全文获取类型
收费全文 | 2070篇 |
免费 | 418篇 |
国内免费 | 510篇 |
专业分类
化学 | 2052篇 |
晶体学 | 25篇 |
力学 | 8篇 |
综合类 | 11篇 |
数学 | 29篇 |
物理学 | 873篇 |
出版年
2024年 | 5篇 |
2023年 | 14篇 |
2022年 | 59篇 |
2021年 | 93篇 |
2020年 | 79篇 |
2019年 | 80篇 |
2018年 | 59篇 |
2017年 | 74篇 |
2016年 | 71篇 |
2015年 | 139篇 |
2014年 | 129篇 |
2013年 | 182篇 |
2012年 | 161篇 |
2011年 | 179篇 |
2010年 | 166篇 |
2009年 | 175篇 |
2008年 | 150篇 |
2007年 | 194篇 |
2006年 | 130篇 |
2005年 | 140篇 |
2004年 | 142篇 |
2003年 | 122篇 |
2002年 | 82篇 |
2001年 | 47篇 |
2000年 | 51篇 |
1999年 | 45篇 |
1998年 | 41篇 |
1997年 | 19篇 |
1996年 | 33篇 |
1995年 | 19篇 |
1994年 | 19篇 |
1993年 | 14篇 |
1992年 | 16篇 |
1991年 | 8篇 |
1990年 | 8篇 |
1989年 | 6篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1986年 | 6篇 |
1985年 | 3篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1980年 | 7篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有2998条查询结果,搜索用时 31 毫秒
971.
Chang‐Liang Sun Xiao‐Nan Jiang Chang‐Sheng Wang 《International journal of quantum chemistry》2013,113(10):1453-1460
The cooperative enhancement of water binding to the antiparallel β‐sheet models has been studied by quantum chemical calculations at the MP2/6‐311++G**//MP2/6‐31G* level. The binding energies of the two antiparallel β‐sheet models consisting of two strands of diglypeptide are calculated by supermolecular approach. Then water molecules are gradually bonded to the diglypeptide by N? H···OH2 and C?O···HOH hydrogen bonds. Our calculation results indicated that the hydrogen bond length and the atom charge distribution are affected by the addition of H2O molecules. The binding energy of antiparallel diglypeptide β‐sheet models has a great improvement by the increasing of the hydrogen bond cooperativity and the more H2O molecules added the more cooperativity enhancement can be found. The orbital interactions are calculated by natural bond orbital analysis, and the results indicate that the cooperative enhancement is closely related to the orbital interaction. © 2012 Wiley Periodicals, Inc. 相似文献
972.
本文利用常微分方程的连续有限元法计算了A2B模型的分子的经典轨迹和能量误差,将计算延长到10^-sS,并与辛算法进行了比较.结果表明,在微观反映动力学研究所考虑的时间范围内,有限元法的结果与理论分析一致,能较长时间保持能量守恒和系统整体结构,并在数值计算上探讨了守恒性和近似程度,结果与理论相吻合。 相似文献
973.
The observed oscillatory linewidths of theV′=3 level ofB
3Π0+ state of I35Cl and I37Cl are explained as due to heterogeneous predissociation caused by the crossing of an unstableZ
1Π state. The crossing point and the slopes of the curves have been fixed to predict the observed linewidths. 相似文献
974.
Pang Xiao-feng Zhang Huai-Wu 《International Journal of Infrared and Millimeter Waves》2006,27(5):735-752
The mechanism and properties of infrared absorption of α-helix protein molecules are studied by a theory of bio-energy transport
established on the basis of molecular structure. From the vibrational energy-spectra of molecules obtained from this theory
we know that the infrared lights with wavelengths of 2 μm −7 μm can be absorbed by α-helix protein molecules. This is basically
consistent with experimental data of infrared absorption of collagen and hemoglobin and bivine serum albumen (BSA) proteins
with α-helix structure. From these results we account further for the mechanism and properties of biological effect of infrared
lights absorbed by the living systems, i.e., the energy of infrared lights is directly absorbed by the amide-Is in amino acid
residues in the protein molecules, which results in vibration of amide-1 and change of conformation of proteins and transport
of bio-energy from one place to other along the protein molecular chains in human beings and animals. This is a kind of non-thermally
biological effect. 相似文献
975.
We demonstrate high-resolution fluorescence imaging of single molecules using near-field scanning optical microscopy (NSOM)
with a tiny aperture probe for two different wavelengths in visible range in the illumination mode of operation. The spatial
resolutions obtained at both excitation wavelengths were almost the same and the highest resolution realized was about 10
nm. To discuss the achievable resolution in aperture NSOM, we also employed a computer simulation by the finite-difference
time-domain method for various aperture sizes and wavelengths. The resolution of 10 nm is predicted to be contributed by the
single peak of localized near-field light around the rim of the aperture. 相似文献
976.
In situ measurements of oligoaniline conductance: Linking electrochemistry and molecular electronics
The single-molecule conductance of a dithiolated aniline trimer has been measured under potential control and also under an inert solvent. In each experiment, two sets of currents are found, differing by a factor 4, and these are tentatively assigned to differing connections to the electrodes (e.g., on-top vs. hollow sites). The conductances peak (to 17 ± 1.6 and 5.8 ± 0.85 nS) between the first and second oxidations of the molecule and change smoothly with surface potential. There is no evidence for a coexistence of oxidized and reduced molecules. Measurements made at a fixed surface potential as a function of tip to substrate bias show a peak current at 0.1 V followed by a region of negative differential resistance. This is accounted for semi-quantitatively by modification of the local potential by the applied bias altering the oxidation state of the molecule under the probe. Measurements made in toluene are Ohmic, indicating that the tip does not alter the oxidation state of the molecule in the absence of screening ions. We discuss the role of gap geometry and bonding in these processes. 相似文献
977.
单分子探测技术是一项超高灵敏度的探测技术,在生物、医学和环境等领域有着广泛的应用。在这里,本文简要介绍了基于激光诱发荧光方法的单分子探测谱仪的原理和装置,以及用CC5染料分子在该探测谱仪上进行的若干实验研究结果,包括样品流速的影响、能量特性、浓度线性、检测限等方面,并讨论了光漂白现象对实验结果的影响。 相似文献
978.
本文利用NdYAG激光倍频光532nm激光分成强度大致相等的两束激光作为泵浦光以2.73°交叉于碘分子样品室中,两束泵浦光发生干涉在碘分子中选择激发形成了空间正弦分布的激光态分子光栅和基态耗尽型光栅。另一束窄线宽染料激光作为探索光射入到激光感生光栅上,沿着布拉格衍射的方向接收信号光。利用泵浦共振为32-0R(55),探索共振为13-0P(55),R(55)和泵浦共振为32-0P(52),探索共振为13-0P(52),R(52)的碘分子双色激光感生光栅光谱谱线强度测定了127I的核自旋,测定值为5/2。 相似文献
979.
首次应用变温实验方法和13C核自旋弛豫方法研究了抗癌药β-榄香烯小分子的内部运动状况。结果表明β-榄香烯分子的六元环在所研究的温度范围(298~318K)内几乎是刚性的。该分子的整体滚动自扩散活化能为14kJ/mol.其六元环外侧链基团CH2=CCH3-和CH2=CH-的整体内旋转扩散活化能均为19kJ/mol.而与该六元环直接相连的甲基的内旋转扩散活化能为18kJ/mol.这个数值大大高于连在六元环上不同位置的两个侧链基团CH2=CCH3一中甲基的内旋转扩散活化能(其数值分别为了7kJ/mol和2.8KJ/mol).3个不同位置的甲基的内旋转扩散活化能有很大差别可能是由它们所处的分子空间环境不同而引起的。 相似文献
980.