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   438818篇
  免费   5672篇
  国内免费   1237篇
化学   235708篇
晶体学   6554篇
力学   18891篇
综合类   13篇
数学   50227篇
物理学   134334篇
  2021年   3823篇
  2020年   4283篇
  2019年   4604篇
  2018年   5955篇
  2017年   5822篇
  2016年   8956篇
  2015年   5660篇
  2014年   8681篇
  2013年   20411篇
  2012年   15956篇
  2011年   19565篇
  2010年   13666篇
  2009年   13504篇
  2008年   17814篇
  2007年   17708篇
  2006年   16406篇
  2005年   14680篇
  2004年   13615篇
  2003年   11984篇
  2002年   11803篇
  2001年   13487篇
  2000年   10140篇
  1999年   7957篇
  1998年   6594篇
  1997年   6357篇
  1996年   6131篇
  1995年   5507篇
  1994年   5455篇
  1993年   5266篇
  1992年   5899篇
  1991年   5968篇
  1990年   5711篇
  1989年   5521篇
  1988年   5522篇
  1987年   5402篇
  1986年   5120篇
  1985年   6588篇
  1984年   6719篇
  1983年   5327篇
  1982年   5417篇
  1981年   5409篇
  1980年   4991篇
  1979年   5378篇
  1978年   5511篇
  1977年   5415篇
  1976年   5345篇
  1975年   4935篇
  1974年   4908篇
  1973年   4905篇
  1972年   3465篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Ferrarini  A.  Finotello  A.  Salsano  G.  Auricchio  F.  Palombo  D.  Spinella  G.  Pane  B.  Conti  M. 《Acta Mechanica Sinica》2021,37(7):1192-1192
Acta Mechanica Sinica - A Correction to this paper has been published: https://doi.org/10.1007/s10409-021-01066-2  相似文献   
32.
Physics of Atomic Nuclei - Emission of short electron bunches with high charge in RF guns is considered. The emission mechanism in the case of picosecond laser pulses and the presence of a strong...  相似文献   
33.
Li  Y.  Shi  W. H.  Dong  L. M.  Xu  S. X.  Huang  H. J.  Yin  J. R. 《Journal of Applied Spectroscopy》2022,89(3):534-541
Journal of Applied Spectroscopy - Sr3B2O6:Dy3+, Eu3+ single-matrix white-light-emitting materials are prepared using the high-temperature solid-state method. The microstructure, emission spectrum,...  相似文献   
34.

Soil–water retention curve (SRWC), also called soil moisture characteristic, is used for simulation models of soil water storage or soil aggregate stability. The present study addresses the modeling of SRWC with particular attention paid to hysteresis effects of water filling and draining the pores attributed to ink-bottle effects. For that purpose, an idealized pore size distribution previously developed for predicting water sorption isotherms on cementitious materials, and which can consider the double porosity structure of soils, is used. The input data of the model are assessed only from mercury intrusion porosimetry tests (MIP) and from grain size distribution (GSD). The hysteretic behavior of SRWC is reproduced in a satisfactory way. The model can also predict the specific surface area.

  相似文献   
35.
Designs, Codes and Cryptography - Given an integer $$k\ge 3$$ and a group G of odd order,  if there exists a 2-(v, k, 1)-design and if v is sufficiently large then there...  相似文献   
36.
The health monitoring has been studied to ensure integrity of design of engine structure by detection, quantification, and prediction of damages. Early detection of faults may allow the downtime of maintenance to be rescheduled, thus preventing sudden shutdown of machines. In cylinder pressure developed, vibrations and noise emissions data provide a rich source of information about condition of engines. Monitoring of vibrations and noise emissions are novel non-intrusive methodologies for which positioning of various transducers are important issue. The presented work shows applicability of these diagnosis methodologies adopted in case of diesel engines. The effects of changing various fuel injection parameters was analyzed. Scope of using non-intrusive technique has been analyzed by changing locations of microphone. Novelty of this worklies in exploring signal processing methods for various locations around the engine test set up. Various frequency ranges of contributing noise and vibration sources were identified. Time-Frequency analysis showed the onset of various cyclic. Based on the identification of various frequency bands, it is possible to device suitable filters in order to extract more information.  相似文献   
37.
Herein, we report a Mott-Schottky catalyst by entrapping cobalt nanoparticles inside the N-doped graphene shell (Co@NC). The Co@NC delivered excellent oxygen evolution activity with an overpotential of merely 248 mV at a current density of 10 mA cm–2 with promising long-term stability. The importance of Co encapsulated in NC has further been demonstrated by synthesizing Co nanoparticles without NC shell. The synergy between the hexagonal close-packed (hcp) and face-centered cubic (fcc) Co plays a major role to improve the OER activity, whereas the NC shell optimizes the electronic structure, improves the electron conductivity, and offers a large number of active sites in Co@NC. The density functional theory calculations have revealed that the hcp Co has a dominant role in the surface reaction of electrocatalytic oxygen evolution, whereas the fcc phase induces the built-in electric field at the interfaces with N-doped graphene to accelerate the H+ ion transport.  相似文献   
38.
Crystallography Reports - Two LiInSe2 single crystals, grown under different conditions, have been studied. Characteristics of these crystals for neutron detection have been compared using...  相似文献   
39.
Journal of Radioanalytical and Nuclear Chemistry - In this paper a study for the selection of an NPE (nonylphenol ethoxylates)—free cocktail is discussed in order to be used for our routine...  相似文献   
40.
Svetlakova  A. V.  Mendez  M. Sanchez  Tuchin  E. S.  Khodan  A. N.  Traore  M.  Azouani  R.  Kanaev  A.  Tuchin  V. V. 《Optics and Spectroscopy》2021,129(8):846-850
Optics and Spectroscopy - We study the photocatalytic activity of nanocomposites based on θ-phase alumina (Al2O3) with different TiO2 concentrations for heterogeneous photocatalysis and...  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