全文获取类型
收费全文 | 16571篇 |
免费 | 1384篇 |
国内免费 | 138篇 |
专业分类
18093篇 |
出版年
2024年 | 26篇 |
2023年 | 172篇 |
2022年 | 162篇 |
2021年 | 313篇 |
2020年 | 273篇 |
2019年 | 297篇 |
2018年 | 672篇 |
2017年 | 526篇 |
2016年 | 622篇 |
2015年 | 617篇 |
2014年 | 625篇 |
2013年 | 1048篇 |
2012年 | 1340篇 |
2011年 | 1448篇 |
2010年 | 775篇 |
2009年 | 538篇 |
2008年 | 1053篇 |
2007年 | 943篇 |
2006年 | 930篇 |
2005年 | 713篇 |
2004年 | 740篇 |
2003年 | 676篇 |
2002年 | 601篇 |
2001年 | 465篇 |
2000年 | 550篇 |
1999年 | 300篇 |
1998年 | 159篇 |
1997年 | 132篇 |
1996年 | 112篇 |
1995年 | 104篇 |
1994年 | 100篇 |
1993年 | 90篇 |
1992年 | 113篇 |
1991年 | 94篇 |
1990年 | 80篇 |
1989年 | 66篇 |
1988年 | 51篇 |
1987年 | 54篇 |
1986年 | 37篇 |
1985年 | 58篇 |
1984年 | 41篇 |
1983年 | 38篇 |
1982年 | 37篇 |
1981年 | 27篇 |
1980年 | 25篇 |
1979年 | 28篇 |
1978年 | 21篇 |
1977年 | 22篇 |
1974年 | 23篇 |
1973年 | 28篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Flavio L. Niño 《Mycopathologia》1959,12(1):46-66
Conclusiones Se efectúa el estudio de 5 observaciones del llamado Micetoma maduromicósico de pulmón en sus aspectos, histopatológico, micológico y clínico.Todas ellas pertenecen a mujeres y configuraron el cuadro de cavidad bronquial empastada, anotando el predominio de su localización en el lóbulo superior izquierdo.Se señala la uniformidad de los caracteres morfológicos que presenta la masa miceliana llamada grano en todos los casos estudiados, en los cuales no fué posible individualizar la existencia de órganos de fructificación que permitiéran una clasificación, cuando más no fuera, genérica del hongo observado.Se critica la aplicación del término Micetoma para éstos casos con igual criterio que el clásico, que supone una enfermedad micótica primitiva, razón por la cual se prefiere hablar de cavidad con contenido micótico o maduromicótico.En el único caso que se logró cultivar al hongo parásito, el estudio micológico del mismo permitió aislar una especie del GéneroAspergillua con caracteres morfológicos sumamente atípicos.
Summary The author presents the study of five observations of the so-called Maduromycosis-mycetoma of the lungs in their clinical, histopathologic and mycologic aspects.The pathologic features in all these cases have been found in bronchial cavities of women, situated in the upper lobe of the lung. A compact mycelial mass, the grain, filled up these cavities.In one of the five cases a fungus was cultivated which was classified as belonging to the GenusAspergillus Michelii, with abnormal and atypical features.Short criticism is presented about the concept Maduromycosis mycetoma of the lung, applied by authors designating this process.相似文献
992.
Molecular insights into cell toxicity of a novel familial amyloidogenic variant of β2‐microglobulin 下载免费PDF全文
Manuela Leri Francesco Bemporad Reinier Oropesa‐Nuñez Claudio Canale Martino Calamai Daniele Nosi Matteo Ramazzotti Sofia Giorgetti Francesco S. Pavone Vittorio Bellotti Massimo Stefani Monica Bucciantini 《Journal of cellular and molecular medicine》2016,20(8):1443-1456
The first genetic variant of β2‐microglobulin (b2M) associated with a familial form of systemic amyloidosis has been recently described. The mutated protein, carrying a substitution of Asp at position 76 with an Asn (D76N b2M), exhibits a strongly enhanced amyloidogenic tendency to aggregate with respect to the wild‐type protein. In this study, we characterized the D76N b2M aggregation path and performed an unprecedented analysis of the biochemical mechanisms underlying aggregate cytotoxicity. We showed that, contrarily to what expected from other amyloid studies, early aggregates of the mutant are not the most toxic species, despite their higher surface hydrophobicity. By modulating ganglioside GM1 content in cell membrane or synthetic lipid bilayers, we confirmed the pivotal role of this lipid as aggregate recruiter favouring their cytotoxicity. We finally observed that the aggregates bind to the cell membrane inducing an alteration of its elasticity (with possible functional unbalance and cytotoxicity) in GM1‐enriched domains only, thus establishing a link between aggregate‐membrane contact and cell damage. 相似文献
993.
994.
Association of a 76 kDa polypeptide with soluble starch synthase I activity in maize (cv B73) endosperm 总被引:1,自引:1,他引:1
Chen Mu Chee Harn Yuan-Tih Ko George W. Singletary Peter L. Keeling Bruce P. Wasserman 《The Plant journal : for cell and molecular biology》1994,6(2):151-159
Soluble starch synthase (SSS) I was purified 361-fold from hand-dissected endosperm tissue of inbred maize (Zea mays, cv. B73) to specific activities ranging between 5 and 9 µmol min−1 mg−1. A key to this purification protocol was the introduction of a size-exclusion chromatography step, a size-based fractionation which provided abundant levels of desalted SSS forms I and II. The native molecular masses calculated for SSS forms I and II were 75.5 kDa and 180 kDa, respectively. SSSI was then further purified by hydrophobic interaction chromatography on Phenyl-Superose and by FPLC on Mono Q. Analysis of column peaks by SDS—PAGE and scanning densitometry revealed that a 76 kDa polypeptide is strongly correlated with SSSI activity. Antibodies were then generated against a 76 kDa polypeptide extracted from starch granules. These antibodies, which were monospecific for the soluble 76 kDa polypeptide, neutralized greater than 90% of SSSI activity, and precipitated the 76 kDa protein. These results establish the 76 kDa protein as an SSSI in the B73 line of inbred maize. An immunologically similar 76 kDa protein also appears to be tightly associated with the starch granule. 相似文献
995.
Moro PL Budke CM Schantz PM Vasquez J Santivañez SJ Villavicencio J 《PLoS neglected tropical diseases》2011,5(5):e1179
Background
Cystic echinococcosis (CE) constitutes an important public health problem in Peru. However, no studies have attempted to estimate the monetary and non-monetary impact of CE in Peruvian society.Methods
We used official and published sources of epidemiological and economic information to estimate direct and indirect costs associated with livestock production losses and human disease in addition to surgical CE-associated disability adjusted life years (DALYs) lost.Findings
The total estimated cost of human CE in Peru was U.S.$2,420,348 (95% CI:1,118,384–4,812,722) per year. Total estimated livestock-associated costs due to CE ranged from U.S.$196,681 (95% CI:141,641–251,629) if only direct losses (i.e., cattle and sheep liver destruction) were taken into consideration to U.S.$3,846,754 (95% CI:2,676,181–4,911,383) if additional production losses (liver condemnation, decreased carcass weight, wool losses, decreased milk production) were accounted for. An estimated 1,139 (95% CI: 861–1,489) DALYs were also lost due to surgical cases of CE.Conclusions
This preliminary and conservative assessment of the socio-economic impact of CE on Peru, which is based largely on official sources of information, very likely underestimates the true extent of the problem. Nevertheless, these estimates illustrate the negative economic impact of CE in Peru. 相似文献996.
Determination of species-area relationships and minimum sampling area for the shrub communities in the arid valley in the upper reach of the Minjiang River, China 下载免费PDF全文
The minimum sampling areas (MSAs) for the shrub communities in the arid valley in the upper reach of the Minjiang River, China, were studied by fitting community species-area relationships using 3 types of equations. The MSAs were determined at the proportional factor (ρ) 0.6, 0.7, 0.8 and 0.9. The proportional factors represent the proportion of the number of species within a sampling plot in the total number of species. The MSAs of the shrub communities at different elevations and on different slope faces for ρ = 0.6, 0.7 and 0.8 were all around 100 m2. Hence, the MSAs could be set to be 100 m2 (10 m × 10 m) at 60%–80% precision levels. For ρ = 0.9, that is, for a 90% precision level, the MSAs were less than 200 m2 (10 m × 20 m). The MSAs and species richness increased gradually with the rising elevation. At the elevation below 2000 m, the MSAs and species richness on the north-facing slope were larger than those on the south-facing slope. However, at the elevation around 2200 m, there was no difference amongst different facing slopes. For the shrub communities in the arid valley in the upper reach of the Minjiang River, the species-area curves by fitting the first two equations are better than that by fitting the third equation. 相似文献
997.
R. Carmona J. A. Guadix E. Cano A. Ruiz‐Villalba V. Portillo‐Sánchez J. M. Pérez‐Pomares R. Muñoz‐Chápuli 《Journal of cellular and molecular medicine》2010,14(8):2066-2072
The epicardium has recently been identified as an active and essential element of cardiac development. Recent reports have unveiled a variety of functions performed by the embryonic epicardium, as well as the cellular and molecular mechanisms regulating them. However, despite its developmental importance, a number of unsolved issues related to embryonic epicardial biology persist. In this review, we will summarize our current knowledge about (i) the ontogeny and evolution of the epicardium, including a discussion on the evolutionary origins of the proepicardium (the epicardial primordium), (ii) the nature of epicardial–myocardial interactions during development, known to be essential for myocardial growth and maturation, and (iii) the contribution of epicardially derived cells to the vascular and connective tissue of the heart. We will finish with a note on the relationships existing between the primordia of the viscera and their coelomic epithelial lining. We would like to suggest that at least a part of the properties of the embryonic epicardium are shared by many other coelomic cell types, such that the role of epicardium in cardiac development is a particular example of a more general mechanism for the contribution of coelomic and coelomic-derived cells to the morphogenesis of organs such as the liver, kidneys, gonads or spleen. 相似文献
998.
Biodegradation of a crude oil by three microbial consortia of different origins and metabolic capabilities 总被引:6,自引:0,他引:6
Viñas M Grifoll M Sabaté J Solanas AM 《Journal of industrial microbiology & biotechnology》2002,28(5):252-260
Microbial consortia were obtained three by sequential enrichment using different oil products. Consortium F1AA was obtained
on a heavily saturated fraction of a degraded crude oil; consortium TD, by enrichment on diesel and consortium AM, on a mixture
of five polycyclic aromatic hydrocarbons [PAHs]. The three consortia were incubated with a crude oil in order to elucidate
their metabolic capabilities and to investigate possible differences in the biodegradation of these complex hydrocarbon mixtures
in relation to their origin. The efficiency of the three consortia in removing the saturated fraction was 60% (F1AA), 48%
(TD) and 34% (AM), depending on the carbon sources used in the enrichment procedures. Consortia F1AA and TD removed 100% of
n-alkanes and branched alkanes, whereas with consortium AM, 91% of branched alkanes remained. Efficiency on the polyaromatic
fraction was 19% (AM), 11% (TD) and 7% (F1AA). The increase in aromaticity of the polyaromatic fraction during degradation
of the crude oil by consortium F1AA suggested that this consortium metabolized the aromatic compounds primarily by oxidation
of the alkylic chains. The 500-fold amplification of the inocula from the consortia by subculturing in rich media, necessary
for use of the consortia in bioremediation experiments, showed no significant decrease in their degradation capability. Journal of Industrial Microbiology & Biotechnology (2002) 28, 252–260 DOI: 10.1038/sj/jim/7000236
Received 12 July 2001/ Accepted in revised form 11 November 2001 相似文献
999.
SSF production of lactic acid from cellulosic biosludges 总被引:2,自引:0,他引:2
The use of cellulosic biosludges generated in a Kraft pulp mill was investigated as substrate for lactic acid production by simultaneous saccharification and fermentation (SSF). The effect of the operation mode (batch or fedbatch), the initial liquid to solid ratio (12 or 30 g/g) and the nutrient supplementation (MRS components or none) on several parameters including lactic acid concentration, volumetric productivity and product yields, were evaluated. When the operation was carried out in fedbatch mode with nutrient supplementation and using a LSR(0)=12 g/g, a broth containing 42 g/L was obtained after 48 h with a volumetric productivity of 0.87 g/L h and a product yield of 37.8 g lactic acid/100 g biosludges. In a similar experiment carried out without nutrient supplementation, a lactic acid concentration of 39.4 g/L was obtained after 48 h with a volumetric productivity of 0.82 g/L h and a product yield of 35.5 g L-lactic acid/100 g biosludges. 相似文献
1000.
The evolution of secondary sexual characters is the subject of controversial debate between those defending their role as
‘viability indicators’ and those arguing that ornaments are purely ‘attractive traits’ selected by females. Recent theoretical
studies suggest that these hypotheses are not mutually exclusive, as both viability and attractiveness can contribute to improve
the reproductive success of progeny and could thus simultaneously underlie female choices. If that is the case, strategies
of cheaper advertisement, allowing the expression of larger ornaments for the same cost, could proliferate even in species
in which honest signalling of viability prevails. Under this scenario, different males could invest a different amount of
resources per ornament unit of expression, thus using different signalling rules. We studied the relationship between tail
feather length (a trait that is the subject of a female mate preference) and feather mass (a measure of investment in feather
production) in a barn swallow Hirundo rustica population. Different males used different and consistent signalling rules when developing ornamental feathers. That is,
to produce a feather of a given length, each male used a constant amount of resources across different years, but this amount
varied between males. Although the amount of material invested in feathers (feather mass) is a condition-dependent trait,
the organization of this material in ornamental feathers (i.e. the signalling rules) was not. Neither survival nor risk of
feather breakage was related to the signalling rules. Thus, these results suggest that both ‘viability’ and ‘runaway’ mechanisms
are independent determinants of the evolution of ornamental sexual feathers in the barn swallow. A preference for long tails
will ensure that females either obtain a sire with high viability, or one transferring the capability to produce longer and
more attractive tails at a lower cost of production to its offspring. 相似文献