全文获取类型
收费全文 | 103460篇 |
免费 | 1180篇 |
国内免费 | 812篇 |
出版年
2022年 | 78篇 |
2021年 | 162篇 |
2020年 | 119篇 |
2019年 | 159篇 |
2018年 | 12003篇 |
2017年 | 10813篇 |
2016年 | 7691篇 |
2015年 | 1018篇 |
2014年 | 718篇 |
2013年 | 932篇 |
2012年 | 4913篇 |
2011年 | 13436篇 |
2010年 | 12409篇 |
2009年 | 8623篇 |
2008年 | 10321篇 |
2007年 | 11926篇 |
2006年 | 800篇 |
2005年 | 1058篇 |
2004年 | 1512篇 |
2003年 | 1570篇 |
2002年 | 1404篇 |
2001年 | 386篇 |
2000年 | 255篇 |
1999年 | 165篇 |
1998年 | 166篇 |
1997年 | 169篇 |
1996年 | 141篇 |
1995年 | 115篇 |
1994年 | 110篇 |
1993年 | 135篇 |
1992年 | 134篇 |
1991年 | 121篇 |
1990年 | 78篇 |
1989年 | 75篇 |
1988年 | 72篇 |
1987年 | 63篇 |
1986年 | 41篇 |
1985年 | 56篇 |
1984年 | 78篇 |
1983年 | 77篇 |
1982年 | 98篇 |
1981年 | 84篇 |
1980年 | 66篇 |
1979年 | 57篇 |
1978年 | 53篇 |
1977年 | 51篇 |
1976年 | 51篇 |
1973年 | 40篇 |
1972年 | 259篇 |
1971年 | 289篇 |
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
761.
Ce catalogue des Vesperidae et Cerambycidae de la faune de France est fondé sur une vaste étude bibliographique et sur les observations des auteurs ainsi que celles, vérifiées, de nombreux amateurs. Les nombreuses modifications montrent la nécessité de la révision du dernier ouvrage de référence (Villiers 1978). Le bilan faunistique des recherches permet de dresser une liste de 251 taxa représentant 242 espèces actuellement présentes en France continentale et en Corse. Cette liste est sujette à de perpétuelles modifications liées aux fluctuations de populations, aux introductions et aux activités de recherche de nombreux amateurs. Ce travail de synthèse systématique, taxinomique et faunistique est une première étape pour la réalisation d’un atlas des Vesperidae et Cerambycidae de France et de Corse. 相似文献
762.
Fabien Cormier Sébastien Faure Pierre Dubreuil Emmanuel Heumez Katia Beauchêne Stéphane Lafarge Sébastien Praud Jacques Le Gouis 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2013,126(12):3035-3048
Key message
By comparing 195 varieties in eight trials, this study assesses nitrogen use efficiency improvement in high and low nitrogen conditions in European winter wheat over the last 25 years.Abstract
In a context where European agriculture practices have to deal with environmental concerns and nitrogen (N) fertiliser cost, nitrogen use efficiency (NUE) has to be improved. This study assessed genetic progress in winter wheat (Triticum aestivum L.) NUE. Two hundred and twenty-five European elite varieties were tested in four environments under two levels of N. Global genetic progress was assessed on additive genetic values and on genotype × N interaction, covering 25 years of European breeding. To avoid sampling bias, quality, precocity and plant height were added as covariates in the analyses when needed. Genotype × environment interactions were highly significant for all the traits studied to such an extent that no additive genetic effect was detected on N uptake. Genotype × N interactions were significant for yield, grain protein content (GPC), N concentration in straw, N utilisation, and NUE. Grain yield improvement (+0.45 % year?1) was independent of the N treatment. GPC was stable, thus grain nitrogen yield was improved (+0.39 % year?1). Genetic progress on N harvest index (+0.12 % year?1) and on N concentration in straw (?0.52 % year?1) possibly revealed improvement in N remobilisation. There has been an improvement of NUE additive genetic value (+0.33 % year?1) linked to better N utilisation (+0.20 % year?1). Improved yield stability was detected as a significant improvement of NUE in low compared to high N conditions. The application of these results to breeding programs is discussed. 相似文献763.
764.
Pierre Le Maréchal Paulette Decottignies Christophe H. Marchand Jeril Degrouard Danièle Jaillard Thierry Dulermo Marine Froissard Aleksey Smirnov Violaine Chapuis Marie-Joelle Virolle 《Applied and environmental microbiology》2013,79(19):5907-5917
Streptomyces lividans TK24 is a strain that naturally produces antibiotics at low levels, but dramatic overproduction of antibiotics occurs upon interruption of the ppk gene. However, the role of the Ppk enzyme in relation to the regulation of antibiotic biosynthesis remains poorly understood. In order to gain a better understanding of the phenotype of the ppk mutant, the proteomes of the wild-type (wt) and ppk mutant strains, grown for 96 h on R2YE medium limited in phosphate, were analyzed. Intracellular proteins were separated on two-dimensional (2D) gels, spots were quantified, and those showing a 3-fold variation or more were identified by mass spectrometry. The expression of 12 proteins increased and that of 29 decreased in the ppk mutant strain. Our results suggested that storage lipid degradation rather than hexose catabolism was taking place in the mutant. In order to validate this hypothesis, the triacylglycerol contents of the wt and ppk mutant strains of S. lividans as well as that of Streptomyces coelicolor M145, a strain that produces antibiotics at high levels and is closely related to S. lividans, were assessed using electron microscopy and thin-layer chromatography. These studies highlighted the large difference in triacylglycerol contents of the three strains and confirmed the hypothetical link between storage lipid metabolism and antibiotic biosynthesis in Streptomyces. 相似文献
765.
Melisa Gualdrón-López Nathalie Chevalier Patrick Van Der Smissen Pierre J. Courtoy Daniel J. Rigden Paul A.M. Michels 《Biochimica et Biophysica Acta (BBA)/Molecular Cell Research》2013,1833(12):3076-3092
Trypanosomatids contain peroxisome-like organelles called glycosomes. Peroxisomal biogenesis involves a cytosolic receptor, PEX5, which, after its insertion into the organellar membrane, delivers proteins to the matrix. In yeasts and mammalian cells, transient PEX5 monoubiquitination at the membrane serves as the signal for its retrieval from the organelle for re-use. When its recycling is impaired, PEX5 is polyubiquitinated for proteasomal degradation. Stably monoubiquitinated TbPEX5 was detected in cytosolic fractions of Trypanosoma brucei, indicative for its role as physiological intermediate in receptor recycling. This modification's resistance to dithiothreitol suggests ubiquitin conjugation of a lysine residue. T. brucei PEX4, the functional homologue of the ubiquitin-conjugating (UBC) enzyme responsible for PEX5 monoubiquitination in yeast, was identified. It is associated with the cytosolic face of the glycosomal membrane, probably anchored by an identified putative TbPEX22. The involvement of TbPEX4 in TbPEX5 ubiquitination was demonstrated using procyclic ?PEX4 trypanosomes. Surprisingly, glycosomal matrix protein import was only mildly affected in this mutant. Since other UBC homologues were upregulated, it might be possible that these have partially rescued PEX4's function in PEX5 ubiquitination. In addition, the altered expression of UBCs, notably of candidates involved in cell-cycle control, could be responsible for observed morphological and motility defects of the ?PEX4 mutant. 相似文献
766.
Andrew L. Robison Todd M. Scanlon Bernard J. Cosby James R. Webb James N. Galloway 《Biogeochemistry》2013,113(1-3):119-136
Micro-organisms are vital for the functioning of all food webs and are the major drivers of the global biogeochemical cycles. The microbial community compositions and physicochemical conditions of the different water masses in the North Sea, a biologically productive sea on the northwestern European continental shelf, were studied during two summer cruises, in order to provide detailed baseline data for this region and examine its microbial biogeography. For each cruise the stations were clustered according to their physicochemical characteristics and their microbial community composition. The largest cluster, which covered most of the central and northern North Sea, consisted of stations that were characterized by a thermally stratified water column and had low chlorophyll a autofluorescence and generally low microbial abundances. The second main cluster contained stations that were dominated by picoeukaryotes and showed the influence of influxes of North Atlantic water via the English Channel and south of the Shetland Islands. The third main cluster was formed by stations that were dominated by cyanobacteria and nanoeukaryotes in the reduced salinity Norwegian Coastal and Skagerrak waters, while the fourth cluster represented the German Bight, a region with strong riverine input, high nutrient concentrations, and consequently high heterotrophic bacterial and viral abundances. Despite the complex and dynamic hydrographic nature of the North Sea, the consistent distinctions in microbiology between these different hydrographic regions during both cruises illustrate the strong links between the microbial community and its environment, as well as the possibility to use microorganisms for long-term monitoring of environmental change. 相似文献
767.
Anne-Christine Hick Anne-Sophie Delmarcelle Mahé Bouquet Sabrina Klotz Tamara Copetti Celine Forez Patrick Van Der Smissen Pierre Sonveaux Jean-François Collet Olivier Feron Pierre J. Courtoy Christophe E. Pierreux 《Developmental biology》2013
The thyroid is a highly vascularized endocrine gland, displaying a characteristic epithelial organization in closed spheres, called follicles. Here we investigate how endothelial cells are recruited into the developing thyroid and if they control glandular organization as well as thyrocytes and C-cells differentiation. We show that endothelial cells closely surround, and then invade the expanding thyroid epithelial cell mass to become closely associated with nascent polarized follicles. This close and sustained endothelial:epithelial interaction depends on epithelial production of the angiogenic factor, Vascular Endothelial Growth Factor-A (VEGF-A), as its thyroid-specific genetic inactivation reduced the endothelial cell pool of the thyroid by >90%. Vegfa KO also displayed decreased C-cells differentiation and impaired organization of the epithelial cell mass into follicles. We developed an ex vivo model of thyroid explants that faithfully mimicks bilobation of the thyroid anlagen, endothelial and C-cells invasion, folliculogenesis and differentiation. Treatment of thyroid explants at e12.5 with a VEGFR2 inhibitor ablated the endothelial pool and reproduced ex vivo folliculogenesis defects observed in conditional Vegfa KO. In the absence of any blood supply, rescue by embryonic endothelial progenitor cells restored folliculogenesis, accelerated lumen expansion and stimulated calcitonin expression by C-cells. In conclusion, our data demonstrate that, in developing mouse thyroid, epithelial production of VEGF-A is necessary for endothelial cells recruitment and expansion. In turn, endothelial cells control epithelial reorganization in follicles and C-cells differentiation. 相似文献
768.
Christel Thauvin-Robinet Martine Auclair Laurence Duplomb Martine Caron-Debarle Magali Avila Judith St-Onge Martine Le?Merrer Bernard Le?Luyer Delphine Héron Michèle Mathieu-Dramard Pierre Bitoun Jean-Michel Petit Sylvie Odent Jeanne Amiel Damien Picot Virginie Carmignac Julien Thevenon Patrick Callier Martine Laville Yves Reznik Cédric Fagour Marie-Laure Nunes Jacqueline Capeau Olivier Lascols Frédéric Huet Laurence Faivre Corinne Vigouroux Jean-Baptiste Rivière 《American journal of human genetics》2013,93(1):141-149
Short stature, hyperextensibility of joints and/or inguinal hernia, ocular depression, Rieger anomaly, and teething delay (SHORT) syndrome is a developmental disorder with an unknown genetic cause and hallmarks that include insulin resistance and lack of subcutaneous fat. We ascertained two unrelated individuals with SHORT syndrome, hypothesized that the observed phenotype was most likely due to de novo mutations in the same gene, and performed whole-exome sequencing in the two probands and their unaffected parents. We then confirmed our initial observations in four other subjects with SHORT syndrome from three families, as well as 14 unrelated subjects presenting with syndromic insulin resistance and/or generalized lipoatrophy associated with dysmorphic features and growth retardation. Overall, we identified in nine affected individuals from eight families de novo or inherited PIK3R1 mutations, including a mutational hotspot (c.1945C>T [p.Arg649Trp]) present in four families. PIK3R1 encodes the p85α, p55α, and p50α regulatory subunits of class IA phosphatidylinositol 3 kinases (PI3Ks), which are known to play a key role in insulin signaling. Functional data from fibroblasts derived from individuals with PIK3R1 mutations showed severe insulin resistance for both proximal and distal PI3K-dependent signaling. Our findings extend the genetic causes of severe insulin-resistance syndromes and provide important information with respect to the function of PIK3R1 in normal development and its role in human diseases, including growth delay, Rieger anomaly and other ocular affections, insulin resistance, diabetes, paucity of fat, and ovarian cysts. 相似文献
769.
Sayali C. Ranade Sarfaraz Nawaz Arnab Chakrabarti Pierre Gressens Shyamala Mani 《Hormones and behavior》2013
"The goal of this study was to examine the effect of maternal iron deficiency on the developing hippocampus in order to define a developmental window for this effect, and to see whether iron deficiency causes changes in glucocorticoid levels. The study was carried out using pre-natal, post-natal, and pre + post-natal iron deficiency paradigm. Iron deficient pregnant dams and their pups displayed elevated corticosterone which, in turn, differentially affected glucocorticoid receptor (GR) expression in the CA1 and the dentate gyrus. Brain Derived Neurotrophic Factor (BDNF) was reduced in the hippocampi of pups following elevated corticosterone levels. Reduced neurogenesis at P7 was seen in pups born to iron deficient mothers, and these pups had reduced numbers of hippocampal pyramidal and granule cells as adults. Hippocampal subdivision volumes also were altered. The structural and molecular defects in the pups were correlated with radial arm maze performance; reference memory function was especially affected. Pups from dams that were iron deficient throughout pregnancy and lactation displayed the complete spectrum of defects, while pups from dams that were iron deficient only during pregnancy or during lactation displayed subsets of defects. These findings show that maternal iron deficiency is associated with altered levels of corticosterone and GR expression, and with spatial memory deficits in their pups." 相似文献
770.
Fateh Chebana Barbara Martel Pierre Gosselin Jean-Xavier Giroux Taha B. M. J. Ouarda 《International journal of biometeorology》2013,57(4):631-644
Several watch and warning systems have been established in the world in recent years to prevent the effects of heat waves. However, many of these approaches can be applied only in regions with perfect conditions (e.g., enough data, stationary series or homogeneous regions). Furthermore, a number of these approaches do not account for possible trend in mortality and/or temperature series, whereas others are generally not adapted to regions with low population densities or low daily mortality levels. In addition, prediction based on multiple days preceding the event can be less accurate if it attributes the same importance to each of these days, since the forecasting accuracy actually decreases with the period. The aim of the present study was to identify appropriate indicators as well as flexible and general thresholds that can be applied to a variety of regions and conditions. From a practical point of view, the province of Québec constitutes a typical case where a number of the above-mentioned constraints are present. On the other hand, until recently, the province’s watch and warning system was based on a study conducted in 2005, covering only the city of Montreal and applied to the whole province. The proposed approach is applied to each one of the other health regions of the province often experiencing low daily counts of mortality and presenting trends. The first constraint led to grouping meteorologically homogeneous regions across the province in which the number of deaths is sufficient to carry out the appropriate data analyses. In each region, mortality trends are taken into account. In addition, the proposed indicators are defined by a 3-day weighted mean of maximal and minimal temperatures. The sensitivity of the results to the inclusion of traumatic deaths is also checked. The application shows that the proposed method improved the results in terms of sensitivity, specificity and number of yearly false alarms, compared to those of the existing and other classical approaches. An additional criterion based on the Humidex is applied in a second step and a local validation is applied to historical observations at reference forecasting stations. An integrated heat health watch and warning system with thresholds that are adapted to the regional climate has thus been established for each sub-region of the province of Quebec and became operational in June 2010. 相似文献