首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   9206篇
  免费   253篇
  国内免费   17篇
电工技术   147篇
综合类   5篇
化学工业   1489篇
金属工艺   117篇
机械仪表   195篇
建筑科学   338篇
矿业工程   17篇
能源动力   191篇
轻工业   709篇
水利工程   75篇
石油天然气   11篇
武器工业   1篇
无线电   879篇
一般工业技术   1241篇
冶金工业   2989篇
原子能技术   74篇
自动化技术   998篇
  2022年   126篇
  2021年   152篇
  2020年   82篇
  2019年   100篇
  2018年   151篇
  2017年   110篇
  2016年   151篇
  2015年   136篇
  2014年   182篇
  2013年   386篇
  2012年   268篇
  2011年   319篇
  2010年   260篇
  2009年   276篇
  2008年   307篇
  2007年   278篇
  2006年   264篇
  2005年   259篇
  2004年   214篇
  2003年   211篇
  2002年   197篇
  2001年   175篇
  2000年   166篇
  1999年   195篇
  1998年   780篇
  1997年   435篇
  1996年   338篇
  1995年   226篇
  1994年   227篇
  1993年   202篇
  1992年   137篇
  1991年   118篇
  1990年   108篇
  1989年   116篇
  1988年   115篇
  1987年   111篇
  1986年   111篇
  1985年   127篇
  1984年   111篇
  1983年   83篇
  1982年   92篇
  1981年   92篇
  1980年   79篇
  1979年   72篇
  1978年   73篇
  1977年   99篇
  1976年   155篇
  1974年   43篇
  1973年   51篇
  1972年   43篇
排序方式: 共有9476条查询结果,搜索用时 31 毫秒
1.
The conversion of food industry by-products to compounds with high added value is nowadays a significant topic, for social, environmental, and economic reasons. In this paper, calcium phosphate-based materials were obtained from black scabbardfish (Aphanopus carbo) bones and grey triggerfish (Balistes capriscus) skin, which are two of the most abundant fish by-products of Madeira Island. Different calcination temperatures between 400 and 1000°C were employed. Materials obtained from calcination of bones of black scabbard fish were composed by homogeneous mixtures of hydroxyapatite (Ca10(PO4)6(OH)2, HAp) and β-tricalcium phosphate (β-Ca3(PO4)2, β-TCP). Because of the high biocompatibility of HAp and the good resorbability of β-TCP, these natural biphasic materials could be very relevant in the field of biomaterials, as bone grafts. The ratio between HAp and β-TCP in the biphasic compound was dependent on the calcination temperature. Differently, the material obtained from skin of grey triggerfish contained HAp as the main phase, together with small amounts of other mineral phases, such as halite and rhenanite, which are known to enhance osteogenesis when used as bone substitutes. In both cases, the increase of calcination temperature led to an increase in the particles size with a consequent decrease in their specific surface area. These results demonstrate that from the fish by-products of the most consumed fishes in Madeira Island it is possible to obtain bioceramic materials with tunable composition and particle morphology, which could be promising materials for the biomedical field.  相似文献   
2.
Colorectal cancer (CRC) is the third most deadly cancer worldwide, and inflammatory bowel disease (IBD) is one of the critical factors in CRC carcinogenesis. IBD is responsible for an unphysiological and sustained chronic inflammation environment favoring the transformation. MicroRNAs (miRNAs) belong to a class of highly conserved short single-stranded segments (18–25 nucleotides) non-coding RNA and have been extensively discussed in both CRC and IBD. However, the role of miRNAs in the development of colitis-associated CRC (CAC) is less clear. The aim of this review is to summarize the major upregulated (miR-18a, miR-19a, miR-21, miR-31, miR-155 and miR-214) and downregulated (miR-124, miR-193a-3p and miR-139-5p) miRNAs in CAC, and their roles in genes’ expression modulation in chronic colonic-inflammation-induced carcinogenesis, including programmed cell-death pathways. These miRNAs dysregulation could be applied for early CAC diagnosis, to predict therapy efficacy and for precision treatment.  相似文献   
3.
4.
5.
正项目地址_中国北京项目面积_8000m~2设计单位_ArkA北京亦庄半岛幼儿园项目是设计团队与半岛教育集团的第二次合作,目标是将蒙特梭利教育理念和建筑设计融为一体,创造出一个更合理的空间和安全的环境,让孩子们能够自由快乐地学习和成长。原有的建筑物是一个开放的空间,整个大空间分作4层。设计团队的首要任务是根据孩子的比例改造空间。在设计时,设计团队加入了许多小房屋的设计,以此让孩子更具有主人感和安全感。对教室的设计是简约的房屋;图书馆则是一个开放空间,在其中央种下一棵树,好似一个乡村小镇的广场;走廊设计成多功能的开放空间,孩子  相似文献   
6.
7.
Linear-viscoelastic characteristics and performance are evaluated throughout the blending process of polyethylene and polypropylene with bitumen. Results indicate that type, form and percentage of polyolefin play a significant role in the time evolution of the composite's mechanical response. Toluene extraction of modified bitumen revealed, for the first time, the formation of a sponge-like polymer network. Visual inspection and Fourier transform infrared analysis of the polyolefins recovered after extraction indicates higher affinity of the polyethylene with bitumen in agreement with the rheological test results. The use of polypropylene is discouraged if rutting performance is a concern, and polyethylene in both pellets and powder form at 4%, and after 210 min of blending produces a modified bitumen with acceptable performance.  相似文献   
8.
9.
This paper presents a novel framework for manufacturing and cost-related knowledge formalization. This artefact allows industries to capitalize the knowled  相似文献   
10.
Understanding the sources and composition of organic aerosol (OA) in indoor environments requires rapid measurements, since many emissions and processes have short timescales. However, real-time molecular-level OA measurements have not been reported indoors. Here, we present quantitative measurements, at a time resolution of five seconds, of molecular ions corresponding to diverse aerosol-phase species, by applying extractive electrospray ionization mass spectrometry (EESI-MS) to indoor air analysis for the first time, as part of the highly instrumented HOMEChem field study. We demonstrate how the complex spectra of EESI-MS are screened in order to extract chemical information and investigate the possibility of interference from gas-phase semivolatile species. During experiments that simulated the Thanksgiving US holiday meal preparation, EESI-MS quantified multiple species, including fatty acids, carbohydrates, siloxanes, and phthalates. Intercomparisons with Aerosol Mass Spectrometer (AMS) and Scanning Mobility Particle Sizer suggest that EESI-MS quantified a large fraction of OA. Comparisons with FIGAERO-CIMS shows similar signal levels and good correlation, with a range of 100 for the relative sensitivities. Comparisons with SV-TAG for phthalates and with SV-TAG and AMS for total siloxanes also show strong correlation. EESI-MS observations can be used with gas-phase measurements to identify co-emitted gas- and aerosol-phase species, and this is demonstrated using complementary gas-phase PTR-MS observations.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号