全文获取类型
收费全文 | 2917篇 |
免费 | 103篇 |
国内免费 | 14篇 |
专业分类
化学 | 2277篇 |
晶体学 | 48篇 |
力学 | 25篇 |
数学 | 110篇 |
物理学 | 574篇 |
出版年
2023年 | 13篇 |
2022年 | 23篇 |
2021年 | 23篇 |
2020年 | 32篇 |
2019年 | 33篇 |
2018年 | 30篇 |
2017年 | 24篇 |
2016年 | 56篇 |
2015年 | 59篇 |
2014年 | 66篇 |
2013年 | 148篇 |
2012年 | 173篇 |
2011年 | 191篇 |
2010年 | 118篇 |
2009年 | 123篇 |
2008年 | 173篇 |
2007年 | 193篇 |
2006年 | 193篇 |
2005年 | 191篇 |
2004年 | 141篇 |
2003年 | 158篇 |
2002年 | 136篇 |
2001年 | 36篇 |
2000年 | 34篇 |
1999年 | 45篇 |
1998年 | 23篇 |
1997年 | 34篇 |
1996年 | 48篇 |
1995年 | 14篇 |
1994年 | 21篇 |
1993年 | 19篇 |
1992年 | 32篇 |
1991年 | 21篇 |
1990年 | 14篇 |
1989年 | 15篇 |
1988年 | 13篇 |
1987年 | 12篇 |
1986年 | 14篇 |
1985年 | 48篇 |
1984年 | 48篇 |
1983年 | 12篇 |
1982年 | 38篇 |
1981年 | 38篇 |
1980年 | 34篇 |
1979年 | 28篇 |
1978年 | 23篇 |
1977年 | 14篇 |
1976年 | 16篇 |
1975年 | 10篇 |
1973年 | 9篇 |
排序方式: 共有3034条查询结果,搜索用时 0 毫秒
91.
We have investigated the molecular orientation of glassy poly(9,9-dioctylfluorenyl-2,7-diyl) (PFO) layers formed on photo-aligned polyimide films with different in-plane anisotropy. The polyimide contains azobenzene in the backbone structure (Azo-PI), allowing us to control the in-plane anisotropy of the film by varying linearly polarized light (LP-L) exposure. The glassy PFO layers (30 nm thick) were obtained by annealing the samples at the liquid crystalline phase of PFO and then quenching them to room temperature. The degree of alignment of PFO was assessed by the polarization ratio of photoluminescence (PL). The PL polarization ratio increased rapidly with the LP-L exposure, and it reached 10 at 2.8 J/cm2. Beyond this LP-L exposure, it became almost constant around 10.4. This PL polarization ratio was much higher than the absorption dichroic ratio of the underlying Azo-PI film. This result suggests that the degree of alignment of PFO is determined by its liquid crystalline nature. The saturation dependence of the degree of alignment is very useful for fabricating alignment patterns by a simple photo-mask exposure method. We have succeeded in fabricating 3 μm line-and-space alignment patterns of PFO. 相似文献
92.
93.
Dihydroxyoligophenylenes (HO-ArPh(m)-OHs) with 9,9-dihexyl-2,7-fluorene (Ar=Flu), 2,5-dioctyloxy-1,4-benzene (Ar=Dob), pyridine (Ar=Py), or thiophene (Ar=Th) rings were synthesized by the Suzuki coupling reaction. Absorption maxima (λmax) of HO-ArPh(m)-OHs shifted progressively toward long wavelengths due to the expansion of the π-conjugation system with an increase in the number of benzene rings. Deprotonation of the OH groups of HO-ArPh(m)-OHs by treatment with NaH caused a bathochromic shift of λmax. The bathochromic shift of the deprotonated species increased with the donor numbers (DNs) of the solvents. The emission peak positions of NaO-ArPh(m)-ONas depended on the DNs of the solvents; therefore, the emission color could be tuned by changing the solvent. 相似文献
94.
The reaction of [(trimethylsilyl)imino]methyldiphenylphosphorane: Ph2MePNSiMe3 (I) with several acid anhydrides or alkyl isocyanates took place by the simple cleavage of silicon-nitrogen bond. In contrast the interaction of (I) with phenyl isocyanate, isothiocyanate or carbon disulphide led to addition-elimination reactions of the Wittig type. Detailed investigation in the case of phenyl isocyanate indicated the usual elimination of Ph2MePO is suppressed by the strong affinity of the trimethylsilyl group for anionic oxygen atom. 相似文献
95.
Dr. Jun Nakamura Hidenori Yamashiro Sayaka Hayashi Mami Yamamoto Kenji Miura Dr. Shu Xu Prof. Dr. Takayuki Doi Dr. Hideki Maki Osamu Yoshida Prof. Dr. Hirokazu Arimoto 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(40):12681-12689
Covalently linked vancomycin dimers have attracted a great deal of attention among researchers because of their enhanced antibacterial activity against vancomycin‐resistant strains. However, the lack of a clear insight into the mechanisms of action of these dimers hampers rational optimization of their antibacterial potency. Here, we describe the synthesis and antibacterial activity of novel vancomycin dimers with a constrained molecular conformation achieved by two tethers between vancomycin units. Conformational restriction is a useful strategy for studying the relationship between the molecular topology and biological activity of compounds. In this study, two vancomycin units were linked at three distinct positions of the glycopeptide (vancosamine residue (V), C terminus (C), and N terminus (N)) to form two types of novel vancomycin cyclic dimers. Active NC‐VV‐linked dimers with a stable conformation as indicated by molecular mechanics calculations selectively suppressed the peptidoglycan polymerization reaction of vancomycin‐resistant Staphylococcus aureus in vitro. In addition, double‐disk diffusion tests indicated that the antibacterial activity of these dimers against vancomycin‐resistant enterococci might arise from the inhibition of enzymes responsible for peptidoglycan polymerization. These findings provide a new insight into the biological targets of vancomycin dimers and the conformational requirements for efficient antibacterial activity against vancomycin‐resistant strains. 相似文献
96.
97.
98.
99.
We discuss how the spectral changes of quarkonia at T
c can reflect the ‘critical’ behaviour of QCD phase transition. Starting from the temperature dependencies of the energy density
and pressure from lattice QCD calculation, we extract the temperature dependencies of the scalar and spin-2 gluon condensates
near T
c. We also parametrize these changes into the electric and magnetic condensate near T
c. While the magnetic condensate hardly changes across T
c, we find that the electric condensate increases abruptly above T
c. Similar abrupt change is also seen in the scalar condensate. Using the QCD second-order Stark effect and QCD sum rules,
we show that these sudden changes induce equally abrupt changes in the mass and width of J/ψ, both of which are larger than 100 MeV at slightly above T
c.
相似文献
100.
Dan Abramovich Kalle Karu Kenji Matsuki Jaroslaw Wlodarczyk 《Journal of the American Mathematical Society》2002,15(3):531-572
Building on work of the fourth author and Morelli's work, we prove the weak factorization conjecture for birational maps in characteristic zero: a birational map between complete nonsingular varieties over an algebraically closed field of characteristic zero is a composite of blowings up and blowings down with nonsingular centers.