全文获取类型
收费全文 | 198569篇 |
免费 | 23918篇 |
国内免费 | 24019篇 |
专业分类
电工技术 | 18672篇 |
技术理论 | 8篇 |
综合类 | 13851篇 |
化学工业 | 41011篇 |
金属工艺 | 7925篇 |
机械仪表 | 12470篇 |
建筑科学 | 8703篇 |
矿业工程 | 2279篇 |
能源动力 | 6564篇 |
轻工业 | 14765篇 |
水利工程 | 2449篇 |
石油天然气 | 7325篇 |
武器工业 | 1942篇 |
无线电 | 30636篇 |
一般工业技术 | 20856篇 |
冶金工业 | 4174篇 |
原子能技术 | 3257篇 |
自动化技术 | 49619篇 |
出版年
2024年 | 1058篇 |
2023年 | 3593篇 |
2022年 | 6402篇 |
2021年 | 7410篇 |
2020年 | 7145篇 |
2019年 | 6488篇 |
2018年 | 5991篇 |
2017年 | 8154篇 |
2016年 | 8805篇 |
2015年 | 9983篇 |
2014年 | 9733篇 |
2013年 | 12971篇 |
2012年 | 14667篇 |
2011年 | 16653篇 |
2010年 | 11943篇 |
2009年 | 11678篇 |
2008年 | 12890篇 |
2007年 | 14367篇 |
2006年 | 13718篇 |
2005年 | 11813篇 |
2004年 | 10020篇 |
2003年 | 7991篇 |
2002年 | 6138篇 |
2001年 | 4719篇 |
2000年 | 4067篇 |
1999年 | 3402篇 |
1998年 | 2794篇 |
1997年 | 2268篇 |
1996年 | 1819篇 |
1995年 | 1521篇 |
1994年 | 1300篇 |
1993年 | 952篇 |
1992年 | 780篇 |
1991年 | 615篇 |
1990年 | 505篇 |
1989年 | 367篇 |
1988年 | 286篇 |
1987年 | 178篇 |
1986年 | 175篇 |
1985年 | 233篇 |
1984年 | 206篇 |
1983年 | 145篇 |
1982年 | 199篇 |
1981年 | 99篇 |
1980年 | 95篇 |
1979年 | 23篇 |
1978年 | 15篇 |
1977年 | 23篇 |
1976年 | 14篇 |
1959年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
191.
192.
193.
Crystallization and thermoelectric properties of poly(ε-caprolactone) (PCL)/poly(vinyl butyral) (PVB)/montmorillonite (MMT) nanocomposites containing carbon black (CB) have been studied as a functions of a small amount of amorphous PVB content and a wide range of molecular weight of PVB. X-ray diffraction data of PCL/PVB/MMT nanocomposites indicates most of the swellable silicate layers are exfoliated and randomly dispersed into PCL/PVB system. The band spacings of PCL spherulites in PCL/PVB/MMT nanocomposites decrease with increasing PVB content, and this indicates that increasing the PVB content greatly shortens the period of lamellar twisting. The presence of 1 wt% MMT and higher molecular weight of PVB also shorten the period of PCL lamellar twisting. Nucleation and crystallization parameters, such as growth rate G and Avrami exponent n, can be determined by using POM and DSC isothermally crystallized at 41 °C. For samples with the same CB content, the intensity of positive temperature coefficient (PTC) (IPTC, defined as the ratio of peak resistivity to resistivity at room temperature) of the nanocomposites was increased as the content and the molecular weight of PVB increases. The change of the PTC property related to the morphological difference (i.e. period of lamellar twisting) in the nanocomposites can be discussed. 相似文献
194.
Sipra Mahapatra Turaga P. Prasad 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1992,53(2):201-203
Hydrolysis of Fe(OH)SO4 was carried out in the presence of metallic iron in order to prevent the formation of iron(III) oxides with strongly bonded sulphate. Under the conditions of the experiment, the products were found to be mixtures of ?-Fe2O3 and α-FeOOH. The occluded sulphate, if any, could be easily washed out with water. The hydrolysis reaction passes through an equilibrium state before coming to completion. The entropy with enthalpy of the hydrolysis corresponding to the equilibrium state were found to be 4 e.u. and 0·5 kJ/mol, respectively. The activation energy of the hydrolysis reaction was found to be 21 kJ/mol. 相似文献
195.
The effects of glycol methacrylate as a dehydrating agent on the dimensional changes of liver tissue
The dimensional changes of liver sections during the course of processing with glycol methacrylate (GMA) or with ethanol are described. Tissue processing with ethanol served as a control. During prolonged processing steps (24 h each), linear shrinkage of tissue specimens dehydrated with GMA at room temperature was 13.2%. Subsequent infiltration with GMA resulted in trivial swelling, and polymerization in slight shrinkage (2.3%). In comparison, processing with cold GMA resulted in shrinkage during dehydration (about 10.8%), a slight swelling in pure GMA, followed by shrinkage during polymerization (2.2%). Short routine processing schedules resulted in similar shrinkage/swelling patterns, although precise values differed slightly. In all experiments, ethanolic dehydration resulted in smaller dimensional tissue changes than did GMA dehydration. The dimensional changes of tissue sections during stretching on water, mounting and drying compensated for the major part of the shrinkage manifested during processing. 相似文献
196.
197.
198.
采用二甲苯为溶剂,将不同乙烯含量(5% ̄15%质量)的抗冲聚丙烯用特定程序进行分级,将各样品分为室温下可溶于甲苯和不可溶于甲苯的两部分。使用^13C-NMR方法和FT-IR方法对各组分进行表征,明确了乙烯链段在聚丙烯链上的分布,并在此基础上提出了产生这种链结构的聚合工艺的特点。 相似文献
199.
针对气测录井中外源气、二次循环气对油气显示层解释的干扰问题,该文提出了用差分色谱法来消除其影响,并就其概念和实现方法做了介绍;对差分色谱的测量条件及影响因素进行了分析,文章还列举了差分色谱的录井应用实例。在满足差分色谱测量条件的前提下,该方法有利于气测录井解释和油气水层评价,为气测录井半定量或定量解释提供一种方法和途径。 相似文献
200.
Francisco Jos Alguacil Concepcin Caravaca María Isabel Martín 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2003,78(10):1048-1053
The transport of chromium(VI) through a flat‐sheet supported liquid membrane containing Cyanex 921 as a carrier has been investigated. The permeation of the metal is investigated as a function of various experimental variables: hydrodynamic conditions, concentration of chromium(VI) and HCl in the feed phase, carrier concentration and diluent in the membrane and strippant concentration in the stripping phase. The mass transfer coefficient and the thickness of the aqueous boundary layer were calculated from the experimental data. Furthermore, the selectivity of Cyanex 921‐based flat‐sheet supported liquid membrane towards different metal ions and the behaviour of the system against other carriers are presented. Copyright © 2003 Society of Chemical Industry 相似文献