全文获取类型
收费全文 | 2609篇 |
免费 | 363篇 |
国内免费 | 213篇 |
专业分类
化学 | 2277篇 |
晶体学 | 26篇 |
力学 | 109篇 |
综合类 | 32篇 |
数学 | 51篇 |
物理学 | 690篇 |
出版年
2024年 | 8篇 |
2023年 | 75篇 |
2022年 | 218篇 |
2021年 | 236篇 |
2020年 | 153篇 |
2019年 | 103篇 |
2018年 | 94篇 |
2017年 | 103篇 |
2016年 | 122篇 |
2015年 | 98篇 |
2014年 | 112篇 |
2013年 | 181篇 |
2012年 | 136篇 |
2011年 | 90篇 |
2010年 | 84篇 |
2009年 | 106篇 |
2008年 | 90篇 |
2007年 | 115篇 |
2006年 | 106篇 |
2005年 | 76篇 |
2004年 | 81篇 |
2003年 | 67篇 |
2002年 | 87篇 |
2001年 | 56篇 |
2000年 | 58篇 |
1999年 | 62篇 |
1998年 | 47篇 |
1997年 | 43篇 |
1996年 | 34篇 |
1995年 | 30篇 |
1994年 | 26篇 |
1993年 | 26篇 |
1992年 | 27篇 |
1991年 | 23篇 |
1990年 | 20篇 |
1989年 | 24篇 |
1988年 | 20篇 |
1987年 | 14篇 |
1986年 | 11篇 |
1985年 | 7篇 |
1984年 | 14篇 |
1983年 | 7篇 |
1981年 | 13篇 |
1980年 | 10篇 |
1979年 | 15篇 |
1978年 | 13篇 |
1977年 | 10篇 |
1976年 | 8篇 |
1973年 | 5篇 |
1972年 | 5篇 |
排序方式: 共有3185条查询结果,搜索用时 193 毫秒
131.
Álvaro Santana-Mayor Ruth Rodríguez-Ramos Bárbara Socas-Rodríguez Miguel Ángel Rodríguez-Delgado Giovanni D'Orazio 《Electrophoresis》2020,41(20):1768-1775
The separation of 11 phthalic acid ester (PAEs) was carried out by nano-liquid chromatography coupled to ultraviolet and MS detection. Preliminary experiments were achieved in order to select suitable stationary phases and chromatographic conditions. The baseline separation was obtained, for all compounds, with an XBridgeTM C18 column in less than 15 min, working in step gradient mode. The sensitivity of the method was improved by on-column focusing. PAEs were extracted from alcoholic and nonalcoholic beverages using vortex-assisted emulsification dispersive liquid–liquid microextration and natural deep eutectic solvents. The whole method was validated in terms of linearity, sensitivity, precision, recovery, and repeatability. Combination of both off-line sample preparation preconcentration and large injection volume led to obtain LOQs in the range 5–47 ng/mL. The developed nano-LC-UV method was extended to MS detection to confirm the presence of PAEs in some beverages commercialized in different types of packaging. 相似文献
132.
Katarina Leko Marko Hanževački Dr. Zlatko Brkljača Dr. Katarina Pičuljan Dr. Rosana Ribić Dr. Josip Požar 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(23):5208-5219
The effects of solvent and temperature on the complexation of adamantyl mannoside with β-cyclodextrin and 6-O-monotosyl-6-deoxy-β-cyclodextrin were explored experimentally and by means of molecular dynamics simulations. Efficient binding was observed only in hydrogen-bonded solvents, which indicated solvophobically driven complexation. The stability of the inclusion complex was considerably higher in aqueous media. A pronounced temperature dependence of ΔrH○ and ΔrS○, resulting in perfect enthalpy–entropy compensation, was observed in water. The complexation thermodynamics was in line with classical rationale for the hydrophobic effect at lower temperatures and the nonclassical explanation at higher temperatures. This finding linked cyclodextrin complexation thermodynamics with insights regarding the effect of temperature on the hydration water structure. The complexation enthalpies and entropies were weakly dependent on temperature in organic media. The signs of ΔrH○ and ΔrS○ were in accordance with the nonclassical hydrophobic (solvophobic) effect. The structures of the optimized product corresponded to those deduced spectroscopically, and the calculated and experimentally obtained values of ΔrG○ were in very good agreement. This investigation clearly demonstrated that solvophobically driven formation of cyclodextrin complexes could be anticipated in structured solvents in general. However, unlike in water, adamantane and the host cavity behaved solely as structure breakers in the organic media explored so far. 相似文献
133.
134.
135.
We study the linear and nonlinear properties of two-dimensional matter-wave pulses in disk-shaped superfluid Fermi gases.A Kadomtsev-Petviashvili I(KPI) solitary wave has been realized for superfluid Fermi gases in the limited cases of Bardeen-Cooper-Schrieffer(BCS) regime,Bose-Einstein condensate(BEC) regime,and unitarity regime.Onelump solution as well as one-line soliton solutions for the KPI equation are obtained,and two-line soliton solutions with the same amplitude are also studied in the limited cases.The dependence of the lump propagating velocity and the sound speed of two-dimensional superfluid Fermi gases on the interaction parameter are investigated for the limited cases of BEC and unitarity. 相似文献
136.
Md. Abdur Razzaque Sarker Satoshi WatauchiMasanori Nagao Takashi WatanabeIsamu Shindo Isao Tanaka 《Physica C: Superconductivity and its Applications》2012,472(1):87-91
Large single crystals of La2−xSrxCuO4 (LSCO) high-Tc superconductors were grown by the infrared heating floating zone (IR-FZ) method using a tilting-mirror-type image furnace. The maximum diameter of the LSCO crystals increased to 10 mm in the tilting-mirror-type image furnace from 6 mm in the conventional image furnace. CuO rich feeds were required for the crystal growth using the tilting-mirror-type image furnace to compensate for the lack of CuO caused by the significant evaporation of CuO during the growth. The evaporation of CuO was affected by the tilting angle of the mirrors of the image furnace and by feed diameter. The optimized growth conditions were as follows: mirror tilting angle, 20°; feed diameter, 10 mm∅; and feed composition 50.7 mol% CuO. 相似文献
137.
A novel set of light-responsive polyelectrolytes has been developed and studied, to control and tune surface wettability by introducing various types of substituted R head-groups of azo polyelectrolytes in self-assembled multilayer (SAMU) films. As part of a larger project to develop polymer surfaces where one can exert precise control over properties important to proteins and cells in contact, photo-reversibly, we describe here how one can tune quite reliably the contact angle of a biocompatible SAMU, containing a photo-reversible azo chromophore for eventual directed cell growth. The azo polyelectrolytes described here have different substituted R head-group pairs of shorter-ionized hydrophilic COOH and SO3H, shorter non-ionized hydrophobic H and OC2H5, and larger non-ionized hydrophobic octyl C8H17 and C8F17, and were employed as polyanions to fabricate the SAMU onto silicon substrates by using the counter-charge polycation PDAC. The prepared SAMU films were primarily characterized by measurement of their contact angles with water. The surface wetting properties of the thin films were found to be dependent on the type of substituted R-groups of the azo polyelectrolytes through their degree of ionization, size, hydrophobicity/hydrophilicity, solubility, conformation, and inter-polymeric association and intra-polymeric aggregation. All these factors appeared to be inter-related, and influenced variations in hydrophobic/hydrophilic character to different extents of aggregates/non-aggregates in solution because of solvation effects of the azo polyanions, and were thus manifested when adsorbed as thin films via the SAMU deposition process. For example, one interesting observation is significantly higher contact angles of 79° for SAMU films of larger octyl R groups of PAPEA-C8F17 and PAPEA-C8H17 than for others with contact angles of 64° observed for non-polar R-groups of OC2H5 and H. Furthermore, lower contact angle values of 59° for SAMU films with polar R-groups of COOH and SO3H relative to that of non-polar R-groups are in accordance with their expected order of the hydrophilicity or hydrophobicity. It is possible that the large octyl groups are more effective in shielding the ionic functional groups on the substrate surface, and contributed less to the water drop-molecule interactions with ionic groups of the PDAC and/or AA groups. In addition, higher hydrophobicity of the SAMU films may be due to the incorporation of bulky and hydrophobic groups in these polyelectrolytes, which can produce aggregates on the surfaces of the SAMU films. Through understanding and controlling the complex aggregation behavior of the different substituted R-groups of these azo polyelectrolytes, and hence their adsorption on substrates, it appears possible to finely tune the surface energy of these biocompatible films over a wide range, enhance the photo-switching capabilities of the SAMU films, and tailor other surface properties for the development and application of new devices in diverse areas of microfluidics, specialty coatings, sensors, and biomedical sciences. 相似文献
138.
《应用有机金属化学》2017,31(11)
A novel hybrid magnetic nanocatalyst was synthesized by covalent coating of Fe3O4 magnetic nanoparticles with choline chloride–urea deep eutectic solvent using 3‐iodopropyltrimethoxysilane as a linker. The structure of this new catalyst was fully characterized via elemental analysis, transmission and scanning electron microscopies, X‐ray diffraction and Fourier transform infrared spectroscopy. It was employed in the synthesis of various 2‐amino‐4H ‐pyran derivatives in water solution via an easy and green procedure. The desired products were obtained in high yields via a three‐component reaction between aromatic aldehyde, enolizable carbonyl and malononitrile at room temperature. The employed nanocatalyst was easily recovered using a magnetic field and reused four times (in subsequent runs) with less than 8% decrease in its catalytic activity. 相似文献
139.
Konstantin V. Pochivalov Yaroslav V. Kudryavtsev Andrey V. Basko Tatyana N. Lebedeva Roman Y. Golovanov 《Journal of Macromolecular Science: Physics》2015,54(12):1427-1437
The full phase diagrams of low-density polyethylene (LDPE), high-density polyethylene (HDPE), and isotactic polypropylene (i-PP) mixtures with 1,2,4,5-tetrachlorobenzene (TeCB), including the solubility curve of TeCB in a solid polymer, were constructed by an optical method. The diagrams contain a eutectic point that corresponds to the situation when the crystallization of TeCB out of its solution in a polyolefin is accompanied by the crystallization of monomer units of the macromolecules. As a result, the polymer acquires a gel structure with crystallites as crosslinks and amorphous regions saturated with TeCB. It is demonstrated that the eutectic point position on the phase diagram can be used for ranking polymers with respect to their thermodynamic affinity to a solvent. For the studied systems, the affinity to TeCB was decreased in the order i-PP, HDPE, and LDPE. Direct experimental evidence was obtained that TeCB crystals can be dissolved in a solid polymer via a vapor phase mechanism, which leads to the polymer amorphization. 相似文献
140.
Mehrdad Mahkam Mohammad Galeh Assadi 《Phosphorus, sulfur, and silicon and the related elements》2013,188(4):842-847
A series of acrylic copolymers containing silyl pendant groups was prepared by free radical cross-linking copolymerization. Me3Si, Et3Si, and Ph3Si together with cubane-1,4-dicarboxylic acid (CDA) were covalently linked with 2-hydroxyethyl methacrylate (HEMA). CDA linked to two HEMA group is the cross-linking agent (CA). Free radical cross-linking copolymerization of the methacrylic acid (MAA) and organosilyl monomers with two different molar ratios of CA was carried out at 60–70°C. The compositions of the cross-linked three-dimensional polymers were determined by FT-IR spectroscopy. The glass transition temperature of the network polymers was determined calorimetrically. Equilibrium swelling studies were carried out in enzyme-free simulated gastric and intestinal fluids (SGF and SIF, respectively). A model hydrophobic drug, the steroid hormone estradiol, was entrapped in these gels, and the in vitro release profiles were established separately in both SGF (pH 1) and SIF (pH 7.4). Incorporation of silyl groups in a new macromolecule system modified network polymers for drug delivery. Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file. 相似文献