全文获取类型
收费全文 | 2631篇 |
免费 | 86篇 |
国内免费 | 11篇 |
专业分类
化学 | 2057篇 |
晶体学 | 43篇 |
力学 | 23篇 |
数学 | 96篇 |
物理学 | 509篇 |
出版年
2022年 | 16篇 |
2021年 | 22篇 |
2020年 | 34篇 |
2019年 | 28篇 |
2018年 | 21篇 |
2017年 | 26篇 |
2016年 | 50篇 |
2015年 | 57篇 |
2014年 | 74篇 |
2013年 | 144篇 |
2012年 | 117篇 |
2011年 | 138篇 |
2010年 | 64篇 |
2009年 | 79篇 |
2008年 | 145篇 |
2007年 | 162篇 |
2006年 | 149篇 |
2005年 | 181篇 |
2004年 | 137篇 |
2003年 | 133篇 |
2002年 | 113篇 |
2001年 | 56篇 |
2000年 | 54篇 |
1999年 | 33篇 |
1998年 | 28篇 |
1997年 | 26篇 |
1996年 | 29篇 |
1995年 | 22篇 |
1994年 | 27篇 |
1993年 | 25篇 |
1992年 | 35篇 |
1991年 | 14篇 |
1990年 | 26篇 |
1989年 | 21篇 |
1988年 | 18篇 |
1987年 | 25篇 |
1986年 | 26篇 |
1985年 | 42篇 |
1984年 | 39篇 |
1983年 | 20篇 |
1982年 | 31篇 |
1981年 | 31篇 |
1980年 | 18篇 |
1979年 | 20篇 |
1978年 | 20篇 |
1977年 | 13篇 |
1976年 | 17篇 |
1975年 | 21篇 |
1974年 | 26篇 |
1973年 | 16篇 |
排序方式: 共有2728条查询结果,搜索用时 0 毫秒
91.
H. Wada 《The European physical journal. E, Soft matter》2009,28(1):11-16
The dynamics of a rotating elastic nano-ring driven in a viscous fluid by an externally applied torque about a specific axis
is studied using elasto-hydrodynamic simulations. We show that a helical deformation of the ring filament is excited, and
that this leads to directed propulsion which is independent of the direction of rotation. It is found that the propulsive
force and efficiency initially increase as the torque is increased, and then decrease discontinuously at a buckling transition
at a critical torque. This unique propulsive behavior at the shape transition arises due to its specific geometry, i.e., circularity of an elastic filament. The implications of the behavior for artificial microscopic devices are discussed. 相似文献
92.
We calculate one-loop contributions to the Kähler potential in 4D effective theory of 5D gauged supergravity (SUGRA) on S1/Z2 with a generic form of the prepotential and arbitrary boundary terms. Our result is applicable to a wide class of 5D SUGRA models. The derivation is systematically performed by means of an N=1 superfield formalism based on the superconformal formulation of 5D SUGRA. As an illustrative example, we provide an explicit expression of the Kähler potential in the case of 5D flat spacetime. 相似文献
93.
94.
Umebayashi Y Mroz B Asada M Fujii K Matsumoto K Mune Y Probst M Ishiguro S 《The journal of physical chemistry. A》2005,109(21):4862-4868
Solvation structure of the zinc(II) ion in N,N-dimethylpropionamide (DMPA) was studied by Raman spectroscopy at varying temperature and by quantum mechanical calculations. No significant ion-pair formation was found for the Zn(ClO4)2 solution in the molality range m(Zn) < 1.5 mol kg(-1), and the solvation number of the zinc(II) ion was determined to be 4, indicating that 6-coordination of DMPA is sterically hindered. Interestingly, DMPA molecules are under equilibrium between planar cis and nonplanar staggered conformers, and the latter is more preferred in the coordination sphere, while the reverse is the case in the bulk. The DeltaG degrees , DeltaH degrees , and TDeltaS degrees values of conformational change from planar cis to nonplanar staggered in the coordination sphere were obtained to be -0.9, -8.5, and -7.5 kJ mol(-1), respectively. Density functional theory (DFT) calculations show that the planar cis conformer is more favorable than the nonplanar staggered one in the 1:2 cluster, as is the case for a single DMPA molecule and H(DMPA)+, indicating that there hardly occurs solvent-solvent interaction through the metal ion in the Zn2+-DMPA 1:2 cluster. On the other hand, the SCF energy of [Zn(planar cis-DMPA)4-n(nonplanar staggered DMPA)n]2+ (n = 0-4) decreases with increasing n, implying that the nonplanar staggered conformer is preferred in the solvate ion. It is thus concluded that solvent-solvent interaction through space, or solvation steric effect, plays a crucial role in the conformational equilibrium in the coordination sphere of the four-solvate metal ion. 相似文献
95.
Yasushi Yokoyama Prof. Dr. Tatsuya Shiozawa Yutaka Tani Dr. Takashi Ubukata Dr. 《Angewandte Chemie (International ed. in English)》2009,48(25):4521-4523
Into my arms : Photochemical cyclization of diarylethenes that have two chiral side arms showed up to 100 % de (see scheme). Introduction of these chiral side arms onto the carbon atoms where ring closure occurs is a general strategy for the highly diastereoselective cyclization of diarylethenes.
96.
An efficient method for the synthesis of 2,5-dihydroisoxazoles and isoxazoles using iodocyclization of N-alkoxycarbonyl O-propargylic hydroxylamines has been developed. 2,5-Dihydro-4-iodoisoxazole underwent the cross-coupling reactions without aromatization to afford polyfunctionalized 2,5-dihydroisoxazoles. This process was applied to the preparation of valdecoxib and its 2,5-dihydro-derivative. 相似文献
97.
N. Wada 《Journal of Radioanalytical and Nuclear Chemistry》1978,44(1):175-187
An improved method based on the moderation of intermediate neutrons for the measurement of hydrogen in small samples is described.
With the aid of boron and cadmium filters, a space shielded from slow neutrons is set up close to an isotopic neutron source
shrouded by water moderator. A BF3 proportional counter enclosed with a sample cell is placed in this space. The neutron count rate of the counter increases
when a hydrogen-containing material is introduced into the cell, due to the moderation of intermediate neutrons passing through
the filters. With a 1.3 μg252Cf neutron source, the lower limit of hydrogen detection for 200 ml samples in 10 min count time is 0.01 wt.%. This method
is suitable for measuring the H2O content of heavy water. 相似文献
98.
Brian N. DiMarco Dmitry E. Polyansky David C. Grills Ping Wang Yutaka Kuwahara Xuan Zhao Etsuko Fujita 《Chemphyschem》2021,22(14):1478-1487
In this work, the differences in catalytic performance for a series of Co hydrogen evolution catalysts with different pentadentate polypyridyl ligands (L), have been rationalized by examining elementary steps of the catalytic cycle using a combination of electrochemical and transient pulse radiolysis (PR) studies in aqueous solution. Solvolysis of the [CoII−Cl]+ species results in the formation of [CoII(κ4-L)(OH2)]2+. Further reduction produces [CoI(κ4-L)(OH2)]+, which undergoes a rate-limiting structural rearrangement to [CoI(κ5-L)]+ before being protonated to form [CoIII−H]2+. The rate of [CoIII−H]2+ formation is similar for all complexes in the series. Using E1/2 values of various Co species and pKa values of [CoIII−H]2+ estimated from PR experiments, we found that while the protonation of [CoIII−H]2+ is unfavorable, [CoII−H]+ reacts with protons to produce H2. The catalytic activity for H2 evolution tracks the hydricity of the [CoII−H]+ intermediate. 相似文献
99.
Kanamitsu N Osaki T Itsuji Y Yoshimura M Tsujimoto H Soga M 《Chemical & pharmaceutical bulletin》2007,55(12):1682-1688
We developed new intravenous sedative-hypnotic compounds with the isoindolin-1-one skeleton focusing on the water-soluble property and in vivo safety. We synthesized approximately 170 derivatives and evaluated their hypnotic effects by intravenous administration of the compounds to mice. A series of the 2-phenyl-3-[2-(4-methyl-1-piperazinyl)-2-oxoethyl]isoindolin-1-one analogs, 3(-), 5(-), 27(-), and 47(-) [JM-1232(-)], showed potent sedative-hypnotic activity with good water solubility and a wide safety margin. The hypnotic doses (HD50s) of these 4 compounds when administered to mice were 2.35, 1.90, 2.17, and 3.12 mg/kg, respectively, and the lethal doses (LD50s) were 88.67, 64.69, >120, and >120 mg/kg, respectively. The therapeutic indexes (LD50/HD50) were 37.73, 34.05, >55.30, and >38.46, respectively. Among these compound, 47(-) [JM-1232(-)] is being considered as the most potential candidate for clinical trials in humans. 相似文献
100.
The number of pigments in single light-harvesting complexes (chlorosomes) were calculated by imaging single chlorosomes in a frozen buffer at cryogenic temperature with a confocal laser fluorescence microscope and pigment extraction. Chlorosomes were isolated from two types of green photosynthetic bacteria Chlorobium (Chl.) tepidum and Chloroflexus (Cfl.) aurantiacus and were individually imaged in the frozen medium. Each fluorescence spot observed mainly came from a single chlorosome and was ascribable to self-aggregates of bacteriochlorophyll (BChl) c molecules as core parts of chlorosomes. A three-dimensional distribution of fluorescence of single chlorosomes was analyzed, and the number of chlorosomes in a volume of 54,000 microm(3) was counted directly. On the basis of the results, averaged numbers of the BChl c molecules contained in a single chlorosome of Chl. tepidum and Cfl. aurantiacus were determined to be 1.4 x 10(5) and 9.6 x 10(4), respectively. The present numbers are almost comparable to those estimated by other methods (Martinez-Planells et al., Photosynth. Res. 2002, 71, 83 and Monta?o et al., Biophys. J. 2003, 85, 2560). 相似文献