全文获取类型
收费全文 | 7941篇 |
免费 | 1483篇 |
国内免费 | 877篇 |
专业分类
化学 | 5810篇 |
晶体学 | 51篇 |
力学 | 459篇 |
综合类 | 45篇 |
数学 | 1011篇 |
物理学 | 2925篇 |
出版年
2024年 | 20篇 |
2023年 | 162篇 |
2022年 | 193篇 |
2021年 | 296篇 |
2020年 | 406篇 |
2019年 | 301篇 |
2018年 | 266篇 |
2017年 | 277篇 |
2016年 | 386篇 |
2015年 | 414篇 |
2014年 | 457篇 |
2013年 | 584篇 |
2012年 | 750篇 |
2011年 | 803篇 |
2010年 | 509篇 |
2009年 | 466篇 |
2008年 | 512篇 |
2007年 | 478篇 |
2006年 | 446篇 |
2005年 | 325篇 |
2004年 | 289篇 |
2003年 | 185篇 |
2002年 | 229篇 |
2001年 | 133篇 |
2000年 | 147篇 |
1999年 | 152篇 |
1998年 | 131篇 |
1997年 | 144篇 |
1996年 | 130篇 |
1995年 | 118篇 |
1994年 | 106篇 |
1993年 | 105篇 |
1992年 | 73篇 |
1991年 | 62篇 |
1990年 | 59篇 |
1989年 | 36篇 |
1988年 | 33篇 |
1987年 | 32篇 |
1986年 | 13篇 |
1985年 | 27篇 |
1984年 | 13篇 |
1983年 | 9篇 |
1982年 | 9篇 |
1981年 | 6篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1928年 | 2篇 |
1916年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 323 毫秒
71.
关于不完全双二次非协调板元的误差估计 总被引:1,自引:0,他引:1
本文在[1,2]的基础上,对不完全双二次板元作了进一步的讨论,不仅得到了最优的L~2—误差估计,改进了[1]的相应结果,而且利用“辅助元技巧”并结合正则Green函数法,得到了拟最优的L~∞—误差估计. 相似文献
72.
本利用矩阵对的标准相关分解,得到了矩阵方程(A^TXB,B^TXB)=(C,D)反对称解存在的充分必要条件及通解表达式,同时给出了解关于已知矩阵的最佳逼近. 相似文献
73.
74.
The effect of pH value on the electrostatic layer-by-layer self-assembly and the photo-responsive behavior of Poly{2-[4-(4-ethoxyphenylazo)phenoxy]ethyl
acrylate-co-acrylic acid} (PEAPE) was studied. Results show that in the studied pH value range, the lower the pH value is, the higher
is the UV-vis absorbance and the larger is the thickness of the multilayer films. FTIR studies indicate that the azo polyelectrolyte
exhibits a different ionization degree in solutions with different pH values. The higher absorbance and the larger thickness
of the layer-by-layer films can be attributed to the low ionization degree and the shrinkage conformation of PEAPE in the
solution with low pH values. FTIR analysis also confirms that the driving force for layer-by-layer self-assembly of PEAPE
and PDAC is the electrostatic interaction.
__________
Translated from Acta Polymerica Sinica, 2007, 5: 440–445 [译自: 高 分子学报] 相似文献
75.
Zhi‐Yong Huang Jin‐Can Shen Zhi‐Xia Zhuang Xiao‐Ru Wang Frank S. C. Lee 《应用有机金属化学》2004,18(6):255-261
Cinnabar, as one of the most widely used mineral drugs in traditional Chinese medicines, has been proven to have prominent curative effects in clinical use for more than 2000 years. But the safety and toxicity of the drug has been under constant debate in clinic usage. Metallothionein (MT) contains about 30% of cysteine in the molecule, and plays an important detoxification role against heavy metals. In this study, it was used as a biomarker to assess mercurial accumulation in rats fed orally with cinnabar. After feeding rats with cinnabar by gastric gavage at different dosages and at different times, the distribution of heavy metals (including mercury, copper and zinc) and MT was investigated among rat tissues, including liver, kidney, heart, brain, testis and blood. Metals and MT determinations were carried out using inductively coupled plasma mass spectrometry (ICP‐MS) and a modified mercury saturation assay technique respectively. The results indicated that mercury was easily accumulated in the tissues of rats exposed to cinnabar, especially in kidney. For example: at a feeding dosage of 5 g kg?1 (bw) for 4 weeks, the mercury concentrations in kidney were 13, 8.7, 21.6 and 26 times those in liver, testis, brain and heart respectively; and at 2.5 g kg?1 (bw) for 2 weeks, the mercury concentrations in kidney were 21, 2.1, 3 and 21 times those in liver, testis, brain and heart respectively. In addition, mercury in kidney and liver of all cinnabar groups was significantly higher than that of the control group (P < 0.01). A high positive correlation observed between MT concentrations and mercury levels in both liver and kidney (R2 = 0.9299, P < 0.02 for liver; R2 = 0.9923, P < 0.0008 for kidney) indicated that MT could be used as a biomarker for mercury in tissues. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
76.
77.
Lanthanide Complexes for Oligomerization of Phenyl Isocyanate 总被引:1,自引:0,他引:1
IntroductionThestudyonthereactivitiesoflanthanidecomplexesto wardisocyanateshasattractedmuchattention .Ithasbeenre portedthatlanthanidealkoxides,1anddivalentdiaza pentadi enyllanthanidecomplexes2 canbeusedasthesinglecompo nentinitiatorsforisocyanatespolymerization .Recentlyourre searchgrouphasalsofoundthatlanthanoceneamide ,3diva lentaryloxideofsamarium4 ,5anddivalentsamarocene6 areallactivefortheoligomerizationofphenylisocyanate,andtheactivespeciesforthesethreesystemswereallsuccessfullyisolat… 相似文献
78.
Wenping Deng Gang Xu Lei Wan Anwen Liu Bo Gao Junhe Du Shuiming Hu Yang Chen 《Acta Physico》2008,24(8):1329-1334
Apparatus integrating a Fourier transform-infrared (FT-IR) spectrometer and a mid-infrared difference frequency generation (DFG) laser spectrometer was built for the study of the matrix isolation spectrum in solid molecular hydrogen. A 3-cm-long molecular hydrogen crystal was grown in a liquid-helium Dewar, and its infrared absorption spectrum in the 1-5 μm region was recorded to test the system. The W0(0) (ν=0←0, J=6←0) line around 2410 cm−1 of solid hydrogen was investigated with the DFG laser spectroscopy. High-resolution matrix isolation spectrum of CO2 co-deposited with hydrogen on a BaF2 cold plate at liquid-helium temperature was studied. 相似文献
79.
KF-Al2O3催化合成2-甲基-1-苄基苯并咪唑 总被引:1,自引:0,他引:1
苯并咪唑类杂环化合物具有杀菌、消炎、抗癌、抗氧化的活性,广泛用于食品的防虫和防腐,用于动、植物病毒的防治,人体疾病和肿瘤的防治[1-3],本文用KF Al2O3作催化剂,用DMF为溶剂,利用2 甲基苯并咪唑与苄基溴反应合成2 甲基 1 苄基苯并咪唑的新型方法,考察了诸因素对产率的影响,找出了最佳的反应条件。合成路线如下:1 实验部分1 1 仪器与试剂Brurer AM 500超导核磁共振波谱仪(溶剂CDCl3);CarloErbal1106型元素分析仪,NicoletIm pact410型红外光谱仪,KBr压片,HP1100型和Finnigan FTMS 2000型质谱仪(以上均由华东理工大学分析… 相似文献
80.
Ru Ju Wang Feng Ying LiTing Zhang Deng Ji Fang WangHong Chen Chang Qing Jin 《Solid State Communications》2003,127(1):47-50
Using pulse echo overlap measurement, the elastic behavior of amorphous carbon has been studied at ambient and low temperatures. The smaller ratio B/G of the bulk modulus to shear modulus and smaller Poisson's ratio σ at room temperature indicate that there is an intrinsic stiffening of transverse acoustic phonons in the amorphous carbon. The acoustic velocity and attenuation for longitudinal modes have been measured between 2.1 and 300 K at three frequencies of 7, 21 and 35 MHz, respectively. Their frequency and temperature dependence are observed. The elastic constant C11 increases with decreasing temperature and show enhanced stiffening at low temperatures. In the 130-220 K region, the abnormal change and effect of longitudinal velocity and attenuation with temperature and frequency, and a phase transition associated with structure relaxations are discussed. 相似文献