全文获取类型
收费全文 | 56690篇 |
免费 | 6126篇 |
国内免费 | 3943篇 |
专业分类
电工技术 | 4419篇 |
技术理论 | 6篇 |
综合类 | 5109篇 |
化学工业 | 8013篇 |
金属工艺 | 3693篇 |
机械仪表 | 3884篇 |
建筑科学 | 4419篇 |
矿业工程 | 1898篇 |
能源动力 | 1423篇 |
轻工业 | 5895篇 |
水利工程 | 1580篇 |
石油天然气 | 2375篇 |
武器工业 | 675篇 |
无线电 | 6166篇 |
一般工业技术 | 5826篇 |
冶金工业 | 2392篇 |
原子能技术 | 755篇 |
自动化技术 | 8231篇 |
出版年
2024年 | 335篇 |
2023年 | 1020篇 |
2022年 | 2102篇 |
2021年 | 2687篇 |
2020年 | 2003篇 |
2019年 | 1514篇 |
2018年 | 1538篇 |
2017年 | 1830篇 |
2016年 | 1601篇 |
2015年 | 2474篇 |
2014年 | 3048篇 |
2013年 | 3682篇 |
2012年 | 4341篇 |
2011年 | 4660篇 |
2010年 | 4112篇 |
2009年 | 3896篇 |
2008年 | 3969篇 |
2007年 | 4006篇 |
2006年 | 3449篇 |
2005年 | 2859篇 |
2004年 | 2000篇 |
2003年 | 1553篇 |
2002年 | 1551篇 |
2001年 | 1351篇 |
2000年 | 1199篇 |
1999年 | 853篇 |
1998年 | 566篇 |
1997年 | 451篇 |
1996年 | 419篇 |
1995年 | 341篇 |
1994年 | 324篇 |
1993年 | 220篇 |
1992年 | 171篇 |
1991年 | 137篇 |
1990年 | 109篇 |
1989年 | 85篇 |
1988年 | 61篇 |
1987年 | 44篇 |
1986年 | 40篇 |
1985年 | 20篇 |
1984年 | 23篇 |
1983年 | 17篇 |
1982年 | 18篇 |
1981年 | 24篇 |
1980年 | 16篇 |
1979年 | 7篇 |
1978年 | 5篇 |
1976年 | 4篇 |
1959年 | 6篇 |
1951年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
为了避免回收单一钕铁硼废料中有价元素带来的操作复杂和资源浪费等问题,本研究采用共沉淀法共沉淀出钕铁硼废料中的有价元素Me(Nd,Pr,Co,Fe),制备可用于生产再生钕铁硼的原料;根据质量守恒和同时平衡原理,采用MATLAB软件建立Me(Nd,Pr,Co,Fe)-OH--NH3热力学模型,绘制lg[Me]-p H曲线模拟共沉淀工艺,并根据模拟结果确立了共沉淀工艺;模拟和实验的结果表明:根据lg[Me]-p H模拟结果可以确立一步共沉淀法的p H:6~10,Fe3+比Fe2+更易于沉淀完全;在上述条件下获得的共沉淀粉末主相均为Nd,Pr,Co,Fe的化合物,且有价元素的百分比含量均大于99.4%;其中,当p H值在8左右时回收率最高,在该条件下金属元素Me(Nd,Pr,Co,Fe)的沉淀效率分别为:98.7%,99.9%,93.6%,99.9%。该结果也表明共沉淀法工艺不仅高效,而且所制备的共沉淀粉末可以满足制备二次钕铁硼的需要。 相似文献
2.
3.
Multifunctional 3D Patternable Drug‐Embedded Nanocarrier‐Based Interfaces to Enhance Signal Recording and Reduce Neuron Degeneration in Neural Implantation 下载免费PDF全文
4.
Jialong Tian M. Babar Shahzad Wei Wang Lichang Yin Zhouhua Jiang Ke Yang 《材料科学技术学报》2018,34(9):1671-1675
The effect of Co addition on the formation of Ni-Ti clusters in maraging stainless steel was studied by three dimensional atom probe (3DAP) and first-principles calculation. The cluster analysis based on the maximum separation approach showed an increase in size but a decrease in density of Ni-Ti clusters with increasing the Co content. The first-principles calculation indicated weaker Co-Ni (Co-Ti) interactions than Co-Ti (Fe-Ti) interactions, which should be the essential reason for the change of distribution characteristics of Ni-Ti clusters in bcc Fe caused by Co addition. 相似文献
5.
Zhao Hongliang Lu Tingting Liu Fengqin Yin Pan Wang Sen 《JOM Journal of the Minerals, Metals and Materials Society》2019,71(5):1643-1649
JOM - The Isa/Ausmelt smelting technology with a top submerged lance (TSL) has been extensively used in copper smelting processes. However, the TSL is extremely vulnerable to damage and failure... 相似文献
6.
Risk allocation decisions are of critical importance in project management. The present study proposes an explanation for how risk allocation in a contract motivates a contractor to cooperate with a project owner. Theories of risk allocation and trust were used to motivate the research. Using a survey methodology, we collected data concerning 124 construction projects in China. We found that risk allocation influenced the contractor’s role behavior through the contractor’s feeling of being trusted but not the contractor’s trust in the owner. Feeling of being trusted partially mediated the effect of risk allocation on the contractor’s in-role (i.e., contractual) behavior and fully mediated the effect on extra-role behavior. The study introduces a social and psychological view of the impacts of risk allocation to the project and engineering management literature. We contribute to theory by arguing and demonstrating the mediating effect of trust on the relationship between risk allocation and contractor behavior. From a practical standpoint, we conclude that contractual risk allocation has a significant impact on building a trusting relationship between owners and contractors and that contractors who feel trusted perform both contractually mandated actions and actions external to the contract more diligently, resulting in the likelihood of improved outcomes for both parties. 相似文献
7.
Y. Yin C.K. Erdonmez A. Cabot S. Hughes A.P. Alivisatos 《Advanced functional materials》2006,16(11):1389-1399
Formation of cobalt sulfide hollow nanocrystals through a mechanism similar to the Kirkendall Effect has been investigated in detail. It is found that performing the reaction at > 120 °C leads to fast formation of a single void inside each shell, whereas at room temperature multiple voids are formed within each shell, which can be attributed to strongly temperature‐dependent diffusivities for vacancies. The void formation process is dominated by outward diffusion of cobalt cations; still, the occurrence of significant inward transport of sulfur anions can be inferred as the final voids are smaller in diameter than the original cobalt nanocrystals. Comparison of volume distributions for initial and final nanostructures indicates excess apparent volume in shells, implying significant porosity and/or a defective structure. Indirect evidence for fracture of shells during growth at lower temperatures was observed in shell‐size statistics and transmission electron microscopy images of as‐grown shells. An idealized model of the diffusional process imposes two minimal requirements on material parameters for shell growth to be obtainable within a specific synthetic system. 相似文献
8.
珠江三角洲近二十年来河床演变浅析 总被引:1,自引:0,他引:1
根据珠江三角洲20世纪80年代及1999年两套实测河道地形资料,从平均河底高程、河相系数及河道容积等方面分析河道的冲淤变化状况,比较了不同网河片区、网河区与口门区、主要汉口的河床演变差异,从中可知珠江三角洲网河河道在80年代后普遍下切,但下切幅度各有差别。通过对引起变化的原因进行分析,为广东省河道采砂规划提供依据。 相似文献
9.
10.
通过对广州市电视台综合信息平台网络系统的应用现状及安全风险进行分析,提出基于网络层、系统层、用户层和安全策略管理全方位的网络信息安全体系. 相似文献