全文获取类型
收费全文 | 378089篇 |
免费 | 5747篇 |
国内免费 | 1715篇 |
专业分类
电工技术 | 5688篇 |
综合类 | 2844篇 |
化学工业 | 54922篇 |
金属工艺 | 16089篇 |
机械仪表 | 11797篇 |
建筑科学 | 9263篇 |
矿业工程 | 2162篇 |
能源动力 | 8476篇 |
轻工业 | 29226篇 |
水利工程 | 4467篇 |
石油天然气 | 6206篇 |
武器工业 | 46篇 |
无线电 | 43429篇 |
一般工业技术 | 75124篇 |
冶金工业 | 57740篇 |
原子能技术 | 7821篇 |
自动化技术 | 50251篇 |
出版年
2021年 | 2587篇 |
2020年 | 2067篇 |
2019年 | 2513篇 |
2018年 | 18235篇 |
2017年 | 17168篇 |
2016年 | 14263篇 |
2015年 | 3710篇 |
2014年 | 5353篇 |
2013年 | 13766篇 |
2012年 | 11263篇 |
2011年 | 19811篇 |
2010年 | 16358篇 |
2009年 | 14885篇 |
2008年 | 16566篇 |
2007年 | 17433篇 |
2006年 | 8569篇 |
2005年 | 8960篇 |
2004年 | 8793篇 |
2003年 | 8567篇 |
2002年 | 7644篇 |
2001年 | 7202篇 |
2000年 | 6881篇 |
1999年 | 7132篇 |
1998年 | 17561篇 |
1997年 | 12410篇 |
1996年 | 9531篇 |
1995年 | 7180篇 |
1994年 | 6304篇 |
1993年 | 6354篇 |
1992年 | 4536篇 |
1991年 | 4320篇 |
1990年 | 4190篇 |
1989年 | 4193篇 |
1988年 | 3861篇 |
1987年 | 3493篇 |
1986年 | 3490篇 |
1985年 | 3864篇 |
1984年 | 3560篇 |
1983年 | 3301篇 |
1982年 | 3109篇 |
1981年 | 3139篇 |
1980年 | 3105篇 |
1979年 | 2887篇 |
1978年 | 2922篇 |
1977年 | 3247篇 |
1976年 | 4280篇 |
1975年 | 2452篇 |
1974年 | 2411篇 |
1973年 | 2426篇 |
1972年 | 2032篇 |
排序方式: 共有10000条查询结果,搜索用时 906 毫秒
31.
Margarita A. Sazonova Vasily V. Sinyov Anastasia I. Ryzhkova Marina D. Sazonova Tatiana V. Kirichenko Victoria A. Khotina Zukhra B. Khasanova Natalya A. Doroschuk Vasily P. Karagodin Alexander N. Orekhov Igor A. Sobenin 《International journal of molecular sciences》2021,22(2)
Chronic stress is a combination of nonspecific adaptive reactions of the body to the influence of various adverse stress factors which disrupt its homeostasis, and it is also a corresponding state of the organism’s nervous system (or the body in general). We hypothesized that chronic stress may be one of the causes occurence of several molecular and cellular types of stress. We analyzed literary sources and considered most of these types of stress in our review article. We examined genes and mutations of nuclear and mitochondrial genomes and also molecular variants which lead to various types of stress. The end result of chronic stress can be metabolic disturbance in humans and animals, leading to accumulation of reactive oxygen species (ROS), oxidative stress, energy deficiency in cells (due to a decrease in ATP synthesis) and mitochondrial dysfunction. These changes can last for the lifetime and lead to severe pathologies, including neurodegenerative diseases and atherosclerosis. The analysis of literature allowed us to conclude that under the influence of chronic stress, metabolism in the human body can be disrupted, mutations of the mitochondrial and nuclear genome and dysfunction of cells and their compartments can occur. As a result of these processes, oxidative, genotoxic, and cellular stress can occur. Therefore, chronic stress can be one of the causes forthe occurrence and development of neurodegenerative diseases and atherosclerosis. In particular, chronic stress can play a large role in the occurrence and development of oxidative, genotoxic, and cellular types of stress. 相似文献
32.
Multicomponent Diamond-Like Semiconductors Based on the InBV–CdS System: Bulk and Surface Properties
Semiconductors - According to developed methods, in the fields of the mutual solubility of initial binary compounds (InP, InSb, and CdS), solid solutions of the InP–CdS and InSb–CdS... 相似文献
33.
The corrosion mechanisms of T24, T92, VM12, and AISI 304 steels are studied under the influence of NaCl–KCl, NaCl–Na2SO4, and KCl–K2SO4 salt mixtures in a dry air atmosphere at 650°C for 15 days. NaCl–KCl was the most aggressive deposit and AISI 304 stainless steel exhibited the highest corrosion resistance. There was no relation between the Cr content of the ferritic steels and their corrosion resistance in NaCl–KCl. In contrast, the resistance of high-Cr steels was better when exposed to NaCl–Na2SO4 and KCl–K2SO4. The high-Cr and the low-Cr steels were more susceptible to NaCl–Na2SO4 and to KCl–K2SO4, respectively. 相似文献
34.
In this communication, the structural, micro-structural, dielectric, electrical, magnetic, and leakage-current characteristics of a double perovskite (Y2CoMnO6) ceramic material have been reported. The material was synthesized via a high-temperature mixed-oxide route. The compound crystallizes in a monoclinic structure which is confirmed from preliminary X-ray structural study. The morphological study by using scanning electron micrograph reveals the almost homogeneous distribution of grains throughout the surface of the sample. The nature of frequency-dependence of dielectric constant has been described by the Maxwell-Wagner model. The occurrence of a dielectric anomaly in the temperature dependence of dielectric permittivity study demonstrates the ferroelectric-paraelectric phase transition in the material. From the Nyquist plots, we found the existence of both grain and grain boundary effects. The frequency dependence of conductivity was studied by the Jonscher’s Power law, and the conduction phenomenon obeys the large overlapping polaron tunneling model. By using the Arrhenius equation, the activation energy has been calculated which is nearly equal to the energy required for the hoping of the electron. Both impedance and conductivity analysis demonstrate that the sample exhibits negative temperature coefficient of resistance (NTCR) properties indicating the semiconducting type of material at high temperatures. The anti-ferromagnetic character of the material is observed from the nature of magnetic hysteresis loop. The leakage current analysis suggests that the conduction process in the material follows the space charge limited conduction phenomenon. Such material will be helpful for modern electronic devices and spintronic applications. 相似文献
35.
Ana Clara Sabbione Santiago Suárez María Cristina Añón Adriana Scilingo 《International Journal of Food Science & Technology》2019,54(5):1506-1513
In this study, amaranth flour was used as an ingredient to prepare gluten-free cookies. The production process and attributes of amaranth cookies were characterised, and the potential use of amaranth flour as a functional ingredient was analysed. Cookies exhibited a non-uniform reddish brown colour and a cookie factor ratio of 4.5 ± 0.6. Storage studies indicated that after 3 weeks at room temperature cookies presented slight variations in the texture. Simulated gastrointestinal digestion of this product was able to release peptides capable of exerting potential antithrombotic and antihypertensive activities, IC50 values of 0.22 ± 0.04 and 0.23 ± 0.03 mg mL−1 protein, respectively. This work demonstrates for the first time that food made with amaranth flour exerts potential antithrombotic and antihypertensive activity. In conclusion, these amaranth cookies could be an alternative way of incorporating potentially health beneficial products for people who choose a conscious diet, including coeliac or vegan consumers. 相似文献
36.
37.
A hybrid sorbent material for removal of hydrogen sulfide from air was developed. The material is based on activated carbon and iron compounds obtained from waste iron(II) sulfate(VI) heptahydrate. The iron salt is deposited on the carbonaceous support and subjected to oxidation (Fe2+ to Fe3+) using atmospheric oxygen under alkaline conditions. An effect of H2O2 addition to the process on the composition of the resultant material was also examined. X-ray diffraction (XRD) analyses confirmed easy conversion of waste FeSO4·7H2O to iron oxides Fe3O4 and FeOOH. The activated carbon supporting iron oxides revealed a higher efficiency in H2S elimination from air compared to the commercial activated carbon, without any modification. 相似文献
38.
Scientometrics - The interdisciplinary nature of library and information science (LIS) research has been highlighted for some time now. The term “interdisciplinary” is used primarily in... 相似文献
39.
Traditionally, in supervised machine learning, (a significant) part of the available data (usually 50%-80%) is used for training and the rest—for validation. In many problems, however, the data are highly imbalanced in regard to different classes or does not have good coverage of the feasible data space which, in turn, creates problems in validation and usage phase. In this paper, we propose a technique for synthesizing feasible and likely data to help balance the classes as well as to boost the performance in terms of confusion matrix as well as overall. The idea, in a nutshell, is to synthesize data samples in close vicinity to the actual data samples specifically for the less represented (minority) classes. This has also implications to the so-called fairness of machine learning. In this paper, we propose a specific method for synthesizing data in a way to balance the classes and boost the performance, especially of the minority classes. It is generic and can be applied to different base algorithms, for example, support vector machines, k-nearest neighbour classifiers deep neural, rule-based classifiers, decision trees, and so forth. The results demonstrated that (a) a significantly more balanced (and fair) classification results can be achieved and (b) that the overall performance as well as the performance per class measured by confusion matrix can be boosted. In addition, this approach can be very valuable for the cases when the number of actual available labelled data is small which itself is one of the problems of the contemporary machine learning. 相似文献
40.
Journal of Communications Technology and Electronics - Abstract—The two-dimensional diffraction problem of a plane polarized TM-wave on two identical solid silver nanocylinders is considered.... 相似文献