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   22740篇
  免费   1103篇
  国内免费   2613篇
化学   11990篇
晶体学   176篇
力学   502篇
综合类   222篇
数学   1465篇
物理学   7752篇
无线电   4349篇
  2024年   26篇
  2023年   217篇
  2022年   302篇
  2021年   267篇
  2020年   352篇
  2019年   374篇
  2018年   309篇
  2017年   437篇
  2016年   514篇
  2015年   518篇
  2014年   919篇
  2013年   1711篇
  2012年   1178篇
  2011年   1301篇
  2010年   1071篇
  2009年   1327篇
  2008年   1440篇
  2007年   1671篇
  2006年   1437篇
  2005年   1147篇
  2004年   1095篇
  2003年   917篇
  2002年   816篇
  2001年   665篇
  2000年   1482篇
  1999年   1051篇
  1998年   998篇
  1997年   402篇
  1996年   390篇
  1995年   348篇
  1994年   293篇
  1993年   265篇
  1992年   248篇
  1991年   192篇
  1990年   114篇
  1989年   117篇
  1988年   83篇
  1987年   58篇
  1986年   46篇
  1985年   59篇
  1984年   43篇
  1983年   26篇
  1982年   35篇
  1981年   48篇
  1980年   26篇
  1979年   22篇
  1978年   22篇
  1977年   16篇
  1976年   14篇
  1973年   18篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
模拟电路课程在理论性、实践性和工程性等方面的表现均十分突出,是高校学员学习非常吃力的一门课程,如何提高课堂效率,充分利用课前、课中、课后的时间提高学员的理论基础和综合素质,是目前高校模拟电路教学工作中亟待解决的问题。本文以模拟电路课程为依托,深入研究课程内容的特点,构思在课程中开展五环导学法的方法,设计教学活动,并给出实施的策略和方法。  相似文献   
52.
This work presents an analysis of the existing dependencies between the tests of the FIPS 140-2 battery. Two main analytical approaches are utilized, the first being a study of correlations through the Pearson’s correlation coefficient that detects linear dependencies, and the second one being a novel application of the mutual information measure that allows detecting possible non-linear relationships. In order to carry out this study, the FIPS 140-2 battery is reimplemented to allow the user to obtain p-values and statistics that are essential for more rigorous end-user analysis of random number generators (RNG).  相似文献   
53.
Antimicrobial resistance (AMR) poses a serious threat to our society from both the medical and economic point of view, while the antibiotic discovery pipeline has been dwindling over the last decades. Targeting non-essential bacterial pathways, such as those leading to antibiotic persistence, a bacterial bet-hedging strategy, will lead to new molecular entities displaying low selective pressure, thereby reducing the insurgence of AMR. Here, we describe a way to target (p)ppGpp (guanosine tetra- or penta-phosphate) signaling, a non-essential pathway involved in the formation of persisters, with a structure-based approach. A superfamily of enzymes called RSH (RelA/SpoT Homolog) regulates the intracellular levels of this alarmone. We virtually screened several fragment libraries against the (p)ppGpp synthetase domain of our RSH chosen model RelSeq, selected three main chemotypes, and measured their interaction with RelSeq by thermal shift assay and STD-NMR. Most of the tested fragments are selective for the synthetase domain, allowing us to select the aminobenzoic acid scaffold as a hit for lead development.  相似文献   
54.
On the basis of the agreement of calculated and measured parameters of some amorphous semiconductors, an argument is stated in favour of the central-symmetric type of random local electric fields. A possible mechanism of the transport of electrons is discussed.  相似文献   
55.
本文所关注的激光干涉测速技术主要用于测试在冲击波或爆轰波作用下各种材料样品的自由面速度随时间变化的过程,介绍了基于光学谐振腔的选频特性利用薄腔法-珀干涉仪直接测量高速飞片所引起的多普勒频移从而获得其速度信息的设想,并根据此设想构建薄腔法-珀干涉测速系统的技术路线。最后描述了利用该项测试技术实际测量金属箔电爆炸驱动的Kapton膜飞片速度的实验并对实验结果进行了分析。与其它激光测速装置相比,该干涉仪具有体积小、结构简单紧凑和成本低的特点。  相似文献   
56.
针对新型的微电阻率成像扫描仪使用的幅度调制信号的特点,提出一种载波相位和调制波幅度的计算方法,重点研究载波相位提取。首先从理论上系统地介绍了基于带通采样和数字正交解调的载波相位和调制波幅度的测量方法,然后通过LabVIEW仿真验证,该方法能实现常温和高温条件下幅度调制信号的载波相位和调制波幅度的高精度测量。  相似文献   
57.
A closed form expression for the bit error rate (BER) performance of frequency domaindifferential demodulation(FDDD) for orthogonal frequency division multiplexing system in flat fadingchannel is derived.The performance is evaluated by computer simulation and compared with the timedomain differential demodulation(TDDD).The results indicate that the performance of FDDD is betterthan that of TDDD,and the lower band of BER in the former is lower than that of the latter.  相似文献   
58.
As a global health problem, liver fibrosis still does not have approved treatment. It was proved that N-(3,4,5-trichlorophenyl)-2(3-nitrobenzenesulfonamide) benzamide (IMB16-4) has anti-hepatic fibrosis activity. However, IMB16-4 displays poor water solubility and poor bioavailability. We are devoted to developing biodegraded liposome-coated polymeric nanoparticles (LNPs) as IMB16-4 delivery systems for improving aqueous solubility, cellular uptake, and anti-fibrotic effects. The physical states of IMB16-4−LNPs were analyzed using a transmission electron microscope (TEM), high-performance liquid chromatography (HPLC), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and differential scanning calorimeter (DSC). The results show that IMB16-4−LNPs increased the drug loading compared to liposomes and enhanced cellular uptake behavior compared with IMB16-4−NPs. In addition, IMB16-4−LNPs could repress the expression of hepatic fibrogenesis-associated proteins, indicating that IMB16-4−LNPs exhibited evident anti-fibrotic effects.  相似文献   
59.
软件测试是开发过程的重要环节。回归错误在开发过程中严重影响着开发的效率,其隐匿特性也使得测试比较困难。因此,本文提出一种非间断测试的模型,用于加强对回归错误的管理,节约不必要的无谓工作时间,提高软件开发的效率。这种模型对用户开发行为进行模拟和推测,在经过大量的数据训练后,寻找测试行为、错误发生等开发动作的捕获点,从而找到最佳的测试策略。在不影响开发人员工作的前提下,可对当前最新的代码进行测试,最大程度上避免回归错误长期隐藏在前期代码中,保持整个开发过程的稳步前进。  相似文献   
60.
A CA19-9 electrochemical immunosensor was constructed using a hybrid self-assembled membrane modified with a gold electrode and applied to detect real samples. Hybrid self-assembled membranes were selected for electrode modification and used to detect antigens. First, the pretreated working electrodes were placed in a 3-mercaptopropionic acid (MPA)/β-mercaptoethanol (ME) mixture for 24 h for self-assembly. The electrodes were then placed in an EDC/NHS mixture for 1 h. Layer modification was performed by stepwise dropwise addition of CA19-9 antibody, BSA, and antigen. Differential pulse voltammetry was used to characterize this immunosensor preparation process. The assembled electrochemical immunosensor enables linear detection in the concentration range of 0.05–500 U/mL of CA19-9, and the detection limit was calculated as 0.01 U/mL. The results of the specificity measurement test showed that the signal change of the interfering substance was much lower than the response value of the detected antigen, indicating that the sensor has good specificity and strong anti-interference ability. The repeatability test results showed that the relative standard deviations were less than 5%, showing good accuracy and precision. The CA19-9 electrochemical immunosensor was used for the actual sample detection, and the experimental results of the standard serum addition method showed that the RSD values of the test concentrations were all less than 10%. The recoveries were 102.4–115.0%, indicating that the assay has high precision, good accuracy, and high potential application value.  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