全文获取类型
收费全文 | 398367篇 |
免费 | 4407篇 |
国内免费 | 1606篇 |
专业分类
化学 | 209199篇 |
晶体学 | 5461篇 |
力学 | 18199篇 |
综合类 | 68篇 |
数学 | 49660篇 |
物理学 | 121793篇 |
出版年
2020年 | 3720篇 |
2019年 | 4106篇 |
2018年 | 5726篇 |
2017年 | 5797篇 |
2016年 | 7984篇 |
2015年 | 4626篇 |
2014年 | 7269篇 |
2013年 | 16440篇 |
2012年 | 13682篇 |
2011年 | 16321篇 |
2010年 | 12152篇 |
2009年 | 11886篇 |
2008年 | 15495篇 |
2007年 | 15350篇 |
2006年 | 14211篇 |
2005年 | 12861篇 |
2004年 | 11752篇 |
2003年 | 10334篇 |
2002年 | 10290篇 |
2001年 | 11316篇 |
2000年 | 8562篇 |
1999年 | 6355篇 |
1998年 | 5503篇 |
1997年 | 5357篇 |
1996年 | 5275篇 |
1995年 | 4697篇 |
1994年 | 4785篇 |
1993年 | 4670篇 |
1992年 | 4987篇 |
1991年 | 5168篇 |
1990年 | 4888篇 |
1989年 | 4827篇 |
1988年 | 4654篇 |
1987年 | 4615篇 |
1986年 | 4443篇 |
1985年 | 5876篇 |
1984年 | 5913篇 |
1983年 | 4982篇 |
1982年 | 5287篇 |
1981年 | 4985篇 |
1980年 | 4601篇 |
1979年 | 5024篇 |
1978年 | 5326篇 |
1977年 | 5418篇 |
1976年 | 5554篇 |
1975年 | 5159篇 |
1974年 | 5165篇 |
1973年 | 5263篇 |
1972年 | 4112篇 |
1971年 | 3527篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
271.
The characterisation of iron-containing species in Chinkombe ilmenite and its reduction products was undertaken using Mössbauer Spectroscopic techniques. The ore was reduced by graphite in an inert atmosphere. The effects of such variables as quantity of reductant, temperature and preoxidation were investigated. The ore was completely reduced to alpha-iron and titanium dioxide with 20% carbon for a period of one hour at 1373 K. Chemical mechanisms are proposed for the reduction and oxidation of Chinkombe ilmenite. In the processing of ilmenite to obtain synthetic rutile, the ultimate desire is to separate the Fe phase from the TiO2. Mössbauer Spectroscopy has unambiguously confirmed the desired transformation of the iron phase according to thermodynamic predictions. The information gained would be used to choose the conditions of the reduction process. The alpha-iron could be separated physically or chemically from the completely reduced product mass to obtain synthetic titanium dioxide suitable for the paint industry. 相似文献
272.
A. Sánchez-Lavega A. Salazar A. Ocariz L. Pottier E. Gomez L.M. Villar E. Macho 《Applied Physics A: Materials Science & Processing》1997,65(1):15-22
Received: 16 September 1996/Accepted: 6 January 1997 相似文献
273.
V. I. Grafutin V. L. Grishkin G. G. Myasishcheva Yu. V. Funtikov Yu. A. Novikov 《Physics of the Solid State》1998,40(4):549-551
The empirical relation θ
p
6
/I
p=aK (where θ
p is the limiting angle of the parabolic component in the angular distributions of annihilation photons in metals, I
p is the integrated contribution of this component, K=1, 2, 3, ... is an integer, and a is a constant independent of the type of metal) observed earlier has been tested on magnesium, aluminum, copper, zinc, lead,
and bismuth samples. The validity of this relation has been substantiated. The value of the dimensionless constant a has been determined and was found to coincide within experimental error with the result obtained in previous measurements.
It is shown that the value of K for the same metal but for different samples may be different. It is conjectured that this may be due to different defect
concentrations in samples.
Fiz. Tverd. Tela (St. Petersburg) 40, 600–602 (April 1998) 相似文献
274.
275.
The microwave subsidiary absorption threshold in tangentially magnetized yttrium-iron-garnet (YIG) films was measured as a function of the static magnetic field, film thickness and decrease in the 0.3–3 μm range is observed. The effect is explained quantitatively by using modified Damon-Eshbach dispersion relations which take into account exchange interactions.
The effect of temperature on hcrit, the smallest threshold field amplitude, in the 250<T< 450 K temperature range can be expressed by an empirical relationship hcrit Ms(T)-1.6 where Ms is the saturation magnetization. This hcrit vs Ms relationship is similar to that obtained for the magnetization dependence of parallel pump thresholds in Li-Ti ferrite compounds. 相似文献
276.
Z. I. Simenog 《Ukrainian Mathematical Journal》1996,48(9):1465-1469
Parasupersymmetric quantum mechanics is generalized to the case of an arbitrary number of parasuperchanrgesN and the order of paraquantizationp. We show that parasuperpotentials can be explicitly expressed via a single arbitrary function.
Institute of Mathematics, Ukrainian Academy of Sciences, Kiev. Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 48,
No. 9, pp. 1291–1294, September, 1996. 相似文献
277.
278.
G. Garcia-Belmonte J. Bisquert L. M. Navarro J. R. Jurado F. M. B. Marques 《Ionics》1995,1(5-6):377-383
In ionic conductors, long range-migrating charges are a main cause of polarization processes. This has complicated, up to
date, the study of ionic thermocurrents (ITC) in solid electrolytes. However, the method is appealing, as it probes directly
charge-formation phenomena that are important both from a scientific point of view and for applications.
This work reports on the observation of ITC in solid electrolytes. Under appropriate experimental conditions, the ITC response
of a zirconia sample electroded with platinum is a reproducible one, thus opening the way to a new characterization method
that may complement other well established methods, such as Impedance Spectroscopy and a number of electrochemical techniques.
The general trends of the response, which is composed of two well resolved ITC peaks, is discussed. One of them, taking place
at higher temperatures, conforms to the standard shape of a first order kinetics depolarization process.
Paper presented at the 2nd Euroconference on Solid State Ionics, Funchal, Madeira, Portugal, Sept. 10–16, 1995 相似文献
279.
ALEPH Collaboration D. Buskulic D. Casper I. De Bonis D. Decamp P. Ghez C. Goy J. -P. Lees A. Lucotte M. -N. Minard et al. 《Zeitschrift fur Physik C Particles and Fields》1995,69(1):379-392
A data sample of about 3.0 million hadronicZ decays collected by the ALEPH experiment at LEP in the years 1991 through 1994 is used to make an inclusive selection of
B hadron events. In this event sample 4227±140±252B* mesons in the decayB*→Bγ and 1944±108±161B**
u,d
mesons decaying into a B meson and a charged pion are reconstructed. Here and in the followingB**
u,d
denotes the eightL=1(bū) and (bd) states and their charge conjugate.
For the well establishedB* meson the following quantities are obtained:ΔM=M
B*−MB=(45.30±0.35±0.87) MeV/c2 andN
B*/(N
B+N
B*)=(77.1±2.6±7.0)%. The angular distribution of the photons in theB* rest frame is used to measure the relative contribution of longitudinalB* polarization states to beσ
L/(σ
L+σ
T)=(33±6±5)%. 相似文献
280.
The micro element content of food is an important quality index due to the action of these elements on human health. In this
article, we discuss how to ensure the reliability of analytical data on micro elements in order to truly represent the condition
of food. Sampling, treatment of the analytical sample, selection of the analytical method, standard solution, and certified
reference material, blank test, calibration of the instrument and equipment, application of the quality control chart, assessment
of the final analytical result, and quality assurance system are briefly described.
Received: 5 July 2001 Accepted: 19 November 2001 相似文献