全文获取类型
收费全文 | 107790篇 |
免费 | 2992篇 |
国内免费 | 1259篇 |
专业分类
电工技术 | 2094篇 |
技术理论 | 1篇 |
综合类 | 3642篇 |
化学工业 | 15703篇 |
金属工艺 | 6048篇 |
机械仪表 | 4309篇 |
建筑科学 | 3995篇 |
矿业工程 | 1127篇 |
能源动力 | 1978篇 |
轻工业 | 5177篇 |
水利工程 | 1601篇 |
石油天然气 | 1675篇 |
武器工业 | 119篇 |
无线电 | 12235篇 |
一般工业技术 | 19364篇 |
冶金工业 | 4008篇 |
原子能技术 | 566篇 |
自动化技术 | 28399篇 |
出版年
2024年 | 59篇 |
2023年 | 390篇 |
2022年 | 629篇 |
2021年 | 1016篇 |
2020年 | 710篇 |
2019年 | 661篇 |
2018年 | 15018篇 |
2017年 | 14056篇 |
2016年 | 10620篇 |
2015年 | 1516篇 |
2014年 | 1460篇 |
2013年 | 1757篇 |
2012年 | 4685篇 |
2011年 | 11037篇 |
2010年 | 9615篇 |
2009年 | 6933篇 |
2008年 | 8061篇 |
2007年 | 8964篇 |
2006年 | 1457篇 |
2005年 | 2366篇 |
2004年 | 1958篇 |
2003年 | 1923篇 |
2002年 | 1289篇 |
2001年 | 636篇 |
2000年 | 699篇 |
1999年 | 656篇 |
1998年 | 624篇 |
1997年 | 491篇 |
1996年 | 487篇 |
1995年 | 357篇 |
1994年 | 288篇 |
1993年 | 197篇 |
1992年 | 184篇 |
1991年 | 137篇 |
1990年 | 90篇 |
1989年 | 72篇 |
1988年 | 96篇 |
1987年 | 47篇 |
1986年 | 44篇 |
1968年 | 45篇 |
1967年 | 34篇 |
1966年 | 44篇 |
1965年 | 49篇 |
1960年 | 30篇 |
1959年 | 35篇 |
1958年 | 39篇 |
1957年 | 36篇 |
1956年 | 34篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
51.
掌握了理论知识并不等于有了实战经验,更不等于有实战能力。从理论到有实战能力的飞跃,只有亲临生产线,在不断解决问题过程中实现。 相似文献
52.
油层水洗级别的热解气相色谱定量判别 总被引:1,自引:0,他引:1
应用热解气相色谱资料开展水淹层评价是储层地球化学研究的一个新领域,目前,这方面的研究尚处于定性评价阶段。文章选择位于渤海湾盆地黄骅坳陷的港东油田和羊二庄油田新近系开发层系(包括馆陶组和明化镇组)为研究目的层,以岩心热解气相色谱分析为手段,开展了油层水洗级别的气相色谱定量判别的尝试。在系统分析各气相色谱参数的地质意义及其与油层水洗的关系的基础上,优选出合理的评价参数,并采用交会图技术建立不同级别水洗油层的定量判别标准,通过其他评价方法的验证,表明该定量判别方法具有实际应用价值。 相似文献
53.
Ferrite particles coated with biocompatible phases can be used for hyperthermia treatment of cancer. We have synthesized substituted
calcium hexaferrite, which is not stable on its own but is stabilized with small substitution of La. Hexaferrite of chemical
composition (CaO)0.75(La203)0.20(Fe2O3)6 was prepared using citrate gel method. Hydroxyapatite was prepared by precipitating it from aqueous solution of Ca(NO3)2 and (NH4)2HPO4 maintaining pH above 11. Four different methods were used for coating of hydroxyapatite on ferrite particles. SEM with EDX
and X-ray diffraction analysis shows clear evidence of coating of hydroxyapatite on ferrite particles. These coated ferrite
particles exhibited coercive field up to 2 kOe, which could be made useful for hysteresis heating in hyperthermia. Studies
by culturing BHK-21 cells and WBC over the samples show evidence of biocompatibility. SEM micrographs and cell counts give
clear indication of cell growth on the surface of the sample. Finally coated ferrite particle was implanted in Kasaulli mouse
to test its biocompatibility. The magnetic properties and biocompatibility studies show that these hydroxyapatite coated ferrites
could be useful for hyperthermia. 相似文献
54.
Chloride doped polyaniline conducting polymer films have been prepared in a protic acid medium (HCl) by potentiodynamic method
in an electrochemical cell and studied by cyclic voltammetry and FTIR techniques. The FTIR spectra confirmed Cl- ion doping in the polymers. The polymerization rate was found to increase with increasing concentration of aniline monomer.
But the films obtained at high monomer concentration were rough having a nonuniform flaky polyaniline distribution. Results
showed that the polymerization rate did not increase beyond a critical HCl concentration. Cyclic voltammetry suggested that,
the oxidation-reduction current increased with an increase in scan rate and that the undoped polyaniline films were not hygroscopic
whereas chloride doped polyaniline films were found to be highly hygroscopic. 相似文献
55.
56.
In this paper we study the optimization issues of ring networks employing novel parallel multi‐granularity hierarchical optical add‐drop multiplexers (OADMs). In particular, we attempt to minimize the number of control elements for the off‐line case. We present an integer linear programming formulation to obtain the lower bound in optimization, and propose an efficient heuristic algorithm called global bandwidth resource assignment that is suitable for the design of large‐scale OADM networks. 相似文献
58.
A coupled finite-element model, CON2D, has been developed to simulate temperature, stress, and shape development during the
continuous casting of steel, both in and below the mold. The model simulates a transverse section of the strand in generalized
plane strain as it moves down at the casting speed. It includes the effects of heat conduction, solidification, nonuniform
superheat dissipation due to turbulent fluid flow, mutual dependence of the heat transfer and shrinkage on the size of the
interfacial gap, the taper of the mold wall, and the thermal distortion of the mold. The stress model features an elastic-viscoplastic
creep constitutive equation that accounts for the different responses of the liquid, semisolid, delta-ferrite, and austenite
phases. Functions depending on temperature and composition are employed for properties such as thermal linear expansion. A
contact algorithm is used to prevent penetration of the shell into the mold wall due to the internal liquid pressure. An efficient
two-step algorithm is used to integrate these highly nonlinear equations. The model is validated with an analytical solution
for both temperature and stress in a solidifying slab. It is applied to simulate continuous casting of a 120 mm billet and
compares favorably with plant measurements of mold wall temperature, total heat removal, and shell thickness, including thinning
of the corner. The model is ready to investigate issues in continuous casting such as mold taper optimization, minimum shell
thickness to avoid breakouts, and maximum casting speed to avoid hot-tear crack formation due to submold bulging. 相似文献
59.
Atsushi Narumi Kosei Kawasaki Harumi Kaga Toshifumi Satoh Naoya Sugimoto Toyoji Kakuchi 《Polymer Bulletin》2003,49(6):405-410
Summary
The potato phosphorylase-catalyzed polymerization of α-D-glucose-1-phosphate (G-1-P) onto poly[styrene-block-(4-vinylbenzyl maltohexaoside)] (1) was performed at the molar ratios of [G-l-P]0 and [maltohexaose]0 of 35, 80, and 250. The product was found to be soluble in dimethyl sulfoxide, which was a good solvent for amylose, and
showed the complex-formation with iodine, indicating that the product was assignable to poly[styrene-block-(styrene-graft-amylose)] (2). The quantitative analysis of the liberated phosphoric acid gave the average degree of polymerization o f the glucose unit
(n) as 27, 5 1, and 180 for 2-I, 2-II, and 2-III, respectively.
Received: 29 November 2002/Accepted: 22 December 2002
Correspondence to Toyoji Kakuchi 相似文献
60.
ZhaoYahong ZhangZhongpei WuWeiling 《电子科学学刊(英文版)》2003,20(3):177-182
Adaptive modulation and power allocation is introduced into the multicarrier DSCDMA system to improve the system performance and bandwidth efficiency.First,the system design appropriate for adaptive modulation and power allocation is given,then the algorithm of adaptive modulation and power allocation is applied.Simulation results demonstrate great performance improvement compared with the fixed modulated one. 相似文献