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   5945篇
  免费   267篇
  国内免费   369篇
化学   446篇
晶体学   7篇
力学   721篇
综合类   34篇
数学   386篇
物理学   405篇
综合类   4582篇
  2024年   33篇
  2023年   69篇
  2022年   123篇
  2021年   143篇
  2020年   142篇
  2019年   118篇
  2018年   109篇
  2017年   142篇
  2016年   138篇
  2015年   154篇
  2014年   263篇
  2013年   250篇
  2012年   325篇
  2011年   332篇
  2010年   246篇
  2009年   266篇
  2008年   310篇
  2007年   387篇
  2006年   321篇
  2005年   307篇
  2004年   290篇
  2003年   264篇
  2002年   246篇
  2001年   228篇
  2000年   167篇
  1999年   131篇
  1998年   132篇
  1997年   142篇
  1996年   115篇
  1995年   106篇
  1994年   97篇
  1993年   77篇
  1992年   86篇
  1991年   63篇
  1990年   62篇
  1989年   53篇
  1988年   52篇
  1987年   32篇
  1986年   33篇
  1985年   6篇
  1984年   3篇
  1983年   1篇
  1982年   5篇
  1981年   2篇
  1980年   2篇
  1979年   2篇
  1978年   1篇
  1971年   3篇
  1957年   1篇
  1955年   1篇
排序方式: 共有6581条查询结果,搜索用时 10 毫秒
151.
The expression of the continuous distribution function F(x) is obtained whenever % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXafv3ySLgzGmvETj2BSbqefm0B1jxALjhiov2D% aebbfv3ySLgzGueE0jxyaibaiGc9yrFr0xXdbba91rFfpec8Eeeu0x% Xdbba9frFj0-OqFfea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs% 0dXdbPYxe9vr0-vr0-vqpWqaaeaabiGaciaacaqabeaadaqaaqGaaO% qaaerbhv2BYDwAHbacfiGaa8xBaiaabIcacaWG4bGaaiilaiaadMha% caqGPaGaa8hiaiaab2dacaWFGaGaa8xraiaa-HcacaWFybGaa8hiai% aa-XhacaWFGaGaa8hEaiaa-bcacqGHKjYOcaWFGaGaa8hwaiaa-bca% cqGHKjYOcaWFGaGaa8xEaiaa-Lcaaaa!53EE!\[m{\rm{(}}x,y{\rm{)}} {\rm{ = }} E(X | x \le X \le y)\]is known. Moreover, we obtain the necessary and sufficient conditions so that any function m: 2 is the conditional expectation % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXafv3ySLgzGmvETj2BSbqefm0B1jxALjhiov2D% aebbfv3ySLgzGueE0jxyaibaiGc9yrFr0xXdbba91rFfpec8Eeeu0x% Xdbba9frFj0-OqFfea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs% 0dXdbPYxe9vr0-vr0-vqpWqaaeaabiGaciaacaqabeaadaqaaqGaaO% qaaiaadweacaGGOaGaamiwaerbhv2BYDwAHbacfiGaa8hiaiaacYha% caWFGaGaa8hEaiaa-bcacqGHKjYOcaWFGaGaa8hwaiaa-bcacqGHKj% YOcaWFGaGaa8xEaiaacMcaaaa!4D0D!\[E(X | x \le X \le y)\]of a random variable X with continuous distribution function. Furthermore, we relate m(x,y) to order statistics.  相似文献   
152.
研究了不同时间腐蚀的多孔硅的光致发光性能与多孔硅的表面形貌和少子寿命之间的关系。结果表明,多孔硅的发光来自与氧空位有关的缺陷,而多孔硅表面的氢原子能够钝化多孔硅表面的非辐射中心从而提高多孔硅的发光效率。多孔硅的空隙度随腐蚀时间的延长而增大,这也导致了多孔硅的少子寿命的降低,从而造成多孔硅的光致发光效率随多孔硅空隙度的增大以及少子寿命的降低而提高。另外,原子力显微照片表明长时间的腐蚀使多孔硅表面层被化学腐蚀,从而降低了多孔硅表面的粗糙度。  相似文献   
153.
154.
155.
156.
The purpose of this retrospective study is to describe results of acoustic, aerodynamic, and videostroboscopic measures in patients complaining of laryngeal fatigue. Data were collected from 88 patients whose primary complaint was chronic laryngeal fatigue in the absence of visible laryngeal pathologies. The results revealed an abnormally high airflow rate and decreased maximum phonation time. An anterior glottal chink, anterior and posterior glottal chinks, or spindle-shaped glottal closure were found in 61% of the subjects.  相似文献   
157.
微通道板增益疲劳机理研究   总被引:2,自引:0,他引:2  
微通道板的增益疲劳是微通道板的主要问题之一,本文分析了微通道板的表面结构模型,同通道板活性表面上碱金属的逸出和碳的增加是导致微通道板的增益疲劳的主要原因,另外,探讨碱金属逸出的机理和碳污染的来源,介绍延长微通道板工作寿命的有效方法。  相似文献   
158.
In the assessment of most complex socioeconomic phenomena with the use of multicriteria methods, continuous data are used, the source of which are most often public statistics. However, there are complex phenomena such as quality of life and quality of services in the assessment, for which questionnaire surveys and ordinal measurement scales are used. In this case, the use of classic multicriteria methods is very difficult, taking into account the way of presenting this type of data by official statistics, as well as their permissible transformations and arithmetic operations. Therefore, the main purpose of this study was the presentation of a novel framework which can be applied for assessing socioeconomic phenomena on the basis of survey data. It was assumed that the object assessments may contain positive or negative opinions and an element of uncertainty expressed in the form a “no”, “difficult to say”, or “no opinion” answers. For this reason, the intuitionistic fuzzy TOPSIS (IF-TOPSIS) method is proposed. To demonstrate the potential of this solution, the results of measuring the subjective quality of life of the inhabitants of 83 cities in EU countries, EFTA countries, the UK, the Western Balkans, and Turkey are presented. For most cities, a high level of subjective quality of life was observed using the proposed approach. The highest level of quality of life was observed in Zurich, whereas the lowest was observed in Palermo.  相似文献   
159.
Structural health monitoring (SHM) is recognized as an efficient tool to interpret the reliability of a wide variety of infrastructures. To identify the structural abnormality by utilizing the electromechanical coupling property of piezoelectric transducers, the electromechanical impedance (EMI) approach is preferred. However, in real-time SHM applications, the monitored structure is exposed to several varying environmental and operating conditions (EOCs). The previous study has recognized the temperature variations as one of the serious EOCs that affect the optimal performance of the damage inspection process. In this framework, an experimental setup is developed in current research to identify the presence of fatigue crack in stainless steel (304) beam using EMI approach and estimate the effect of temperature variations on the electrical impedance of the piezoelectric sensors. A regular series of experiments are executed in a controlled temperature environment (25°C–160°C) using 202 V1 Constant Temperature Drying Oven Chamber (Q/TBXR20-2005). It has been observed that the dielectric constant ε33T which is recognized as the temperature-dependent constant of PZT sensor has sufficiently influenced the electrical impedance signature. Moreover, the effective frequency shift (EFS) approach is optimized in term of significant temperature compensation for the current impedance signature of PZT sensor relative to the reference signature at the extended frequency bandwidth of the developed measurement system with better outcomes as compared to the previous literature work. Hence, the current study also deals efficiently with the critical issue of the width of the frequency band for temperature compensation based on the frequency shift in SHM. The results of the experimental study demonstrate that the proposed methodology is qualified for the damage inspection in real-time monitoring applications under the temperature variations. It is capable to exclude one of the major reasons of false fault diagnosis by compensating the consequence of elevated temperature at extended frequency bandwidth in SHM.  相似文献   
160.
以 YBCO(YBa2Cu3 O7 -δ ) 为代表的二代高温超导带材因具有高临界转变温度、 高临界磁场和强载流能力,受到了国际学界高度关注, 在各个领域具有广泛的应用前景. 二代高温超导带材在绕制、 冷却和运行过程中会受到不同来源的外力作用, 且超导带材的韧性、 延展性较差, 因此其机械性能是影响安全性与设备运行可靠性的关键.本文基于二代超导带材各向异性的特点, 对超导带材轴向、 横向、 弯曲三个方向的静态机械性能及疲劳性能进行了介绍. 同时, 也对超导带材各方向机械性能的测试方法、 影响因素及机理进行了总结  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