全文获取类型
收费全文 | 5931篇 |
免费 | 503篇 |
国内免费 | 2篇 |
出版年
2021年 | 69篇 |
2020年 | 72篇 |
2019年 | 77篇 |
2018年 | 108篇 |
2017年 | 87篇 |
2016年 | 127篇 |
2015年 | 204篇 |
2014年 | 225篇 |
2013年 | 332篇 |
2012年 | 353篇 |
2011年 | 359篇 |
2010年 | 252篇 |
2009年 | 205篇 |
2008年 | 286篇 |
2007年 | 295篇 |
2006年 | 304篇 |
2005年 | 256篇 |
2004年 | 259篇 |
2003年 | 266篇 |
2002年 | 259篇 |
2001年 | 86篇 |
2000年 | 73篇 |
1999年 | 107篇 |
1998年 | 82篇 |
1997年 | 54篇 |
1996年 | 55篇 |
1995年 | 61篇 |
1994年 | 58篇 |
1993年 | 60篇 |
1992年 | 65篇 |
1991年 | 43篇 |
1990年 | 49篇 |
1989年 | 52篇 |
1988年 | 45篇 |
1987年 | 46篇 |
1986年 | 42篇 |
1985年 | 55篇 |
1984年 | 67篇 |
1983年 | 40篇 |
1982年 | 62篇 |
1981年 | 45篇 |
1980年 | 64篇 |
1979年 | 49篇 |
1978年 | 40篇 |
1977年 | 37篇 |
1976年 | 37篇 |
1975年 | 31篇 |
1974年 | 31篇 |
1973年 | 31篇 |
1969年 | 21篇 |
排序方式: 共有6436条查询结果,搜索用时 15 毫秒
991.
992.
993.
Redouane Fodil Lydia Brugel-Ribere Céline Croce Gabriela Sbirlea-Apiou Christian Larger Jean-Fran?ois Papon Christophe Delclaux André Coste Daniel Isabey Bruno Louis 《Journal of applied physiology》2005,98(1):288-295
We have developed a discrete multisegmental model describing the coupling between inspiratory flow and nasal wall distensibility. This model is composed of 14 individualized compliant elements, each with its own relationship between cross-sectional area and transmural pressure. Conceptually, this model is based on flow limitation induced by the narrowing of duct due to collapsing pressure. For a given inspiratory pressure and for a given compliance distribution, this model predicts the area profile and inspiratory flow. Acoustic rhinometry and posterior rhinomanometry were used to determine the initial geometric area and mechanical characteristics of each element. The proposed model, used under steady-state conditions, is able to simulate the pressure-flow relationship observed in vivo under normal conditions (4 subjects) and under pathological conditions (4 vasomotor rhinitis and 3 valve syndrome subjects). Our results suggest that nasal wall compliance is an essential parameter to understand the nasal inspiratory flow limitation phenomenon and the associated increase of resistance that is well known to physiologists. By predicting the functional pressure-flow relationship, this model could be a useful tool for the clinician to evaluate the potential effects of treatments. 相似文献
994.
Robert P. Favier Bart Spee Louis C. Penning Bas Brinkhof Jan Rothuizen 《Mammalian genome》2005,16(6):460-463
The recently discovered locus for copper toxicosis (CT) in Bedlington terriers (BT) has a 13-kb deletion enveloping the 187-bp exon-2 of the MURR1 gene. This MURR1 gene is not only involved with biliary copper excretion but also associated with HIV-1 replication. The microsatellite C04107 lying in an intron of the MURR1 gene is highly associated with the disease but shows haplotype diversity. The only solid molecular test for the disease is by showing the deletion in exon-2 in cDNA in liver tissue; this test is not robust on RNA from peripheral leukocytes because of their low MURR1 expression level. Because of these drawbacks, we developed a new quantitative PCR (Q-PCR) protocol. Here we show that the MURR1 exon-2/exon-3 ratio measured by Q-PCR on genomic DNA correlates perfectly with the microsatellite marker and with RT-PCR data from blood samples, buccal swabs, and liver biopsies. In view of the important role of MURR1 in cells of many tissues, this new test has a wide range of applications in comparative biomedical research. Furthermore, Q-PCR on DNA may be a new tool in general to analyze mutations that cannot be approached by standard methods.Robert P. Favier and Bart Spee contributed equally to this work. 相似文献
995.
The mechanisms of longevity have been the subject of investigations for a number of years. Although the role of genetic factors is generally acknowledged, important questions persist regarding the relative impact of environmental exposures, lifestyle characteristics, and genes. The BALSAC population register offers a unique opportunity to study longevity from an intergenerational and genealogical point of view. Individuals from the Saguenay-Lac-St-Jean population who died at age 90 or older between 1950 and 1974 were selected from this database (n?=?576), along with a control group of individuals born in the same period who died between 50 and 75 years of age. For these subjects and controls, spouses’ ages at death and parental ages at death and at their birth were investigated using regression analysis. Genealogical reconstructions were carried out for each individual, and various analyses were performed on both groups. Both fathers’ and mothers’ mean ages at death were significantly higher among the longer-lived cases than among controls whereas spouses’ ages at death and parental ages at birth had no effect. Regression analysis confirmed the positive effect of both fathers’ and mothers’ age at death. Mean kinship coefficients for the parents’ generations displayed significant differences, indicating that kinship was higher among subjects than controls (this effect was stronger among the oldest 10% of the subjects). Frequencies and genetic contributions of ancestors were very similar for the two groups, and none of these ancestors appeared more likely to have introduced genetic variants involved in longevity patterns in this French Canadian population. 相似文献
996.
997.
The diversity and spatial distribution of vascular epiphytes were surveyed in two biotopes (dryland forest and swamp-inundated
forest) of the semi-deciduous rain forest area in Cameroon. Eight sites in each biotope were selected, which included 530
individuals of phorophytes in dryland forest and 460 in swamp-inundated forest. A total of 148 epiphyte species were recorded,
which showed that semi-deciduous rain forests represent a major source of African-epiphyte diversity. Dryland forest hosted
110 epiphyte species, while the swamp-inundated forest harboured 108. A total of 56 species were found only in the dryland
forest and 60 were restricted to the swamp-inundated forest. At family level, Orchidaceae exhibited the highest-species richness
within both biotopes. Pteridophytes were more abundant in the swamp-inundated forest. A TWINSPAN analysis of the floristic
similarities separated the two investigated forest types very clearly. No significant difference existed between the two biotopes
regarding vertical distribution of epiphytes within single trees. The swamp-inundated forests may serve as a refuge for many
epiphytes that occur in the outer canopy of the dryland forests, both because they are inherently less vulnerable to timber
extraction, and enjoy better protection by legislation. 相似文献
998.
Plant species traits are the predominant control on litter decomposition rates within biomes worldwide 总被引:9,自引:0,他引:9
Cornwell WK Cornelissen JH Amatangelo K Dorrepaal E Eviner VT Godoy O Hobbie SE Hoorens B Kurokawa H Pérez-Harguindeguy N Quested HM Santiago LS Wardle DA Wright IJ Aerts R Allison SD van Bodegom P Brovkin V Chatain A Callaghan TV Díaz S Garnier E Gurvich DE Kazakou E Klein JA Read J Reich PB Soudzilovskaia NA Vaieretti MV Westoby M 《Ecology letters》2008,11(10):1065-1071
Worldwide decomposition rates depend both on climate and the legacy of plant functional traits as litter quality. To quantify the degree to which functional differentiation among species affects their litter decomposition rates, we brought together leaf trait and litter mass loss data for 818 species from 66 decomposition experiments on six continents. We show that: (i) the magnitude of species-driven differences is much larger than previously thought and greater than climate-driven variation; (ii) the decomposability of a species' litter is consistently correlated with that species' ecological strategy within different ecosystems globally, representing a new connection between whole plant carbon strategy and biogeochemical cycling. This connection between plant strategies and decomposability is crucial for both understanding vegetation-soil feedbacks, and for improving forecasts of the global carbon cycle. 相似文献
999.
Sourrouille C Marquet-Blouin E D'Aoust MA Kiefer-Meyer MC Seveno M Pagny-Salehabadi S Bardor M Durambur G Lerouge P Vezina L Gomord V 《Plant biotechnology journal》2008,6(7):702-721
Compared with other plant expression systems used for pharmaceutical protein production, alfalfa offers the advantage of very homogeneous N -glycosylation. Therefore, this plant was selected for further attempts at glycoengineering. Two main approaches were developed in order to humanize N -glycosylation in alfalfa. The first was a knock-down of two plant-specific N -glycan maturation enzymes, β1,2-xylosyltransferase and α1,3-fucosyltransferases, using sense, antisense and RNA interference strategies. In a second approach, with the ultimate goal of rebuilding the whole human sialylation pathway, human β1,4-galactosyltransferase was expressed in alfalfa in a native form or in fusion with a targeting domain from N -acetylglucosaminyltransferase I, a glycosyltransferase located in the early Golgi apparatus in Nicotiana tabacum . Both knock-down and knock-in strategies strongly, but not completely, inhibited the biosynthesis of α1,3-fucose- and β1,2-xylose-containing glycoepitopes in transgenic alfalfa. However, recombinant human β1,4-galactosyltransferase activity in transgenic alfalfa completely prevented the accumulation of the Lewis a glycoepitope on complex N -glycans. 相似文献
1000.
Alexander Witek Holger Herlyn Achim Meyer Louis Boell Gregor Bucher Thomas Hankeln 《BMC evolutionary biology》2008,8(1):345