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   19324篇
  免费   1140篇
  国内免费   934篇
电工技术   1170篇
综合类   985篇
化学工业   5394篇
金属工艺   1757篇
机械仪表   929篇
建筑科学   951篇
矿业工程   233篇
能源动力   266篇
轻工业   1066篇
水利工程   81篇
石油天然气   492篇
武器工业   150篇
无线电   1892篇
一般工业技术   2027篇
冶金工业   559篇
原子能技术   251篇
自动化技术   3195篇
  2024年   60篇
  2023年   242篇
  2022年   563篇
  2021年   606篇
  2020年   451篇
  2019年   404篇
  2018年   324篇
  2017年   417篇
  2016年   545篇
  2015年   575篇
  2014年   855篇
  2013年   1021篇
  2012年   1141篇
  2011年   1441篇
  2010年   1201篇
  2009年   1310篇
  2008年   1178篇
  2007年   1388篇
  2006年   1337篇
  2005年   1052篇
  2004年   858篇
  2003年   783篇
  2002年   661篇
  2001年   474篇
  2000年   403篇
  1999年   302篇
  1998年   237篇
  1997年   183篇
  1996年   167篇
  1995年   112篇
  1994年   96篇
  1993年   110篇
  1992年   86篇
  1991年   74篇
  1990年   64篇
  1989年   65篇
  1988年   45篇
  1987年   41篇
  1986年   54篇
  1985年   56篇
  1984年   46篇
  1983年   39篇
  1982年   35篇
  1981年   33篇
  1980年   34篇
  1978年   35篇
  1977年   39篇
  1976年   43篇
  1975年   48篇
  1974年   39篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
本文讨论了含4-(2’,4’,6’-三甲苯基)氨基蒽醌染料的合成,包括酸性染料和活性染料。这类染料染羊毛、聚酰胺、皮革及棉为艳蓝色和艳紫色,并具极好的耐光和耐湿处理牢度。  相似文献   
992.
对百菌清及其含氟衍生物对稻瘟病病原的抑菌作用进行了对比试验。  相似文献   
993.
《云南化工》2017,(11):91-92
鄂尔多斯盆地南部黄陵地区延长组长6、长8储层主要发育残余粒间孔、溶蚀粒间孔和溶蚀粒内孔等孔隙类型,多为小-微孔—微细喉型和中孔—细-微细喉型孔隙结构。通过储层物性与电性特征分析等途径认识储层性质。研究区长6储层属于特低孔、超低渗储层,长8储层属于超低孔、超低渗储层。长6、长8储层测井解释孔隙度、渗透率结果与岩心物性实测结果差别较大。  相似文献   
994.
Adsorption of a typical example of a new class of amino cellulose, namely 6‐deoxy‐6‐(2‐aminoethyl)amino cellulose at different pH‐values and in the presence of electrolytes, onto cellulose model substrates is studied with surface plasmon resonance and quartz crystal microbalance with dissipation monitoring. Unexpectedly, adsorption is consistently higher at a higher pH‐value of 10, indicating that solubility and interactions between amine moieties and cellulose are more important than electrostatic interactions. The findings are highly relevant for the process to modify material surfaces with amino cellulose in water‐based systems as a universal tool for changing the surface properties and chemistry. Potential applications for an antimicrobial all biobased material could be found, e.g., as medical textiles or in the biotechnology sector.

  相似文献   

995.
Lithium–sulfur batteries have attracted considerable attention due to its high theoretical specific capacity, low cost, environmental friendliness, etc. However, the dissolution of polysulfide intermediate in the electrolyte leads to rapid capacity decay in the charge–discharge process. A sulfur‐based cathode with the specific discharge capacity of 630 mAh g−1 and ultrahigh capacity retention ratio of 0.11% per cycle after 400 cycles at 0.5 C that simply blend the sublimed sulfur and acetylene black in the mortar with the polyamide‐6 (PA6) as binder is reported. The intense complexation between the lithium polysulfide and amide groups ( CO NH ) in PA6 can effectively inhibit the “shuttling effect” and reduce the loss of active materials during the charge–discharge process. The discovery provides a handy and practicable strategy for developing the excellent cycling stability lithium–sulfur batteries.

  相似文献   

996.
Siglecs are members of the immunoglobulin gene family containing sialic acid binding N-terminal domains. Among them, Siglec-8 is expressed on various cell types of the immune system such as eosinophils, mast cells and weakly on basophils. Cross-linking of Siglec-8 with monoclonal antibodies triggers apoptosis in eosinophils and inhibits degranulation of mast cells, making Siglec-8 a promising target for the treatment of eosinophil- and mast cell-associated diseases such as asthma. The tetrasaccharide 6’-sulfo-sialyl Lewisx has been identified as a specific Siglec-8 ligand in glycan array screening. Here, we describe an extended study enlightening the pharmacophores of 6’-sulfo-sialyl Lewisx and the successful development of a high-affinity mimetic. Retaining the neuraminic acid core, the introduction of a carbocyclic mimetic of the Gal moiety and a sulfonamide substituent in the 9-position gave a 20-fold improved binding affinity. Finally, the residence time, which usually is the Achilles tendon of carbohydrate/lectin interactions, could be improved.  相似文献   
997.
The need for electronics to operate at temperatures of 200°C and above continues to grow. These applications include avionics, aerospace, automotive, downhole drilling, mining, and many others. To satisfy this demand, a significant amount of research and development has been conducted. Despite the efforts, the number of new electronic components designed specifically for high-temperature operation is still relatively limited. In Low Temperature Co-fired Ceramic (LTCC) packages, LTCC materials are generally used as the host media for a number of pre-fabricated semiconductor components. As a result, reliability of the entire LTCC package largely depends on the performance of the least robust component. Ferro A6M-E and Ferro L8 are the two well-established and recognized LTCC dielectrics widely used for mid and high frequency LTCC applications, including several high reliability aerospace and defense applications that require demanding Mil-Spec qualifications. This study is our first attempt to characterize and understand basic high-temperature dielectric properties of these two commercial LTCC materials. The secondary objective is to initiate a dialogue in attempt to establish reliability requirements for LTCC packages dedicated for high-temperature operation.  相似文献   
998.
The red emission with suitable peak wavelength and narrow band is acutely required for high color rendering index (CRI) white LEDs without at the cost of the luminous efficacy. Herein, the Li2Ca2Mg2Si2N6:Eu2+ red phosphor was prepared with facile solid-state method using Ca3N2, Mg3N2, Si3N4, Li3N, and Eu2O3 as the safety raw materials under atmospheric pressure for the first time, which shows red emission peaking at 638 nm with full width at half maximum (FWHM) of 62 nm under blue light irradiation and becomes the desired red phosphor to realize the balance between luminous efficacy and high CRI in white LEDs. The morphology, structure, luminescence properties, thermal quenching behavior, and chromaticity stability of the Li2Ca2Mg2Si2N6:Eu2+ phosphor are investigated in detail. Concentration quenching occurs when the Eu2+ content exceeds 1.0 mol%, whereas high-temperature photoluminescent measurements show a 32% drop from the room-temperature efficiency at 423 K. In view of the excellent luminescence performances of Li2Ca2Mg2Si2N6:Eu2+ phosphor, a white LEDs with CRI of 91 as a proof-of-concept experiment was fabricated by coating the title phosphor with Y3Al5O12:Ce3+ on a blue LED chip. In addition, the potential application of the title phosphor in plant growth LED device was also demonstrated. All the results indicate that Li2Ca2Mg2Si2N6:Eu2+ is a promising red-emitting phosphor for blue LED-based high CRI white LEDs and plant growth lighting sources.  相似文献   
999.
Obesity-associated low-grade inflammation favors weight gain, whereas systemic infection frequently leads to anorexia. Thus, inflammatory signals can either induce positive or negative energy balance. In this study, we used whole-cell patch-clamp to investigate the acute effects of three important proinflammatory cytokines, tumor necrosis factor α (TNF-α), interleukin-6, and interleukin-1β (IL-1β) on the membrane excitability of agouti-related peptide (AgRP)- or proopiomelanocortin (POMC)-producing neurons. We found that both TNF-α and IL-1β acutely inhibited the activity of 35–42% of AgRP-producing neurons, whereas very few POMC neurons were depolarized by TNF-α. Interleukin-6 induced no acute changes in the activity of AgRP or POMC neurons. Our findings indicate that the effect of TNF-α and IL-1β, especially on the activity of AgRP-producing neurons, may contribute to inflammation-induced anorexia observed during acute inflammatory conditions.  相似文献   
1000.
Sjögren’s syndrome (SS) is a systemic rheumatic disease that predominantly affects salivary and lacrimal glands resulting in oral and ocular dryness, respectively, referred to as sicca symptoms. The clinical presentation of ocular dryness includes keratoconjunctivitis sicca (KCS), resulting from the inflammatory damage to the ocular surface tissues of cornea and conjunctiva. The diagnostic evaluation of KCS is a critical component of the classification criteria used by clinicians worldwide to confirm SS diagnosis. Therapeutic management of SS requires both topical and systemic treatments. Several mouse models of SS have contributed to our current understanding of immunopathologic mechanisms underlying the disease. This information also helps develop novel therapeutic interventions. Although these models address glandular aspects of SS pathology, their impact on ocular surface tissues is addressed only in a few models such as thrombospondin (TSP)-1 deficient, C57BL/6.NOD.Aec1Aec2, NOD.H2b, NOD.Aire KO, and IL-2Rα (CD25) KO mice. While corneal and/or conjunctival damage is reported in most of these models, the characteristic SS specific autoantibodies are only reported in the TSP-1 deficient mouse model, which is also validated as a preclinical model. This review summarizes valuable insights provided by investigations on the ocular spectrum of the SS pathology in these models.  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