全文获取类型
收费全文 | 1222篇 |
免费 | 44篇 |
国内免费 | 12篇 |
专业分类
化学 | 825篇 |
晶体学 | 4篇 |
力学 | 40篇 |
数学 | 183篇 |
物理学 | 226篇 |
出版年
2023年 | 5篇 |
2022年 | 14篇 |
2021年 | 10篇 |
2020年 | 17篇 |
2019年 | 17篇 |
2018年 | 23篇 |
2017年 | 14篇 |
2016年 | 36篇 |
2015年 | 32篇 |
2014年 | 48篇 |
2013年 | 59篇 |
2012年 | 82篇 |
2011年 | 69篇 |
2010年 | 46篇 |
2009年 | 30篇 |
2008年 | 79篇 |
2007年 | 79篇 |
2006年 | 83篇 |
2005年 | 112篇 |
2004年 | 63篇 |
2003年 | 49篇 |
2002年 | 41篇 |
2001年 | 22篇 |
2000年 | 8篇 |
1999年 | 5篇 |
1998年 | 17篇 |
1997年 | 16篇 |
1996年 | 20篇 |
1995年 | 11篇 |
1994年 | 7篇 |
1993年 | 8篇 |
1992年 | 6篇 |
1991年 | 7篇 |
1990年 | 6篇 |
1988年 | 4篇 |
1985年 | 5篇 |
1984年 | 7篇 |
1983年 | 10篇 |
1982年 | 6篇 |
1981年 | 8篇 |
1980年 | 13篇 |
1979年 | 6篇 |
1978年 | 8篇 |
1977年 | 8篇 |
1976年 | 8篇 |
1975年 | 10篇 |
1973年 | 7篇 |
1970年 | 3篇 |
1969年 | 6篇 |
1881年 | 3篇 |
排序方式: 共有1278条查询结果,搜索用时 546 毫秒
121.
122.
123.
Substituted carbonylmanganese cations [Mn(CO)5L]+, where L=py, PPh3 and PPh2Me, readily react with various organoborate anions (tetramethylborate, methyltriphenylborate and tetraphenylborate) in THF solution to afford a mixture of dimanganese carbonyls, hydridomanganese carbonyls and alkylmanganese carbonyls. The formation of the dimanganese carbonyl dimers as well as the hydridomanganese carbonyls suggests the involvement of 19-electron carbonylmanganese radicals that stem from an initial electron transfer. On the other hand, the acetonitrile-substituted analogue [Mn(CO)5(CH3CN)]+ reacts with the same borate anions to afford the alkylated RMn(CO)5, where R=CH3 and C6H5, as the sole carbonylmanganese product. As such, this alkylative annihilation is best formulated as a direct attack on the carbonyl carbon by the borate nucleophile. The two different pathways can be understood in terms of the balance between the electrophilicity of the carbonyl ligand and the electron affinity of the carbonylmanganese cation. 相似文献
124.
Fast (6250 Hz) line-of-sight measurements of infrared spectral radiation intensities (Iλ) from a luminous flame and a new deconvolution technique for the estimate of local scalar properties using inverse radiation calculations are reported. Time series data of Iλ for one diametric and nine chord-like radiation paths in a representative horizontal plane were measured. Statistical properties of Iλ, including mean, root mean square (rms), probability density function, autocorrelation coefficient, and power spectral density, were obtained from the time series data. The measured statistical properties of Iλ at two representative wavelengths, which are dominated by carbon dioxide (CO2) and soot radiation, respectively, are reported. The autocorrelation coefficient data show large negative loops with repeatable zero crossings at 20 ms and minimum values as low as −0.2 at 30–40 ms. Radial distributions of mean and rms CO2 mole fractions and temperatures were estimated using inverse calculations of mean Iλ at two different wavelengths dominated by CO2 radiation in conjunction with the relationship of these quantities to mixture fractions. Soot volume fraction distributions were also estimated using inverse calculations of mean Iλ at a wavelength dominated by continuum soot radiation. The estimated local mixture fraction distributions were in reasonably good agreement with sampling data from similar flames. The calculated mean Iλ from 1.4 to 4.8 μm other than those used in the inverse calculations matched the experimental data well. The present method provides non-intrusive measurements of major gas species and temperature statistics in turbulent soot containing flames not accessible to other optical diagnostics. 相似文献
125.
126.
127.
F. Jay Breid Richard A. Davis Keh-Shin Lh Murray Rosenblatt 《Journal of multivariate analysis》1991,36(2)
We discuss a maximum likelihood procedure for estimating parameters in possibly noncausal autoregressive processes driven by i.i.d. non-Gaussian noise. Under appropriate conditions, estimates of the parameters that are solutions to the likelihood equations exist and are asymptotically normal. The estimation procedure is illustrated with a simulation study for AR(2) processes. 相似文献
128.
We provide sufficient conditions for strong ellipticity for a general class of anisotropic hyperelastic materials. This general class includes as a subclass transversely isotropic materials. Our sufficient conditions require that the first partial derivatives of the reduced-stored energy function satisfy some simple inequalities and that the second partial derivatives satisfy a convexity condition. We also characterize a restricted type of strong ellipticity for a subclass of transversely isotropic materials undergoing pure homogeneous deformations. We apply our results to a model of soft tissue from the biomechanics literature. 相似文献
129.
Phase Behavior of a Designed Cyclopropyl Analogue of Monoolein: Implications for Low‐Temperature Membrane Protein Crystallization
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Livia Salvati Manni Dr. Alexandru Zabara Dr. Yazmin M. Osornio Jendrik Schöppe Dr. Alexander Batyuk Prof. Dr. Andreas Plückthun Prof. Dr. Jay S. Siegel Prof. Dr. Raffaele Mezzenga Prof. Dr. Ehud M. Landau 《Angewandte Chemie (International ed. in English)》2015,54(3):1027-1031
Lipidic cubic phases (LCPs) are used in areas ranging from membrane biology to biodevices. Because some membrane proteins are notoriously unstable at room temperature, and available LCPs undergo transformation to lamellar phases at low temperatures, development of stable low‐temperature LCPs for biophysical studies of membrane proteins is called for. Monodihydrosterculin (MDS) is a designer lipid based on monoolein (MO) with a configurationally restricted cyclopropyl ring replacing the olefin. Small‐angle X‐ray scattering (SAXS) analyses revealed a phase diagram for MDS lacking the high‐temperature, highly curved reverse hexagonal phase typical for MO, and extending the cubic phase boundary to lower temperature, thereby establishing the relationship between lipid molecular structure and mesophase behavior. The use of MDS as a new material for LCP‐based membrane protein crystallization at low temperature was demonstrated by crystallizing bacteriorhodopsin at 20 °C as well as 4 °C. 相似文献
130.
Direct C(sp2)C(sp3) Cross‐Coupling of Diaryl Zinc Reagents with Benzylic,Primary, Secondary,and Tertiary Alkyl Halides
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Jay J. Dunsford Dr. Ewan R. Clark Dr. Michael J. Ingleson 《Angewandte Chemie (International ed. in English)》2015,54(19):5688-5692
The direct C(sp2)? C(sp3) cross‐coupling of diaryl zinc reagents with benzylic, primary, secondary, and tertiary alkyl halides proceeded in the absence of coordinating ethereal solvents at ambient temperature without the addition of a catalyst. The C(sp2)? C(sp3) cross‐coupling showed excellent functional‐group tolerance, and products were isolated in high yields, generally without the requirement for purification by chromatography. This process represents an expedient, operationally simple method for the construction of new C(sp2)? C(sp3) bonds. 相似文献