全文获取类型
收费全文 | 25165篇 |
免费 | 2652篇 |
国内免费 | 2099篇 |
专业分类
化学 | 8739篇 |
晶体学 | 401篇 |
力学 | 1589篇 |
综合类 | 166篇 |
数学 | 1407篇 |
物理学 | 6641篇 |
综合类 | 10973篇 |
出版年
2024年 | 76篇 |
2023年 | 221篇 |
2022年 | 507篇 |
2021年 | 564篇 |
2020年 | 590篇 |
2019年 | 551篇 |
2018年 | 555篇 |
2017年 | 725篇 |
2016年 | 849篇 |
2015年 | 790篇 |
2014年 | 1131篇 |
2013年 | 1748篇 |
2012年 | 1338篇 |
2011年 | 1455篇 |
2010年 | 1060篇 |
2009年 | 1248篇 |
2008年 | 1334篇 |
2007年 | 1641篇 |
2006年 | 1486篇 |
2005年 | 1378篇 |
2004年 | 1280篇 |
2003年 | 1100篇 |
2002年 | 1066篇 |
2001年 | 907篇 |
2000年 | 836篇 |
1999年 | 748篇 |
1998年 | 617篇 |
1997年 | 574篇 |
1996年 | 500篇 |
1995年 | 495篇 |
1994年 | 459篇 |
1993年 | 429篇 |
1992年 | 358篇 |
1991年 | 236篇 |
1990年 | 229篇 |
1989年 | 180篇 |
1988年 | 182篇 |
1987年 | 118篇 |
1986年 | 76篇 |
1985年 | 60篇 |
1984年 | 35篇 |
1983年 | 22篇 |
1982年 | 39篇 |
1981年 | 16篇 |
1980年 | 24篇 |
1979年 | 14篇 |
1978年 | 12篇 |
1977年 | 6篇 |
1976年 | 18篇 |
1973年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
271.
272.
Thomas C. Amu 《Journal of solution chemistry》1981,10(1):69-78
Interdiffusion coefficient have been measured for 1,1,2,2-tetrabromoethane in 21 organic solvents in order to ascertain the influence of shape, size, viscosity, nature and degree of branching, of the solvent molecules on transport properties. None of the existing correlations for diffusion in binary liquid systems appear to fit all the experimental data. Steric effects due to the solvent molecules are shown to be very important in the interpretation of the diffusion process. 相似文献
273.
Thermal decomposition of transition metal malonates, MCH2C2O4?xH2O and transition metal succinates, M(CH2)2C2O4?xH2O (M=Mn, Fe, Co, Ni, Cu, Zn) has been studied employing TG, DTG, DTA, XRD, SEM, IR and Mössbauer spectroscopic techniques. After dehydration, the anhydrous metal malonates and succinates decompose directly to their respective metal oxides in the temperature ranges 310–400 and 400–525°C, respectively. The oxides obtained have been found to be nanosized. The thermal stability of succinates have been found to be higher than that of the respective malonates. 相似文献
274.
Bredikhin A. A. Lazarev S. N. Bredikhina Z. A. Savel"ev D. V. Vandyukova I. I. Gubaidullin A. T. Litvinov I. A. 《Russian Chemical Bulletin》2003,52(4):846-852
Crystalline specimens of homochiral and racemic glycidyl p-toluenesulfonate were studied by IR spectroscopy, differential scanning calorimetry, and X-ray diffraction analysis. The melting phase diagram of glycidyl p-toluenesulfonate was constructed. The stacking effect in the crystals of the racemic sulfonate is responsible for a more dense molecular packing, with the result that a heterochiral type of crystallization becomes more favorable. 相似文献
275.
Balek V. Zeleňák V. Mitsuhashi T. Bakardjieva S. Šubrt J. Haneda H. 《Journal of Thermal Analysis and Calorimetry》2002,67(1):83-89
Results of emanation thermal analysis (ETA) characterizing microstructure changes of SiC based materials during heat treatment in argon are demonstrated. This method made it possible to reveal fine changes of the texture of SiC nano-sized powders, SiC micro-sized powders and SiC whiskers under in situconditions of the heating. ETA curves can serve as fingerprints of the respective samples.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
276.
The effect of pressure during thermal plasma chemical vapor deposition of diamond films has been investigated for a pressure range from 100 to 760 Torr. The maximum growth rate in our experiments occurs at 270 Torr for substrate temperatures around 1000°C. The existence of an optimum pressure for diamond deposition may he related to the balance between generation and recombination of atomic hydrogen and carbon-containing active species in front of the substrate. To estimate the concentrations of atomic hydrogen and methyl radicals under thermal plasma conditions, calculations based on thermodynamic equilibrium have been performed. This approximate evaluation provides useful guidelines because rapid diffusion results in a near frozen chemistry within the boundary layer. The effect of substrate pretreatment on diamond deposition depends on the type of substrate used. Two growth modes have been observed-layer growth and island growth of diamond crystals on various substrates. Screw dislocations have been observed in diamond deposition in thermal plasmas, and defects such as secondary nucleations are more concentrated along (III) directions than along (100) directions. 相似文献
277.
Summary The concept of a diffusion-averaged molecular weight, Md is presented, and Md is defined for polydisperse samples. It is shown via oligostyrene mixtures that Md can be determined in 20 minutes with common chromatographic equipment. If Md is measured and Mn or Mw is known, the polydispersity can be obtained. 相似文献
278.
A series of ferrocene‐containing liquid‐crystalline polyphosphonates with an even number of methylene groups are reported. All the polymers gave birefringent melts. The mesophase was identified as transparent with an increase in the spacer. The effects of pendant substitution and the spacer were studied with thermogravimetric analysis and differential scanning calorimetry. The effects of the phosphonate group in the spacer and the ferrocene ester group in the mesogen were examined. The presence of a steplike mesogenic structure and a pendant phenyl group in the spacer led to reductions in the glass‐transition and melting temperatures. The ferrocene moiety in the mesogen might be one of the reasons for the increased thermal stability and decreased liquid crystallinity. An energy‐minimized structure for the mesogenic and spacer segments was created with computer‐modeling programs, and it suggested the reason for the reductions in the glass‐transition and melting temperatures. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2256–2263, 2002 相似文献
279.
Golodnitsky Diana Ulus Avi Ishay Jacob S. 《Journal of Thermal Analysis and Calorimetry》2003,74(1):85-96
In this paper we try to establish a link between the microclimate in the wasp nest and the structure and thermal stability
of vespid silk. We suggest that there are at least two types of water that is absorbed by the silk of Oriental hornets, namely,
surface water and intrinsic structural water. The release of both types of water was found to be reversible. The enthalpy
values of the endothermic peaks associated with the release of water from different silk samples do not differ substantially
and are in the range of 106 to 130 J g-1 for the Vespa orientalis male larvae silk (sample #1), Paravespula germanica (yellowjacket) worker larvae silk (#3) and Vespa orientalis nest envelope(#4). For the Vespa orientalis worker larvae silk (sample #2), however, it is twice as large (228 J g-1). This is in agreement with the increased total amount of absorbed water. The silk studied has a fibrilar structure with
interconnecting surfaces overlying entire regions. It is assumed that the initial water loss stems from water evaporation
from the coat of the fibers - a daily occurrence in the hornets' nest. Heating to above 70°C may result in structural changes
in the silk core.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
280.
Tuoto C. V. Regina A. Nagy J. B. Nastro A. 《Journal of Thermal Analysis and Calorimetry》1998,54(3):891-899
DSC, TG and quadrupole mass spectrometer data concerning methylquinuclidinium iodide (MeQ1), dried precursor gel, and crystalline
levyne-type zeolite are discussed together with the thermal degradation of MeQ1 mixed with single inorganic components of
the gel.
It is shown that MeQ+ions play a role in the organization of the gel structure.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献