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   92828篇
  免费   791篇
  国内免费   2167篇
电工技术   1317篇
综合类   888篇
化学工业   8779篇
金属工艺   2640篇
机械仪表   4548篇
建筑科学   5322篇
矿业工程   3361篇
能源动力   480篇
轻工业   17410篇
水利工程   2008篇
石油天然气   2514篇
武器工业   405篇
无线电   8991篇
一般工业技术   28922篇
冶金工业   1893篇
原子能技术   952篇
自动化技术   5356篇
  2021年   252篇
  2015年   253篇
  2014年   497篇
  2013年   525篇
  2012年   8538篇
  2011年   10674篇
  2010年   2390篇
  2009年   1476篇
  2008年   7418篇
  2007年   7087篇
  2006年   6071篇
  2005年   5467篇
  2004年   4889篇
  2003年   3950篇
  2002年   3560篇
  2001年   3029篇
  2000年   2898篇
  1999年   1891篇
  1998年   1224篇
  1997年   1277篇
  1996年   1216篇
  1995年   1180篇
  1994年   1201篇
  1993年   729篇
  1992年   932篇
  1991年   1022篇
  1990年   1004篇
  1989年   992篇
  1988年   788篇
  1987年   959篇
  1986年   917篇
  1985年   990篇
  1984年   934篇
  1983年   873篇
  1982年   850篇
  1981年   740篇
  1980年   601篇
  1979年   489篇
  1978年   318篇
  1977年   345篇
  1976年   358篇
  1975年   403篇
  1974年   396篇
  1973年   271篇
  1972年   312篇
  1971年   278篇
  1970年   272篇
  1967年   375篇
  1965年   437篇
  1964年   255篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
At present, the development and implementation of digital transformation are the keys to promoting high-quality industry development. The new digital fabrication method of robotic 3D printing is a research area being studied by many to tackle the issue of the declining productivity of traditional construction methods. Although many studies have been done, most of the current 3D printing projects are facing limitations in terms of scale. In order to bridge the gap, this article proposed a mass customization 3D printing framework system for large-scale projects. This article discusses how mass customization is made possible through the joint operation of the FUROBOT software and 3D printing hardware. By taking the east gate of Nanjing Happy Valley Plaza as a case study, the article demonstrates and studies the feasibility of the large-scale mass customization 3D printing framework system.  相似文献   
2.
Watermelon peel residues were used to produce a new biochar by dehydration method. The new biochar has undergone two methods of chemical modification and the effect of this chemical modification on its ability to adsorb Cr(VI) ions from aqueous solution has been investigated. Three biochars, Melon-B, Melon-BO-NH_2 and Melon-BO-TETA, were made from watermelon peel via dehydration with 50% sulfuric acid to give Melon-B followed by oxidation with ozone and amination using ammonium hydroxide to give Melon-BO-NH_2 or Triethylenetetramine(TETA) to give Melon-BO-TETA. The prepared biochars were characterized by BET, BJH,SEM, FT-IR, TGA, DSC and EDAX analyses. The highest removal percentage of Cr(VI) ions was 69% for Melon-B,98% for Melon-BO-NH_2 and 99% for Melon-BO-TETA biochars of 100 mg·L~(-1) Cr(VI) ions initial concentration and 1.0 g·L~(-1) adsorbents dose. The unmodified biochar(Melon-B) and modified biochars(Melon-BO-NH_2 and Melon-BO-TETA) had maximum adsorption capacities(Qm) of 72.46, 123.46, and 333.33 mg·g~(-1), respectively.The amination of biochar reduced the pore size of modified biochar, whereas the surface area was enhanced.The obtained data of isotherm models were tested using different error function equations. The Freundlich,Tempkin and Langmuir isotherm models were best fitted to the experimental data of Melon-B, Melon-BO-NH_2 and Melon-BO-TETA, respectively. The adsorption rate was primarily controlled by pseudo-second–order rate model. Conclusively, the functional groups interactions are important for adsorption mechanisms and expected to control the adsorption process. The adsorption for the Melon-B, Melon-BO-NH_2 and Melon-BO-TETA could be explained for acid–base interaction and hydrogen bonding interaction.  相似文献   
3.
4.
人体大脑和身体的发育,需要从食物中摄取均衡的营养物质。人类大脑是区分人类和其他动物的特征。食物中的必需脂肪酸是机体组织结构和功能的必要组成部分。Omega-6(O6)亚油酸(LA6)是皮肤组织的组成成分,且是炎症、血栓形成、免疫和其他信号分子的前体;Omega-3(O3)α-亚麻酸(ALA3),特别是其长链代谢产物——二十二碳六烯酸(DHA3),是大脑、视网膜和部分神经组织中的关键组分。从富含LA6脂肪酸(缺乏O3脂肪酸)的植物籽中提取出的廉价而优质油脂,是20世纪的西方国家食品工业生产的主要脂肪来源。在代谢通路中,高浓度的LA6脂肪酸可拮抗O3脂肪酸代谢,造成O3脂肪酸不足,因此,在给怀孕动物的饲料中,只提供富含LA6但缺乏O3脂肪酸的油脂作为唯一的脂肪来源,会导致幼崽大脑发育不良。过去20~30年的研究表明,低含量LA6且含DHA3的油脂可改善大脑的功能。近年来的研究较多集中在营养因素对大脑发育的影响,最新研究数据表明,脂肪酸平衡对营养不良儿童的大脑发育尤为重要。世界卫生组织(WHO)越来越重视大脑的营养健康,通过其下属的食品法典委员会,建议用于治疗严重急性营养不良儿童的即食治疗食品中,使用含有均衡脂肪酸组成/构成的脂肪。同样,脂肪酸均衡对老年人可能也很重要。目前,业界已经有了调整油脂成分的方法,以确保脂肪酸均衡,从而维持人体整个生命周期的大脑健康。  相似文献   
5.
Covalent triazine frameworks (CTFs) have been recently employed for visible light-driven photocatalysis due to their unique optical and electronic properties. However, the usually highly hydrophobic nature of CTFs, which originates from their overall aromatic backbone, leads to limitations of CTFs for applications in aqueous media. In this study, we aim to extend the range of the application media of CTFs and design hybrid material of a CTF and mesoporous silica (SBA-15) for efficient photocatalysis in aqueous medium. A thiophene-containing CTF was directly synthesized in mesopores of SBA-15. Due to the high surface area and the added hydrophilic properties by silica, the hybrid material demonstrated excellent adsorption of organic molecules in water. This leads not only to high photocatalytic performance of the hybrid material for the degradation of organic dyes in water, but also for efficient photocatalysis in solvent-free and solid state. Furthermore, the reusability, stability and easy recovery of the hybrid material offers promising metal-free heterogeneous photocatalyst for broader applications in different reaction media.  相似文献   
6.
The objective of this research is the rapid reconstruction of ancient buildings of historical importance using a single image. The key idea of our approach is to reduce the infinite solutions that might otherwise arise when recovering a 3D geometry from 2D photographs. The main outcome of our research shows that the proposed methodology can be used to reconstruct ancient monuments for use as proxies for digital effects in applications such as tourism, games, and entertainment, which do not require very accurate modeling. In this article, we consider the reconstruction of ancient Mughal architecture including the Taj Mahal. We propose a modeling pipeline that makes an easy reconstruction possible using a single photograph taken from a single view, without the need to create complex point clouds from multiple images or the use of laser scanners. First, an initial model is automatically reconstructed using locally fitted planar primitives along with their boundary polygons and the adjacency relation among parts of the polygons. This approach is faster and more accurate than creating a model from scratch because the initial reconstruction phase provides a set of structural information together with the adjacency relation, which makes it possible to estimate the approximate depth of the entire structural monument. Next, we use manual extrapolation and editing techniques with modeling software to assemble and adjust different 3D components of the model. Thus, this research opens up the opportunity for the present generation to experience remote sites of architectural and cultural importance through virtual worlds and real-time mobile applications. Variations of a recreated 3D monument to represent an amalgam of various cultures are targeted for future work.  相似文献   
7.
For the characterization of the behaviors of a metal material in events like expanding warheads, it is necessary to know its strength and ductility at high strain rates, around 104e105/s. The flyer plate impact testing produces the uniform stress and strain rates but the testing is expensive. The Taylor test is relatively inexpensive but produces non-uniform stress and strain fields, and the results are not so easily inferred for material modeling. In the split-Hopkinson bar(SHB), which may be used in compression, tension and torsion testing, the strain rates never exceeds 103/s. In the present work, we use the expanding ring test where the strain rate is 104e105/s. A streak camera is used to examine the expanding ring velocity, and a water tank is used to collect the fragments. The experimental results are compared with the numerical simulations using the hydrocodes AUTODYN, IMPETUS Afea and a regularized smooth particle(RSPH) software. The number of fragments increases with the increase in the expansion velocity of the rings. The number of fragments is similar to the experimental results. The RSPH software shows much the same results as the AUTODYN where the Lagrangian solver is used for the ring. The IMPETUS Afea solver shows a somewhat different fragmentation characteristic due to the node splitting algorithm that induces pronounced tensile splitting.  相似文献   
8.
正1.引言世界日益增长的人口使粮食需求增加,加之农业集约化生产导致农药的广泛使用,目的是使作物产量最大化。历史表明,农药管理不善可能会对人类和动物的健康以及环境造成严重的危害。监管机构要求合理使用杀虫剂,减少食品和环境中的农药残留,并提供关于农药及其残留物风险的更多信息。从这个意义上讲,国家和国际机构以及环保机构都对保护公众健康和环境进行了严格的监管。  相似文献   
9.
The critical properties of the mixed manganite La0.67–x Y x Ba0.23Ca0.1Mn O3 with x=0.10 and x=0.15 around the paramagnetic(PM)-ferromagnetic(FM) phase transition were investigated through various techniques. These involved modified Arrott plots, Kouvel-Fisher method and Widom scaling relation. Magnetic data, analyzed in the critical region, using the above methods, yielded the critical exponents for(x=0.10) La0.57Y0.10Ba0.23Ca0.1Mn O3(β=0.312±0.002 and γ=1.147±0.003 at T C=299.23±0.05 K). Moreover, the estimated critical exponents of(x=0.15) La0.52Y0.15Ba0.23Ca0.1Mn O3 were β=0.286±0.004 and γ=0.943±0.002 at T C=289.53±0.06 K. The critical exponents’ values were close to the theoretical values of 3D-Ising model and tricritical mean-field model. These results suggested that the present composition should be close to a tricritical point in the La0.67–x Y x Ba0.23Ca0.1Mn O3 phase diagram. Expressing the field dependence as ΔS M∝H n allowed us to establish a relationship between the exponent n and the critical exponents of the material and to propose a phenomenological universal curve for the field dependence of ΔS M.  相似文献   
10.
在这个泛偶像的时代,有太多风采照人、气质高雅的“星”和学富五车、雄韬伟略的“家”,他们固然值得仰望和崇拜;但是,这也是一个反偶像的时代,当正统的“偶像文化”被推到极致后,许多人产生“审美疲劳”,他们开始有意识地颠覆传统,告别英雄、躲避崇高。“芙蓉姐姐”的出现和风起云涌正是如此:“她颠覆了理想型偶像的高大全假大空,掏出大众心中的真、小乃至庸常的一面,甚至以反讽、自嘲的面目出现。”殊途同归的是,在民众的集体狂欢之后,所谓的反偶像,最终又走上了炮制偶像的路子——在博客江湖,一切成为平民的现实:一个渺小的,甚至和明星毫无关联的  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