全文获取类型
收费全文 | 1128篇 |
免费 | 27篇 |
国内免费 | 4篇 |
专业分类
化学 | 834篇 |
晶体学 | 12篇 |
力学 | 18篇 |
数学 | 89篇 |
物理学 | 206篇 |
出版年
2023年 | 4篇 |
2022年 | 5篇 |
2021年 | 17篇 |
2020年 | 12篇 |
2019年 | 12篇 |
2018年 | 14篇 |
2017年 | 9篇 |
2016年 | 22篇 |
2015年 | 20篇 |
2014年 | 24篇 |
2013年 | 44篇 |
2012年 | 61篇 |
2011年 | 63篇 |
2010年 | 45篇 |
2009年 | 28篇 |
2008年 | 89篇 |
2007年 | 79篇 |
2006年 | 82篇 |
2005年 | 83篇 |
2004年 | 83篇 |
2003年 | 46篇 |
2002年 | 50篇 |
2001年 | 16篇 |
2000年 | 16篇 |
1999年 | 14篇 |
1998年 | 10篇 |
1997年 | 11篇 |
1996年 | 16篇 |
1995年 | 14篇 |
1994年 | 19篇 |
1993年 | 9篇 |
1992年 | 7篇 |
1991年 | 11篇 |
1990年 | 10篇 |
1989年 | 7篇 |
1988年 | 4篇 |
1987年 | 6篇 |
1986年 | 7篇 |
1985年 | 9篇 |
1984年 | 7篇 |
1983年 | 6篇 |
1982年 | 3篇 |
1981年 | 6篇 |
1980年 | 12篇 |
1979年 | 6篇 |
1978年 | 8篇 |
1977年 | 6篇 |
1976年 | 10篇 |
1974年 | 10篇 |
1972年 | 4篇 |
排序方式: 共有1159条查询结果,搜索用时 15 毫秒
951.
This paper is concerned with the initial value problem for semilinear systems of wave equations. First we show a global existence
result for small amplitude solutions to the systems. Then we study asymptotic behavior of the global solution. We underline
that ``modified' free profiles are obtained for all global solutions to the systems even in the case where the free profile
might not exist. Moreover, we prove non–existence of any free profiles for the global solution in some cases where the effect
of the nonlinearity is strong enough.
The first author was partially supported by Grant-in-Aid for Science Research (14740114), JSPS. 相似文献
952.
Aira Matsugaki Hideaki Takechi Hideaki Monjushiro Hitoshi Watarai 《Analytical sciences》2008,24(2):297-300
A microscope device to measure the circular dichroism (CD) spectra of a specified microscopic region of chiral samples was constructed by combining of a couple of objective lenses and a CCD camera, which was installed in a sample chamber of a commercially available CD spectropolarimeter. By using this apparatus, high quality micro-CD spectra in the 60 x 60 microm region of samples could be measured. Micro-CD spectra of thin film of chiral DNA samples on glass and a natural kidney bean leaf were measured, and the potential of the micro-CD apparatus was successfully demonstrated. 相似文献
953.
Satoshi Ninomiya Kazuya Ichiki Hideaki Yamada Yoshihiko Nakata Toshio Seki Takaaki Aoki Jiro Matsuo 《Rapid communications in mass spectrometry : RCM》2009,23(20):3264-3268
In this study, we present molecular depth profiling of multilayer structures composed of organic semiconductor materials such as tris(8‐hydroxyquinoline)aluminum (Alq3) and 4,4′‐bis[N‐(1‐naphthyl)‐N‐phenylamino]biphenyl (NPD). Molecular ions produced from Alq3 and NPD were measured by linear‐type time‐of‐flight (TOF) mass spectrometry under 5.5 keV Ar700 ion bombardment. The organic multilayer films were analyzed and etched with large Ar cluster ion beams, and the interfaces between the organic layers were clearly distinguished. The effect of temperature on the diffusion of these materials was also investigated by the depth profiling analysis with Ar cluster ion beams. The thermal diffusion behavior was found to depend on the specific materials, and the diffusion of Alq3 molecules was observed to start at a lower temperature than that of NPD molecules. These results prove the great potential of large gas cluster ion beams for molecular depth profiling of organic multilayer samples. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
954.
Both the amount of water and the number of calcium ions are main factors affecting the dissolution of chitin in calcium chloride dihydrate-saturated methanol (calcium solvent). The higher degree of N-acetylation of the chitin was also indicated by its higher solubility in calcium solvent. The chitin hydrogel was prepared by adding a large excess of water to the chitin solution with vigorous stirring, followed by extensive dialysis against water or by filtration to remove the methanol and calcium ions. The water content of the chitin hydrogel was approximately 94–96% (w/v) and could be controlled by centrifugation. The chitin gel was also prepared by the addition of a large excess of alcohol, such as ethanol and iso-propanol, and these protocols were found to be effective under anhydrous conditions because the alcohols were exchangeable with other organic solvents in solution. The chitin hydrogel was more susceptible to lysozyme than to chitinase, and showed and a poor susceptibility to chitosanase. A α-chitin-type crystalline structure was regenerated from chitin sheets prepared from both α-chitin and β-chitin solutions in calcium solvent, but the β-chitin-type sheet was formed from the β-chitin hydrogel prepared by mechanical agitation in water. The α-chitin hydrogel solidified when thawed after freezing, but the β-chitin hydrogel prepared by mechanical agitation maintained its gel form even after prolonged freezing. Animal studies revealed a low toxicity for the chitin sheet and an acceleration of epidermal cell regeneration. 相似文献
955.
To synchronize a control signal with a packet signal in response to changing timing jitter, we investigate ultra-short pulse tracking by using wavelength dispersion for a short-time optical buffer in an optical router. 相似文献
956.
Shintaro Nomura Masumi Yamaguchi Tatsushi Akazaki Hiroyuki Tamura Hideaki Takayanagi Yoshiro Hirayama 《Physica E: Low-dimensional Systems and Nanostructures》2006,34(1-2):292
The electron–hole states in the fractional quantum Hall regime is investigated with a back-gated undoped quantum well by photoluminesccence in magnetic fields. The evolution of the photoluminescence spectra is discussed depending on the electron density. We find anomalies of the photoluminescence at the integer as well as the fractional filling factors. 相似文献
957.
In this contribution, we give a brief survey of some elementary many body processes observable at surfaces. We begin the survey by discussing how the electron ground state would behave and look like in real space at surfaces. Next, we discuss how these electrons behave when they are perturbed by external fields characterized by ultrashort time scales. We follow this with a discussion of how the dynamics of electrons would then affect the motion of adsorbates on surfaces. Finally, we cite some possible technological applications utilizing this knowledge. We also discuss possible trends or directions of scientific research in this century. 相似文献
958.
959.
Terence G Henares Fumio Mizutani Ryuichi Sekizawa Hideaki Hisamoto 《Analytical sciences》2008,24(1):127-132
The experimental conditions of the sample delivery inside the reagent-release capillary-based capillary-assembled microchip (RRC-based CAs-CHIP) were optimized and the reagent release procedure in the RRC is discussed. Recently, our group introduced the basic concept of the "drop-and-sip" fluid handling technique (Anal. Chem., 2007, 79, 908). A microliter volume of sample solution is dropped on the inlet hole and is sipped into another hole, producing a sample plug flow in the main poly(dimethyl siloxane) (PDMS) channel, concurrently filling each sensing capillary that faces the main PDMS channel. However, the detailed evaluation of the successful sample delivery condition and the reagent release behavior in the RRC has not been fully discussed. Under our experimental conditions, ca. 0.6 - 2.4 s of sample plug-RRC contact time allowed the successful sample introduction into the RRC by capillary force without any reagent leakage or disturbance of the sample plug flow. On the other hand, reagent release behavior inside the RRC is governed by both convective and diffusive mass transport, which leads to a faster mixing time of the sample with reagents immobilized inside the RRC compared to that expected from the simple diffusion alone. 相似文献
960.
Nakamura H Mogi Y Hattori H Kita Y Hattori D Yoshimura A Karube I 《Analytica chimica acta》2008,620(1-2):127-133
Salt-tolerant yeast Saccharomyces cerevisiae ARIF KD-003 was applied to highly sensitive and reproducible absorbance-based biochemical oxygen demand (BODAB-ScII) measurement for seawater. In the previous work, we have studied the BODAB-ScI method using normal Baker's yeast S. cerevisiae, and the excellent feature of the Baker's yeast as uniformly sustainable in solution could successfully be utilized. However, the BODAB-ScI responses were disappeared by the existence of chloride ion as well as seawater. In the present method, uniformity in solution was also observed with S. cerevisiae ARIF KD-003, and salt-tolerance of the yeast was observed even in saturate concentration of sodium chloride. Next, characterizations of the influences of pH and incubation temperature were investigated. After optimum conditions were obtained, two calibration curves were made between 0.33 and 22 mg O2 L−1 BOD using standard solution of glucose glutamic acid (GGA) or mixture of GGA and artificial seawater. Then, excellent reproducibility as the averages of relative standard deviation (R.S.D.av) in two calibration curves (nine points each) was successfully obtained at 1.10% at pure water or 1.03% at artificial seawater standard, respectively. In addition, the 3σ lower detection limit was calculated to be 0.07 mg O2 L−1 BOD, and 0.11 mg O2 L−1 BOD was experimentally detected by increase of the sample volume at 1.5-folds. The storage stability of the S. cerevisiae ARIF KD-003 was obtained at least 4 weeks. 相似文献