全文获取类型
收费全文 | 4719篇 |
免费 | 348篇 |
专业分类
5067篇 |
出版年
2023年 | 39篇 |
2022年 | 72篇 |
2021年 | 163篇 |
2020年 | 135篇 |
2019年 | 143篇 |
2018年 | 176篇 |
2017年 | 164篇 |
2016年 | 230篇 |
2015年 | 269篇 |
2014年 | 324篇 |
2013年 | 352篇 |
2012年 | 375篇 |
2011年 | 300篇 |
2010年 | 198篇 |
2009年 | 200篇 |
2008年 | 249篇 |
2007年 | 210篇 |
2006年 | 188篇 |
2005年 | 165篇 |
2004年 | 161篇 |
2003年 | 108篇 |
2002年 | 121篇 |
2001年 | 88篇 |
2000年 | 89篇 |
1999年 | 67篇 |
1998年 | 43篇 |
1997年 | 25篇 |
1996年 | 21篇 |
1995年 | 36篇 |
1994年 | 13篇 |
1993年 | 13篇 |
1992年 | 31篇 |
1991年 | 20篇 |
1990年 | 19篇 |
1989年 | 15篇 |
1988年 | 30篇 |
1987年 | 25篇 |
1986年 | 16篇 |
1985年 | 19篇 |
1984年 | 16篇 |
1983年 | 13篇 |
1982年 | 13篇 |
1976年 | 7篇 |
1975年 | 8篇 |
1974年 | 9篇 |
1973年 | 8篇 |
1972年 | 9篇 |
1971年 | 9篇 |
1969年 | 6篇 |
1968年 | 7篇 |
排序方式: 共有5067条查询结果,搜索用时 0 毫秒
991.
Marco Júnio Peres-Filho Alexandre Pereira dos Santos Thais Leite Nascimento Renato Ivan de Ávila Fabrícia Saba Ferreira Marize Campos Valadares Eliana Martins Lima 《AAPS PharmSciTech》2018,19(1):201-212
Co-encapsulation of anticancer drugs paclitaxel and imatinib in nanocarriers is a promising strategy to optimize cancer treatment. Aiming to combine the cytotoxic and antiangiogenic properties of the drugs, a liposome formulation targeted to folate receptor co-encapsulating paclitaxel and imatinib was designed in this work. An efficient method was optimized for the synthesis of the lipid anchor DSPE-PEG(2000)-folic acid (FA). The structure of the obtained product was confirmed by RMN, FT-IR, and ESI-MS techniques. A new analytical method was developed and validated for simultaneous quantification of the drugs by liquid chromatography. Liposomes, composed of phosphatidylcholine, cholesterol, and DSPE-mPEG(2000), were prepared by extrusion. Their surface was modified by post-insertion of DSPE-PEG(2000)-FA. Reaction yield for DSPE-PEG(2000)-FA synthesis was 87%. Liposomes had a mean diameter of 122.85 ± 1.48 nm and polydispersity index of 0.19 ± 0.01. Lyophilized formulations remained stable for 60 days in terms of size and drug loading. FA-targeted liposomes had a higher effect on MCF7 cell viability reduction (p < 0.05) when compared with non-targeted liposomes and free paclitaxel. On PC-3 cells, viability reduction was greater (p < 0.01) when cells were exposed to targeted vesicles co-encapsulating both drugs, compared with the non-targeted formulation. VEGF gene expression was reduced in MCF7 and PC-3 cells (p < 0.0001), with targeted vesicles exhibiting better performance than non-targeted liposomes. Our results demonstrate that multifunctional liposomes associating molecular targeting and multidrug co-encapsulation are an interesting strategy to achieve enhanced internalization and accumulation of drugs in targeted cells, combining multiple antitumor strategies. 相似文献
992.
Koppole Kamakshi J. P. B. Silva K. C. Sekhar J. Agostinho Moreira A. Almeida M. Pereira M. J. M. Gomes 《Plasmonics (Norwell, Mass.)》2018,13(4):1235-1241
This work reports the substrate temperature-influenced change in the structural, morphological, optical, and glucose sensing properties of silver (Ag) nanoparticles (NPs) deposited on p-type Si (100) wafers. AgNP films grown at temperatures ranging from RT to 600 °C clearly show a dependence of orientation texture and surface morphology on substrate temperature (T s). As T s increases from RT towards 600 °C, the preferred orientation of AgNP film changes from (111) to (200). The AgNPs size, that is T s-dependent, reaches the maximum value at T s = 300 °C. This result is attributed to restructuring of AgNPs texture. Moreover, the AgNP shape also changes from ellipsoid to sphere as T s increases from RT to 600 °C. Surface plasmon enhancement in photoluminescence intensity is observed with increase in T s. It is found also that the AgNP film deposited at 300 °C has considerable reflectance reduction relative to the silicon substrate, in wavelength range of 300–800 nm and a progressive red shift of localized surface plasmon resonances caused by the adding of increasing quantities of glucose has been observed. As a proof of concept, we also demonstrate the capability of grown AgNP substrates for glucose detection based on surface enhanced Raman spectroscopy in physiological concentration range with short integration time 10 s, varying with T s. 相似文献
993.
Spondias mombin supplementation attenuated cardiac remodelling process induced by tobacco smoke 下载免费PDF全文
Maria Angélica Martins Lourenço Mariana Gobbo Braz Aline Garcia Aun Bruna Letícia Buzati Pereira Amanda Menezes Figueiredo Renata Aparecida Cândido da Silva Elisa Moya Kazmarek Patrícia Helena Correa Alegre Tatiana Fernanda Bachiega Silmeia Garcia Zanati Paula Schmidt Azevedo Bertha Furlan Polegato Ana Angélica Henrique Fernandes Sergio Alberto Rupp de Paiva Leonardo Antonio Mamede Zornoff Marcos Ferreira Minicucci 《Journal of cellular and molecular medicine》2018,22(8):3996-4004
The objective of this study was to investigate the influence of Spondias mombin (SM) supplementation on the cardiac remodelling process induced by exposure to tobacco smoke (ETS) in rats. Male Wistar rats were divided into 4 groups: group C (control, n = 20) comprised animals not exposed to cigarette smoke and received standard chow; group ETS (n = 20) comprised animals exposed to cigarette smoke and received standard chow; group ETS100 (n = 20) received standard chow supplemented with 100 mg/kg body weight/d of SM; and group ETS250 (n = 20) received standard chow supplemented with 250 mg/kg body weight/d of SM. The observation period was 2 months. The ETS animals had higher values of left cardiac chamber diameters and of left ventricular mass index. SM supplementation attenuated these changes. In addition, the myocyte cross‐sectional area (CSA) was lower in group C compared with the ETS groups; however, the ETS250 group had lower values of CSA compared with the ETS group. The ETS group also showed higher cardiac levels of lipid hydroperoxide (LH) compared with group C; and, groups ETS100 and ETS250 had lower concentrations of LH compared with the ETS group. Regarding energy metabolism, SM supplementation decreased glycolysis and increased the β‐oxidation and the oxidative phosphorylation. There were no differences in the expression of Nrf‐2, SIRT‐1, NF‐κB, interferon‐gamma and interleukin 10. In conclusion, our results suggest that ETS induced the cardiac remodelling process. In addition, SM supplementation attenuated this process, along with oxidative stress reduction and energy metabolism modulation. 相似文献
994.
Alann Thaffarell Portilho Souza Gileade Pereira Freitas Helena Bacha Lopes Emanuela Prado Ferraz Fabiola Singaretti Oliveira Marcio Mateus Beloti Adalberto Luiz Rosa 《Cytotherapy》2018,20(10):1267-1277
Background aims
Regenerative medicine strategies based on cell therapy are considered a promising approach to repair bone defects. The aims of this study were to evaluate the effect of subculturing on the osteogenic potential of osteoblasts derived from newborn rat calvaria and the effect of these osteoblasts on bone repair of rat calvaria defects.Methods
Cells were obtained from 50 newborn rat calvaria, and primary osteoblasts (OB) were compared with first passage (OB-P1) in terms of osteogenic potential by assaying cell proliferation, alkaline phosphatase (ALP) activity, extracellular matrix mineralization and gene expression of the osteoblastic markers RUNX2, ALP, osteocalcin and bone sialoprotein. Then, 5-mm calvaria defects were created in 24 Wistar rats, and after 2 weeks, they were locally injected with 50 µL of phosphate-buffered saline containing either 5?×?106 osteoblasts (OB-P1, n?=?12) or no cells (control, n?=?12). Four weeks post-injection, the bone formation was evaluated by micro-computed tomography and histological analyses. Data were compared by analysis of variance, followed by the Student-Newman-Keuls's test or Student's t-test (P ≤ 0.05).Results
OB-P1 showed high proliferation and ALP activity, and despite the reduced gene expression of osteoblastic markers and extracellular matrix mineralization compared with OB, they displayed osteogenic potential, being a good choice for injection into calvaria defects. The micro-tomographic and histological data showed that defects treated with OB-P1 presented higher bone formation compared with control defects.Discussion
Our results indicate that cells derived from newborn rat calvaria retain osteoblastic characteristics after subculturing and that these osteoblasts stimulate bone repair in a rat calvaria defect model. 相似文献995.
I C Reis C T Codeço D C P Câmara J J Carvajal G R Pereira E C Keppeler N A Honório 《Neotropical Entomology》2018,47(3):412-417
The genus Anopheles encompasses several species considered as vectors of human infecting Plasmodium. Environmental changes are responsible for behavior changes in these vectors and therefore the pattern of malaria transmission. To better understand the dynamics of malaria transmission, this study aimed at identify the species of adult anophelines found in a malaria endemic urban area of the Amazon region, Mâncio Lima, located in the Acre State Brazil. Using Shannon-type light traps installed at 11 collection points near fish ponds, a total of 116 anophelines were collected belonging to nine species. Anopheles darlingi Root 1926 and An. albitarsis s.l. Lynch-Arribalzaga 1878 were the most abundant and predominant species. Despite the low number of captured adult anophelines, the occurrence of An. darlingi throughout all urban area and the presence of secondary vectors reinforce the need of a permanent and continuous entomological surveillance. 相似文献
996.
Sidney Luiz Stürmer Karl Kemmelmeier Bruno Coutinho Moreira Maria Catarina Megumi Kasuya Gilmara Maria Duarte Pereira Krisle da Silva 《Mycological Progress》2018,17(10):1149-1159
Savanna vegetation in the northern region of Brazil is jeopardized by several anthropogenic activities including cattle ranching and extensive agriculture, and soil biota of these ecosystems is virtually unknown. The soils in savannas are poor in nutrients, very acidic, and subject to drought, and under these conditions, arbuscular mycorrhizal fungi (AMF) are likely to play a key role on plant nutrition and improving soil structure. In this study, we surveyed AMF communities in five savanna locations in Roraima state, Northern Brazil. AMF species were identified using two approaches: field collected spores and trap cultures. Twenty-three AMF species were identified, including 21 species in field samples, 8 species in trap cultures, of which 15 and 2 were unique to field and trap culture samples, respectively. Gigaspora margarita, Dentiscutata heterogama, and Glomus sp1 were the most frequent species recovered from all locations. AMF communities were dominated by members of Gigasporaceae that accounted for 50 to 87% of the total species richness within each location. Spore numbers differed across locations and ranged from 5 to 25 spores 100 cm?3 soil. Redundancy analysis indicated that soil organic matter was the only selected predictor among soil parameters and correlated positively with occurrence of Glomus heterosporum. We conclude that savannas in Roraima harbor a high sporulating AMF species richness with communities dominated by members of Gigasporaceae and that organic carbon is an important edaphic factor influencing AMF community composition in this ecosystem. 相似文献
997.
Bijeesh Kozhikkodan Veettil Sebastian Felipe Ruiz Pereira Ngo Xuan Quang 《Hydrobiologia》2018,814(1):19-30
IPCC predictions indicate an increase in temperatures by 1.5–7°C in some Amazonian regions during the twenty-first century. These changes could disrupt the present distribution patterns of organisms, including wetland plant species. In this work, we determined in microcosms the effects of scenarios combining elevated temperature and atmospheric CO2 concentration on the germination and initial growth of the arborescent Amazonian aquatic macrophyte Montrichardia arborescens. Seeds were germinated, and seedlings produced were monitored over a 5-month period in four microcosms: Control: ambient temperature and CO2 level; Mild: Control + 1.5°C and + 200 ppm CO2; intermediate: control + 2.5°C and + 400 ppm CO2; Extreme: Control + 4.5°C and + 850 ppm of CO2. Rapid light response curves and Fv/Fm values taken in seedlings showed a decrease in electron transportation rate with CO2 and temperature elevation. Mild and Intermediate treatments stimulated biomass production; Extreme treatment and Control produced similar results. The severe climatic changes expected in the future may negatively influence carbon accumulation in M. arborescens. Since aquatic macrophytes in Amazonian wetlands and wetlands worldwide are key plant species, further studies are needed to predict their fate in a global change perspective. 相似文献
998.
Fernanda Pozzan Paim Kim Valenta Colin A. Chapman Adriano Pereira Paglia Helder Lima de Queiroz 《Primates; journal of primatology》2018,59(4):395-404
Integration between ecology and biogeography provides insights into how niche specialization affects the geographical distribution of species. Given that rivers are not effective barriers to dispersal in three parapatric species of squirrel monkeys (Saimiri vanzolinii, S. cassiquiarensis and S. macrodon) inhabiting floodplain forests of Central Amazonia, we tested whether forest structure and tree diversity may explain species differences in niche specialization and spatial segregation. We sampled 6617 trees of 326 species in three habitats (high várzea, low várzea and chavascal) used by three Saimiri species, and estimated tree species richness in each of them. For each tree, we measured variables known to influence habitat use in primates, such as crown area and presence of lianas, epiphytes and hemi-epiphytes. We used ANOVA to compare these variables and performed multivariate analyses (NMDS, ANOSIM and SIMPER) to evaluate dissimilarities in forest structure among each habitat inhabited by the three Saimiri species. We identified differences in the tree species richness, crown area and presence of lianas, epiphytes and hemi-epiphytes between the three habitats for all Saimiri species. NMDS demonstrated that areas of high and low várzeas occupied by S. vanzolinii were clearly separated from the other species. We also found that different plant species contributed to dissimilarity among Saimiri ranges. Our findings support the hypothesis that tree community structure may promote niche specialization and spatial segregation among primates. We discuss how these patterns could have been favored by historical changes in forest flood patterns, the evolutionary history of Saimiri spp., and past competition. 相似文献
999.
Colorimetric protein determination in microalgae (Chlorophyta): association of milling and SDS treatment for total protein extraction 下载免费PDF全文
Elba P. S. Bon Marcoaurelio A. Rodrigues Suely Pereira Freitas 《Journal of phycology》2018,54(4):577-580
The use of colorimetric methods for protein quantification in microalgae is hindered by their elevated amounts of membrane‐embedded intracellular proteins. In this work, the protein content of three species of microalgae was determined by the Lowry method after the cells were dried, ball‐milled, and treated with the detergent sodium dodecyl sulfate (SDS). Results demonstrated that the association of milling and SDS treatment resulted in a 3‐ to 7‐fold increase in protein quantification. Milling promoted microalgal disaggregation and cell wall disruption enabling access of the SDS detergent to the microalgal intracellular membrane proteins and their efficient solubilization and quantification. 相似文献
1000.
Lucas Roberto Pereira Gomes Márcia Souto Couri Claudio José Barros de Carvalho 《Revista Brasileira de Entomologia》2018,62(1):51-56
Drepanocnemis Stein (Diptera, Muscidae) is a small genus of flies that occur in high altitudes in the Colombian Andes, Ecuador, Peru and Bolivia. Herein we describe Drepanocnemis aurifronssp. nov. from Cuzco, Peru, which is found from high (2904 m) to lower altitudes (707 m). An updated phylogeny, key to species and map of species’ distributions are provided, together with images and illustrations of the male and the female terminalia. 相似文献