全文获取类型
收费全文 | 75035篇 |
免费 | 4972篇 |
国内免费 | 10篇 |
专业分类
80017篇 |
出版年
2023年 | 522篇 |
2022年 | 643篇 |
2021年 | 1313篇 |
2020年 | 1065篇 |
2019年 | 1232篇 |
2018年 | 2258篇 |
2017年 | 2082篇 |
2016年 | 2745篇 |
2015年 | 3594篇 |
2014年 | 3729篇 |
2013年 | 4980篇 |
2012年 | 5796篇 |
2011年 | 5277篇 |
2010年 | 3420篇 |
2009年 | 2766篇 |
2008年 | 4044篇 |
2007年 | 3802篇 |
2006年 | 3640篇 |
2005年 | 3123篇 |
2004年 | 3025篇 |
2003年 | 2725篇 |
2002年 | 2510篇 |
2001年 | 1666篇 |
2000年 | 1615篇 |
1999年 | 1289篇 |
1998年 | 647篇 |
1997年 | 481篇 |
1996年 | 469篇 |
1995年 | 449篇 |
1994年 | 336篇 |
1993年 | 328篇 |
1992年 | 644篇 |
1991年 | 553篇 |
1990年 | 501篇 |
1989年 | 498篇 |
1988年 | 468篇 |
1987年 | 431篇 |
1986年 | 396篇 |
1985年 | 388篇 |
1984年 | 394篇 |
1983年 | 270篇 |
1982年 | 265篇 |
1981年 | 199篇 |
1980年 | 206篇 |
1979年 | 249篇 |
1978年 | 242篇 |
1975年 | 218篇 |
1974年 | 241篇 |
1973年 | 241篇 |
1972年 | 207篇 |
排序方式: 共有10000条查询结果,搜索用时 20 毫秒
991.
Linda H Münger Mar Garcia-Aloy Rosa Vázquez-Fresno Doreen Gille Albert Remus R Rosana Anna Passerini María-Trinidad Soria-Florido Grégory Pimentel Tanvir Sajed David S Wishart Cristina Andres Lacueva Guy Vergères Giulia Praticò 《Genes & nutrition》2018,13(1):26
Dairy and egg products constitute an important part of Western diets as they represent an excellent source of high-quality proteins, vitamins, minerals and fats. Dairy and egg products are highly diverse and their associations with a range of nutritional and health outcomes are therefore heterogeneous. Such associations are also often weak or debated due to the difficulty in establishing correct assessments of dietary intake. Therefore, in order to better characterize associations between the consumption of these foods and health outcomes, it is important to identify reliable biomarkers of their intake. Biomarkers of food intake (BFIs) provide an accurate measure of intake, which is independent of the memory and sincerity of the subjects as well as of their knowledge about the consumed foods. We have, therefore, conducted a systematic search of the scientific literature to evaluate the current status of potential BFIs for dairy products and BFIs for egg products commonly consumed in Europe. Strikingly, only a limited number of compounds have been reported as markers for the intake of these products and none of them have been sufficiently validated. A series of challenges hinders the identification and validation of BFI for dairy and egg products, in particular, the heterogeneous composition of these foods and the lack of specificity of the markers identified so far. Further studies are, therefore, necessary to validate these compounds and to discover new candidate BFIs. Untargeted metabolomic strategies may allow the identification of novel biomarkers, which, when taken separately or in combination, could be used to assess the intake of dairy and egg products. 相似文献
992.
Graça Soveral Catarina Prista Teresa F. Moura Maria C. Loureiro‐Dias 《Biology of the cell / under the auspices of the European Cell Biology Organization》2011,103(1):35-54
In yeast, the presence of orthodox aquaporins has been first recognized in Saccharomyces cerevisiae, in which two genes (AQY1 and AQY2) were shown to be related to mammal and plant water channels. The present review summarizes the putative orthodox aquaporin protein sequences found in available genomes of yeast and filamentous fungi. Among the 28 yeast genomes sequenced, most species present only one orthodox aquaporin, and no aquaporins were found in eight yeast species. Alignment of amino acid sequences reveals a very diverse group. Similarity values vary from 99% among species within the Saccharomyces genus to 34% between ScAqy1 and the aquaporin from Debaryomyces hansenii. All of the fungal aquaporins possess the known characteristic sequences, and residues involved in the water channel pore are highly conserved. Advances in the establishment of the structure are reviewed in relation to the mechanisms of selectivity, conductance and gating. In particular, the involvement of the protein cytosolic N‐terminus as a channel blocker preventing water flow is addressed. Methodologies used in the evaluation of aquaporin activity frequently involve the measurement of fast volume changes. Particular attention is paid to data analysis to obtain accurate membrane water permeability parameters. Although the presence of aquaporins clearly enhances membrane water permeability, the relevance of these ubiquitous water channels in yeast performance remains obscure. 相似文献
993.
Plants harbor diverse communities of fungi and other microorganisms. Fungi are known to occur both on plant surfaces (epiphytes)
and inside plant tissues (endophytes), but the two communities have rarely been compared. We compared epiphytic and endophytic
fungal communities associated with leaves of coffee (Coffea arabica) in Puerto Rico. We asked whether the dominant fungi are the same in both communities, whether endophyte and epiphyte communities
are equally diverse, and whether epiphytes and endophytes exhibit similar patterns of spatial heterogeneity among sites. Leaves
of naturalized coffee plants were collected from six sites in Puerto Rico. Epiphytic and endophytic fungi were isolated by
placing leaf pieces on potato dextrose agar without and with surface sterilization, respectively. A total of 821 colonies
were isolated and grouped into 131 morphospecies. The taxonomic affinities of the four most common nonsporulating fungi were
determined by sequencing the nuclear ribosomal internal transcribed spacer (ITS) region: two grouped with Xylaria and one each with Botryosphaeria and Guignardia. Of the most common genera, Pestalotia and Botryosphaeria were significantly more common as epiphytes; Colletotrichum, Xylaria, and Guignardia were significantly more common as endophytes. Suprisingly, more morphospecies occurred as endophytes than as epiphytes. Differences
among sites in number of fungi per plant were significant. Thus epiphytic and endophytic communities differed greatly on a
single leaf, despite living only millimeters apart, and both communities differed from site to site. Significant correlations
between occurrence of fungal morphospecies suggested that fungi may have positive or negative effects on their neighbors.
This is the first quantitative comparison of epiphytic and endophytic fungal floras in any plant, and the first to examine
endophytic fungi or epiphytic fungi in leaves of coffee, one of the world’s most valuable crops. 相似文献
994.
995.
F Barros P Domínguez G Velasco P S Lazo 《Biochemical and biophysical research communications》1986,134(2):827-834
Fluorescence quenching of the pH gradient sensitive dye acridine orange and that of the membrane potential sensitive dye Di-S-C3(5) have been studied in purified basolateral membrane vesicles obtained from rabbit small intestine. Basolateral membranes contain an electroneutral, carrier mediated, Na+/H+ exchange activity. They also appear to contain an electrogenic pathway for H+ movement. Based on the comparison of acridine orange fluorescence quenching in the presence of an outwardly directed Na+ gradient and in the presence of known K+ diffusion gradients it can be estimated that at least 50% of the observed proton fluxes are due to the activity of the exchanger. Acridine orange fluorescence recovery measurements have been used to assess the kinetic properties of the exchanger. 相似文献
996.
997.
The effects of vetrabutin chlorhydrate and oxytocin on stillbirth rate and asphyxia in swine 总被引:1,自引:0,他引:1
Mota-Rojas D Rosales AM Trujillo ME Orozco H Ramírez R Alonso-Spilsbury M 《Theriogenology》2005,64(9):1889-1897
Oxytocin and vetrabutin chlorhydrate (VC) are used to reduce the duration of farrowing in swine. The objective of the present study was to evaluate the use of these products on intra-partum stillbirth (IPS) rate and asphyxia. At the onset of parturition, sows (n=180) were allocated to receive 2 mL of saline (control group), oxytocin (40 IU i.m.) or 100mg of VC per 60 kg of body weight, with all treatments given i.m. Oytocin-treated sows had a higher number of IPS than the VC and Control groups (means, 1.2, 0.8 and 0.6, respectively; P<0.001), and the highest percentage of ruptured umbilical cords (76.0, 9.4 and 37.5%; P<0.003). There were differences among groups for duration of farrowing (means, 163.0, 211.2 and 306.9 min in the oxytocin, VC and control groups; P<0.001), interval between piglets (13.9, 19.2 and 28.1 min; P<0.001), and in IPS, the incidence of ruptured umbilical cords was 76.0, 9.4 and 37.5% (P<0.003) and absence of a fetal heartbeat was 53.3, 16.9 and 12.5% (P<0.05). Although oxytocin decreased both duration of farrowing and interval between piglets by approximately 50% relative to control sows, it resulted in a significantly higher rate of IPS, in association with a much higher incidence of ruptured umbilical cord and absence of a fetal heartbeat. Treatment with VC reduced farrowing duration by approximately 1.5h, with an IPS rate that was not significantly different from controls but significantly lower than that of oxytocin-treated sows. 相似文献
998.
Activation of interferon regulatory factor 3 is inhibited by the influenza A virus NS1 protein 总被引:14,自引:0,他引:14 下载免费PDF全文
Talon J Horvath CM Polley R Basler CF Muster T Palese P García-Sastre A 《Journal of virology》2000,74(17):7989-7996
We present a novel mechanism by which viruses may inhibit the alpha/beta interferon (IFN-alpha/beta) cascade. The double-stranded RNA (dsRNA) binding protein NS1 of influenza virus is shown to prevent the potent antiviral interferon response by inhibiting the activation of interferon regulatory factor 3 (IRF-3), a key regulator of IFN-alpha/beta gene expression. IRF-3 activation and, as a consequence, IFN-beta mRNA induction are inhibited in wild-type (PR8) influenza virus-infected cells but not in cells infected with an isogenic virus lacking the NS1 gene (delNS1 virus). Furthermore, NS1 is shown to be a general inhibitor of the interferon signaling pathway. Inhibition of IRF-3 activation can be achieved by the expression of wild-type NS1 in trans, not only in delNS1 virus-infected cells but also in cells infected with a heterologous RNA virus (Newcastle disease virus). We propose that inhibition of IRF-3 activation by a dsRNA binding protein significantly contributes to the virulence of influenza A viruses and possibly to that of other viruses. 相似文献
999.
1000.
SSS Sarma Lynda Beladjal S Nandini Gerardo Cerón-Martínez Karina Tavera-Briseño 《Aquatic biosystems》2005,1(1):1-7