全文获取类型
收费全文 | 226192篇 |
免费 | 22034篇 |
国内免费 | 12782篇 |
专业分类
电工技术 | 16007篇 |
技术理论 | 13篇 |
综合类 | 16671篇 |
化学工业 | 34681篇 |
金属工艺 | 13141篇 |
机械仪表 | 14667篇 |
建筑科学 | 17084篇 |
矿业工程 | 7218篇 |
能源动力 | 6460篇 |
轻工业 | 18134篇 |
水利工程 | 5124篇 |
石油天然气 | 12565篇 |
武器工业 | 2178篇 |
无线电 | 26780篇 |
一般工业技术 | 25242篇 |
冶金工业 | 10481篇 |
原子能技术 | 3136篇 |
自动化技术 | 31426篇 |
出版年
2024年 | 605篇 |
2023年 | 4083篇 |
2022年 | 7429篇 |
2021年 | 10661篇 |
2020年 | 8057篇 |
2019年 | 6190篇 |
2018年 | 6948篇 |
2017年 | 7655篇 |
2016年 | 6887篇 |
2015年 | 9676篇 |
2014年 | 12071篇 |
2013年 | 14434篇 |
2012年 | 16393篇 |
2011年 | 17286篇 |
2010年 | 15324篇 |
2009年 | 14678篇 |
2008年 | 14180篇 |
2007年 | 13310篇 |
2006年 | 12858篇 |
2005年 | 10907篇 |
2004年 | 7444篇 |
2003年 | 5834篇 |
2002年 | 5287篇 |
2001年 | 4900篇 |
2000年 | 4465篇 |
1999年 | 4461篇 |
1998年 | 3498篇 |
1997年 | 2983篇 |
1996年 | 2724篇 |
1995年 | 2228篇 |
1994年 | 1792篇 |
1993年 | 1309篇 |
1992年 | 1051篇 |
1991年 | 779篇 |
1990年 | 573篇 |
1989年 | 478篇 |
1988年 | 366篇 |
1987年 | 246篇 |
1986年 | 211篇 |
1985年 | 124篇 |
1984年 | 111篇 |
1983年 | 85篇 |
1982年 | 82篇 |
1981年 | 77篇 |
1980年 | 72篇 |
1979年 | 37篇 |
1978年 | 25篇 |
1977年 | 24篇 |
1976年 | 26篇 |
1951年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
31.
目的:研究抗坏血酸(ascorbic acid,AsA)-还原型谷胱甘肽(reduced glutathione,GSH)循环代谢在水杨酸处理采后甜瓜诱导的过量H2O2清除过程中的作用。方法:用4 mmol/L水杨酸浸泡‘玉金香’厚皮甜瓜10 min,测定处理后果实常温贮藏过程中丙二醛(malondialdehyde,MDA)含量,分析活性氧的积累水平、超氧化物歧化酶(superoxide dismutase,SOD)和过氧化氢酶(catalase,CAT)活力,以及AsA-GSH循环过程相关酶活力及产物和底物含量。结果:水杨酸处理降低了果实MDA含量,第10天处理组MDA含量较对照组降低14.6%;显著提高了果实O2-·的产生速率和H2O2含量(P<0.05),其中处理后第2天O2-·的产生速率高出同期对照组的1.9 倍,第6天H2O2含量高出对照组果实29.7%;提高了果实SOD活力,但抑制了CAT活力,说明H2O2的清除可能是依赖于除酶促系统外的其他系统。此外,水杨酸处理提高了果实抗坏血酸过氧化物酶、单脱氢抗坏血酸过氧化物酶、脱氢抗坏血酸还原酶和谷胱甘肽还原酶的活力,增加了AsA和氧化型谷胱甘肽的含量,降低了脱氢抗坏血酸和GSH的含量。结论:水杨酸处理诱导了厚皮甜瓜果实的氧爆,抑制了MDA产生,由水杨酸诱导产生的过量H2O2主要依靠AsA-GSH循环系统清除。 相似文献
32.
Changbai Long Ning Ji Li Yang Wenjie Zhou Kun Zheng Wei Ren Laijun Liu 《Journal of the European Ceramic Society》2021,41(6):3369-3378
With co-substitution of (Li0.5Sm0.5) at A site and W at B site, the electrical properties of modified Ca0.92(Li0.5Sm0.5)0.08Bi2Nb2-xWxO9 [(CLS)BN-xW, x = 0, 0.015 and 0.03] piezoceramics with ultrahigh Curie temperature (TC) of > 930 °C were enhanced dramatically. The increased resistivity induced by the co-substitution ensure them to be polarized under an enough high field. Combined with the increase of spontaneous ferroelectric polarization (PS), the significant enhancements in the piezoelectric, dielectric and ferroelectric properties can be obtained in the composition x = 0.015. Furthermore, the piezoelectric activity (d33) and bulk resistivity (ρb) of (CLS)BN-0.015 W can be further enhanced at an appropriate sintering temperature. This optimum composition sintered at 1170 °C shows ultrahigh TC of ~948 °C, d33 of ~17.3 pC/N and ρb of ~6.9 MΩ cm at 600 °C, which are comparable to those of the reported high-temperature Aurivillius piezoceramics with TC > 850 °C. 相似文献
33.
Corey Andrews Yiting Xu Michael Kirberger Jenny J. Yang 《International journal of molecular sciences》2021,22(1)
Calmodulin (CaM) is an important intracellular protein that binds Ca2+ and functions as a critical second messenger involved in numerous biological activities through extensive interactions with proteins and peptides. CaM’s ability to adapt to binding targets with different structures is related to the flexible central helix separating the N- and C-terminal lobes, which allows for conformational changes between extended and collapsed forms of the protein. CaM-binding targets are most often identified using prediction algorithms that utilize sequence and structural data to predict regions of peptides and proteins that can interact with CaM. In this review, we provide an overview of different CaM-binding proteins, the motifs through which they interact with CaM, and shared properties that make them good binding partners for CaM. Additionally, we discuss the historical and current methods for predicting CaM binding, and the similarities and differences between these methods and their relative success at prediction. As new CaM-binding proteins are identified and classified, we will gain a broader understanding of the biological processes regulated through changes in Ca2+ concentration through interactions with CaM. 相似文献
34.
For the purpose of developing biodegradable magnesium alloys with suitable properties for biomedical applications, Mg–Zn–Ca–Cu metallic glasses were prepared by copper mold injection methods. In the present work, the effect of Cu doping on mechanical properties, corrosion behavior, and glass-forming ability of Mg66Zn30Ca4 alloy was studied. The experimental findings demonstrated that the incorporation of Cu decreases the corrosion resistance of alloys, but increases the microhardness and degradation rate slightly. However, the addition of a trace amount of Cu can make the samples have antibacterial properties. Therefore, Mg–Zn–Ca–Cu has great advantages in clinical implantation and is the potential implant material. 相似文献
37.
38.
39.
In this study, a kind of Ni-based superalloy specially designed for additive manufacturing (AM) was investigated. Thermo-Calc simulation and differential scanning calorimetry (DSC) analysis were used to determine phases and their transformation temperature. Experimental specimens were prepared by laser metal deposition (LMD) and traditional casting method. Microstructure, phase constitution and mechanical properties of the alloy were characterized by scanning electron microscopy (SEM), transmission scanning electron microscopy (TEM), X-ray diffraction (XRD) and tensile tests. The results show that this alloy contains two basic phases, γ/γ', in addition to these phases, at least two secondary phases may be present, such as MC carbides and Laves phases. Furthermore, the as-deposited alloy has finer dendrite, its mean primary dendrite arm space (PDAS) is about 30-45 μm, and the average size of γ' particles is 100-150 nm. However, the dendrite size of the as-cast alloy is much larger and its PDAS is 300-500 μm with secondary and even third dendrite arms. Correspondingly, the alloy displays different tensile behavior with different processing methods, and the as-deposited specimen shows better ultimate tensile stress (1,085.7±51.7 MPa), yield stress (697±19.5 MPa) and elongation (25.8%±2.2%) than that of the as-cast specimen. The differences in mechanical properties of the alloy are due to the different morphology and size of dendrites, γ', and Laves phase, and the segregation of elements, etc. Such important information would be helpful for alloy application as well as new alloy development. 相似文献
40.
Sheng Mingming Yang Rongkun Gong Hongyu Zhang Yujun Lin Xiao Jing Jie 《Journal of Materials Science》2022,57(10):5805-5824
Journal of Materials Science - With the extensive use of high-power electronic appliances, polymer-based thermal insulation composites with excellent thermal properties are utilized in the field of... 相似文献