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   43469篇
  免费   4865篇
  国内免费   2747篇
电工技术   3992篇
技术理论   2篇
综合类   3653篇
化学工业   6067篇
金属工艺   2860篇
机械仪表   2949篇
建筑科学   3468篇
矿业工程   1762篇
能源动力   1400篇
轻工业   3142篇
水利工程   1301篇
石油天然气   2120篇
武器工业   652篇
无线电   4768篇
一般工业技术   4430篇
冶金工业   1853篇
原子能技术   745篇
自动化技术   5917篇
  2024年   195篇
  2023年   625篇
  2022年   1470篇
  2021年   2121篇
  2020年   1490篇
  2019年   1146篇
  2018年   1300篇
  2017年   1563篇
  2016年   1348篇
  2015年   2045篇
  2014年   2554篇
  2013年   2996篇
  2012年   3544篇
  2011年   3607篇
  2010年   3272篇
  2009年   3196篇
  2008年   3170篇
  2007年   3002篇
  2006年   2653篇
  2005年   2164篇
  2004年   1510篇
  2003年   1050篇
  2002年   990篇
  2001年   833篇
  2000年   717篇
  1999年   549篇
  1998年   352篇
  1997年   311篇
  1996年   245篇
  1995年   192篇
  1994年   155篇
  1993年   120篇
  1992年   88篇
  1991年   78篇
  1990年   55篇
  1989年   41篇
  1988年   26篇
  1987年   30篇
  1986年   28篇
  1985年   20篇
  1984年   16篇
  1983年   13篇
  1982年   17篇
  1981年   20篇
  1980年   20篇
  1979年   17篇
  1977年   11篇
  1976年   10篇
  1973年   12篇
  1959年   12篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
111.
川东地区长兴组缝洞型储层的识别   总被引:1,自引:0,他引:1  
本文针对四川东部地区上二叠统长兴组(P_2~2)缝洞型储层的低孔、低渗及非均质性等特点,分析了影响这类储层识别的主要因素,提出了利用现有的地球物理测井手段定性识别储层的指标和定量综合识别储层的方法,这可望提高测试成功率。  相似文献   
112.
讨论了激光微焊点焊接质量的模糊识别的概念,数学模型及其应用方法,并介绍了系统的硬件组成。  相似文献   
113.
韩光武  马受武 《核技术》1995,18(12):759-764
用Monte Carlo法模拟计算了30keV和200keV的N^+与110keV的Fe^+在模拟细胞中的射程分布和径迹结构,并将110keVFe^+模拟计算的结果与RSB测量的结果相比较,发现计算与测量的结果吻合较好,离子的作用范围小于1μm。计算和实验的结果都说明能量相当低的重离子不大可能直接作用引起麦胚深层生物效应。  相似文献   
114.
介绍了一种光纤式机器人触觉传感器,分析了这种传感器的静态特性,并通过理论分析和实验研究提出了一种消除干扰的方法。实验结果证明,传感器的最大绝对误差为0.053kg,相对误差为0.62%。  相似文献   
115.
本文研究了二烷基硫代磷酸铵(RO)2PSONH4(R=乙基、丁基、己基、烯丙烯)系列捕收剂对非硫化矿孔雀石、锡石、赤铁矿、白铅矿、方解石和菱锌矿的浮选性能,并就药剂结构与性能关系进行了分析讨论.  相似文献   
116.
By using the technology of the sequential interpenetrating polymer network, a series of novel damping materials based on a polydimethylsiloxane (PDMS)/polyacrylate (PAC) matrix with polymethacrylate (PMAC) were synthesized. They have a controllable broad transition peak spanning the temperature range of 150–220°C and the medial value of loss factor with maximum of 0.35–0.60. Dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), and atomic force microscopy (AFM) were applied to analyze and characterize the transition behavior and the microphase structure of the materials. It was found that the size and height of a transition peak at both the low‐ and the high‐temperature zones change as a function not only of the concentration of PMAC and PDMS but also of the kind of PMAC; simultaneously, the low‐ temperature behavior was also governed by the crystallization of PDMS. The content of the crosslinking agent exerts a significant influence on the configuration of the curves of the transition peaks. AFM shows a characteristic phase morphology of double‐phase continuity containing a transition layer and domain less than 1 μm, indicating that the interwoven multilayer networks are the key to incorporation of the immiscible components and form a broad damping functional region. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 545–551, 2002  相似文献   
117.
Quantum-mechanical reaction rate constants were calculated from centroid molecular dynamics (CMD) simulations, for the case of barrier crossing in an asymmetrical double-well potential bilinearly coupled to a harmonic bath. The calculation is based on a recently proposed formulation of the reaction rate constant in terms of the position—flux correlation function, which can be approximated via CMD in a well-defined manner. The predictions of CMD and various simplified versions of it are compared to exact results, which were obtained via the quasi-adiabatic propagator path integral (QUAPI) method, and/or path integral quantum transition state theory (PI-QTST). The predictions based on CMD are found to be in good agreement with both.  相似文献   
118.
通过对桥梁加固技术的研究,讨论了体系转换法和粘贴碳纤维布加固法的具体应用。  相似文献   
119.
A pure, acicular lead titanate (PbTiO3) fine powder with a white color has been prepared by hydrothermal synthesis. It is a new phase of PbTiO3 with I 4 symmetry, cell parameters of a = 12.358 Å and b = 14.541 Å, and a density of 6.80 g.cm−3. The influences of pH (12.5 to 14.4), Pb/Ti ratio (1.0 to 1.6) in the feedstock, reaction temperature (130° to 230°C), time (0.25 to 4 h), starting materials, and additives on the formation of acicular PbTiO3 under hydrothermal conditions have been investigated. The acicular PbTiO3 with I 4 symmetry, referred to as the PX phase, can be converted to the perovskite-type (PE phase) of PbTiO3 at about 605°C while its acicular morphology is essentially unchanged. The preferable conditions for preparing pure acicular PX-phase PbTiO3 are that the pH is 13.0 to 14.0, Pb/Ti ratio is >1.3, reaction temperature is 170° to 200°C, time is 0.5 to 1.0 h, titanium butoxide (Ti[O(CH2)3CH3]4) is the starting material, and poly(vinyl alcohol) is an additive. The acicular grain of the PX phase is usually less than 100 nm in diameter and more than 1000 nm in length.  相似文献   
120.
Functional neuroimaging suggests that limbic regions of the medial frontal cortex may be abnormally active in individuals with depression. These regions, including the anterior cingulate cortex, are engaged in both action regulation, such as monitoring errors and conflict, and affect regulation, such as responding to pain. The authors examined whether clinically depressed subjects would show abnormal sensitivity of frontolimbic networks as they evaluated negative feedback. Depressed subjects and matched control subjects performed a video game in the laboratory as a 256-channel EEG was recorded. Speed of performance on each trial was graded with a feedback signal of A, C, or F. By 350 ms after the feedback signal, depressed subjects showed a larger medial frontal negativity for all feedback compared with control subjects with a particularly striking response to the F grade. This response was strongest for moderately depressed subjects and was attenuated for subjects who were more severely depressed. Localization analyses suggested that negative feedback engaged sources in the anterior cingulate and insular cortices. These results suggest that moderate depression may sensitize limbic networks to respond strongly to aversive events. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  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