全文获取类型
收费全文 | 6949篇 |
免费 | 1017篇 |
国内免费 | 606篇 |
专业分类
化学 | 5006篇 |
晶体学 | 36篇 |
力学 | 371篇 |
综合类 | 32篇 |
数学 | 823篇 |
物理学 | 2304篇 |
出版年
2024年 | 15篇 |
2023年 | 171篇 |
2022年 | 188篇 |
2021年 | 284篇 |
2020年 | 318篇 |
2019年 | 260篇 |
2018年 | 226篇 |
2017年 | 188篇 |
2016年 | 305篇 |
2015年 | 285篇 |
2014年 | 376篇 |
2013年 | 464篇 |
2012年 | 613篇 |
2011年 | 635篇 |
2010年 | 426篇 |
2009年 | 359篇 |
2008年 | 429篇 |
2007年 | 379篇 |
2006年 | 355篇 |
2005年 | 272篇 |
2004年 | 204篇 |
2003年 | 158篇 |
2002年 | 132篇 |
2001年 | 132篇 |
2000年 | 126篇 |
1999年 | 137篇 |
1998年 | 115篇 |
1997年 | 99篇 |
1996年 | 127篇 |
1995年 | 106篇 |
1994年 | 73篇 |
1993年 | 67篇 |
1992年 | 73篇 |
1991年 | 58篇 |
1990年 | 79篇 |
1989年 | 56篇 |
1988年 | 35篇 |
1987年 | 30篇 |
1986年 | 24篇 |
1985年 | 18篇 |
1984年 | 16篇 |
1983年 | 16篇 |
1982年 | 15篇 |
1981年 | 10篇 |
1979年 | 20篇 |
1978年 | 15篇 |
1977年 | 14篇 |
1976年 | 10篇 |
1975年 | 13篇 |
1973年 | 13篇 |
排序方式: 共有8572条查询结果,搜索用时 296 毫秒
91.
Drummy LF Koerner H Farmer K Tan A Farmer BL Vaia RA 《The journal of physical chemistry. B》2005,109(38):17868-17878
With the use of high-resolution transmission electron microscopy the structure and morphology of montmorillonite (MMT), a material of current interest for use in polymer nanocomposites, was characterized. Using both imaging theory and experiment, the procedures needed to generate lattice images from MMT were established. These procedures involve careful control of the microscope's objective lens defocus to maximize contrast from features of a certain size, as well as limiting the total dose of electrons received by the sample. Direct images of the MMT lattice were obtained from neat Na+ MMT, organically modified MMT, and organically modified MMT/epoxy nanocomposites. The degree of crystallinity and turbostratic disorder were characterized using electron diffraction and high-resolution electron microscopy (HREM). Also, the extent of the MMT sheets to bend when processed into an epoxy matrix was directly visualized. A minimum radius of curvature tolerable for a single MMT sheet during bending deformation was estimated to be 15 nm, and from this value a critical failure strain of 0.033 was calculated. HREM can be used to improve the understanding of the structure of polymer nanocomposites at the nanometer-length scale. 相似文献
92.
James Elver Johnson Joanne A. Maia Karen Tan Abdolkarim Ghafouripour Patrice De Meester Shirley S. C. Chu 《Journal of heterocyclic chemistry》1986,23(6):1861-1868
O-Methyl-α-ketophenylacetohydroximoyl chloride ( 1 ) was prepared by the reaction of O-methyl-α-methoxyphenylacetohydroximoyl chloride ( 5 ) with N-bromosuccinimide and concentrated hydrobromic acid. Reaction of 1 with ethylenediamine gave 3-phenyl-5,6-dihydro-2(1H)-pyrazinone-O-methyloxime ( 6 ). 3-Phenyl-5,6-cyclohexano-5,6-dihydro-2(1H)-pyrazininone-O-methyloxime ( 7 ) was prepared by reaction of 1 with trans-1,2-diaminocyclohexane. The X-ray structure of 6 has been determined. The crystals are orthorhombic, space group Pbca with a = 10.264(3), b = 18.262(4), c = 23.530(4)Å, V = 4411(2)Å3, and Z = 16. The structure, which was refined to R = 0.038 using 1652 observed reflections, shows the amidoxime moiety to be the Z configuration. Reaction of benzohydroximoyl chloride with aziridine gave (Z)-aziridinylbenzaldoxime ( 16a ). Ultraviolet irradiation of a benzene solution of 16a gave a mixture of the Z and E isomers 16a and 16b . The E isomer 16b underwent thermal isomerization to 16a at 100°. Reaction of 16a with dimethyl sulfate in sodium hydroxide solution gave (Z)-O-methylaziridinylbenzaldoxime ( 17a ). Photoisomerization of a hexane solution of 17a gave a mixture of the Z and E isomers 17a and 17b which were separated by preparative glc. The isomers 17a and 17b are resistant to thermal Z = E isomerization. The mechanisms of thermal isomerization of benzamidoximes are discussed. 相似文献
93.
[reaction: see text] A protocol for the copper(II)-catalyzed etherification of aliphatic alcohols under mild and essentially neutral conditions is described. Air- and moisture-stable potassium alkenyl- and aryltrifluoroborate salts undergo cross-coupling with a variety of aliphatic primary and secondary alcohols and phenols, and are tolerant of a range of functional groups. The optimized conditions utilize catalytic copper(II) acetate with 4-(dimethylamino)pyridine as ligand in the presence of 4 A molecular sieves under an atmosphere of oxygen. 相似文献
94.
95.
Sm(NO_3)_3·6H_2O热分解过程的研究工作虽有文献报道,但结果不尽相同。文献[2]不同于文献[1,3],认为分解过程中存在无水盐阶段;文献[3]不同于文献[1,2],认为分解过程中存在低水合物。而且文献尚缺低水合物热分解机理的报道。我们也曾做过一些工作,但脱水阶段也不详尽。为此,我们详细地研究了Sm(NO_3)_3·nH_2O(n= 相似文献
96.
富镉Hg_(1-x)Cd_xTe是一种新型的光电转换材料,已用于固体结太阳能光伏电池:ITO/CdS/Hg_(1-)Cd_xTe/Au。我们曾对Hg_(1-x)Cd_xTe的电沉积机理作过研究。最近我们用电沉积制备的Hg_(0.09)Cd_(0.91)Te多晶薄膜做成了液体结太阳能光电化学电池并观察到明显光电响应。 相似文献
97.
98.
This review aims to provide a summary of the progress in organic small molecular fluorescent dyes for photodynamic therapy in recent years and it is classified according to the structures of dyes including cyanines, phthalocyanine, BODIPYs and other agents. 相似文献
99.
Novel carboxylated oligothiophenes as sensitizers in photoelectric conversion systems 总被引:1,自引:0,他引:1
Tan S Zhai J Fang H Jiu T Ge J Li Y Jiang L Zhu D 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(21):6272-6276
Novel carboxylated oligothiophenes with different thiophene units were designed and synthesized as photosensitizers in dye-sensitized solar cells (DSSCs) for efficient opto-electric materials. The introduction of -COOH into thiophene molecules can lead to a red shift of UV-visible absorption, increase light-harvesting efficiency, and enhance photoinduced charge transport by forming efficient covalent bonds to the substrate surface. A red shift of the absorption spectrum of oligothiophene is also achieved by the increase in the number of thiophene units. The DSSCs based on the oligomers have excellent photovoltaic performances. Under 100 mW cm(-2) irradiation a short-circuit current of 10.57 mA cm(-2) and an overall energy conversion efficiency of 3.36 % is achieved when pentathiophene dicarboxylated acid was used as a sensitizer. The incident photo-to-current conversion efficiency (IPCE) has a maximum as high as 80 %. In addition, photovoltage and photocurrent transients show that slow charge recombination in DSSCs is important for efficient charge separation and excellent photoelectric conversion properties of the oligomers. These initial and promising results suggest that carboxylated oligothiophenes are efficient photosensitizers. 相似文献
100.
Boron-doped diamond (BDD) electrodes were used to investigate the possibility of detecting aniline by linear-sweep cathodic stripping voltammetry. It was found that the dimeric species (p-aminodiphenylamine and benzidine) formed by anodic oxidation of aniline during the accumulation period are involved in electrochemically reversible redox processes and, in acidic media, the shape of the stripping voltammetric response is suitable for aniline detection in the micromolar concentration range. The low background current of conductive diamond is an advantage compared to other electrode materials and allows a detection limit of 1 μM. Weak adsorption properties and the extreme electrochemical stability are additional advantages of BDD and it was found that, even after long-time measurements, the electrode surface can regain its initial activity by an anodic polarization in the potential region of water decomposition. 相似文献