全文获取类型
收费全文 | 1503篇 |
免费 | 43篇 |
国内免费 | 2篇 |
专业分类
化学 | 1130篇 |
晶体学 | 15篇 |
力学 | 33篇 |
数学 | 142篇 |
物理学 | 228篇 |
出版年
2023年 | 10篇 |
2022年 | 45篇 |
2021年 | 57篇 |
2020年 | 45篇 |
2019年 | 32篇 |
2018年 | 30篇 |
2017年 | 23篇 |
2016年 | 49篇 |
2015年 | 55篇 |
2014年 | 53篇 |
2013年 | 105篇 |
2012年 | 121篇 |
2011年 | 115篇 |
2010年 | 60篇 |
2009年 | 81篇 |
2008年 | 107篇 |
2007年 | 89篇 |
2006年 | 72篇 |
2005年 | 51篇 |
2004年 | 63篇 |
2003年 | 47篇 |
2002年 | 41篇 |
2001年 | 24篇 |
2000年 | 27篇 |
1999年 | 19篇 |
1998年 | 9篇 |
1997年 | 15篇 |
1996年 | 7篇 |
1995年 | 5篇 |
1994年 | 9篇 |
1993年 | 8篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 10篇 |
1989年 | 9篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1985年 | 9篇 |
1983年 | 5篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1948年 | 1篇 |
1938年 | 1篇 |
1934年 | 2篇 |
1925年 | 2篇 |
1924年 | 2篇 |
排序方式: 共有1548条查询结果,搜索用时 437 毫秒
71.
Anderson R. L. Caires Luciano R. Costa Joelson Fernandes 《Central European Journal of Chemistry》2013,11(1):111-115
In the last few years, silver nanoparticles have been proposed as a promising alternative for the label-free detection of proteins via metal-enhanced fluorescence. Generally, the aromatic amino acid tryptophan is most frequently used in this type of studies, because the intrinsic fluorescence of proteins is usually dominated by tryptophan emissions. In the present study, we evaluated the fluorescence behavior of tryptophan in the presence of a silver colloid with nanoparticles of 100 nm in diameter. The results showed that a nanoparticles concentration of 32 mg L?1 induced maximum fluorescence enhancement. However, the metal-enhanced fluorescence was dependent on the emission wavelength of tryptophan, and this phenomenon was closely related to the metal surface reabsorption process (inner filter effect), suggesting that the plasmon resonance reabsorption effect should be taken into account in analyses involving protein studies by metal-enhanced fluorescence. 相似文献
72.
Núbia Boechat Jorge Carlos Santos da Costa Jorge de Souza Mendonça Karla Ceodaro Paes Elisa Lopes Fernandes Pedro Santos Mello de Oliveira 《合成通讯》2013,43(24):3187-3190
Some heteroaromatic esters were reduced to the corresponding alcohols by using a sodium borohydride–methanol system. The reduction was completed within 0.15–2.0 h in refluxing THF. The alcohol products were isolated after aqueous workup in moderate to excellent yield (48–97%). 相似文献
73.
Flávia Mafra de Lima Regiane Albertini Yvana Dantas Antonio Luis Maia‐Filho Cristiano de Loura Santana Hugo Caire Castro‐Faria‐Neto Cristiane França Antonio Balbin Villaverde Flávio Aimbire 《Photochemistry and photobiology》2013,89(1):179-188
It remains unknown if the oxidative stress can be regulated by low‐level laser therapy (LLLT) in lung inflammation induced by intestinal reperfusion (i‐I/R). A study was developed in which rats were irradiated (660 nm, 30 mW, 5.4 J) on the skin over the bronchus and euthanized 2 h after the initial of intestinal reperfusion. Lung edema and bronchoalveolar lavage fluid neutrophils were measured by the Evans blue extravasation and myeloperoxidase (MPO) activity respectively. Lung histology was used for analyzing the injury score. Reactive oxygen species (ROS) was measured by fluorescence. Both expression intercellular adhesion molecule 1 (ICAM‐1) and peroxisome proliferator‐activated receptor‐y (PPARy) were measured by RT‐PCR. The lung immunohistochemical localization of ICAM‐1 was visualized as a brown stain. Both lung HSP70 and glutathione protein were evaluated by ELISA. LLLT reduced neatly the edema, neutrophils influx, MPO activity and ICAM‐1 mRNA expression. LLLT also reduced the ROS formation and oppositely increased GSH concentration in lung from i‐I/R groups. Both HSP70 and PPARy expression also were elevated after laser irradiation. Results indicate that laser effect in attenuating the acute lung inflammation is driven to restore the balance between the pro‐ and antioxidants mediators rising of PPARy expression and consequently the HSP70 production. 相似文献
74.
Ultrasonic irradiation substantially improves the reaction of cyclohexene with I2 in aqueous dioxane in the presence of Cu(OAc)2 · H2O to generate the expected iodohydrin in high yield. The product undergoes cyclization to the epoxide by biphasic treatment with either Na2CO3 or KOH in a sonication‐sensitive step. 相似文献
75.
D.M. Fernandes J.L. Andrade M.K. Lima M.F. Silva L.H.C. Andrade S.M. Lima A.A. Winkler Hechenleitner E.A. Gómez Pineda 《Polymer Degradation and Stability》2013
Ni0.04Zn0.96O and Fe0.03Zn0.97O with average diameter of 23 and 19 nm, respectively, have been synthesized by a modified sol–gel method to be used in the preparation of (100 − x)/x poly(vinyl alcohol)/oxide nanocomposite films, with x = 0, 1, 3 and 5 (in wt.%). A 125 W-Hg vapor lamp with emission above 254 nmwas used to irradiate PVA/Ni0.04Zn0.96O and PVA/Fe0.03Zn0.97O films. The effect on their structural, thermal, morphological and optical properties was studied by TG, DSC, DRX, AFM, UV–vis and PL spectrophotometry. The Ni0.04Zn0.96O addition on PVA films decreases the thermal stability of the polymer in inert and in oxidative atmosphere. In contrast, the Fe0.03Zn0.97O presence in the PVA films seems to increase the thermal stability of the polymer. The characteristic peak of the crystalline phase of PVA and wurtzite phase of the zinc oxide were identified through X-ray diffraction in both films. The crystallinity of the PVA film increases with UV irradiation and with the presence of Ni0.04Zn0.96O and Fe0.03Zn0.97O. The roughness of the PVA film was not modified by the addition of the doped oxides; however, it increases after UV irradiation, more significantly in the films containing the oxides. The PVA film exhibits absorption around 280 nm characteristic of π–π∗ transitions related to carbonyl groups from residuals acetate, while the 95/05 PVA/Ni0.04Zn0.96O and 95/05 PVA/Fe0.03Zn0.97O nanocomposite films show absorption at the visible region which is characteristics of the band gap reduction of the doped oxides. The photoluminescence of PVA was modified by the presence of the oxides in the film. These nanocomposite films are interesting due to their thermal, mechanical (flexible) properties and low cost of production. In addition they are also able to exhibit peculiar optical properties showing potential to be used in photonic devices, gas sensors and organic solar cell applications. 相似文献
76.
77.
André Luís Branco de Barros Saulo Fernandes de Andrade José Dias de Souza Filho Valbert Nascimento Cardoso Ricardo José Alves 《Journal of Radioanalytical and Nuclear Chemistry》2013,298(1):605-609
Glycodendrimers are neoglycoconjugates that can be considered as bioisosters of glycoproteins, since they can mimic the multivalent interactions of lectin-carbohydrate. The ability of glycodendrimers to present multivalent interactions with lectins as compared to a monovalent ligand is referred to as “cluster effect”. It is expected that, because of the cluster effect, glycodendrimers would result in a better association with lectins than mono-carbohydrate anchored systems. Radioisotopes are useful to evaluate biodistribution of molecules. This study is important to obtain information about molecule–receptor interactions. Indeed, such study can provide an exquisite tool to evaluate the affinity of certain molecules to specific areas in the body, leading to the development of new radiopharmaceuticals and/or drug delivery systems. Herein, we describe a d-galactose coated low molecular weight PAMAM G0 dendrimer that was successfully radiolabeled with technetium-99m. Biodistribution studies and scintigraphic images were performed in healthy mice. It was observed high liver uptake which was significantly reduced in blocking studies, indicating hepatic specificity. Therefore, low molecular weight glycodendrimer can be considered as useful platform for selective targeting of drugs to the liver and to assess hepatic function. 相似文献
78.
B. S. Fernandes N. K. Saavedra S. I. Maintinguer L. D. Sette V. M. Oliveira M. B. A. Varesche M. Zaiat 《Applied biochemistry and biotechnology》2013,170(6):1348-1366
The aim of this study was to investigate the effect of the support material used for biomass attachment and bed porosity on the potential generation of hydrogen gas in an anaerobic bioreactor treating low-strength wastewater. For this purpose, an upflow anaerobic packed-bed (UAPB) reactor fed with sucrose-based synthetic wastewater was used. Three reactors with various support materials (expanded clay, vegetal coal, and low-density polyethylene) were operated for hydraulic retention time (HRT) of 0.5 and 2 h. Based on the results obtained, three further reactors were operated with low-density polyethylene as a material support using various bed porosities (91, 75, and 50 %) for an HRT of 0.5 h. The UAPB reactor was found to be a feasible technology for hydrogen production, reaching a maximum substrate-based hydrogen yield of 7 mol H2 mol?1 sucrose for an HRT of 0.5 h. The type of support material used did not affect hydrogen production or the microbial population inside the reactor. Increasing the bed porosity to 91 % provided a continuous and cyclic production of hydrogen, whereas the lower bed porosities resulted in a reduced time of hydrogen production due to biomass accumulation, which resulted in a decreasing working volume. 相似文献
79.
Alliny F. Naves Henrique T. C. Fernandes Ana P. S. Immich Luiz H. Catalani 《Journal of polymer science. Part A, Polymer chemistry》2013,51(18):3881-3891
The search for materials produced from renewable sources aiming at the substitution of petroleum‐based derivates is an area of intense investigation. In this work, the enzymatic copolymerization of isosorbide or isomannide with diethyl adipate and fractions of different unsaturated diesters (diethyl itaconate, diethyl fumarate, diethyl glutaconate, and diethyl hydromuconate) were examined using CAL‐B as catalyst. The polyesters prepared using one‐step syntheses were characterized by SEC, NMR, and MALDI‐TOF MS. In addition, syntheses with linear diols were carried out in bulk to evaluate the reactivity of cyclic diols in producing unsaturated polyesters using enzymatic catalysis, as well as to evaluate the occurrence of addition side reactions on the double bonds. Isosorbide and isomannide yielded unsaturated polymers with values in the order of 4,000‐16,000 when fumarate or glutaconate esters were added in 5 mol % ratio against adipate. In all cases MALDI‐TOF confirmed the presence of unsaturated units. Although these polyesters have unreacted double bonds they are prone to crosslinking and ready to further functionalization, like anchoring bioactive molecules. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 3881–3891 相似文献
80.
Liliana C. Tomé Susana C. M. Fernandes Denilson Silva Perez Patrizia Sadocco Armando J. D. Silvestre Carlos Pascoal Neto Isabel M. Marrucho Carmen S. R. Freire 《Cellulose (London, England)》2013,20(4):1807-1818
Thin nanocomposite films of thermoplastic starch, chitosan and cellulose nanofibers (bacterial cellulose or nanofibrillated cellulose) were prepared for the first time by solvent casting of water based suspensions of the three polysaccharides. The role of the different bioploymers on the final properties (thermal stability, transparency, mechanical performance and antimicrobial activity) of the films was related with their intrinsic features, contents and synergic effects resulting from the establishment of interactions between them. Thermoplastic starch displays an important role on the thermal stability of the films because it is the most stable polysaccharide; however it has a negative impact on the mechanical performance and transparency of the films. The addition of chitosan improves considerably the transparency (up to 50 % transmittance for 50 % of chitosan, in respect to the amount of starch), mechanical performance and antimicrobial properties (at least 25 % of chitosan and no more than 10 % of cellulose nanofibers are required to observe bacteriostatic or bactericidal activity) but decrease their thermal stability. The incorporation of cellulose nanofibers had the strongest positive impact on the mechanical properties of the materials (increments of up to 15 and 30 MPa on the Young′s modulus and Tensile strength, respectively, for films with 20 % of BC or NFC). Nonetheless, the impact in thermal stability and mechanical performance of the films, promoted by the addition of chitosan and cellulose nanofibres, respectively, was higher than the expected considering their percentage contents certainly because of the establishment of strong and complex interactions between the three polysaccharides. 相似文献