全文获取类型
收费全文 | 1329篇 |
免费 | 54篇 |
国内免费 | 6篇 |
专业分类
化学 | 1006篇 |
晶体学 | 16篇 |
力学 | 21篇 |
数学 | 89篇 |
物理学 | 257篇 |
出版年
2023年 | 11篇 |
2022年 | 11篇 |
2021年 | 17篇 |
2020年 | 17篇 |
2019年 | 25篇 |
2018年 | 22篇 |
2017年 | 15篇 |
2016年 | 26篇 |
2015年 | 37篇 |
2014年 | 40篇 |
2013年 | 68篇 |
2012年 | 100篇 |
2011年 | 113篇 |
2010年 | 45篇 |
2009年 | 41篇 |
2008年 | 95篇 |
2007年 | 71篇 |
2006年 | 68篇 |
2005年 | 79篇 |
2004年 | 66篇 |
2003年 | 56篇 |
2002年 | 64篇 |
2001年 | 16篇 |
2000年 | 18篇 |
1999年 | 11篇 |
1998年 | 7篇 |
1997年 | 21篇 |
1996年 | 18篇 |
1995年 | 10篇 |
1994年 | 13篇 |
1993年 | 11篇 |
1992年 | 11篇 |
1991年 | 10篇 |
1990年 | 14篇 |
1989年 | 4篇 |
1988年 | 7篇 |
1987年 | 7篇 |
1986年 | 5篇 |
1985年 | 13篇 |
1984年 | 11篇 |
1983年 | 6篇 |
1982年 | 5篇 |
1981年 | 9篇 |
1980年 | 7篇 |
1979年 | 13篇 |
1978年 | 9篇 |
1977年 | 12篇 |
1976年 | 6篇 |
1975年 | 4篇 |
1974年 | 8篇 |
排序方式: 共有1389条查询结果,搜索用时 15 毫秒
11.
Tetsuya Noda 《European Polymer Journal》2007,43(6):2321-2330
Continuous ATRP of MMA was carried out in a flow tubular reactor with varying flow rate, temperature, and [monomer]/[initiator] ratios. Changing the flow rate directly relates to the reaction time. This process produces polymer continuously with the conversion increasing with decreasing flow rate. The molecular weight (relating to the flow rate) increases linearly with conversion which is also observed when the [monomer]/[initiator] ratio was changed. The effect of altering the reaction temperature was studied and the apparent activation energy of the propagation reaction of MMA in this system was calculated to be ∼56.9 kJ mol−1, close to the values reported previously. Preparation of diblock copolymers is also reported with varying comonomers and the conversion, and SEC results suggested that this continuous system is an excellent and facile way to have a continuous ATRP process. 相似文献
12.
Tetsuya Okuyama Masaru Nakayama Yoshitsugu Tomokiyo Omer Van Der Biest 《Microscopy and microanalysis》2002,8(1):11-15
Lattice strains around a platelet oxygen precipitate in Si wafer is studied by energy filtering convergent-beam electron diffraction (CBED) and calculations based on the finite element method (FEM). Local lattice strains are measured from CBD patterns obtained with a probe size less than 2 nm in a specimen thicker than 450 nm. Strains measured are compressive along a direction normal to a plate of the precipitation and tensile along a direction parallel to the plate. Two-dimensional stress fields near the precipitate are obtained with FEM computer analyses by fitting the measured strains. It appears that shear stresses are concentrated at the end of the precipitate edge and the maximum shear stress at an interface between the precipitate and the Si-matrix is 1.9 GPa. It is demonstrated that a combination of the energy filtering CBED and FEM is very useful for the study of local strains near interfaces in semiconductor devices, in particular for the study of stress fields that are too steep for application of the conventional CBED technique. 相似文献
13.
Kullback-Leibler divergence and the Neyman-Pearson lemma are two fundamental concepts in statistics. Both are about likelihood ratios: Kullback-Leibler divergence is the expected log-likelihood ratio, and the Neyman-Pearson lemma is about error rates of likelihood ratio tests. Exploring this connection gives another statistical interpretation of the Kullback-Leibler divergence in terms of the loss of power of the likelihood ratio test when the wrong distribution is used for one of the hypotheses. In this interpretation, the standard non-negativity property of the Kullback-Leibler divergence is essentially a restatement of the optimal property of likelihood ratios established by the Neyman-Pearson lemma. The asymmetry of Kullback-Leibler divergence is overviewed in information geometry. 相似文献
14.
15.
We compute the cyclic homology of the coordinate ring A(SLq(2)) of the quantum algebraic group SL
q
(2). We observe a degeneration of the noncommutative de Rham complex. The results are also verified from the point of view of Connes' noncommutative differential geometry. 相似文献
16.
Shizuko Eguchi Mitsuru Nakayama Shûichi Hayashi 《Journal of mass spectrometry : JMS》1976,11(6):574-581
The doubly charged ion mass spectra of anhydropisatin, 4-methoxyanhydropisatin, 3, 8, 9-trimethoxypterocarpen and 3, 4, 8, 9-tetramethoxypterocarpen were determined, and the fragmentation was explained by assuming that the paired electrons were partially localized in the fragmentations and by comparing the spectra with that of 3-(CD3)-anhydropisatin. Conventional mass spectra of these compounds were very simple, but the doubly charged ion spectra were sufficiently characteristic for the reliable identification. 相似文献
17.
Kazuhiko Matsumoto Tetsuya Tsuda Toshiyuki Nohira Rika Hagiwara Yasuhiko Ito Osamu Tamada 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(3):m186-m187
In the title complex, (C6H11N2)3[LaCl6], centrosymmetric octahedral hexachlorolanthanate anions are located at the corners and face‐centers of the monoclinic unit cell. The ring H atoms of the cations interact with the Cl atoms of the anions via hydrogen bonding, and bifurcation of the hydrogen bonding is observed. Cation–cation interactions via hydrogen bonding between the ring H atoms and π‐electrons of aromatic rings are also observed as in other imidazolium salts. 相似文献
18.
19.
20.
Labeling experiments using several deuterated lipids were pursued to study the biosynthesis of macrocyclic isoprenoidal lipids of thermophilic methanogenic archaea, Methanothermobacter thermautotrophicus. The isopropylidene terminal of geranylgeranyl group of monomeric precursor appeared to be important for the CC bond formation at the hydrophobic end in the macrocyclic lipids. A mechanism involving a radical trigger at the allylic methyl group is proposed for this CC bond formation. 相似文献