全文获取类型
收费全文 | 7087篇 |
免费 | 741篇 |
国内免费 | 1046篇 |
专业分类
化学 | 5272篇 |
晶体学 | 85篇 |
力学 | 168篇 |
综合类 | 90篇 |
数学 | 1039篇 |
物理学 | 2220篇 |
出版年
2024年 | 8篇 |
2023年 | 63篇 |
2022年 | 89篇 |
2021年 | 177篇 |
2020年 | 230篇 |
2019年 | 207篇 |
2018年 | 197篇 |
2017年 | 235篇 |
2016年 | 262篇 |
2015年 | 203篇 |
2014年 | 285篇 |
2013年 | 513篇 |
2012年 | 467篇 |
2011年 | 428篇 |
2010年 | 320篇 |
2009年 | 447篇 |
2008年 | 428篇 |
2007年 | 476篇 |
2006年 | 410篇 |
2005年 | 395篇 |
2004年 | 352篇 |
2003年 | 336篇 |
2002年 | 266篇 |
2001年 | 255篇 |
2000年 | 196篇 |
1999年 | 188篇 |
1998年 | 172篇 |
1997年 | 155篇 |
1996年 | 139篇 |
1995年 | 119篇 |
1994年 | 125篇 |
1993年 | 84篇 |
1992年 | 95篇 |
1991年 | 72篇 |
1990年 | 72篇 |
1989年 | 66篇 |
1988年 | 53篇 |
1987年 | 41篇 |
1986年 | 45篇 |
1985年 | 30篇 |
1984年 | 26篇 |
1983年 | 12篇 |
1982年 | 24篇 |
1981年 | 27篇 |
1980年 | 15篇 |
1979年 | 16篇 |
1978年 | 13篇 |
1977年 | 12篇 |
1976年 | 11篇 |
1973年 | 7篇 |
排序方式: 共有8874条查询结果,搜索用时 31 毫秒
101.
A method is described for the rapid and automatic analysis of flexible molecular alignments using multidimensional scaling and a normalized scoring scheme. A projection scheme was devised to separate orientational and conformational effects. It is shown that the approach can be utilized for the identification of common binding orientations or to the study of differences in partioning behavior. It is suggested that the method can be employed as a novel approach exploring molecular similarity as a dynamic property, so that it includes aspects of motion (by way of mutual orientations), conformations and molecular properties. 相似文献
102.
采用分子量500万的聚氧化乙烯和无水溴化铜,通过混溶蒸发法制备成高聚物固体电解质P(EO)n-CuBr2薄膜,并在0.1~300MPa范围不同的流体静水压下详细测量其复平面阻抗谱,分别得到在不同压力下离子电导率和介电常数与测量频率的关系.进一步解谱准确地求出P(EO)n-CuBr2(n=12、16)薄膜离子电导率和介电常数的静水压效应,并结合X-光物相分析,根据离子迁移通道的物理图象和高聚物的极化机构进行了初步的讨论.添加20%的增塑剂碳酸丙烯酯,较大改进了压力下的导电性.120~300MPa的离子电导率提高一个数量级 相似文献
103.
IntroductionElectrontransferreactionsarethekeystepsinphoto synthesis ,respirationandmanyotherbiochemicalprocess es.1Cytochromeb5isaredoxproteinexistingwidelyinnature ,whichactsasanelectron carrierduringvariouselectrontransferprocessesinthebiologicalsystem .2Cytochromeb5isamembraneproteinwithmolecularweightofapproximately 16kDa ,ofwhichthehydrophobicC terminaldomainanchorscytochromeb5tothemem brane ,andthehydrophilicN terminaldomaincontainshemeprostheticgroupandexhibitsthebiologicalfunctionsof… 相似文献
104.
Densities of four aqueous NaNO3 solutions (0.100, 0.303, 0.580, 0.892 mol-kg–1 H2O) have been measured in the liquid phase with a constant-volume piezometer immersed in a precision liquid thermostat. Measurements were made at ten isotherms between 292 and 573 K. The range of pressure was 0.1–30 MPa. The total uncertainty of density, pressure, temperature, and concentration measurements were estimated to be less than 0.06%, 0.05%, 10 mK, and 0.014%, respectively. Values of saturated densities were determined by extrapolating experimental P- data to the vapor pressure at fixed temperature and composition. Apparent molar volumes were derived using measured values of density for the solutions and for pure water. The apparent molar volumes were extrapolated to zero concentration to yield partial molar volumes at infinite dilution. The temperature, pressure, and concentration dependence of partial and apparent molar volumes were studied. The measured values of density and apparent and partial molar volume were compared with data reported in the literature. 相似文献
105.
106.
Grell D. Grell E. Bugnon P. Dietrich B. Lehn J.-M. 《Journal of Thermal Analysis and Calorimetry》2004,77(2):483-495
The coordination of divalent and monovalent inorganic anions to synthetic polyammonium receptors is investigated in aqueous
solution around neutral pH by titration calorimetry and NMR spectroscopy. High-affinity 1:1 complexes are formed by a pyrrole
type cryptand (1) with sulfate and phosphate, characterized by association constants of almost 107 M-1. Affinities close to 105 M-1 are found for polyazacryptands (3 and 4) exhibiting F-/Cl- selectivity. The binding affinities and the anion selectivities are mainly caused by the charges of ligands and anions, which
is discussed on the basis of simple calculations of the electrostatic contribution to the anion/receptor interactions. The
binding of all investigated anions is exothermic at 298.2 K. The contribution of the large negative ΔH values to the free
energy of anion binding of the pyrrole type ligand is partially compensated by marked negative ΔS values. These unfavorable
entropic contributions are attributed to the additional inclusion of water molecules in the anion/receptor complexes.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
107.
Studies were performed to determine the effect of pH on chromium (Cr) binding by native, esterified, and hydrolyzed saltbush (Atriplex canescens) biomass. In addition, X-ray absorption spectroscopy studies were performed to determine the oxidation state of Cr atoms bound to the biomass. The amounts of Cr adsorbed by saltbush biomass were determined by inductively coupled plasma-optical emission spectroscopy (ICP-OES). For Cr(III), the results showed that the percentages bound by native stems, leaves, and flowers at pH 4.0 were 98%, 97%, and 91%, respectively. On the other hand, the Cr(VI) binding by the three tissues of the native and hydrolyzed saltbush biomass decreased as pH increased. At pH 2.0 the stems, leaves, and flowers of native biomass bound 31%, 49%, and 46%, of Cr(VI), respectively. The results of the XAS experiments showed that Cr(VI) was reduced in some extend to Cr(III) by saltbush biomass at both pH 2.0 and pH 5.0. The XANES analysis of the Cr(III) reaction with the saltbush biomass parts showed an octahedral arrangement of oxygen atoms around the central Cr(III) atom. The EXAFS studies of saltbush plant samples confirmed these results. 相似文献
108.
The title reaction has been used as an example to test the importance of using a hindered rotor treatment instead of a harmonic oscillator model for calculating vibrational partition functions corresponding to low-frequency internal rotation modes. First, a normal-mode analysis according to the Ayala and Schlegel's algorithm has been used to identify the internal rotation modes of methanethiol and the transition state structure. Then, after calculation of the energy barrier for each internal rotation, the corresponding hindered rotor partition functions have been calculated following the CW scheme of Chuang and Truhlar. The results show that the anharmonic treatment produces a rather modest improvement of the rate constants at room temperature or below. 相似文献
109.
110.