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   106929篇
  免费   9430篇
  国内免费   5831篇
化学   62079篇
晶体学   1461篇
力学   6038篇
综合类   336篇
数学   10444篇
物理学   41832篇
  2023年   1183篇
  2022年   1637篇
  2021年   2246篇
  2020年   2650篇
  2019年   2503篇
  2018年   2303篇
  2017年   2191篇
  2016年   3366篇
  2015年   3112篇
  2014年   3923篇
  2013年   6231篇
  2012年   6939篇
  2011年   7623篇
  2010年   5301篇
  2009年   5161篇
  2008年   5973篇
  2007年   5401篇
  2006年   4985篇
  2005年   4366篇
  2004年   3643篇
  2003年   3095篇
  2002年   2868篇
  2001年   3901篇
  2000年   2837篇
  1999年   2442篇
  1998年   1803篇
  1997年   1739篇
  1996年   1543篇
  1995年   1459篇
  1994年   1289篇
  1993年   1111篇
  1992年   1346篇
  1991年   1304篇
  1990年   1153篇
  1989年   964篇
  1988年   897篇
  1987年   944篇
  1986年   800篇
  1985年   996篇
  1984年   898篇
  1983年   650篇
  1982年   607篇
  1981年   569篇
  1980年   517篇
  1979年   634篇
  1978年   652篇
  1977年   675篇
  1976年   590篇
  1975年   497篇
  1974年   528篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Artificial humic acids (A‐HA) made from biomass in a hydrothermal process turn otherwise highly insoluble phosphates (e.g. iron phosphate as a model) into highly available phosphorus, which contributes to the fertility of soils and the coupled plant growth. A detailed electron microscopy study revealed etching of the primary iron phosphate crystals by the ‐COOH and phenolic groups of humic acids, but also illustrated the importance of the redox properties of humic matter on the nanoscale. The combined effects result in the formation of then bioavailable phosphate nanoparticles stabilized by humic matter. Typical agricultural chemical tests indicate that the content of total P and directly plant‐available P improved largely. Comparative pot planting experiments before and after treatment of phosphates with A‐HA demonstrate significantly enhanced plant growth, as quantified in higher aboveground and belowground plant biomass.  相似文献   
62.
Guo  J.  Dadashi  S.  Bender  M.  Paruchuri  S. T.  Powell  N.  Sharma  Y.  Kurdila  H.  McGlothlin  J. W.  Kurdila  A. J. 《Nonlinear dynamics》2019,98(1):195-213
Nonlinear Dynamics - In contrast to many systems studied in the field of classical mechanics, models of animal motion are often distinguished in that they are both highly uncertain and evolve in a...  相似文献   
63.
Archive of Applied Mechanics - Membranes are widely applied in the large-span buildings and spatial deployable structures. They are prone to wrinkle under compression due to their small bending...  相似文献   
64.
Aiming to obtain the more effective pathogen inhibitive ingredients and explore the influence of introducing different heterocyclic units to carvacrol and thymol esters, twenty ester derivatives with different heterocyclic units were synthesized. And the in vitro antifungal activity of title compounds against five plant pathogenic fungi was evaluated by mycelium growth rate method. The results showed that some carvacrol and thymol esters showed good to excellent antifungal activity, and compound 9d (4-bromo-5-isopropyl-2-methylphenyl picolinate) exhibited a broad antifungal spectrum. Preliminary study indicated that the introduction of furan, thiophene and pyridine unit could enhance the antifungal activity of carvacrol and thymol esters against Botrytis cinerea and a bromine atom on the para position of benzene moiety could enhance their antifungal activity.  相似文献   
65.
66.
Journal of Radioanalytical and Nuclear Chemistry - A castable polyurethane (PUR) with soft segment made by polytetrahydrofuran polyol (or polytretramethylene ether glycol?=?PTMEG)...  相似文献   
67.
Conductive hydrogels with ionic compounds possess great potential for the development of soft smart devices. A dielectric scarfskin is typically required for these devices to prevent short circuiting, leading to devices with lower stretchability than the hydrogel. Henceforth, commonly used dielectric materials, such as PDMS and Ecoflex, cannot be largely stretched. Hydrogel devices with ultrastretchability are required to accommodate hostile application environments. Herein, we propose a hydrogel fiber coated with a dielectric layer that can be stretched to over 2000% of its initial length. The fiber remains conductive when stretched to ~1300%. In addition, the core/sheath hydrogel fiber can be endowed with a variety of functional properties, such as electroluminescence (EL), photoluminescence (PL), and magnetic‐responsiveness, demonstrating scalability of the resultant fiber. The present work can pave the way for numerous next‐generation soft devices, such as smart textiles and wearable electronics. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 272–280  相似文献   
68.
The first alkaline-earth metal tin(II) phosphate, BaSn2(PO4)2, has been discovered, which consists of layered structures constructed from strictly alternating [SnO3]4− and [PO4]3− moieties. This compound is expected to have a large birefringence with Δn≈0.071 at 1064 nm, owing to the presence of stereochemically active lone pair metal cations.  相似文献   
69.
International Journal of Theoretical Physics - The dynamics of entanglement measured by concurrence and quantum correlation described by quantum discord under Ornstein-Uhlenbeck noise are...  相似文献   
70.
Two-dimensional(2D) magnetic materials have been experimentally recognized recently,however,the Curie temperatures(TC) of known 2D systems are quite low.Generally,magnetic systems can be seen as constituent magnetic elements providing spins and the non-magnetic elements providing frameworks to host the magnetic elements.Short bond lengths between the magnetic and non-magnetic elements would be beneficial for strong magnetic interactions and thus high TC.Based on this,we propose to combine the magnetic element Cr and the non-magnetic element boron to design novel 2D magnetic systems.Using our self-developed software package IM2 ODE,we design a series of chromium-boride based 2D magnetic materials.Nine stable magnetic systems are identified.Among them,we find that CrB4-Ⅰ,CrB4-Ⅱ and CrBs-Ⅰ with common structural units [CrB8] are ferromagnetic metals with estimated TC of 270 K,120 K and 110 K,respectively.On the other hand,five CrB3 phases with structural units [Cr2B12] are antiferromagnetic metals.Additionally,we also find one antiferromagnetic semiconductor CrB2-Ⅰ.Our work may open new directions for identifying 2D magnetic systems with high TC.  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