全文获取类型
收费全文 | 112630篇 |
免费 | 2337篇 |
国内免费 | 519篇 |
专业分类
电工技术 | 1177篇 |
综合类 | 2545篇 |
化学工业 | 16726篇 |
金属工艺 | 5400篇 |
机械仪表 | 3657篇 |
建筑科学 | 3183篇 |
矿业工程 | 655篇 |
能源动力 | 2090篇 |
轻工业 | 7552篇 |
水利工程 | 1508篇 |
石油天然气 | 505篇 |
武器工业 | 6篇 |
无线电 | 11535篇 |
一般工业技术 | 20394篇 |
冶金工业 | 9076篇 |
原子能技术 | 504篇 |
自动化技术 | 28973篇 |
出版年
2023年 | 157篇 |
2022年 | 439篇 |
2021年 | 857篇 |
2020年 | 587篇 |
2019年 | 669篇 |
2018年 | 15002篇 |
2017年 | 14041篇 |
2016年 | 10617篇 |
2015年 | 1193篇 |
2014年 | 1146篇 |
2013年 | 1761篇 |
2012年 | 4444篇 |
2011年 | 11010篇 |
2010年 | 9434篇 |
2009年 | 6786篇 |
2008年 | 7851篇 |
2007年 | 8716篇 |
2006年 | 981篇 |
2005年 | 2106篇 |
2004年 | 2059篇 |
2003年 | 2015篇 |
2002年 | 1354篇 |
2001年 | 822篇 |
2000年 | 741篇 |
1999年 | 598篇 |
1998年 | 2138篇 |
1997年 | 1395篇 |
1996年 | 999篇 |
1995年 | 630篇 |
1994年 | 504篇 |
1993年 | 565篇 |
1992年 | 245篇 |
1991年 | 311篇 |
1990年 | 239篇 |
1989年 | 202篇 |
1988年 | 223篇 |
1987年 | 166篇 |
1986年 | 166篇 |
1985年 | 181篇 |
1984年 | 129篇 |
1983年 | 93篇 |
1982年 | 118篇 |
1981年 | 121篇 |
1980年 | 116篇 |
1979年 | 91篇 |
1978年 | 75篇 |
1977年 | 141篇 |
1976年 | 237篇 |
1975年 | 82篇 |
1954年 | 70篇 |
排序方式: 共有10000条查询结果,搜索用时 979 毫秒
941.
Ionically conductive polypyrrole films have been deposited at 295 K from anhydrous acetonitrile, acetonitrile/H2O and NaBF4 aqueous solutions onto platinum, mild steel and stainless steel discs, using cyclic voltammetry, potentiostatic and galvanostatic techniques. Cyclic voltammetry of the polymer films has been studied as a function of water content of the acetonitrile solvent, polypyrrole concentration and potential sweep rate. Potentiostatic growth of thicker (< 30 micron) films on stainless steel allowed free-standing polypyrrole membranes to be produced. Well adherent and conductive films were deposited at constant potential in stirred solutions from acetonitrile electrolytes containing 1% (v/v) of water. The membrane resistivity of the reduced films in 0.5 mol dm− 3 KCl(aq) at 295 K was ≈ 1 × 106 Ω cm, while the resistivity of the oxidised membrane was 2700 Ω cm. 相似文献
942.
Felipe Herrera 《JOM Journal of the Minerals, Metals and Materials Society》1963,15(6):443-445
Revolutionary developments in the patterns of world trade have taken place during the past five years, and Latin America is no exception. This article discusses the effects of the Latin American Free Trade Association, the Central American Common Market, and the Inter-American Development Bank on the economic integration of Latin America. 相似文献
943.
944.
945.
946.
947.
The application of remote sensing monitoring techniques plays a crucial role in evaluating and governing the vast amount of ecological construction projects in China. However, extracting information of ecological engineering target through high-resolution satellite image is arduous due to the unique topography and complicated spatial pattern on the Loess Plateau of China. As a result, enhancing classification accuracy is a huge challenge to high-resolution image processing techniques. Image processing techniques have a definitive effect on image properties and the selection of different parameters may change the final classification accuracy during post-classification processing. The common method of eliminating noise and smoothing image is majority filtering. However, the filter function may modify the original classified image and the final accuracy. The aim of this study is to develop an efficient and accurate post-processing technique for acquiring information of soil and water conservation engineering, on the Loess Plateau of China, using SPOT image with 2.5 m resolution. We argue that it is vital to optimize satellite image filtering parameters for special areas and purposes, which focus on monitoring ecological construction projects. We want to know how image filtering influences final classified results and which filtering kernel is optimum. The study design used a series of window sizes to filter the original classified image, and then assess the accuracy of each output map and image quality. We measured the relationship between filtering window size and classification accuracy, and optimized the post-processing techniques of SPOT5 satellite images. We conclude that (1) smoothing with the majority filter is sensitive to the information accuracy of soil and water conservation engineering, and (2) for SPOT5 2.5 m image, the 5×5 pixel majority filter is most suitable kernel for extracting information of ecological construction sites in the Loess Plateau of China. 相似文献
948.
Silvia Saturio Alicja M. Nogacka Marta Surez Nuria Fernndez Laura Mantecn Leonardo Mancabelli Christian Milani Marco Ventura Clara G. de los Reyes-Gaviln Gonzalo Solís Silvia Arboleya Miguel Gueimonde 《International journal of molecular sciences》2021,22(7)
The establishment of the gut microbiota poses implications for short and long-term health. Bifidobacterium is an important taxon in early life, being one of the most abundant genera in the infant intestinal microbiota and carrying out key functions for maintaining host-homeostasis. Recent metagenomic studies have shown that different factors, such as gestational age, delivery mode, or feeding habits, affect the gut microbiota establishment at high phylogenetic levels. However, their impact on the specific bifidobacterial populations is not yet well understood. Here we studied the impact of these factors on the different Bifidobacterium species and subspecies at both the quantitative and qualitative levels. Fecal samples were taken from 85 neonates at 2, 10, 30, 90 days of life, and the relative proportions of the different bifidobacterial populations were assessed by 16S rRNA–23S rRNA internal transcribed spacer (ITS) region sequencing. Absolute levels of the main species were determined by q-PCR. Our results showed that the bifidobacterial population establishment is affected by gestational age, delivery mode, and infant feeding, as it is evidenced by qualitative and quantitative changes. These data underline the need for understanding the impact of perinatal factors on the gut microbiota also at low taxonomic levels, especially in the case of relevant microbial populations such as Bifidobacterium. The data obtained provide indications for the selection of the species best suited for the development of bifidobacteria-based products for different groups of neonates and will help to develop rational strategies for favoring a healthy early microbiota development when this process is challenged. 相似文献
949.
Evan M. de Joya Brett M. Colbert Pei-Ciao Tang Byron L. Lam Jun Yang Susan H. Blanton Derek M. Dykxhoorn Xuezhong Liu 《International journal of molecular sciences》2021,22(8)
Hearing loss is the most common sensory disorder with ~466 million people worldwide affected, representing about 5% of the population. A substantial portion of hearing loss is genetic. Hearing loss can either be non-syndromic, if hearing loss is the only clinical manifestation, or syndromic, if the hearing loss is accompanied by a collage of other clinical manifestations. Usher syndrome is a syndromic form of genetic hearing loss that is accompanied by impaired vision associated with retinitis pigmentosa and, in many cases, vestibular dysfunction. It is the most common cause of deaf-blindness. Currently cochlear implantation or hearing aids are the only treatments for Usher-related hearing loss. However, gene therapy has shown promise in treating Usher-related retinitis pigmentosa. Here we review how the etiologies of Usher-related hearing loss make it a good candidate for gene therapy and discuss how various forms of gene therapy could be applied to Usher-related hearing loss. 相似文献
950.
Rocío Mato-Basalo Miriam Morente-Lpez Onno J Arntz Fons A. J. van de Loo Juan Fafin-Labora María C. Arufe 《International journal of molecular sciences》2021,22(7)
Mesenchymal stem cells have an important potential in the treatment of age-related diseases. In the last years, small extracellular vesicles derived from these stem cells have been proposed as cell-free therapies. Cellular senescence and proinflammatory activation are involved in the loss of therapeutic capacity and in the phenomenon called inflamm-aging. The regulators of these two biological processes in mesenchymal stem cells are not well-known. In this study, we found that p65 is activated during cellular senescence and inflammatory activation in human umbilical cord-derived mesenchymal stem cell. To demonstrate the central role of p65 in these two processes, we used small-molecular inhibitors of p65, such as JSH-23, MG-132 and curcumin. We found that the inhibition of p65 prevents the cellular senescence phenotype in human umbilical cord-derived mesenchymal stem cells. Besides, p65 inhibition produced the inactivation of proinflammatory molecules as components of a senescence-associated secretory phenotype (SASP) (interleukin-6 and interleukin-8 (IL-6 and IL-8)). Additionally, we found that the inhibition of p65 prevents the transmission of paracrine senescence between mesenchymal stem cells and the proinflammatory message through small extracellular vesicles. Our work highlights the important role of p65 and its inhibition to restore the loss of functionality of small extracellular vesicles from senescent mesenchymal stem cells and their inflamm-aging signature. 相似文献