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   2468篇
  免费   137篇
  国内免费   107篇
电工技术   127篇
综合类   122篇
化学工业   301篇
金属工艺   418篇
机械仪表   104篇
建筑科学   76篇
矿业工程   59篇
能源动力   95篇
轻工业   131篇
水利工程   28篇
石油天然气   120篇
武器工业   27篇
无线电   250篇
一般工业技术   241篇
冶金工业   239篇
原子能技术   117篇
自动化技术   257篇
  2024年   8篇
  2023年   33篇
  2022年   41篇
  2021年   54篇
  2020年   50篇
  2019年   50篇
  2018年   54篇
  2017年   62篇
  2016年   90篇
  2015年   73篇
  2014年   131篇
  2013年   147篇
  2012年   139篇
  2011年   154篇
  2010年   111篇
  2009年   149篇
  2008年   113篇
  2007年   156篇
  2006年   143篇
  2005年   145篇
  2004年   97篇
  2003年   111篇
  2002年   96篇
  2001年   82篇
  2000年   68篇
  1999年   54篇
  1998年   52篇
  1997年   50篇
  1996年   30篇
  1995年   25篇
  1994年   45篇
  1993年   13篇
  1992年   11篇
  1991年   5篇
  1990年   5篇
  1988年   6篇
  1987年   2篇
  1986年   3篇
  1985年   5篇
  1984年   3篇
  1983年   5篇
  1982年   3篇
  1981年   8篇
  1980年   2篇
  1979年   5篇
  1978年   6篇
  1977年   2篇
  1976年   2篇
  1974年   2篇
  1967年   2篇
排序方式: 共有2712条查询结果,搜索用时 15 毫秒
1.
湖南省郴州市饭垄堆北段锡钨多金属矿位于湘南钨锡钼铋多金属成矿带东坡矿田内,成矿地质条件优越,具有很好的找矿前景。根据该矿床地质特征以及已有的地质矿产勘查成果,系统总结了矿区101、102、103号主矿体特征。在此基础上,进一步讨论了该类裂隙充填细脉带型锡钨多金属矿床在勘查过程中探矿工程布置的优化方法:即:①探矿工程不宜按每个矿带单独控制,应对整个赋矿层位进行整体控制;②应对含有毒砂、锡、钨细脉的岩性段进行连续取样化验,既可避免漏矿,又可以为将来工业指标调整后重新圈定矿体提供直接依据。  相似文献   
2.
采用光学显微镜(OM)、扫描电镜(SEM)、电子探针显微分析(EPMA)、X射线衍射(XRD)以及扫描透射电镜(STEM),研究了一种高Cu含量Al-2.35Cu-4.6Li-0.12Sc(at%)合金在均匀化热处理过程中微观组织演变以及W(Al8Cu4Sc)相的形成机制。结果表明:铸态时,合金中的主要凝固相为TB(Al7Cu4Li)相,Sc主要以过饱和固溶体的形式存在于基体中;均匀化后,TB相完全溶解,基体中的Cu含量增加,Sc含量减少,稳定的W相形成。分析表明,由于TB相与基体界面是非共格的,W相优先在此界面形核将有利于其形核能的降低。W相形核后通过不断消耗其附着的TB相上的Cu原子和Al基体中的过饱和Sc原子而逐渐长大,直至形成尺寸1 μm左右的稳定粒子。  相似文献   
3.
采用直流电化学刻蚀方法制备扫描隧道显微镜钨针尖,研究了电化学刻蚀过程中NaOH溶液浓度、钨丝浸入长度和刻蚀电压对针尖形貌的影响。通过扫描电子显微镜(SEM)测量针尖曲率半径和针尖纵横比值,以表征针尖的尺寸和形状;通过能谱仪(EDS)分析针尖表面成分,以表征表面清洁度;通过场发射显微镜(FEM)得到Fowler-Nordheim (F-N)曲线来检测针尖发射性能。实验结果表明,当溶液浓度为2 mol/L、钨丝浸入长度为4 mm、刻蚀电压为3 V时,可以得到曲率半径约为100 nm、纵横比值为13的针尖,且表面无钨的氧化层。FEM结果显示当对针尖施加500 V的负偏压时,针尖可以稳定发射50 nA量级的电流,且针尖性能具有良好的一致性。  相似文献   
4.
1-read/1-write (1R1W) register file (RF) is a popular memory configuration in modern feature rich SoCs requiring significant amount of embedded memory. A memory compiler is constructed using the 8T RF bitcell spanning a range of instances from 32 b to 72 Kb. An 8T low-leakage bitcell of 0.106 μm2 is used in a 14 nm FinFET technology with a 70 nm contacted gate pitch for high-density (HD) two-port (TP) RF memory compiler which achieves 5.66 Mb/mm2 array density for a 72 Kb array which is the highest reported density in 14 nm FinFET technology. The density improvement is achieved by using techniques such as leaf-cell optimization (eliminating transistors), better architectural planning, top level connectivity through leaf-cell abutment and minimizing the number of unique leaf-cells. These techniques are fully compatible with memory compiler usage over the required span. Leakage power is minimized by using power-switches without degrading the density mentioned above. Self-induced supply voltage collapse technique is applied for write and a four stack static keeper is used for read Vmin improvement. Fabricated test chips using 14 nm process have demonstrated 2.33 GHz performance at 1.1 V/25 °C operation. Overall Vmin of 550 mV is achieved with this design at 25 °C. The inbuilt power-switch improves leakage power by 12x in simulation. Approximately 8% die area of a leading 14 nm SoC in commercialization is occupied by these compiled RF instances.  相似文献   
5.
基于压铸模用钢3Cr2W8V的成分及性能特点,分析了3Cr2W8V传统热处理工艺的不足.结合生产实践,对压铸模用钢3Cr2W8V的热处理工艺进行了改进,针对压铸模具的应用条件,提出了几种不同热处理工艺方案.经生产实践检验,改进后的热处理工艺方案合理、科学,具有经济性和应用价值.  相似文献   
6.
Grape (Kyoho) skin, used to retard lipid oxidation in edible oil foods, was investigated to reduce lipid oxidation in an oil-in-water (O/W) emulsion during 20 day of storage. The antioxidant efficacy of Kyoho skin extracts in O/W emulsions was determined by the measurement of secondary oxidation products. Moreover, principal component analysis (PCA) was conducted to determine similarities between emulsions treated with or without Kyoho skin extracts and standards. The data revealed that Kyoho skin extracts exhibited >93% inhibition and reported a similar p-anisidine (4.30–20.71) and TBARS (6.08–11.15 mg MDA L−1) values over the standards during 20 day of storage. PCA (PCs 1 (51.83%) and 2 (18.85%)) demonstrated a similarity in the contribution of Kyoho skin extracts over the synthetic antioxidants in O/W emulsion. Overall, these findings highlighted the possibility of using Kyoho skin extracts as natural antioxidants to decrease oxidative rancidity in foods.  相似文献   
7.
The effects of diacylglycerols rich in medium‐ and long‐chain fatty acids (MLCD) on the crystallization of hydrogenated palm oil (HPO) and formation of 10% water‐in‐oil (W/O) emulsion are studied, and compared with the common surfactants monostearoylglycerol (MSG) and polyglycerol polyricinoleate (PGPR). Polarized light microscopy reveals that emulsions made with MLCD form crystals around dispersed water droplets and promotes HPO crystallization at the oil‐water interface. Similar behavior is also observed in MSG‐stabilized emulsions, but is absent from emulsions made with PGPR. The large deformation yield value of the test W/O emulsion is increased four‐fold versus those stabilized via PGPR due to interfacial crystallization of HPO. However, there are no large differences in droplet size, solid fat content (SFC), thermal behavior or polymorphism to account for these substantial changes, implying that the spatial distribution of the HPO crystals within the crystal network is the driving factor responsible for the observed textural differences. MLCD‐covered water droplets act as active fillers and interact with surrounding fat crystals to enhance the rigidity of emulsion. This study provides new insights regarding the use of MLCD in W/O emulsions as template for interfacial crystallization and the possibility of tailoring their large deformation behavior. Practical Applications: MLCD is applied in preparing W/O emulsion. It is found that MLCD forms unique interfacial Pickering crystals around water droplets, which promote the surface‐inactive HPO nucleation at the oil‐water interface. Thus MLCD‐covered water droplets act as active fillers and interact with surrounding fat crystals, which can greatly enhance the rigidity of emulsion. This observation would provide a theoretical reference and practical basis for the application of the MLCD with appreciable nutritional properties in lipid‐rich products such as whipped cream, shortenings margarine, butter and ice cream, so as to substitute hydrogenated oil. MLCD‐stabilized emulsions can also be explored for the development of novel confectionery products, lipsticks, or controlled release matrices.  相似文献   
8.
In this work, cobalt–tungsten–boron nanoparticles (Co–W–B) have been successfully deposited on foam Ni to manufacture thin-film catalysts by electroless plating technique and applied in hydrogen generation from ammonia borane (NH3BH3) hydrolysis. Physicochemical properties of Co–W–B nanoparticles are characterized by XRD (Powder X–ray diffraction), SEM (Scanning electron microscopy), and EDS (Energy dispersive X–ray spectroscopy). It is observed that Co–W–B showed irregular spherical structure on the surface of foam Ni substrate. An increase of depositional pH value in the preparation process leads to the change of particle size. When the pH value is equal to 11.5, as-synthesized Co–W–B exhibits the smaller particle size, which suggests that depositional pH value has directly impacted the nucleation and growth of catalysis particles. The optimized Co–W–B catalyst displays higher catalytic activity toward NH3BH3 hydrolysis with a specific rate of hydrogen generation of 12933.3 mL min?1·g?1 at room temperature. Moreover, the lower apparent activation energy of 47.3 kJ mol?1 is achieved. Compared with previously reported catalysts, the as-obtained catalytic performance is situated at the better rank. Moreover, the reusability has been investigated under the mild NH3BH3 hydrolysis conditions. It reveals that as-fabricated thin-film Co–W–B maintains excellent durability after five cycles. A possible mechanism for the released hydrogen from NH3BH3 hydrolysis using Co–W–B catalyst has been proposed.  相似文献   
9.
Mangiferin (MGF) is a phenolic compound isolated from mango, but its poor solubility significantly limits its use. In this study, MGF was embedded into the inner aqueous phase of W1/O/W2 emulsions. Firstly, the dissolution method of MGF was determined. MGF remained stable in solution with pH 13 at 30 min, and its solubility reached 10 mg mL−1. When the pH of MGF solutions was adjusted from pH 13 to pH 6, MGF did not immediately crystallise, providing sufficient time to construct the MGF-loaded W1/O/W2 emulsions. Subsequently, the MGF-loaded W1/O/W2 emulsions were constructed using polyglycerol polyricinoleate (PGPR) and calcium caseinate (CAS). The formation and stability of the W1/O/W2 emulsions were investigated. The MGF-loaded W1/O/W2 emulsions stabilised with 1% PGPR and 1% – 3% CAS exhibited a low viscosity, limited loading capacity, and poor stability. Conversely, the MGF-loaded W1/O/W2 emulsions stabilised by 3%PGPR–3%CAS exhibited optimal loading capacity (encapsulation efficiency = 95.31% and loading efficiency = 0.91%) and stability, which was attributed to the fact that high viscosity and gel state retarded the migration of inner aqueous phase. These results indicated that the W1/O/W2 emulsions stabilised by PGPR and CAS may be a potential alternative for encapsulating mangiferin.  相似文献   
10.
In this paper, 1Cr11Ni2W2MoV steel that is aerial engine blade materials was hot dipped Al-6%Si-4%RE in order to improve its application temperature. According to GB/T13303 - 91 standard, samples with coating and without coating were oxidated at 700℃ from 5 h to 600 h. Two oxidation kinetics curves were drawn in terms of data of tests. The results showed that oxidation resistance of 1Cr11Ni2W2MoV steel hot-dipped Al-6% Si-4%RE is better than one without coating. From SEM and EMPA, the surface of coating formed dense and uninterrupted α-Al2O3, which is the bars of oxidation resistance. In addition, according to one crossing point of the two curves, it was suggested that hot dipped aluminum steel should be annealed before used.  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