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   534528篇
  免费   4860篇
  国内免费   1315篇
化学   272954篇
晶体学   7746篇
力学   26217篇
综合类   17篇
数学   68704篇
物理学   165065篇
  2021年   5059篇
  2020年   5536篇
  2019年   6270篇
  2018年   8443篇
  2017年   8601篇
  2016年   11688篇
  2015年   6252篇
  2014年   10539篇
  2013年   23799篇
  2012年   18554篇
  2011年   22059篇
  2010年   16567篇
  2009年   16452篇
  2008年   20927篇
  2007年   20801篇
  2006年   18898篇
  2005年   16875篇
  2004年   15677篇
  2003年   14157篇
  2002年   14045篇
  2001年   14851篇
  2000年   11491篇
  1999年   8817篇
  1998年   7664篇
  1997年   7539篇
  1996年   7029篇
  1995年   6348篇
  1994年   6386篇
  1993年   6170篇
  1992年   6514篇
  1991年   6960篇
  1990年   6660篇
  1989年   6584篇
  1988年   6393篇
  1987年   6226篇
  1986年   5955篇
  1985年   7559篇
  1984年   7883篇
  1983年   6604篇
  1982年   6906篇
  1981年   6415篇
  1980年   6103篇
  1979年   6603篇
  1978年   6834篇
  1977年   6714篇
  1976年   6685篇
  1975年   6385篇
  1974年   6233篇
  1973年   6511篇
  1972年   4751篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
251.
252.
Siberian Mathematical Journal - Under study are the right-symmetric algebras over a field  $ F $ which possess a “unital” matrix subalgebra  $...  相似文献   
253.
Vlasov  V. V.  Rautian  N. A. 《Doklady Mathematics》2021,103(1):10-13
Doklady Mathematics - Integro-differential equations with unbounded operator coefficients in a Hilbert space are studied. The equations under consideration are abstract hyperbolic equations...  相似文献   
254.
A 1.5-μm eye-safe, 3-D scanning, and compact Mie LIght Detection and Ranging (LIDAR) is presented. The transmitter of the LIDAR is based on a KTA optical parameter oscillator (OPO) resonator. For detecting return signals, an InGaAs APD is used. The all solid-state OPO laser transmitter has the feature of small volume and lightweight, which allows a 165-lb compact eye-safe scanning LIDAR to be constructed. A system simulation using our own model was conducted to direct the system development. A method to solve the problem with small active area APD detectors was developed and described. The preliminary field-test measurement results indicated that the LIDAR has the capability to detect aerosols and clouds in lower atmospheres up to three dimensions.  相似文献   
255.
In this work, the variation of the magnetic moments of the Ni/Pt multilayers are studied using the linearized augmented plane waves (LAPW) method in the framework of the density functional theory (DFT) implemented in the version of WIEN2K program. The systems have been modeled by seven layers slab separated in z direction by a vacuum region of four substrate layers. We present the results of the dependence of the magnetic properties with respect to the thickness variation of the different multilayers. The modeling of these systems finds an important empirical support. Experiment and theory show the same trends for the magnetic moments: hybridization effects between Ni and Pt are mostly localized at the interface.  相似文献   
256.
257.
    
The reaction of [{(η5-C5Me5)M(μ-Cl)Cl}2] {where M = Rh (1), Ir (2)} with functionalized phosphine viz., diphenyl-2-pyridylphosphine (PPh2Py) in dichloromethane solvent yield neutral ϰ1-P-coordinated rhodium and iridium complexes [(η5-C5Me5)RhCl21-P-PPh2Py)]3 and [(η5-C5Me5) IrCl21-P-PPh2Py)]4. Reaction of complexes 1 and 2 with the ligand PPh2Py in methanol under reflux give bis-substituted complexes such as [(η5-C5Me5)RhCl(ϰ1-P-PPh2Py)2]+ 5 and [(η5-C5Me5)IrCl(ϰ1-P-PPh2Py)2]+ 6, whereas stirring in methanol at room temperature gives P-, N-chelating complexes of the type [(η5-C5Me5)RhCl(ϰ2-P-N-PPh2Py)]+ 7 and [(η5-C5Me5)IrCl(ϰ2-P-N-PPh2Py)]+ 8. Neutral ϰ1-P-coordinated complexes [(η5-C5Me5)RhCl21-P-PPh2Py)]3 and [(η5-C5Me5)IrCl21-P-PPh2Py)]4 easily undergo conversion to the cationic P-, N-chelating complexes [(η5-C5Me5)RhCl(ϰ2-P-N-PPh2Py)]+ 7 and [(η5-C5Me5) IrCl(ϰ2-P, N-PPh2Py)]+ 8 on stirring in methanol at room temperature. These complexes are characterized by FT-IR and FT-NMR spectroscopy as well as analytical methods. The molecular structures of the representative complexes [(η5-C5Me5)RhCl21-P-PPh2Py)]3, [(η5-C5Me5)IrCl21-P-PPh2Py)]4 and hexafluorophosphate salt of complex [(η5-C5Me5)IrCl(ϰ2-P-PPh2Py)2]+ 6 are established by single-crystal X-ray diffraction methods  相似文献   
258.
The European Physical Journal E - The isothermal gas adsorption of two hexane isomers (n-hexane and cyclohexane) in the mesopores of MCM-41 silica have been investigated by small angle neutron...  相似文献   
259.
260.
In this paper, integration of interference phenomenon into femtosecond laser micromachining was reported as the femtosecond laser pulses were reshaped spatially to perform ablation. The generation of circular interference pattern was demonstrated by overlapping infrared femtosecond laser pulses. The interference pattern was subsequently focused on a copper substrate to ablate microstructures of concentric circular rings. The present technique is expected to open up new applications in the areas of rapid fabrication of micro-Fresnel lenses, hybrid microlenses and lens arrays.  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