全文获取类型
收费全文 | 327415篇 |
免费 | 7488篇 |
国内免费 | 2767篇 |
学科分类
工业技术 | 337670篇 |
出版年
2021年 | 4159篇 |
2020年 | 3113篇 |
2019年 | 3359篇 |
2018年 | 5150篇 |
2017年 | 5129篇 |
2016年 | 5318篇 |
2015年 | 4323篇 |
2014年 | 6455篇 |
2013年 | 14674篇 |
2012年 | 9559篇 |
2011年 | 12318篇 |
2010年 | 10013篇 |
2009年 | 11051篇 |
2008年 | 11349篇 |
2007年 | 10960篇 |
2006年 | 10095篇 |
2005年 | 9124篇 |
2004年 | 8111篇 |
2003年 | 7733篇 |
2002年 | 7729篇 |
2001年 | 7466篇 |
2000年 | 7110篇 |
1999年 | 7204篇 |
1998年 | 15550篇 |
1997年 | 11725篇 |
1996年 | 8837篇 |
1995年 | 6955篇 |
1994年 | 6234篇 |
1993年 | 5972篇 |
1992年 | 4620篇 |
1991年 | 4585篇 |
1990年 | 4387篇 |
1989年 | 4362篇 |
1988年 | 4272篇 |
1987年 | 3614篇 |
1986年 | 3602篇 |
1985年 | 4133篇 |
1984年 | 3934篇 |
1983年 | 3590篇 |
1982年 | 3393篇 |
1981年 | 3518篇 |
1980年 | 3400篇 |
1979年 | 3325篇 |
1978年 | 3421篇 |
1977年 | 3874篇 |
1976年 | 5007篇 |
1975年 | 3124篇 |
1974年 | 2974篇 |
1973年 | 3001篇 |
1972年 | 2625篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Multimedia Tools and Applications - Remote Sensing categorical signature classification has gained significant implications on spatial resolution image analysis due to differences in the... 相似文献
2.
Zhao Jiandong Lei Wei Li Zijian Zhao Dongfeng Han Mingmin Hou Xiaoqing 《Multimedia Tools and Applications》2022,81(4):4753-4780
Multimedia Tools and Applications - The crowding in bus is an important factor affecting passenger satisfaction and bus dispatching level. However, how to use video images to detect crowding... 相似文献
3.
Chumakov Yu. A. Knyazeva A. G. Pribytkov G. A. 《Theoretical Foundations of Chemical Engineering》2021,55(3):490-503
Theoretical Foundations of Chemical Engineering - On the basis of the classic concepts of the theory of solid-phase combustion, for the first time, a model with a detailed scheme of chemical... 相似文献
4.
5.
7.
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
8.
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
9.
Qian Wu Xiangmei Liu Bo Li Lei Tan Yong Han Zhaoyang Li Yanqin Liang Zhenduo Cui Shengli Zhu Shuilin Wu Yufeng Zheng 《材料科学技术学报》2021,67(8):70-79
Pathogens pose a serious challenge to environmental sanitation and a threat to public health.The frequent use of chemicals for sterilization in recent years has not only caused secondary damage to the environment but also increased pathogen resistance to drugs,which further threatens public health.To address this issue,the use of non-chemical antibacterial means has become a new trend for environmental disinfection.In this study,we developed red phosphorus nanoparticles(RPNPs),a safe and degradable photosensitive material with good photocatalytic and photothermal properties.The red phosphorus nanoparticles were prepared using a template method and ultrasonication.Under the irradiation of simulated sunlight for 20 min,the RPNPs exhibited an efficiency of 99.98%in killing Staphylococcus aureus due to their excellent photocatalytic and photothermal abilities.Transmission electron microscopy and ultraviolet–visible spectroscopy revealed that the RPNPs exhibited degradability within eight weeks.Both the RPNPs and their degradation products were nontoxic to fibroblast cells.Therefore,such RPNPs are expected to be used as a new type of low-cost,efficient,degradable,biocompatible,and eco-friendly photosensitive material for environmental disinfection. 相似文献
10.
延安以东和以北的鄂尔多斯盆地东北部地区曾被认为位处三叠纪延长组7段(长7段)沉积期古湖盆的"边缘",一些学者认为该区延长组烃源岩不发育,因而其油藏原油系湖盆中心生成的原油经长距离侧向运移而来;但也有研究认为,包括盆地边缘在内的整个鄂尔多斯盆地致密油藏均为近源成藏。为明确盆地东部地区延长组原油来源,对三叠纪湖盆"东缘"七里村油田的主力油层延长组6段(长6段)原油开展了原油地球化学和油源对比研究。七里村油田长6段原油具有高饱和烃、高饱芳比、低非烃和低沥青质的特征,正构烷烃呈前高单峰型,主峰碳为C19,生物标志化合物分析显示长6段原油为同源成熟原油,生油母质以藻类等低等水生生物为主,混有陆源高等植物,母源沉积环境为偏还原性的淡水湖泊。七里村油田长6段原油与本地区长7段黑色泥页岩和暗色泥岩2种烃源岩均具有明显亲缘关系,而与志丹、富县等湖盆中心地区的长7段烃源岩在族组成、生物标志化合物和稳定碳同位素特征上均存在明显区别。综合分析认为七里村油田长6段原油并非湖盆中心长7段优质烃源岩所生油气经长距离运移而来,而主要为原位长7段烃源岩生成的原油经垂向运移和短距离侧向运移在长6段等储层中聚集成藏,属于近源成藏。 相似文献