全文获取类型
收费全文 | 92099篇 |
免费 | 1756篇 |
国内免费 | 809篇 |
专业分类
电工技术 | 1310篇 |
综合类 | 3009篇 |
化学工业 | 12673篇 |
金属工艺 | 5240篇 |
机械仪表 | 3599篇 |
建筑科学 | 2893篇 |
矿业工程 | 783篇 |
能源动力 | 1344篇 |
轻工业 | 4292篇 |
水利工程 | 1448篇 |
石油天然气 | 731篇 |
武器工业 | 68篇 |
无线电 | 10155篇 |
一般工业技术 | 17167篇 |
冶金工业 | 3026篇 |
原子能技术 | 337篇 |
自动化技术 | 26589篇 |
出版年
2024年 | 32篇 |
2023年 | 153篇 |
2022年 | 201篇 |
2021年 | 362篇 |
2020年 | 302篇 |
2019年 | 220篇 |
2018年 | 14663篇 |
2017年 | 13605篇 |
2016年 | 10178篇 |
2015年 | 932篇 |
2014年 | 639篇 |
2013年 | 692篇 |
2012年 | 3704篇 |
2011年 | 9982篇 |
2010年 | 8811篇 |
2009年 | 6045篇 |
2008年 | 7285篇 |
2007年 | 8189篇 |
2006年 | 578篇 |
2005年 | 1589篇 |
2004年 | 1426篇 |
2003年 | 1536篇 |
2002年 | 895篇 |
2001年 | 411篇 |
2000年 | 369篇 |
1999年 | 282篇 |
1998年 | 199篇 |
1997年 | 169篇 |
1996年 | 167篇 |
1995年 | 105篇 |
1994年 | 92篇 |
1993年 | 66篇 |
1992年 | 63篇 |
1991年 | 57篇 |
1990年 | 26篇 |
1988年 | 24篇 |
1969年 | 24篇 |
1968年 | 43篇 |
1967年 | 33篇 |
1966年 | 42篇 |
1965年 | 44篇 |
1963年 | 28篇 |
1962年 | 22篇 |
1960年 | 30篇 |
1959年 | 36篇 |
1958年 | 37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 15 毫秒
31.
32.
四川盆地及邻区上二叠统一下三叠统海槽的深水沉积特征 总被引:10,自引:0,他引:10
四川盆地及邻区广元-旺苍、城口-鄂西、开江-梁平海槽是上二叠统一下三叠统飞仙关组(P3-T1f)的深水碳酸盐沉积区。该区上二叠统上部大隆组是硅质岩、硅质泥岩、硅质灰岩组合,含放射虫、有孔虫等化石,厚125—29.0m,为海槽裂陷期凝缩沉积。三叠系飞仙关组下部为远洋沉积的暗色泥岩、微晶碎屑灰岩和重力流沉积的浊积岩、角砾灰岩组成的深水碳酸盐沉积,厚50.0~300.0m,是裂陷期后的海槽充填沉积。海槽相区沉积在晚二叠统世末达到最大海泛面沉积了大隆组。海平面缓慢下降期沉积了补偿充填性质的飞仙关组深水碳酸盐岩。海槽相区上二叠统一下三叠统飞仙关组构成了一个完整的三级层序。深水沉积物的有机碳平均值高达6.21%,是良好的烃源岩。但在海槽相区上二叠统不发育生物礁,飞仙关组缺乏鲕粒岩。 相似文献
33.
34.
35.
36.
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
37.
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
38.
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
39.
As an aid towards improving the treatment of exchange and correlation effects in electronic structure calculations, it is
desirable to have a clear picture of the errors introduced by currently popular approximate exchange-correlation functionals.
We have performed ab initio density functional theory and density functional perturbation theory calculations to investigate
the thermal properties of bulk Cu, using both the local density approximation (LDA) and the generalized gradient approximation
(GGA). Thermal effects are treated within the quasiharmonic approximation. We find that the LDA and GGA errors for anharmonic
quantities are an order of magnitude smaller than for harmonic quantities; we argue that this might be a general feature.
We also obtain much closer agreement with experiment than earlier, more approximate calculations. 相似文献
40.