全文获取类型
收费全文 | 3880篇 |
免费 | 168篇 |
国内免费 | 47篇 |
专业分类
化学 | 2681篇 |
晶体学 | 31篇 |
力学 | 152篇 |
数学 | 353篇 |
物理学 | 878篇 |
出版年
2023年 | 14篇 |
2022年 | 11篇 |
2021年 | 62篇 |
2020年 | 72篇 |
2019年 | 58篇 |
2018年 | 46篇 |
2017年 | 43篇 |
2016年 | 100篇 |
2015年 | 84篇 |
2014年 | 140篇 |
2013年 | 232篇 |
2012年 | 245篇 |
2011年 | 287篇 |
2010年 | 180篇 |
2009年 | 202篇 |
2008年 | 240篇 |
2007年 | 199篇 |
2006年 | 191篇 |
2005年 | 177篇 |
2004年 | 171篇 |
2003年 | 156篇 |
2002年 | 164篇 |
2001年 | 105篇 |
2000年 | 112篇 |
1999年 | 60篇 |
1998年 | 55篇 |
1997年 | 48篇 |
1996年 | 62篇 |
1995年 | 50篇 |
1994年 | 45篇 |
1993年 | 44篇 |
1992年 | 29篇 |
1991年 | 26篇 |
1990年 | 23篇 |
1989年 | 32篇 |
1988年 | 16篇 |
1987年 | 25篇 |
1986年 | 26篇 |
1985年 | 33篇 |
1984年 | 28篇 |
1983年 | 29篇 |
1982年 | 19篇 |
1981年 | 21篇 |
1980年 | 12篇 |
1979年 | 13篇 |
1978年 | 12篇 |
1977年 | 16篇 |
1976年 | 20篇 |
1975年 | 17篇 |
1974年 | 10篇 |
排序方式: 共有4095条查询结果,搜索用时 528 毫秒
891.
892.
Chang-Jo F. Chung Miklós Csörgő Lajos Horváth 《Annals of the Institute of Statistical Mathematics》1990,42(1):21-36
Some new confidence bands are established for the quantile function from randomly censored data. The method does not require estimation of the density function. As an application, we construct bands for the quantile function of the length of fractures in the granitic plutons near Lac du Bonnet, Manitoba, where an Underground Research Laboratory is being built for the nuclear waste disposal program in Canada.Geological Survey of Canada Contribution Number 10386.Research partially supported by an NSERC Canada Grant.Research done while at Carieton University, supported by NSERC Canada and EMR Canada Grants of M. Csörg. 相似文献
893.
894.
Poly-gamma-glutamic acid (gamma-PGA) is a very promising biodegradable polymer that is produced by Bacillus subtilis. Gamma-PGA is water-soluble, anionic, biodegradable, and edible. This paper reviews the production of a strain of gamma-PGA and recent developments with respect to applications in terms of Ca absorption, moisturizing properties, gamma-PGA conjugation, super absorbent polymer, and so on. Our recent research shows that gamma-PGA can be used as an immune-stimulating and anti-tumor agent, especially at high molecular weight. 相似文献
895.
Oh C Chung SC Shin SI Kim YC Im SS Oh SG 《Journal of colloid and interface science》2002,254(1):79-86
The distribution of macropores in silica particles prepared by the hydrolysis and condensation of TEOS in a hexane/water/decyl alcohol (O(1)/W/O(2)) multiple emulsion was investigated. To stabilize the emulsion structure, hydroxypropyl cellulose (HPC) was added into the O(2) phase and polyethylene glycol (PEG) was added into the water phase. Without HPC, the particles have an irregular shape and hardly have particulate forms. As the concentration of HPC increases, the shape of particles becomes more and more spherical and the size decreases. The size of silica particles was varied from 5 to 1 microm as the concentration of HPC increased from 0.5 to 0.7 wt%. The number and size of the macropores in silica particles were affected by PEG polymer concentration. With the variation in the concentration of PEG, macropores in silica particles were located at the surface of or inside the particles. At high concentrations of PEG, the macropores in particles were located inside the particles, but at low concentrations of PEG the macropores were located at the surfaces of particles. Interestingly, the particles of dimpled surfaces were formed when the molar ratio of water to TEOS (R(w)) was 4.0 and the concentrations of PEG and HPC were 2.0 and 0.7 wt% respectively. The surface areas of dimpled silica particles and completely spherical particles, measured by the BET method, were 409 and 433 m(2)/g respectively. 相似文献
896.
Daryle H. Busch Rebecca A. Roesner Thomas L. Allison II Elena V. Rybak-Akimova Liszu Chung 《Journal of inclusion phenomena and macrocyclic chemistry》1998,30(3):185-196
The compressibilities of seven liquidphase, macrocyclic host-guest systems were determinedat approximately 25 °C and 3.4 × 107 Pa.Each two-component system consisted of a cyclodextrin,a calixarene, or a crown ether as host and anappropriate solvent as guest. In each case studied,the host-guest system was found to be lesscompressible than the pure solvent, with thedifferences ranging from 2 to 18% of the magnitudesof the pure solvent compressibilities. These findingshave enabled us to better understand how strong,ambient pressure, intermolecular host–guestinteractions influence the compressibility ofsolutions. Both inclusion and solvationcontribute. 相似文献
897.
The least protonated hexamolybdoplatinate(IV) polyanion, [H2α‐PtMo6O24]6?, is isolated by using Nd3+ as a counter‐cation. Two O atoms of the central PtO6 octahedron are protonated. The Mo—Mo distances are 3.244 (2), 3.295 (2) and 3.393 (1) Å, and the Pt—Mo distances are 3.251 (1), 3.332 (2) and 3.338 (1) Å. The anion has the Pt atom on an inversion centre and has close to m symmetry, with Pt—O bond lengths in the range 2.002 (8)–2.015 (8) Å and Mo—O bond lengths in the ranges 1.689 (9)–1.747 (8), 1.890 (8)–2.037 (8) and 2.109 (8)–2.384 (8) Å. 相似文献
898.
ZnO-SnO2纳米复合氧化物的制备、表征及其气敏性质的研究(英) 总被引:1,自引:0,他引:1
本文用可控湿化学共沉淀法研制了ZnO-SnO2纳米晶体复合气敏材料并考察其对有毒气体CO和NO2的气敏性质。用TEM、BET和XRD等方法表征了纳米复合物的粒度、形貌、比表面、热稳定性和相稳定性。研究了制备的可控参数,如金属阳离子总浓度、沉淀pH值和老化时间等对复合物气敏性质的影响。研究结果表明,该纳米复合氧化物具有化学均一性,高度热稳定和相稳定性,对CO和NO2具有高的灵敏度和选择性,其气敏性质依赖于复合物组成、焙烧温度和操作温度。通过2wt%金属Cd的掺杂和10wt% Al2O3氧化物的表面包覆大大提高了气体的灵敏度和选择性。用程序升温吸脱附研究了纳米复合物表面对气体的吸脱附性能,并探讨了气敏机理。 相似文献
899.
900.
Lee SK Lee SS Song IS Kim YS Park YW Joo JY Um HS Kim JW Kim KY Choi SJ Jung KH Chung SI 《Experimental & molecular medicine》2004,36(3):259-267
Innate elastase inhibitors are known to be putatively involved in the regulation of tissue inflammation by inhibiting polymorphonuclear leukocyte (PMN) derived proteinases. The aim of this study was to evaluate affects of leukocyte elastase suppression and PMN infiltration on wound healing in mouse by administering the recombinant elastase inhibitor guamerin (rEIG) in two different wound models; 1) impaired pin-punctured dorsal mucosa of anterior tongue wound, 60 mice, treated with saline containing rEIG that were fed ad libitum and 2) stable linear excisional cutaneous wound, 40 mice, covered with fibrin sealant containing rEIG. The progress of healing was analyzed by histological methods. The tongue wounds treated with rEIG became edematous around the pin-punctured tongue wound, and influx of inflammatory cells and PMN into the underlying stromal tissue were seen rapidly after wounding and peaked between 2-4 days. Whereas the control mice showed almost no wheal formation in the pin-punctured wound, a far lesser levels of PMN infiltration, and almost complete wound closure in 4 days. In the other model, the liner excisional cutaneous wound treated with fibrin sealant containing rEIG showed early wound constriction, lesser degree of inflammatory cells influx, and complete reepithelialization in 4-5 days, whereas the wound of control mice with the fibrin sealant alone showed contrary delayed reepithelialization, greater degree of inflammatory cell infiltration, and consequencial formation of greater granulation tissue at wound site. Taken together, these data suggest paradoxical effects of rEIG on the wound healing where in the wound exposed to infiltrating milieu of microorganisms in the oral cavity, the rEIG aggravates the wound healing by interfering with other innate defensive factors and extended greater flux of PMNs to inflamed wound site, while in the wound enclosed by fibrin, the rEIG accelerated wound healing by inhibiting the inflammation-generated proteases and the acute inflammatory reaction. 相似文献