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   2780篇
  免费   646篇
  国内免费   297篇
化学   1712篇
晶体学   31篇
力学   175篇
综合类   19篇
数学   218篇
物理学   1568篇
  2024年   11篇
  2023年   25篇
  2022年   55篇
  2021年   78篇
  2020年   94篇
  2019年   117篇
  2018年   86篇
  2017年   139篇
  2016年   153篇
  2015年   161篇
  2014年   178篇
  2013年   212篇
  2012年   180篇
  2011年   189篇
  2010年   170篇
  2009年   192篇
  2008年   177篇
  2007年   165篇
  2006年   169篇
  2005年   150篇
  2004年   154篇
  2003年   130篇
  2002年   108篇
  2001年   99篇
  2000年   86篇
  1999年   69篇
  1998年   66篇
  1997年   58篇
  1996年   35篇
  1995年   39篇
  1994年   29篇
  1993年   27篇
  1992年   33篇
  1991年   18篇
  1990年   9篇
  1989年   10篇
  1988年   11篇
  1987年   5篇
  1986年   6篇
  1985年   3篇
  1984年   4篇
  1982年   6篇
  1980年   4篇
  1979年   5篇
  1978年   1篇
  1977年   1篇
  1975年   1篇
  1973年   2篇
  1967年   1篇
  1957年   1篇
排序方式: 共有3723条查询结果,搜索用时 46 毫秒
991.
The transmission spectrum of four-level atoms in a cavity is calculated. It is shown that the four separate peaks associated with normal mode splitting and intra-cavity double dark states can be observed simultaneously. The position and intensity of the four peaks can be controlled by the intensity of the third interacting light. Therefore, the enhancement of normal mode splitting by a third coupling light of the intra-cavity four-level atoms is developed.   相似文献   
992.
A highly refractive and transparent aromatic polyimide (PI) containing a selenophene unit has been developed. The PI was prepared by a two‐step polycondensation procedure from 2,5‐bis(4‐aminophenylenesulfanyl)selenophene (APSP) and 4,4′‐[p‐thiobis(phenylenesulfanyl)]diphthalic anhydride (3SDEA), and shows high thermal stabilities, such as a relatively high‐glass transition temperature of 189 °C and 5% weight loss temperature (T5%) of 418 °C. The optical transmittance of the PI film at 450 nm is higher than 50%. The selenophene unit provides the PI with a refractive index of 1.7594, which is higher than corresponding PIs containing a thiophene or a phenyl unit because of the high polarizability per unit volume of the selenium atom. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4428–4434, 2009  相似文献   
993.
Amphilic triblock copolymers with varying ratios of hydrophilic poly[bis (methoxyethoxyethoxy)phosphazene] (MEEP) and relatively hydrophobic poly(propylene glycol) (PPG) blocks were synthesized via the controlled cationic‐induced living polymerization of a phosphoranimine (Cl3P?NSiMe3) at ambient temperature. A PPG block can function as either a classical hydrophobic block or a less hydrophobic component by varying the nature of a phosphazene block. The aqueous phase behavior of MEEP‐PPG‐MEEP block copolymers was investigated using fluorescence techniques, TEM, and dynamic light scattering (DLS). The critical micelle concentrations (cmcs) of MEEP‐PPG‐MEEP block copolymers were determined to be in the range of 3.7–16.8 mg/L. The mean diameters of MEEP‐PPG‐MEEP polymeric micelles, measured by DLS, were between 31 and 44 nm. The equilibrium constants of pyrene in these micelles ranged from 4.7 × 104 to 9.6 × 104. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 692–699, 2009  相似文献   
994.
995.
Additives for improving the flow uniformity during secondary oil recovery are partially retained in the rock. The flow improval effects continue to be observed even when the chemical solution is succeeded by pure water. Considerable flushing with water is required before the old permeability of the rock is restored to its original higher level. This effect is extremely advantageous for the application to water flooding profiles in oil recovery. It makes possible an alternating water slug/chemical solution flooding program which further reduces the already relatively small amount of chemicals required in the operation.  相似文献   
996.
High speed neutral clusters and mercury droplets from a gas jet impactor are allowed to collide with graphite surfaces. These collisions produce a variety of dislocations. One of the dislocations is a narrow dislocation band with atomic resolution. This band has two partial dislocations on the sides of a central region of abc structure.  相似文献   
997.
实时测量308 nm 激光对薄膜的损伤阈值   总被引:2,自引:2,他引:0       下载免费PDF全文
 用散射光法, 建立了一套实时监视与测量308nm 激光对全反膜和增透膜的损伤的实验装置。实时观察到了损伤从起始、加深直至饱和的整个过程的波形。用这一装置测量了全反膜和增透膜在308nm 激光作用下的损伤阈值。测得全反膜在0°与45°入射角时的损伤阈值分别为1.7与1.0J/cm2。而增透膜的阈值为1.3J/cm2。  相似文献   
998.
反射相移对光学玻璃电流传感器抗电磁干扰能力的影响   总被引:1,自引:0,他引:1  
孙伟民 Ning.  YN 《光学学报》1998,18(9):249-1254
在光学玻璃电流传感器中,如果光线反射转向时在光的p,s分量之间引入反射相移,则会对该传感器的抗电磁干扰能力产生不良影响,本文对这种情况进行了理论上的分析,并给出了数值模拟和实验的结果。  相似文献   
999.
YANG Wenge  Amitabh Joshi  王海  肖敏 《物理》2006,35(3):202-206
在包含三能级原子的环形腔的输出光场中,观察到了由电磁感应透明(EIT)效应导致的动态非稳及混沌.该动态非稳及向混沌的过渡可以通过耦合光场而加以很好地控制.同时,由三能级EIT导致的原子相干改变了系统的吸收、色散及非线性效应,从而极大地增强了系统的动态非稳和混沌过渡特性.建立了一个理论模型来定量地解释观察到的现象.  相似文献   
1000.
We recently presented a short communication on the preparation of epoxy‐based monoliths possessing highly ordered structures by polymerization induced phase separation based on the spinodal decomposition. In this article, we describe in detail on reaction mechanisms and structural properties of the epoxy‐based monoliths with well‐controlled macropores in the micrometer range. We prepared epoxy‐based monoliths based on diglycidyl ether of bisphenol A, bis(4‐aminocyclohexyl)methane, and polyethylene glycol with a bicontinuous structure by in situ step‐growth polymerization. Different morphology of epoxy‐based monoliths could be obtained by changing formulation of monomers and porogenic solvents. Characterizations of their morphologies were performed using scanning electron microscopy, mercury intrusion porosimetry, small angle X‐ray scattering, and gas adsorption measurement (BET method). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3272–3281, 2008  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