全文获取类型
收费全文 | 4826篇 |
免费 | 284篇 |
国内免费 | 2篇 |
专业分类
5112篇 |
出版年
2023年 | 56篇 |
2022年 | 78篇 |
2021年 | 151篇 |
2020年 | 107篇 |
2019年 | 146篇 |
2018年 | 178篇 |
2017年 | 135篇 |
2016年 | 187篇 |
2015年 | 299篇 |
2014年 | 297篇 |
2013年 | 365篇 |
2012年 | 391篇 |
2011年 | 371篇 |
2010年 | 211篇 |
2009年 | 209篇 |
2008年 | 240篇 |
2007年 | 228篇 |
2006年 | 236篇 |
2005年 | 167篇 |
2004年 | 140篇 |
2003年 | 136篇 |
2002年 | 114篇 |
2001年 | 89篇 |
2000年 | 85篇 |
1999年 | 60篇 |
1998年 | 40篇 |
1997年 | 24篇 |
1996年 | 21篇 |
1995年 | 19篇 |
1994年 | 17篇 |
1993年 | 13篇 |
1992年 | 29篇 |
1991年 | 24篇 |
1990年 | 15篇 |
1989年 | 23篇 |
1988年 | 12篇 |
1987年 | 16篇 |
1986年 | 20篇 |
1985年 | 16篇 |
1984年 | 12篇 |
1983年 | 10篇 |
1982年 | 10篇 |
1981年 | 14篇 |
1979年 | 15篇 |
1978年 | 9篇 |
1976年 | 6篇 |
1975年 | 9篇 |
1974年 | 10篇 |
1973年 | 7篇 |
1968年 | 5篇 |
排序方式: 共有5112条查询结果,搜索用时 15 毫秒
991.
André dos Santos Bragança Gil Climbiê Ferreira Hall Volker Bittrich Maria do Carmo Estanislau do Amaral 《Nordic Journal of Botany》2016,34(5):559-564
A new species of Neomarica from the Brazilian Atlantic Forest is described and illustrated. Neomarica sergipensis A. Gil & M.C.E. Amaral sp. nov. (Trimezieae, Iridoideae, Iridaceae) grows in restinga forests (forests on the coastal plains dominated by sandy soils) in the state of Sergipe, northeastern Brazil. The new species resembles Neomarica northiana, especially due to the white flowers with the basal third of the tepals yellow and covered by brown maculae, but differs by the inner tepals of with the center of the apical third is tinted violet to purple, yellow stigmatic crests with fimbriate to erose margins, and the endemic occurrence in Sergipe. 相似文献
992.
993.
994.
Nogueira Angélica Maria Ferreira Adésio da Silva Ferreira Marcia Flores 《Plant Molecular Biology Reporter》2016,34(1):249-256
Plant Molecular Biology Reporter - Myrtaceae has many fruit-bearing species of economic and ecological relevance worldwide, but with microsatellite molecular markers (simple sequence repeats, SSR)... 相似文献
995.
Bruno Ferreira Viana Flávio Oliveira Pires Allan Inoue Dominic Micklewright Tony Meireles Santos 《Applied psychophysiology and biofeedback》2016,41(1):1-7
This study examined the relationship between mood and rating of perceived exertion (RPE) during a simulated multiple-lap time trial (MLTT). Nineteen male cyclists performed a MLTT consisting of four 9.9 km laps, each lap with a gradient ranging from 0 to 10 %. Mood as measured by the Profile of Mood States Questionnaire (POMS) and perceived exertion as measured by the Borg CR100 scale (RPE) were obtained at the end of each lap. A categorical multiple regressive model, having median of POMS subscales as independent variables, was obtained to explain the variance in median RPE responses. Increases in POMS fatigue scores and decreases in POMS vigour scores were observed throughout the MLTT (P < 0.001). A linear increase in RPE during the MLTT was also observed (P < 0.001). POMS fatigue subscale scores accounted for 88 % of the variance in RPE during the MLTT (R2 = 0.88, P = 0.002), and no other POMS subscale improved the final predictive model. With the exception of fatigue these results suggest that most aspects of mood do not have a discernable effect on RPE during a MLTT. The rate of increase in RPE can predict the MLTT endpoint. 相似文献
996.
Heros Ribeiro Ferreira Pamela Gill Ferreira Jo?o Paulo Loures José Fernandes Filho Luiz Cláudio Fernandes Hudson Sousa Buck Wagner Ricardo Montor 《PloS one》2016,11(4)
The purpose of this investigation was to determine lipid peroxidation markers, physiological stress and muscle damage in elite kayakers in response to a maximum 4-min kayak ergometer test (KE test), and possible correlations with individual 1000m kayaking performances. The sample consisted of twenty-three adult male and nine adult female elite kayakers, with more than three years’ experience in international events, who voluntarily took part in this study. The subjects performed a 10-min warm-up, followed by a 2-min passive interval, before starting the test itself, which consisted of a maximum 4-min work paddling on an ergometer; right after the end of the test, an 8 ml blood sample was collected for analysis. 72 hours after the test, all athletes took part in an official race, when then it was possible to check their performance in the on site K1 1000m test (P1000m). The results showed that all lipoproteins and hematological parameters tested presented a significant difference (p≤0.05) after exercise for both genders. In addition, parameters related to muscle damage such as lactate dehydrogenase (LDH) and creatine kinase (CK) presented significant differences after stress. Uric acid presented an inverse correlation with the performance (r = -0.76), while CK presented a positive correlation (r = 0.46) with it. Based on these results, it was possible to verify muscle damage and the level of oxidative stress caused by indoor training with specific ergometers for speed kayaking, highlighting the importance of analyzing and getting to know the physiological responses to this type of training, in order to provide information to coaches and optimize athletic performance. 相似文献
997.
Flávia Gon?alves Míriam Santos de Moraes Lorraine Braga Ferreira Ana Cláudia Oliveira Carreira Patrícia Mayumi Kossugue Letícia Cristina Cidreira Boaro Ricardo Bentini Célia Regina da Silva Garcia Mari Cleide Sogayar Victor Elias Arana-Chavez Luiz Henrique Catalani 《PloS one》2016,11(3)
Regeneration of periodontal tissues requires a concerted effort to obtain consistent and predictable results in vivo. The aim of the present study was to test a new family of bioactive polymeric membranes in combination with stem cell therapy for periodontal regeneration. In particular, the novel polyester poly(isosorbide succinate-co-L-lactide) (PisPLLA) was compared with poly(L-lactide) (PLLA). Both polymers were combined with collagen (COL), hydroxyapatite (HA) and the growth factor bone morphogenetic protein-7 (BMP7), and their osteoinductive capacity was evaluated via in vitro and in vivo experiments. Membranes composed of PLLA/COL/HA or PisPLLA/COL/HA were able to promote periodontal regeneration and new bone formation in fenestration defects in rat jaws. According to quantitative real-time polymerase chain reaction (qRT-PCR) and Alizarin Red assays, better osteoconductive capacity and increased extracellular mineralization were observed for PLLA/COL/HA, whereas better osteoinductive properties were associated with PisPLLA/COL/HA. We concluded that membranes composed of either PisPLLA/COL/HA or PLLA/COL/HA present promising results in vitro as well as in vivo and that these materials could be potentially applied in periodontal regeneration. 相似文献
998.
Carla Foditsch Georgios Oikonomou Vinícius Silva Machado Marcela Luccas Bicalho Erika Korzune Ganda Svetlana Ferreira Lima Rodolfo Rossi Bruno Leonardo Ribeiro Arieli Kussler Rodrigo Carvalho Bicalho 《PloS one》2016,11(1)
The main objectives of this prospective cohort study were a) to describe lameness prevalence at drying off in large high producing New York State herds based on visual locomotion score (VLS) and identify potential cow and herd level risk factors, and b) to develop a model that will predict the probability of a cow developing claw horn disruption lesions (CHDL) in the subsequent lactation using cow level variables collected at drying off and/or available from farm management software. Data were collected from 23 large commercial dairy farms located in upstate New York. A total of 7,687 dry cows, that were less than 265 days in gestation, were enrolled in the study. Farms were visited between May 2012 and March 2013, and cows were assessed for body condition score (BCS) and VLS. Data on the CHDL events recorded by the farm employees were extracted from the Dairy-Comp 305 database, as well as information regarding the studied cows’ health events, milk production, and reproductive records throughout the previous and subsequent lactation period. Univariable analyses and mixed multivariable logistic regression models were used to analyse the data at the cow level. The overall average prevalence of lameness (VLS > 2) at drying off was 14%. Lactation group, previous CHDL, mature equivalent 305-d milk yield (ME305), season, BCS at drying off and sire PTA for strength were all significantly associated with lameness at the drying off (cow-level). Lameness at drying off was associated with CHDL incidence in the subsequent lactation, as well as lactation group, previous CHDL and ME305. These risk factors for CHDL in the subsequent lactation were included in our predictive model and adjusted predicted probabilities for CHDL were calculated for all studied cows. ROC analysis identified an optimum cut-off point for these probabilities and using this cut-off point we could predict CHDL incidence in the subsequent lactation with an overall specificity of 75% and sensitivity of 59%. Using this approach, we would have detected 33% of the studied population as being at risk, eventually identifying 59% of future CHDL cases. Our predictive model could help dairy producers focusing their efforts on CHDL reduction by implementing aggressive preventive measures for high risk cows. 相似文献
999.
Mechanism of escape of exoerythrocytic forms (EEF) of malaria parasites from the inhibitory effects of interferon-gamma 总被引:3,自引:0,他引:3
U Vergara A Ferreira H Schellekens V Nussenzweig 《Journal of immunology (Baltimore, Md. : 1950)》1987,138(12):4447-4449
We have studied the mechanism of inhibition by interferon-gamma (IFN-gamma) of the development of exoerythrocytic forms (EEF) of Plasmodium berghei in the livers of rats. At the time corresponding to the maximum development of EEF (44 hr after injection of sporozoites), the livers of the IFN-gamma-treated rats contained less parasite DNA as compared with controls. Twenty-four to 72 hr later, the livers of both groups of animals were free of parasites; that is, IFN-gamma treatment does not delay the development of the EEF. The decrease in parasite DNA observed in the IFN-gamma-treated rats was due to a diminution in the number, but not the size, of EEF. It appears, therefore, that treatment with the lymphokine either destroys the parasites or does not affect their replication. To study the mechanism of resistance to IFN-gamma of a small population of EEF, we subjected the parasites to four cycles of selection by IFN-gamma. The parasites from the "selected" and "nonselected" populations were equally susceptible to inhibition by IFN-gamma, indicating that the escape from IFN-gamma activity is not inherited. 相似文献
1000.
Two techniques for rapid diagnosis, immunofluorescence (IFAT) and enzyme immunoassay (EIA), have been compared with virus isolation in tissue culture for the detection of respiratory syncytial virus (RSV) in specimens of nasopharyngeal secretions. The specimens were obtained from children under five years of age suffering from acute respiratory illness, during a period of six months from January to June 1982. Of 471 specimens examined 54 (11.5%) were positive by virus isolation and 180 (38.2%) were positive by immunofluorescence. The bacterial contamination of inoculated tissue cultures unfortunately prevented the isolation of virus from many samples. Specimens from 216 children were tested to compare enzyme immunoassay and immunofluorescence. Of these 60 (27%) were positive by EIA and 121 (56%) were positive by IFAT. Our results suggest that the EIA technique although highly specific is rather insensitive. This may be because by the time these tests were done the original nasopharyngeal secretions were considerably diluted and contained more mucus fragments than the cell suspension used for IFAT. Of the three techniques, IFAT gives the best results although EIA may be useful where IFAT is not possible. 相似文献