全文获取类型
收费全文 | 974篇 |
免费 | 26篇 |
国内免费 | 6篇 |
专业分类
化学 | 732篇 |
晶体学 | 2篇 |
力学 | 17篇 |
数学 | 155篇 |
物理学 | 100篇 |
出版年
2023年 | 4篇 |
2022年 | 15篇 |
2021年 | 15篇 |
2020年 | 7篇 |
2019年 | 17篇 |
2018年 | 14篇 |
2017年 | 11篇 |
2016年 | 17篇 |
2015年 | 20篇 |
2014年 | 21篇 |
2013年 | 50篇 |
2012年 | 70篇 |
2011年 | 51篇 |
2010年 | 39篇 |
2009年 | 40篇 |
2008年 | 71篇 |
2007年 | 55篇 |
2006年 | 56篇 |
2005年 | 75篇 |
2004年 | 61篇 |
2003年 | 41篇 |
2002年 | 42篇 |
2001年 | 13篇 |
2000年 | 14篇 |
1999年 | 5篇 |
1998年 | 11篇 |
1997年 | 6篇 |
1995年 | 9篇 |
1994年 | 7篇 |
1993年 | 4篇 |
1992年 | 10篇 |
1991年 | 4篇 |
1990年 | 5篇 |
1989年 | 5篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1985年 | 5篇 |
1984年 | 13篇 |
1983年 | 8篇 |
1982年 | 6篇 |
1981年 | 8篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1977年 | 5篇 |
1974年 | 3篇 |
1939年 | 3篇 |
1915年 | 4篇 |
1913年 | 5篇 |
1902年 | 3篇 |
1889年 | 3篇 |
排序方式: 共有1006条查询结果,搜索用时 0 毫秒
1.
Wen Zhang Hui Huang Yu Ding Margherita Gavagnin Ernesto Mollo Guido Cimino Yue‐Wei Guo 《Helvetica chimica acta》2006,89(4):813-820
Three new polyoxygenated steroids, muricesteroid ( 1 ), and menellsteroids A ( 2 ) and B ( 3 ), were isolated from two species of the South China Sea gorgonian Muricella flexuosa and Menella verrucosa Brundin , respectively. The structures of these new compounds were elucidated on the basis of extensive spectroscopic analysis, chemical methods and comparison with known related compounds. 相似文献
2.
Ernesto Quesada 《Tetrahedron letters》2004,45(25):4877-4881
The first syntheses of newly isolated members of the Preussomerin family, Preussomerins K and L, are reported. Key steps include the functionalisation of a 2-arylacetal anion, one-pot Friedel-Crafts cyclisation-deprotection and reductive opening of epoxides. 相似文献
3.
The linearized stability of charged thin shell wormholes under spherically symmetric perturbations is analyzed. It is shown that the presence of a large value of charge provides stabilization to the system, in the sense that the constraints onto the equation of state are less severe than for non-charged wormholes. 相似文献
4.
5.
6.
Angel L. Esteban Maria P. Galache Francisco Mora Ernesto Diez Jesus San Fabian 《Journal of computational chemistry》1989,10(7):887-895
An equation is formulated on the basis of theoretical INDO/FPT calculations which describes the angular dependence of the propanic long-range coupling constant 4JMeH in substituted HCCCH3 fragments. This equation is a truncated Fourier series in the torsion angle ?, HCCMe, which takes into account the dependence of the Fourier coefficients on the bond angle θ, CCMe. The substituent effects are assumed to be additive. Some parameters in the equation may be obtained from the 4JMeH couplings in propane and neopentane derivatives. The calculated effect upon 4JMeH of changes in the bond angle θ is significant and it seems to be in part the cause of some effects which have been attributed to conformational dependence. 相似文献
7.
8.
The effect of low-energy ion bombardment on CD4/O2 and CF3X (X=F, Cl, Br) plasma etching has been assessed by applying controlled rf bias voltages on polystyrene (PS) and polymethylmethacrylate (PMMA) samples. In both cases ion bombardment has been found to have a chemical effect. In the case of CF4/O2 discharges, ion bombardment has been found to change the relative etching efficiency of different mixtures. In the case of CF3X plasmas, ion bombardment has been found to alter PMMA and PS etch rates in a different way. In particular, the ratios between CF4 and CF3X (X=Cl, Br) etch rates of PS have been found to decrease with increasing bias voltage. This effect has been tentatively attributed to an ion bombardment-induced enhancement of the reaction between the aromatic ring and halogen molecules formed in CF3Cl and CF3Br discharges. 相似文献
9.
Grumelli DE Forzani ES Morales GM Miras MC Barbero CA Calvo EJ 《Langmuir : the ACS journal of surfaces and colloids》2004,20(6):2349-2355
The sulfonation of polyaniline (PANI) films by nucleophilic addition of sulfite ion has been controlled through the polymer oxidation state under electrochemical control. The process was monitored by in situ electrochemical quartz crystal microbalance (EQCM), and the polymer oxidation was accomplished by electrode potential steps in sulfite aqueous solutions. The nucleophilic addition of sulfite to PANI only takes place on the oxidized polymer. From the ratio of added mass to the injected charge, the degree of sulfonation has been obtained with a yield as high as 50%. It has been observed that the ion-exchange mechanism during the oxidation-reduction process in the resulting sulfonated polymer is analogous to the polymer produced by electrophilic sulfonation of polyaniline or by copolymerization of aniline with aminosulfonic acids, unlike the ionic exchange observed for unmodified PANI. 相似文献
10.
Geneviéve Cerveau Ernesto Colomer Robert J.P. Corriu J.Colin Young 《Journal of organometallic chemistry》1981,205(1):31-45
We report the chemical behavior of cobalt-stabilized carbenes, R3M(CO)3CoC(OEt)R′, and their parent anions, R3M(CO)3CoC(O?)R′, where M = Si or Ge. The anions where M = Si, R′ = Ph decompose thermally into the corresponding benzoylsilanes; when the silicon atom is chiral (R3 = MePh-1-Np) optically active R3SiCOPh is obtained with complete retention of configuration. 相似文献