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   15388篇
  免费   1271篇
  国内免费   609篇
电工技术   853篇
技术理论   2篇
综合类   876篇
化学工业   2699篇
金属工艺   956篇
机械仪表   967篇
建筑科学   1145篇
矿业工程   535篇
能源动力   444篇
轻工业   900篇
水利工程   247篇
石油天然气   1205篇
武器工业   104篇
无线电   1693篇
一般工业技术   1911篇
冶金工业   847篇
原子能技术   147篇
自动化技术   1737篇
  2024年   79篇
  2023年   305篇
  2022年   488篇
  2021年   669篇
  2020年   532篇
  2019年   451篇
  2018年   524篇
  2017年   520篇
  2016年   443篇
  2015年   605篇
  2014年   773篇
  2013年   830篇
  2012年   941篇
  2011年   1018篇
  2010年   887篇
  2009年   856篇
  2008年   876篇
  2007年   747篇
  2006年   795篇
  2005年   658篇
  2004年   540篇
  2003年   446篇
  2002年   434篇
  2001年   365篇
  2000年   344篇
  1999年   402篇
  1998年   295篇
  1997年   283篇
  1996年   239篇
  1995年   219篇
  1994年   175篇
  1993年   122篇
  1992年   107篇
  1991年   68篇
  1990年   65篇
  1989年   47篇
  1988年   28篇
  1987年   25篇
  1986年   16篇
  1985年   12篇
  1984年   13篇
  1983年   5篇
  1982年   5篇
  1981年   7篇
  1980年   3篇
  1979年   3篇
  1978年   1篇
  1977年   1篇
  1970年   1篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
Hyperlipidemia and oxidative stress with elevated oxidized low-density lipoprotein (ox-LDL) exacerbate hepatic inflammation and fibrosis. The plasma level of low-density lipoprotein (LDL) is controlled by proprotein convertase subtilisin/kexin 9 (PCSK9). Alirocumab is a monoclonal antibody that decreases LDL via inhibiting PCSK9 function. Apart from lipid-lowering effects, alirocumab exerts anti-inflammation, anti-angiogenesis and anti-oxidant effects. This study aims to investigate the impact of alirocumab treatment on common bile duct ligation (BDL)-induced biliary cirrhotic rats. After a 4-week treatment of alirocumab, the hemodynamic data, blood biochemistry, ox-LDL level, oxidative stress markers, severity of hepatic encephalopathy and abnormal angiogenesis of BDL rats were measured and compared to the control group. BDL rats presented cirrhotic pictures and elevated ammonia, total cholesterol, LDL and ox-LDL levels compared to the control group. Alirocumab decreased plasma levels of total cholesterol, LDL, and oxidative stress markers; however, it did not affect the hemodynamics, liver and renal biochemistry, and the plasma levels of ammonia and ox-LDL. The motor activities, portal-systemic collaterals and mesenteric vascular density were not significantly different between alirocumab-treated and control groups. In addition, it did not affect hepatic inflammation, intrahepatic angiogenesis, liver fibrosis and free cholesterol accumulation in the liver of BDL rats. In conclusion, PCSK9 inhibition by alirocumab treatment ameliorates hyperlipidemia and systemic oxidative stress in biliary cirrhotic rats. However, it does not affect the plasma level of ox-LDL, intrahepatic inflammation and fibrosis. In addition, PCSK9 inhibition has a neutral effect on abnormal angiogenesis and hepatic encephalopathy in biliary cirrhotic rats.  相似文献   
53.
Smolting is an important development stage of salmonid, and an energy trade-off occurs between osmotic regulation and growth during smolting in rainbow trout (Oncorhynchus mykiss). Growth hormone releasing hormone, somatostatin, growth hormone and insulin-like growth factor (GHRH-SST-GH-IGF) axis exhibit pleiotropic effects in regulating growth and osmotic adaptation. Due to salmonid specific genome duplication, increased paralogs are identified in the ghrh-sst-gh-igf axis, however, their physiology in modulating osmoregulation has yet to be investigated. In this study, seven sst genes (sst1a, sst1b, sst2, sst3a, sst3b, sst5, sst6) were identified in trout. We further investigated the ghrh-sst-gh-igf axis of diploid and triploid trout in response to seawater challenge. Kidney sst (sst1b, sst2, sst5) and sstr (sstr1b1, sstr5a, sstr5b) expressions were changed (more than 2-fold increase (except for sstr5a with 1.99-fold increase) or less than 0.5-fold decrease) due to osmoregulation, suggesting a pleiotropic physiology of SSTs in modulating growth and smoltification. Triploid trout showed significantly down-regulated brain sstr1b1 and igfbp2a1 (p < 0.05), while diploid trout showed up-regulated brain igfbp1a1 (~2.61-fold, p = 0.057) and igfbp2a subtypes (~1.38-fold, p < 0.05), suggesting triploid trout exhibited a better acclimation to the seawater environment. The triploid trout showed up-regulated kidney igfbp5a subtypes (~6.62 and 7.25-fold, p = 0.099 and 0.078) and significantly down-regulated igfbp5b2 (~0.37-fold, p < 0.05), showing a conserved physiology of teleost IGFBP5a in regulating osmoregulation. The IGFBP6 subtypes are involved in energy and nutritional regulation. Distinctive igfbp6 subtypes patterns (p < 0.05) potentially indicated trout triggered energy redistribution in brain and kidney during osmoregulatory regulation. In conclusion, we showed that the GHRH-SST-GH-IGF axis exhibited pleiotropic effects in regulating growth and osmoregulatory regulation during trout smolting, which might provide new insights into seawater aquaculture of salmonid species.  相似文献   
54.
Ten-eleven translocation (Tet) dioxygenases can induce DNA demethylation by catalyzing 5-methylcytosine(5mC) to 5-hydroxymethylcytosine(5hmC), and play important roles during mammalian development. In mouse, Tet1 and Tet2 are not expressed in pronucleus-staged embryos and are not involved in the genomic demethylation of early zygotes. Here, we investigated the influence of Tet1 and Tet2 on methylation of parental genomes by ectopically expressing Tet1 and Tet2 in zygotes. Immunofluorescence staining showed a marked 5hmC increase in the maternal pronucleus after injection of Tet1 or Tet2 mRNA into zygotes. Whole-genome bisulfite sequencing further revealed that Tet2 greatly enhanced the global demethylation of both parental genomes, while Tet1 only promoted the paternal demethylation. Tet1 and Tet2 overexpression altered the DNA methylation across genomes, including various genic elements and germline-specific differently methylated regions. Tet2 exhibited overall stronger demethylation activity than Tet1. Either Tet1 or Tet2 overexpression impaired preimplantation embryonic development. These results demonstrated that early expression of Tet1 and Tet2 could substantially alter the zygotic methylation landscape and damage embryonic development. These findings provide new insights into understanding the function of Tet dioxygenases and the mechanism of DNA methylation in relation to embryogenesis.  相似文献   
55.
In this article, an encoder Application Specific Integrated Circuit (ASIC) for high-speed serial data transmission is presented. The ASIC implements a low-latency and low-overhead line code and is fabricated with a commercial 0.25-µm Silicon-on-Sapphire CMOS technology. The ASIC operates at 640 MHz with a latency of no greater than 6.25 ns and the overhead of 14.3%. The encoder will be integrated with a serialiser and will be used in the A Toroidal LHC ApparatuS Liquid Argon (LAr) calorimeter Phase-I trigger upgrade.  相似文献   
56.
The nanocrystal (NC) work-function engineering, which plays an important role on the NC memory characteristics such as memory window and retention time, were long regarded as a matter of choice on NC materials. In this letter, we report opposite polarities of charge storage in Au NC memories with different control oxides. The effective NC work function is found to be not only a bulk property of the NC, but also governed by the interface with surrounding dielectric, as a result of the Fermi-level pinning. By replacing Au NCs with C60 molecules, we also show the pinning effect generally exists at quantum-dot-based devices with high density of interface states. This fundamental interface property should be taken into account in the selection of NC and dielectric materials for the NC memory optimization  相似文献   
57.
The deformation behavior involved in Nb/NiTi composite for biomedical applications within a large macroscopic strain range was investigated by tensile loading-unloading test and in situ synchrotron X-ray diffraction(SXRD).Experimental results show that during loading,the Nb/NiTi composite experiences the elastic elongation of B2-NiTi austenitic,B19'-NiTi martensitic and β-Nb phases,B2→ B19' stress-induced martensitic(SIM) transformation and tensile plastic deformation of β-Nb phase.During unloading,the deformation behavior involved in Nb/NiTi composite includes the elastic recovery of B2-NiTi austenitic,B19'-NiTi martensitic and β-Nb phases,reverse phase transformation B19'→B2 and compressive deformation of p-Nb phase.The martensitic transformation in this composite is almost reversible and occurs in a localized manner.These results might contribute to a comprehensive understanding of the deformation mechanism involved in Nb/NiTi composite and shed some light on design and development of novel composites with a combination of good biocompatibility and excellent superelasticity for biomedical applications.  相似文献   
58.
The white-backed planthopper (WBPH), Sogatella furcifera, is one of the most important piercing-sucking pests of rice (Oryza sativa) in Asia. Mucin-like salivary protein (SFMLP) is highly expressed in the salivary glands of WBPH, which plays an important role in WBPH feeding. In this study, WBPH injected with dsSFMLP had difficulty in sucking phloem sap from rice plants, which significantly reduced their food intake, weight, and survival. In contrast, the knockdown of the SFMLP gene had only a marginal effect on the survival of WBPH fed an artificial diet. Further studies showed that silencing SFMLP resulted in the short and single-branched salivary sheaths secretion and less formation of salivary flanges in rice. These data suggest that SFMLP is involved in the formation of the salivary sheath and is essential for feeding in WBPH. Overexpression of the SFMLP gene in rice plants promoted the feeding of WBPH, whereas silencing the gene in rice plants significantly decreased WBPH performance. Additionally, it was found that overexpression of SFMLP in rice plants elicited the signalling pathway of SA (salicylic acid) while suppressing JA (jasmonic acid); in contrast, silencing of the SFMLP gene in rice plants showed the opposite results. This study clarified the function of SFMLP in WBPH feeding as well as mediating rice defences.  相似文献   
59.
GR-3500型氧弹式量热计做燃烧焓的测定实验时间长,操作难度大,实验一次性成功率低.通过放宽对实验过程中夹层与量热容器的水温差值要求,实验结果表明夹层水温高于量热容器水温的0.5~3.0℃都是可行的,这样便于学生调节水温,缩短实验时间,取得良好的实验效果.  相似文献   
60.
利用差示扫描量热分析(DSC)、红外光谱(IR)、粉末X射线衍射(XRD)等手段对抗氧剂1010样品进行了晶体结构分析。不同方法各有特点,分析结果应是几种方法的相互印证与归纳统一。  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