全文获取类型
收费全文 | 1283篇 |
免费 | 66篇 |
国内免费 | 4篇 |
专业分类
化学 | 1070篇 |
晶体学 | 1篇 |
力学 | 14篇 |
数学 | 134篇 |
物理学 | 134篇 |
出版年
2023年 | 10篇 |
2022年 | 9篇 |
2021年 | 17篇 |
2020年 | 34篇 |
2019年 | 27篇 |
2018年 | 10篇 |
2017年 | 9篇 |
2016年 | 62篇 |
2015年 | 45篇 |
2014年 | 58篇 |
2013年 | 69篇 |
2012年 | 112篇 |
2011年 | 99篇 |
2010年 | 65篇 |
2009年 | 50篇 |
2008年 | 94篇 |
2007年 | 74篇 |
2006年 | 89篇 |
2005年 | 66篇 |
2004年 | 82篇 |
2003年 | 61篇 |
2002年 | 48篇 |
2001年 | 30篇 |
2000年 | 15篇 |
1999年 | 15篇 |
1998年 | 13篇 |
1997年 | 12篇 |
1996年 | 19篇 |
1995年 | 15篇 |
1994年 | 19篇 |
1993年 | 2篇 |
1992年 | 5篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1976年 | 3篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1967年 | 1篇 |
1965年 | 1篇 |
1963年 | 1篇 |
排序方式: 共有1353条查询结果,搜索用时 0 毫秒
91.
The synthesis of two 12-nordrimanes and yahazunol was achieved via 8-oxo-12-nordrimanic acid methyl ester. The cytotoxic activity of yahazunol and seven other sesquiterpene hydroquinones and sesquiterpene quinones has been determined. 相似文献
92.
Stokes–Einstein (SE) and Stokes–Einstein–Debye (SED) relations in the neat ionic liquid (IL) [C2mim][NTf2] and IL/chloroform mixtures are studied by means of molecular dynamics (MD) simulations. For this purpose, we simulate the translational diffusion coefficients of the cations and anions, the rotational correlation times of the C(2)? H bond in the cation C2mim+, and the viscosities of the whole system. We find that the SE and SED relations are not valid for the pure ionic liquid, nor for IL/chloroform mixtures down to the miscibility gap (at 50 wt % IL). The deviations from both relations could be related to dynamical heterogeneities described by the non‐Gaussian parameter α(t). If α(t) is close to zero, at a concentration of 1 wt % IL in chloroform, both relations become valid. Then, the effective radii and volumes calculated from the SE and SED equations can be related to the structures found in the MD simulations, such as aggregates of ion pairs. Overall, similarities are observed between the dynamical properties of supercooled water and those of ionic liquids. 相似文献
93.
Block copolymers are well‐known for their large number of microphase morphologies on mesoscopic length scales. After a short review of the different morphologies observed in binary block copolymers and ternary triblock copolymers, the self‐assembling in blends of different block copolymers into common superlattices is discussed in detail. Besides similar morphologies known for pure triblock and diblock copolymers, the blends can also show new morphologies. Examples of such new morphologies are periodic non‐centrosymmetric lamellae and multiple gyroid interface structures. The discussion of the superlattices is primarily based on investigations by transmission electron microscopy (TEM), which are supplemented in a few cases by small angle X‐ray scattering (SAXS) or results from computer simulations. 相似文献
94.
95.
96.
Jos I. Urgel Marco Di Giovannantonio Kristjan Eimre Thorsten G. Lohr Junzhi Liu Shantanu Mishra Qiang Sun Amogh Kinikar Roland Widmer Samuel Stolz Max Bommert Reinhard Berger Pascal Ruffieux Carlo A. Pignedoli Klaus Müllen Xinliang Feng Roman Fasel 《Angewandte Chemie (International ed. in English)》2020,59(32):13281-13287
Cumulene compounds are notoriously difficult to prepare and study because their reactivity increases dramatically with the increasing number of consecutive double bonds. In this respect, the emerging field of on‐surface synthesis provides exceptional opportunities because it relies on reactions on clean metal substrates under well‐controlled ultrahigh‐vacuum conditions. Here we report the on‐surface synthesis of a polymer linked by cumulene‐like bonds on a Au(111) surface via sequential thermally activated dehalogenative C?C coupling of a tribenzoazulene precursor equipped with two dibromomethylene groups. The structure and electronic properties of the resulting polymer with cumulene‐like pentagon–pentagon and heptagon–heptagon connections have been investigated by means of scanning probe microscopy and spectroscopy methods and X‐ray photoelectron spectroscopy, complemented by density functional theory calculations. Our results provide perspectives for the on‐surface synthesis of cumulene‐containing compounds, as well as protocols relevant to the stepwise fabrication of carbon–carbon bonds on surfaces. 相似文献
97.
Holger Gedanitz María J. Dávila Elmar Baumhögger Roland Span 《The Journal of chemical thermodynamics》2010,42(4):478-483
An apparatus for accurate measurements of the sound velocity in fluids is described, which is based on the pulse-echo technique, and operates up to 30 MPa in the temperature range between (250 and 350) K. The expanded uncertainties (k = 2) in the speed of sound measurements are 0.006%, 6 mK in the temperature, 2.1 hPa in the pressure up to 3 MPa, and 23.9 hPa above this value. Measurements of the speed of sound for nitrogen from (250 to 350) K and for water at temperatures between (303.15 and 323.15) K are presented at pressures up to 30 MPa to validate the new apparatus. The expanded overall uncertainty of the measurements on nitrogen and water were estimated to be 0.011% and 0.006%, respectively. The speed of sound of both fluids was compared with literature sources showing an excellent agreement among them, with relative deviations lower than 0.01% in nitrogen and 0.006% in water. 相似文献
98.
Wissdorf W Pohler L Klee S Müller D Benter T 《Journal of the American Society for Mass Spectrometry》2012,23(2):397-406
Results obtained with two computational approaches for the simulation of ion motion at elevated pressure are compared with
experimentally derived ion current data. The computational approaches used are charged particle tracings with the software
package SIMION ver. 8 and finite element based calculations using the software package Comsol Multiphysics ver. 4.0/4.0a.
The experimental setup consisted of a tubular corona discharge ion source coupled to a cylindrical measurement chamber held
at atmospheric pressure. Generated ions are flown into the chamber at essentially subsonic laminar isothermal conditions.
In the simulations, strictly stationary conditions were assumed. The results show very good agreement between the SIMION/SDS
model and experimental data. For the Comsol model, only qualitative agreement is observed. 相似文献
99.
This work features an analysis for the acceleration technique DIIS that is standardly used in most of the important quantum
chemistry codes, e.g. in DFT and Hartree–Fock calculations and in the Coupled Cluster method. Taking up results from Harrison
(J Comput Chem 25:328, 2003), we show that for the general nonlinear case, DIIS corresponds to a projected quasi-Newton/secant method. For linear systems,
we establish connections to the well-known GMRES solver and transfer according (positive as well as negative) convergence
results to DIIS. In particular, we discuss the circumstances under which DIIS exhibits superlinear convergence behaviour.
For the general nonlinear case, we then use these results to show that a DIIS step can be interpreted as step of a quasi-Newton
method in which the Jacobian used in the Newton step is approximated by finite differences and in which the according linear
system is solved by a GMRES procedure, and give according convergence estimates. 相似文献
100.
Thorsten Allscher Peter Klüfers 《Acta Crystallographica. Section C, Structural Chemistry》2010,66(7):o321-o323
In methyl β‐d ‐fructopyranoside, C7H14O6, the thermodynamically most stable methyl glycoside of the ketose d ‐fructose, the pyranose ring is close to being an ideal 2C5 chair. The compound forms bilayers involving a complex hydrogen‐bonding pattern of five independent hydrogen bonds. Graph‐set analysis was applied to distinguish the hydrogen‐bond patterns at unary and higher level graph sets. 相似文献