全文获取类型
收费全文 | 169680篇 |
免费 | 13787篇 |
国内免费 | 11259篇 |
专业分类
电工技术 | 10145篇 |
技术理论 | 3篇 |
综合类 | 11408篇 |
化学工业 | 38216篇 |
金属工艺 | 12271篇 |
机械仪表 | 11291篇 |
建筑科学 | 6341篇 |
矿业工程 | 3509篇 |
能源动力 | 5171篇 |
轻工业 | 11334篇 |
水利工程 | 1742篇 |
石油天然气 | 6701篇 |
武器工业 | 1431篇 |
无线电 | 20893篇 |
一般工业技术 | 20608篇 |
冶金工业 | 5453篇 |
原子能技术 | 2058篇 |
自动化技术 | 26151篇 |
出版年
2024年 | 573篇 |
2023年 | 2632篇 |
2022年 | 4568篇 |
2021年 | 5446篇 |
2020年 | 4686篇 |
2019年 | 4426篇 |
2018年 | 4072篇 |
2017年 | 5208篇 |
2016年 | 5643篇 |
2015年 | 5747篇 |
2014年 | 8298篇 |
2013年 | 9383篇 |
2012年 | 10307篇 |
2011年 | 12720篇 |
2010年 | 10034篇 |
2009年 | 11413篇 |
2008年 | 10526篇 |
2007年 | 11789篇 |
2006年 | 11020篇 |
2005年 | 9123篇 |
2004年 | 7574篇 |
2003年 | 7103篇 |
2002年 | 5782篇 |
2001年 | 4515篇 |
2000年 | 4134篇 |
1999年 | 3292篇 |
1998年 | 2472篇 |
1997年 | 1965篇 |
1996年 | 1818篇 |
1995年 | 1684篇 |
1994年 | 1524篇 |
1993年 | 1239篇 |
1992年 | 964篇 |
1991年 | 661篇 |
1990年 | 445篇 |
1989年 | 414篇 |
1988年 | 275篇 |
1987年 | 209篇 |
1986年 | 215篇 |
1985年 | 138篇 |
1984年 | 107篇 |
1983年 | 83篇 |
1982年 | 90篇 |
1981年 | 76篇 |
1980年 | 64篇 |
1979年 | 52篇 |
1978年 | 32篇 |
1977年 | 33篇 |
1976年 | 40篇 |
1975年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
随着计算机网络技术的发展,远程教学系统的结构发生了重大的变化,逐步由原来的客户机/服务器(C/S)结构转变为基于Internet的浏览器/服务器(B/S)结构。本文提出了基于CORBA技术的B/S结构系统模型。分析了其运行过程,并与传统的结构进行了比较,指明了其优越性。在本文的结尾。指出了使用这种技术的一个具体例子。 相似文献
42.
43.
介绍了3G技术在国内外的发展情况,阐述了发展趋势,对3G技术的分类和所采用的主流技术、标准化情况进行了论述,并对CDMA2000,WCDMA和TD-SCDMA三种3G的三大主流应用技术标准进行比较分析。 相似文献
44.
45.
Diphenylzinc, alone or in combination with water and butanone as coinitiators, was used as a polymerization initiator system for a variety of lactones at varying temperatures. The resulting data indicate that the course of the polymerization is greatly influenced by the lactone structure, as well as by the molar ratio of coinitiator to diphenylzinc. When used alone, diphenylzinc exhibited high activity as an initiator in δ‐valerolactone polymerizations, although it was less efficient when used in the β‐butyrolactone and the β‐propiolactone polymerizations. Activity in the polymerization of β‐lactones was increased by adding small amounts of butanone or water. It was also observed that the diphenylzinc–butanone combination was more effective than the diphenylzinc–water mixture in the polymerizations of β‐butyrolactone and β‐propiolactone. Copyright © 2003 Society of Chemical Industry 相似文献
46.
Use of the Retarded Solution-Reprecipitation Process to Attain a Higher Initial Permeability in MnZn Ferrites 总被引:1,自引:0,他引:1
Miha Drofenik rej nidari Darko Makovec 《Journal of the American Ceramic Society》2003,86(9):1601-1604
We investigated the effect of various amounts of liquid phase on microstructure development during sintering and the resulting magnetic permeability of MnZn ferrite (MZF) samples. Our results revealed that the microstructure and the final magnetic permeability depend on the thickness of the liquid-phase film during sintering. The solution-reprecipitation (S-R) process, which is associated with an intensive microstructure development in MZF, starts when a continuous liquid-phase film of critical thickness δo , which wets the MZF grains, is formed. The solid-state sintering that takes place before the formation of the continuous liquid-phase film is essential for the final microstructure of MZF. 相似文献
47.
A cell vertex finite volume method for the solution of steady compressible turbulent flow problems on unstructured hybrid
meshes of tetrahedra, prisms, pyramids and hexahedra is described. These hybrid meshes are constructed by firstly discretising
the computational domain using tetrahedral elements and then by merging certain tetrahedra. A one equation turbulence model
is employed and the solution of the steady flow equations is obtained by explicit relaxation. The solution process is accelerated
by the addition of a multigrid method, in which the coarse meshes are generated by agglomeration, and by parallelisation.
The approach is shown to be effective for the simulation of a number of 3D flows of current practical interest.
Sponsored by The Research Council of Norway, project number 125676/410
Dedicated to the memory of Prof. Mike Crisfield, a respected colleague 相似文献
48.
Mitsuo Miyazawa Hideki Kawazoe Mitsuro Hyakumachi 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2003,78(6):620-625
The microbial transformation of l‐menthol ( 1 ) was investigated by using 12 isolates of soil‐borne plant pathogenic fungi, Rhizoctonia solani (AG‐1‐IA Rs24, Joichi‐2, RRG97‐1; AG‐1‐IB TR22, R147, 110.4; AG‐1‐IC F‐1, F‐4, P‐1; AG‐1‐ID RCP‐1, RCP‐3, and RCP‐7) as a biocatalyst. Rhizoctonia solani F‐1, F‐4 and P‐1 showed 89.7–99.9% yields of converted product from 1 , RCP‐1, RCP‐3, and RCP‐7 26.0–26.9% and the other isolates 0.1–12.0%. In the cases of F‐1, F‐4 and P‐1, substrate 1 was converted to (?)‐(1S,3R,4S,6S)‐6‐hydroxymenthol ( 2 ), (?)‐(1S,3R,4S)‐1‐hydroxymenthol ( 3 ) and (+)‐(1S,3R,4R,6S)‐6,8‐dihydroxymenthol ( 4 ), which was a new compound. Substrate 1 was converted to 2 and/or 3 by RRG97‐1, 110.4, RCP‐1, RCP‐3 and RCP‐7. The structures of the metabolic products were elucidated on the basis of their spectral data. In addition, metabolic pathways of the biotransformation of 1 by Rhizoctonia solani are discussed. Finally, from the main component analysis and the differences in the yields of converted product from 1 , the 12 isolates of Rhizoctonia solani were divided into three groups based on an analysis of the metabolites. Copyright © 2003 Society of Chemical Industry 相似文献
49.
Gas/liquid mass transfer has been investigated using a stirred vessel gas/liquid contactor using non‐Newtonian media and carbon dioxide as absorbent and gas phase, respectively. The volumetric mass transfer coefficients at different operational variables have been determined. Non‐Newtonian media (liquid phase) were prepared as aqueous solutions of sodium carboxymethyl cellulose salt. The influence of the rheological properties, polymer concentration, stirring rate, and gas flow rate on mass transfer was studied for these liquid phases. Kinematic viscosity and density experimental data were used to calculate the average molecular weight corresponding to the polymer employed. The Ostwald model has been used to fit the rheological behavior of aqueous solutions of the polymer employed as absorbent phase. Reasonably good agreement was found between the predictions of the proposed models and the experimental data of mass transfer coefficients. 相似文献
50.
The structure and properties of high density polyethylene (HDPE) functionalized by ultraviolet irradiation at different light intensities in air were studied by electron analysis, FTIR spectroscopy, contact angle with water, differential scanning calorimetry and mechanical properties measurement. The results show that oxygen‐containing groups such as C?O, C—O and C(?O)O were introduced onto the molecular chain of HDPE following irradiation, and the rate and efficiency of HDPE functionalization increased with enhancement of irradiation intensity. After irradiation, the melting temperature, contact angle with water and notched impact strength of HDPE decreased, the degree of crystallinity increased, and their variation amplitude increased with irradiation intensity. Compared with HDPE, the yield strength of HDPE irradiated at lower light intensity (32 W m?2 and 45 W m?2) increases monotonically with irradiation time, and the yield strength of HDPE irradiated at higher light intensity (78 W m?2) increases up to 48 h and then decreased with further increase in irradiation time. The irradiated HDPE behaved as a compatibilizer in HDPE/polycarbonate (PC) blends, and the interface bonding between HDPE and PC was ameliorated. After adding 20 wt% HDPE irradiated at 78 W m?2 irradiation intensity for 24 h to HDPE/PC blends, the tensile yield strength and notched Izod impact strength of the blend were increased from 26.3 MPa and 51 J m?1 to 30.2 MPa and 158 J m?1, respectively. Copyright © 2003 Society of Chemical Industry 相似文献