全文获取类型
收费全文 | 10646篇 |
免费 | 158篇 |
国内免费 | 39篇 |
专业分类
化学 | 6092篇 |
晶体学 | 87篇 |
力学 | 361篇 |
数学 | 1732篇 |
物理学 | 2571篇 |
出版年
2022年 | 101篇 |
2021年 | 114篇 |
2020年 | 132篇 |
2019年 | 129篇 |
2018年 | 119篇 |
2017年 | 109篇 |
2016年 | 186篇 |
2015年 | 167篇 |
2014年 | 169篇 |
2013年 | 589篇 |
2012年 | 367篇 |
2011年 | 448篇 |
2010年 | 332篇 |
2009年 | 283篇 |
2008年 | 410篇 |
2007年 | 376篇 |
2006年 | 364篇 |
2005年 | 327篇 |
2004年 | 352篇 |
2003年 | 284篇 |
2002年 | 279篇 |
2001年 | 193篇 |
2000年 | 185篇 |
1999年 | 151篇 |
1998年 | 117篇 |
1997年 | 133篇 |
1996年 | 167篇 |
1995年 | 127篇 |
1994年 | 136篇 |
1993年 | 163篇 |
1992年 | 162篇 |
1991年 | 165篇 |
1990年 | 122篇 |
1989年 | 130篇 |
1988年 | 136篇 |
1987年 | 187篇 |
1986年 | 155篇 |
1985年 | 201篇 |
1984年 | 190篇 |
1983年 | 149篇 |
1982年 | 179篇 |
1981年 | 183篇 |
1980年 | 177篇 |
1979年 | 181篇 |
1978年 | 173篇 |
1977年 | 170篇 |
1976年 | 146篇 |
1975年 | 165篇 |
1974年 | 133篇 |
1973年 | 130篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
The surface morphology of hollow silica microspheres has influence on their applications. After a thorough investigation of the deposition of silica nanoparticles on polystyrene (PS) beads and the surface morphology and texture of the resultant hollow silica shells with scanning electron microscopy, transmission electron microscopy, and N2-sorption measurements, the influence of surfactant [cetyltrimethylammonium bromide (CTAB)] concentration on the surface morphology of hollow silica microspheres templated by PS beads is explained. Previously, CTAB was believed to turn the surface charge of PS beads from negative into positive so that negatively charged silica could be deposited on the PS template. Here, we show CTA+ cations preferentially assemble with silica species to form silica-CTA+ composite nanoparticles. Since the zeta potential of silica-CTA+ composite nanoparticles is smaller than that of pure silica nanoparticles, these composite nanoparticles encounter less repulsion when they are deposited on the surface of PS beads and close to each other. As more CTAB is added, the silica-CTA+ nanoparticles are less negatively charged, and more compact and smooth hollow silica microspheres are obtained. 相似文献
972.
Aerts A Follens LR Biermans E Bals S Van Tendeloo G Loppinet B Kirschhock CE Martens JA 《Physical chemistry chemical physics : PCCP》2011,13(10):4318-4325
Synchrotron small angle X-ray scattering (SAXS) was used to characterize silicalite-1 zeolite crystallization from TEOS/TPAOH/water clear sol. SAXS patterns were recorded over a broad range of length scales, enabling the simultaneous monitoring of nanoparticles and crystals occurring at various stages of the synthesis. A simple two-population model accurately described the patterns. Nanoparticles were modeled by polydisperse core-shell spheres and crystals by monodisperse oblate ellipsoids. These models were consistent with TEM images. The SAXS results, in conjunction with in situ light scattering, showed that nucleation of crystals occurred in a short period of time. Crystals were uniform in size and shape and became increasingly anisotropic during growth. In the presence of nanoparticles, crystal growth was fast. During crystal growth, the number of nanoparticles decreased gradually but their size was constant. These observations suggested that the nanoparticles were growth units in an aggregative crystal growth mechanism. Crystals grown in the presence of nanoparticles developed a faceted habit and intergrowths. In the final stages of growth, nanoparticles were depleted. Concurrently, the crystal growth rate decreased significantly. 相似文献
973.
Van Duzor M Mbaiwa F Lasinski J Holtgrewe N Mabbs R 《The Journal of chemical physics》2011,134(21):214301
We present the results of a photoelectron imaging study of the I(-)·(CH(3)I)(2) cluster anion over excitation wavelengths 355-260 nm. The resulting spectra and photoelectron angular distributions (PADs) suggest extensive electron-molecule interaction following photoexcitation. Fragmentation channels are observed subsequent to excitation between 355 and 330 nm. The origin of these features, which begin 200 meV and peak 70 meV below the X band direct detachment threshold, is described in terms of a predissociative dipole bound state. The nature of the fragments detected and the energetics of the channel opening argue strongly in favor of an asymmetric, head to tail cluster anion geometry posited by Dessent et al. [Acc. Chem. Res. 31, 527 (1998)]. Above the direct detachment threshold, PADs display evidence of phenomena akin to electron-molecule scattering. The fragment anions disappear above the X band threshold but reappear some distance below the second (A) direct detachment band. At these energies there is also rapid variation of the X band PAD, an observation attributed to autodetachment via spin-orbit relaxation of the iodine core of the cluster. 相似文献
974.
Hosseinidoust Z Van de Ven TG Tufenkji N 《Langmuir : the ACS journal of surfaces and colloids》2011,27(9):5472-5480
The rise of antibiotic-resistant bacteria has directed substantial attention toward the use of bacteriophages as a means to control bacterial populations. It has been proposed that bacteriophages can be applied as a coating on surfaces in healthcare settings or on indwelling medical devices to create an antimicrobial surface. In this study, antimicrobial model surfaces functionalized with five different types of bacteriophage were prepared and characterized with X-ray photoelectron spectroscopy and atomic force microscopy. The bacterial capture efficiency of these functionalized surfaces was studied for two common bacteria, Escherichia coli and Salmonella typhimurium. Binding of the phages to a solid surface affected their biofunctionality as expressed by the capture efficiency and rate of host membrane disruption. Moreover, the size and shape of the bacteriophage and positioning of its specific binding proteins significantly affected its bacterial capture capability in the immobilized state. Symmetric bacteriophages were found to be a better choice for antibacterial surfaces compared to more asymmetric tailed bacteriophages. Immobilized phages were found to disrupt the membranes of attached bacteria and are thus proposed as a candidate for antimicrobial surfaces. 相似文献
975.
Poiroux G Pitié M Culerrier R Ségui B Van Damme EJ Peumans WJ Bernadou J Levade T Rougé P Barre A Benoist H 《Photochemistry and photobiology》2011,87(2):370-377
Porphyrins are used as photosensitizer (PS) in photodynamic therapy in cancer treatment. Nevertheless, the development of photochemotherapy in oncology remains limited, because of the low selectivity of PSs. In order to allow PS targeting toward tumor-associated antigens, for the first time a white-light activatable porphyrin, [5-(4-(5-carboxy-1-butoxy)-phenyl)-10,15,20-tris(4-N-methyl)-pyridiniumyl)-porphyrin] (TrMPyP) was covalently linked to Morniga G (MorG), a galactose-specific binding plant lectin, known to recognize with high-affinity tumor-associated T/Tn antigen in cell-free systems. Firstly, using fluorescein-labeled MorG, the sugar-dependent binding and uptake of lectin by Tn-positive (Jurkat lymphoid leukemia) cells was demonstrated. Secondly, the TrMPyP-MorG conjugate was molecularly characterized. Cytometric and confocal microscopic analysis demonstrated that PS covalent linking to MorG preserved sugar-dependent specific binding and uptake of lectin by Jurkat leukemia lymphocytes. Thirdly, the conjugate (with a 1:1 PS:lectin ratio) that was bound and quickly (5 min) taken-up, induced greater than 90% cytotoxicity upon irradiation at 10 nm concentration, whereas the free PS was absolutely nontoxic. On the contrary, normal lymphocytes strongly resisted to the conjugate-mediated phototoxicity. Thus, owing to their binding and endocytosis capacities, plant lectins represent promising molecules for targeting of tumor glycan alteration and to enhance the efficiency of specific delivery of PSs to tumor cells. 相似文献
976.
Punyawudho K Ma S Van Zee JW Monnier JR 《Langmuir : the ACS journal of surfaces and colloids》2011,27(12):7524-7530
Adsorption of SO(2) in the presence of O(2) on Pt/C catalysts often used as electrocatalysts has been investigated by temperature programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). The amounts of SO(2) adsorption on Pt/C in the presence of O(2) were much higher than those in the absence of O(2) (SO(2)-N(2)) and from the carbon support (Vulcan XC-72) alone. Adsorption is dependent on oxygen concentration over the range 0-20% but reaches saturation at 20% O(2). The spillover of SO(2) from Pt to the carbon support has been proposed for 10, 20, and 40% Pt loadings, characterized by desorption temperatures of approximately 150 and 260 °C for SO(2) adsorbed on Pt and carbon, respectively. Adsorbed Pt-S, C-S, C-SO(x), and Pt-SO(4) species were identified by XPS as S-containing species on both Pt and carbon. Both TPD and XPS indicate that the carbon support plays a major role in SO(2) adsorption, primarily as SO(x) (x = 3, 4). The bonding of S and SO(x) on the carbon support was strong enough that back diffusion to the Pt surface did not occur. 相似文献
977.
Tran Van Hung 《Journal of Radioanalytical and Nuclear Chemistry》2011,287(1):103-106
The neutron temperature is a characteristic parameter in irradiation channels of reactor. For nuclides which have resonances in the thermal neutron energy range, their Westcott g-factors are different from unity. The values of g-factors and cross-sections of (n, γ) reaction of these nuclides are temperature dependence. The standard energy for tabulation of thermal neutron cross-section (σ0) is that of room temperature (293.59 K or 20.43 °C), corresponding to a neutron energy 0.0253 eV or to a neutron velocity of 2200 m/s. However, in the irradiation channels of reactor, the temperature is not exact at 20.43 °C. Thus, the temperature at the irradiation position must be known to convert σ0 to σ(T). A method for determination of the neutron temperature in irradiation channels of Dalat reactor is presented by fitting the thermal neutron spectrum obtained from the calculation using MCNP code. 相似文献
978.
Nguyen Van Suc Nguyen Mong Sinh 《Journal of Radioanalytical and Nuclear Chemistry》1993,176(5):383-389
Radiochemical neutron activation analysis (RNAA) has been applied for determination of rare earth elements (REE) in Vietnamese monazite. The chemical separation procedure used is based on the chromatographic elution of rare earth groups, after the separation of233Pa(Th) in irradiated monazite samples by coprecipitation with MnO2, the rare earth elements were retained by Biorad AG1×8 resin column in 10% 15.4M HNO3-90% methanol solution. The elution of heavy rare earth (HREE) and middle rare earth (MREE) groups was carried out with 10% 1M HNO3-90% methanol and 10% 0.05M HNO3-90% methanol solution, respectively; while the light rare earths (LREE) were eluted from the column by 0.1M HNO3 solution. The accuracy of the method was checked by the analysis of granodiorite GSP-I and the rare earth values were in good agreement. 相似文献
979.
980.