全文获取类型
收费全文 | 265733篇 |
免费 | 22870篇 |
国内免费 | 11706篇 |
专业分类
电工技术 | 16187篇 |
技术理论 | 16篇 |
综合类 | 16880篇 |
化学工业 | 44339篇 |
金属工艺 | 14094篇 |
机械仪表 | 16137篇 |
建筑科学 | 21333篇 |
矿业工程 | 6910篇 |
能源动力 | 7424篇 |
轻工业 | 18989篇 |
水利工程 | 4831篇 |
石油天然气 | 13309篇 |
武器工业 | 2096篇 |
无线电 | 32184篇 |
一般工业技术 | 32415篇 |
冶金工业 | 13408篇 |
原子能技术 | 3003篇 |
自动化技术 | 36754篇 |
出版年
2024年 | 1260篇 |
2023年 | 4364篇 |
2022年 | 8191篇 |
2021年 | 10926篇 |
2020年 | 8105篇 |
2019年 | 6704篇 |
2018年 | 7313篇 |
2017年 | 8407篇 |
2016年 | 7586篇 |
2015年 | 10072篇 |
2014年 | 13251篇 |
2013年 | 16580篇 |
2012年 | 17214篇 |
2011年 | 18955篇 |
2010年 | 16451篇 |
2009年 | 15886篇 |
2008年 | 15191篇 |
2007年 | 14652篇 |
2006年 | 14405篇 |
2005年 | 12500篇 |
2004年 | 8626篇 |
2003年 | 7209篇 |
2002年 | 6598篇 |
2001年 | 5780篇 |
2000年 | 5845篇 |
1999年 | 6342篇 |
1998年 | 5628篇 |
1997年 | 4672篇 |
1996年 | 4238篇 |
1995年 | 3537篇 |
1994年 | 2938篇 |
1993年 | 2317篇 |
1992年 | 1791篇 |
1991年 | 1349篇 |
1990年 | 1063篇 |
1989年 | 930篇 |
1988年 | 719篇 |
1987年 | 510篇 |
1986年 | 409篇 |
1985年 | 339篇 |
1984年 | 226篇 |
1983年 | 203篇 |
1982年 | 168篇 |
1981年 | 153篇 |
1980年 | 149篇 |
1979年 | 104篇 |
1978年 | 63篇 |
1977年 | 65篇 |
1976年 | 78篇 |
1975年 | 38篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Mitigating gibbsite particle cracking and breakage during industrial alumina production can increase the quality of smelter grade alumina product by reducing the ultrafine particle content. Therefore, it is essential to investigate the particle cracking during static calcination and the breakage of calcined gibbsite particles under external force. In this work, we investigated the impact of the calcination ramping rate and the crystallite size on gibbsite particle cracking during static calcination. A slow ramping rate and a large pristine crystallite size tend to increase particle cracking. Apart from the study of particle cracking behaviour, we also investigated the breakage of calcined gibbsite particle under external force. Cracks on the particle surface can initiate breakage within the crystallite and along the grain boundary under external force. The breakage within crystallite occurs as the cleavage of the crystallite, while the breakage along the grain boundary leads to the shedding of a whole crystallite. We further explored the factors influencing the strength of calcined gibbsite particles. With increasing calcination temperature, the strength of particle increases when gibbsite converts to boehmite, and then decreases when boehmite converts into amorphous alumina. Particles containing smaller crystallites and calcined with fast ramping rates exhibit higher resistance to breakage. 相似文献
62.
63.
Wireless Networks - TCP latency is critical to the performance of Web services. However, packet loss greatly impairs the TCP performance due to its poor loss recovery mechanisms. Recent work FUSO... 相似文献
64.
Borazine rings act as a pivotal part in siliconboroncarbonitride ceramics (SiBCN) for high-temperature stability and great resistance to crystallization. A detailed investigation of the ring formation mechanism will guide the design and synthesis of SiBCN to meet application requirements under extreme conditions. Boron trichloride (BCl3) and hexamethyldisilazane (HN(SiMe3)2) are common raw materials for the synthesis of precursors for SiBCN. In this paper, quantum chemical calculation was used to study the cyclization reaction mechanism between BCl3 and HN(SiMe3)2 to form trichloroborazine (TCBZ) at the MP2/6-31G (d,p) level of theory. We discussed the structure properties, reaction pathways, energy barriers, reaction rates, and other aspects in detail. The results show that BCl3 and HN(SiMe3)2 alternately participate in the reaction process, accompanied by the release of trimethylchlorosilane (TMCS), and that the entire reaction shows an absolute advantage in terms of energy. In the Step by step reaction, lower reaction barriers are formed due to the introduction of BCl3 with more heat released compared to that for the introduction of HN(SiMe3)2. The final single-molecule cyclization and TMCS elimination steps are found to be faster compared to all previous bimolecular reactions. 相似文献
65.
Cheng-Chin Huang Ching-Yao Yang Chin-Chuan Su Kai-Min Fang Cheng-Chieh Yen Ching-Ting Lin Jui-Min Liu Kuan-I Lee Ya-Wen Chen Shing-Hwa Liu Chun-Fa Huang 《International journal of molecular sciences》2021,22(9)
4-methyl-2,4-bis(4-hydroxyphenyl)pent-1-ene (MBP), a major active metabolite of bisphenol A (BPA), is generated in the mammalian liver. Some studies have suggested that MBP exerts greater toxicity than BPA. However, the mechanism underlying MBP-induced pancreatic β-cell cytotoxicity remains largely unclear. This study demonstrated the cytotoxicity of MBP in pancreatic β-cells and elucidated the cellular mechanism involved in MBP-induced β-cell death. Our results showed that MBP exposure significantly reduced cell viability, caused insulin secretion dysfunction, and induced apoptotic events including increased caspase-3 activity and the expression of active forms of caspase-3/-7/-9 and PARP protein. In addition, MBP triggered endoplasmic reticulum (ER) stress, as indicated by the upregulation of GRP 78, CHOP, and cleaved caspase-12 proteins. Pretreatment with 4-phenylbutyric acid (4-PBA; a pharmacological inhibitor of ER stress) markedly reversed MBP-induced ER stress and apoptosis-related signals. Furthermore, exposure to MBP significantly induced the protein phosphorylation of JNK and AMP-activated protein kinase (AMPK)α. Pretreatment of β-cells with pharmacological inhibitors for JNK (SP600125) and AMPK (compound C), respectively, effectively abrogated the MBP-induced apoptosis-related signals. Both JNK and AMPK inhibitors also suppressed the MBP-induced activation of JNK and AMPKα and of each other. In conclusion, these findings suggest that MBP exposure exerts cytotoxicity on β-cells via the interdependent activation of JNK and AMPKα, which regulates the downstream apoptotic signaling pathway. 相似文献
66.
This article proposes an active balancer, which features bidirectional charge shuttling and adaptive equalization current control, to fast counterbalance the state of charge (SOC) of cells in a lithium-ion battery (LIB) string. The power circuit consists of certain bidirectional buck-boost converters to transfer energy among the different cells back and forth. Owing to the characterization of the open-circuit voltage (OCV) vs SOC in LIB being relatively smooth near the SOC middle range, the SOC-inspected balance strategy can achieve more precise and efficient equilibrium than the voltage-based control. Accordingly, a compensated OCV-based SOC estimation is put forward to take into account the discrepancy of SOC estimation. Besides, the varied-duty-cycle (VDC) and curve-fitting modulation (CFM) methods are devised herein to tackle the problems of slow equalization rate and low balance efficacy, which arise from the diminution in balancing current as the SOC difference between the cells decreases in the later duration of equalization especially. The proposed strategies have taken the battery nonlinear characteristic and circuit parameter nonideality into account and can adaptively modulate the duty cycle with the SOC difference to keep balancing current constant throughout the balancing cycle. Simulated and experimental results are given to demonstrate the feasibility and effectiveness of the same prototype constructed. Compared with the fixed duty cycle and the VDC methods, the proposed CFM has the best balancing efficiency of 81.4%, and the balance time is shortened by 27.1% and 18.6%, respectively. 相似文献
67.
全球炼化工程总承包市场呈现出垄断竞争型特征,欧美和日韩国际工程公司由于技术和报价竞争力较强,一直占据本行业高端市场,中国炼化工程企业尚有差距.文章综合考虑投标报价阶段竞争者分析路径,提出了随机型和不完全信息静态博弈综合集成分析的投标报价最优决策模型,并以中东海湾地区某炼化工程总承包项目为例,进行多维度的实证分析,提出模型的有效性和可行性,为中国炼化工程企业"走出去"高质量发展提供有益的决策支持和信息参考. 相似文献
68.
目的:鉴定中国白酒发酵过程中的微生物种类,研究关键酶的特征与作用机制有利于提高白酒的优质品率。方法:本研究用形态学和生理学、16S rRNA、gyr B基因和antiSMASH分析的方法对酒曲中的一株微生物进行了验证;对该菌株的特性进行了研究,采用分子建模的方法获得了羧酸酯酶的3D模型,用分子对接的方法探讨了该菌株的羧酸酯酶的机理。结果:该菌株为产羧酸酯酶的革兰氏阴性菌Pb1(MW580690);该菌株呈现典型的S型生长曲线,产物曲线为S型,羧酸酯酶活化最优pH范围为5.0~9.0。分子对接结果显示Phe21A为该酶具有催化活性的主要氨基酸,水解三丁酸甘油酯为丁酸和甘油。分子对接结果显示三丁酸甘油酯经过构象变化被转移到催化中心后,进一步被加工;酶的亲水性和疏水性的相互作用表面有利于配体向下转移,进而从疏水性通道释放产物到的酶表面。结论:产羧酸酯酶的菌株为贝莱斯芽胞杆菌,并为羧酸酯酶水解三丁酸甘油酯类物质的底物识别、转移和催化机理提供了新的见解。 相似文献
69.
Amino acid modified polyaspartic acids were evaluated as calcium-scale inhibitors. Feasibility of scale inhibition experiments was analyzed by molecular dynamics simulation and Gaussian optimization, and the scale inhibition mechanism was theoretically analyzed. Scale inhibition performance was studied by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, static scale inhibition experiments, and electrochemical performance testing, which provided an experimental basis for the molecular dynamics simulation. The experimental results showed that Arg-SA-PASP has better scale inhibition and corrosion inhibition performance than His-SA-PASP. The scale inhibition effect increased with increasing concentration. Electrochemical tests indicated that Arg-SA-PASP is an excellent scale and corrosion inhibitor. 相似文献
70.
Fluorescence‐Activated Cell Sorters: Standing Surface Acoustic Wave (SSAW)‐Based Fluorescence‐Activated Cell Sorter (Small 40/2018)
下载免费PDF全文
![点击此处可从《Small (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)