全文获取类型
收费全文 | 1510篇 |
免费 | 142篇 |
国内免费 | 2篇 |
专业分类
1654篇 |
出版年
2023年 | 7篇 |
2022年 | 15篇 |
2021年 | 58篇 |
2020年 | 16篇 |
2019年 | 28篇 |
2018年 | 27篇 |
2017年 | 40篇 |
2016年 | 51篇 |
2015年 | 72篇 |
2014年 | 57篇 |
2013年 | 102篇 |
2012年 | 109篇 |
2011年 | 117篇 |
2010年 | 71篇 |
2009年 | 55篇 |
2008年 | 94篇 |
2007年 | 79篇 |
2006年 | 71篇 |
2005年 | 64篇 |
2004年 | 49篇 |
2003年 | 58篇 |
2002年 | 40篇 |
2001年 | 19篇 |
2000年 | 21篇 |
1999年 | 29篇 |
1998年 | 12篇 |
1997年 | 14篇 |
1996年 | 15篇 |
1995年 | 9篇 |
1994年 | 7篇 |
1993年 | 15篇 |
1992年 | 13篇 |
1991年 | 13篇 |
1990年 | 12篇 |
1989年 | 15篇 |
1988年 | 15篇 |
1987年 | 10篇 |
1986年 | 15篇 |
1985年 | 10篇 |
1984年 | 7篇 |
1983年 | 10篇 |
1982年 | 13篇 |
1981年 | 9篇 |
1979年 | 10篇 |
1978年 | 9篇 |
1977年 | 8篇 |
1976年 | 10篇 |
1974年 | 6篇 |
1973年 | 6篇 |
1968年 | 8篇 |
排序方式: 共有1654条查询结果,搜索用时 0 毫秒
121.
Una nueva especie de <Emphasis Type="Italic">Pseudomiltemia</Emphasis> (Rubiaceae) de Chiapas,México
Ruben Martínez-Camilo Nayely Martínez-Melendez Miguel A. Perez-Farrera David H. Lorence 《Brittonia》2011,63(2):197-202
Pseudomiltemia davidsonii is described and illustrated as a new endemic species from the Sierra Madre of Chiapas, Mexico. It is a shrub or small tree characterized by having flowers axillary and solitary or in monochasia and with large yellow corollas. Pseudomiltemia davidsonii differs from P. filisepala, the only other species in this genus, by its opposite leaves with longer petioles, inflorescences with shorter peduncles 5–13 mm long, smaller bracts, longer pedicels 6–15 mm long, and narrower fruits 3.5–4.5 mm in diameter. 相似文献
122.
Ruben Leal Mubarqui Rene Cano Perez Roberto Angulo Kladt Jose Luis Zavala Lopez Andrew Parker Momar Talla Seck Baba Sall Jérémy Bouyer 《PloS one》2014,9(7)
Background
Beyond insecticides, alternative methods to control insect pests for agriculture and vectors of diseases are needed. Management strategies involving the mass-release of living control agents have been developed, including genetic control with sterile insects and biological control with parasitoids, for which aerial release of insects is often required. Aerial release in genetic control programmes often involves the use of chilled sterile insects, which can improve dispersal, survival and competitiveness of sterile males. Currently available means of aerially releasing chilled fruit flies are however insufficiently precise to ensure homogeneous distribution at low release rates and no device is available for tsetse.Methodology/Principal Findings
Here we present the smart aerial release machine, a new design by the Mubarqui Company, based on the use of vibrating conveyors. The machine is controlled through Bluetooth by a tablet with Android Operating System including a completely automatic guidance and navigation system (MaxNav software). The tablet is also connected to an online relational database facilitating the preparation of flight schedules and automatic storage of flight reports. The new machine was compared with a conveyor release machine in Mexico using two fruit flies species (Anastrepha ludens and Ceratitis capitata) and we obtained better dispersal homogeneity (% of positive traps, p<0.001) for both species and better recapture rates for Anastrepha ludens (p<0.001), especially at low release densities (<1500 per ha). We also demonstrated that the machine can replace paper boxes for aerial release of tsetse in Senegal.Conclusions/Significance
This technology limits damages to insects and allows a large range of release rates from 10 flies/km2 for tsetse flies up to 600 000 flies/km2 for fruit flies. The potential of this machine to release other species like mosquitoes is discussed. Plans and operating of the machine are provided to allow its use worldwide. 相似文献123.
Markus Möst Adam Petrusek Ruben Sommaruga Petr Jan Juračka Miroslav Slusarczyk Marina Manca Piet Spaak 《Hydrobiologia》2013,715(1):51-62
The occurrence of members of the highly diverse Daphnia longispina complex in Southern and Central Asian high-mountain lakes has been recognized for more than a century. Until now, however, no molecular data have been available for these populations inhabiting the “Roof of the World.” Here, we present the first identification for D. gr. longispina from that region based on a molecular phylogeny. Our findings show that alpine lakes in the Pamir and Himalaya mountains host populations of widespread species of the complex, for which these are the highest known localities. A spineless morph from the Himalaya region, previously labeled as D. longispina var. aspina, was clustering tightly with D. dentifera, while a population from the Pamir mountain range was grouped with D. longispina. In addition, we analyzed ecological data available for lakes in the Khumbu region (Himalaya) to investigate ecological preferences of non-pigmented D. gr. longispina. The identified factors can at least partly be related to avoidance of high UV conditions by this species. We conclude that the widespread species D. dentifera and D. longispina also colonized the Asian high-mountain lakes, and identify the need for further research to trace the possible effect of rapid environmental changes in this region on the diversity and ecology of high-altitude Daphnia populations. 相似文献
124.
Benedetta Artegiani Lisa van Voorthuijsen Rik G.H. Lindeboom Daniëlle Seinstra Inha Heo Pablo Tapia Carmen López-Iglesias Daniel Postrach Talya Dayton Rurika Oka Huili Hu Ruben van Boxtel Johan H. van Es Johan Offerhaus Peter J. Peters Jacco van Rheenen Michiel Vermeulen Hans Clevers 《Cell Stem Cell》2019,24(6):927-943.e6
125.
Daniel Ajona Cristina Razquin Maria Dolores Pastor Maria Jose Pajares Javier Garcia Felipe Cardenal Michael Fleischhacker Maria Dolores Lozano Javier J. Zulueta Bernd Schmidt Ernest Nadal Luis Paz-Ares Luis M. Montuenga Ruben Pio 《PloS one》2015,10(3)
Molecular markers in bronchial fluids may contribute to the diagnosis of lung cancer. We previously observed a significant increase of C4d-containing complement degradation fragments in bronchoalveolar lavage (BAL) supernatants from lung cancer patients in a cohort of 50 cases and 22 controls (CUN cohort). The present study was designed to determine the diagnostic performance of these complement fragments (hereinafter jointly referred as C4d) in bronchial fluids. C4d levels were determined in BAL supernatants from two independent cohorts: the CU cohort (25 cases and 26 controls) and the HUVR cohort (60 cases and 98 controls). A series of spontaneous sputum samples from 68 patients with lung cancer and 10 controls was also used (LCCCIO cohort). Total protein content, complement C4, complement C5a, and CYFRA 21-1 were also measured in all cohorts. C4d levels were significantly increased in BAL samples from lung cancer patients. The area under the ROC curve was 0.82 (95%CI = 0.71–0.94) and 0.67 (95%CI = 0.58–0.76) for the CU and HUVR cohorts, respectively. In addition, unlike the other markers, C4d levels in BAL samples were highly consistent across the CUN, CU and HUVR cohorts. Interestingly, C4d test markedly increased the sensitivity of bronchoscopy in the two cohorts in which cytological data were available (CUN and HUVR cohorts). Finally, in the LCCCIO cohort, C4d levels were higher in sputum supernatants from patients with lung cancer (area under the ROC curve: 0.7; 95%CI = 0.56–0.83). In conclusion, C4d is consistently elevated in bronchial fluids from lung cancer patients and may be used to improve the diagnosis of the disease. 相似文献
126.
127.
Endothelin-1 (ET-1) and bradykinin (BK) are endogenous peptides that signal through Gαq/11-protein coupled receptors (GPCRs) to produce nociceptor sensitization and pain. Both peptides activate phospholipase C to stimulate Ca2+ accumulation, diacylglycerol production, and protein kinase C activation and are rapidly desensitized via a G-protein receptor kinase 2-dependent mechanism. However, ET-1 produces a greater response and longer lasting nocifensive behavior than BK in multiple models, indicating a potentially divergent signaling mechanism in primary afferent sensory neurons. Using cultured sensory neurons, we demonstrate significant differences in both Ca2+ influx and Ca2+ release from intracellular stores following ET-1 and BK treatments. As intracellular store depletion may contribute to the regulation of other signaling cascades downstream of GPCRs, we concentrated our investigation on store-operated Ca2+ channels. Using pharmacological approaches, we identified transient receptor potential canonical channel 3 (TRPC3) as a dominant contributor to Ca2+ influx subsequent to ET-1 treatment. On the other hand, BK treatment stimulated Orai1 activation, with only minor input from TRPC3. Taken together, data presented here suggest that ET-1 signaling targets TRPC3, generating a prolonged Ca2+ signal that perpetuates nocifensive responses. In contrast, Orai1 dominates as the downstream target of BK receptor activation and results in transient intracellular Ca2+ increases and abridged nocifensive responses. 相似文献
128.
Ruben D. Arroyo-Olarte Jos F. Brouwers Arunakar Kuchipudi J. Bernd Helms Aindrila Biswas Ildiko R. Dunay Richard Lucius Nishith Gupta 《PLoS biology》2015,13(11)
The major membrane phospholipid classes, described thus far, include phosphatidylcholine (PtdCho), phosphatidylethanolamine (PtdEtn), phosphatidylserine (PtdSer), and phosphatidylinositol (PtdIns). Here, we demonstrate the natural occurrence and genetic origin of an exclusive and rather abundant lipid, phosphatidylthreonine (PtdThr), in a common eukaryotic model parasite, Toxoplasma gondii. The parasite expresses a novel enzyme PtdThr synthase (TgPTS) to produce this lipid in its endoplasmic reticulum. Genetic disruption of TgPTS abrogates de novo synthesis of PtdThr and impairs the lytic cycle and virulence of T. gondii. The observed phenotype is caused by a reduced gliding motility, which blights the parasite egress and ensuing host cell invasion. Notably, the PTS mutant can prevent acute as well as yet-incurable chronic toxoplasmosis in a mouse model, which endorses its potential clinical utility as a metabolically attenuated vaccine. Together, the work also illustrates the functional speciation of two evolutionarily related membrane phospholipids, i.e., PtdThr and PtdSer. 相似文献
129.
Marc Guaita Umberto Melia Montserrat Vallverdú Pere Caminal Isabel Vilaseca Josep M. Montserrat Carles Gaig Manel Salamero Joan Santamaria 《PloS one》2015,10(4)
Aim
The present study aimed to analyse the autonomic nervous system activity using heart rate variability (HRV) to detect sleep disordered breathing (SDB) patients with and without excessive daytime sleepiness (EDS) before sleep onset.Methods
Two groups of 20 patients with different levels of daytime sleepiness -sleepy group, SG; alert group, AG- were selected consecutively from a Maintenance of Wakefulness Test (MWT) and Multiple Sleep Latency Test (MSLT) research protocol. The first waking 3-min window of RR signal at the beginning of each nap test was considered for the analysis. HRV was measured with traditional linear measures and with time-frequency representations. Non-linear measures -correntropy, CORR; auto-mutual-information function, AMIF- were used to describe the regularity of the RR rhythm. Statistical analysis was performed with non-parametric tests.Results
Non-linear dynamic of the RR rhythm was more regular in the SG than in the AG during the first wakefulness period of MSLT, but not during MWT. AMIF (in high-frequency and in Total band) and CORR (in Total band) yielded sensitivity > 70%, specificity >75% and an area under ROC curve > 0.80 in classifying SG and AG patients.Conclusion
The regularity of the RR rhythm measured at the beginning of the MSLT could be used to detect SDB patients with and without EDS before the appearance of sleep onset. 相似文献130.