全文获取类型
收费全文 | 9191篇 |
免费 | 1491篇 |
国内免费 | 893篇 |
专业分类
化学 | 4089篇 |
晶体学 | 68篇 |
力学 | 842篇 |
综合类 | 49篇 |
数学 | 363篇 |
物理学 | 6164篇 |
出版年
2024年 | 15篇 |
2023年 | 83篇 |
2022年 | 224篇 |
2021年 | 237篇 |
2020年 | 261篇 |
2019年 | 261篇 |
2018年 | 246篇 |
2017年 | 270篇 |
2016年 | 345篇 |
2015年 | 332篇 |
2014年 | 458篇 |
2013年 | 756篇 |
2012年 | 547篇 |
2011年 | 688篇 |
2010年 | 489篇 |
2009年 | 613篇 |
2008年 | 625篇 |
2007年 | 690篇 |
2006年 | 593篇 |
2005年 | 469篇 |
2004年 | 402篇 |
2003年 | 364篇 |
2002年 | 396篇 |
2001年 | 294篇 |
2000年 | 296篇 |
1999年 | 212篇 |
1998年 | 203篇 |
1997年 | 154篇 |
1996年 | 125篇 |
1995年 | 144篇 |
1994年 | 107篇 |
1993年 | 132篇 |
1992年 | 87篇 |
1991年 | 69篇 |
1990年 | 59篇 |
1989年 | 38篇 |
1988年 | 38篇 |
1987年 | 29篇 |
1986年 | 29篇 |
1985年 | 37篇 |
1984年 | 43篇 |
1983年 | 16篇 |
1982年 | 26篇 |
1981年 | 19篇 |
1980年 | 11篇 |
1979年 | 8篇 |
1978年 | 9篇 |
1977年 | 6篇 |
1976年 | 5篇 |
1973年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
201.
The possibility of detection of the electron spin of a single paramagnetic species (an atom, a radical, or an ion) on the
surface was discussed. The analysis was based on spin chemistry laws taking into account the statistics of the spin states
of both the tunneling electron and paramagnetic center. The equations for the tunneling current as a function of temperature
and magnetic field strength were derived.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1732–1734, September, 1998. 相似文献
202.
Yuji Naruse Atsushi Takamori Itsuki Nagasawa 《Phosphorus, sulfur, and silicon and the related elements》2020,195(7):523-525
AbstractWe previously designed and prepared the first molecules to exhibit observable CD spectra by n-σ* excitation, 2,6-dithiaspiro[3.3]heptane 2,6-dioxide. Spiro[3.3]heptane frameworks possess axial asymmetry due to puckering of 2 four-membered rings; the ring bonds are rich in p-character due to acute bond angles, which lowers the σ* energy levels. In contrast, the lone pairs are rich in s-character, which results in a good donor with conformational fixation. We expected that, instead of lone pairs as donating orbitals, the use of σ-electron-donating Si-Si bonds should result in UV absorption in the observable range (>180?nm), so that the Cotton effect could appear, at least partially, in that range. We designed 2,6-disilyl-2,6-disilaspiro[3.3]heptanes as models, and performed theoretical calculations to confirm our idea. 相似文献
203.
Paramagnetic metal ions bound to proteins generate a dipolar field that can be accurately probed by pseudocontact shifts (PCS) displayed by the protein's nuclear spins. PCS are highly useful for determining the coordinates of individual spins in the molecule and for rapid structure determinations of entire protein-protein and protein-ligand complexes. However, PCS measurements require reliable resonance assignments for the molecule in its paramagnetic state and in a diamagnetic reference state. This article discusses different approaches for pairwise resonance assignments, with emphasis on a strategy which exploits chemical exchange between the two states. 相似文献
204.
205.
Chaikovskaya O. N. Levin P. P. Sul"timova N. B. Sokolova I. V. Kuz"min A. V. 《Russian Chemical Bulletin》2004,53(2):313-317
The spectra and kinetics of short-lived intermediates formed from aqueous (0.1 N NaOH) solutions of the natural mixture of humic and fulvic acids (HFA) were studied by laser flash photolysis using excitation wavelengths of 337, 390, 470, and 520 nm. Laser photolysis of HFA with light of 520 and 470 nm results in the formation of triplet excited states (THFA) characterized by the broad absorption spectrum with a maximum near 630 nm and lifetimes of 0.15 ms in deoxygenated solutions. The formation of two types of THFA with lifetimes of 0.1 and 2 ms and absorption spectra with maxima at 570 nm is observed under photolysis with light of 337 and 390 nm. The estimation of quantum yields of THFA gives 1 and 0.3% under photolysis with excitation wavelengths of 337 and 520 nm, respectively. The rate constants of THFA quenching by molecular oxygen are equal to (7—8)·108 L mol–1 s–1. 相似文献
206.
207.
本文对月光花素甲(Calonyctin A)的整体分子结构分析加以完善并进行总结。前文报道月光花素甲是两个分子量相差28a.m.u的糖甙类同系物分子的混合物。这两个分子(简称M_1和M_2)分别称为月光花素甲(Ⅰ)与月光花素甲(Ⅱ)(Calonyctm A_1,CalonyctinA_2),分子量分别为938与910。它们分别含 相似文献
208.
N.D. Yordanov V. Gancheva M. Radicheva B. Hristova M. Guelev O. Penchev 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》1998,54(14):2413-2419
Non irradiated and γ-irradiated dry herbs savoury (Savoury), wild thyme (Thymus serpollorium) and marjoram (Origanum) with absorbed dose of 8 kGy have been investigated by the methods of elecrtron paramagnetic resonance (EPR) and thermoluminescence (TL). Non-irradiated herbs exhibit only one weak siglet EPR signal whereas in irradiated samples its intensity increase and in addition two satelite lines are recorded. This triplet EPR spectrum is attributed to cellulose free radical generated by irradiation. It has been found that upon keeping the samples under the normal stock conditions the life-time of the cellulose free radical in the examined samples is ∼60–80 days. Thus the conclusion has been made that the presence of the EPR signal of cellulose free radical is unambiguous indication that the sample under study has been irradiated but its absence can not be considered as the opposite evidence. In the case when EPR signal was absent the method of TL has been used to give the final decision about the previous radiation treatment of the sample. 相似文献
209.
Ema I García De La Vega JM Ramírez G López R Fernández Rico J Meissner H Paldus J 《Journal of computational chemistry》2003,24(7):859-868
We present three Slater-type atomic orbital (STO) valence basis (VB) sets for the first and second row atoms, referred to as the VB1, VB2, and VB3 bases. The smallest VB1 basis has the following structure: [3, 1] for the H and He atoms, [5, 1] for Li and Be, and [5, 3, 1] for the B to Ne series. For the VB2 and VB3 bases, both the number of shells and the number of functions per shell are successively increased by one with respect to VB1. With the exception of the H and Li atoms, the exponents for the VB1 bases were obtained by minimizing the sum of the Hartree-Fock (HF) and frozen-core singles and doubles configuration interaction (CISD FC) energies of the respective atoms in their ground state. For H and Li, we minimized the sum of the HF and CISD FC energies of the corresponding diatoms (i.e., of H(2) or Li(2)) plus the ground-state energy of the atom. In the case of the VB2 basis sets, the sum that was minimized also included the energies of the positive and negative ions, and for the VB3 bases, the energies of a few lowest lying excited states of the atom. To account for the core correlations, the VBx (x = 1, 2, and 3) basis sets for the Li to Ne series were enlarged by one function per shell. The exponents of these extended (core-valence, CV) basis sets, referred to, respectively, as the CVBx (x = 1, 2, and 3) bases, were optimized by relying on the same criteria as in the case of the VBx (x = 1, 2, and 3) bases, except that the full CISD rather than CISD FC energies were employed. We show that these polarized STO basis sets provide good HF and CI energies for the ground and excited states of the atoms considered, as well as for the corresponding ions. 相似文献
210.
本文应用取代基效应(SCS)方法研究了乙烯-乙烯醇(EVA)共聚物,得到了羟基(-OH)在两种不同溶剂中的SCS参数:在苯酚+重水(80/20W/W)中参数为S_1=42.77±0.08ppm,S_2=7.155±0.06ppm,S_3(s)=-4.08±0.02ppm,S_3(t)=-3.09±0.02ppm,S_4=0.48±0.03ppm,S_5=0.26±0.05ppm,在以邻二氯苯为溶剂时参数为S_1=44.97±0.61ppm,S_2=7.40±0.00ppm,S_3(s)=-4.51±0.17ppm,S_3(t)=-3.13±0.00ppm,S_4=0.63±0.04ppm,S_5=0.36±0.00ppm,同时利用所得到的SCS参数对该共聚物的~(13)C NMR谱进行了归属。 相似文献