全文获取类型
收费全文 | 83089篇 |
免费 | 11992篇 |
国内免费 | 4995篇 |
专业分类
电工技术 | 5660篇 |
技术理论 | 3篇 |
综合类 | 6016篇 |
化学工业 | 14281篇 |
金属工艺 | 2971篇 |
机械仪表 | 5253篇 |
建筑科学 | 6087篇 |
矿业工程 | 2698篇 |
能源动力 | 1457篇 |
轻工业 | 7256篇 |
水利工程 | 1657篇 |
石油天然气 | 2992篇 |
武器工业 | 1367篇 |
无线电 | 11117篇 |
一般工业技术 | 7406篇 |
冶金工业 | 3522篇 |
原子能技术 | 731篇 |
自动化技术 | 19602篇 |
出版年
2024年 | 189篇 |
2023年 | 1572篇 |
2022年 | 3010篇 |
2021年 | 4672篇 |
2020年 | 2963篇 |
2019年 | 2718篇 |
2018年 | 2824篇 |
2017年 | 3584篇 |
2016年 | 4839篇 |
2015年 | 5533篇 |
2014年 | 6476篇 |
2013年 | 6177篇 |
2012年 | 5701篇 |
2011年 | 5259篇 |
2010年 | 4152篇 |
2009年 | 4236篇 |
2008年 | 4188篇 |
2007年 | 5568篇 |
2006年 | 5404篇 |
2005年 | 4784篇 |
2004年 | 3430篇 |
2003年 | 3026篇 |
2002年 | 2262篇 |
2001年 | 1554篇 |
2000年 | 1124篇 |
1999年 | 881篇 |
1998年 | 563篇 |
1997年 | 485篇 |
1996年 | 449篇 |
1995年 | 379篇 |
1994年 | 306篇 |
1993年 | 215篇 |
1992年 | 179篇 |
1991年 | 160篇 |
1990年 | 170篇 |
1989年 | 131篇 |
1988年 | 84篇 |
1987年 | 77篇 |
1986年 | 72篇 |
1985年 | 73篇 |
1984年 | 80篇 |
1983年 | 48篇 |
1982年 | 40篇 |
1981年 | 36篇 |
1980年 | 48篇 |
1966年 | 25篇 |
1965年 | 22篇 |
1964年 | 34篇 |
1962年 | 64篇 |
1955年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
21.
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
22.
Hepatocellular carcinoma (HCC) is one of the most prevalent malignancies worldwide. HCC is associated with several etiological factors, including HBV/HCV infections, cirrhosis, and fatty liver diseases. However, the molecular mechanism underlying HCC development remains largely elusive. The advent of high-throughput sequencing has unveiled an unprecedented discovery of a plethora of long noncoding RNAs (lncRNAs). Despite the lack of coding capacity, lncRNAs have key roles in gene regulation through interacting with various biomolecules. It is increasingly evident that the dysregulation of lncRNAs is inextricably linked to HCC cancer phenotypes, suggesting that lncRNAs are potential prognostic markers and therapeutic targets. In light of the emerging research in the study of the regulatory roles of lncRNAs in HCC, we discuss the association of lncRNAs with HCC. We link the biological processes influenced by lncRNAs to cancer hallmarks in HCC and describe the associated functional mechanisms. This review sheds light on future research directions, including the potential therapeutic applications of lncRNAs. 相似文献
23.
24.
Hui Huang Bradi R. Lorenz Paula Horn Zelmanovitz Catherine B. Chan 《International journal of molecular sciences》2021,22(1)
Prediabetes is a high-risk condition for type 2 diabetes (T2D). Pancreatic β-cells adapt to impaired glucose regulation in prediabetes by increasing insulin secretion and β-cell mass expansion. In people with prediabetes, metformin has been shown to prevent prediabetes conversion to diabetes. However, emerging evidence indicates that metformin has negative effects on β-cell function and survival. Our previous study established the Nile rat (NR) as a model for prediabetes, recapitulating characteristics of human β-cell compensation in function and mass expansion. In this study, we investigated the action of metformin on β-cells in vivo and in vitro. A 7-week metformin treatment improved glucose tolerance by reducing hepatic glucose output and enhancing insulin secretion. Although high-dose metformin inhibited β-cell glucose-stimulated insulin secretion in vitro, stimulation of β-cell insulin secretion was preserved in metformin-treated NRs via an indirect mechanism. Moreover, β-cells in NRs receiving metformin exhibited increased endoplasmic reticulum (ER) chaperones and alleviated apoptotic unfold protein response (UPR) without changes in the expression of cell identity genes. Additionally, metformin did not suppress β-cell mass compensation or proliferation. Taken together, despite the conflicting role indicated by in vitro studies, administration of metformin does not exert a negative effect on β-cell function or cell mass and, instead, early metformin treatment may help protect β-cells from exhaustion and decompensation. 相似文献
25.
Parkinson’s disease (PD) is a neurodegenerative disorder that affects 1% of the population over the age of 60. Diabetes Mellitus (DM) is a metabolic disorder that affects approximately 25% of adults over the age of 60. Recent studies showed that DM increases the risk of developing PD. The link between DM and PD has been discussed in the literature in relation to different mechanisms including mitochondrial dysfunction, oxidative stress, and protein aggregation. In this paper, we review the common microRNA (miRNA) biomarkers of both diseases. miRNAs play an important role in cell differentiation, development, the regulation of the cell cycle, and apoptosis. They are also involved in the pathology of many diseases. miRNAs can mediate the insulin pathway and glucose absorption. miRNAs can also regulate PD-related genes. Therefore, exploring the common miRNA biomarkers of both PD and DM can shed a light on how these two diseases are correlated, and targeting miRNAs is a potential therapeutic opportunity for both diseases. 相似文献
26.
27.
28.
29.
相比ADAMS仿真的不稳定性,利用ADAMS和MATLAB联合仿真对双足机器人运动轨迹规划和控制设计的可靠性及高效性进行了研究。首先绘制双足机器人三维参数模型进行逆运动学分析,验证其合理性后导入ADAMS中添加约束,进行动力学仿真。基于此,在MATLAB中使用多项式插值法完成模型的步态规划。最后利用Simulink试验台建立控制系统的框图,由ADAMS输入关节角之后控制台输出关节的驱动力矩,完成双足机器人ADAMS和MATLAB的联合仿真。仿真结果显示,联合仿真相较于ADAMS仿真的波动性所获得的数据更加稳定,此法高效可行,可作为下一步设计双足机器人的控制系统电机选型的重要理论依据。 相似文献
30.
《International Journal of Hydrogen Energy》2022,47(10):6700-6709
Water electrolysis is the most clean and high-efficiency technology for production of hydrogen, an ultimate clean energy in future. Highly efficient non-noble electrocatalysts for hydrogen evolution reaction (HER) are desirable for large scale production of hydrogen by water electrolysis. Especially, exposing as many active sites as possible is a vital way to improve activities of the catalysts. Herein, a series of new hydrangea like composite catalysts of ultrathin Mo2S3 nanosheets assembled uprightly and interlacedly on N, S-dual-doped graphitic biocarbon spheres were facilely prepared. The unique structure endowed the catalysts highly exposed edge active sites and prominently high activities for HER. Especially, the optimized catalyst Mo2S3/NSCS-50 exhibited as low as 106 mV of overpotential at 10 mA/cm2 (denoted as ?10). The catalyst also showed low Tafel slope of 53 mV/dec, low electron transfer resistance of 34 Ω and high stability evidenced by the result that the current density only attenuated 11.7% after 10 h i-t test. The catalyst has shown broad prospect for commercial application in water electrolysis. 相似文献