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   4902篇
  免费   821篇
  国内免费   546篇
化学   3395篇
晶体学   47篇
力学   348篇
综合类   24篇
数学   605篇
物理学   1850篇
  2024年   24篇
  2023年   103篇
  2022年   165篇
  2021年   195篇
  2020年   201篇
  2019年   193篇
  2018年   184篇
  2017年   137篇
  2016年   277篇
  2015年   230篇
  2014年   259篇
  2013年   380篇
  2012年   479篇
  2011年   456篇
  2010年   309篇
  2009年   287篇
  2008年   306篇
  2007年   249篇
  2006年   243篇
  2005年   210篇
  2004年   185篇
  2003年   158篇
  2002年   132篇
  2001年   111篇
  2000年   94篇
  1999年   100篇
  1998年   73篇
  1997年   73篇
  1996年   73篇
  1995年   60篇
  1994年   45篇
  1993年   45篇
  1992年   27篇
  1991年   38篇
  1990年   35篇
  1989年   26篇
  1988年   12篇
  1987年   12篇
  1986年   14篇
  1985年   18篇
  1984年   9篇
  1983年   10篇
  1982年   7篇
  1981年   4篇
  1974年   2篇
  1944年   4篇
  1943年   1篇
  1942年   3篇
  1941年   1篇
  1940年   1篇
排序方式: 共有6269条查询结果,搜索用时 15 毫秒
181.
研究含汞土壤的修复问题,采用热解析和低温等离子体综合技术探究新途径,调整温度、添加剂、时间等因素来判断脱汞效果并探究其不同形态,分析工艺过程废料的内部联系,并对废气处理进行分析实验。结论如下:(1)通过改良技术的BCR连续萃取法,得出研究区汞的形态主要为有机结合态(53%)。之后依次是氧化物结合态(33%)、酸可提取态(8%)、残渣态(6%)。(2)温度对热解析程度影响较大。在500℃以上的热解析条件下,土壤中的汞浓度不足1.5 mg·kg-1。(3)当选用400℃的解析温度时,40 min汞去除总体完成。在低于1 700 mg·kg-1的浓度下,汞去除率随着土壤中的含量的增大而减小。(4)氯化钙对于热解析的促进作用最强,柠檬酸、升华硫也有一定作用,硫化钠对于汞去除形成阻滞。(5)低温等离子体的最佳状态是电源设置电压为22 kV,频率为660 Hz。整个系统的汞去除程度可达近90%。  相似文献   
182.
183.
184.
We demonstrate the generation of two-mode continuous-variable (CV) entanglement in a V-type three-level atom trapped in a doubly resonant cavity using a microwave field driving a hyperfine transition between two upper excited states. By numerically simulating the dynamics of this system, our results show that the CV entanglement with large mean number of photons can be generated even in presence of the atomic relaxation and cavity losses. More interestingly, it is found that the intensity and period of entanglement can be enhanced significantly with the increasing of the atomic relaxation due to the existence of the perfect spontaneously generated interference between two atomic decay channels. Moreover, we also show that the entanglement can be controlled efficiently by tuning the intensity of spontaneously generated interference and the detuning of the cavity field.  相似文献   
185.
This paper summarizes the main achievements about the structure–activity relationships of anthocyanidin glycosylation. Anthocyanidin glycosylation is the essential step of anthocyanin biosynthesis and also the prerequisite of the further modifications of anthocyanins, which is jointly characterized by the glycosylation site, the type and number of the glycosyl as well as the glycosidic bond type. It generally enhances the stability, results in the hypsochromic effect and blueing, decreases the bioavailability and anticancer activity, and decreases, increases, or does not change the antioxidant activity of the anthocyanidins or anthocyanins, which is synergetically determined by the glycosylation site and the type and number of the glycosyl. Thereinto, in nature, the blue hues caused by the glycosylation may also be reinforced by the formation of the anthocyanic vacuolar inclusions. This review could provide a reference for the research of the structure-optimizing and function-exploiting of anthocyanins.  相似文献   
186.
187.
Recently, slow light in metamaterials has been investigated based on the coupling between two quasi-bound states, in classic analogue of electromagnetically induced transparency in atomic systems. Here we demonstrate the feasibility in achieving slow light in metamaterials, based on the mechanism of coupling between a quasi-bound state and a continuum state. The theoretical prediction by a two-particle model is in good agreement with the experimental result in the metamaterial composed of the cut and continuous metal strips. The present work illustrates the versatility of metamaterials, implying the great potential in many applications.  相似文献   
188.
Zhang  Jingbo  Sun  Chuanzhen  Li  Yajiao  Bai  Shouli  Luo  Ruixian  Chen  Aifan  Liu  Kun  Lin  Yuan 《Journal of Solid State Electrochemistry》2017,21(3):883-889
Journal of Solid State Electrochemistry - We report on the interfacial passivation mechanism in CdSe quantum dot-sensitized ZnO nanocrystalline thin film, where different sulfide semiconductors...  相似文献   
189.
Lu H  Wang W  Bai B 《Discrete Mathematics》2011,311(18-19):2044-2048
Let k, m, and r be three integers such that 2≤k≤m≤r. Let G be a 2r-regular, 2m-edge-connected graph of odd order. We obtain some sufficient conditions for G-v to contain a k-factor for all v∈V(G).  相似文献   
190.
We investigate the stability and phase transition of localized modes in Bose–Einstein Condensates (BECs) in an optical lattice with the discrete nonlinear Schrödinger model by considering both two- and three-body interactions. We find that there are three types of localized modes, bright discrete breather (DB), discrete kink (DK), and multi-breather (MUB). Moreover, both two- and three-body on-site repulsive interactions can stabilize DB, while on-site attractive three-body interactions destabilize it. There is a critical value for the three-body interaction with which both DK and MUB become the most stable ones. We give analytically the energy thresholds for the destabilization of localized states and find that they are unstable (stable) when the total energy of the system is higher (lower) than the thresholds. The stability and dynamics characters of DB and MUB are general for extended lattice systems. Our result is useful for the blocking, filtering, and transfer of the norm in nonlinear lattices for BECs with both two- and three-body interactions.  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