全文获取类型
收费全文 | 1894821篇 |
免费 | 77758篇 |
国内免费 | 36519篇 |
学科分类
工业技术 | 2009098篇 |
出版年
2022年 | 21750篇 |
2021年 | 33706篇 |
2020年 | 25355篇 |
2019年 | 25382篇 |
2018年 | 27357篇 |
2017年 | 28468篇 |
2016年 | 33244篇 |
2015年 | 35299篇 |
2014年 | 50648篇 |
2013年 | 114322篇 |
2012年 | 67203篇 |
2011年 | 81032篇 |
2010年 | 73976篇 |
2009年 | 80792篇 |
2008年 | 75852篇 |
2007年 | 72074篇 |
2006年 | 70164篇 |
2005年 | 60656篇 |
2004年 | 56852篇 |
2003年 | 51438篇 |
2002年 | 49769篇 |
2001年 | 45868篇 |
2000年 | 42763篇 |
1999年 | 37990篇 |
1998年 | 50841篇 |
1997年 | 42446篇 |
1996年 | 37505篇 |
1995年 | 32064篇 |
1994年 | 29765篇 |
1993年 | 29723篇 |
1992年 | 26496篇 |
1991年 | 23584篇 |
1990年 | 23989篇 |
1989年 | 23020篇 |
1988年 | 21409篇 |
1987年 | 19650篇 |
1986年 | 19062篇 |
1985年 | 22412篇 |
1984年 | 22518篇 |
1983年 | 20458篇 |
1982年 | 19411篇 |
1981年 | 19569篇 |
1980年 | 18212篇 |
1979年 | 18689篇 |
1978年 | 17879篇 |
1977年 | 17893篇 |
1976年 | 19046篇 |
1975年 | 15881篇 |
1974年 | 15412篇 |
1973年 | 15493篇 |
排序方式: 共有10000条查询结果,搜索用时 656 毫秒
31.
Deepika M. Malini Raajan N. R. Srinivasan A. 《Multimedia Tools and Applications》2022,81(9):12701-12724
Multimedia Tools and Applications - The three-dimensional models of brain tumors serve as diagnostic assistance for physicians, surgeons, and radiologists. The proposed system establishes an... 相似文献
32.
33.
Karimi Bayan Chang Yu-Cheng Pekola Jukka P. 《Journal of Low Temperature Physics》2022,207(3-4):220-225
We discuss the temperature dependence of a common low temperature local thermometer, a tunnel junction between a superconductor and a normal metal (NIS junction). Towards the lowest temperatures its characteristics tend to saturate, which is usually attributed to selfheating effects. In this technical note, we reanalyze this saturation and show that the temperature independent subgap current of the junction alone explains in some cases the low temperature behavior quantitatively.
相似文献34.
为了探索三维石墨烯-碳纳米管(G-CNTs)/水泥净浆的压敏性能,采用四电极法研究了荷载作用下GCNTs/水泥净浆的电阻率变化,并分析不同G-CNTs掺量、加载幅度、加载速度以及恒定荷载对电阻率变化的影响。研究表明:随着G-CNTs掺量的增加,电阻率呈先减小后稳定的变化趋势,在G-CNTs掺量由0.2wt%增加至1.6wt%时,电阻率下降51.8%;电阻率与温度呈负相关;G-CNTs掺量高于0.8wt%时可以显著提高水泥净浆的压敏性能,且电阻率变化率与应力应变有明显的对应关系,1.2wt%G-CNTs掺量下试件的应力灵敏系数和应变灵敏系数分别为2.3%/MPa和291;G-CNTs/水泥净浆电阻率变化率幅值随着加载幅度增大而相应增加,其电阻率变化率曲线在不同加载速度以及恒定荷载作用下均与应力-应变曲线一一对应,具有良好的压敏特性。 相似文献
35.
纤维素和几丁质具有相似的结构,是自然界中储量丰富的两类天然多糖。经2, 2, 6, 6-四甲基哌啶氮氧化物(TEMPO)氧化修饰制备的纤维素和几丁质纳米纤维,不仅具有多糖类物质的良好亲水性、生物可降解性、生物相容性及丰富的官能团(羟基、羧基、乙酰氨基和氨基等)所带来的特定化学性质,而且还具有纳米纤维的纳米尺寸效应、大比表面积、高表面活性、高结晶度和手性液晶相结构等特点,已成为生物质纳米材料领域的研究重点之一。本文对TEMPO氧化修饰制备天然多糖纳米纤维的方法及剥离机制进行了总结,同时重点综述了TEMPO氧化修饰的天然多糖纳米纤维在薄膜、凝胶、导电、医用、电磁屏蔽及环境等复合材料的增强和功能升级等方面的研究进展,强调了纤维素和几丁质纳米纤维的官能团及纳米尺寸在复合材料中的增效机制。最后,对天然多糖纳米纤维的发展方向及其在各领域应用的机遇与挑战进行了展望。 相似文献
36.
Engineering new glass compositions have experienced a sturdy tendency to move forward from (educated) trial-and-error to data- and simulation-driven strategies. In this work, we developed a computer program that combines data-driven predictive models (in this case, neural networks) with a genetic algorithm to design glass compositions with desired combinations of properties. First, we induced predictive models for the glass transition temperature (Tg) using a dataset of 45,302 compositions with 39 different chemical elements, and for the refractive index (nd) using a dataset of 41,225 compositions with 38 different chemical elements. Then, we searched for relevant glass compositions using a genetic algorithm informed by a design trend of glasses having high nd (1.7 or more) and low Tg (500 °C or less). Two candidate compositions suggested by the combined algorithms were selected and produced in the laboratory. These compositions are significantly different from those in the datasets used to induce the predictive models, showing that the used method is indeed capable of exploration. Both glasses met the constraints of the work, which supports the proposed framework. Therefore, this new tool can be immediately used for accelerating the design of new glasses. These results are a stepping stone in the pathway of machine learning-guided design of novel glasses. 相似文献
37.
Journal of Chemical Ecology - Biocontrol agents such as parasitic wasps use long-range volatiles and host-associated cues from lower trophic levels to find their hosts. However, this chemical... 相似文献
39.
40.
Kathleen T. Lauser Amy L. Rueter Michelle A. Calabrese 《American Institute of Chemical Engineers》2022,68(12):e17850
While protein medications are promising for treatment of cancer and autoimmune diseases, challenges persist in terms of development and injection stability of high-concentration formulations. Here, the extensional flow properties of protein-excipient solutions are examined via dripping-onto-substrate extensional rheology, using a model ovalbumin (OVA) protein and biocompatible excipients polysorbate 20 (PS20) and 80 (PS80). Despite similar PS structures, differences in extensional flow are observed based on PS identity in two regimes: at moderate total concentrations where surface tension differences drive changes in extensional flow behavior, and at small PS:OVA ratios, which impact the onset of weakly elastic flow behavior. Undesirable elasticity is observed in ultra-concentrated formulations, independent of PS identity; higher PS contents are required to observe these effects than in analogous polymeric excipient solutions. These studies reveal novel extensional flow behaviors in protein-excipient solutions, and provide a straightforward methodology for assessing the extensional flow stability of new protein-excipient formulations. 相似文献