首页 | 官方网站   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   48480篇
  免费   4352篇
  国内免费   1965篇
工业技术   54797篇
  2024年   101篇
  2023年   856篇
  2022年   1198篇
  2021年   1897篇
  2020年   1523篇
  2019年   1285篇
  2018年   1449篇
  2017年   1610篇
  2016年   1432篇
  2015年   1999篇
  2014年   2370篇
  2013年   2889篇
  2012年   2932篇
  2011年   3306篇
  2010年   2964篇
  2009年   2822篇
  2008年   3020篇
  2007年   2519篇
  2006年   2599篇
  2005年   2286篇
  2004年   1436篇
  2003年   1349篇
  2002年   1213篇
  2001年   1081篇
  2000年   1185篇
  1999年   1410篇
  1998年   1099篇
  1997年   925篇
  1996年   828篇
  1995年   758篇
  1994年   624篇
  1993年   465篇
  1992年   352篇
  1991年   256篇
  1990年   213篇
  1989年   147篇
  1988年   131篇
  1987年   81篇
  1986年   56篇
  1985年   29篇
  1984年   25篇
  1983年   25篇
  1982年   22篇
  1981年   14篇
  1980年   11篇
  1979年   4篇
  1978年   1篇
排序方式: 共有10000条查询结果,搜索用时 130 毫秒
31.
Diabetic kidney disease (DKD) is the leading cause of kidney failure. RhoA/Rho-associated protein kinase (ROCK) signaling is a recognized mediator of its pathogenesis, largely through mediating the profibrotic response. While RhoA activation is not feasible due to the central role it plays in normal physiology, ROCK inhibition has been found to be effective in attenuating DKD in preclinical models. However, this has not been evaluated in clinical studies as of yet. Alternate means of inhibiting RhoA/ROCK signaling involve the identification of disease-specific activators. This report presents evidence showing the activation of RhoA/ROCK signaling both in vitro in glomerular mesangial cells and in vivo in diabetic kidneys by two recently described novel pathogenic mediators of fibrosis in DKD, activins and cell-surface GRP78. Neither are present in normal kidneys. Activin inhibition with follistatin and neutralization of cell-surface GRP78 using a specific antibody blocked RhoA activation in mesangial cells and in diabetic kidneys. These data identify two novel RhoA/ROCK activators in diabetic kidneys that can be evaluated for their efficacy in inhibiting the progression of DKD.  相似文献   
32.
Despite being difficult to identify, extremely dilute oxygen vacancies have been widely reported to play an important role in enhancing magnetism in ZnFe2O4. The mechanisms underlying this enhanced magnetism have not been well understood for a long time and remain controversial because the formation of oxygen vacancy-rich ZnFe2O4 can be accompanied by changes in the chemical/physical characteristics, especially the composition, particle size, surface morphology and cation distribution, which can significantly affect the magnetization. An open and important question is whether and to what extent the enhanced magnetization can be attributed only to oxygen vacancies. In this study, the relationship between the magnetization and oxygen vacancies in ZnFe2O4 was definitively determined by using a carefully designed “shake-and-heat” treatment to prepare vacancy-rich samples while keeping the other crystal/surface parameters constant. Compared to the nearly vacancy-free paramagnetism samples, the vacancy-rich samples exhibited a higher magnetization of approximately 5 emu/g at both 300 K and 2 K. The Fe3+-O2--Fe3+ superexchange paths broken by oxygen vacancies then resulting in the Fe3+-Fe3+ ferromagnetism configuration. Meanwhile, the oxygen vacancy is highly diluted then the ferromagnetism configuration is confined in a single super-cell, favoring a short-range magnetic ordering at room temperature. The concentration of oxygen vacancies was calculated to be 0.68% by magnetization measurement. Our results may shed a light on how oxygen vacancies affect magnetism.  相似文献   
33.
In this work, gallium doped copper sulfide (Ga-doped CuS) nanocrystals were prepared using a solvothermal method. The effects of Ga doping on the crystal structures, chemical composition, morphology, optical properties and thermal performance of copper sulfide (CuS) were investigated. The Ga-doped CuS nanocrystals had a hexagonal structure comparable to that of pure CuS. The Cu+/Cu2+ ratio first decreased and then increased with increasing Ga3+ doping. Both CuS and Ga-doped CuS exhibited nanoplate and nanorod morphologies. The visible transmittance of the Ga-doped CuS films was in the range of 61–77.1%. Importantly, the near-infrared (NIR) shielding performance of the films can be tuned by adjusting the concentration of the Ga dopant. The NIR shielding value of the optimal Ga-doped CuS film was 72.4%, which was approximately 1.5 times as high as that of the pure CuS film. This can be ascribed to the enhanced plasmonic NIR absorption that resulted from an increase in the hole concentration after doping with Ga3+ ions. In the thermal performance test, the Ga-doped CuS film lowered the interior temperature of the heat box by 9.1 °C. Therefore, the integration of good visible transmittance and high NIR shielding performance make the Ga-doped CuS nanocrystals a promising candidate for energy-efficient window coatings.  相似文献   
34.
Mercury, lead, and cadmium are among the most toxic and carcinogenic heavy metal ions (HMIs), posing serious threats to the sustainability of aquatic ecosystems and public health. There is an urgent need to remove these ions from water by a cheap but green process. Traditional methods have insufficient removal efficiency and reusability. Structurally robust, large surface-area adsorbents functionalized with high-selectivity affinity to HMIs are attractive filter materials. Here, an adsorbent prepared by vulcanization of polyacrylonitrile (PAN), a nitrogen-rich polymer, is reported, giving rise to PAN-S nanoparticles with cyclic π-conjugated backbone and electronic conductivity. PAN-S can be coated on ultra-robust melamine (ML) foam by simple dipping and drying. In agreement with hard/soft acid/base theory, N- and S-containing soft Lewis bases have strong binding to Hg2+, Pb2+, Cu2+, and Cd2+, with extraordinary capture efficiency and performance stability. Furthermore, the used filters, when collected and electrochemically biased in a recycling bath, can release the HMIs into the bath and electrodeposit on the counter-electrode as metallic Hg0, Pb0, Cu0, and Cd0, and the PAN-S@ML filter can then be reused at least 6 times as new. The electronically conductive PAN-S@ML filter can be fabricated cheaply and holds promise for scale-up applications.  相似文献   
35.
The energy density of a flexible all-solid-state supercapacitor (ASC) requires new electrode material with special structure and morphology as a prerequisite for its secured improvement. In this paper, a new morphological exploration of chicken nuggets-like core/shell NiCo2O4/MnO2 (NCM) nanosheet arrays on Ni foam was employed. The application of this special morphology aims to greatly improve the electrochemical performance of the cathode electrode. Additionally, Buckwheat Biochar (BBC) is utilized as the anode while the PVA/KOH thin film is prepared as the separator. The chicken nuggets-like core/shell NCM nanosheet arrays were obtained by a two-step hydrothermal method. A series of characterization methods were carried out to further support the core/shell's well-designed structure and precise composition. The tests exhibited excellent specific capacitance of 593.3 F g?1 at 5 mA cm?2 and outstanding cycling stability with a retention of 90% after 10000 cycles. Furthermore, the assembled NCM//BBC ASC device indicated a high specific capacitance (239 F g?1 at the current density of 5 mA cm?2), this is in due part of the unique architecture of NCM nanosheet arrays and interconnected special porous structure of the BBC and the thin film PVA/KOH. Hence, the assembled ASC device exhibited high energy density (an energy density of 58 Wh·kg?1 at 3263 W kg?1) and remarkable cycling stability.  相似文献   
36.
Manganese monoxide (MnO) nanowire@reduced graphene oxide (rGO) nanocomposites are synthesized using a simple hydrothermal method combined with a calcination process. The structural and morphological characterization of the composites indicates that the MnO nanowires homogeneously anchor on both sides of the cross-linked rGO. The nanocomposites exhibit a high surface area of 126.5?m2 g?1. When employed as an anode material for lithium-ion batteries, the nanocomposites exhibit a reversible capacity of 1195 mAh g?1 at a current density of 0.1?A?g?1, with a high charge-discharge efficiency of 99.2% after 150 cycles. The three-dimensional architecture of the present materials exhibits high porosity and electron conductivity, significantly shortening the diffusion path of lithium ions and accelerating their reaction with the electrolyte, which greatly improves the lithium-ion storage properties. These excellent electrochemical performances make the composite a promising electrode material for lithium-ion batteries.  相似文献   
37.
数值模拟软件逐渐成为预测地下水演化更普遍的工具,并且广泛应用于地下水动态变化研究.以乌苏市平原区为例,结合区域水文地质条件及钻井资料,利用Processing Modflow建立三维水流数值模拟模型,并对该模型进行平面流场拟合,验证出模拟值基本符合2018年实测地下水位,通过模型模拟2018—2027年不同条件地下水位变化趋势,结果显示,2027年现状条件下比用水总量条件下浅埋深面积减少了550km2.  相似文献   
38.
39.
To improve the hydrophobicity of bagasse hemicellulose-based films, glutaraldehyde was applied when preparing films of original and cationic bagasse hemicellulose with the addition of polyvinyl alcohol and sorbitol. The results showed that the cationic modification could increase the hydrophobicity of the hemicellulose-based film, and the hydrophobicity of hemicellulose-based films crosslinked with glutaraldehyde also increased. However, cationic modification of hemicellulose decreased the stress of the hemicellulose-based film. While crosslinking with glutaraldehyde increased the stress of both the original and cationic hemicellulose-based films. Macrophotography indicated that the film formability of the original hemicellulose was better than that of cationic hemicellulose. Through SEM observation, the degree of bonding of different components of the films was found to be increased due to crosslinking with glutaraldehyde. The crosslinking reaction between glutaraldehyde and hemicellulose was further confirmed by FT-IR spectroscopy.  相似文献   
40.
喀斯特地貌复杂的岩溶地质构造和大量的地下岩溶水,给工程项目的设计和建设带来了很多难题.需要应用科学的方法,将场地和建筑群作为相互关联的整体,对建筑功能、场地地貌及高差、地下空间、交通及停车场、岩溶地质与地基基础、地下岩溶水等因素进行综合分析研究,因地制宜、趋利避害,治理与利用并举,运用集约化整合利用技术有效解决各种问题,提高项目资源的利用效率,获得了较好的社会效益和经济效益.  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-23

京公网安备 11010802026262号