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   21573篇
  免费   1898篇
  国内免费   923篇
电工技术   1159篇
技术理论   4篇
综合类   1432篇
化学工业   4050篇
金属工艺   1311篇
机械仪表   1242篇
建筑科学   1561篇
矿业工程   566篇
能源动力   551篇
轻工业   1346篇
水利工程   345篇
石油天然气   1337篇
武器工业   124篇
无线电   2483篇
一般工业技术   2779篇
冶金工业   1019篇
原子能技术   258篇
自动化技术   2827篇
  2025年   1篇
  2024年   281篇
  2023年   473篇
  2022年   582篇
  2021年   846篇
  2020年   709篇
  2019年   577篇
  2018年   605篇
  2017年   699篇
  2016年   569篇
  2015年   789篇
  2014年   952篇
  2013年   1194篇
  2012年   1265篇
  2011年   1349篇
  2010年   1250篇
  2009年   1254篇
  2008年   1153篇
  2007年   1121篇
  2006年   1102篇
  2005年   1000篇
  2004年   683篇
  2003年   667篇
  2002年   699篇
  2001年   566篇
  2000年   543篇
  1999年   662篇
  1998年   510篇
  1997年   431篇
  1996年   391篇
  1995年   346篇
  1994年   300篇
  1993年   202篇
  1992年   160篇
  1991年   128篇
  1990年   80篇
  1989年   100篇
  1988年   53篇
  1987年   30篇
  1986年   21篇
  1985年   14篇
  1984年   13篇
  1983年   5篇
  1982年   6篇
  1981年   8篇
  1980年   4篇
  1979年   1篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Brucellosis is a severe zoonotic infectious disease caused by the infection of the Brucella, which is widespread and causes considerable economic losses in underdeveloped areas. Brucella is a facultative intracellular bacteria whose main target cells for infection are macrophages, placental trophoblast cells and dendritic cells. The main clinical signs of Brucella infection in livestock are reproductive disorders and abortion. At present, the pathogenesis of placentitis or abortion caused by Brucella in livestock is not fully understood, and further research on the effect of Brucella on placental development is still necessary. This review will mainly introduce the research progress of Brucella infection of placental trophoblast cells as well as the inflammatory response caused by it, explaining the molecular regulation mechanism of Brucella leading to reproductive system disorders and abortion, and also to provide the scientific basis for revealing the pathogenesis and infection mechanism of Brucella.  相似文献   
22.
Background: Cibotii rhizoma (CR) is a famous traditional Chinese medicine (TCM) used to treat bleeding, rheumatism, lumbago, etc. However, its therapeutic effects and mechanism against thrombocytopenia are still unknown so far. In the study, we investigated the effects of aqueous extracts of Cibotii rhizoma (AECRs) against thrombocytopenia and its molecular mechanism.Methods: Giemsa staining, phalloidin staining, and flow cytometry were performed to measure the effect of AECRs on the megakaryocyte differentiation in K562 and Meg-01 cells. A radiation-induced thrombocytopenia mouse model was constructed to assess the therapeutic actions of AECRs on thrombocytopenia. Network pharmacology and experimental verification were carried out to clarify its mechanism against thrombocytopenia. Results: AECRs promoted megakaryocyte differentiation in K562 and Meg-01 cells and accelerated platelet recovery and megakaryopoiesis with no systemic toxicity in radiation-induced thrombocytopenia mice. The PI3K/AKT, MEK/ERK, and JAK2/STAT3 signaling pathways contributed to AECR-induced megakaryocyte differentiation. The suppression of the above signaling pathways by their inhibitors blocked AERC-induced megakaryocyte differentiation. Conclusions: AECRs can promote megakaryopoiesis and thrombopoiesis through activating PI3K/AKT, MEK/ERK, and JAK2/STAT3 signaling pathways, which has the potential to treat radiation-induced thrombocytopenia in the clinic.  相似文献   
23.
24.
Since the beginning of the 21st century, humans have experienced three coronavirus pandemics, all of which were transmitted to humans via animals. Recent studies have found that porcine deltacoronavirus (PDCoV) can infect humans, so swine enteric coronavirus (SeCoV) may cause harm through cross-species transmission. Transmissible gastroenteritis virus (TGEV) and PDCoV have caused tremendous damage and loss to the pig industry around the world. Therefore, we analyzed the genome sequence data of these two SeCoVs by evolutionary dynamics and phylogeography, revealing the genetic diversity and spatiotemporal distribution characteristics. Maximum likelihood and Bayesian inference analysis showed that TGEV could be divided into two different genotypes, and PDCoV could be divided into four main lineages. Based on the analysis results inferred by phylogeography, we inferred that TGEV might originate from America, PDCoV might originate from Asia, and different migration events had different migration rates. In addition, we also identified positive selection sites of spike protein in TGEV and PDCoV, indicating that the above sites play an essential role in promoting membrane fusion to achieve adaptive evolution. In a word, TGEV and PDCoV are the past and future of SeCoV, and the relatively smooth transmission rate of TGEV and the increasing transmission events of PDCoV are their respective transmission characteristics. Our results provide new insights into the evolutionary characteristics and transmission diversity of these SeCoVs, highlighting the potential for cross-species transmission of SeCoV and the importance of enhanced surveillance and biosecurity measures for SeCoV in the context of the COVID-19 epidemic.  相似文献   
25.
Powdery mildew caused by Blumeria graminis f. sp. tritici is a devastating disease that reduces wheat yield and quality worldwide. The exploration and utilization of new resistance genes from wild wheat relatives is the most effective strategy against this disease. Psathyrostachys huashanica Keng f. ex P. C. Kuo (2n = 2x = 14, NsNs) is an important tertiary gene donor with multiple valuable traits for wheat genetic improvement, especially disease resistance. In this study, we developed and identified a new wheat—P. huashanica disomic addition line, 18-1-5—derived from a cross between P. huashanica and common wheat lines Chinese Spring and CSph2b. Sequential genomic and multicolor fluorescence in situ hybridization analyses revealed that 18-1-5 harbored 21 pairs of wheat chromosomes plus a pair of alien Ns chromosomes. Non-denaturing fluorescence in situ hybridization and molecular marker analyses further demonstrated that the alien chromosomes were derived from chromosome 7Ns of P. huashanica. The assessment of powdery mildew response revealed that line 18-1-5 was highly resistant at the adult stage to powdery mildew pathogens prevalent in China. The evaluation of agronomic traits indicated that 18-1-5 had a significantly reduced plant height and an increased kernel length compared with its wheat parents. Using genotyping-by-sequencing technology, we developed 118 PCR-based markers specifically for chromosome 7Ns of P. huashanica and found that 26 of these markers could be used to distinguish the genomes of P. huashanica and other wheat-related species. Line 18-1-5 can therefore serve as a promising bridging parent for wheat disease resistance breeding. These markers should be conducive for the rapid, precise detection of P. huashanica chromosomes and chromosomal segments carrying Pm resistance gene(s) during marker-assisted breeding and for the investigation of genetic differences and phylogenetic relationships among diverse Ns genomes and other closely related ones.  相似文献   
26.
近期, 住建部发布《2016-2020年建筑业信息化发展纲要》, 充分发挥信息化在建筑业发展中的支撑和引领作用, 落实国家大数据战略、互联网+行动等相关要求, 大力推进建筑业信息化。形成一批在信息化上具有较强创新能力、达到国际先进水平的信息化建筑企业, 塑造工业化、绿色化、智能化新型建筑业态。建筑业的信息化, 必将以项目信息化为基础。没有项目管理的信息, 就没有建筑业的信息。没有项目管理的信息, 就没有项目管理的现代化。没有项目管理的信息化, 就没有项目管理的国际化。没有项目管理的国际化, 就没有建筑企业的国际化。本文从除了政治和战争等不可抗力的风险因素外, 论述了信息化技术的充分运用是国际工程项目进行风险管理的利器之一。  相似文献   
27.
针对互联网音频大数据的高速检索问题,结合音频指纹技术与过滤-提纯思想,提出一种面向音频大数据的鲁棒高效检索方法.在经典的Philips音频指纹基础上,提出了一种基于bag-of-features(BoF)的音频中间过滤指纹用于快速缩小检索范围,与Fibonacci Hashing检索相比提高检索速度约130倍;并设计了一种基于阈值的固定间隔抽样匹配方法,大幅减少匹配计算量,进一步提高检索速度可达140倍.实验结果显示:使用该方法在约10万首音频中对不同时长的音频片段进行批量检索,平均检索时间均小于1s;对音频进行MP3转换、重采样、随机剪切后再检索,召回率均在99.47%以上,理论准确率接近100%.  相似文献   
28.
Wireless communication involving un-manned aerial vehicles (UAVs) is expected to play an important role in future wireless networks.However,different from conve...  相似文献   
29.
Two-dimensional (2D) perovskites are known as one of the most promising luminescent materials due to their structural diversity and outstanding optoelectronic p...  相似文献   
30.
分布式的Internet网络测量和分析技术已成为目前网络行为学研究的热门课题之一。文章提出了一种基于A-gent的分布式网络测量和分析模型系统,并且详细地介绍了这种系统的具体实现方法。  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