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   2124篇
  免费   192篇
  国内免费   54篇
电工技术   213篇
综合类   66篇
化学工业   318篇
金属工艺   74篇
机械仪表   84篇
建筑科学   115篇
矿业工程   25篇
能源动力   73篇
轻工业   152篇
水利工程   23篇
石油天然气   84篇
武器工业   15篇
无线电   379篇
一般工业技术   386篇
冶金工业   147篇
原子能技术   15篇
自动化技术   201篇
  2025年   25篇
  2024年   117篇
  2023年   120篇
  2022年   129篇
  2021年   163篇
  2020年   112篇
  2019年   62篇
  2018年   69篇
  2017年   91篇
  2016年   78篇
  2015年   78篇
  2014年   65篇
  2013年   98篇
  2012年   103篇
  2011年   83篇
  2010年   85篇
  2009年   64篇
  2008年   72篇
  2007年   60篇
  2006年   81篇
  2005年   64篇
  2004年   47篇
  2003年   45篇
  2002年   53篇
  2001年   38篇
  2000年   45篇
  1999年   44篇
  1998年   68篇
  1997年   50篇
  1996年   31篇
  1995年   25篇
  1994年   14篇
  1993年   14篇
  1992年   7篇
  1991年   2篇
  1990年   5篇
  1989年   7篇
  1988年   5篇
  1987年   4篇
  1986年   8篇
  1985年   2篇
  1984年   4篇
  1983年   7篇
  1982年   6篇
  1981年   2篇
  1980年   3篇
  1979年   4篇
  1978年   3篇
  1977年   2篇
  1976年   4篇
排序方式: 共有2370条查询结果,搜索用时 15 毫秒
51.
Ricin toxin binding subunit B (RTB) is one of the subunits of the ricin protein. RTB has been used as adjuvant, but little is known about its mechanism. In this study, we found that RTB increased not only nitric oxide (NO) release, but also tumor necrosis factor (TNF)-α and interleukin (IL)-6 production in mouse macrophage cell line RAW264.7 cells. They subsequently exhibited enhanced ConA-induced T-cell and LPS-induced B-cell proliferative responses. We also examined the cytokines that were produced from splenocytes following in vitro RTB administration. Increased levels of IL-2, interferon (IFN)-γ and TNF-α were observed, while IL-4 and IL-5 were unaffected. These results demonstrate that recombinant RTB can act on the immune system and activate T-cells by introducing a Th1 immune response. Th1 cells might be the primary cellular target affected by RTB. Our results suggest that the recombinant RTB can promote the activation of macrophages and has a beneficial effect on immunomodulatory activity.  相似文献   
52.
[60]Fullerene (C60) was mono-substituted with well-defined poly(methyl methacrylate) (PMMA-b-C60) using the atom transfer radical polymerization (ATRP) technique. The self-assembly behaviors of PMMA-b-C60 in ethyl acetate (EA) and decalin mixtures were studied using laser light scattering (LLS) and transmission electron microscopy (TEM). Homogeneous solutions of PMMA-b-C60 can be obtained in the solvent mixtures containing more than 40 wt% EA, where the molar ratio of decalin to EA is close to 1. For each solvent mixture, unimers coexist with micelles and large aggregates. The sizes of PMMA-b-C60 micelles and aggregates are independent of polymer concentration, confirming that they are produced via the closed association mechanism. For the various solvent mixtures, the weight-averaged molecular weights, Mw of the PMMA-b-C60 aggregates range from 4.1×107 to 12.5×107 g/mol. The hydrodynamic radii of the large aggregate, Rh, vary from 90 to 136 nm, while the z-averaged radii of gyration, Rg, range from 210 to 311 nm. The Rg/Rh value for each solvent mixture is ∼2.3, which is independent of decalin contents in the mixed solvents. The morphological study using the transmission electron microscope suggests that the large aggregates are composed of porous large compound micelles (LCM) in solution.  相似文献   
53.
The present study found that ricin toxicity did not only manifest itself as inhibition of protein synthesis, but also induced apoptosis of immune cells and played an extremely significant role in intestinal injury. In this report, we describe a novel method to estimate binding events occurring on intestinal brush border membranes (BBM) based on SPR technology in an attempt to mimic the real intestinal surface capable of interacting physically and/or actively with certain biological molecules. Combined with HPCE-ESI-MS indentification, we obtained 28 kinds of proteins in BBM that interacted with ricin.  相似文献   
54.
The Okinawan folks in Japan use Ficus pumila L. as a beverage or herbal medicine to treat diabetes and high blood pressure. Four flavonoid glycosides were isolated and identified as rutin (1 and 3), apigenin 6-neohesperidose (2), kaempferol 3-robinobioside (4) and kaempferol 3-rutinoside (5). Among these compounds, rutin exhibited the strongest antioxidant activity in DPPH radical scavenging assay and superoxide radical inhibition assay. The preparation of Ooitabi leaves in water provide sufficient amount of flavonoid glycosides to the Okinawan although 50% of aqueous ethanol extracted these flavonoid glycosides more effectively. These results show the potential of Ooitabi leaves as a natural source of antioxidant for health management.  相似文献   
55.
Dielectric loss tangent and permittivity of polytetrafluoroethylene (Teflon), high-density (HD) polyethylene, and cross-linked polystyrene (Rexolite) were measured at temperature range from 28 to 84 K and frequency of approximately 18 GHz. The material properties were determined by measurements of the resonant frequency and the Q factor of a TE011 mode cylindrical superconducting cavity containing a sample under test. It has been demonstrated that these materials exhibit very low losses at cryogenic temperatures (2×10-6 for Teflon, 5×10-5 for HD polyethylene and 1.1×10-4 for Rexolite). Due to low losses, these materials can be useful in construction of various high-Q factor microwave devices for operation at cryogenic temperatures  相似文献   
56.
为解决由行人姿态、环境等复杂因素导致的行人特征表达能力弱、识别率低等问题,本文通过对AlignedReID++模型进行改进,提出了基于跨纬度交互注意力机制的行人重识别方法.首先,在特征提取部分,将跨纬度交互注意力Triplet At?tention模块嵌入到ResNet50网络中,捕获空间维度和通道维度之间跨纬度的交互...  相似文献   
57.
A new transient two-dimensional model with non-constant condensing pressure for a zeolite/water adsorption cooling cycle is proposed in this paper. This numerical model focuses on the heat and mass transfer behaviors in the adsorber and is solved by the control volume method. Due to the heat transfer limitation in the condenser, the simulated pressure during the isobaric generation phase of the cycle is not constant and will decrease with time. Compared with the model for constant condensing pressure, the cycle duration and cycled adsorbate for the base case are increased. Furthermore, the effect of mass flow rate of condenser cooling water on system performance is also investigated. It is found that both COP and SCP increase with an increase in the mass flow rate of cooling water in the condenser.  相似文献   
58.
A wireless sensor server is developed based on a reconfigurable active smart-antenna/retrodirective array. The system can serve as both a retrodirective array transponder and a smart-antenna receiver simply by changing the frequency of the local oscillator applied to the mixers, enabling it to utilize its hardware best to suit its communication environment. When operating as a direct-conversion receiver, the receiver array successfully demodulates a quaternary phase-shift keying (QPSK) modulated signal with circuit gain of 7 dB, and E/sub b//N/sub 0/ for BER=10/sup -4/ is approximately 12 dB without any error correction. In the retrodirective array mode, the system provides 20 dB circuit gain and 20 dB radio-frequency/intermediate-frequency isolation at the center frequency as well as phase conjugation, exhibiting excellent retrodirectivity. The mixers perform phase conjugation and modulation simultaneously, enabling the transmission of locally stored data. The local data is successfully extracted by an interrogator.  相似文献   
59.
Leong  D. 《Potentials, IEEE》2009,28(6):32-33
Network-attached storage (NAS) and storage area network (SAN) are the enterprise storage architectures that are commonly deployed in data centers. However, as storage demands escalate over time, none of these storage networks support aggressive concurrency and per-server throughput requirements for the applications on highly scalable computing clusters. In recent times, efforts have been set to incorporate the strengths of existing storage architectures into a unique framework that accomplished the performance, scalability, manageability, and a high level of data security. The approach has led to the design of novel storage architecture that support next generation object-based storage technology.  相似文献   
60.
    
DNA nanostructures as scaffolds for drug delivery, biosensing, and bioimaging are hindered by its vulnerability in physiological settings, less favorable of incorporating arbitrary guest molecules and other desirable functionalities. Noncanonical self‐assembly of DNA nanostructures with small molecules in an alternative system is an attractive strategy to expand their applications in multidisciplinary fields and is rarely explored. This work reports a nitrogen‐enriched carbon dots (NCDs)‐mediated DNA nanostructure self‐assembly strategy. Given the excellent photoluminescence and photodynamic properties of NCDs, the obtained DNA/NCDs nanocomplex holds great potential for bioimaging and anticancer therapy. NCDs can mediate DNA nanoprism (NPNCD) self‐assembly isothermally at a large temperature and pH range in a magnesium‐free manner. To explore the suitability of NPNCD in potential biomedical applications, the cytotoxicity and cellular uptake efficiency of NPNCD are evaluated. NPNCD with KRAS siRNA (NPNCDK) is further conjugated for KRAS‐mutated nonsmall cell lung cancer therapy. The NPNCDK shows excellent gene knockdown efficiency and anticancer effect in vitro. The current study suggests that conjugating NCDs with programmable DNA nanostructures is a powerful strategy to endow DNA nanostructures with new functionalities, and NPNCD may be a potential theranostic platform with further fine‐tuned properties of CDs such as near‐red fluorescence or photothermal activities.  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