全文获取类型
收费全文 | 38834篇 |
免费 | 2902篇 |
国内免费 | 114篇 |
专业分类
电工技术 | 947篇 |
综合类 | 877篇 |
化学工业 | 12070篇 |
金属工艺 | 740篇 |
机械仪表 | 636篇 |
建筑科学 | 1324篇 |
矿业工程 | 133篇 |
能源动力 | 969篇 |
轻工业 | 4523篇 |
水利工程 | 266篇 |
石油天然气 | 162篇 |
武器工业 | 7篇 |
无线电 | 2326篇 |
一般工业技术 | 5749篇 |
冶金工业 | 6246篇 |
原子能技术 | 244篇 |
自动化技术 | 4631篇 |
出版年
2023年 | 696篇 |
2022年 | 827篇 |
2021年 | 1380篇 |
2020年 | 1111篇 |
2019年 | 1071篇 |
2018年 | 1157篇 |
2017年 | 1103篇 |
2016年 | 1219篇 |
2015年 | 1140篇 |
2014年 | 1478篇 |
2013年 | 2213篇 |
2012年 | 1672篇 |
2011年 | 1895篇 |
2010年 | 1782篇 |
2009年 | 1887篇 |
2008年 | 1379篇 |
2007年 | 1198篇 |
2006年 | 914篇 |
2005年 | 993篇 |
2004年 | 1107篇 |
2003年 | 962篇 |
2002年 | 973篇 |
2001年 | 775篇 |
2000年 | 560篇 |
1999年 | 582篇 |
1998年 | 2085篇 |
1997年 | 1363篇 |
1996年 | 986篇 |
1995年 | 687篇 |
1994年 | 542篇 |
1993年 | 659篇 |
1992年 | 301篇 |
1991年 | 355篇 |
1990年 | 311篇 |
1989年 | 279篇 |
1988年 | 275篇 |
1987年 | 251篇 |
1986年 | 265篇 |
1985年 | 264篇 |
1984年 | 209篇 |
1983年 | 198篇 |
1982年 | 191篇 |
1981年 | 225篇 |
1980年 | 197篇 |
1979年 | 156篇 |
1978年 | 110篇 |
1977年 | 199篇 |
1976年 | 273篇 |
1975年 | 145篇 |
1973年 | 182篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
J. E. DUTRA de OLIVEIRA NELSON de SOUZA TIBERE ALVEZ de REZENDE LIA R. VALENTE V. F. BOYD ELMER E. DAGGY 《Journal of food science》1967,32(1):131-135
SUMMARY-The development of food mixtures containing vegetable protein concentrates, minerals, and vitamins represents an important approach to the problem of protein-calorie malnutrition of preschool children in many parts of the world. In Brazil, soy flour is the most readily available good-quality protein for this purpose. Protein efficiency-ratio studies in rats demonstrated that soy flour with a PER value of 1.99 was available in large quantities. Accordingly, a formula containing 19.50% soy flour, 4.50% nonfat milk powder, 32.28% corn starch, 39.00% sucrose, and 4.72% vitamins and minerals was thoroughly tested as an infant food. The PER value of the protein in rats was 2.31. Amino acid assay demonstrated that the protein compared favorably with the essential amino acid pattern of the FAO/WHO reference protein (FAO/WHO, 196.5) except for methionine-cystine, The formula was well accepted and tolerated by children and adults. Average nitrogen absorption and retention of the formula as the sole food of malnourished children were 72.68 and 23.82%; values for milk protein were 80.17 and 30.13%. Average nitrogen absorption and retention were 63.4 and 22.0% when the formula provided one-half (15 g) of the daily protein for normal children consuming a typical diet of the region, comparing favorably with values of 69.3 and 21.3% for milk protein. 相似文献
994.
The commenter corrects and comments on a few results reported in the paper by H. Takagi (see ibid., vol.COM-35, p.248-50, Feb. 1987). In addition, it is shown how these results can be utilized to give the average message delay for token passing protocols where each network station is allowed to send a maximum of one fixed-length packet per cycle (known as chaining discipline) 相似文献
995.
Svetlana S. van Bavel Maik Bärenklau Gijsbertus de With Harald Hoppe Joachim Loos 《Advanced functional materials》2010,20(9):1458-1463
The performance of polymer solar cells (PSC) strongly depends on the 3D morphological organization of the donor and acceptor compounds within the bulk heterojunction active layer. The technique of electron tomography is a powerful tool for studying 3D morphology of the layers composed of poly(3‐hexylthiophene) (P3HT) and a fullerene derivative ([6,6]‐phenyl‐C61‐butyric acid methyl ester; PCBM), especially to quantify the amount and distribution of fibrillar P3HT nanocrystals throughout the volume of the active layer. In this study, electron tomography is used to characterize P3HT/PCBM layers with different blend compositions, both before and after thermal annealing. The power conversion efficiency of the corresponding PSCs is strongly dependent on the overall crystallinity of P3HT and the way P3HT crystals are distributed throughout the thickness of the active layer. 相似文献
996.
997.
Hatzis C Godleski JJ González-Flecha B Wolfson JM Koutrakis P 《Environmental science & technology》2006,40(8):2805-2811
A primary mechanistic hypothesis by which ambient air particles have a significant negative impact on human health is via the induction of pulmonary inflammatory responses mediated through the generation of reactive oxygen species (ROS). Development of a biosensor for the assessment of particulate ROS activity would be a significant advance in air pollution monitoring. The objective of this study was to evaluate whether air particulates interact directly with protective enzymes involved in oxidative stress responses. We performed enzyme activity assays on four enzymes involved in oxidative stress responses (Cu/Zn superoxide dismutase, Mn superoxide dismutase, glutathione peroxidase, and glutathione reductase) in the presence of particles of varying toxicities and found distinctive inhibition patterns. On the basis of these findings, we suggest a strategy for an enzyme bioassay that could be used to assess the potential of particles to generate ROS-induced responses. 相似文献
998.
999.
Luiz Guilherme Meira de Souza Flavio Anselmo Silva de Lima Luiz Guilherme Vieira Meira de Souza Natanaeyfle Randemberg Gomes dos Santos Jailton Weber Gomes 《机械工程与自动化:英文版》2014,(9):716-720
The science space in a state school in Natal city was built using a composite consisting of gypsum, EPS (expanded polystyrene), shredded tire, cement and water. Mechanical and thermal resistances were evaluated. Inside the blocks, three types of fillings (EPS plates, aluminum cans and 500 mL bottles of mineral water) were placed in order to obtain a walls with higher thermal resistance, but also to give it an ecologically correct order, considering that both the tire and the EPS occupy a large space in landfills and require years to be degraded when released into the environment. Compression tests were conducted according to the rules. The experiments demonstrated that the temperature difference between the internal and external surfaces on the walls reached levels above 12.0 ℃. It was also demonstrated that the proposed composite has adequate mechanical strength to be used for sealing walls. The proposed use of the composite can contribute to reduce the significant housing deficit of Brazil, producing popular houses at low cost and with little time to work. 相似文献
1000.
Jiayu Zeng Minhui Liu Dr. Songjiao Li Prof. Dr. Dan Cheng Prof. Dr. Longwei He Prof. Dr. Lin Yuan 《Chembiochem : a European journal of chemical biology》2023,24(12):e202300035
Conventional chemotherapy (CT) is associated with severe side effects and inducible resistance, making it difficult to meet clinical requirements, forcing the development of new multifunctional prodrugs for precision medicine. In recent decades, researchers and clinicians have focused on developing of multifunctional chemotherapeutic prodrugs with tumor-targeting capability, activatable and traceable chemotherapeutic activity, as a powerful tool to improve theranostic outcomes in cancer treatment. The conjugates of near-infrared (NIR) organic fluorophores and chemotherapy reagents create an exciting avenue for real-time monitoring of drug delivery and distribution, as well as the combination of chemotherapy and photodynamic therapy (PDT). Therefore, there are great opportunities for researchers to conceive and exploit multifunctional prodrugs that can visualize chemo-drugs release and tumor treatment in vivo. In this review, the design strategy and the recent progress of multifunctional organic chemotherapeutic prodrugs for activating NIR fluorescence imaging-guided therapy are described and discussed in detail. Finally, the prospects and challenges of multifunctional chemotherapeutic prodrugs for NIR fluorescence imaging-guided therapy are provided. 相似文献