全文获取类型
收费全文 | 492500篇 |
免费 | 4837篇 |
国内免费 | 1465篇 |
专业分类
化学 | 263574篇 |
晶体学 | 7439篇 |
力学 | 22385篇 |
综合类 | 16篇 |
数学 | 56469篇 |
物理学 | 148919篇 |
出版年
2020年 | 3852篇 |
2019年 | 4383篇 |
2018年 | 5470篇 |
2017年 | 5383篇 |
2016年 | 8331篇 |
2015年 | 5361篇 |
2014年 | 8389篇 |
2013年 | 21570篇 |
2012年 | 16660篇 |
2011年 | 20272篇 |
2010年 | 14051篇 |
2009年 | 14205篇 |
2008年 | 18834篇 |
2007年 | 19064篇 |
2006年 | 17801篇 |
2005年 | 16064篇 |
2004年 | 14700篇 |
2003年 | 13221篇 |
2002年 | 13124篇 |
2001年 | 14614篇 |
2000年 | 11113篇 |
1999年 | 8695篇 |
1998年 | 7164篇 |
1997年 | 7068篇 |
1996年 | 6933篇 |
1995年 | 6241篇 |
1994年 | 6124篇 |
1993年 | 5867篇 |
1992年 | 6604篇 |
1991年 | 6614篇 |
1990年 | 6254篇 |
1989年 | 6177篇 |
1988年 | 6347篇 |
1987年 | 6048篇 |
1986年 | 5828篇 |
1985年 | 7974篇 |
1984年 | 8119篇 |
1983年 | 6683篇 |
1982年 | 7001篇 |
1981年 | 6990篇 |
1980年 | 6587篇 |
1979年 | 7048篇 |
1978年 | 7045篇 |
1977年 | 7232篇 |
1976年 | 7182篇 |
1975年 | 6902篇 |
1974年 | 6686篇 |
1973年 | 6937篇 |
1972年 | 4521篇 |
1971年 | 3733篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
R. Grosseuvres A. Comandini A. Bentaib N. Chaumeix 《Proceedings of the Combustion Institute》2019,37(2):1537-1546
The present work reports new experimental and numerical results of the combustion properties of hydrogen based mixtures diluted by nitrogen and steam. Spherical expanding flames have been studied in a spherical bomb over a large domain of equivalence ratios, initial temperatures and dilutions at an initial pressure of 100 kPa (Tini = 296, 363, 413 K; N2/O2 = 3.76, 5.67, 9; %Steam = 0, 20, 30). From these experiments, the laminar flame speed , the Markstein length L’, the activation energy Ea and the Zel'dovich β number have been determined. These parameters were also simulated using COSILAB® in order to verify the validity of the Mével et al. [1] detailed kinetic mechanism. Other parameters as the laminar flame thickness δ and the effective Lewis number Leeff were also simulated. These new results aim at providing an extended database that will be very useful in the hydrogen combustion hazard assessment for nuclear reactor power plant new design. 相似文献
2.
3.
4.
The structure, chemical composition, and magnetic properties of electrochemically deposited nanocrystalline Co-Ni-Fe films
were investigated using a number of techniques. A high saturation magnetic induction up to B
s
= 21 kG was attained. An enhancement of the saturation magnetization compared to the ideal anticipated one was revealed,
which correlated with the nonlinear behavior of the structural phase composition and lattice parameters with the change of
the composition.
The text was submitted by the authors in English. 相似文献
5.
N. I. Golovina G. N. Nechiporenko G. G. Nemtsev G. P. Dolganova V. P. Roshchupkin D. B. Lempert G. B. Manelis 《Russian Journal of Applied Chemistry》2007,80(1):24-30
Methods for phase stabilization of ammonium nitrate were sought for in order to considerably expand the application area of this oxidizing agent in various-purpose self-combustible formulations, including that in a new generation of gas-generating formulations for automobile air bags. New methods for stabilization of ammonium nitrate were studied and, in particular, a search was made for organic compounds that can stabilize ammonium nitrate even at their low content. The mechanism of phase state stabilization of ammonium nitrate by compounds of this kind was examined. 相似文献
6.
Padavattan Govindaswamy Patrick J. Carroll Yurij A. Mozharivskyj Mohan Rao Kollipara 《Journal of Chemical Sciences》2006,118(4):319-326
The reaction of [{(η5-C5Me5)M(μ-Cl)Cl}2] {where M = Rh (1), Ir (2)} with functionalized phosphine viz., diphenyl-2-pyridylphosphine (PPh2Py) in dichloromethane solvent yield neutral ϰ1-P-coordinated rhodium and iridium complexes [(η5-C5Me5)RhCl2(κ1-P-PPh2Py)]3 and [(η5-C5Me5) IrCl2(ϰ1-P-PPh2Py)]4. Reaction of complexes 1 and 2 with the ligand PPh2Py in methanol under reflux give bis-substituted complexes such as [(η5-C5Me5)RhCl(ϰ1-P-PPh2Py)2]+
5 and [(η5-C5Me5)IrCl(ϰ1-P-PPh2Py)2]+
6, whereas stirring in methanol at room temperature gives P-, N-chelating complexes of the type [(η5-C5Me5)RhCl(ϰ2-P-N-PPh2Py)]+ 7 and [(η5-C5Me5)IrCl(ϰ2-P-N-PPh2Py)]+
8. Neutral ϰ1-P-coordinated complexes [(η5-C5Me5)RhCl2(ϰ1-P-PPh2Py)]3 and [(η5-C5Me5)IrCl2(ϰ1-P-PPh2Py)]4 easily undergo conversion to the cationic P-, N-chelating complexes [(η5-C5Me5)RhCl(ϰ2-P-N-PPh2Py)]+
7 and [(η5-C5Me5) IrCl(ϰ2-P, N-PPh2Py)]+
8 on stirring in methanol at room temperature. These complexes are characterized by FT-IR and FT-NMR spectroscopy as well as
analytical methods. The molecular structures of the representative complexes [(η5-C5Me5)RhCl2(ϰ1-P-PPh2Py)]3, [(η5-C5Me5)IrCl2(ϰ1-P-PPh2Py)]4 and hexafluorophosphate salt of complex [(η5-C5Me5)IrCl(ϰ2-P-PPh2Py)2]+
6 are established by single-crystal X-ray diffraction methods 相似文献
7.
The European Physical Journal E - The isothermal gas adsorption of two hexane isomers (n-hexane and cyclohexane) in the mesopores of MCM-41 silica have been investigated by small angle neutron... 相似文献
8.
The paper discusses the applicability of quasi-crystalline approximation to describing the thermal motion of water molecules in their normal and supercooled states. The problem is subjected to the critical analysis of experimental data on incoherent scattering of slow neutrons based on theories developed by Singwi-Sjolander [1] and Oskotsky [2] modified to duly take into account the limited applicability range of diffusion approximation. The applicability conditions of quasi-crystalline approximation are shown to be consistently satisfied only when water is in supercooled state and within a narrow temperature range above the melting temperature. 相似文献
9.
Investigated is the dependency of the crack tip opening displacement (CTOD) on the local microstructure of the heat affected zone in high-strength low-alloy (HSLA) microalloyed steel. Since the initiation of the crack tip location could not be controlled in fatigue, any possible correlation between heat iput in welding and fracture toughness could be smeared. Modified CTOD data are defined; they show that the fracture resistance of the weld joint decreased as the heat input increased. 相似文献
10.
A. N. Grishkov 《Algebra and Logic》1998,37(5):294-306
Ordinary cohomologies in an algebra most often exhibit themselves either as objects that describe extensions (of algebras,
groups, or modules) or as subjects hindering the existence of algebraic constructions. We introduce the notion of nonlinear
cohomologies at a level of cochain complexes, furnish particular examples for Lie algebras, and give an interpretation of
first nonlinear cohomologies in terms of “quasiextensions” of orthogonal modules.
Translated fromAlgebra i Logika, Vol. 37, No. 5, pp. 522–541, September–October, 1998. 相似文献