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   8982篇
  免费   1711篇
  国内免费   965篇
化学   6050篇
晶体学   86篇
力学   730篇
综合类   65篇
数学   1132篇
物理学   3595篇
  2024年   38篇
  2023年   189篇
  2022年   308篇
  2021年   325篇
  2020年   353篇
  2019年   324篇
  2018年   296篇
  2017年   296篇
  2016年   435篇
  2015年   426篇
  2014年   473篇
  2013年   653篇
  2012年   763篇
  2011年   845篇
  2010年   562篇
  2009年   535篇
  2008年   634篇
  2007年   490篇
  2006年   523篇
  2005年   391篇
  2004年   327篇
  2003年   259篇
  2002年   237篇
  2001年   202篇
  2000年   193篇
  1999年   194篇
  1998年   182篇
  1997年   173篇
  1996年   169篇
  1995年   137篇
  1994年   121篇
  1993年   112篇
  1992年   91篇
  1991年   69篇
  1990年   75篇
  1989年   61篇
  1988年   45篇
  1987年   34篇
  1986年   34篇
  1985年   22篇
  1984年   18篇
  1983年   14篇
  1982年   15篇
  1981年   3篇
  1980年   7篇
  1979年   2篇
  1975年   1篇
  1957年   2篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
971.
On strictly separating vectors and reflexivity   总被引:5,自引:0,他引:5  
It is shown that the set of strongly disjoint pairs of strictly separating vectors for an operator space is open, and an operator subspace having a strongly disjoint pair of strictly separating vectors is reflexive. Some applications are discussed.  相似文献   
972.
本文讨论的两个时偶问题涉及来一个泊松过程与一个更新过程穿越时间和更新数的联合分布.利用向量马氏过程方法得到了这些联合分布的变换,给出了一个与分布均值有关量的数值结果.  相似文献   
973.
刘安雯  胡水明  丁昀  朱清时 《中国物理》2005,14(10):1946-1953
Stretching vibrational band intensities of XH3 (X=N, Sb) molecules are investigated employing three-dimensional dipole moment surfaces combined with the local mode Hamiltonian model.The dipole moment surfaces of NH3 and SbH3 are calculated with the density functional theory and at the correlated MP2 level,respectively. The calculated band intensities are in good agreement with the available experimental data. The contribution to the band intensities from the different terms in the polynomial expansion of the dipole moments of four group V hydrides (NH3, PH3,AsH3 and SbH3) are discussed. It is concluded that the breakdown of the bond dipole approximation must be considered. The intensity “borrowing” effect due to the wave function mixing among the stretching vibrational states is found to be less significant for the molecules that reach the local mode limit.  相似文献   
974.
甲醇在纳米TiO2作用下进行光催化氧化反应的机理研究   总被引:7,自引:0,他引:7  
以纳米TiO2 为催化剂 ,以主波长为 36 4nm的汞灯为光源 ,用气相色谱法分别考察了 0 .1mol/L的甲醇、甲醛和甲酸水溶液进行光催化氧化反应的动力学规律 .Langmuir Hinshelwood方程进行核算结果证明 ,该组反应均为零级反应 .用TEM、XRD、SSA和XPS对催化剂进行表征 .根据XPS的检测结果提出了甲醇光催化氧化的反应机理 .TiO2 光激发活化时间约为 30~ 6 0min ,生成物及剩余反应物浓度随时间变化的曲线表明 ,该反应速率为HCH2 OH 相似文献   
975.
类氦离子的KLL双电子复合过程的相对论理论研究   总被引:3,自引:0,他引:3       下载免费PDF全文
在相对论多组态Dirac-Fock理论基础上,发展了计算双电子复合截面的程序.并以类锂C3+,Ar15+,Kr33+和U89+等离子为例,详细计算了共振双激发态1s2l2l′的辐射衰变率、Auger衰变率及相应的双电子复合截面.对于C4+,Arl6+和Kr34+离子的结果与已有的计算和实验结果都能很好地符合;对于U90+离子,则重点 关键词: 双电子复合 截面 MCDF  相似文献   
976.
Some new generalized G-KKM and generalized S-KKM theorems are proved under the noncompact setting of generalized convex spaces. As applications, some new minimax inequalities, saddle point theorems, a coincidence theorem, and a fixed point theorem are given in generalized convex spaces. These theorems improve and generalize many important known results in recent literature.  相似文献   
977.
匙玉华  刘学深  丁培柱 《物理学报》2006,55(12):6320-6325
应用经典理论并采用辛算法,计算了HF分子在啁啾激光作用下的经典解离.讨论了激光场中HF分子的解离概率随时间的变化以及考虑振动-转动能级跃迁对分子解离概率的影响.计算结果与理论分析相符,说明运用经典理论并采用辛格式计算双原子分子在激光作用下的经典解离是有效和可行的. 关键词: 啁啾激光场 经典解离 辛算法  相似文献   
978.
Acoustic signals from wild Neophocaena phocaenoides sunameri were recorded in the waters off Liao-dong-wan Bay located in Bohai Sea, China. Signal analysis shows that N. p. sunameri produced "typical" phocoenid clicks. The peak frequencies f(p) of clicks ranged from 113 to 131 kHz with an average of 121+/-3.78 kHz (n=71). The 3 dB bandwidths delta f ranged from 10.9 to 25.0 kHz with an average of 17.5+/-3.30 kHz. The signal durations delta t ranged from 56 to 109 micros with an average 80+/-11.49 micros. The number of cycles N(c) ranged from 7 to 13 with an average of 9+/-1.48. With increasing peak frequency there was a faint tendency of decrease in bandwidth, which implies a nonconstant value of f(p)/delta f. On occasion there were some click trains with faint click energy presenting below 70 kHz, however, it was possibly introduced by interference effect from multiple pulses structures. The acoustic parameters of the clicks were compared between the investigated population and a riverine population of finless porpoise.  相似文献   
979.
In order to achieve a higher lateral resolution required for ultraprecision measurement of microstructural workpieces, phase-only pupil filtering differential confocal microscopy (PFDCM), a new approach is proposed based on the differential confocal microscopy (DCM), which uses a three-zone phase-only pupil filter with lateral super-resolution capability obtained through optimized design to change the distribution of DCM three-dimensional point spread function, so that the DCM lateral resolution is therefore significantly improved while its axial resolution is slightly improved. Preliminary experimental comparison and analyses indicate that, the lateral and axial resolutions of PFDCM are better than 0.2 μm and 2 nm, respectively, when wavelength of incidence laser beam , numerical aperture of measuring lens NA=0.85, and lateral spot size with a three-zone phase-only pupil filter GT=0.65. It is therefore concluded that PFDCM is a new approach to further improvement of lateral resolution in laser probe measurement systems.  相似文献   
980.
A method employing an isosceles prism and a right-angle one is developed for loss measurement in planar waveguides. During the measuring process, the isosceles prism is fixed and the right-angle prism fixed on the waveguide slides by following the waveguide. Only by adjusting the gap thickness we can realize the loss measurement in planar waveguides. The method is demonstrated with an Ag/Na ion-exchanged waveguide fabricated on BK7 glass from AgNO3 melt diluted with NaNO3 (mass ratio 1:9), with the condition of 4 h and . The experimental results show that the method has the advantages on convenient operation, accurate results and no required end polishing.  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