全文获取类型
收费全文 | 2097篇 |
免费 | 72篇 |
国内免费 | 6篇 |
专业分类
化学 | 1686篇 |
晶体学 | 29篇 |
力学 | 28篇 |
数学 | 98篇 |
物理学 | 334篇 |
出版年
2023年 | 16篇 |
2022年 | 20篇 |
2021年 | 31篇 |
2020年 | 23篇 |
2019年 | 32篇 |
2018年 | 25篇 |
2017年 | 18篇 |
2016年 | 41篇 |
2015年 | 40篇 |
2014年 | 47篇 |
2013年 | 98篇 |
2012年 | 92篇 |
2011年 | 119篇 |
2010年 | 64篇 |
2009年 | 71篇 |
2008年 | 145篇 |
2007年 | 140篇 |
2006年 | 128篇 |
2005年 | 162篇 |
2004年 | 115篇 |
2003年 | 80篇 |
2002年 | 84篇 |
2001年 | 46篇 |
2000年 | 38篇 |
1999年 | 21篇 |
1998年 | 32篇 |
1997年 | 26篇 |
1996年 | 33篇 |
1995年 | 16篇 |
1994年 | 22篇 |
1993年 | 16篇 |
1992年 | 20篇 |
1991年 | 14篇 |
1990年 | 13篇 |
1989年 | 17篇 |
1988年 | 12篇 |
1987年 | 12篇 |
1986年 | 19篇 |
1985年 | 23篇 |
1984年 | 24篇 |
1983年 | 11篇 |
1982年 | 23篇 |
1981年 | 15篇 |
1980年 | 24篇 |
1979年 | 13篇 |
1978年 | 14篇 |
1977年 | 11篇 |
1976年 | 13篇 |
1974年 | 11篇 |
1973年 | 10篇 |
排序方式: 共有2175条查询结果,搜索用时 15 毫秒
91.
The surface pressure-molecular area curve of the mixed monolayer of 16-(9-anthroyloxy) palmitic acid (16AP) and fatty acid (palmitic or stearic acids) showed various kink points which indicated the phase transitions of the monolayer. On the basis of the surface phase rule, the phase diagrams of the mixed monolayer were elucidated. The bifunctional molecule, 16AP, takes two orientations in a monolayer state, that is, horizontal and vertical ones. Horizontally oriented 16AP and vertically oriented fatty acid form a mixed monolayer but this exhibits deviation from the ideal mixing, which was interpreted in terms of the surface regular solution theory. On the other hand, the 16AP molecule in the vertical state was found to be immiscible with the fatty acid molecule in a monolayer de spite both molecules being vertical to the surface and parallel to each other. This was caused by the participation of the 9-anthroyloxy moiety of 16AP in the interaction of 16AP and fatty acid in the hydrophobic region of the monolayer. 相似文献
92.
Hideki Takayasu Misako Takayasu Astero Provata Greg Huber 《Journal of statistical physics》1991,65(3-4):725-745
We study a generalized aggregation process in which charged particles diffuse and coalesce randomly on a lattice. For one-dimensional and mean-field models, we show that there exists a statistically-invariant steady state when randomly charged particles are continuously injected. The steady-state charge distribution obeys a power law with the exponent depending both on the type of the injection and on the spatial dimension. The response of the system to a perturbation (i.e., relaxation) is characterized by either a power law decay (t
–
,1) or a compressed exponential decay [exp(–t
),>1]. 相似文献
93.
Production of hybrid 16-membered macrolides by expressing combinations of polyketide synthase genes in engineered Streptomyces fradiae hosts 总被引:1,自引:0,他引:1
Reeves CD Ward SL Revill WP Suzuki H Marcus M Petrakovsky OV Marquez S Fu H Dong SD Katz L 《Chemistry & biology》2004,11(10):1465-1472
Combinations of the five polyketide synthase (PKS) genes for biosynthesis of tylosin in Streptomyces fradiae (tylG), spiramycin in Streptomyces ambofaciens (srmG), or chalcomycin in Streptomyces bikiniensis (chmG) were expressed in engineered hosts derived from a tylosin-producing strain of S. fradiae. Surprisingly efficient synthesis of compounds predicted from the expressed hybrid PKS was obtained. The post-PKS tailoring enzymes of tylosin biosynthesis acted efficiently on the hybrid intermediates with the exception of TylH-catalyzed hydroxylation of the methyl group at C14, which was efficient if C4 bore a methyl group, but inefficient if a methoxyl was present. Moreover, for some compounds, oxidation of the C6 ethyl side chain to an unprecedented carboxylic acid was observed. By also expressing chmH, a homolog of tylH from the chalcomycin gene cluster, efficient hydroxylation of the 14-methyl group was restored. 相似文献
94.
The carbon-fluorine bond of a trifluoromethyl group attached to a π system can be activated by metallic magnesium in the system TMSCl-THF or DMF providing a variety of difluorinated compounds via a selective CF bond cleavage. Thus, trifluoromethyl ketones, α,β-unsaturated ketones, esters, imines, and aromatics can be transformed into the corresponding difluoroenol silyl ethers, enamines, and difluoro(trimethylsilyl)methyl aromatics in good to excellent yields, respectively. This protocol enabled us to synthesize β,β-difluoroamino acids, difluoroheterocycles, and functionalized difluoroacetates. 相似文献
95.
96.
A mononuclear five-coordinate molybdenum(IV) monosulfide complex, (Et4N)2[MoS(L)2] (L = cyclohexene-1,2-dithiolate) (1), was obtained and characterized by IR, UV-vis spectroscopic methods, and X-ray crystallography. 1 was oxidized by an equivalent ferrocenium cation to give the corresponding mononuclear molybdenum(V) complex, (Et4N)[MoS(L)2] (2), which was stable for a few minutes under a lower concentration than 0.3 mM and then further dimerized to (Et4N)2[Mo(L)2]2(mu-S)2 (3). 相似文献
97.
We have shown the Lennard-Jones (LJ) phase diagram for a slit-shaped nanopore by molecular simulations and thermodynamically
predicted the results with no adjustable parameter. With this success, LJ phase diagrams are predictable. In this study, the
freezing of an LJ CH4 capillary condensate under a tensile condition in a nonstructural carbon nanopore with a cylindrical geometry was examined
using molecular dynamics (MD) simulation. We employ a unit cell in contact with a bulk vapor phase, which is useful for the
determination of the bulk vapor pressure in equilibrium with the molecules in a pore. The MD simulation results show liquid-solid
(amorphous) phase transitions with a variation in the bulk vapor pressure. The frozen particles are arranged in concentric
circular regions along the wall similar to those reported by Maddox and Gubbins. The freezing points are determined from the
variations in density, enthalpy, arrangement, and structural functions. The obtained liquid-solid coexistence points are found
to exhibit a significant dependence of the freezing point on the equilibrium bulk vapor pressure, forming an extraordinarily
skewed curve on the p-T diagram, in contrast to the bulk phase coexistence that is represented by an almost vertical line.
The origin of the significant dependence is considered to be the Laplace effect on the capillary condensate similar to the
case with a slit-shaped pore. A simple model, which the authors earlier presented for slit-shaped nanopores, successfully
predicted the p-T relation of the freezing point for cylindrical nanopores as well. 相似文献
98.
Arsenic-speciation analysis in marine samples was performed by high-pressure liquid chromatography (HPLC) with ICP–MS detection.
Separation of eight arsenic species—AsIII, MMA, DMA, AsV, AB, TMAO, AC and TeMAs+—was achieved on a C18 column with isocratic elution (pH 3.0), under which conditions AsIII and MMA co-eluted. The entire separation was accomplished in 15 min. The HPLC–ICP–MS detection limits for the eight arsenic
species were in the range 0.03–0.23 μg L−1 based on 3σ for the blank response (n=5). The precision was calculated to be 2.4–8.0% (RSD) for the eight species. The method was successfully applied to several
marine samples, e.g. oysters, fish, shrimps, and marine algae. Low-power microwave digestion was employed for extraction of
arsenic from seafood products; ultrasonic extraction was employed for the extraction of arsenic from seaweeds. Separation
of arsenosugars was achieved on an anion-exchange column. Concentrations of arsenosugars 2, 3, and 4 in marine algae were
in the range 0.18–9.59 μg g−1.
This paper was presented at the European Winter Conference 2005 相似文献
99.
Ayumi Yoshida Hitoshi Yamauchi Hideki Sakai Norimichi Kawashima Masahiko Abe 《Colloids and surfaces. B, Biointerfaces》1997,8(6):191-342
Molecular interactions between lipid bilayers (liposomes) and chondroitin sulfate C (CS), a water soluble polymer, have been investigated in terms of zeta-potential, particle size, microscopic-viscosity, microscopic-polarity of liposomes and permeability of calcein. Microscopic morphology is dramatically changed by the addition of CS to the positively charged liposomes (Pos.L), while it is not changed by the addition to uncharged liposomes (Unc.L) or negatively charged liposomes (Neg.L). The absolute value of the particle size of Pos.L increases with the addition of CS, while the zeta- potential of Pos.L decreases. Permeability of Pos.L decreases with an increase in the concentration of CS. Phase transition temperature of Pos.L is changed after the addition of CS. These values, however, are not changed for the other liposomes by the addition of CS. The results of gel filtration chromatography show that CS is absorbed on the Pos.L surface. Microscopic viscosity is also increased by the addition of CS to Pos.L due to the adsorption of CS. 相似文献
100.
Ikeda Y Nakamura T Yorimitsu H Oshima K 《Journal of the American Chemical Society》2002,124(23):6514-6515
A cobalt complex, CoCl2[1,6-bis(diphenylphosphino)hexane], catalyzes an alkylation reaction of styrenes in the presence of Me3SiCH2MgCl in ether to yield beta-alkylstyrenes. A variety of alkyl halides including alkyl chlorides can be employed as an alkyl source. A radical mechanism is strongly suggested for this alkylation reaction. 相似文献