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   253505篇
  免费   48152篇
  国内免费   38016篇
化学   132243篇
晶体学   2437篇
力学   13541篇
综合类   803篇
数学   24829篇
物理学   94167篇
无线电   71653篇
  2024年   1005篇
  2023年   5045篇
  2022年   5431篇
  2021年   7291篇
  2020年   7734篇
  2019年   8381篇
  2018年   7500篇
  2017年   8058篇
  2016年   10810篇
  2015年   11677篇
  2014年   13013篇
  2013年   17155篇
  2012年   19554篇
  2011年   20579篇
  2010年   19453篇
  2009年   19266篇
  2008年   14050篇
  2007年   12642篇
  2006年   11945篇
  2005年   10761篇
  2004年   9338篇
  2003年   7740篇
  2002年   7154篇
  2001年   6816篇
  2000年   5922篇
  1999年   6345篇
  1998年   5547篇
  1997年   4972篇
  1996年   5583篇
  1995年   5250篇
  1994年   5120篇
  1993年   4755篇
  1992年   4334篇
  1991年   3720篇
  1990年   2999篇
  1989年   2796篇
  1988年   2524篇
  1987年   1679篇
  1986年   1709篇
  1985年   1335篇
  1984年   1332篇
  1983年   597篇
  1982年   1093篇
  1981年   869篇
  1980年   867篇
  1979年   587篇
  1978年   570篇
  1977年   671篇
  1976年   1082篇
  1972年   558篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
152.
153.
154.
Dioscin (DIS), one of the most abundant bioactive steroidal saponins in Dioscorea sp., is used as a complementary medicine to treat coronary disease and angina pectoris in China. Although the pharmacological activities and pharmacokinetics of DIS have been well demonstrated, information regarding the final metabolic fates is very limited. This study investigated the in vivo metabolic profiles of DIS after oral administration by ultra‐performance liquid chromatography quadrupole time‐of‐flight mass spectrometry method. The structures of the metabolites were identified and tentatively characterized by means of comparing the molecular mass, retention time and fragmentation pattern of the analytes with those of the parent compound. A total of eight metabolites, including seven phase I and one phase II metabolites, were detected and tentatively identified for the first time. Oxidation, deglycosylation and glucuronidation were found to be the major metabolic processes of the compound in rats. In addition, a possible metabolic pathway on the biotransformation of DIS in vivo was proposed. This study provides valuable and new information on the metabolism of DIS, which will be helpful for further understanding its mechanism of action. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   
155.
156.
In this Letter,a novel system for adaptively correcting the phase of a dynamic multimode beam is proposed.While using merely one spatial light modulator,the phase measurement of the first-order diffraction pattern and the correction of the zeroth diffraction order are simultaneously realized.The real-time experimental result is obtained at a control rate of 10 Hz.The power-in-the-bucket value is improved from 38.5%to 61.8%,even with fundamental mode content that is consistently below 30%.To the best of our knowledge,this is the first implementation of real-time adaptive correction of the entire multimode beam.  相似文献   
157.
Floquet engineering appears as a new protocol for designing topological states of matter,and features anomalous edge modes pinned at quasi-energy π/T with vanished topological index.We propose how to predict the anomalous edge modes via the bulk Hamiltonian in frequency space,and use Zak phase to quantitatively index the topological properties.The above methods are clarified by the example of time periodic Kitaev chain with chemical potential of harmonic driving and pulse driving,and topological phase transitions are manifested at different driving frequencies.  相似文献   
158.
Homogenous amphiphilic crosslinked polymer films comprising of poly(ethylene oxide) and polysiloxane were synthesized utilizing thiol‐ene “ click ” photochemistry. A systematic variation in polymer composition was Carried out to obtain high quality films with varied amount of siloxane and poly(ethylene oxide). These films showed improved gas separation performance with high gas permeabilities with good CO2/N2 selectivity. Furthermore, the resulting films were also tested for its biocompatibility, as a carrier media which allow human adult mesenchymal stem cells to retain their capacity for osteoblastic differentiation after transplantation. The obtained crosslinked films were characterized using differential scanning calorimetry, dynamic mechanical analysis, thermogravimetric analysis, FTIR, Raman‐IR , and small angle X‐ray scattering. The synthesis ease and commercial availability of the starting materials suggests that these new crosslinked polymer networks could find applications in wide range of applications. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1548–1557  相似文献   
159.
Chen  Cui  Wang  Ya-Nan  Yan  Jun 《中国科学 数学(英文版)》2021,64(8):1789-1800
In this paper,we investigate the non-autonomous Hamilton-Jacobi equation ■ where H is 1-periodic with respect to t and M is a compact Riemannian manifold without boundary.We obtain the viscosity solution denoted by T_(t_0)~tφ(x) and show T_(t_0)~tφ(x) converges uniformly to a time-periodic viscosity solution u~*(x,t) of ?_tu+H(t,x,?_xu,u)=0.  相似文献   
160.
在课程群的教学中由于每门课程各自独立开展教学,缺乏知识的融合和衔接,导致学生运用综合知识解决问题的能力较弱。在课程群的教学中采用案例嵌入协同教学模式,将完整的工程案例嵌入到课程群各门课程的教学中,协同规划各门课程的教学任务,每门课程再围绕案例展开研究性教学。通过嵌入的工程案例衔接各门课程的知识点,帮助学生建构完整的知识体系,强化工程应用的概念;同时通过研究性教学,培养学生分析问题和解决问题的能力,两部分相结合,提高了学生运用综合知识解决复杂问题的能力。  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