全文获取类型
收费全文 | 6211篇 |
免费 | 1081篇 |
国内免费 | 779篇 |
专业分类
化学 | 4231篇 |
晶体学 | 42篇 |
力学 | 454篇 |
综合类 | 33篇 |
数学 | 757篇 |
物理学 | 2554篇 |
出版年
2024年 | 14篇 |
2023年 | 134篇 |
2022年 | 197篇 |
2021年 | 189篇 |
2020年 | 221篇 |
2019年 | 248篇 |
2018年 | 184篇 |
2017年 | 188篇 |
2016年 | 276篇 |
2015年 | 306篇 |
2014年 | 304篇 |
2013年 | 367篇 |
2012年 | 545篇 |
2011年 | 595篇 |
2010年 | 399篇 |
2009年 | 319篇 |
2008年 | 421篇 |
2007年 | 376篇 |
2006年 | 358篇 |
2005年 | 333篇 |
2004年 | 281篇 |
2003年 | 196篇 |
2002年 | 175篇 |
2001年 | 146篇 |
2000年 | 111篇 |
1999年 | 149篇 |
1998年 | 106篇 |
1997年 | 118篇 |
1996年 | 126篇 |
1995年 | 116篇 |
1994年 | 82篇 |
1993年 | 67篇 |
1992年 | 58篇 |
1991年 | 65篇 |
1990年 | 67篇 |
1989年 | 53篇 |
1988年 | 41篇 |
1987年 | 27篇 |
1986年 | 34篇 |
1985年 | 27篇 |
1984年 | 14篇 |
1983年 | 9篇 |
1982年 | 11篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1979年 | 2篇 |
1976年 | 2篇 |
1974年 | 1篇 |
1957年 | 3篇 |
排序方式: 共有8071条查询结果,搜索用时 15 毫秒
101.
Dai H Choe WS Thai CK Sarikaya M Traxler BA Baneyx F Schwartz DT 《Journal of the American Chemical Society》2005,127(44):15637-15643
We show that a protein with no intrinsic inorganic synthesis activity can be endowed with the ability to control the formation of inorganic nanostructures under thermodynamically unfavorable (nonequilibrium) conditions, reproducing a key feature of biological hard-tissue growth and assembly. The nonequilibrium synthesis of Cu(2)O nanoparticles is accomplished using an engineered derivative of the DNA-binding protein TraI in a room-temperature precursor electrolyte. The functional TraI derivative (TraIi1753::CN225) is engineered to possess a cysteine-constrained 12-residue Cu(2)O binding sequence, designated CN225, that is inserted into a permissive site in TraI. When TraIi1753::CN225 is included in the precursor electrolyte, stable Cu(2)O nanoparticles form, even though the concentrations of [Cu(+)] and [OH(-)] are at 5% of the solubility product (K(sp,Cu2O)). Negative control experiments verify that Cu(2)O formation is controlled by inclusion of the CN225 binding sequence. Transmission electron microscopy and electron diffraction reveal a core-shell structure for the nonequilibrium nanoparticles: a 2 nm Cu(2)O core is surrounded by an adsorbed protein shell. Quantitative protein adsorption studies show that the unexpected stability of Cu(2)O is imparted by the nanomolar surface binding affinity of TraIi1753::CN225 for Cu(2)O (K(d) = 1.2 x 10(-)(8) M), which provides favorable interfacial energetics (-45 kJ/mol) for the core-shell configuration. The protein shell retains the DNA-binding traits of TraI, as evidenced by the spontaneous organization of nanoparticles onto circular double-stranded DNA. 相似文献
102.
利用FT-IR,测定了四种异构丁醇十四氯化碳、+正庚烷, +苯和1,2-二氯乙烷稀溶液在3800—3000 cm~(-1)内的红外吸收光谱。缔合峰与自由羟基峰的面积之比与溶质、溶剂的性质有关, 且在极稀溶液区与溶质的质量百分比浓度之间有良好的直线关系。本文又运用1-n(环状)模型对有关体系进行了对比研究。结果表明, 丁醇分子支链度的增加以及丁醇分子与苯和1,2-二氯乙烷之间的特殊相互作用, 降低了醇分子的缔合能力。稀溶液中, 丁醇分子在苯和1,2-二氯乙烷中主要以单体和环状二聚体形式存在, 在四氯化碳中以单体和环状三聚体形式存在, 而正丁醇分子在正庚烷中主要为单体和环状四聚体, 异、仲、特丁醇主要为环状三聚体和单体。 相似文献
103.
104.
105.
由4',5'-二碘苯并15冠5,4',5'-二溴苯并15冠5,4'-溴-5'-硝基苯并15冠5,四溴二苯并18冠6与过渡全属Mn(Ⅱ)、Co(Ⅱ)、Cu(Ⅱ)、Zn(Ⅱ)、Ag(Ⅱ)、Cd(Ⅱ)的硝酸盐、高氯酸盐、气化物合成了19个未见报道的固态配合物。用元素分析、红外光谱、摩尔电导和差热-热重分析等表征了它们的组成和性质。 相似文献
106.
The benzamide-derived P,O-ligands efficiently promoted the Pd-catalyzed Suzuki cross-coupling reactions of aryl bromides with phenylboronic acid at 0.01 mol % of Pd loading at 60-80 °C to form biaryls in excellent yields. A sterically hindered arylboronic acid gave a quantitative yield of the coupling product at 110 °C with 1 mol % Pd. 相似文献
107.
Thermodynamically stable vesicle formation from glycolipid biosurfactant sponge phase 总被引:3,自引:0,他引:3
Imura T Yanagishita H Ohira J Sakai H Abe M Kitamoto D 《Colloids and surfaces. B, Biointerfaces》2005,43(2):115-121
Thermodynamically stable vesicle (L(alpha1)) formation from glycolipid biosurfactant sponge phase (L(3)) and its mechanism were investigated using a "natural" biocompatible mannosyl-erythritol lipid-A (MEL-A)/L-alpha-dilauroylphosphatidylcholine (DLPC) mixture by varying the composition. The trapping efficiency for calcein and turbidity measurements clearly indicated the existence of three regions: while the trapping efficiencies of the mixed MEL-A/DLPC assemblies at the compositions with X(DLPC)< or =0.1 or X(DLPC)> or =0.8 were almost zero, the mixed assemblies at the compositions with 0.1 or =0.8 were multilamellar vesicles (L(alpha)) with diameter from 2 to 10 microm. Meanwhile, dynamic light scattering (DLS) measurement revealed that the average size of the vesicles at the composition of X(DLPC)=0.3 was 633.2 nm, which is remarkably small compared to other compositions. Moreover, the mixed vesicle solution at the composition of X(DLPC)=0.3 was slightly bluish and turbid and kept its dispersion stability at 25 degrees C for more than 3 months, indicating the formation of a thermodynamically stable vesicle (L(alpha1)). These results exhibited the formation of a thermodynamically stable vesicle (L(alpha1)) with a high dispersibility from the MEL-A/DLPC mixture. The asymmetric distribution of MEL-A and DLPC in the two vesicle monolayers caused by the difference in geometrical structures is very likely to have changed their self-assembled structure from a sponge phase (L(3)) to a thermodynamically stable vesicle (L(alpha1)). 相似文献
108.
109.
K3 [Fe(CN)6] and KFe[Fe(CN)6] are classical coordination compounds. However, the mechanism of decomposition reactions has not been well expounded. The gas products of thermal decomposition were examined by gas chroma tography (GC) , and the structure of the solid products by Mossbauer spectroscopy(MS) and X-ray diffraction(XRD). The findings are explained in terms of the theory of coordination chemistry and a decomposition mechanism is proposed in this study. On the basis of various experimental results, the first stage of the decomposition of K3[Fe(CN)6] in He was found to be the evolution of(CN)2 resulting in the reduction of Fe(Ⅲ)12K3 [Fe(CN)6]→9K4[Fe(CN)6] + Fe2 [Fe(CN)6] + 6 ( CN )For KFe [Fe(CN) 6 ], the first stage of decomposition man be represented as6KFe[Fe(CN)6]→3K2Fe[Fe(CN)6] + 2Fe2[Fe(CN)6 + 3(CN)2At higher temperatures, the decomposition of both K3[Fe(CN)6) andKFe[Fe(CN)6] to form KCN and Fe2C was accomplished by the release of(CN)2 and N2. 相似文献
110.
Density functional theory (DFT) and Monte Carlo (MC) simulation with free energy perturbation (FEP) techniques have been used to study the tautomeric proton transfer reaction of 2-amino-2-oxazoline, 2-amino-2-thiazoline, and 2-amino-2-imidazoline in the gas phase and in water. Two reaction pathways were considered: the direct and water-assisted transfers. The optimized structures and thermodynamic properties of stationary points for the title reaction system in the gas phase were calculated at the B3LYP/6-311+G(d, p) level of theory. The potential energy profiles along the minimum energy path in the gas phase and in water were obtained. The study of the solvent effect of water on the proton transfer of 2-amino-2-oxozoline, 2-amino-2-thiazoline, and 2-amino-2-imidazoline indicates that water as a solvent is favorable for the water-assisted process and slows down the rate of the direct transfer pathway. 相似文献