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   34689篇
  免费   6500篇
  国内免费   3624篇
化学   24538篇
晶体学   382篇
力学   2079篇
综合类   190篇
数学   3462篇
物理学   14162篇
  2024年   151篇
  2023年   775篇
  2022年   1355篇
  2021年   1455篇
  2020年   1587篇
  2019年   1537篇
  2018年   1328篇
  2017年   1169篇
  2016年   1804篇
  2015年   1723篇
  2014年   2185篇
  2013年   2727篇
  2012年   3204篇
  2011年   3189篇
  2010年   2110篇
  2009年   1969篇
  2008年   2226篇
  2007年   1961篇
  2006年   1813篇
  2005年   1433篇
  2004年   1071篇
  2003年   865篇
  2002年   855篇
  2001年   675篇
  2000年   550篇
  1999年   705篇
  1998年   579篇
  1997年   582篇
  1996年   559篇
  1995年   490篇
  1994年   389篇
  1993年   322篇
  1992年   306篇
  1991年   249篇
  1990年   220篇
  1989年   161篇
  1988年   97篇
  1987年   84篇
  1986年   116篇
  1985年   78篇
  1984年   38篇
  1983年   45篇
  1982年   30篇
  1981年   25篇
  1980年   7篇
  1979年   4篇
  1976年   1篇
  1975年   1篇
  1957年   7篇
  1923年   1篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Based on the quantum fluctuations, we adopt the method of generalized V1 criterion to investigate multipartite entanglement characteristics in an optical parametric amplification system with the consideration of dispersion. The nonlinear interaction becomes strong because of the existence of dispersion coefficient σ. Considering the influence of dispersion factor σ, with increasing the pump parameter μ, the value of minimum variance V1 decreases and the squeezing curve nearly equals 1/(1 + μ). The larger particle number N results in a smaller variance and higher entanglement.  相似文献   
32.
Guided by the self-penetrating features can improve the stability of metal organic frameworks (MOFs), an unprecedented 3D self-penetrated framework, {[Zn (tptc)0.5(bimb)]·H2O}n ( NUC-6 , here NUC corresponding to North University of China), with 3D (4,4)-c {86} net, was designed. Benefit from the high chemical stability and excellent luminescent property, NUC-6 can be act as an efficient multi-response chemo-sensor in detecting dichloronitroaniline pesticide and nitrofuran antibiotics in water with the detection limits are 116 ppb for DCN pesticide, 16 ppb for NFT antibiotic, and 12 ppb for NTZ antibiotic. Besides, the mechanisms of luminescence quenching were revealed from the viewpoint of internal filter effect (IFE) and photo-induced electron transfer (PET), implied by the optical spectroscopy and quantum chemical calculation. This work provides a promising strategy to design stable MOFs by improving the self-penetrating features and to expand their practical applications in the detection of organic pollutants in aqueous medium.  相似文献   
33.
A high‐throughout bioanalytical method based on salting‐out‐assisted liquid/liquid extraction (SALLE) method with acetonitrile and mass spectrometry‐compatible salts followed by LC‐MS/MS analysis of trimetazidine in rat plasma is presented. It required only 50 μL of plasma and allows the use of minimal volumes of organic solvents. The seamless interface of SALLE and LC‐MS eliminated the drying‐down step and the extract was diluted and injected into an LC‐MS/MS system with a cycle time of 2.5 min/sample. The retention times of trimetazidine and IS were approximately 1.1 and 1.7 min, respectively. Calibration curves were linear over the concentration range of 0.1–100 ng/mL, which can be extended to 500 ng/mL by dilution. The intra‐ and inter‐batch precision, accuracy and the relative standard deviation were all <15%. This method was successfully applied to determine trimetazidine concentrations in rat plasma. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   
34.
35.
36.
37.
38.
Shi  D.  Feng  J.  Wang  J.  Zhao  W.  Li  X. 《Kinetics and Catalysis》2020,61(5):750-757
Kinetics and Catalysis - A series of Cu-SSZ-13@CeO2 catalysts with surface modification with CeO2 was prepared by the modified self-resemble method based on the one-pot synthesized Cu-SSZ-13...  相似文献   
39.
40.
Abstract

Gastrodigenin, also known as 4-hydroxybenzyl alcohol (HBA), is one of the main components of Gastrodia elata, which is a perfect lead compound of natural products. In order to get new active compounds, we modified the structure of HBA through esterification with carboxylic acid, and got a series of derivatives in which 4-hydroxybenzyl alcohol 2-naphthoate (NHBA) showed stronger antidepressant activity than HBA. In this paper, we firstly evaluated the antidepressant activity of NHBA by tail suspension test (TST) and forced swimming test (FST). Then, we carried out the biochemical assay and western blot to determine its mechanism. The results displayed that NHBA could increase the content of serotonin, dopamine, norepinephrine, γ-aminobutyric acid, brain-derived neurotrophic factor (BDNF) and tropomyosin receptor kinase B (TrkB) in mice brain. It suggested that NHBA exhibited an antidepressant-like effect through monoaminergic system, GABAergic system and BDNF/TrkB signaling pathways.  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