全文获取类型
收费全文 | 14178篇 |
免费 | 2220篇 |
国内免费 | 1180篇 |
专业分类
电工技术 | 1481篇 |
综合类 | 1421篇 |
化学工业 | 2851篇 |
金属工艺 | 702篇 |
机械仪表 | 1555篇 |
建筑科学 | 1054篇 |
矿业工程 | 669篇 |
能源动力 | 547篇 |
轻工业 | 219篇 |
水利工程 | 522篇 |
石油天然气 | 623篇 |
武器工业 | 230篇 |
无线电 | 2117篇 |
一般工业技术 | 1960篇 |
冶金工业 | 318篇 |
原子能技术 | 194篇 |
自动化技术 | 1115篇 |
出版年
2024年 | 160篇 |
2023年 | 358篇 |
2022年 | 547篇 |
2021年 | 647篇 |
2020年 | 702篇 |
2019年 | 572篇 |
2018年 | 564篇 |
2017年 | 644篇 |
2016年 | 643篇 |
2015年 | 728篇 |
2014年 | 887篇 |
2013年 | 945篇 |
2012年 | 1169篇 |
2011年 | 1168篇 |
2010年 | 808篇 |
2009年 | 792篇 |
2008年 | 737篇 |
2007年 | 851篇 |
2006年 | 759篇 |
2005年 | 638篇 |
2004年 | 553篇 |
2003年 | 438篇 |
2002年 | 394篇 |
2001年 | 303篇 |
2000年 | 256篇 |
1999年 | 242篇 |
1998年 | 187篇 |
1997年 | 157篇 |
1996年 | 142篇 |
1995年 | 128篇 |
1994年 | 109篇 |
1993年 | 75篇 |
1992年 | 73篇 |
1991年 | 48篇 |
1990年 | 43篇 |
1989年 | 33篇 |
1988年 | 26篇 |
1987年 | 8篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 7篇 |
1983年 | 4篇 |
1982年 | 6篇 |
1980年 | 4篇 |
1979年 | 7篇 |
1978年 | 2篇 |
1973年 | 1篇 |
1965年 | 1篇 |
1959年 | 2篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
水肥耦合规律试验研究 总被引:2,自引:0,他引:2
不同的水肥处理对于水稻的长势形态和生理状态的影响是不同的,随着农业水资源的日益紧缺,以减少水稻的灌溉用水和肥料高效利用实现水稻稳产高产的各项理论技术研究受到广泛重视. 相似文献
962.
高外水作用下,深埋软岩隧洞围岩-支护结构安全将受到极大挑战。为了降低高外水压对软岩隧洞围岩-支护体系的影响,较常见的工程处理措施为在隧洞周围布置排水结构,以降低洞周外水压力。笔者首先提出了一种简便的隧洞围岩-衬砌结构渗流-应力分析思路。然后,以某过断层带深埋软岩隧洞为研究对象,通过开展隧洞施工期、运行期渗流-应力耦合分析,研究了软岩隧洞排水结构的排水效应。研究发现,在注浆圈和排水结构的综合作用下,隧洞衬砌附近的水力比降较小,注浆圈水力比降较大,使注浆圈承担绝大部分外水荷载,而衬砌承担少部分外水荷载;在软岩和衬砌的变形协调作用下,最终形成注浆圈与衬砌的协同承载效应,有效提高了隧洞的运行安全水平。 相似文献
963.
研制了对混凝土坝及基岩进行水弹性模拟的新配方和材料,并用此材料成功地对黄河拉西瓦高拱坝坝身泄漏的流激振动进行水弹性模拟试验。在比尺为1:150的拱坝-地基-库水耦合系统的水弹性整体模型上,进行了实验模态分析,给出系统的空、满库的模态特性并与理论模态相比较;测定了拱坝坝身泄洪水舌跌落水垫塘消能时,紊流流振动的动力响应,定量地给出响应的强度和频谱;论证了高拱坝坝身泄洪的安全性。 相似文献
964.
系统介绍了土石坝防渗加固工程中高聚物防渗墙的施工方法和步骤,在考虑实际工程条件基础上,建立坝体正常蓄水情况下高聚物防渗墙土石坝应力场与渗流场耦合分析的数值模型。高聚物防渗墙堤坝在考虑渗流-应力耦合作用时,坝体不同位置处的最大压应力的结果要大于不计耦合时的压应力值,且高聚物防渗墙竖向位移和水平位移值考虑耦合时明显大于不计耦合时,坝体内浸润线位置也有同样变化。分析结果说明忽略渗流与应力耦合作用会导致坝体和墙体的位移和应力计算结果偏小,为今后高聚物防渗墙除险加固工程的设计及施工提供理论依据。 相似文献
965.
966.
The domestic coffee machines market has widely expanded in the last five years. The core of these machines is an electro-pump that allows the correct water distribution. In this paper a root cause failure analysis was conducted utilizing some electro-pumps samples taken from a corroded batch. Several examinations were carried out in order to identify the root cause of the failure: visual examination, SEM-EDS analysis and microstructural characterization. The corrosion phenomenon is located at the piston-spring interface. As result of the examinations carried out, it has been possible to identify that the corrosion mechanism is due to different interacting factors: high chlorine concentration, potential dynamic difference between piston and spring materials, material sensitization and iron-manganese bacteria growth. 相似文献
967.
968.
Farida Benmouna Ulrich Maschke Xavier Coqueret Mustapha Benmouna 《Polymer International》2001,50(4):469-474
The phase behaviour of binary nematogen mixtures of side‐chain liquid crystal crosslinked polymers and low molecular weight liquid crystals is investigated with particular emphasis on the effects of nematic coupling. The cross nematic quadrupole parameter ν12 is assumed to be proportional to the geometric average of ν11 and ν22 characteristic of single nematogens. In the weak coupling limit, the proportionality constant is lower than 1, and the phase diagram exhibits a reduced miscibility of the nematogens. In the case of strong coupling, the proportionality constant exceeds 1 resulting in higher miscibility. This is characterized by a nematic order that extends to temperatures above the upper nematic–isotropic transition temperature. A wide region of miscibility emerges showing a single nematic phase. Nematogens having similar nematic–isotropic transition temperatures exhibit different phase properties from systems with widely separated transition temperatures. Effects of the polymer volume fraction at crosslinking, rubber elasticity parameters of the network, and the Flory–Huggins interaction parameter on the equilibrium phase diagram of these systems are discussed. © 2001 Society of Chemical Industry 相似文献
969.
Andr Luís Muller Eurípedes do Amaral Vargas Jr. Luiz Eloy Vaz Clemente Jos Gonalves 《Journal of Petroleum Science and Engineering》2009,68(3-4):268-276
In general, analysis of oil producing wells is carried out considering that both hydraulic and mechanical parameters of the rock mass are deterministic. Mechanical and hydraulic properties of rock masses and in particular sedimentary rock masses may show a considerable degree of spatial variability. This paper focuses on the evaluation of the three-dimensional borehole response, particularly of the plastic zone, taking into account the spatial variability of both hydraulic and mechanical properties. The analysis is performed with a developed finite element program that incorporates spatial variability, coupled fluid-mechanical effects and elastoplastic behavior of the rock mass. Examples are shown and conclusions are drawn regarding the effect of spatial variability on the three-dimensional borehole analysis. 相似文献
970.
ALCELL lignin has been employed as a coupling agent in oil palm empty fruit bunch (EFB)–polypropylene (PP) composites. The lignin has been chemically modified with hexamethylene diisocyanate (HMDI). Evidence for the reaction between HMDI and lignin has been observed by using Fourier transform infrared (FTIR) analysis. The effect of lignin as a coupling agent on the flexural properties has been studied. The results show that the HMDI‐modified lignin is able to impart greater compatibility between EFB and PP. This is reflected in the greater flexural strength shown by the composites with HMDI‐modified lignin than those with the unmodified lignin. Scanning electron microscopy studies show that HMDI‐modification of lignin results in a better blending and compatibility between lignin and PP matrix. The glass transition temperature of lignin increases as the level of HMDI modification is increased. © 2001 Society of Chemical Industry 相似文献