 32465篇 |
技术理论 | 14篇 |
综合类 | 26304篇 |
化学工业 | 37129篇 |
金属工艺 | 29271篇 |
机械仪表 | 11322篇 |
建筑科学 | 18726篇 |
矿业工程 | 15315篇 |
能源动力 | 10691篇 |
轻工业 | 26085篇 |
水利工程 | 8686篇 |
石油天然气 | 17600篇 |
武器工业 | 4223篇 |
无线电 | 38236篇 |
一般工业技术 | 39296篇 |
冶金工业 | 10464篇 |
原子能技术 | 2152篇 |
自动化技术 | 59976篇 |
出版年
2024年 | 3034篇 |
2023年 | 5787篇 |
2022年 | 7312篇 |
2021年 | 8899篇 |
2020年 | 11187篇 |
2019年 | 20089篇 |
2018年 | 21782篇 |
2017年 | 23287篇 |
2016年 | 22794篇 |
2015年 | 22374篇 |
2014年 | 22046篇 |
2013年 | 22005篇 |
2012年 | 21764篇 |
2011年 | 18389篇 |
2010年 | 16592篇 |
2009年 | 13220篇 |
2008年 | 11182篇 |
2007年 | 10573篇 |
2006年 | 9571篇 |
2005年 | 8593篇 |
2004年 | 10026篇 |
2003年 | 8394篇 |
2002年 | 7788篇 |
2001年 | 7020篇 |
2000年 | 6665篇 |
1999年 | 6582篇 |
1998年 | 5695篇 |
1997年 | 4961篇 |
1996年 | 4680篇 |
1995年 | 4579篇 |
1994年 | 3769篇 |
1993年 | 3300篇 |
1992年 | 3080篇 |
1991年 | 2250篇 |
1990年 | 1795篇 |
1989年 | 1609篇 |
1988年 | 1245篇 |
1987年 | 444篇 |
1986年 | 384篇 |
1985年 | 283篇 |
1984年 | 193篇 |
1983年 | 133篇 |
1982年 | 180篇 |
1981年 | 168篇 |
1980年 | 121篇 |
1976年 | 228篇 |
1975年 | 207篇 |
1972年 | 237篇 |
1971年 | 128篇 |
1960年 | 206篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
通过制备不同晶相结构〔单斜相(m-ZrO_2)、四方相(t-ZrO_2)和无定型(a-ZrO_2)〕ZrO_2载体,再通过沉积沉淀法制得Cu/m-ZrO_2、Cu/t-ZrO_2和Cu/a-ZrO_2催化剂,分别用于催化二乙醇胺脱氢合成亚氨基二乙酸反应。采用XRD、氮气物理吸附脱附、XPS、H_2-TPR、CO_2-TPD对催化剂的结构进行了表征。结果表明,Cu/m-ZrO_2催化剂界面更加有利于Cu~+/Cu~0稳定存在,具有更多的碱性位点,且抗氧化性较好。在二乙醇胺脱氢反应中,Cu/m-ZrO_2催化剂性能最好,反应时间为2.5 h,亚氨基二乙酸收率为97.64%。 相似文献
3.
采用异佛尔酮二异氰酸酯(IPDI)、聚乙二醇200、400、600、800(PEG200、PEG400、PEG600、PEG800)、2,2-二羟甲基丙酸(DMPA)、1-苯基-1,2-乙二醇、中和剂三乙胺(TEA)、甲乙酮肟等为原料,制备了一种阴离子聚氨酯分散剂.通过FTIR、GPC、TG表征了分散剂的结构与性能.利用自制的分散剂采用研磨法制备了液体靛蓝分散液,以液体靛蓝分散液粒径、离心稳定性、储存稳定性为指标,探讨了分散剂链长、用量对分散液性能的影响.结果表明,研磨1 h后,以PEG400为软段合成的聚氨酯分散剂用量为染料质量的60%时制备的液体靛蓝粒径为277.1 nm,1000 r/min离心稳定性达到93.98%,3000 r/min离心稳定性为51.13%,常温放置7 d后粒径变化在20 nm以内,染色后织物的颜色深度(K/S)为10左右,约是粉状靛蓝染色K/S的2倍,染色织物的颜色性能并未改变,SEM显示分散体颗粒大小分布均匀,与分散剂甲基萘磺酸钠的甲醛缩合物(MF)和木质素85A相比,其分散体系稳定性差别不大. 相似文献
4.
5.
6.
Over tensile stress ranges giving creep lives up to 2000 hours at 373 to 463 K, the creep and creep fracture properties of
7010 are compared with results recorded for 7075 and other precipitation-hardened aluminum alloys. Using the ϕ methodology
to quantify the systematic variations in creep curve shape with changing test conditions, the behavior patterns displayed
by the different alloys are shown to depend on the extent to which precipitate coarsening causes a progressive loss of creep
strength with increasing test duration and temperature. The ϕ relationships also introduce new approaches for rationalization
and interpretation of creep data sets, based on the activation energy for lattice diffusion in the alloy matrices and the
yield stress or UTS at the creep temperatures. 相似文献
7.
An inventory analysis of rural pollution loads in China. 总被引:1,自引:0,他引:1
Rural pollution has attracted increasing attention over the past decade for its important consequences on surface and groundwater quality. This is particularly so in China due to the wide and effective control of industrial and municipal wastewater discharges over the past decade. Based on the discussion of rural activities in China, this paper develops a new method of inventory analysis through the definition of elementary unit (EU). This inventory analysis approach is then applied to estimate the total rural pollution loads of COD, TN and TP, as well as their spatial distributions in China. Further analysis is also conducted to investigate the correlations between rural pollution loads and agricultural production outputs, as well as population. It is found that China's agriculture is developing largely at the cost of environment quality, and a high population, as well as the increasing demand for agricultural products, is one of the dominant driving forces. The constructed EKC, which describes the relationship between rural pollution loads and agricultural income, also reveals that current agricultural development in China is mostly far from de-locked from the environmental problem. 相似文献
8.
Supported metal catalysts, particularly noble metals supported on SiO2, have attracted considerable attention due to the importance of the silica–metal interface in heterogeneous catalysis and in electronic device fabrication. Several important issues, e.g., the stability of the metal–oxide interface at working temperatures and pressures, are not well-understood. In this review, the present status of our understanding of the metal–silica interface is reviewed. Recent results of model studies in our laboratories on Pd/SiO2/Mo(1 1 2) using LEED, AES and STM are reported. In this work, epitaxial, ultrathin, well-ordered SiO2 films were grown on a Mo(1 1 2) substrate to circumvent complications that frequently arise from the silica–silicon interface present in silica thin films grown on silicon. 相似文献
9.
Performance study of iSCSI-based storage subsystems 总被引:9,自引:0,他引:9
iISCSI is emerging as an end-to-end protocol for transporting storage I/O block data over IP networks. By exploiting the ubiquitous Internet infrastructure, iSCSI greatly facilitates remote storage, remote backup, and data mirroring. This article evaluates the performance of two typical iSCSI storage subsystems by measuring and analyzing block-level I/O access performance and file-level access performance. In the file-level performance study, we compare file access performance in an NAS scheme with that in an iSCSI-based SAN scheme. Our test results show that Gigabit Ethernet-based iSCSI can reach very high bandwidth, close to that of a direct FC disk access in block I/O access. However, when the iSCSI traverses through longer distance, throughput relies heavily on the available bandwidth between the initiator and the target. On the other hand, the file-level performance shows that iSCSI-based file access (SAN scheme) provides higher performance than using NFS protocol in Linux and SMB protocol in Windows (NAS scheme). However, the advantage of using iSCSI-based file accesses decreases as the file size increases. The obtained experimental results shed some light on the performance of applications based on iSCSI storage. 相似文献
10.
Rheological properties of MR fluids under large step strain shear are presented in this paper. The experiments were carried out using a rheometer with parallel-plate geometry. Under the large step strain shear, MR fluids behave as nonlinear viscoelastic properties, where the stress relaxation modulus, G(t, γ), shows a decreasing trend with step strain. The experimental results indicate that G(t, γ) obeys time-strain separability. Thus, a mathematical form based on finite exponential serials is proposed to predict MR behavior. In this model, G(t, γ) is represented as the product of a linear stress relaxation, G(t), and the damping function, h(γ), i.e. G(t, γ)=G(t) h(γ). G(t) is simply represented as a three-parameter exponential serial and h(γ) has a sigmoidal form with two parameters. The parameters are identified by adopting an efficient optimization method proposed by Stango et al. The comparison between the experimental results and the model-predicted values indicates that this mathematical model can accurately predict MR behavior. 相似文献