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   34991篇
  免费   1630篇
  国内免费   922篇
工业技术   37543篇
  2023年   327篇
  2022年   389篇
  2021年   656篇
  2020年   631篇
  2019年   592篇
  2018年   545篇
  2017年   746篇
  2016年   1060篇
  2015年   1827篇
  2014年   2175篇
  2013年   2038篇
  2012年   2258篇
  2011年   3484篇
  2010年   2875篇
  2009年   2876篇
  2008年   2433篇
  2007年   2424篇
  2006年   1838篇
  2005年   1533篇
  2004年   1355篇
  2003年   1329篇
  2002年   1141篇
  2001年   600篇
  2000年   428篇
  1999年   397篇
  1998年   299篇
  1997年   236篇
  1996年   169篇
  1995年   126篇
  1994年   132篇
  1993年   82篇
  1992年   57篇
  1991年   42篇
  1990年   44篇
  1989年   46篇
  1988年   20篇
  1987年   14篇
  1986年   17篇
  1985年   25篇
  1984年   30篇
  1983年   22篇
  1982年   33篇
  1981年   30篇
  1980年   79篇
  1979年   16篇
  1978年   5篇
  1977年   11篇
  1975年   6篇
  1974年   8篇
  1973年   9篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
随着科学技术的快速发展与进步,当今社会要求学生学习知识水平越来越高,要求其学习范围更为广泛。因此目前学生仅依凭英语课堂学习还远远不够,很多时候根本无法适应社会发展的需要,所以培养学生自学能力就显得非常重要。由此提出开发一款英语自学系统为英语爱好者提供自学英语平台。文章立足于Web网络,依托B/C结构,应用ASP.NET和数据库进行相互融入技术;然后从功能模块,数据库等设计详细分析本系统设计;最后从聊天室、BBS论坛、以及留言板等方面来实现本系统的在线沟通与交流,从而完成了本系统研究。该系统不但能使学生学习英语不受时空限制,而且对于提升他们学习英语效果与使用英语能力均有很大帮助。  相似文献   
2.
3.
通过溶剂热法制备BiOCl纳米片,共沉淀法制备Ag_2CO_3和复合催化剂Ag_2CO_3/BiOCl,研究各材料可见光催化降解罗丹明B的效果,确定Ag_2CO_3与BiOCl的最佳配比,并通过表征分析复合材料的结构和异质结光催化降解机理。结果表明,当Ag_2CO_3与BiOCl的质量比为50%时,Ag_2CO_3/BiOCl异质结催化剂的可见光催化效率最高,其一级动力学反应速率常数是BiOCl和Ag_2CO_3的6.79和12.58倍。紫外可见漫反射分析证明,Ag_2CO_3的加入使Ag_2CO_3/BiOCl对可见光的吸收增加,拓宽了光响应范围。XPS价带谱证明,调控后的BiOCl纳米片能带位置上移。通过自由基捕获实验和电子顺磁共振(ESR)证明,其主要活性物种是·O~-_2、h~+和·OH,从而推断Ag_2CO_3与BiOCl构成Z型异质结,相比Ⅱ型异质结拥有较高的氧化还原能力,可充分利用水中的溶解氧(O_2)和OH~-,大大提升了光催化效率。  相似文献   
4.
In this study, we investigate the immunomodulatory effects of a novel antimicrobial peptide, YD1, isolated from Kimchi, in both in vitro and in vivo models. We establish that YD1 exerts its anti-inflammatory effects via up-regulation of the Nrf2 pathway, resulting in the production of HO-1, which suppresses activation of the NF-κB pathway, including the subsequent proinflammatory cytokines IL-1β, IL-6, and TNF-α. We also found that YD1 robustly suppresses nitric oxide (NO) and prostaglandin E2 (PGE2) production by down-regulating the expression of the upstream genes, iNOS and COX-2, acting as a strong antioxidant. Collectively, YD1 exhibits vigorous anti-inflammatory and antioxidant activity, presenting it as an interesting potential therapeutic agent.  相似文献   
5.
S355钢作为低合金钢,在焊接过程中会伴随着固态相变现象。在考虑S355钢的固态相变效应基础上,建立了焊接过程的热弹塑性有限元模型。通过引入相变转变模型、相变塑性和相变体积模型,计算获得焊后组织分布云图,并分析了焊缝和热影响区典型节点的组织演变规律。结果表明,与不考虑固态相变效应相比,紧邻焊缝两侧的热影响区的Mises应力大幅降低,计算得到的残余应力值与实测值吻合较好。  相似文献   
6.
构建下转换荧光-适配体免疫层析试纸条用于食品中黄曲霉毒素B1(aflatoxin B1,AFB1)的快速高效检测。体系中AFB1存在会减弱下转换荧光-适配体纳米颗粒层析至T线时与AFB1半抗原的结合能力,从而导致下转换荧光信号衰减,进而实现对AFB1的高效检测。该方法在AFB1质量浓度1~40 ng/mL范围内与荧光信号呈良好的线性关系,线性相关系数为0.994,检测限为0.287 ng/mL。该方法利用稀土掺杂荧光纳米颗粒的长寿命发光及近红外荧光特性,有效降低了生物背景荧光干扰并提高了检测体系的特异性。该方法在AFB1的快速高灵敏检测中具有良好的应用前景。  相似文献   
7.
With the goal to produce a hard and tough coating intended for tribological applications, CrAlN/TiSiN nanolayer coating was prepared by alternative deposition of CrAlN and TiSiN layers. In the first part of the article, a detailed study of phase composition, microstructure, and layer structure of CrAlN/TiSiN coating is presented. In the second part, its mechanical properties, fracture and tribological behavior are compared to the nanocomposite TiSiN coating. An industrial magnetron sputtering unit was used for coating deposition. X-ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy were used for compositional and microstructural analysis. Mechanical properties and fracture behavior were studied by instrumented indentation and focused ion beam techniques. Tribological properties were evaluated by ball-on-disk test in a linear reciprocal mode. A complex layer structure was found in the nanolayer coating. The TiSiN layers were epitaxially stabilized inside the coating which led to formation of dislocations at interfaces, to introduction of disturbances in the coating growth, and as a result, to development of fine-grained columnar microstructure. Indentation load required for the onset of fracture was twice lower for the nanolayer CrAlN/TiSiN, compared to the nanocomposite TiSiN coating. This agrees very well with their mechanical properties, with H3/E2 being twice higher for the TiSiN coating. However, the nanolayer coating experienced less severe damage, which had a strong impact on tribological behavior. A magnitude of order lower wear rate and four times lower steady state friction coefficient were found for the nanolayer coating.  相似文献   
8.
《Ceramics International》2021,47(24):34278-34288
Materials exhibiting colossal dielectric constant are the most sought-after materials due to their variety of applications in various electronics industries. NiFe2O4 and LaFeO3 belonging to the spinel and perovskite structures, respectively, were coupled into a nanocomposite by adapting a one-pot sol-gel synthesis. The ratio of NiFe2O4:LaFeO3 was varied and the synthesized materials were studied for their dielectric behaviors. Interestingly, among the samples studied, the nanocomposite with the ratio of 1:2 of NiFe2O4–LaFeO3 exhibited a high dielectric constant value of 10390 at a frequency of 1 kHz with a several-fold increase in conductivity. The high conductivity resulted in a high dielectric loss. The origin of such a high dielectric constant and loss have been attributed to the Maxwell-Wagner type space charge polarization arising from the microstructure that consists of large and continuous grain boundaries, and the conducting phase at the interface, respectively.  相似文献   
9.
The introduction of multiple heterogeneous interfaces in a ceramic is an efficient way to increase its thermal resistance. Novel porous SiC–SiO2–Al2O3–TiO2 (SSAT) ceramics were fabricated to achieve multiple heterogeneous interfaces by sintering equal volumes of SiC, SiO2, Al2O3, and TiO2 compacted powders with polysiloxane as a bonding phase and carbon as a template at 600 °C in air. The porosity could be controlled between 66% and 74% by adjusting the amounts of polysiloxane and the carbon template. The lowest thermal conductivity (0.059 W/(m·K) at 74% porosity) obtained in this study is an order of magnitude lower than those (0.2–1.3 W/(m·K)) of porous monolithic SiC, SiO2, Al2O3, and TiO2 ceramics at an equivalent porosity. The typical specific compressive strength value of the porous SSAT ceramics at 74% porosity was 3.2 MPa cm3/g.  相似文献   
10.
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