全文获取类型
收费全文 | 1353篇 |
免费 | 16篇 |
专业分类
化学 | 1007篇 |
晶体学 | 11篇 |
力学 | 9篇 |
数学 | 134篇 |
物理学 | 208篇 |
出版年
2022年 | 6篇 |
2021年 | 8篇 |
2020年 | 6篇 |
2019年 | 12篇 |
2018年 | 8篇 |
2016年 | 17篇 |
2015年 | 13篇 |
2014年 | 13篇 |
2013年 | 55篇 |
2012年 | 55篇 |
2011年 | 45篇 |
2010年 | 36篇 |
2009年 | 37篇 |
2008年 | 75篇 |
2007年 | 80篇 |
2006年 | 75篇 |
2005年 | 79篇 |
2004年 | 60篇 |
2003年 | 66篇 |
2002年 | 75篇 |
2001年 | 24篇 |
2000年 | 21篇 |
1999年 | 15篇 |
1998年 | 16篇 |
1997年 | 26篇 |
1996年 | 19篇 |
1995年 | 8篇 |
1994年 | 21篇 |
1993年 | 9篇 |
1992年 | 21篇 |
1991年 | 7篇 |
1990年 | 8篇 |
1989年 | 8篇 |
1988年 | 11篇 |
1987年 | 16篇 |
1986年 | 14篇 |
1985年 | 26篇 |
1984年 | 35篇 |
1983年 | 15篇 |
1982年 | 34篇 |
1981年 | 31篇 |
1980年 | 22篇 |
1979年 | 16篇 |
1978年 | 15篇 |
1977年 | 15篇 |
1976年 | 17篇 |
1975年 | 22篇 |
1974年 | 8篇 |
1973年 | 7篇 |
1971年 | 6篇 |
排序方式: 共有1369条查询结果,搜索用时 312 毫秒
91.
Susumu Tajima Yukiyoshi Nagai Osamu Sekiguchi Masao Fujishige Nozomu Uchida 《Journal of the American Society for Mass Spectrometry》1995,6(3):202-206
The spontaneous unimolecular dissociation reaction of methyl lactate (1) ionized by electron impact was investigated by a combination of mass-analyzed ion kinetic energy spectrometry and deuterium labeling. The metastable ions 1+· decompose in a variety of ways: four fragment peaks are observed at m/z 89, 76, 61, and 45, which correspond to the losses of ?H3, CO, CH3?O, and ?OOCH3, respectively. Double hydrogen atom transfer occurs in the third reaction. The source-generated m/z 61 ions decompose into oxygen-protonated methanols at m/z 33 ([CH3OH 2 + ]) by the loss of CO with double hydrogen atom migration. Both hydroxyl and methyne hydrogen atoms in 1 +· are present in the resultant protonated methanols. 相似文献
92.
Koji Nemoto 《Tetrahedron letters》2009,50(31):4512-7862
The Lewis acid-mediated carboxylation of arenes with CO2 has been successfully applied to 1-substituted indoles and pyrroles by using dialkylaluminum chlorides instead of aluminum trihalides. Thus, the carboxylation of 1-methylindoles, 1-benzyl-, and 1-phenylpyrroles proceeds regioselectively with the aid of an equimolar amount of Me2AlCl under CO2 pressure (3.0 MPa) at room temperature to afford the corresponding indole-3-carboxylic acids and pyrrole-2-carboxylic acids in 61-85% yields, while the same treatment of 1,2,5-trimethylpyrrole affords the 3-carboxylic acid in 52% yield. 相似文献
93.
In Pang and Fukushima (Comput Manage Sci 2:21–56, 2005), a sequential penalty approach was presented for a quasi-variational
inequality (QVI) with particular application to the generalized Nash game. To test the computational performance of the penalty
method, numerical results were reported with an example from a multi-leader-follower game in an electric power market. However,
due to an inverted sign in the penalty term in the example and some missing terms in the derivatives of the firms’ Lagrangian
functions, the reported numerical results in Pang and Fukushima (Comput Manage Sci 2:21–56, 2005) are incorrect. Since the
numerical examples of this kind are scarce in the literature and this particular example may be useful in the future research,
we report the corrected results.
The online version of the original article can be found under doi:. 相似文献
94.
Masao Sumita Hibeki Abe Hiroyuki Kayaki Keizo Miyasaka 《Journal of Macromolecular Science: Physics》2013,52(1-2):171-184
The electrical conductivities of carbon-black-filled low-density polyethylene (LDPE), poly(methyl methacrylate) (PMMA), and poly(vinyl chloride)-vinyl acetate (PVC/ VAc) copolymer were measured as functions of carbon content and melt viscosity of the matrix at the temperatures at which the composites were prepared. Sharp breaks in the relationship between the carbon filler content and the conductivity of composites were observed in all specimens at some content of the carbon filler. The conductivity jumps as much as 10 orders of magnitude at the break point. This phenomenon has been known as the “percolation threshold”. The critical carbon content corresponding to the break point 相似文献
95.
Masao Hirano Shigetaka Yakabe James H. Clark Hiroyuki Kudo Takashi Morimoto 《合成通讯》2013,43(10):1875-1886
A wide variety of sulphides can be readily converted to the corresponding sulphoxides in good to excellent yields by treatment with a combination of sodium chlorite, (salen)manganese(III) complex, and chromatographic alumina in dichloromethane under mild and neutral conditions. 相似文献
96.
Kohei HayashidaHideaki Fujii Shigeto HirayamaToru Nemoto Hiroshi Nagase 《Tetrahedron》2011,67(35):6682-6688
We describe the rearrangement of a carbamoylepoxy 4,5α-epoxymorphinan derivative that provided a novel 4,5α-epoxymorphinan derivative with an oxazatricyclodecane structure via an oxabicyclo[2.2.2]octane intermediate. We proposed the mechanism of the rearrangement reaction based on results observed in different deprotonation conditions. Epimerization occurred during rearrangement under reversible, but not irreversible, deprotonation conditions. The rearrangement product had a novel fundamental structure with moderate affinities for opioid receptors (Ki (μ)=47.7 nM, Ki (δ)=174.6 nM, and Ki (κ)=248.1 nM). Thus, the rearrangement products might have high potency as opioid ligands. 相似文献
97.
98.
99.
Akagi M Omae D Tamura Y Ueda T Kumashiro T Urata H 《Chemical & pharmaceutical bulletin》2002,50(6):866-868
L-Ribose was synthesized by a simple four-step method with overall yield of 76.3% from a protected L-arabinose derivative, which is a compatible intermediate for the synthesis of L-deoxyribose. The key step of this strategy is the Swern oxidation and subsequent stereoselective reduction accompanied by inversion of the 2-hydroxy group of protected L-arabinose. 相似文献
100.
Toshio Motojima Shun-Ichi Ikawa Masao Kimura 《Journal of Quantitative Spectroscopy & Radiative Transfer》1981,25(1):29-33
Infrared absorption intensities of the fundamental vibrations of liquid H2O have been obtained by measuring transmissions at two sample thicknesses (about 9 and 0.9 μ). The effect of multiple internal reflections on the observed absorptions is examined in terms of thin-film optics. It is shown that this simple method yields precise absorption intensities, without corrections for the effects of multiple internal reflections. The resulting intensities are 89.9 × 103 cm/mmol and 5.91 × 103 cm/mmol for the stretching and bending vibrations, respectively. The latter value was estimated after eliminating the absorption of intermolecular vibrations from the 1400–2400 cm-1 region by means of computer simulation. 相似文献