全文获取类型
收费全文 | 153036篇 |
免费 | 11790篇 |
国内免费 | 8941篇 |
专业分类
电工技术 | 6094篇 |
技术理论 | 2篇 |
综合类 | 10211篇 |
化学工业 | 47094篇 |
金属工艺 | 13101篇 |
机械仪表 | 5264篇 |
建筑科学 | 6124篇 |
矿业工程 | 3000篇 |
能源动力 | 5623篇 |
轻工业 | 9286篇 |
水利工程 | 1227篇 |
石油天然气 | 7677篇 |
武器工业 | 920篇 |
无线电 | 14037篇 |
一般工业技术 | 19836篇 |
冶金工业 | 7004篇 |
原子能技术 | 2032篇 |
自动化技术 | 15235篇 |
出版年
2024年 | 454篇 |
2023年 | 2371篇 |
2022年 | 4764篇 |
2021年 | 5255篇 |
2020年 | 4113篇 |
2019年 | 3756篇 |
2018年 | 3535篇 |
2017年 | 4371篇 |
2016年 | 4832篇 |
2015年 | 4742篇 |
2014年 | 7597篇 |
2013年 | 8200篇 |
2012年 | 9638篇 |
2011年 | 11325篇 |
2010年 | 8922篇 |
2009年 | 10470篇 |
2008年 | 9150篇 |
2007年 | 11326篇 |
2006年 | 10702篇 |
2005年 | 8314篇 |
2004年 | 6293篇 |
2003年 | 5951篇 |
2002年 | 4685篇 |
2001年 | 3752篇 |
2000年 | 3456篇 |
1999年 | 2835篇 |
1998年 | 2175篇 |
1997年 | 1628篇 |
1996年 | 1500篇 |
1995年 | 1246篇 |
1994年 | 1119篇 |
1993年 | 843篇 |
1992年 | 701篇 |
1991年 | 573篇 |
1990年 | 485篇 |
1989年 | 380篇 |
1988年 | 277篇 |
1987年 | 227篇 |
1986年 | 229篇 |
1985年 | 216篇 |
1984年 | 186篇 |
1983年 | 127篇 |
1982年 | 140篇 |
1981年 | 144篇 |
1980年 | 139篇 |
1979年 | 105篇 |
1978年 | 96篇 |
1977年 | 98篇 |
1976年 | 103篇 |
1975年 | 101篇 |
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
101.
Carboxymethyl-2-diethylaminoethylcellulose (CM-DEAE cellulose) was prepared by etherification of carboxymethylcellulose with diethylaminoethyl chloride in a NaOH solution. The behaviour of CM-DEAE cellulose in aqueous solution was studied by viscosity and GPC measurements. The degree of substitution (DS) and existing states of DEAE substituents were examined by the use of proton NMR, and those of the CM substituents were observed with FT-IR. The results reveal that the reduced viscosity and apparent molecular size of CM-DEAE cellulose vary with the concentration of sodium chloride and changes in pH and DS. These phenomena can be explained in terms of inter- and intra-molecular ionic interactions. 相似文献
102.
Analysis of characteristic odors from human male axillae 总被引:7,自引:0,他引:7
Xiao -nong Zeng James J. Leyden Henry J. Lawley Kiyohito Sawano Isao Nohara George Preti 《Journal of chemical ecology》1991,17(7):1469-1492
A number of studies concerning the analysis of axillary odors have assumed that the characteristic odor produced in the axillae is due to volatile steroids and isovaleric acid. Organoleptic evaluation of Chromatographic eluants from axillary extracts was employed to isolate the region in the chromatogram where the characteristic odor eluted. The odor of the dissolved eluant was eliminated when it was treated with base, suggesting that acids make up the characteristic axillary odor. Subsequent extraction of the pH-adjusted axillary extract in conjunction with organoleptic evaluation of the Chromatographic eluant, preparative gas chromatography, and analysis by GC-MS as well as GC-FTIR showed the presence of a number of C6 to C11 straight-chain, branched, and unsaturated acids as important contributors to the axillary odor. The major odor component is (E)-3-methyl-2-hexenoic acid. Three homologous series of minor components are also important odor contributors; these consist of the terminally unsaturated acids, the 2-methyl-C6 to -C10 acids and the 4-ethyl-C5 to -C11 acids. These types of acids have not been reported previously as components of the human axillary secretions and have not been proposed previously as part of the principal odor components in this area. 相似文献
103.
The chemical reaction between lanthanum oxide and molybdenum carbide was studied by thermodynamic calcu-lation, thermal analysis and in-situ X-ray Photoelectron Spectroscopy. The theoretical results show that at the environment allowing for the evaporation of lanthanum, such as in high vacuum, La2O3 in the La2O3-Mo materials can be reduced to metallic lanthanum by molybdenum carbide (Mo2C). To confirm the conclusion, many analysis methods such as XRD, SPS, and TG-DTA were taken. The experimental results show that the chemical state of lanthanum changes during heat-ing. It was proved, for the first time, that reacted metallic lanthanum appears at the surface of this kind of material at high temperature. 相似文献
104.
Abstract— We have developed a process to fabricate optical components, such as a lens, prism, or diffuser, directly on to a glass substrate. Processes include precision mastering by diamond cutting and multi‐layer photopolymer (2P) molding to realize flat surfaces and the integration of multiple components with an alignment within a few micrometers. 相似文献
105.
沈大海 《电脑编程技巧与维护》2007,(10):69-73
介绍使用J2ME技术开发益智游戏华容道的实现结构,以及面向对象设计思想、算法设计、数组在游戏设计中的应用 相似文献
106.
H. de Groot 《Materialwissenschaft und Werkstofftechnik》2007,38(12):965-968
Ischemia‐reperfusion injury of the bone occurs due to traumatic and non‐traumatic alterations affecting blood supply to the bone. It is likely to occur also upon insertion of an implant. Ischemia‐reperfusion injury of the bone has been studied by interruption of blood supply in situ, in limb replantation/transplantation models, in revascularized bone grafts and non‐vascularized bone fragments, as well as in isolated cultured cells. All cells of the bone are affected, including osteoblasts, osteocytes, osteoclasts, chondrocytes, and bone marrow cells. Critical ischemia times for induction of bone cell death, either in the ischemic period or following reperfusion, are in the range of 3 to 7 h. These critical ischemia times are significantly increased by decreasing the temperature from 37 °C to 0–4 °C. Anoxia is the most likely trigger of cell injury in the ischemic phase. In the reperfusion phase, reactive oxygen species are decisively involved in the injurious process. In general, however, the available information on the mechanism of ischemia‐reperfusion injury of the bone is relatively sparse. On the other hand, there are clear similarities to the mechanisms of ischemia‐reperfusion injury known from other organs, and there is a clear potential for protection against ischemia‐reperfusion injury of the bone. 相似文献
107.
U(Ⅳ)-U(Ⅵ)同位素交换反应动力学研究 Ⅰ.Fe~(2+)对U(Ⅳ)-U(Ⅵ)同位素交换反应的催化作用 总被引:1,自引:0,他引:1
一、前言由于U(IV)-U(VI)同位素交换体系具有相当大的同位素效应和很好的稳定性,并且容易实现两相回流,这对于分离U同位素的工业应用都是十分有利的。但是,U(IV)-U(VI)同位素交换反应速度非常慢,常温下H~+浓度为1.0—4.0 mol/l时,速度常数为1.0×10~(-4)l~2/mol·s。因此要用U(IV)-U(VI)交换体系浓缩铀同位素,必须研究U(IV)-U(VI)交换反应动力学,找到加快交换反应的方法。 相似文献
108.
109.
本文用不同的测试技术和方法测定了锗酸铋(BGO)单晶的比热(300~800K)热膨胀系数(100~1100K)和导温系数(140~700K),进而导出了 BGO 单晶不同温度下的导热系数、定容比热、德拜温度和格虑内森数。本文还对 BGO 单晶热物理性质的变化规律作了理论解释。 相似文献
110.