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   16758篇
  免费   1317篇
  国内免费   637篇
电工技术   945篇
技术理论   2篇
综合类   1108篇
化学工业   3032篇
金属工艺   855篇
机械仪表   1037篇
建筑科学   1385篇
矿业工程   555篇
能源动力   437篇
轻工业   1068篇
水利工程   271篇
石油天然气   971篇
武器工业   90篇
无线电   1904篇
一般工业技术   2119篇
冶金工业   787篇
原子能技术   289篇
自动化技术   1857篇
  2024年   46篇
  2023年   290篇
  2022年   356篇
  2021年   530篇
  2020年   456篇
  2019年   450篇
  2018年   458篇
  2017年   503篇
  2016年   425篇
  2015年   615篇
  2014年   792篇
  2013年   931篇
  2012年   987篇
  2011年   1002篇
  2010年   897篇
  2009年   982篇
  2008年   895篇
  2007年   890篇
  2006年   940篇
  2005年   786篇
  2004年   597篇
  2003年   554篇
  2002年   563篇
  2001年   531篇
  2000年   449篇
  1999年   531篇
  1998年   372篇
  1997年   350篇
  1996年   349篇
  1995年   283篇
  1994年   255篇
  1993年   156篇
  1992年   125篇
  1991年   88篇
  1990年   68篇
  1989年   64篇
  1988年   49篇
  1987年   30篇
  1986年   17篇
  1985年   15篇
  1984年   7篇
  1983年   6篇
  1982年   7篇
  1981年   5篇
  1980年   8篇
  1979年   2篇
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
101.
油气沉积学原理及其在勘探开发中的应用   总被引:2,自引:0,他引:2  
本文以油气藏形成条件中的生、储、盖、运、圈为纲讨论了油气勘探沉积学;以油气藏开发过程中与沉积、成岩的关系讨论了油气开发沉积学。在油气勘探沉积学中重点论述了陆相沉积与储层及圈闭的关系;在油气开发沉积学中重点论述了储层研究的基础—储层的沉积属性和成岩特征。强调储层沉积、成岩研究应成为储层评价最重要的内容。  相似文献   
102.
This paper considers the robust stability of a linear time-invariant state space model subject to real parameter perturbations. The problem is to find the distance of a given stable matrix from the set of unstable matrices. A new method, based on the properties of the Kronecker sum and two other composite matrices, is developed to study this problem; this new method makes it possible to distinguish real perturbations from complex ones. Although a procedure to find the exact value of the distance is still not available, some explicit lower bounds on the distance are obtained. The bounds are applicable only for the case of real plant perturbations, and are easy to compute numerically; if the matrix is large in size, an iterative procedure is given to compute the bounds. Various examples including a 46th-order spacecraft system are given to illustrate the results obtained. The examples show that the new bounds obtained can have an arbitrary degree of improvement over previously reported ones. This work has been supported by the Natural Sciences and Engineering Research Council of Canada under Grant No. A4396.  相似文献   
103.
物理所2×1.7MV串列加速器的运行与使用   总被引:1,自引:1,他引:0  
周俊思  徐天冰 《核技术》1992,15(6):354-357
  相似文献   
104.
Qiu Tu  Qing Li  Fang Zhong Guo 《低温学》2003,43(6):351-357
The network model is given and used to calculate the oscillating frequency of thermoacoustic prime mover. Theoretically calculated frequency by the model is plural, whose real part denotes actual frequency of the system, and imaginary part means attenuation coefficient of acoustic pressure. Numerical calculation is made under different conditions including different acoustic cavities, spacing between each parallel plate, gas pressures and system lengths. Theoretically calculated frequency and experimentally measured frequency are in quite good agreement.  相似文献   
105.
Hyperspectral image fusion is a key technique of hyperspectral data processing. In recent years, many fusion methods have been proposed, but there is little work concerning evaluation of the performances of different image fusion methods. In this paper, a method called quantitative correlation analysis (QCA) is proposed, which provides a quantitative measure of the information transferred by an image fusion technique into the output image. Using the proposed method, the performances of different image fusion methods can be compared and analyzed directly based on the images of before and after performing the fusion. The correlation information entropy, based on the developed QCA, is also proposed and testified by numerical simulations. Typical hyperspectral data are applied to the proposed method. The results show that the method is effective, and its conclusions agree with the classification results in applications.  相似文献   
106.
建立五大创新体系促进绿色建筑发展   总被引:2,自引:0,他引:2  
我们正站在一个新的历史起点上,同时处在一个非常重要的关口。在世界范围内,以大量消耗原材料和能源为特征的传统经济正在逐渐失去昔日的荣耀。由资源依赖型转向创新驱动型,真正实现经济增长方式的转变,已成为正处于快速城镇化、工业化与机动化进程之中的我国经济发展面临的非常迫切的重大战略选择。在未来30年内,我国还需建造400亿m2的新建筑,建筑数量和建设速度都是世界发展史上所罕见的。建筑属于长期的消费品,不可能进行频繁的更新。仅延长建筑使用寿命或装修期限,就意味着能源和资源的大量节约与环境污染的减少。绿色建筑是指为人们提…  相似文献   
107.
The fabrication of one kind of large core area Nd3 doped silicate glass photonic crystal fiber, and demonstration of the fiber's waveguidence properties were reported. This fiber owns a random air hole distribution in the cladding. The measured minimum loss of this kind of fiber is 10 dB·m-1 at 660 nm. These fibers can sustain only a single mode at least over wavelength ranging from 660 nm to 980 nm.  相似文献   
108.
The authors of this paper synthesized a series of amphiphilic triblock copolymers of polystyrene-b-poly(ethylene glycol)-b-polystyrene (PS-PEG-PS) having different PEG/PS ratios with nearly identical molecular weights of the entire copolymers. The interfacial interactions in the composites consisting of carbon black and the copolymers can thus be tailored. When these conducting composites are exposed to certain solvent vapors, their electrical resistances greatly increase, showing the gas sensitivity. The present work indicated that this switching behavior is controlled by the structural relaxation of the composites because matrix swelling acts as the main mechanism. The response time has been correlated with absolute temperature by Arrhenius equation, and the estimated activation energy reflects mobility of the fillers involved in the solvent induced expansion of the surrounding polymer. Therefore, by using the gas sensibility of the conductive composites, the structure evolution of the composite materials in solid state and the effect of filler/matrix interfacial interaction on the relaxation property of the matrix polymer has been inspected. It was found that lower activation energy represents stronger interfacial interaction in case good solvent of the matrix was used for the test.  相似文献   
109.
Spherical nano-hydroxyapatite (nano-HA) was synthesized successfully by a biomimetic method using Ca(NO3)2·4H2O and (NH4)3PO4·3H2O as reagents in the presence of polyethylene glycol (PEG). The crystalline phase, microstructure, chemical composition, and morphology of the obtained samples were characterized by X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and transmission electron microscopy (TEM). The results show that spherical nano-HA with diameter of 30–50 nm can be synthesized in the presence of a certain concentration (2–6%) of PEG. The crystallinity of HA powder synthesized in the presence of PEG was higher than that synthesized in the absence of PEG, but the crystallinity of HA reduced with increasing the concentration of PEG. The electrical conductivity (EC) of the solution revealed that PEG reduced the transfer rate of Ca2+ in the process of HA crystallization, indicating the interaction between PEG and HA. The possible mechanism of formation spherical nano-HA was discussed.  相似文献   
110.
对某自动驾驶仪可靠性增长工作进行研究,提出了对现役机载电子设备可靠性增长的一些成功、可借鉴的经验。对增长试验过程中发现的问题和管理方面的不足之处,提出一些建议。  相似文献   
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