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   1315290篇
  免费   43633篇
  国内免费   19016篇
化学   656481篇
晶体学   14424篇
力学   77947篇
综合类   762篇
数学   246539篇
物理学   381786篇
  2021年   15262篇
  2020年   18918篇
  2019年   19290篇
  2018年   13732篇
  2016年   30705篇
  2015年   24209篇
  2014年   35051篇
  2013年   80277篇
  2012年   42157篇
  2011年   36616篇
  2010年   40322篇
  2009年   43105篇
  2008年   34435篇
  2007年   28613篇
  2006年   36637篇
  2005年   27000篇
  2004年   28708篇
  2003年   26464篇
  2002年   24611篇
  2001年   24203篇
  2000年   21456篇
  1999年   20630篇
  1998年   19718篇
  1997年   20251篇
  1996年   20282篇
  1995年   19577篇
  1994年   18978篇
  1993年   18231篇
  1992年   17651篇
  1991年   17921篇
  1990年   17038篇
  1989年   16987篇
  1988年   16439篇
  1987年   16479篇
  1986年   15336篇
  1985年   21845篇
  1984年   23232篇
  1983年   19406篇
  1982年   21164篇
  1981年   20383篇
  1980年   19667篇
  1979年   19747篇
  1978年   21185篇
  1977年   20776篇
  1976年   20465篇
  1975年   19136篇
  1974年   18745篇
  1973年   19290篇
  1972年   13819篇
  1967年   12253篇
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
31.
Artyukh  A. A.  Chernozatonskii  L. A. 《JETP Letters》2022,116(10):737-744
JETP Letters - The mechanical characteristics of diamond-like films, such as Dn21.8, Dn27.8, and Dn29.4 moiré diamanes, formed by the hydrogenation of graphene layers twisted at an angle of...  相似文献   
32.
Journal of Applied Spectroscopy - IR reflectance spectroscopy at 50–450 cm–1 was used to study homogeneous monocrystals of (FeIn2S3)x?(In2S3)1–x grown by the method of...  相似文献   
33.

The machining process is primarily used to remove material using cutting tools. Any variation in tool state affects the quality of a finished job and causes disturbances. So, a tool monitoring scheme (TMS) for categorization and supervision of failures has become the utmost priority. To respond, traditional TMS followed by the machine learning (ML) analysis is advocated in this paper. Classification in ML is supervised based learning method wherein the ML algorithm learn from the training data input fed to it and then employ this model to categorize the new datasets for precise prediction of a class and observation. In the current study, investigation on the single point cutting tool is carried out while turning a stainless steel (SS) workpeice on the manual lathe trainer. The vibrations developed during this activity are examined for failure-free and various failure states of a tool. The statistical modeling is then incorporated to trace vital signs from vibration signals. The multiple-binary-rule-based model for categorization is designed using the decision tree. Lastly, various tree-based algorithms are used for the categorization of tool conditions. The Random Forest offered the highest classification accuracy, i.e., 92.6%.

  相似文献   
34.
Balygin  K. A.  Kulik  S. P.  Molotkov  S. N. 《JETP Letters》2022,116(2):128-132
JETP Letters - A simple fundamental modification of quantum key distribution protocols has been proposed: it is not required to protect the results of avalanche detectors from an eavesdropper, but...  相似文献   
35.
Yin  Qingqing  Xu  Fen  Sun  Lixian  Li  Yaying  Liao  Lumin  Wang  Tao  Guan  Yanxun  Xia  Yongpeng  Zhang  Chenchen  Wei  Sheng  Zhang  Huanzhi  Li  Bin 《Journal of Thermal Analysis and Calorimetry》2022,147(12):6583-6592
Journal of Thermal Analysis and Calorimetry - Polyethylene glycol (PEG) is widely used as phase change materials (PCMs). However, the leakage and low thermal conductivity issues restrict its...  相似文献   
36.
Juglandis Mandshuricae Cortex is the bark of Juglans mandshurica Maxim., which has been used as a folk medicine plant in China and India. In this study, an ultra-high performance liquid chromatography–quadrupole/orbitrap high-resolution mass spectrometry method was developed to clarify and quantify the chemical profiling of Juglandis Mandshuricae Cortex rapidly. A total of 113 compounds were characterized. Among them, seven flavonoids were simultaneously quantified in 15 min, including myricetin, myricetrin, taxifolin, kaempferol, quercetin, quercitrin, and naringenin. The method was validated for accuracy, precision, and the limits of detection and quantification. All calibration curves showed a good linear relationship (r > 0.9990) within test ranges. The intra- and inter-day relative standard deviations were less than 2.16%. Accuracy validation showed that the recovery was between 95.6 and 101.3% with relative standard deviation values below 2.85%. The validated method was successfully applied to determine the contents of seven flavones in Juglandis Mandshuricae Cortex from seven sources and the contents of these places were calculated respectively. This method provides a theoretical basis for further developing the medicinal value of Juglandis Mandshuricae Cortex.  相似文献   
37.
The requirement of green and sustainable materials to prepare heterogeneous catalysts has intensified for practical reasons over the past few decades. Carbohydrates are possibly the most plentiful and renewable organic materials in nature with inimitable physiochemical properties, plausible low-cost and large-scale production, and sustainability features could be exploited in the generation of nanostructured heterogeneous catalysts. This review article outlines the organic transformations catalyzed by diverse carbohydrate-based nanostructured catalysts in greener and environmentally friendly processes. Selected examples are highlighted for a variety of organic reactions exploiting the proposed catalysts’ reactivity and reusability, and interactions with the intrinsic nature of the applied carbohydrate supports; advantages and speculated challenges of the introduced catalysts are deliberated as well.  相似文献   
38.
Crystallography Reports - A geometrical and topological analysis has been performed, and self-assembly of the crystal structures of intermetallic compounds CsnMk (М = Na, K, Rb, Pt, Au, Hg,...  相似文献   
39.
Crystallography Reports - A surface structural analysis of two ceramic samples of zirconium oxide (ZrO2) sintered at 1550°C, stabilized in the tetragonal form, before and after hydrothermal...  相似文献   
40.
Journal of Applied Mechanics and Technical Physics - Main correlations in the theory of bending of thin electromagnetoelastic plates are obtained, in which complex potentials are used. Exact...  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