全文获取类型
收费全文 | 279篇 |
免费 | 16篇 |
国内免费 | 1篇 |
专业分类
化学 | 202篇 |
晶体学 | 1篇 |
数学 | 26篇 |
物理学 | 67篇 |
出版年
2023年 | 3篇 |
2022年 | 7篇 |
2021年 | 9篇 |
2020年 | 12篇 |
2019年 | 8篇 |
2018年 | 7篇 |
2017年 | 5篇 |
2016年 | 11篇 |
2015年 | 6篇 |
2014年 | 8篇 |
2013年 | 12篇 |
2012年 | 26篇 |
2011年 | 28篇 |
2010年 | 9篇 |
2009年 | 5篇 |
2008年 | 19篇 |
2007年 | 14篇 |
2006年 | 12篇 |
2005年 | 15篇 |
2004年 | 5篇 |
2003年 | 7篇 |
2002年 | 4篇 |
2001年 | 5篇 |
2000年 | 2篇 |
1999年 | 4篇 |
1996年 | 3篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1990年 | 3篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 5篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1964年 | 1篇 |
1963年 | 2篇 |
1961年 | 2篇 |
1959年 | 2篇 |
1958年 | 1篇 |
1956年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有296条查询结果,搜索用时 31 毫秒
91.
A sensitive and selective column adsorption method is proposed for the preconcentration and determination of atrazine and simazine. Atrazine and simazine were preconcentrated on heat-treated diatomaceous earth as an adsorbent and then determined by high-performance liquid chromatography (HPLC). Several parameters on the recoveries of the analytes were investigated. The experimental results showed that it was possible to obtain quantitative analysis when the solution pH was 2 using 100 mL of validation solution containing 1.5 μg of triazines and 5 mL of ethanol as an eluent. Recoveries of atrazine and simazine were 95.7 ± 4.2% and 75.0 ± 1.9% with a relative standard deviation for seven determinations of 4.7% and 2.7% under optimum conditions. The maximum preconcentration factor was 100 for triazines when 500 mL of sample solution volume was used. The linear ranges of calibration curves for atrazine and simazine were 1-150 ng mL−1 and 1-300 ng mL−1, respectively, with correlation coefficients of 0.999 and the detection limits (3Signal-to-Noise) were 0.24 ng mL−1 and 0.21 ng mL−1 for atrazine and simazine. The capacity of the adsorbent was also examined and found to be 0.8 mg g−1 and 1.3 mg g−1 for atrazine and simazine, respectively. The proposed method was successfully applied to the determination of triazines in river water and tap water samples with high precision and accuracy. 相似文献
92.
Let R = K[x
1, x
2, x
3, x
4] be the polynomial ring over a field of characteristic zero. For the ideal (x1a, x2b, x3c, x4d) ì R{(x_1^a, x_2^b, x_3^c, x_4^d) \subset R}, where at least one of a, b, c and d is equal to two, we prove that its generic initial ideal with respect to the reverse lexicographic order is the almost revlex
ideal corresponding to the same Hilbert function. 相似文献
93.
94.
Dr. Masahiro Yamashina Sho Matsuno Dr. Yoshihisa Sei Prof. Dr. Munetaka Akita Dr. Michito Yoshizawa 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(40):14147-14150
The methyl group is a small substituent, usually showing relatively weak or no interactions with other functional groups and metal ions. Herein, we present the recognition of the number of methyl groups on synthetic and natural aromatic compounds (i.e., benzene and xanthine derivatives, respectively) by the 1 nm‐sized polyaromatic cavity of a coordination capsule in water. Detailed competitive encapsulation experiments as well as X‐ray crystallographic analysis revealed that multiple guest–host CH3–polyaromatic interactions in the confined nanospace are key driving forces for the high selectivity. 相似文献
95.
96.
Kimura H Kanesaka S Kuroki S Ando I Asano A Kurosu H 《Magnetic resonance in chemistry : MRC》2005,43(3):209-216
The structure of poly(diethylsiloxane) (PDES) has been characterized using solid-state NMR of (17)O. The sample studied had a weight-average molecular weight of 2.45 x 10(5). The sample was prepared by utilizing the cationic ring-opening polymerization of (17)O-enriched hexacyclotrisiloxane. Solid-state NMR of (17)O-enriched PDES was measured on the low-temperature beta(1) phase, the high-temperature beta(2) phase, the two-phase system consisting of the liquid crystal and isotropic liquid phase and the isotropic phase. From these data, the molecular structure and dynamics of PDES in the various phases were characterized via the chemical shifts of (17)O, and electric field gradient parameters were determined from NMR and ab initio molecular orbital (MO) calculations. In addition to the solid-state NMR of (1)H, (13)C and (29)Si previously reported on these samples, knowledge of the dynamic behavior of PDES as inferred from the NMR of (17)O in the present study was enhanced significantly. Further, the potential of combining the experimental NMR of (17)O with ab initio MO calculations to characterize the dynamics of polymers containing oxygen is demonstrated. 相似文献
97.
A sensitive and selective batch adsorption method is proposed for the preconcentration and determination of simazine. Simazine was preconcentrated on diatomaceous earth as an adsorbent and then determined by high-performance liquid chromatography (HPLC). Several parameters on the recovery of the analyte were investigated. The experimental results showed that it was possible to obtain quantitative analysis when the solution pH was 2 using 100 mL of validation solution containing 1.5 μg of simazine and 5 mL of ethanol as an eluent. Recovery of simazine was 89.0 ± 1.6% with a relative standard deviation for seven determinations of 1.5% under optimum conditions. The maximum preconcentration factor was 100 for simazine when 500 mL of sample solution volume was used. The linear range of calibration curve was 1-200 ng mL−1 with a correlation coefficient of 0.996 and the detection limit (3S/N) was 0.3 ng mL−1. The capacity of the adsorbent was also examined and found to be 1.1 mg g−1 for simazine. The proposed method was successfully applied to the determination of simazine in river water with high precision and accuracy. 相似文献
98.
Ch. Binek T. Kato W. Kleemann O. Petracic D. Bertrand F. Bourdarot P. Burlet H. Aruga Katori K. Katsumata K. Prokes S. Welzel 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(1):35-40
In order to clarify the nature of the additional phase transition at H
1
(
T
) <
H
c
(
T
) of the layered antiferromagnetic (AF) insulator FeBr
2
as found by Aruga Katori et al. (1996) we measured the intensity of different Bragg-peaks in different scattering geometries. Transverse AF ordering is observed
in both AF phases, AF I and AF II. Its order parameter exhibits a peak at T
1
=
T
(
H
1
) in temperature scans and does not vanish in zero field. Possible origins of the step-like increase of the transverse ferromagnetic
ordering induced by a weak in-plane field component when entering AF I below T1 are discussed.
Received 27 September 1999 and Received in final form 6 December 1999 相似文献
99.
M. Hagiwara K. Katsumata H. Yamaguchi M. Tokunaga I. Yamada M. Gross P. Goy 《International Journal of Infrared and Millimeter Waves》1999,20(4):617-622
Antiferromagnetic resonance (AFMR) measurements on a well characterized single crystal sample of MnF2 have been performed using various kinds of millimeter and submillimeter sources up to 570 GHz and a superconducting magnet up to 20 T. All the AFMR modes predicted from the theory have been observed. We report a complete frequency-field chart for these AFMR modes. 相似文献
100.
Sho Kujirai 《哲学杂志》2020,100(16):2106-2127
ABSTRACT The mechanical properties of metals used as structural materials are significantly affected by hot (or warm) plastic working. Therefore, it is industrially important to predict the microscopic behaviour of materials in the deformation process during heat treatment. In this process, a number of nuclei are generated in the vicinity of grain boundaries owing to thermal fluctuation or the coalescence of subgrains, and dynamic recrystallisation (DRX) occurs along with the deformation. In this paper, we develop a DRX model by coupling a dislocation-based crystal plasticity model and a multi-phase-field (MPF) model through the dislocation density. Then, the temperature dependence of the hardening tendency in the recrystallisation process is introduced into the DRX model. A multiphysics simulation for pure Ni is conducted, and then the validity of the DRX model is investigated by comparing the numerical results of microstructure formation and the nominal stress–strain curve during DRX with experimental results. The obtained results indicate that in the process of DRX, nucleation and grain growth occur mainly around grain boundaries with high dislocation density. As deformation progresses, new dislocations pile up and subsequent nucleation occurs in the recrystallised grains. The influence of such microstructural evolution appears as oscillation in the stress–strain curve. From the stress–strain curves, the temperature dependence in DRX is observed mainly in terms of the yield stress, the hardening ratio, and the change in the hardening tendency after nucleation occurs. 相似文献