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   6301篇
  免费   909篇
  国内免费   863篇
化学   1352篇
晶体学   32篇
力学   479篇
综合类   184篇
数学   3466篇
物理学   2560篇
  2024年   22篇
  2023年   103篇
  2022年   113篇
  2021年   118篇
  2020年   97篇
  2019年   85篇
  2018年   81篇
  2017年   115篇
  2016年   140篇
  2015年   233篇
  2014年   475篇
  2013年   312篇
  2012年   560篇
  2011年   520篇
  2010年   487篇
  2009年   436篇
  2008年   595篇
  2007年   352篇
  2006年   364篇
  2005年   332篇
  2004年   306篇
  2003年   295篇
  2002年   271篇
  2001年   237篇
  2000年   171篇
  1999年   167篇
  1998年   160篇
  1997年   149篇
  1996年   132篇
  1995年   132篇
  1994年   108篇
  1993年   71篇
  1992年   78篇
  1991年   69篇
  1990年   62篇
  1989年   72篇
  1988年   19篇
  1987年   14篇
  1986年   3篇
  1985年   2篇
  1984年   3篇
  1983年   5篇
  1982年   5篇
  1980年   1篇
  1979年   1篇
排序方式: 共有8073条查询结果,搜索用时 0 毫秒
91.
唐军  梅坚 《教学与科技》2005,18(1):40-42
本文就如何在素质教育中培养出创造性人才的问题,以及在培养过程中要正确处理的四个关系和培养中的主要途径进行了探讨。  相似文献   
92.
 法国傅立叶大学和劳厄-朗之万研究所,以马里·普拉扎纳为首的科学家制取一种能在加热时凝固和在冷却时变成液体的特殊物质。科学家早已知道提高温度时能凝固的物质成分,其中包括在聚合作用时观察到的这类现象,但是相反的冷却时能变成液体是首次成功实现。在实验过程中利用了α环化糊精和四甲基吡啶水溶液。  相似文献   
93.
The microwave (MW) transmission method is employed to measure both the plasma density and the plasma decay time in the hollow cathode discharge (HCD) in argon at low pressure. The plasma density in DC-driven or pulsed HCD is on the order of 1012 cm-3, which can block the X-band MW effectively. In the case of pulsed HCD, the MW transmittance shows the same waveform as the pulsed current during the rising edge if the driving frequency is low, but with a longer delay during the falling edge. The MW transmittance reaches a constant low level when the driving frequency is high enough. The plasma decay time in the HCD system is measured to be about 100 μs around a pressure of 120 Pa. The ambipolar diffusion is considered to be the major mechanism in the decay process.  相似文献   
94.
In the integrated circuit manufacturing process, the critical area extraction is a bottleneck to the layout optimization and the integrated circuit yield estimation. In this paper, we study the problem that the missing material defects may result in the open circuit fault. Combining the mathematical morphology theory, we present a new computation model and a novel extraction algorithm for the open critical area based on the net flow-axis. Firstly, we find the net flow-axis for different nets. Then, the net flow-edges based on the net flow-axis are obtained. Finally, we can extract the open critical area by the mathematical morphology. Compared with the existing methods, the nets need not to divide into the horizontal nets and the vertical nets, and the experimental results show that our model and algorithm can accurately extract the size of the open critical area and obtain the location information of the open circuit critical area.  相似文献   
95.
The 3s–np photoionization processes of the ground state 2P1/2 and the metastable state 2P3/2 of Ar5+ are investigated using our recently developed relativistic R-matrix code, where the interactions between the bound states and the continuum states are included. Both resonance positions and the oscillator strengths are in much better agreement with the absolute experimental measurements by Wang et al.[Wang J C, Lu M, Esteves D, Habibi M, Alna’washi G and Phaneuf R A 2007 Phys. Rev. A 75 062712] with a resolution of 80 meV than their theoretical results. The contributions of the two experimental unresolved transitions are distinguished in our calculations, which show that the transitions from the ground state also make significant contributions to some resonances. Our theoretical results are also in good agreement with the measurements for the first resonance with a higher resolution of 20 meV.  相似文献   
96.
利用差示扫描量热法(DSC)和X射线衍射(XRD)研究了在不同丙烯腈/尿素投料比情况下的丙烯腈-尿素包合物的形成过程和组成. 实验结果表明DSC是一种研究包合物的客主比及分解热的有效方法. 测定了丙烯腈-尿素包合物的客主比和分解热分别为1.17和5361.53 J/mol. 同时发现丙烯腈-尿素包合物的形成依赖于冷冻时间,在足够长的冷冻时间之后丙烯腈-尿素包合物的组成达到稳定状态. 实验结果表明,丙烯腈分子可能是采用堆叠的方式排布在尿素晶道结构中. XRD结果表明只要丙烯腈分子进入尿素晶格中,丙烯腈-尿素包合物的结构便形成了,并且这种结构与形成过程终了时的结构是一致的. 只要丙烯腈是足量的,包合物中的丙烯腈分子排列会随冷冻时间的延长而增长,直到尿素的晶道结构被丙烯腈分子填满.  相似文献   
97.
Through a series of studies on arithmetic coding and arithmetic encryption, a novel image joint compression- encryption algorithm based on adaptive arithmetic coding is proposed. The contexts produced in the process of image compression are modified by keys in order to achieve image joint compression encryption. Combined with the bit-plane coding technique, the discrete wavelet transform coefficients in different resolutions can be encrypted respectively with different keys, so that the resolution selective encryption is realized to meet different application needs. Zero-tree coding is improved, and adaptive arithmetic coding is introduced. Then, the proposed joint compression-encryption algorithm is simulated. The simulation results show that as long as the parameters are selected appropriately, the compression efficiency of proposed image joint compression-encryption algorithm is basically identical to that of the original image compression algorithm, and the security of the proposed algorithm is better than the joint encryption algorithm based on interval splitting.  相似文献   
98.
The effects of clouds, sea surface temperature, and its diurnal variation on precipitation efficiency are investigated using grid-scale data from nine equilibrium sensitivity cloud-resolving model experiments driven without large-scale vertical velocity. The precipitation efficiencies are respectively defined in surface rainfall, cloud, and rain microphysical budgets. We mathematically and physically demonstrate the relationship between these precipitation efficiencies. The 2℃ increases in spatiotemporal invariant sea surface temperature (SST) from 27℃ to 29℃ and from 29℃ to 31℃, and the inclusion of diurnal SST difference 1℃ and the 1℃ increase in diurnal SST difference generate opposite changes in the precipitation efficiency by changing ice cloud-radiation interactions. The radiative and microphysical processes of ice clouds have opposite effects on the precipitation efficiency because of the rainfall increase associated with the reduction in the saturation mixing ratio caused by the exclusion of radiative effects and the decrease in rainfall related to the reduction in net condensation caused by the exclusion of deposition processes. The radiative effects of water clouds on the precipitation efficiency are statistically insensitive to the radiative effects of ice clouds.  相似文献   
99.
《发光学报》2013,(4):535
一、《发光学报》是中国物理学会发光分会主办的,以凝聚态物质中的激发态过程研究为专业方向的综合性学术刊物。它的任务是反映各学科间该专业研究领域的科研和技术成就,及时报道国内、外的学术动态,开展学术讨论和交流,提高从事各学科间该研究领域工作的专业人员的专业知识水平,为提高我国该学科的学术水平服务。  相似文献   
100.
During the last decade, striking improvements could be achieved for the precise control of deposition processes in optical coating technology. For example, as a consequence of enormous progresses in measure- ment and computer technology, direct optical monitoring in a broad spectral range can be considered as a common tool in many production environments nowadays. Besides the development of the corresponding hardware and measurement channels, advanced approaches for the evaluation of the acquired data and new multiple sensor monitoring strategies moved into the focus of modern research on the way towards de- terministic deposition techniques. In this context, also innovative concepts for the simulation of deposition processes to forecast the result for a specified coating design and automatic online correction algorithms gained of importance to reduce the risk of failure in coating production. The present contribution will be dedicated to selected aspects in this field, especially addressing broad band optical monitoring systems. A short review on examples for existing hardware configurations and software tools will be presented illus- trating the advantages of modern process control techniques. Novel approaches based on the modeling of thin film growth are discussed as an additional strategy to improve the predictability of coating processes.  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