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   612篇
  免费   16篇
  国内免费   5篇
化学   392篇
晶体学   5篇
力学   16篇
数学   80篇
物理学   140篇
  2022年   3篇
  2021年   3篇
  2020年   5篇
  2019年   8篇
  2018年   3篇
  2016年   12篇
  2015年   6篇
  2014年   11篇
  2013年   26篇
  2012年   36篇
  2011年   34篇
  2010年   14篇
  2009年   11篇
  2008年   41篇
  2007年   47篇
  2006年   31篇
  2005年   40篇
  2004年   38篇
  2003年   32篇
  2002年   22篇
  2001年   13篇
  2000年   8篇
  1999年   8篇
  1998年   5篇
  1997年   7篇
  1996年   10篇
  1995年   16篇
  1994年   9篇
  1993年   10篇
  1992年   10篇
  1991年   11篇
  1990年   9篇
  1989年   4篇
  1988年   3篇
  1987年   5篇
  1986年   6篇
  1985年   6篇
  1984年   7篇
  1983年   8篇
  1982年   5篇
  1981年   3篇
  1979年   3篇
  1978年   4篇
  1977年   3篇
  1976年   4篇
  1975年   3篇
  1974年   5篇
  1973年   2篇
  1937年   4篇
  1931年   3篇
排序方式: 共有633条查询结果,搜索用时 46 毫秒
31.
Direct observations of infrared absorption in the weakly bound dimer of carbonyl sulphide, produced in pulsed molecular beams, have been made. Diode laser spectra in the 5 micron, carbonyl stretching, wavelength region were recorded with FWHM linewidths of approximately 100 MHz. All of the observations are consistent with OCS dimer having a C 2h , centrosymmetric geometry, with the centres of mass of the monomers nearly opposite one another. This essentially perpendicular structure places the S atoms close to the centre of the complex. The perpendicular distance between the monomer axes is 3·64 Å. Intermolecular potential functions containing dispersion and electrostatic contributions are discussed.  相似文献   
32.
33.
34.
35.
The conversion of cyclic imides to the corresponding N-cyanoimides has been carried out using cyanogen bromide as the nitrile source. This methodology provides a convenient route for the preparation of both aromatic and aliphatic N-cyanoimides.  相似文献   
36.
The Berkeley Center for Structural Biology (BCSB) operates and develops a suite of protein crystallography beamlines at the Advanced Light Source (ALS) located at Lawrence Berkeley National Laboratory (LBNL). Although the ALS was conceived as a low-energy (1.9-GeV), third-generation synchrotron source of vacuum ultraviolet (VUV) and soft X-ray radiation, it was realized during the development of the facility in the mid-1990s that a multipole wiggler coupled with brightness-preserving optics would result in a beamline whose performance in the energy range of 5 to 15 keV would be sufficient for most protein crystallographic experiments. Later, the hard X-ray capabilities of the ALS were expanded by the addition of three superconducting bending magnets, resulting in additional protein crystallography facilities at the ALS [1 A.A. MacDowell, J Synchrotron Radiation 11(6), 44755 (2004).[Crossref], [PubMed], [Web of Science ®] [Google Scholar]].  相似文献   
37.
We designed, synthesized, and characterized a new Zr‐based metal–organic framework material, NU‐1100 , with a pore volume of 1.53 ccg?1 and Brunauer–Emmett–Teller (BET) surface area of 4020 m2g?1; to our knowledge, currently the highest published for Zr‐based MOFs. CH4/CO2/H2 adsorption isotherms were obtained over a broad range of pressures and temperatures and are in excellent agreement with the computational predictions. The total hydrogen adsorption at 65 bar and 77 K is 0.092 g g?1, which corresponds to 43 g L?1. The volumetric and gravimetric methane‐storage capacities at 65 bar and 298 K are approximately 180 vSTP/v and 0.27 g g?1, respectively.  相似文献   
38.
The accurate prediction of the solar diffuse fraction (DF), sometimes called the diffuse ratio, is an important topic for solar energy research. In the present study, the current state of Diffuse irradiance research is discussed and then three robust, machine learning (ML) models are examined using a large dataset (almost eight years) of hourly readings from Almeria, Spain. The ML models used herein, are a hybrid adaptive network-based fuzzy inference system (ANFIS), a single multi-layer perceptron (MLP) and a hybrid multi-layer perceptron grey wolf optimizer (MLP-GWO). These models were evaluated for their predictive precision, using various solar and DF irradiance data, from Spain. The results were then evaluated using frequently used evaluation criteria, the mean absolute error (MAE), mean error (ME) and the root mean square error (RMSE). The results showed that the MLP-GWO model, followed by the ANFIS model, provided a higher performance in both the training and the testing procedures.  相似文献   
39.
40.
A behavioral response paradigm was used to measure masked underwater hearing thresholds in a bottlenose dolphin (Tursiops truncatus) and a white whale (Delphinapterus leucas) before and after exposure to single underwater impulsive sounds produced from a seismic watergun. Pre- and postexposure thresholds were compared to determine if a temporary shift in masked hearing thresholds (MTTS), defined as a 6-dB or larger increase in postexposure thresholds, occurred. Hearing thresholds were measured at 0.4, 4, and 30 kHz. MTTSs of 7 and 6 dB were observed in the white whale at 0.4 and 30 kHz, respectively, approximately 2 min following exposure to single impulses with peak pressures of 160 kPa, peak-to-peak pressures of 226 dB re 1 microPa, and total energy fluxes of 186 dB re 1 microPa2 x s. Thresholds returned to within 2 dB of the preexposure value approximately 4 min after exposure. No MTTS was observed in the dolphin at the highest exposure conditions: 207 kPa peak pressure, 228 dB re 1 microPa peak-to-peak pressure, and 188 dB re 1 microPa2 x s total energy flux.  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