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   583959篇
  免费   8583篇
  国内免费   1855篇
化学   317550篇
晶体学   8170篇
力学   25616篇
综合类   18篇
数学   70571篇
物理学   172472篇
  2021年   4771篇
  2020年   5419篇
  2019年   5792篇
  2018年   7387篇
  2017年   7119篇
  2016年   11428篇
  2015年   7881篇
  2014年   11178篇
  2013年   27694篇
  2012年   22129篇
  2011年   26862篇
  2010年   18093篇
  2009年   17824篇
  2008年   24336篇
  2007年   24285篇
  2006年   22603篇
  2005年   20511篇
  2004年   18782篇
  2003年   16468篇
  2002年   16021篇
  2001年   17341篇
  2000年   13213篇
  1999年   10361篇
  1998年   8467篇
  1997年   8231篇
  1996年   8132篇
  1995年   7195篇
  1994年   7036篇
  1993年   6809篇
  1992年   7633篇
  1991年   7641篇
  1990年   7257篇
  1989年   7037篇
  1988年   7040篇
  1987年   6892篇
  1986年   6531篇
  1985年   8715篇
  1984年   8871篇
  1983年   7054篇
  1982年   7372篇
  1981年   7243篇
  1980年   6797篇
  1979年   7168篇
  1978年   7355篇
  1977年   7171篇
  1976年   7137篇
  1975年   6731篇
  1974年   6651篇
  1973年   6699篇
  1972年   4487篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Crystallography Reports - Electron backscattered diffraction (EBSD) has been used to analyze structures of natural minerals and artificial compounds for almost three decades. In recent years, it is...  相似文献   
52.
53.
Optical and Quantum Electronics - Classification of hyperspectral image (HSI) is widely used for the study of remotely sensed images. Convolutional Neural Networks (CNNs) are one of the most...  相似文献   
54.
Physics of the Solid State - The external factors which influence the ferromagnetic resonance (FMR) line width in bilayer (ferromagnet/antiferromagnet) exchange-biased systems are studied. The...  相似文献   
55.
A temperature control unit was implemented to vary the temperature of samples studied on a commercial Mobile Universal Surface Explorer nuclear magnetic resonance (MOUSE-NMR) apparatus. The device was miniaturized to fit the maximum MOUSE sampling depth (25 mm). It was constituted by a sample holder sandwiched between two heat exchangers placed below and above the sample. Air was chosen as the fluid to control the temperature at the bottom of the sample, at the interface between the NMR probe and the sample holder, in order to gain space. The upper surface of the sample was regulated by the circulation of water inside a second heat exchanger placed above the sample holder. The feasibility of using such a device was demonstrated first on pure water and then on several samples of bread dough with different water contents. For this, T1 relaxation times were measured at various temperatures and depths and were then compared with those acquired with a conventional compact closed-magnet spectrometer. Discussion of results was based on biochemical transformations in bread dough (starch gelatinization and gluten heat denaturation). It was demonstrated that, within a certain water level range, and because of the low magnetic field strength of the MOUSE, a linear relationship could be established between T1 relaxation times and the local temperature in the dough sample.  相似文献   
56.
Crystallography Reports - The orientation of grains and the special boundaries formed by them in multicrystalline silicon has been studied by electron backscattered diffraction. It is found that...  相似文献   
57.
Theoretical and Mathematical Physics - The fractional derivative method is used to take wave dispersion into account in the wave equation when describing the propagation of gravitational soliton...  相似文献   
58.
A facile biosynthesis route was followed to prepare zinc oxide nanoparticles (ZnO NPs) using Euphorbia milii (E. milii) leaf constituents. The SEM images exhibited presence of spherical ZnO NPs and the corresponding TEM images disclosed monodisperse nature of the ZnO NPs with diameter ranges between 12 and 20 nm. The Brunauer–Emmett–Teller (BET) analysis revealed that the ZnO NPs have specific surface area of 20.46 m2/g with pore diameter of 2 nm–10 nm and pore volume of 0.908 cm3/g. The EDAX spectrum exemplified the existence of Zn and O elements and non-appearance of impurities that confirmed pristine nature of the ZnO NPs. The XRD pattern indicated crystalline peaks corresponding to hexagonal wurtzite structured ZnO with an average crystallite size of 16.11 nm. The FTIR spectrum displayed strong absorption bands at 512 and 534 cm?1 related to ZnO. The photocatalytic action of ZnO NPs exhibited noteworthy degradation of methylene blue dye under natural sunlight illumination. The maximum degradation efficiency achieved was 98.17% at an illumination period of 50 min. The reusability study proved considerable photostability of the ZnO NPs during photocatalytic experiments. These findings suggest that the E. milii leaf constituents can be utilized as suitable biological source to synthesis ZnO NPs for photocatalytic applications.  相似文献   
59.
60.
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