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   3839篇
  免费   350篇
  国内免费   146篇
化学   680篇
晶体学   6篇
力学   396篇
综合类   26篇
数学   391篇
物理学   834篇
无线电   2002篇
  2024年   12篇
  2023年   44篇
  2022年   68篇
  2021年   69篇
  2020年   105篇
  2019年   49篇
  2018年   50篇
  2017年   137篇
  2016年   144篇
  2015年   159篇
  2014年   251篇
  2013年   236篇
  2012年   218篇
  2011年   263篇
  2010年   189篇
  2009年   208篇
  2008年   222篇
  2007年   235篇
  2006年   204篇
  2005年   200篇
  2004年   150篇
  2003年   159篇
  2002年   145篇
  2001年   109篇
  2000年   98篇
  1999年   72篇
  1998年   96篇
  1997年   56篇
  1996年   75篇
  1995年   55篇
  1994年   34篇
  1993年   31篇
  1992年   30篇
  1991年   21篇
  1990年   20篇
  1989年   7篇
  1988年   18篇
  1987年   15篇
  1986年   6篇
  1985年   14篇
  1984年   16篇
  1983年   14篇
  1982年   15篇
  1981年   2篇
  1980年   2篇
  1979年   2篇
  1978年   3篇
  1977年   3篇
  1973年   1篇
  1969年   1篇
排序方式: 共有4335条查询结果,搜索用时 15 毫秒
71.
检验检测服务模式发展滞后于检验检测行业发展的重要原因之一就是缺乏针对于服务模式的理论定义。采用概念分析法,以服务模式的定义和检验检测行业的服务特点为逻辑,研究了相关的代表性理论,认为服务模式主要由服务的基本要素和服务的商业模式两方面的内容组成,并深入探讨了检验检测的服务模式,提出了构建检验检测服务模式这一概念的重要意义。  相似文献   
72.
Bipolar electrode-based (BPE-based) electrochromic devices have garnered increasing attention in the past decade. These BPE-based electrochromic devices have been used for analytical health monitoring, point-of-care (POC) diagnostics, and chemical sensing. In this review, we highlight recent progress made regarding BPE-based electrochromic devices constructed for these analytical applications. Various, available electrochromic materials are summarized in the first section, after which the different device types (e. g., paper-based and self-powered) are discussed. Biological- and chemical-based analytical demonstrations of these devices are then reviewed. Finally, we conclude this review with a perspective on the future developments of BPE-based electrochromic devices in analytical applications.  相似文献   
73.
Electrochemical glucose sensors have garnered considerable attention because of their attractive prospect in point-of-care testing (POCT). In this review, we firstly introduce the principles and challenges of electrochemical glucose sensors. Subsequently, we present an overview of the application of electrochemical glucose sensors and discuss their advantages and drawbacks. Wearable and implantable devices based on diverse target biofluid and platforms provide a considerable prospect of accurate and continuous monitoring. Thus, we believe that the future development direction of electrochemical glucose sensors is non-invasive, wearable devices and implantable devices with minimally invasive for continuous glucose monitoring in real time.  相似文献   
74.
Cr3+-doped phosphors show significant application potential in near-infrared (NIR) light-emitting diodes (LEDs). However, the development of thermally stable and efficient NIR phosphors still faces enormous challenges. Herein, NIR phosphors K2NaMF6:Cr3+ (M3+ = Al3+, Ga3+, and In3+) were synthesized by the hydrothermal method. The represented K2NaAlF6:Cr3+ phosphor can be effectively excited by blue light (~430 nm) to present broadband emission at half a maximum of 96 nm peaking at ~ 728 nm. Meanwhile, the K2NaAlF6:Cr3+ phosphor exhibits excellent internal quantum efficiency (IQE = 68.08%) and nearly zero-thermal-quenching behavior, which is able to maintain 96.5% emission intensity at 150 °C of the initial value at 25 °C. The NIR phosphor-converted LED was fabricated based on K2NaAlF6:Cr3+ phosphor and a blue LED chip, showing a NIR output power of 394.39 mW at 300 mA with a high photoelectric conversion efficiency of 10.9% at 20 mA. Using the high-power NIR LED as a lighting source, transparent and quick veins imaging as well as non-destructive testing were demonstrated, suggesting the NIR phosphor has a wide range of practical applications.  相似文献   
75.
In this study, two‐phase hollow‐fiber liquid‐phase microextraction and three‐phase hollow‐fiber liquid‐phase microextraction based on two immiscible organic solvents were compared for extraction of oxazepam and Lorazepam. Separations were performed on a liquid chromatography with mass spectrometry instrument. Under optimal conditions, three‐phase hollow‐fiber liquid‐phase microextraction based on two immiscible organic solvents has a better extraction efficiency. In a urine sample, for three‐phase hollow fiber liquid‐phase microextraction based on two immiscible organic solvents, the calibration curves were found to be linear in the range of 0.6–200 and 0.9–200 μg L?1 and the limits of detection were 0.2 and 0.3 μg L?1 for oxazepam and lorazepam, respectively. For two‐phase hollow fiber liquid‐phase microextraction, the calibration curves were found to be linear in the range of 1–200 and 1.5–200 μg L?1 and the limits of detection were 0.3 and 0.5 μg L?1 for oxazepam and lorazepam, respectively. In a urine sample, for three‐phase hollow‐fiber‐based liquid‐phase microextraction based on two immiscible organic solvents, relative standard deviations in the range of 4.2–4.5% and preconcentration factors in the range of 70–180 were obtained for oxazepam and lorazepam, respectively. Also for the two‐phase hollow‐fiber liquid‐phase microextraction, preconcentration factors in the range of 101–257 were obtained for oxazepam and lorazepam, respectively.  相似文献   
76.
The development of novel microanalytical techniques forin situ chemical characterization of the terrestrial subsurface environment has grown significantly over the last decade, particularly those instruments that are interfaced to the cone penetrometer. Cone penetrometer testing (CPT) has emerged as an effective means to introduce samplers and probes forin situ analysis of contaminants in soil and groundwater matrices. A variety ofin situ chemical samplers for CPT have been developed that can be driven into the subsurface to collect soil gas, groundwater, or soil samples at depth, thus providing a means of determining the vertical and horizontal extent of contamination. Cone penetrometer testing is also being explored as a means to deliverin situ subsurface sensor probes, including probes based on laser-induced fluorescence, Raman, and infrared spectroscopies for organics; on laser-induced breakdown and X-ray fluorescence spectroscopies for heavy metals; and on passive gamma-ray spectroscopy for radionuclides. The range of analytical technologies used in CPT for the determination of organic and inorganic species in the subsurface is described.  相似文献   
77.
An application of automated on-line HPLC-HRGC is described for direct analysis of edible oils for migrated polymer additives. The sample preparation, separating the additive from the oil triglycerides, is carried out using normal phase HPLC. The fraction of the eluent containing the additive is automatically transferred to a HRGC where a second and final separation of the additive from minor oil components takes place. The method compares well with off-line separation methods. Migration data for Tinuvin 1577 from PET and PC polymers as well as an unspecified experimental polymer is given. The advantages and disadvantages of using different edible oils as food simulants are discussed.  相似文献   
78.
探讨了土壤中重金属检测能力验证的质量控制措施,为确保能力验证结果的准确性及不断提高实验室的检测技术水平提供参考.  相似文献   
79.
为实现对卡塞格林光学系统中的非球面主镜表面面形的高精度检测,设计了一种二元位相型计算全息图(CGH)。介绍了工作原理,对CGH的相位模型参数的优化设计、衍射次级分离以及台阶位置与深度计算等关键问题进行了讨论。通过引入虚拟玻璃的概念快速建立非球面检测模型,针对卡塞格林系统主镜中心开孔的特点,通过加入同轴载波实现了衍射次级的完全分离,相比目前常用的倾斜载波方法简化了相位量化复杂度,数值仿真计算出了最优的台阶深度,降低了加工难度。给出了相应的设计方法及实例,研制投产了CGH。测试得到主镜面形的均方根误差为0.018λ,并与传统补偿器结果(RMS=0.019λ)进行对比,两者测试结果吻合,验证了该设计与检测方法的正确性,该设计方法简单快捷,适用于卡塞格林光学系统主镜面形检测。  相似文献   
80.
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