全文获取类型
收费全文 | 1348篇 |
免费 | 40篇 |
国内免费 | 24篇 |
专业分类
化学 | 1040篇 |
晶体学 | 21篇 |
力学 | 11篇 |
数学 | 59篇 |
物理学 | 281篇 |
出版年
2022年 | 7篇 |
2021年 | 8篇 |
2020年 | 12篇 |
2019年 | 11篇 |
2018年 | 11篇 |
2017年 | 10篇 |
2016年 | 17篇 |
2015年 | 26篇 |
2014年 | 20篇 |
2013年 | 61篇 |
2012年 | 63篇 |
2011年 | 74篇 |
2010年 | 42篇 |
2009年 | 36篇 |
2008年 | 96篇 |
2007年 | 106篇 |
2006年 | 80篇 |
2005年 | 78篇 |
2004年 | 79篇 |
2003年 | 65篇 |
2002年 | 51篇 |
2001年 | 45篇 |
2000年 | 38篇 |
1999年 | 25篇 |
1998年 | 16篇 |
1997年 | 20篇 |
1996年 | 15篇 |
1995年 | 19篇 |
1994年 | 5篇 |
1993年 | 8篇 |
1992年 | 20篇 |
1991年 | 9篇 |
1990年 | 11篇 |
1989年 | 12篇 |
1988年 | 14篇 |
1987年 | 10篇 |
1986年 | 12篇 |
1985年 | 21篇 |
1984年 | 19篇 |
1983年 | 17篇 |
1982年 | 9篇 |
1981年 | 12篇 |
1980年 | 9篇 |
1979年 | 13篇 |
1978年 | 11篇 |
1977年 | 10篇 |
1976年 | 6篇 |
1975年 | 9篇 |
1974年 | 6篇 |
1973年 | 6篇 |
排序方式: 共有1412条查询结果,搜索用时 15 毫秒
81.
82.
本文研究表明通过膜厚控制和表面等离激元增强方法可有效区分隐藏界面和空气表面的和频振动光谱信号. 以氟化钙基底支撑的PMMA薄膜为模型,观察到隐藏界面和空气表面对和频信号贡献的变化. 通过监控羰基和甲基伸缩振动基团,发现薄PMMA膜的和频信号来自PMMA/空气表面的化学基团-CH2、-CH3、-OCH3和C=O,而厚PMMA膜的和频信号则来自基底/PMMA埋层界面的-OCH3和C=O基团. 随制膜浓度增大,埋层界面C=O基团的取向角从65°下降到43°,且浓度大于或等于0.5 wt%时,取向角等于45°±2°. 相比之下,空气表面C=O的取向角落在21°∽38°之间. 在金纳米棒存在条件下,表面等离激元可以极大地增强和频信号,尤其是来自埋层界面信号. 相似文献
83.
Kenji Yoshikawa Miki Shimizu Toshiro Matsumura Akio Sakuragawa 《International journal of environmental analytical chemistry》2018,98(8):789-798
Capillary zone electrophoresis with indirect UV detection was developed for the simultaneous analysis of inorganic anions and organic acids using a mixed solution of 2,6-pyridinedicarboxylic acid and cetyltrimethylammonium hydroxide as the background electrolyte (BGE). The parameters which influence the separation, such as indirect UV detection wavelength, BGE conditions, applied voltage and extraction conditions were investigated. Thirteen inorganic anions and organic acids were detected within 20 min. The calibration curves of each analyte were linear with correlation coefficients greater than 0.991. The relative standard deviations (n = 10) of the peak areas ranged from 0.6% to 3.3%. The detection limits for these species ranged from 0.4 to 1.4 mg/L at a signal-to-noise ratio of 3. The recovery rate of each analyte was more than 80% under optimised extraction conditions, except for nitrite. The proposed method was applied towards the analysis of inorganic anions and organic acids in the atmospheric particulate matter using an Andersen sampler. The particle size of the particulate matter was determined, but not the size of the anions. 相似文献
84.
Michio Iwaoka Shuji Tomoda 《Phosphorus, sulfur, and silicon and the related elements》2013,188(3-4):755-766
Weak nonbonded interaction between a divalent selenium and an oxygen atom (i.e., Se···O interaction) frequently plays important roles in chemical and biological functions of selenium compounds. To establish that 77 Se NMR is an easy experimental probe to diagnose the strength of an Se···O interaction, 3 series of 2-substituted benzeneselenenyl derivatives, which have an intramolecular Se···O interaction in solution, were employed. By comparing the 77 Se NMR chemical shifts (δ Se ) with those observed for other series of selenium compounds, which have an intramolecular Se···Y (Y = N, O, F, Cl, or Br) interaction, approximate linear correlation was found between the δ Se values and the strengths of the nonbonded Se···Y interactions evaluated by natural bond orbital analysis at the B3LYP level. The correlation will be useful for estimating the strength of an Se···O interaction simply from the 77 Se NMR chemical shift. By extending the chemistry of nonbonded Se···O interactions to structural biology, analogous S···O interactions have been discovered in protein architecture. The directional features were, however, different from those of Se···O and S···O interactions of small organic compounds. 相似文献
85.
86.
Hiroyuki Kawano Haruhiko Shimoji Shoji Yoshikawa Katsumasa Miyatake Kazumori Hama Shuji Nakamura 《Optical Review》2008,15(2):118-124
Alignment error of an image sensor relative to the optical axis of a star sensor head and alignment errors between four heads
were calculated from pictures taken in an orbital experiment. When comparing the image sensor alignment parameters in the
orbital test and a ground test, both values matched well. By determining the relative relationship of the four heads using
four pictures taken at the same moment in orbit and uploading the parameters to the star sensor system in orbit, the estimated
attitude error was improved from 0.29 to 0.17°, though the accuracy was limited by the ±0.2° determination accuracy of the
satellite itself. We estimated the attitude determination accuracy from separation angles between boresights of the four heads,
calculated from pattern matching between downloaded pictures and a star catalogue. The estimated accuracy, in terms of potential
optical performance, was 0.60 arcmin at 3σ, which is sufficient to satisfy the specification of 1 arcmin. 相似文献
87.
The relationship between the flexural wave velocity and the excited vibration mode of a thin cylindrical shell is investigated. The natural frequency corresponding to the vibration mode is obtained as the solution of characteristic equation of thin cylindrical shell. However, all of these vibration modes are not excited actually. To estimate the excited vibration mode, the concept of "modified bending stiffness" is introduced, and the influence of each stress component upon the modified bending stiffness is analyzed. The excited mode is theoretically discriminated from the nonexcited mode based on the smallness of this modified bending stiffness. The validity of our theory is confirmed by an excellent agreement between theoretical and experimental results on flexural wave velocity. 相似文献
88.
Hashi K Shimizu T Goto A Kiyoshi T Matsumoto S Wada H Fujito T Hasegawa K Yoshikawa M Miki T Ito S Hamada M Hayashi S 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2002,156(2):318-321
We have developed a 920-MHz NMR system and performed the proton NMR measurement of H(2)O and ethylbenzene using the superconducting magnet operating at 21.6 T (920 MHz for proton), which is the highest field produced by a superconducting NMR magnet in the persistent mode. From the NMR measurements, it is verified that both homogeneity and stability of the magnet have a specification sufficient for a high resolution NMR. 相似文献
89.
Masanori Yoshikawa Michio Sorai Hiroshi Suga Syŭzŏ Seki 《Journal of Physics and Chemistry of Solids》1983,44(4):311-321
Heat capacity measurements have been made for six kinds of specimens prepared by different methods. Among them, Sample A exhibited a A-type ferromagnetic pahse transition at 1.347 K and a Schottky-type anomaly due to the zero-field splitting around 9K. The total entropy and enthalpy were (11.05 ± 0.04) J K?1mol?1 and (97.0 ± 0.4) J mol?1, respectively. Sample B exhibited a Sehottky-type anomaly around 0.4 K due to the ferro-magnetic dimeric coupling with as well as the Schottky-type anomaly at 9K. The total magnetic entropy and enthalpy were (11.45 ± 0.03) JK?1 mol?1 and (93.8 ± 0.8) J mol?1, respectively. The remaining samples are simple mixtures of the λ-type modification and the dimeric modification. Irrespective of the magnetic behavior at low temperatures, all the samples showed a non-magnetic first-order phase transition around 270 K. The heat capacity and entropy of this phase transition have been accounted for in terms of the Frenkel theory of heterophase fluctuation. Construction of an adiabatic-type calorimeter workable between 1.5 and 393 K has been also presented. 相似文献
90.
The cw dye laser excitation spectrum of the vibronic band of HCCl was observed between 16 539 and 16 656 cm?1 with the Doppler-limited resolution, 0.03 cm?1. The HCCl molecule was generated by the reaction of discharged CF4 with CH3Cl. The observed spectra were assigned to c-type transitions with ΔKa = ±1 and also to axis-switching transitions with ΔKa = 0 or ?2, but all with K′a = 0, both for HC35Cl and HC37Cl. A rotational analysis yielded the rotational constants and quartic centrifugal distortion constants for the ground vibronic state and the band origin. A weak vibronic band, about one-third as intense as the main band, was found at about 57 cm?1 to the violet of the main band for both isotopic species, and was ascribed to a transition from the ground vibronic state to a vibrational level, possibly (041), of the à state. The rotational levels of HC35Cl in the à state showed a large perturbation; the J′ = 8, 9, and 10 levels were found to be split into two components. A normal coordinate analysis was carried out to calculate the centrifugal distortion constants and the inertia defect, which were in fair agreement with the observed values. The molecular structure of HCCl in the ground vibronic state was recalculated from the rotational constants of the two isotopic species combined with the 0.75B0 + 0.25C0 value previously reported for DC35Cl. 相似文献