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   302223篇
  免费   3096篇
  国内免费   1243篇
化学   142615篇
晶体学   4149篇
力学   15836篇
综合类   38篇
数学   45517篇
物理学   98407篇
  2021年   1356篇
  2020年   1510篇
  2019年   1574篇
  2018年   10773篇
  2017年   11650篇
  2016年   7147篇
  2015年   3300篇
  2014年   3368篇
  2013年   9421篇
  2012年   12014篇
  2011年   22035篇
  2010年   13476篇
  2009年   13611篇
  2008年   19335篇
  2007年   22760篇
  2006年   8440篇
  2005年   14722篇
  2004年   10433篇
  2003年   9329篇
  2002年   7226篇
  2001年   7321篇
  2000年   5726篇
  1999年   4212篇
  1998年   3220篇
  1997年   3100篇
  1996年   2901篇
  1995年   2721篇
  1994年   2583篇
  1993年   2388篇
  1992年   2763篇
  1991年   2737篇
  1990年   2445篇
  1989年   2388篇
  1988年   2478篇
  1987年   2393篇
  1986年   2248篇
  1985年   3233篇
  1984年   3249篇
  1983年   2581篇
  1982年   2798篇
  1981年   2684篇
  1980年   2584篇
  1979年   2640篇
  1978年   2698篇
  1977年   2601篇
  1976年   2563篇
  1975年   2477篇
  1974年   2365篇
  1973年   2500篇
  1972年   1494篇
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
31.
32.
33.
Su  X. F.  Zhang  Y. L.  Maximov  A. L.  Zhang  K.  Xin  Q.  Feng  C. Q.  Bai  X. F.  Wu  W. 《Russian Journal of Applied Chemistry》2020,93(1):127-136
Russian Journal of Applied Chemistry - Nanoscale ZSM-5 (AlZ5-D) and Ga-substituted ZSM-5 zeolites ((Al,Ga)Z5-D and GaZ5-D) were synthesized by a green dry-gel conversion strategy. For comparison,...  相似文献   
34.
35.
The results of investigation of optical image detectors designed for the largest problem, near-VUV, range of the spectrum are presented. The possibility of using a dual-stage image detection system to appreciably lower the sensitivity threshold and make computer data processing feasible is considered. The integration of a UV module into a wideband image detector is studied.  相似文献   
36.
37.
Two new compounds of fluorine: (C2H5)4N[I2F] and (C2H5)4N[Br2F], have been easily synthesized in a nearly quantitative by a direct reaction of (C2H5)4NF, I2 and Br2. The products were isolated and characterized by elemental analysis and spectroscopic methods such as: Fourier transform infrared spectroscopy (FTIR) and ultraviolet-visible spectroscopy (UV-Vis). These compounds have been studied computationally with the Scalar ZORA relativistic level of theory using the ADF program package. The molecular parameters, and vibrational spectra were calculated. The excitation energies were found by timedependent perturbation density functional theory (TD-DFT). Molecule optimization, frequencies and excitation energies were calculated with standard Slatertype-orbital (STO) basis sets with triple-zeta quality double plus polarization functions (TZ2P) for all atoms. The FTIR, UV-Vis spectra and assignment of principal transitions and total density of state (TDOS) were extracted using the GaussSum 2.2 program. The comparison between experimental and calculated values showes that the experimental results correlate well with the predicted data.  相似文献   
38.
39.
ABSTRACT

This study was to investigate the piezotolerance and diversity indices of microflora of Indian white prawn (Fenneropenaeus indicus) after high pressure (HP)-treatment. Indian white prawns subjected to HP-treatments and its effect was studied up to species level and compared with unpressurized samples. The bacterium was identified by using bacterial identification schemes, biochemical tests and API kits (bioMérieux, Marcyl’Etoile, France). Diversity analysis was performed using PRIMER (Plymouth Routines in Multivariate Research) software v 5.2.2. The significant elimination of microflora was found to be proportional with the pressure level. In the case of spore formers, mere destruction was noticed after HP-treatment. Arthrobacter spp., Listeria grayi and Corynebacterium spp. were the most piezotolerant bacteria in HP-treated samples. Diversity indices revealed a significant reduction of microflora of Indian white prawn. The apparent reduction of microflora with pressure level was clearly evident from the diversity indices; moreover a diminished piezotolerance of Gram negative spoilage bacteria was also observed.  相似文献   
40.
Journal of Thermal Analysis and Calorimetry - In recent decades, the growth of heat transfer using nanomaterials in the conventional base fluid has caught the attention of researchers...  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