全文获取类型
收费全文 | 32241篇 |
免费 | 2507篇 |
国内免费 | 1209篇 |
专业分类
电工技术 | 825篇 |
综合类 | 2007篇 |
化学工业 | 11409篇 |
金属工艺 | 1032篇 |
机械仪表 | 682篇 |
建筑科学 | 1941篇 |
矿业工程 | 839篇 |
能源动力 | 3123篇 |
轻工业 | 2309篇 |
水利工程 | 360篇 |
石油天然气 | 4860篇 |
武器工业 | 184篇 |
无线电 | 689篇 |
一般工业技术 | 3487篇 |
冶金工业 | 838篇 |
原子能技术 | 235篇 |
自动化技术 | 1137篇 |
出版年
2024年 | 129篇 |
2023年 | 526篇 |
2022年 | 1008篇 |
2021年 | 1200篇 |
2020年 | 1139篇 |
2019年 | 954篇 |
2018年 | 746篇 |
2017年 | 952篇 |
2016年 | 912篇 |
2015年 | 886篇 |
2014年 | 1604篇 |
2013年 | 1855篇 |
2012年 | 2268篇 |
2011年 | 2304篇 |
2010年 | 1840篇 |
2009年 | 1770篇 |
2008年 | 1541篇 |
2007年 | 1962篇 |
2006年 | 1803篇 |
2005年 | 1629篇 |
2004年 | 1376篇 |
2003年 | 1278篇 |
2002年 | 1030篇 |
2001年 | 902篇 |
2000年 | 780篇 |
1999年 | 685篇 |
1998年 | 559篇 |
1997年 | 453篇 |
1996年 | 384篇 |
1995年 | 296篇 |
1994年 | 260篇 |
1993年 | 205篇 |
1992年 | 154篇 |
1991年 | 122篇 |
1990年 | 109篇 |
1989年 | 68篇 |
1988年 | 46篇 |
1987年 | 36篇 |
1986年 | 37篇 |
1985年 | 24篇 |
1984年 | 21篇 |
1983年 | 11篇 |
1982年 | 15篇 |
1981年 | 5篇 |
1980年 | 12篇 |
1977年 | 4篇 |
1964年 | 5篇 |
1957年 | 3篇 |
1956年 | 3篇 |
1951年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
11.
12.
13.
Craig S. Long Albert A. Groenwold 《International journal for numerical methods in engineering》2004,61(6):837-855
Reduced integration is frequently used in evaluating the element stiffness matrix of quadratically interpolated finite elements. Typical examples are the serendipity (Q8) and Lagrangian (Q9) membrane finite elements, for which a reduced 2 × 2 Gauss–Legendre integration rule is frequently used, as opposed to full 3 × 3 Gauss–Legendre integration. This ‘softens’ these element, thereby increasing accuracy, albeit at the introduction of spurious zero energy modes on the element level. This is in general not considered problematic for the ‘hourglass’ mode common to Q8 and Q9 elements, since this spurious mode is non‐communicable. The remaining two zero energy modes occurring in the Q9 element are indeed communicable. However, in topology optimization for instance, conditions may arise where the non‐communicable spurious mode associated with the elements becomes activated. To effectively suppress these modes altogether in elements employing quadratic interpolation fields, two modified quadratures are employed herein. For the Q8 and Q9 membrane elements, the respective rules are a five and an eight point rule. As compared to fully integrated elements, the new rules enhance element accuracy due to the introduction of soft, higher‐order deformation modes. A number of standard test problems reveal that element accuracy remains comparable to that of the under‐integrated counterparts. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
14.
PDC钻头在东海西湖凹陷的实践与认识 总被引:1,自引:1,他引:0
文章针对在东海西湖凹陷六口井 31 1 .2mm及 2 1 5 .9mm井眼所使用的PDC钻头统计分析 ,并结合笔者自己使用PDC钻头的实践 ,提出使用PDC钻头时注意环节 ,建议针对西湖凹陷地层的特点选择适合该地区的PDC钻头类型 相似文献
15.
16.
An increasing number of connectionist models have been proposed to explain behavioral deficits in developmental disorders. These simulations motivate serious consideration of the theoretical implications of the claim that a developmental disorder fits within the parameter space of a particular computational model of normal development. The authors examine these issues in depth with respect to a series of new simulations investigating past-tense formation in Williams syndrome. This syndrome and the past-tense domain are highly relevant because both have been used to make strong theoretical claims about the processes underlying normal language acquisition. The authors conclude that computational models have great potential to advance psychologists' understanding of developmental deficits because they focus on the developmental process itself as a pivotal causal factor in producing atypical phenotypic outcomes. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
17.
Fernando J Beltrn F Javier Rivas Olga Gimeno 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2005,80(9):973-984
Photocatalytic ozonation (1O3 + VUV + TiO2), ozonation (O3), catalytic ozonation (O3 + TiO2), ozone photolysis (O3 + VUV), photocatalysis (TiO2 + VUV) and photolysis (VUV) have been compared in terms of formation of intermediates, extent of, mineralization (TOC, COD, chloride, nitrate) and kinetics in the aqueous treatment of three phenols (phenol, p‐chlorophenol and p‐nitrophenol). In all cases, photocatalytic ozonation led to lower degradation times for chemical oxygen demand and total organic carbon removal. Intermediates formed were similar in the different oxidation systems with some exceptions. They can be classified into three different types: polyphenols (resorcinol, catechol, hydroquinone), unsaturated carboxylic acids (maleic and fumaric acids) and saturated carboxylic acids (glyoxylic, formic and oxalic acids). First order kinetic equations have been checked for the oxidation processes studied in the case of the parent compound. Rate constants of these systems have also been calculated. Copyright © 2005 Society of Chemical Industry 相似文献
18.
PVDF中空纤维滤膜的形态结构 总被引:3,自引:0,他引:3
用L-S相转换法制备了聚偏氟乙烯(PVDF)中空纤维不对称滤膜。铸膜液由聚合物、溶剂和添加剂组成。用电子显微镜(SEM)考察了聚合物浓度、添加剂用量及种类对膜形态结构的影响。实验结果表明,聚合物浓度对膜形态结构有显著影响,当铸膜液中聚合物浓度较低时,无论用什么种类添加剂,都能形成大、且多的孔,但孔的形状随添加剂不同而异。当恒定聚合物浓度时,添加剂的用量对膜形态结构有很大的影响,但孔的大小及多少与添加剂含量的多少不成正比。 相似文献
19.
20.
进行了PAA(PolyacrylicAcid)-PSF(Polysulfone)交联复合膜的制备,研究了交联剂、添加剂对膜性能的影响,并通过扫描电镜观察了膜的断面结构.研究了PAA-PSF交联复合膜对低浓度有机醇类水溶液反渗透分离性能.发现对于1000×10-6乙醇水溶液截留率达到66.2%,透过流束可达0.9×10-6(m3·m-2·s-1).随醇的分子量的增加,截留率不断上升,对戊醇的截留率达94.3%,而透过流束则保持相对稳定.对不同结构醇类的分离性能研究表明,截留率存在有:tert->sec->iso->n-的规律. 相似文献