全文获取类型
收费全文 | 1439篇 |
免费 | 37篇 |
国内免费 | 16篇 |
专业分类
化学 | 1072篇 |
晶体学 | 14篇 |
力学 | 7篇 |
数学 | 213篇 |
物理学 | 186篇 |
出版年
2023年 | 12篇 |
2021年 | 11篇 |
2020年 | 18篇 |
2019年 | 15篇 |
2018年 | 13篇 |
2017年 | 9篇 |
2016年 | 16篇 |
2015年 | 26篇 |
2014年 | 36篇 |
2013年 | 90篇 |
2012年 | 58篇 |
2011年 | 82篇 |
2010年 | 44篇 |
2009年 | 47篇 |
2008年 | 81篇 |
2007年 | 79篇 |
2006年 | 79篇 |
2005年 | 85篇 |
2004年 | 93篇 |
2003年 | 86篇 |
2002年 | 80篇 |
2001年 | 20篇 |
2000年 | 25篇 |
1999年 | 24篇 |
1998年 | 18篇 |
1997年 | 18篇 |
1996年 | 20篇 |
1995年 | 7篇 |
1994年 | 11篇 |
1993年 | 9篇 |
1992年 | 13篇 |
1991年 | 10篇 |
1990年 | 11篇 |
1988年 | 9篇 |
1987年 | 9篇 |
1986年 | 6篇 |
1985年 | 16篇 |
1984年 | 21篇 |
1983年 | 12篇 |
1982年 | 15篇 |
1981年 | 14篇 |
1980年 | 21篇 |
1979年 | 20篇 |
1978年 | 7篇 |
1976年 | 6篇 |
1974年 | 26篇 |
1973年 | 10篇 |
1972年 | 8篇 |
1971年 | 5篇 |
1968年 | 5篇 |
排序方式: 共有1492条查询结果,搜索用时 15 毫秒
91.
The vectorial Debye integral shows that tightly focused Laguerre-Gaussian (LG) beams have a residual intensity at the focal point for linear polarization, for a topological charge of m=1 and 2. We measured the shapes of linearly and circularly polarized LG beams and found that a central intensity appeared at m=1 and 2 for linear and right-handed circular polarization, however, it is completely canceled for left-handed circular polarization. In general, when the orbital angular momentum of the LG beam is parallel to the spin angular momentum of the photons, zero intensity is always achieved at the focus. 相似文献
92.
Yuetian Yan Masaaki Ubukata Robert B. Cody Timothy E. Holy Michael L. Gross 《Journal of the American Society for Mass Spectrometry》2014,25(8):1404-1411
A method for structural elucidation of biomolecules dating to the 1980s utilized high-energy collisions (~10 keV, laboratory frame) that induced charge-remote fragmentations (CRF), a class of fragmentations particularly informative for lipids, steroids, surfactants, and peptides. Unfortunately, the capability for high-energy activation has largely disappeared with the demise of magnetic sector instruments. With the latest designs of tandem time-of-flight mass spectrometers (TOF/TOF), however, this capability is now being restored to coincide with the renewed interest in metabolites and lipids, including steroid-sulfates and other steroid metabolites. For these metabolites, structure determinations are required at concentration levels below that appropriate for NMR. To meet this need, we explored CRF with TOF/TOF mass spectrometry for two groups of steroid sulfates, 3-sulfates and 21-sulfates. We demonstrated that the current generation of MALDI TOF/TOF instruments can generate charge-remote fragmentations for these materials. The resulting collision-induced dissociation (CID) spectra are useful for positional isomer differentiation and very often allow the complete structure determination of the steroid. We also propose a new nomenclature that directly indicates the cleavage sites on the steroid ring with carbon numbers. Figure
? 相似文献
93.
94.
95.
We prove that the difference between the numbers of positive swallowtails and negative swallowtails of the Blaschke normal map for a given convex surface in affine space is equal to the Euler number of the subset where the affine shape operator has negative determinant. 相似文献
96.
97.
Sekiguchi A Ishida Y Fukaya N Ichinohe M Takagi N Nagase S 《Journal of the American Chemical Society》2002,124(7):1158-1159
Dark red crystals of the halogen-substituted cyclotrigermenes [(tBu3Si)3Ge3X; X = Cl, Br, I] were obtained in good yields by the reaction of [(tBu3Si)3Ge3]+.TTFPB- (TTFPB- = tetrakis(2,3,5,6-tetrafluorophenyl)borate) with potassium halides (KCl, KBr, or KI) in diethyl ether. The crystal structures of the halogen-substituted cyclotrigermenes reveal a cis-bent Ge=Ge double bond, caused by the introduction of the electronegative halogen atom on the sp3 germanium atom of cyclotrigermene. In solution, an intramolecular halogen migration over the three-membered ring skeleton was observed. Facial stereoselectivity in the Diels-Alder reaction of new cyclotrigermenes with 2,3-dimethyl-1,3-butadiene is also reported. 相似文献
98.
99.
Munetaka Nakata Masaaki Sugie Harutoshi Takeo Chi Matsumura Tsutomu Fukuyama Kozo Kuchitsu 《Journal of Molecular Spectroscopy》1981,86(1):241-249
The microwave spectra of four isotopic species of dichlorine monoxide (OCl2) have been observed, and the rotational constants have been obtained. The rm structure for each isotopic species has been determined by Watson's method. The equilibrium structure has been estimated by taking proper averages of rm structures to be and ∠eClOCl = 110.886(6)°. The general applicability and the merit of the present method for estimating the equilibrium structure are pointed out. 相似文献
100.