全文获取类型
收费全文 | 28159篇 |
免费 | 2559篇 |
国内免费 | 943篇 |
专业分类
电工技术 | 1231篇 |
综合类 | 1604篇 |
化学工业 | 5638篇 |
金属工艺 | 1071篇 |
机械仪表 | 1141篇 |
建筑科学 | 1570篇 |
矿业工程 | 444篇 |
能源动力 | 774篇 |
轻工业 | 4528篇 |
水利工程 | 530篇 |
石油天然气 | 731篇 |
武器工业 | 136篇 |
无线电 | 2268篇 |
一般工业技术 | 3329篇 |
冶金工业 | 1406篇 |
原子能技术 | 234篇 |
自动化技术 | 5026篇 |
出版年
2024年 | 89篇 |
2023年 | 356篇 |
2022年 | 942篇 |
2021年 | 1249篇 |
2020年 | 942篇 |
2019年 | 802篇 |
2018年 | 932篇 |
2017年 | 975篇 |
2016年 | 924篇 |
2015年 | 1256篇 |
2014年 | 1647篇 |
2013年 | 2116篇 |
2012年 | 2372篇 |
2011年 | 2560篇 |
2010年 | 2128篇 |
2009年 | 2026篇 |
2008年 | 1890篇 |
2007年 | 1752篇 |
2006年 | 1391篇 |
2005年 | 1058篇 |
2004年 | 722篇 |
2003年 | 560篇 |
2002年 | 472篇 |
2001年 | 309篇 |
2000年 | 261篇 |
1999年 | 219篇 |
1998年 | 345篇 |
1997年 | 245篇 |
1996年 | 178篇 |
1995年 | 158篇 |
1994年 | 108篇 |
1993年 | 91篇 |
1992年 | 57篇 |
1991年 | 57篇 |
1990年 | 47篇 |
1989年 | 44篇 |
1988年 | 34篇 |
1987年 | 37篇 |
1986年 | 34篇 |
1985年 | 33篇 |
1984年 | 29篇 |
1983年 | 28篇 |
1982年 | 15篇 |
1981年 | 25篇 |
1980年 | 19篇 |
1979年 | 15篇 |
1978年 | 15篇 |
1977年 | 22篇 |
1976年 | 30篇 |
1975年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
31.
32.
33.
Enrique Alexandre Antonio Pena Manuel Sobreira 《IEEE transactions on information technology in biomedicine》2006,10(4):809-811
This paper discusses the convenience of using two-dimensional (2-D) coding techniques for the compression of electrocardiogram (ECG) signals. These signals present a very clear periodicity that can be exploited by the use of a 2-D time/frequency transform to decorrelate it as much as possible. A brief theoretical approach is given to justify the use of this technique, and a comparison is made between a 2-D and a one-dimensional (1-D) uniform quantization scenarios. The influence of the error as well as the frame size on the estimation of the fundamental period is studied. 相似文献
34.
Francisco Hernndez-Beltrn Juan Carlos Moreno-Mayorga María de Lourdes Guzmn-Castillo Juan Navarrete-Bolaos Montserrat Gonzlez-Gonzlez Brent E. Handy 《Applied Catalysis A: General》2003,240(1-2):41-51
The evolution of the properties of a REUSY zeolite contained in a fluid cracking catalyst was investigated under laboratory steam deactivation procedures and in age fractions of the corresponding equilibrium catalyst (Ecat). The aging pattern, defined by the evolution of the zeolite surface area (ZSA) related to the decrease of the unit cell size (UCS), was similar between lab-steamed zeolites and Ecat fractions. A sharp drop in ZSA occurred at ca. 2.430 nm UCS. A study done by FT-IR spectroscopy suggested that zeolite dealumination initially took place more extensively on the sodalite cages and double six-member rings (D6R) of the structure and that the final collapse of the zeolite framework occurred through destruction of the 12-member rings (12M). This can be explained by a crystal fracture and break down process and disassembling of the sodalite cages in the faujasite structure. NH3 microcalorimetry showed that strong acid sites in faujasites are destroyed by steam aging, but this effect does not lead to a reduction in the cracking activity of the Ecat form. The microactivity test (MAT) showed that the specific activity declined sharply at 2.430 nm UCS. Differences in product selectivity were related to the extent of damage of the zeolite, extra-framework alumina and mesoporosity. While further aging canceled the effect attributed to extra-framework alumina differences attributed to mesoporosity increased. 相似文献
35.
A comprehensive study of hazelnut oil composition with comparisons to other vegetable oils,particularly olive oil. 总被引:4,自引:0,他引:4
Benitez-Sánchez Pedro Luis León-Camacho Manuel Aparicio Ramón 《European Food Research and Technology》2003,218(1):13-19
Crude and refined hazelnut oils from different countries were characterised by major and minor compounds. Fatty acids, triacylglycerides, waxes, sterols, methyl-sterols, terpenic and aliphatic alcohols, tocopherols, tocotrienols and hydrocarbons were identified and quantified by gas chromatography and high-performance liquid chromatography. The levels of these chemical compounds in hazelnut oils together with the equivalent carbon numbers and triacylglyceride carbon numbers, were compared with the results of analyses of samples of other vegetable oils. The statistical procedure of cluster analysis was used to characterise hazelnut oils versus other edible oils. 相似文献
36.
37.
Daniela M. Nevskaia Maria Luisa Rojas Cervantes Antonio Guerrero Ruíz Juan de Dios Lpez Gonzlez 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1995,63(3):249-256
Adsorption of Triton X-100 on various silica substrates has been investigated. A number of solids, including a natural quartz, this quartz washed with HCl acid and subsequently heated at 1273 K; two aerosils and one Kieselgel silicas were studied. These solids exhibit surface areas in the range of 5 to 430 m2 g?1. All the Triton adsorption isotherms display an S-shape at the adsorption temperatures studied (298 and 308 K). It has been found that the pretreatments of natural quartz (by water washing, impurities removed by acid and/or high temperature calcination) affect considerably the amounts of TX-100 adsorbed. Measurements of surface composition have been made by X-ray photoelectron spectroscopy (XPS) with particular emphasis on the presence of impurities and on the number of OH groups at the surface of the samples. The nature of the surface hydroxyl has also been studied by infrared spectroscopy. Furthermore, the specific number of hydroxyl groups on the surface of the silica samples has been determined by thermogravimetric analysis. Finally an attempt to correlate solid surface characteristics with adsorption isotherms has been developed. 相似文献
38.
OH Del Brutto 《Canadian Metallurgical Quarterly》1997,49(4):1185-1186
39.
F Sartucci L Bonfiglio C Del Seppia P Luschi S Ghione L Murri F Papi 《Canadian Metallurgical Quarterly》1997,769(2):362-366
cDNA selection was used to isolate coding sequences from cosmids mapping to the gene-rich telomeric region of human chromosome 21q. A novel cDNA, termed SMT3A, was isolated and mapped between the loci PFKL and D21S171, about 2.2 Mb proximal to the telomere. The predicted protein of 103 amino acids appears to be a homologue of the Saccharomyces cerevisiae SMT3 protein, whose gene was previously isolated as a suppressor of mutations in the MIF2 gene. The yeast MIF2 gene encodes an essential centromeric protein and shows homology to mammalian CENP-C, an integral component of active kinetochores. SMT3A was found to be highly homologous to two other recently isolated human genes, suggesting the presence of a new gene family. Homologous sequences were also found in protozoa, metazoa, and plants. Moreover, all predicted proteins show significant homology to ubiquitin. The proposed role of yeast SMT3 as centromeric protein and the strong evolutionary conservation of the SMT3A gene suggest an involvement of the encoded protein in the function and/or structure of the eukaryotic kinetochore. 相似文献
40.
AI Quintero Del Río 《Canadian Metallurgical Quarterly》1997,89(1-3):12-14
Motor vehicle accidents are the main cause of death and disability between 1 and 4 years of age. Since 1980 the Academy of Pediatrics has been promoting the correct use of car seats. The major reason that car seats are not fulfilling their full potential is their incorrect or lack of use. In order to evaluate parental knowledge about car seat use for children and their actual use in the population visiting HURRA, a survey was performed which demonstrated that only 57.6% of the parents interviewed had infant car seats and that only 83.3% of owners actually use it. As many as 94.4% had correct knowledge about car seat use, but the majority of correct information was not provided by the medical staff. The majority of parents use seat belts for their own protection but a significantly smaller percentage use car seats for their own children. 相似文献