全文获取类型
收费全文 | 111314篇 |
免费 | 19篇 |
国内免费 | 31篇 |
专业分类
化学 | 38359篇 |
晶体学 | 1623篇 |
力学 | 7697篇 |
数学 | 26048篇 |
物理学 | 37637篇 |
出版年
2018年 | 9764篇 |
2017年 | 10734篇 |
2016年 | 4494篇 |
2015年 | 986篇 |
2014年 | 151篇 |
2013年 | 224篇 |
2012年 | 4845篇 |
2011年 | 13928篇 |
2010年 | 7951篇 |
2009年 | 8094篇 |
2008年 | 11848篇 |
2007年 | 15821篇 |
2006年 | 274篇 |
2005年 | 7665篇 |
2004年 | 3910篇 |
2003年 | 3875篇 |
2002年 | 1663篇 |
2001年 | 242篇 |
2000年 | 411篇 |
1999年 | 100篇 |
1998年 | 96篇 |
1997年 | 57篇 |
1996年 | 231篇 |
1995年 | 147篇 |
1994年 | 128篇 |
1993年 | 123篇 |
1992年 | 108篇 |
1991年 | 113篇 |
1990年 | 114篇 |
1989年 | 123篇 |
1988年 | 127篇 |
1987年 | 148篇 |
1986年 | 122篇 |
1985年 | 148篇 |
1984年 | 162篇 |
1983年 | 138篇 |
1982年 | 146篇 |
1981年 | 138篇 |
1980年 | 134篇 |
1979年 | 153篇 |
1978年 | 153篇 |
1977年 | 66篇 |
1976年 | 96篇 |
1975年 | 78篇 |
1974年 | 72篇 |
1973年 | 128篇 |
1972年 | 55篇 |
1969年 | 80篇 |
1968年 | 111篇 |
1966年 | 55篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
J. L. Souza A. F. Santos L. Polese Marisa S. Crespi C. A. Ribeiro 《Journal of Thermal Analysis and Calorimetry》2007,87(3):673-677
Poly(3-hydroxybutyrate), PHB has been structurally
modified through reaction with maleic anhydride, MA. Transesterification reaction
was carried out fixing the PHB and MA and besides time and temperature the
concentration of the triethylamine (used as catalyst) was changed. Glass transition,
melting and crystallization temperature obtained from DSC curves and thermal
degradation temperatures obtained from TG traces were used to evaluate the
influence of the reaction conditions on the modification of PHB according
to factorial design. On the base of the results the optimum conditions are
to perform the PHB modification reaction with MA reaction at 110°C for
1 h with 5% v/v triethylamine. 相似文献
962.
T. Martinez M. Navarrete L. Cabrera F. Juárez A. Ramos K. Vazquez 《Journal of Radioanalytical and Nuclear Chemistry》2007,273(3):569-572
Nine brands of tobacco cigarettes manufactured and distributed in the Mexican market were analyzed by γ-spectrometry to certify
their non-artificial radioactive contamination. Since natural occurring radioactive materials (NORM) 40K, 232Th, 235U, and 239U (and decay products from the latter three nuclides) are the main sources for human radiation exposure, the aim of this work
was to determine the activity of 40K and potassium concentration. Averages of 40K and potassium concentration were of 1.29±0.18 Bq·g−1, and 4.0±0.57%. The annual dose equivalents to the whole body from ingestion and inhalation of 26 Bq 40K were 0.23 μSv and 15.8 μSv, respectively. The corresponding 50 years committed dose equivalents was 0.23 μSv. The total
committed dose to the lungs due to inhalation of 40K in tobacco was 16 μSv. Potassium concentrations obtained in this work were in the same range of those obtained by INAA,
so showing that the used technique is acute, reproducible, and accessible to laboratories equipped with low background scintillation
detectors. 相似文献
963.
964.
965.
We have studied the temperature dependence of the radiative deactivation of the Pd-porphine triplet states in Shpol’skii matrices
in the temperature range 1.2–210 K. A substantial transformation of the phosphorescence spectra is observed as the temperature
increases and is due to the inclusion of thermally activated Pd-porphine states in the radiative deactivation processes. The
activation energy Ea of these Pd-porphine states is measured in matrices of n-octane and n-nonane. The splitting of the lowest quasidegenerate
triplet state ΔE(T2−T1) is determined for planar and distorted conformations of the Pd-porphine macrocycle in the n-octane matrix as 40 and 57 cm−1, respectively. The ability to use the temperature dependence of the phosphorescence properties of Pd-porphine to fabricate
molecular thermometers for the low-temperature range is analyzed.
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 4, pp. 460–464, July–August, 2007. 相似文献
966.
Using temperature-modulated
differential scanning calorimetry, the melting behaviour of poly(oxytetramethylene)-alt-(aromatic oligoamide) (POTM-alt-AOA)
has been studied in comparison with that of polyoxytetramethylene glycohols
(POTMGs). The apparent melting temperature of the block copolymers is found
to be less than that of the corresponding POTMGs by approximately 30°C.
The relaxation time of melting of a POTM segment has been estimated and compared
with that of POTMG. The relaxation time of POTM-alt-AOA
is slightly shorter than that of POTMG when the molar mass of the POTM segment
is 2900; however, it is longer when the molar mass is 1400. 相似文献
967.
A. L. Sokolov 《Optics and Spectroscopy》2007,103(4):640-645
The technique of calculation of polarization aberrations with the help of the method of polarizationwave matrices is proposed. Radiation is represented as a coherent set of the Hermitian-Gaussian modes with a certain amplitude, phase, and polarization state; the longitudinal component of the field is also taken into account. Polarization aberrations are considered as a set of spurious modes. Polarization aberrations caused by a cylindrical converging lens and a diaphragm are studied. 相似文献
968.
Diffraction of light by acoustic waves that are generated in the acoustooptic cells of piezoelectric transducers with complex geometry is studied. The diffraction by acoustic beams with triangular, quadrangular (rhombic), hexagonal, etc., cross sections, when the lengths of light-sound interaction in the cross-sectional area of the light beam are different, is considered in the plane wave approximation. The difference in the length of interaction affects the instrument function of acoustooptic devices and provides the suppression of the side lobes in their transmission function. The advantages of using cells with complex-geometry transducers in tunable acoustooptic filters that are incorporated into fiber-optic communication lines with wavelength-division multiplexing (WDM) are discussed. 相似文献
969.
970.
L. V. Stepanova 《Journal of Applied Mechanics and Technical Physics》2008,49(1):142-147
This paper discusses the problem of finding the eigenvalue spectrum in determining the stress and strain fields at the tip
of an antiplane-shear crack in a power-law material. It is shown that the perturbation method provides an analytical dependence
of the eigenvalue on the material nonlinearity parameter and the eigenvalue of the linear problem. Thus, it is possible to
find the entire spectrum of eigenvalues and not only the eigenvalue of the Hutchinson-Rice-Rosengren problem.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 1, pp. 173–180, January–February, 2008. 相似文献