全文获取类型
收费全文 | 5612篇 |
免费 | 265篇 |
国内免费 | 464篇 |
专业分类
化学 | 2838篇 |
晶体学 | 245篇 |
力学 | 84篇 |
综合类 | 59篇 |
数学 | 2075篇 |
物理学 | 1040篇 |
出版年
2024年 | 11篇 |
2023年 | 56篇 |
2022年 | 61篇 |
2021年 | 107篇 |
2020年 | 102篇 |
2019年 | 116篇 |
2018年 | 96篇 |
2017年 | 105篇 |
2016年 | 121篇 |
2015年 | 120篇 |
2014年 | 156篇 |
2013年 | 384篇 |
2012年 | 208篇 |
2011年 | 394篇 |
2010年 | 379篇 |
2009年 | 404篇 |
2008年 | 392篇 |
2007年 | 398篇 |
2006年 | 314篇 |
2005年 | 268篇 |
2004年 | 254篇 |
2003年 | 213篇 |
2002年 | 351篇 |
2001年 | 142篇 |
2000年 | 140篇 |
1999年 | 130篇 |
1998年 | 107篇 |
1997年 | 76篇 |
1996年 | 96篇 |
1995年 | 79篇 |
1994年 | 66篇 |
1993年 | 41篇 |
1992年 | 39篇 |
1991年 | 29篇 |
1990年 | 15篇 |
1988年 | 10篇 |
1987年 | 7篇 |
1985年 | 38篇 |
1984年 | 19篇 |
1983年 | 20篇 |
1982年 | 23篇 |
1981年 | 44篇 |
1980年 | 29篇 |
1979年 | 13篇 |
1978年 | 24篇 |
1977年 | 30篇 |
1976年 | 26篇 |
1975年 | 20篇 |
1974年 | 24篇 |
1973年 | 20篇 |
排序方式: 共有6341条查询结果,搜索用时 281 毫秒
61.
62.
This study investigates the effect of surface immobilization on the bactericidal function of a quaternary ammonium compound. Quaternary ammonium silane (QAS) coated planar surfaces did not produce any measurable mortality of Staphylococcus aureus, while 1 µm QAS‐coated microparticles did produce S. aureus mortality. The experiments using QAS‐coated microparticles indicate that the ability of QAS molecules to disrupt the cell wall is not hindered by covalent immobilization of QAS to a surface. These results provide evidence that S. aureus cells on a QAS‐coated planar surface are not exposed to a sufficient number of QAS molecules to produce significant mortality. This result has important implications for the development of self‐decontaminating coatings. Covalent immobilization is used to prevent leaching of the bactericidal compound. However, covalent immobilization may result in a significant tradeoff in bactericidal performance. Published in 2007 by John Wiley & Sons, Ltd. 相似文献
63.
首次研究了碳化钨负载S2 O2 -8 ZrO2 (PSZ)固体超强酸催化剂 (WC PSZ)上正戊烷的反应情况及影响催化剂活性的各种因素 ,并用GC MS ,XRD ,BET等手段分析了正戊烷反应产物和催化剂的物理化学性质等 .结果表明 :WC PSZ对正戊烷具有异构化和裂解的双重催化作用 .PSZ在负载适量碳化钨后对正戊烷反应的活性和选择性显著提高 ,显示出优于Pt PSZ催化剂的效果 ,碳化钨的负载量为 2 0 %的效果最佳 .适当的焙烧、活化和反应温度等条件是取得良好反应效果的关键 相似文献
64.
F. Garcias J. A. Alonso M. Barranco J. M. López A. Mañanes J. Németh 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1994,31(4):275-277
The competition experimentally observed between asymmetric fission and neutral monomer evaporation as dissociation channels of excited doubly charged sodium clusters has been investigated by means of an axially symmetric, fully selfconsistent Kohn-Sham method. Ellipsoidal equilibrium configurations for parent and daughter clusters have been considered using a deformed jellium model.This paper was originally submitted in connection with the 2nd. Int. Conference on Atomic and Nuclear Clusters held in Santorini from 28. June–2. July 1993 and is published here as a regular article after an independent refereeing procedure according to the standards of Z. Phys. D 相似文献
65.
66.
Harry J. Whitlow Margaretha Andersson Mikael Hult Leif Persson Mohamed El Bouanani Mikael Östling Carina Zaring Nils Lundberg David D. Cohen Nick Dytlewski Peter N. Johnston Ian F. Bubb Scott R. Walker Erik Johanson Sture Hogmark P. Anders Ingemarsson 《Mikrochimica acta》1995,120(1-4):171-181
Recoil Spectrometry covers a group of techniques that are very similar to the well known Rutherford backscattering Spectrometry technique, but with the important difference that one measures the recoiling target atom rather than the projectile ion. This makes it possible to determine both the identity of the recoil and its depth of origin from its energy and velocity, using a suitable detector system. The incident ion is typically high-energy (30–100MeV)35C1,81Br or127I. Low concentrations of light elements such as C, O and N can be profiled in a heavy matrix such as Fe or GaAs. Here we present an overview of mass and energy dispersive recoil Spectrometry and illustrate its successful use in some typical applications. 相似文献
67.
In the past several decades, much attention has been paid to optically active, C2-asymmetric 1,1′-binaphthalene-2,2′-diol and its derivatives because of their application in inducing chirality in asymmetric synthesis[1,2]. Enantiomerically pure 1,1′-binaphthalene-2,2′-diol has been prepared by many methods ranging from the classical resolution via crystallization of the diastereoisomeric salts[3] to asymmetric oxidative coupling[4~6]. 相似文献
68.
采用SCF-X_α-MS方法, 对于C(2×2)S/Fe(001)吸附体系, 选择Fe_5S和Fe_9S两种原子簇模型, 研究了该吸附体系的电子结构、吸附成键特征及其相互作用图象。结果表明, S吸附于Fe(001)单晶表面具有较强的定域性质, S原子与底物Fe原子之间的吸附相互作用主要表现为S(3p)-Fe(4s,3d)之间的轨道相互作用。通过对表面吸附键长的优化, 其结果与X.S.Zhang等的ARPEFS的实验结果一致。 相似文献
69.
The effect of a series of novel Schiff base compounds on Staphylococcus aureus was studied by microcalorimetric method at 37 °C The results showed that all of the organic compounds had the capacity to inhibit the growth of S. aureus in different extent. And the extent and duration of the inhibitory effect on the growth of S. aureus, judged from the rate constant (k), varied with the different structure of the Schiff base compounds. According to the power-time curves, the multiplication rate constant and inhibition ratio were calculated. The growth rate constant of S. aureus (in log phase) in the presence of Schiff base compounds decreased with the increasing of the concentrations of these compounds regularly. The experimental results revealed that the hydrophilicity of Schiff bases had a great influence on their antibacterial activity. Of these Schiff bases, the greater their hydrophilicity, the higher their antibacterial activity. The antibacterial structure-activity relationship (SAR) of Schiff base derivatives was also briefly discussed. 相似文献
70.
以(S)-2-氨基丙醇为手性源与α-溴-3-氯苯丙酮反应, (R)-2-氨基丙醇为手性源与6-甲氧基-2-(2-溴丙酰基)萘反应, 分别合成了手性纯化合物(2R,3R,5S)-3,5-二甲基-2-(3-氯苯基)-2-吗啉醇盐酸盐(4a)和(2S,3S,5R)-3,5-二甲基-2-(6-甲氧基-2-萘基)-2-吗啉醇盐酸盐(4b), 利用X射线单晶衍射仪测定了两化合物的晶体结构和两化合物的空间结构, 并初步分析两化合物空间结构, 化合物4a晶体属正交晶系, 空间群为P21212, 晶胞参数为: a=0.8718(2) nm, b=0.7883(2) nm, c=2.0247(6) nm, Z=4, V=1.3915(7) nm3, Dc=1.328 g/cm3, F(000)=584, R1=0.0399, wR2=0.0797, S=1.042. 化合物4b晶体属正交晶系, 空间群为P212121, 晶胞参数为: a=0.71035 (9) nm, b=0.77703(10) nm, c=2.9820(4) nm, Z=4, V=1.6318(4) nm3, Dc=1.318 g/cm3, F(000)=688, R1=0.0520, wR2=0.1108, S=0.994. 相似文献