全文获取类型
收费全文 | 6409篇 |
免费 | 471篇 |
国内免费 | 1篇 |
出版年
2023年 | 19篇 |
2022年 | 66篇 |
2021年 | 131篇 |
2020年 | 79篇 |
2019年 | 139篇 |
2018年 | 181篇 |
2017年 | 144篇 |
2016年 | 224篇 |
2015年 | 288篇 |
2014年 | 381篇 |
2013年 | 454篇 |
2012年 | 496篇 |
2011年 | 468篇 |
2010年 | 311篇 |
2009年 | 252篇 |
2008年 | 381篇 |
2007年 | 350篇 |
2006年 | 292篇 |
2005年 | 295篇 |
2004年 | 302篇 |
2003年 | 269篇 |
2002年 | 242篇 |
2001年 | 103篇 |
2000年 | 79篇 |
1999年 | 74篇 |
1998年 | 53篇 |
1997年 | 40篇 |
1996年 | 58篇 |
1995年 | 32篇 |
1994年 | 33篇 |
1993年 | 33篇 |
1992年 | 57篇 |
1991年 | 48篇 |
1990年 | 43篇 |
1989年 | 34篇 |
1988年 | 39篇 |
1987年 | 29篇 |
1986年 | 28篇 |
1985年 | 31篇 |
1984年 | 19篇 |
1983年 | 31篇 |
1982年 | 26篇 |
1981年 | 24篇 |
1980年 | 23篇 |
1979年 | 18篇 |
1977年 | 18篇 |
1976年 | 15篇 |
1975年 | 19篇 |
1974年 | 17篇 |
1972年 | 16篇 |
排序方式: 共有6881条查询结果,搜索用时 203 毫秒
171.
Coral Díez Pérez Rosa Rodríguez Ferro Manuel Penín Álvarez 《Endocrinología y nutrición》2013,60(9):513-516
The American Diabetes Association issues annually its recommendations for diabetes mellitus screening. Although there is a high proportion of people with undiagnosed diabetes in the general population, it is suspected that many of these screening tests could be needless.An analysis was made of the number of venous blood glucose measurements that did not meet the American Diabetes Association requirements performed in 150 people seen in primary care.On average, an unnecessary venous blood glucose measurement is performed every 15 months. The number is significantly higher in people over 45 years of age, and also in women as compared to men (although with a p value slighty higher than 0.05). 相似文献
172.
Candy Kumps Annelies Fieuw Pieter Mestdagh Bj?rn Menten Steve Lefever Filip Pattyn Sara De Brouwer Tom Sante Johannes Hubertus Schulte Alexander Schramm Nadine Van Roy Tom Van Maerken Rosa Noguera Valérie Combaret Christine Devalck Frank Westermann Geneviève Laureys Angelika Eggert Jo Vandesompele Katleen De Preter Frank Speleman 《PloS one》2013,8(1)
Neuroblastoma is an embryonic tumor arising from immature sympathetic nervous system cells. Recurrent genomic alterations include MYCN and ALK amplification as well as recurrent patterns of gains and losses of whole or large partial chromosome segments. A recent whole genome sequencing effort yielded no frequently recurring mutations in genes other than those affecting ALK. However, the study further stresses the importance of DNA copy number alterations in this disease, in particular for genes implicated in neuritogenesis. Here we provide additional evidence for the importance of focal DNA copy number gains and losses, which are predominantly observed in MYCN amplified tumors. A focal 5 kb gain encompassing the MYCN regulated miR-17∼92 cluster as sole gene was detected in a neuroblastoma cell line and further analyses of the array CGH data set demonstrated enrichment for other MYCN target genes in focal gains and amplifications. Next we applied an integrated genomics analysis to prioritize MYCN down regulated genes mediated by MYCN driven miRNAs within regions of focal heterozygous or homozygous deletion. We identified RGS5, a negative regulator of G-protein signaling implicated in vascular normalization, invasion and metastasis, targeted by a focal homozygous deletion, as a new MYCN target gene, down regulated through MYCN activated miRNAs. In addition, we expand the miR-17∼92 regulatory network controlling TGFß signaling in neuroblastoma with the ring finger protein 11 encoding gene RNF11, which was previously shown to be targeted by the miR-17∼92 member miR-19b. Taken together, our data indicate that focal DNA copy number imbalances in neuroblastoma (1) target genes that are implicated in MYCN signaling, possibly selected to reinforce MYCN oncogene addiction and (2) serve as a resource for identifying new molecular targets for treatment. 相似文献
173.
Giovanna Poce Robert H. Bates Salvatore Alfonso Martina Cocozza Giulio Cesare Porretta Lluís Ballell Joaquin Rullas Fátima Ortega Alessandro De Logu Emanuela Agus Valentina La Rosa Maria Rosalia Pasca Edda De Rossi Baojie Wae Scott G. Franzblau Fabrizio Manetti Maurizio Botta Mariangela Biava 《PloS one》2013,8(2)
1,5-Diphenyl pyrroles were previously identified as a class of compounds endowed with high in vitro efficacy against M. tuberculosis. To improve the physical chemical properties and drug-like parameters of this class of compounds, a medicinal chemistry effort was undertaken. By selecting the optimal substitution patterns for the phenyl rings at N1 and C5 and by replacing the thiomorpholine moiety with a morpholine one, a new series of compounds was produced. The replacement of the sulfur with oxygen gave compounds with lower lipophilicity and improved in
vitro microsomal stability. Moreover, since the parent compound of this family has been shown to target MmpL3, mycobacterial mutants resistant to two compounds have been isolated and characterized by sequencing the mmpL3 gene; all the mutants showed point mutations in this gene. The best compound identified to date was progressed to dose-response studies in an acute murine TB infection model. The resulting ED99 of 49 mg/Kg is within the range of commonly employed tuberculosis drugs, demonstrating the potential of this chemical series. The in vitro and in vivo target validation evidence presented here adds further weight to MmpL3 as a druggable target of interest for anti-tubercular drug discovery. 相似文献
174.
Geoffrey D. Coxon Derek Craig Rosa Milagros Corrales Emilie Vialla Laila Gannoun-Zaki Laurent Kremer 《PloS one》2013,8(1)
Defining the pharmacological target(s) of currently used drugs and developing new analogues with greater potency are both important aspects of the search for agents that are effective against drug-sensitive and drug-resistant Mycobacterium tuberculosis. Thiacetazone (TAC) is an anti-tubercular drug that was formerly used in conjunction with isoniazid, but removed from the antitubercular chemotherapeutic arsenal due to toxic side effects. However, several recent studies have linked the mechanisms of action of TAC to mycolic acid metabolism and TAC-derived analogues have shown increased potency against M. tuberculosis. To obtain new insights into the molecular mechanisms of TAC resistance, we isolated and analyzed 10 mutants of M. tuberculosis that were highly resistant to TAC. One strain was found to be mutated in the methyltransferase MmaA4 at Gly101, consistent with its lack of oxygenated mycolic acids. All remaining strains harbored missense mutations in either HadA (at Cys61) or HadC (at Val85, Lys157 or Thr123), which are components of the β-hydroxyacyl-ACP dehydratase complex that participates in the mycolic acid elongation step. Separately, a library of 31 new TAC analogues was synthesized and evaluated against M. tuberculosis. Two of these compounds, 15 and 16, exhibited minimal inhibitory concentrations 10-fold lower than the parental molecule, and inhibited mycolic acid biosynthesis in a dose-dependent manner. Moreover, overexpression of HadAB HadBC or HadABC in M. tuberculosis led to high level resistance to these compounds, demonstrating that their mode of action is similar to that of TAC. In summary, this study uncovered new mutations associated with TAC resistance and also demonstrated that simple structural optimization of the TAC scaffold was possible and may lead to a new generation of TAC-derived drug candidates for the potential treatment of tuberculosis as mycolic acid inhibitors. 相似文献
175.
Rosa Anna Iorio Stefano Del Duca Elisabetta Calamelli Chiara Pula Magda Lodolini Fortuna Scamardella Andrea Pession Giampaolo Ricci 《PloS one》2013,8(1)
Allergy to citrus fruits is often associated with pollinosis and sensitization to other plants due to a phenomenon of cross-reactivity. The aims of the present study were to highlight the cross-reactivity among citrus and the major allergenic pollens/fruits, throughout clinical and molecular investigations, and to evaluate the sensitization frequency to citrus fruits in a population of children and adults with pollinosis. We found a relevant percentage of sensitisation (39%) to citrus fruits in the patients recruited and in all of them the IgE-mediated mechanism has been confirmed by the positive response to the prick-to-prick test. RT-PCR experiments showed the expression of Cit s 1, Cit s 3 and a profilin isoform, already described in apple, also in Citrus clementine pollen. Data of multiple sequence alignments demonstrated that Citrus allergens shared high percentage identity values with other clinically relevant species (i.e. Triticum aestivum, Malus domestica), confirming the possible cross-allergenicity citrus/grasses and citrus/apple. Finally, a novelty of the present work has been the expression of two phospholipaseA2 isoforms (PLA2 α and β) in Citrus as well as in Triticum pollens; being PLA2 able to generate pro-inflammatory factors, this enzyme could participate in the activation of the allergenic inflammatory cascade. 相似文献
176.
Monica Martinez-Haro Mark A. Taggart Hugues Lefranc Rosa C. Martín-Doimeadiós Andy J. Green Rafael Mateo 《PloS one》2013,8(2)
Lead exposure in waterfowl was studied using noninvasive fecal sampling in the Guadalquivir Marshes in Spain, an area affected by the 1998 Aznalcóllar mine disaster. Feces of greylag geese (Anser anser, n = 191) and purple gallinule (Porphyrio porphyrio, n = 91) were collected from three different impacted sites (Entremuros, Caracoles and Cerro de los Ánsares) during the winters of 2004 to 2008. Lead and aluminium (an indicator of sediment ingestion) and Pb isotope signatures (to discriminate between sources of Pb exposure) were analyzed in freeze-dried, acid digested samples. The concentrations of fecal porphyrins and biliverdin were determined as noninvasive biomarkers to study Pb exposure effects. Results showed a decrease in Pb exposure over time in wintering greylag geese. In contrast, for purple gallinule resident in the Entremuros a clear trend was not evident. For both species, sediment ingestion appeared to be the main source of exposure to Pb. In the Entremuros, some samples from purple gallinule were detected with higher Pb levels than expected for simple soil ingestion, and these had Pb isotopic profiles compatible with mining sludge or Pb shot. Whilst fecal Pb isotopic profiles were effective in differentiating between samples from sites with different levels and sources of pollution, the combined use of element ratios (such as Pb/Al) and other non-traditional stable isotope signatures may also prove worthwhile. Overall, the fecal Pb levels detected were below those described in feces for waterfowl from other uncontaminated areas(<10 µg/g d.w.). Despite this, for both species fecal Pb levels were positively correlated with porphyrin excretion, and for purple gallinule, with the coproporphyrin III/I ratio, suggesting some subtle effects on heme synthesis in birds. Ten years after the mine spill, Pb contamination in birds by this pollution source was still detectable and subtlethal effects may persist. 相似文献
177.
Cristina Virto Carlos A. Zárate Miguel López-Ferber Rosa Murillo Primitivo Caballero Trevor Williams 《PloS one》2013,8(8)
With the development of sensitive molecular techniques for detection of low levels of asymptomatic pathogens, it becoming clear that vertical transmission is a common feature of some insect pathogenic viruses, and likely to be essential to virus survival when opportunities for horizontal transmission are unfavorable. Vertical transmission of Spodoptera exigua multiple nucleopolyhedrovirus (SeMNPV) is common in natural populations of S. exigua. To assess whether gender affected transgenerational virus transmission, four mating group treatments were performed using healthy and sublethally infected insects: i) healthy males (H♂)×healthy females (H♀); ii) infected males (I♂)×healthy females (H♀); iii) healthy males (H♂)×infected females (I♀) and iv) infected males (I♂)×infected females (I♀). Experimental adults and their offspring were analyzed by qPCR to determine the prevalence of infection. Both males and females were able to transmit the infection to the next generation, although female-mediated transmission resulted in a higher prevalence of infected offspring. Male-mediated venereal transmission was half as efficient as maternally-mediated transmission. Egg surface decontamination studies indicated that the main route of transmission is likely transovarial rather than transovum. Both male and female offspring were infected by their parents in similar proportions. Incorporating vertically-transmitted genotypes into virus-based insecticides could provide moderate levels of transgenerational pest control, thereby extending the periods between bioinsecticide applications. 相似文献
178.
Jordi Gamir Rocío Torres-Vera Carlos Rial Estefanía Berrio Pedro M. de Souza Campos Rosa M. Varela Francisco A. Macías María J. Pozo Victor Flors Juan A. López-Ráez 《Plant, cell & environment》2020,43(7):1655-1668
Strigolactones (SLs) are important ex-planta signalling molecules in the rhizosphere, promoting the association with beneficial microorganisms, but also affecting plant interactions with harmful organisms. They are also plant hormones in-planta, acting as modulators of plant responses under nutrient-deficient conditions, mainly phosphate (Pi) starvation. In the present work, we investigate the potential role of SLs as regulators of early Pi starvation signalling in plants. A short-term pulse of the synthetic SL analogue 2′-epi-GR24 promoted SL accumulation and the expression of Pi starvation markers in tomato and wheat under Pi deprivation. 2′-epi-GR24 application also increased SL production and the expression of Pi starvation markers under normal Pi conditions, being its effect dependent on the endogenous SL levels. Remarkably, 2′-epi-GR24 also impacted the root metabolic profile under these conditions, promoting the levels of metabolites associated to plant responses to Pi limitation, thus partially mimicking the pattern observed under Pi deprivation. The results suggest an endogenous role for SLs as Pi starvation signals. In agreement with this idea, SL-deficient plants were less sensitive to this stress. Based on the results, we propose that SLs may act as early modulators of plant responses to P starvation. 相似文献
179.
Marcelo F. G. Brito Ayda V. Alcântara Daniela C. O. Rosa Bruno E. Soares 《Zeitschrift fur angewandte Ichthyologie》2020,36(5):753-756
Length-weight relationships (LWR) and length-length relationships (LLR) were provided for eight species inhabiting Northeastern Brazilian coast. Nine transects (5, 15, 30 m deep) between Sergipe and Vaza-Barris rivers mouths were sampled monthly from September 2013 to August 2014. Each sampling was carried out using a shrimp boat equipped with double ring nets (4 m mouth wide, 10 m long and 20 mm mesh size) and trawlings were performed for 15 min. Fishes were measured (standard and total length, 0.1 cm) and weighted (total weight, 0.01 g). We provide LWR and LLR coefficients for these eight species, including new maximum TL for five species, and discuss the similarity of these results with estimates available in Fishbase. 相似文献
180.