全文获取类型
收费全文 | 1625篇 |
免费 | 32篇 |
国内免费 | 3篇 |
专业分类
化学 | 785篇 |
晶体学 | 10篇 |
力学 | 33篇 |
数学 | 154篇 |
物理学 | 678篇 |
出版年
2021年 | 10篇 |
2020年 | 17篇 |
2019年 | 20篇 |
2018年 | 10篇 |
2017年 | 14篇 |
2016年 | 26篇 |
2015年 | 21篇 |
2014年 | 27篇 |
2013年 | 68篇 |
2012年 | 67篇 |
2011年 | 63篇 |
2010年 | 47篇 |
2009年 | 35篇 |
2008年 | 64篇 |
2007年 | 71篇 |
2006年 | 69篇 |
2005年 | 66篇 |
2004年 | 51篇 |
2003年 | 23篇 |
2002年 | 51篇 |
2001年 | 36篇 |
2000年 | 27篇 |
1999年 | 14篇 |
1998年 | 22篇 |
1997年 | 27篇 |
1996年 | 46篇 |
1995年 | 47篇 |
1994年 | 37篇 |
1993年 | 53篇 |
1992年 | 42篇 |
1991年 | 23篇 |
1990年 | 38篇 |
1989年 | 16篇 |
1988年 | 20篇 |
1987年 | 16篇 |
1986年 | 17篇 |
1985年 | 20篇 |
1984年 | 17篇 |
1983年 | 18篇 |
1982年 | 20篇 |
1981年 | 23篇 |
1980年 | 18篇 |
1979年 | 25篇 |
1978年 | 21篇 |
1977年 | 19篇 |
1976年 | 16篇 |
1975年 | 20篇 |
1974年 | 12篇 |
1973年 | 10篇 |
1972年 | 10篇 |
排序方式: 共有1660条查询结果,搜索用时 359 毫秒
51.
The variations of yields of CO2 from the gas phase H2O2 + NO2 + CO chain reaction system with added nitromethane or methyl nitrite have given rate constants for reactions of OH radicals with these substrates. At 292 K these are (5.5 ± 0.6) × 108 and (8.0 ± 1.1) × 108 dm3 mol?1 s?1 respectively. 相似文献
52.
53.
54.
A. D. Campbell 《Mikrochimica acta》1968,56(4):833-835
Summary A method is described for the construction of aluminium foil capsules in which hygroscopic samples may be dried to constant weight for combustion analysis.
Zusammenfassung Die Herstellung von Kapseln aus Aluminiumfolie wird beschrieben. Hygroskopische Substanzen lassen sich darin bis zur Gewichtskonstanz trocknen, ehe sie analysiert werden.相似文献
55.
Microgram amounts of selenium(IV) are determined by measuring the decrease in absorbance of dithizone in carbon tetrachloride solution at 620 nm. Relative standard deviations for samples containing 0.20 and 1.00 μg of selenium(IV) are 0.6% and 0.4%, respectively. Of several metals tested only copper (at the 1.0-μg level) and iron (at the 100-μg level) interfere but high concentrations of nitric or perchloric acid cause low results. A reinvestigation of the reaction of selenium(IV) with dithizone suggests a formula Se(HDz)4 for the dithizonate. 相似文献
56.
R. Witte E. E. B. Campbell C. Richter H. Schmidt I. V. Hertel 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1987,5(2):101-111
A collisional alignment and orientation study with planar symmetry is described, determining the complete density matrix for resonant charge transfer from laser excited atoms. Results are reported for the Na++Na*(3p) system over the collision energy rangeE c.m.=50?100 eV. We communicate the optimal alignment angle γ and linear polarisationP l + of the charge cloud as well as its relative height ρ00 and the angular momentumL ⊥ + transferred in the collision as a function of the scattering angle. For preparation of the sodium 3p orbital in the scattering plane (positive reflection symmetry) we observe that at small reduced scattering angles (<20 eV°) the preparation of apσ at large internuclear distances contributes most to the scattering intensity whereas at larger reduced scattering angles (>60 eV°) apπ+ preparation is more important. In contrast, preparation of thepπ? orbital (perpendicular to the scattering plane) is large at small and vanishes at larger scattering angles. We conclude that orbital following cannot be assumed in this resonant charge transfer process. The angular momentum transfer is observed to be small, indicating only little coherence in the process, but shows nevertheless an interesting behaviour as a function of scattering angle. 相似文献
57.
In an effort to build effective photovoltaic cells based on porphyrin-functionalised polythiophenes we have focused on synthetic routes to three monomer types. By controlling the geometric structure of the monomer, oxidation of these materials should produce polymers with different architectural structures, and as a result, different opto-electronic properties. Employing Wittig protocols allowed access to monomers in which the porphyrin moiety is connected to the beta-position of the thiophene via an alkene linkage. In addition, monomers were constructed using porphyrin condensation methods to afford alpha-thiophene meso-substituted porphryins. Another set of monomers was also prepared via porphyrin condensation routes, but instead utilising beta-formylthiophenes. By utilising different formyloligothiophenes we were able to generate a series of monomers that can be used to control the loading of the porphyrin in the polythiophene matrix. 相似文献
58.
Taglialatela-Scafati O Deo-Jangra U Campbell M Roberge M Andersen RJ 《Organic letters》2002,4(23):4085-4088
The known antimitotic agent eleutherobin and the briarane diterpenoids erythrolides A and B have been isolated from cultured specimens of Erythropodium caribaeorum in amounts comparable to those reported from wild-harvested reef animals. The novel diterpenoid aquariolide A, having an unprecedented highly rearranged carbon skeleton (named aquariane), has also been found. The aquariane skeleton can be formally derived from the briarane skeleton by sequential di-pi-methane and vinyl-cyclopropane rearrangements. [structure: see text] 相似文献
59.
60.
Fine structure is reported in the 69,71Ga NQR spectra of GaS and GaSe. The 69Ga (I = 32) and 71Ga (I = 32) spectra are different for each compound. This is attributed to an indirect spin-spin interaction between nearest-neighbour Ga atom pairs. A model giving reasonable quantitative agreement with experiment is presented. 相似文献