全文获取类型
收费全文 | 513篇 |
免费 | 21篇 |
国内免费 | 1篇 |
专业分类
化学 | 393篇 |
晶体学 | 10篇 |
力学 | 12篇 |
数学 | 16篇 |
物理学 | 104篇 |
出版年
2021年 | 7篇 |
2020年 | 5篇 |
2019年 | 9篇 |
2017年 | 3篇 |
2016年 | 9篇 |
2015年 | 6篇 |
2014年 | 23篇 |
2013年 | 17篇 |
2012年 | 21篇 |
2011年 | 20篇 |
2010年 | 27篇 |
2009年 | 12篇 |
2008年 | 17篇 |
2007年 | 18篇 |
2006年 | 22篇 |
2005年 | 20篇 |
2004年 | 32篇 |
2003年 | 22篇 |
2002年 | 17篇 |
2001年 | 13篇 |
2000年 | 10篇 |
1999年 | 7篇 |
1998年 | 2篇 |
1997年 | 6篇 |
1996年 | 13篇 |
1995年 | 8篇 |
1994年 | 6篇 |
1993年 | 4篇 |
1992年 | 7篇 |
1991年 | 13篇 |
1990年 | 7篇 |
1989年 | 12篇 |
1988年 | 11篇 |
1987年 | 10篇 |
1986年 | 10篇 |
1985年 | 10篇 |
1984年 | 14篇 |
1983年 | 6篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 10篇 |
1978年 | 4篇 |
1977年 | 6篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1973年 | 3篇 |
1972年 | 2篇 |
1968年 | 3篇 |
1963年 | 2篇 |
排序方式: 共有535条查询结果,搜索用时 234 毫秒
91.
Copper(II)-acid co-catalyzed intermolecular substitution of electron-rich aromatics with diazoesters
The intermolecular aromatic substitution of N,N-dialkylanilines and alkoxybenzenes with diazoesters is shown to proceed in the presence of catalytic amounts of both copper(II) salt and acid (Lewis or Brønsted). This method is a mild and rare metal-free C-C bond formation reaction between aromatic (sp2) and aliphatic (sp3) carbons. 相似文献
92.
93.
Derivatization of the pyrimidine nucleobases and nucleosides with 4-bromomethyl-7-methoxycoumarin was studied with the aim of developing a sensitive and selective column liquid chromatographic method for these substances in serum. The labeling reactions and the nature of derivatives are discussed, together with the chromatographic properties of these derivatives. The derivatives are stable for at least several weeks. Typical detection limits are 50 pg for inosine, 150 pg for uridine, 50 pg for uracil, 50 pg for thymine and 100 pg for fluorodeoxyuridine, respectively. Within-day coefficients of variation averaged 5.0% for the stored-frozen serum pools; the mean day-to-day value was 5.2%. Thirty samples could be processed per working day. 相似文献
94.
Masaru Takeya Takehiro Matsuda Masao Iwamoto Norimichi Tsumura Toshiya Nakaguchi Yoichi Miyake 《Optical Review》2007,14(2):97-104
We propose a technique for estimating gene expression values for duplicated data on cDNA microarrays. In the scatter plots,
the distribution is constructed from a mixture of normal two-dimensional distributions, which represent fluctuations in gene
expression values due to noise. An expectation-maximization (EM) algorithm is used for estimating the modeling parameters.
The probability that duplicated data is shifted by noise is calculated using Bayesian estimation. Six data sets of rice cDNA
microarray assays were used to test the proposed technique. Genes in the data sets were subjected to clustering based on probability
of true value. Clustering successfully identified candidate genes regulated by circadian rhythms in rice. 相似文献
95.
96.
97.
98.
99.
Linda L. Maggiora James D. Petke Dama Gopal Reynold T. Iwamoto Gerald M. Maggiora 《Photochemistry and photobiology》1985,42(1):69-75
Abstract— A protonated Schiff base of Ni (II)-pyrochlorophyll a has been synthesized which exhibits a reversible bathochromic shift of 504 cm-1 relative to Ni (II)-pyrochlorophyll a. The magnitude of this shift lies between those observed for P700 and P680, the photoactive pigments of photosystems I and II in plants. Cyclic voltammetric measurements show that the protonated Schiff base is about 0.2 V more difficult to oxidize than its unprotonated form. These results suggest that a protonated Schiff base may be a better model for P680 than, as was originally assumed, for P700. In addition, the results of solvent and counterion effect studies show that microenvironmental perturbations in the neighborhood of the protonated Schiff base moiety are unlikely to induce further spectral shifts. Ab initio quantum mechanical calculations show a small hypsochromic shift rather than the observed bathochromic one, and the reasons for this discrepancy are discussed. 相似文献
100.
Based on a constant-pressure Monte Carlo molecular simulation, we have studied orientationally ordered transitions of small anisotropic molecules confined in two parallel hard walls. These molecules are modeled by the hard Gaussian overlap model. The molecular elongations of the chosen molecules are so small that the molecules cannot form stable liquid-crystal (LC) phases in the bulk. But in the slit pores, we found, while the distance between two walls of the pores decreases to the molecular scale, an orientationally ordered phase can form. It shows that even hard confining surfaces favor the alignment of the small anisotropic molecules. Thus we conclude that the required molecular elongation for forming LC phases will decrease in confinement. Our results indicate that some non-LC small molecules may form stable LC phases due to the inducement of confining surfaces. 相似文献