全文获取类型
收费全文 | 19673篇 |
免费 | 1960篇 |
国内免费 | 1258篇 |
专业分类
电工技术 | 533篇 |
技术理论 | 2篇 |
综合类 | 2664篇 |
化学工业 | 2159篇 |
金属工艺 | 339篇 |
机械仪表 | 720篇 |
建筑科学 | 722篇 |
矿业工程 | 195篇 |
能源动力 | 494篇 |
轻工业 | 3264篇 |
水利工程 | 136篇 |
石油天然气 | 205篇 |
武器工业 | 126篇 |
无线电 | 1440篇 |
一般工业技术 | 1642篇 |
冶金工业 | 831篇 |
原子能技术 | 76篇 |
自动化技术 | 7343篇 |
出版年
2024年 | 79篇 |
2023年 | 497篇 |
2022年 | 627篇 |
2021年 | 852篇 |
2020年 | 701篇 |
2019年 | 613篇 |
2018年 | 549篇 |
2017年 | 605篇 |
2016年 | 596篇 |
2015年 | 639篇 |
2014年 | 1057篇 |
2013年 | 1042篇 |
2012年 | 1188篇 |
2011年 | 1361篇 |
2010年 | 1014篇 |
2009年 | 1063篇 |
2008年 | 1166篇 |
2007年 | 1341篇 |
2006年 | 1180篇 |
2005年 | 1102篇 |
2004年 | 914篇 |
2003年 | 844篇 |
2002年 | 594篇 |
2001年 | 533篇 |
2000年 | 420篇 |
1999年 | 358篇 |
1998年 | 256篇 |
1997年 | 218篇 |
1996年 | 194篇 |
1995年 | 211篇 |
1994年 | 193篇 |
1993年 | 140篇 |
1992年 | 116篇 |
1991年 | 90篇 |
1990年 | 62篇 |
1989年 | 53篇 |
1988年 | 50篇 |
1987年 | 28篇 |
1986年 | 27篇 |
1985年 | 41篇 |
1984年 | 37篇 |
1983年 | 27篇 |
1982年 | 19篇 |
1981年 | 16篇 |
1980年 | 19篇 |
1979年 | 17篇 |
1978年 | 13篇 |
1977年 | 12篇 |
1975年 | 16篇 |
1961年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Donatella Restuccia Gianluca Giorgi Umile Gianfranco Spizzirri Fabio Sciubba Giorgio Capuani Vittoria Rago Gabriele Carullo Francesca Aiello 《International Journal of Food Science & Technology》2019,54(4):1313-1320
Seeds and skins from grape pomaces of Pecorello and Mantonico cv underwent extraction (ultrasound–assisted or maceration), in order to obtain added-value ingredients for the production of a functional pear jam. The antioxidant features of the extracts were tested by in vitro colorimetric assays. Among seeds, Mantonico by maceration (MSC) showed the best results, as well as Mantonico by ultrasound-assisted extraction (MBs) among skin extracts. The selected extracts were fully characterised by NMR and MS techniques, confirming the presence of many polyphenols, flavonoids and tannins among others. Pectin was then derivatised by the grafting procedure with the active molecules of MBs and MSC. The latter produced the best antioxidant polymer also without toxicity evaluated using Caco-2 cells and was used for the jam preparation. The functional pear jam showed improved antioxidant performances in comparison with its non-functional counterparts as well as its maintenance over time (15 days). 相似文献
92.
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
93.
Kai Cheng Chunchun Li Changzhi Yin Ying Tang Yihua Sun Liang Fang 《Journal of the European Ceramic Society》2019,39(13):3738-3743
The effects of Sr2+ substitution for Ba2+ on microwave dielectric properties and crystal structure of Ba3-xSrx(VO4)2 (0 ≤ x ≤ 3, BSVO) solid solution were investigated. Such Sr2+ substitution contributes to significant reduction in sintering temperature from 1400 °C to 1150 °C. Both permittivity (∑r) and quality factor (Q × f) values decreased with increasing x value, which was determined to be related with the descending values of average polarizability and packing fraction, whereas the increase in τf value was explained by the decreased average VO bond length, A-site bond valence. BSVO ceramics possessed encouraging dielectric performances with ∑r = 12.2–15.6 ± 0.1, Q × f = 44,340 - 62,000 ± 800 GHz, and τf = 24.5–64.5 ± 0.2 ppm/°C. Low-temperature sintering was manipulated by adding B2O3 as sintering additive for the representative Sr3V2O8 (SVO) ceramic and only 1 wt.% B2O3 addition successfully contributed to a 21.7% decrease in sintering temperature to 900 °C, showing good chemical compatibility with silver electrodes, which render BSVO series and SVO ceramics potential candidates in multilayer electronic devices fabrication. 相似文献
94.
95.
96.
Chao Ma Anke Malessa Arnold J. Boersma Kai Liu Andreas Herrmann 《Advanced materials (Deerfield Beach, Fla.)》2020,32(20):1905309
Electrostatic interactions play a vital role in nature. Biomacromolecules such as proteins are orchestrated by electrostatics, among other intermolecular forces, to assemble and organize biochemistry. Natural proteins with a high net charge exist in a folded state or are unstructured and can be an inspiration for scientists to artificially supercharge other protein entities. Recent findings show that supercharging proteins allows for control of their properties such as temperature resistance and catalytic activity. One elegant method to transfer the favorable properties of supercharged proteins to other proteins is the fabrication of fusions. Genetically engineered, supercharged unstructured polypeptides (SUPs) are just one promising fusion tool. SUPs can also be complexed with artificial entities to yield thermotropic and lyotropic liquid crystals and liquids. These architectures represent novel bulk materials that are sensitive to external stimuli. Interestingly, SUPs undergo fluid–fluid phase separation to form coacervates. These coacervates can even be directly generated in living cells or can be combined with dissipative fiber assemblies that induce life-like features. Supercharged proteins and SUPs are developed into exciting classes of materials. Their synthesis, structures, and properties are summarized. Moreover, potential applications are highlighted and challenges are discussed. 相似文献
97.
Muhammad Aminur RAHAMAN Mahmood JASIM Md. Haider ALI Md. HASANUZZAMAN 《Frontiers of Computer Science》2020,14(3):143302-64
Because of using traditional hand-sign segmentation and classification algorithm,many diversities of Bangla language including joint-letters,dependent vowels etc.and representing 51 Bangla written characters by using only 36 hand-signs,continuous hand-sign-spelled Bangla sign language(BdSL)recognition is challenging.This paper presents a Bangla language modeling algorithm for automatic recognition of hand-sign-spelled Bangla sign language which consists of two phases.First phase is designed for hand-sign classification and the second phase is designed for Bangla language modeling algorithm(BLMA)for automatic recognition of hand-sign-spelled Bangla sign language.In first phase,we have proposed two step classifiers for hand-sign classification using normalized outer boundary vector(NOBV)and window-grid vector(WGV)by calculating maximum inter correlation coefficient(ICC)between test feature vector and pre-trained feature vectors.At first,the system classifies hand-signs using NOBV.If classification score does not satisfy specific threshold then another classifier based on WGV is used.The system is trained using 5,200 images and tested using another(5,200×6)images of 52 hand-signs from 10 signers in 6 different challenging environments achieving mean accuracy of 95.83%for classification with the computational cost of 39.972 milliseconds per frame.In the Second Phase,we have proposed Bangla language modeling algorithm(BLMA)which discovers all"hidden characters"based on"recognized characters"from 52 hand-signs of BdSL to make any Bangla words,composite numerals and sentences in BdSL with no training,only based on the result of first phase.To the best of our knowledge,the proposed system is the first system in BdSL designed on automatic recognition of hand-sign-spelled BdSL for large lexicon.The system is tested for BLMA using hand-sign-spelled 500 words,100 composite numerals and 80 sentences in BdSL achieving mean accuracy of 93.50%,95.50%and 90.50%respectively. 相似文献
98.
Theoretical investigation of anisotropic mechanical and thermal properties of ABO3 (A=Sr,Ba; B=Ti,Zr, Hf) perovskites 下载免费PDF全文
Yuchen Liu Bin Liu Huimin Xiang Yanchun Zhou Hongqiang Nian Hongfei Chen Guang Yang Yanfeng Gao 《Journal of the American Ceramic Society》2018,101(8):3527-3540
As promising TBC (thermal barrier coating) candidates, perovskite oxides own designable properties for their various options of cations and structural diversity, but limited comprehensions of structure‐property relationship delay their engineering applications. In this work, mechanical/thermal properties of ABO3 (A=Sr, Ba; B=Ti, Zr, Hf) perovskites and their anisotropic nature are predicted employing density functional theory. Their theoretical minimum thermal conductivities range from 1.09 to 1.74 W·m?1·K?1, being lower than Y2O3 partially stabilized ZrO2. Reduced thermal conductivities up to 16% along particular directions are reached after considering thermal conductivity anisotropy. All compounds own high hardness while SrZrO3, SrHfO3, and BaHfO3 possess well damage tolerance. We found that small electronegativity discrepancy leads to big anisotropy of chemical bond, Young's/shear moduli and thermal conductivities, together with good damage tolerance. These results suggest that the next generation TBCs with extra low thermal conductivity should be achieved through combining material design and orientation‐growth tailoring. 相似文献
99.
100.
M. Kamal Warshi Vikash Mishra Vinayak Mishra Rajesh Kumar P.R. Sagdeo 《Ceramics International》2018,44(12):13507-13512
Rare-earth orthoferrites (RFeO3) are well-known for the antiferromagnetic ground state. However, some of the recent experimental results suggest that the few members of RFeO3 family possess ferromagnetism. In the present investigation we report the possible origin of ferromagnetism in antiferromagnetic YFeO3 using density functional theory. For this purpose, we have considered pure as well as self-doping in YFeO3 i.e. by considering the point defect at Y, Fe and O sites. Our finding suggests that the point defects in YFeO3 results in the mixed-valence state of Fe, which may result in ferromagnetism through Zener double exchange mechanism. 相似文献