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   423篇
  免费   3篇
  国内免费   4篇
化学   203篇
晶体学   11篇
力学   3篇
数学   10篇
物理学   149篇
无线电   54篇
  2023年   8篇
  2022年   7篇
  2021年   4篇
  2020年   11篇
  2019年   13篇
  2018年   13篇
  2016年   8篇
  2015年   7篇
  2014年   4篇
  2013年   24篇
  2012年   16篇
  2011年   18篇
  2010年   15篇
  2009年   19篇
  2008年   9篇
  2007年   21篇
  2006年   19篇
  2005年   17篇
  2004年   9篇
  2003年   9篇
  2002年   11篇
  2000年   3篇
  1999年   8篇
  1998年   9篇
  1997年   3篇
  1996年   6篇
  1995年   6篇
  1994年   8篇
  1993年   5篇
  1992年   6篇
  1991年   5篇
  1990年   6篇
  1989年   2篇
  1988年   8篇
  1987年   5篇
  1986年   6篇
  1985年   10篇
  1984年   12篇
  1983年   6篇
  1982年   2篇
  1981年   12篇
  1980年   4篇
  1979年   4篇
  1977年   6篇
  1974年   3篇
  1973年   4篇
  1972年   2篇
  1971年   5篇
  1955年   2篇
  1954年   2篇
排序方式: 共有430条查询结果,搜索用时 15 毫秒
61.
Wireless Personal Communications - Sparse representation-based classification (SRC) has been successfully used in facial expression recognition, well-known for its high accuracy and robustness to...  相似文献   
62.
The emergence of untreatable drug-resistant strains of Mycobacterium tuberculosis is a major public health problem worldwide, and the identification of new efficient treatments is urgently needed. Mycobacterium tuberculosis cytochrome P450 CYP121A1 is a promising drug target for the treatment of tuberculosis owing to its essential role in mycobacterial growth. Using a rational approach, which includes molecular modelling studies, three series of azole pyrazole derivatives were designed through two synthetic pathways. The synthesized compounds were biologically evaluated for their inhibitory activity towards M. tuberculosis and their protein binding affinity (KD). Series 3 biarylpyrazole imidazole derivatives were the most effective with the isobutyl ( 10 f ) and tert-butyl ( 10 g ) compounds displaying optimal activity (MIC 1.562 μg/mL, KD 0.22 μM ( 10 f ) and 4.81 μM ( 10 g )). The spectroscopic data showed that all the synthesised compounds produced a type II red shift of the heme Soret band indicating either direct binding to heme iron or (where less extensive Soret shifts are observed) putative indirect binding via an interstitial water molecule. Evaluation of biological and physicochemical properties identified the following as requirements for activity: LogP >4, H-bond acceptors/H-bond donors 4/0, number of rotatable bonds 5–6, molecular volume >340 Å3, topological polar surface area <40 Å2.  相似文献   
63.
JPC – Journal of Planar Chromatography – Modern TLC - Inula cappa (family Compositae) is used in the Ayurvedic medicinal system for the treatment of bronchitis, diabetes, fever,...  相似文献   
64.
65.
Wireless Personal Communications - In the current generation of information technology, mobile applications (apps) have become an essential and momentous source to publicize the information across...  相似文献   
66.
Wireless Personal Communications - Early diagnosis of diseases related with retina such as glaucoma is of utmost importance in current scenario as it is the second most prevailing cause of...  相似文献   
67.

Energy conservation in wireless sensor networks (WSNs) is a fundamental issue. For certain surveillance applications in WSN, coverage lifetime is an important issue and this is related to energy consumption significantly. In order to handle these two interlinked aspects in WSN, a new scheme named Weight based Coverage Enhancing Protocol (WCEP) has been introduced. The WCEP aims to obtain longer full coverage and better network life time. The WCEP is based on assigning different weight values to certain governing parameters which are residual energy, overlapping degree, node density and degree of sensor node. These governing parameters affect the energy and coverage aspects predominantly. Further, these four different parameters are prime elements in cluster formation process and node scheduling mechanisms. The weight values help in selection of an optimal group of Cluster Heads and Cluster Members, which result in enhancement of complete coverage lifetime. The simulation results indicate that WCEP performs better in terms of energy consumption also. The enhancement of value 24% in full coverage lifetime has been obtained as compared to established existing techniques.

  相似文献   
68.
In the present work, the oxygen reduction reaction (ORR) is explored in an acidic medium with two different catalytic supports (multi-walled carbon nanotubes (MWCNTs) and nitrogen-doped multi-walled carbon nanotubes (NMWCNTs)) and two different catalysts (copper phthalocyanine (CuPc) and sulfonic acid functionalized CuPc (CuPc-SO3)). The composite, NMWCNTs-CuPc-SO3 exhibits high ORR activity (assessed based on the onset potential (0.57 V vs. reversible hydrogen electrode) and Tafel slope) in comparison to the other composites. Rotating ring disc electrode (RRDE) studies demonstrate a highly selective four-electron ORR (less than 2.5 % H2O2 formation) at the NMWCNTs-CuPc-SO3. The synergistic effect of the catalyst support (NMWCNTs) and sulfonic acid functionalization of the catalyst (in CuPc-SO3) increase the efficiency and selectivity of the ORR at the NMWCNTs-CuPc-SO3. The catalyst activity of NMWCNTs-CuPc-SO3 has been compared with many reported materials and found to be better than several catalysts. NMWCNTs-CuPc-SO3 shows high tolerance for methanol and very small deviation in the onset potential (10 mV) between the linear sweep voltammetry responses recorded before and after 3000 cyclic voltammetry cycles, demonstrating exceptional durability. The high durability is attributed to the stabilization of CuPc-SO3 by the additional coordination with nitrogen (Cu-Nx) present on the surface of NMWCNTs.  相似文献   
69.
Photodynamic therapy (PDT), the combined action of a photosensitizer and light to produce a cytotoxic effect, is an approved therapy for a number of diseases. At present, clinical PDT treatments involve one-photon excitation of the photosensitizer. A major limitation is that damage may be caused to healthy tissues that have absorbed the drug and lie in the beam path. Two-photon excitation may minimize this collateral damage, as the probability of absorption increases with the square of the light intensity, enabling spatial confinement of the photosensitizer activation. A potential application is the treatment of the wet-form of age-related macular degeneration, the foremost cause of central vision loss in the elderly. Herein, the commercial photosensitizers Visudyne and Photofrin are used to demonstrate quantitative in vitro two-photon PDT. A uniform layer of endothelial cells (YPEN-1) was irradiated with a Ti:sapphire laser (300 fs, 865 nm, 90 MHz) using a confocal scanning microscope. Quantification of the two-photon PDT effect was achieved using the permeability stain Hoechst 33258 and a SYTOX Orange viability stain. Visudyne was found to be around seven times more effective as a two-photon photosensitizer than Photofrin under the conditions used, consistent with its higher two-photon absorption cross-section. We also demonstrate for the first time the quadratic intensity dependence of cellular two-photon PDT. This simple in vitro method for quantifying the efficacy of photosensitizers for two-photon excited PDT will be valuable to test specifically designed two-photon photosensitizers before proceeding to in vivo studies in preclinical animal models.  相似文献   
70.
Summary: The predictions of the model developed in Part 1 of this series are compared with experimental values taken from literature. Initially, the method of solution of the population balance equation and the simulation algorithm are given. Various radical entry mechanisms are discussed in adequate detail. Plausible arguments are given to identify the correct radical entry mechanism. An expression to evaluate the radical exit coefficient is given. Model predictions of a number of variables are discussed. These include average number of radicals per particle, particle phase monomer volume fraction, average number of radicals averaged over all particles, monomer volume fraction averaged over all particles, variation of nucleation rate, variation of fraction of droplets nucleated, variation of average diameter, variation of standard deviation, variation of polydispersity index, and development of particle size distribution with time. Finally, model predictions for the variation of conversion with time for five different initiator concentrations, number average diameter, standard deviation and full distribution are compared with experimental values.

Variation in the average number of radicals per particle with time, at different collocation points.  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