全文获取类型
收费全文 | 2884篇 |
免费 | 111篇 |
国内免费 | 8篇 |
专业分类
化学 | 2366篇 |
晶体学 | 25篇 |
力学 | 21篇 |
数学 | 171篇 |
物理学 | 420篇 |
出版年
2023年 | 26篇 |
2022年 | 25篇 |
2021年 | 39篇 |
2020年 | 68篇 |
2019年 | 56篇 |
2018年 | 20篇 |
2017年 | 15篇 |
2016年 | 65篇 |
2015年 | 64篇 |
2014年 | 80篇 |
2013年 | 143篇 |
2012年 | 179篇 |
2011年 | 197篇 |
2010年 | 107篇 |
2009年 | 92篇 |
2008年 | 207篇 |
2007年 | 194篇 |
2006年 | 195篇 |
2005年 | 190篇 |
2004年 | 184篇 |
2003年 | 139篇 |
2002年 | 142篇 |
2001年 | 42篇 |
2000年 | 44篇 |
1999年 | 47篇 |
1998年 | 37篇 |
1997年 | 41篇 |
1996年 | 24篇 |
1995年 | 23篇 |
1994年 | 19篇 |
1993年 | 17篇 |
1992年 | 17篇 |
1991年 | 14篇 |
1989年 | 17篇 |
1988年 | 12篇 |
1987年 | 11篇 |
1985年 | 27篇 |
1984年 | 23篇 |
1983年 | 14篇 |
1982年 | 21篇 |
1981年 | 22篇 |
1980年 | 17篇 |
1979年 | 13篇 |
1978年 | 7篇 |
1977年 | 13篇 |
1976年 | 10篇 |
1975年 | 6篇 |
1974年 | 6篇 |
1973年 | 7篇 |
1972年 | 6篇 |
排序方式: 共有3003条查询结果,搜索用时 15 毫秒
991.
Zameer Shervani Yutaka Ikushima Masahiro Sato Hajime Kawanami Yukiya Hakuta Toshirou Yokoyama Takako Nagase Hironobu Kuneida Kenji Aramaki 《Colloid and polymer science》2008,286(4):403-410
We have employed a number of reducing and capping agents to obtain Ag(0) metallic nanoparticles of various sizes and morphologies.
The size and morphology were tuned by selecting reducing and capping agents. Spherical particles of 15 and 43 nm diameter
were obtained when 1 wt% aqueous starch solution of AgNO3 precursor salt was reduced by d(+)-glucose and NaOH, respectively, on heating at 70 °C for 30 min. Smaller size particles obtained in the case of d(+)-glucose reduction has been attributed to the slow reduction rate by mild reducing agent d(+)-glucose compared to strong NaOH. Conducting the reduction at ambient temperature of silver salt in liquid crystalline
pluronic P123 and L64 also gave spherical particles of 8 and 24 nm, respectively, without the addition of any separate reducing
agent. NaOH reduction of salt in ethylene glycol (11 g)/polyvinyl pyrolidone (PVP; 0.053 g) mixture produced large self-assembled
cubes of 520 nm when smaller (26–53 nm) star-shaped sharp-edged structures formed initially aggregated on heating the preparation
at 190 °C for 1 h. Increasing the amount of PVP (0.5 g) in ethylene glycol (11 g) and heating at 70 °C for 30 min yielded
a mixture of spherical and non-spherical (cubes, hexagons, pentagons, and triangle) particles without the addition of an extra
reducing agent. Addition of 5 wt% PVP to 1 wt% aqueous starched solution resulted in the formation of a mixture of spherical
and anisotropic structures when solution heated at 70 °C for 1 h. Homogeneous smaller sized (29 nm) cubes were synthesized
by NaOH reduction of AgNO3 in 12.5 wt% of water-soluble polymer poly(methyl vinyl ether) at ambient temperature in 30 min reaction time. 相似文献
992.
Hiroyuki Morita Shintaro Tashiro Masahiro Takeda Nobuhiko Yamada Md. Chanmiya Sheikh Hiroyuki Kawaguchi 《Tetrahedron》2008,64(19):4496-4505
We have examined the reactivities of α-phosphorylmethyl benzothiazolyl sulfoxides in the thermolyses and in the presence of several amines, such as aniline, benzylamine, piperidine, morpholine, and pyrrolidine. Thermolyses of the derivatives in the presence of 2,3-dimethyl-1,3-butadiene afforded 2-phosphoryl substituted 4,5-dimethyl-3,6-dihydro-2H-thiopyran S-oxide. In the reaction with amines, the complex product mixture, which contains α-phosphorylmethyl benzothiazolyl sulfides (2 and 5), α-phosphorylmethyl disulfides (15 and 16), and 2-amino substituted benzothiazole 14 was found to be formed besides the target phosphinecarbothioamides. Several mechanistic studies were performed to elucidate the formation mechanism, particularly for deoxygenated products from the starting sulfoxides, i.e., 2 and 5 from 3 and 6, respectively. 相似文献
993.
994.
995.
A one-pot tandem isomerization/carbon-carbon bond forming sequence catalyzed by a ruthenium complex/Br?nsted acid binary system is demonstrated. The method enables the use of readily available allylamides to deliver reactive imines under relay catalysis using a binary catalytic system. Subsequent Br?nsted acid catalyzed carbon-carbon bond forming reactions of the generated imines with nucleophilic components afforded Friedel-Crafts and Mannich products in good yields. 相似文献
996.
Tanaka K Fujii Y Atarashi H Akabori K Hino M Nagamura T 《Langmuir : the ACS journal of surfaces and colloids》2008,24(1):296-301
Density profiles of a perdeuterated poly(methyl methacrylate) (dPMMA) film spin-coated on a substrate in water, hexane, and methanol, which are "nonsolvents" for dPMMA, were examined along the direction normal to the interface by specular neutron reflectivity (NR). The interfaces of dPMMA with the liquids were diffuse in comparison with the pristine interface with air; the interfacial width with water was thicker than that with hexane. Interestingly, in water, the dPMMA film was composed of a swollen layer and the interior region, which also contained water, in addition to the diffused layer. The interface of dPMMA with hexane was sharper than that with water. Although there were slight indications of a swollen layer for the dPMMA in hexane, the solvent molecules did not penetrate significantly into the film. On the other hand, in methanol, the whole region of the dPMMA film was strikingly swollen. To conserve mass, the swelling of the film by the nonsolvents is accompanied by an increase in the film thickness. The change in the film thickness estimated by NR was in excellent accord with the results of direct observations using atomic force microscopy (AFM). The modulus of dPMMA in the vicinity of the interfaces with liquids was also examined on the basis of force-distance curves measured by AFM. The modulus decreased closer to the outermost region of the film. The extent to which the modulus decreased in the interfacial region was consistent with the amount of liquid sorbed into the film. 相似文献
997.
Higuchi M Nagata K Abiko S Tanaka M Kinoshita T 《Langmuir : the ACS journal of surfaces and colloids》2008,24(23):13359-13363
Gold nanoparticles having sequential alternating amphiphilic peptide chains, Phe-(Leu-Glu)8, on the surface have been prepared. We describe structural control of the amphiphilic peptide coated gold nanoparticle assembly by a conformational transition of the surface peptides. Under the acidic condition, the conformation of the surface amphiphilic peptide was converted to a beta-sheet structure from an aggregated alpha-helix by incubation. Under this condition, the amphiphilic peptide coated gold nanoparticles formed a nanosheet assembly. The plasmon absorption maximum of the gold nanoparticles shifted to a shorter wavelength with the formation of the beta-sheet assembly of the surface peptide. This suggests that the structure of the peptide coated gold nanoparticle assembly could be controlled by the conformational transition of the surface peptide. Furthermore, the core gold nanoparticle could be fixed in the beta-sheet assembly in the state that stood alone. This system may be useful for novel molecular devices that exhibit quantized properties. 相似文献
998.
Hossain MK Shimada T Kitajima M Imura K Okamoto H 《Langmuir : the ACS journal of surfaces and colloids》2008,24(17):9241-9244
Spatial distribution of surface enhanced Raman activity is visualized for two-dimensional (2D) nearly close-packed and well-ordered monolayer array of gold nanoparticles by using scanning near-field optical microscope. The 2D arrays exhibit highly nonuniform enhancement in Raman scattering, i.e., the regions along the edge of the 2D array are preferentially enhanced. We demonstrate that the spatial distribution of the localized electric field is also nonuniform and agrees well with that of the Raman enhancement. 相似文献
999.
Minji Jin Yu Nagaoka Kazuomi Nishi Kinuyo Ogawa Shoji Nagahata Toshihide Horikawa Masahiro Katoh Tahei Tomida Jun’ichi Hayashi 《Adsorption》2008,14(2-3):257-263
Photocatalysts of TiO2 and La-doped TiO2 were prepared by calcining the pure TiO2 sols and the sols mixed with La(NO3)3⋅6H2O at 873 K, respectively. These photocatalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy
(XPS), scanning electron microscopy (SEM) and N2 adsorption-desorption isotherms measurement. As results, the BET surface area, pore diameter, mesopore volume and micropore
volume slightly increased, while the crystallite size and the phase structure were little affected by lanthanum doping. The
equilibrium adsorption of methylene blue (MB) on the photocatalysts were measured in a dark room. The adsorption isotherms
were confirmed to fit to the Langmuir theory. Photocatalytic activities of the photocatalysts were studied by employing the
photocatalytic degradation of MB in water and degradation of acetaldehyde in air under UV-irradiation using a black light.
Kinetic analysis revealed that the rate controlling steps could be the surface reaction of the adsorbed MB on the catalyst
surface for MB degradation and the reaction of adsorbed acetaldehyde with the gaseous acetaldehyde for degradation of acetaldehyde,
respectively. 相似文献
1000.
Yamada M Wakahara T Tsuchiya T Maeda Y Kako M Akasaka T Yoza K Horn E Mizorogi N Nagase S 《Chemical communications (Cambridge, England)》2008,(5):558-560
Dimetallofullerene Ce(2)@C(78) and its bis-silylated derivative (1) were successfully prepared and fully characterized. 相似文献