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   479207篇
  免费   7297篇
  国内免费   1333篇
化学   261150篇
晶体学   5850篇
力学   20224篇
综合类   15篇
数学   59160篇
物理学   141438篇
  2021年   4370篇
  2020年   4878篇
  2019年   5223篇
  2018年   7153篇
  2017年   6732篇
  2016年   10313篇
  2015年   6902篇
  2014年   9913篇
  2013年   23027篇
  2012年   18744篇
  2011年   22530篇
  2010年   15438篇
  2009年   15036篇
  2008年   20438篇
  2007年   20278篇
  2006年   18723篇
  2005年   16870篇
  2004年   15473篇
  2003年   13554篇
  2002年   13116篇
  2001年   14070篇
  2000年   10721篇
  1999年   8358篇
  1998年   6921篇
  1997年   6677篇
  1996年   6556篇
  1995年   5765篇
  1994年   5742篇
  1993年   5540篇
  1992年   6195篇
  1991年   6076篇
  1990年   5847篇
  1989年   5622篇
  1988年   5609篇
  1987年   5529篇
  1986年   5174篇
  1985年   6815篇
  1984年   6941篇
  1983年   5446篇
  1982年   5631篇
  1981年   5596篇
  1980年   5155篇
  1979年   5545篇
  1978年   5704篇
  1977年   5545篇
  1976年   5534篇
  1975年   5085篇
  1974年   5059篇
  1973年   5067篇
  1972年   3522篇
排序方式: 共有10000条查询结果,搜索用时 468 毫秒
31.
Gawad  Dina A.  Elnaggar  Mai M.  Belal  Tarek S. 《Chromatographia》2022,85(7):617-628
Chromatographia - The present work deals with the optimization, validation and application of a versatile HPLC–DAD method for concurrent estimation of nine antimicrobials and proton pump...  相似文献   
32.
Set-Valued and Variational Analysis - R. Tyrell Rockafellar and his collaborators introduced, in a series of works, new regression modeling methods based on the notion of superquantile (or...  相似文献   
33.
Pentafluorosulfanyl (SF5)-containing compounds and corresponding analogs are a highly valuable class of fluorine-containing building blocks owing to their unique properties. The reason for that is the set of peculiar and tremendously beneficial characteristics they can impart on molecules once introduced onto them. Despite this, their application in distinct scientific fields remains modest, given the extremely harsh reaction conditions needed to access such compounds. The recent synthetic approaches via S−F, and C−SF5 bond formation as well as the use of SF5-containing building blocks embody a “stairway-to-heaven” loophole in the synthesis of otherwise-inaccessible chemical scaffolds only a few years ago. Herein, we report and evaluate the properties of the SF5 group and analogs, by summarizing synthetic methodologies available to access them as well as following applications in material science and medicinal chemistry since 2015.  相似文献   
34.
Doklady Mathematics - The integrability of certain classes of homogeneous dynamical systems on the tangent bundles of four-dimensional manifolds is shown. The force fields involved in the systems...  相似文献   
35.
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   
36.
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   
37.
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   
38.
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   
39.
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   
40.
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   
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