首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   20964篇
  免费   1921篇
  国内免费   1235篇
电工技术   410篇
技术理论   1篇
综合类   2957篇
化学工业   499篇
金属工艺   325篇
机械仪表   1007篇
建筑科学   7877篇
矿业工程   1079篇
能源动力   346篇
轻工业   135篇
水利工程   1117篇
石油天然气   5117篇
武器工业   72篇
无线电   428篇
一般工业技术   1592篇
冶金工业   227篇
原子能技术   165篇
自动化技术   766篇
  2024年   25篇
  2023年   181篇
  2022年   522篇
  2021年   601篇
  2020年   729篇
  2019年   588篇
  2018年   563篇
  2017年   616篇
  2016年   701篇
  2015年   735篇
  2014年   1281篇
  2013年   1185篇
  2012年   1680篇
  2011年   1799篇
  2010年   1278篇
  2009年   1351篇
  2008年   1191篇
  2007年   1387篇
  2006年   1245篇
  2005年   1139篇
  2004年   890篇
  2003年   783篇
  2002年   634篇
  2001年   542篇
  2000年   428篇
  1999年   398篇
  1998年   325篇
  1997年   256篇
  1996年   200篇
  1995年   160篇
  1994年   166篇
  1993年   108篇
  1992年   92篇
  1991年   82篇
  1990年   70篇
  1989年   54篇
  1988年   25篇
  1987年   21篇
  1986年   7篇
  1985年   6篇
  1984年   11篇
  1983年   4篇
  1982年   3篇
  1981年   2篇
  1980年   32篇
  1979年   11篇
  1964年   2篇
  1961年   1篇
  1959年   6篇
  1955年   2篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
41.
42.
为了缓解新疆CO2气体控排压力,扭转严峻的节能减排形势,做好能源行业领域的减排技术发展规划,基于现阶段较为成熟的CCUS技术,探讨了对CO2捕集、运输、利用和封存几个环节不同的方案,针对性的提出现阶段新疆油气行业可行的CCUS技术方案。结果表明:短期内新疆地区以化石能源消费的结构不会发生较大变化,限制碳排放量可从开展CCUS技术入手;规划合适的碳源是开展CCUS技术的重要前提,在条件允许的情况下,对排碳设备(燃烧器)进行改造对提高捕集效率有正相关性;CO2运输方式的合理性直接影响了CCUS技术产业布局和使用效率;推广和开拓CO2的使用方式和途径,对响应国家低碳环保政策、调整新疆能源产业结构有积极意义。  相似文献   
43.
44.
In the present article, a planar crack of arbitrary shape embedded in three-dimensional isotropic hygrothermoelastic media is investigated. Based on the general solutions and Hankel transform technique, the fundamental solutions for unit-point and extended displacement discontinuities (EDD; including the displacement discontinuities, moisture concentration discontinuity, and the temperature discontinuity) are derived. The EDD boundary integral equations for an arbitrarily shaped, planar crack in the hygrothermoelastic medium are established in terms of the EDD. Utilizing the boundary integral equation method, the singularities of near-crack front fields are analyzed, and the stress, moisture flux, and heat flux intensity factors are all derived in terms of the EDD. As a special case, the analytical solution for a penny-shaped crack under uniform combined loadings is presented. The EDD boundary element method is proposed for numerical simulation. The numerical result for a penny-shaped crack subjected to uniform mechanical–moisture–thermal loading is compared with the analytical solution to verify the correctness of the proposed method. Two coplanar elliptical cracks subjected to combined loadings are simulated as an application, and the influences of applied loadings and the ellipticity ratio are discussed.  相似文献   
45.
川西彭州地区三叠系雷口坡组雷四上亚段潮坪相薄储层识别难度极大。围绕如何从复合地震强反射中区分并识别上、下两套储层面临的地球物理难题,采用先“分”后“合”的研究思路,基于实际地层结构及不同储层叠加样式建立正演模型,利用全波场波动方程正演模拟技术,剖析了不同主频条件下薄储层的地震响应特征,通过波形差异化分析,从复合地震响应中“剥离”出了两套储层所引起的地震响应特征及变化规律,明确了两套储层在不同频带下的地震识别标志和识别方法,为该区强反射界面干扰下两套薄互层储层辨识机理分析及精准预测奠定了基础。基于不同频带下薄储层辨识机理的分析结果,定性预测了薄储层平面展布,提出了深层潮坪相薄储层识别和预测难题的解决方案,为该区地震资料品质评价、面向薄储层的地震采集技术设计、地震资料处理及薄储层预测提供了依据和指导。  相似文献   
46.
The common cushion layer used in the geomembrane face rockfill dam is made of granular materials such as gravel and non-fine concrete where bulge deformation or failure of geomembrane is very likely to occur in its surface holes. The curve intersection method based on the thin film theory is the common method used to analyze the bulge deformation of the geomembrane in the surface holes of cushion layer. However, it is inaccurate due to the neglection of horizontal (tangential) displacement of the geomembrane. Based on the FEM theory, a new method is proposed, which takes the horizontal (tangential) displacement of geomembrane into consideration, and is validated by the bulge tests on the geomembrane in a circular hole. The deformations and strains of the geomembrane in different shapes of holes are analyzed by this method, and different strain distributions and failure modes are obtained. The curve intersection method is also used to compare with the new method under the same condition. It is indicated that there is less difference in the deformation and average strain of the geomembrane when the water pressure is low. However, when the water pressure is relatively high, the influences of horizontal (tangential) displacement of the geomembrane on its strain should not be neglected.  相似文献   
47.
Experimental and analytical investigation of the seismic out‐of‐plane behavior of unreinforced masonry walls In addition to the vertical and horizontal load‐bearing in‐plane, masonry must also withstand out‐of‐plane loads that occur in earthquake scenarios. The out‐of‐plane behavior of unreinforced masonry walls depends on a variety of parameters and is very complex due to the strong non‐linearity. Current design methods in German codes and various international codes have not been explicitly developed for out‐of‐plane behavior and contain considerable conservatism. In the present work, shaking‐table experiments with heat‐insulating masonry walls have been conducted to investigate the out‐of‐plane behavior of vertical spanning unreinforced masonry walls. As shown in previous numerical investigations, important parameters are neglected in existing design and analysis models and the out‐of‐plane capacity is underestimated significantly. In the conducted experiments the results of these numerical investigations are verified. Furthermore, the development of an analytical design model to determine the force‐displacement relationship and the out‐of‐plane load‐bearing capacity considering all significant parameters is presented.  相似文献   
48.
高耸的风力机塔架结构属于典型的顶部附有大集中质量的细长柔性体的力学结构,相比传统建筑结构差异性较大,极易受到地震载荷影响。基于有限元分析软件ABAQUS建立风力机塔架、基础平台和土体模型,通过FAST导出风轮非定常推力,作用在塔顶机舱,土体底部施加地震加速度时间序列,进行风力机结构模态分析、稳定性分析和动力学响应分析。研究表明:塔架主要的运动形式为摇摆运动和弯曲振动;塔架一阶固有频率为0.290 Hz,大于风轮的额定旋转频率0.202 Hz,因此叶片旋转不会引起风力机塔架发生共振;风载荷作用下,塔架发生横向屈曲,屈曲位置位于塔架底部且随模态阶数增大而逐渐向上发展,屈曲因子较大;地震载荷作用下,塔架发生纵向屈曲,屈曲位置同样位于塔架底部且随模态阶数增大而逐渐向上发展,较风载荷发生屈曲区域相对更大,屈曲因子相对较小。  相似文献   
49.
This paper presents influence analysis of bracket set on seismic performance of steel eave columns in Chinese traditional style buildings. Eight 1/1.5‐scale steel eave columns were constructed and tested under low cyclic reversed loading, including 4 specimens with bracket set and 4 specimens without bracket set. Based on the analysis of the strain of the specimens, the failure modes of the specimens were obtained. In addition, the hysteresis loops, skeleton curves, degradations of stiffness and strength, ductility, and dissipation capacities of the specimens were analyzed. Bracket set changed the force transfer mechanisms and failure modes of the specimens and had a significant influence on the seismic performance of the specimens. Compared with the specimens without bracket set, the yielded and ultimate bearing capacities of the specimens with bracket set improved by 30.7% and 24.0%, respectively. And also, the stiffness of the specimens with bracket set at the yielded and ultimate points increased by 52.8% and 135.6%. The dissipation capacities of the specimens with bracket set were 2.12 times those of the specimens without bracket set at yielded load. However, the ductility of the specimens with bracket set slightly decreased by 8.5%. It was shown that the seismic performance of the specimens with bracket set was better than that of the specimens without bracket set. The work in this paper provides a basis for further theoretical study on the seismic performance of steel eave columns in Chinese traditional style buildings.  相似文献   
50.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号