全文获取类型
收费全文 | 41559篇 |
免费 | 3152篇 |
国内免费 | 9篇 |
出版年
2023年 | 247篇 |
2022年 | 201篇 |
2021年 | 498篇 |
2020年 | 508篇 |
2019年 | 504篇 |
2018年 | 972篇 |
2017年 | 886篇 |
2016年 | 1423篇 |
2015年 | 2158篇 |
2014年 | 2104篇 |
2013年 | 2832篇 |
2012年 | 3751篇 |
2011年 | 3429篇 |
2010年 | 1948篇 |
2009年 | 1568篇 |
2008年 | 2710篇 |
2007年 | 2617篇 |
2006年 | 2539篇 |
2005年 | 2234篇 |
2004年 | 2187篇 |
2003年 | 2002篇 |
2002年 | 1892篇 |
2001年 | 749篇 |
2000年 | 838篇 |
1999年 | 488篇 |
1998年 | 316篇 |
1997年 | 190篇 |
1996年 | 209篇 |
1995年 | 225篇 |
1994年 | 193篇 |
1993年 | 182篇 |
1992年 | 187篇 |
1991年 | 160篇 |
1990年 | 135篇 |
1989年 | 131篇 |
1988年 | 108篇 |
1987年 | 75篇 |
1986年 | 81篇 |
1985年 | 98篇 |
1984年 | 123篇 |
1983年 | 79篇 |
1982年 | 97篇 |
1981年 | 69篇 |
1980年 | 66篇 |
1979年 | 62篇 |
1978年 | 55篇 |
1977年 | 46篇 |
1976年 | 66篇 |
1975年 | 52篇 |
1974年 | 54篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
981.
José Rodrigues Coura Pedro Albajar Vi?as Lucia Maria Brum-Soares Andréa Silvestre de Sousa Sérgio Salles Xavier 《Memórias do Instituto Oswaldo Cruz》2013,108(8):1009-1013
A case-control study on the morbidity of Chagas heart disease was carried out in the
municipality of Barcelos in the microregion of the Rio Negro, state of Amazonas. One
hundred and six individuals, who were serologically positive for Trypanosoma
cruzi infection, as confirmed by at least two techniques with different
principles, were matched according to age and sex with an equal number of
seronegative individuals. The cases and controls were evaluated using an
epidemiological questionnaire and clinical, electrocardiograph and echocardiograph
examinations. In the seroepidemiological evaluation, 62% of the interviewees
recognised triatomines and most of them confirmed that they had seen these insects in
the piassava plantations of the riverside communities of the Negro River tributaries.
Of the seropositive patients, 25.8% affirmed that they had been stung by the
triatomines and 11.7% denied having been stung. The principal clinical manifestations
of the seropositive individuals were palpitations, chest pain and dyspnoea upon
effort. Cardiac auscultation revealed extrasystoles, bradycardia and systolic
murmurs. The electrocardiographic alterations were ventricular extrasystoles, left
and right bundle branch block, atrioventricular block and primary T wave alterations.
The echocardiogram was altered in 22.6% of the seropositive individuals and in 8.5%
of the seronegative individuals. 相似文献
982.
One of the most common environmental stressors is a shortage or suboptimal quality of food, thus all animals deal with periods of starvation. In the present study we examine variation in starvation resistance, longevity and body lipid content and the correlations between traits along an environmental gradient using isofemale lines recently derived from natural populations of Drosophila melanogaster from South America. The use of isofemale lines and controlled rearing laboratory conditions allows us to investigate within and among population components of genetic variation and the potential associations among starvation resistance, longevity and body lipid content. All these traits were analyzed separately in females and males, improving our understanding of sexual dimorphism. Our results revealed significant differences among populations in starvation resistance and longevity. Actually, the opposing latitudinal cline detected for starvation resistance suggests that natural selection played an essential role in shaping the pattern of geographic variation in this trait. Moreover, we also detected a positive relationship between starvation resistance and body lipid content in both sexes, providing evidence for a physiological and/or evolutionary association between these traits. Conversely, starvation resistance was not correlated with longevity indicating that these traits might be enabled to evolve independently. Finally, our study reveals that there is abundant within population genetic variation for all traits that may be maintained by sex-specific effects. 相似文献
983.
984.
Application of Hazard Analysis and Critical Control Points (HACCP) to the Cultivation Line of Mushroom and Other Cultivated Edible Fungi 总被引:1,自引:0,他引:1
José E. Pardo Vinícius Reis de Figueirêdo Manuel Álvarez-Ortí Diego C. Zied Jesús A. Peñaranda Eustáquio Souza Dias Arturo Pardo-Giménez 《Indian journal of microbiology》2013,53(3):359-369
The Hazard analysis and critical control points (HACCP) is a preventive system which seeks to ensure food safety and security. It allows product protection and correction of errors, improves the costs derived from quality defects and reduces the final overcontrol. In this paper, the system is applied to the line of cultivation of mushrooms and other edible cultivated fungi. From all stages of the process, only the reception of covering materials (stage 1) and compost (stage 3), the pre-fruiting and induction (step 6) and the harvest (stage 7) have been considered as critical control point (CCP). The main hazards found were the presence of unauthorized phytosanitary products or above the permitted dose (stages 6 and 7), and the presence of pathogenic bacteria (stages 1 and 3) and/or heavy metals (stage 3). The implementation of this knowledge will allow the self-control of their productions based on the system HACCP to any plant dedicated to mushroom or other edible fungi cultivation. 相似文献
985.
José Rodrigues Coura 《Memórias do Instituto Oswaldo Cruz》2013,108(8):962-967
From an epidemiological point of view, Chagas disease and its reservoirs and vectors
can present the following characteristics: (i) enzooty, maintained by wild animals
and vectors, with broad occurrence from southern United States of America (USA) to
southern Argentina and Chile (42ºN 49ºS), (ii) anthropozoonosis, when man invades the
wild ecotope and becomes infected with Trypanosoma cruzi from wild
animals or vectors or when the vectors and wild animals, especially marsupials,
invade the human domicile and infect man, (iii) zoonosis-amphixenosis and exchanged
infection between animals and humans by domestic vectors in endemic areas and (iv)
zooanthroponosis, infection that is transmitted from man to animals, by means of
domestic vectors, which is the rarest situation in areas endemic for Chagas disease.
The characteristics of Chagas disease as an enzooty of wild animals and as an
anthropozoonosis are seen most frequently in the Brazilian Amazon and in the
Pan-Amazon region as a whole, where there are 33 species of six genera of wild
animals: Marsupialia, Chiroptera, Rodentia, Edentata (Xenarthra), Carnivora and
Primata and 27 species of triatomines, most of which infected with T.
cruzi . These conditions place the resident populations of this area or
its visitors - tourists, hunters, fishermen and especially the people whose
livelihood involves plant extraction - at risk of being affected by Chagas disease.
On the other hand, there has been an exponential increase in the acute cases of
Chagas disease in that region through oral transmission of T. cruzi
, causing outbreaks of the disease. In four seroepidemiological surveys that were
carried out in areas of the microregion of the Negro River, state of Amazonas, in
1991, 1993, 1997 and 2010, we found large numbers of people who were serologically
positive for T. cruzi infection. The majority of them and/or their
relatives worked in piassava extraction and had come into contact with and were stung
by wild triatomines in that area. Finally, a characteristic that is greatly in
evidence currently is the migration of people with Chagas disease from endemic areas
of Latin America to non-endemic countries. This has created a new dilemma for these
countries: the risk of transmission through blood transfusion and the onus of
controlling donors and treating migrants with the disease. As an enzooty of wild
animals and vectors, and as an anthropozoonosis, Chagas disease cannot be eradicated,
but it must be controlled by transmission elimination to man. 相似文献
986.
987.
Natalia Jiménez José Antonio Curiel Inés Reverón Blanca de las Rivas Rosario Mu?oz 《Applied and environmental microbiology》2013,79(14):4253-4263
Lactobacillus plantarum is a lactic acid bacterium able to degrade tannins by the subsequent action of tannase and gallate decarboxylase enzymes. The gene encoding tannase had previously been identified, whereas the gene encoding gallate decarboxylase is unknown. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of gallic-acid induced L. plantarum extracts showed a 54-kDa protein which was absent in the uninduced cells. This protein was identified as Lp_2945, putatively annotated UbiD. Homology searches identified ubiD-like genes located within three-gene operons which encoded the three subunits of nonoxidative aromatic acid decarboxylases. L. plantarum is the only bacterium in which the lpdC (lp_2945) gene and the lpdB and lpdD (lp_0271 and lp_0272) genes are separated in the chromosome. Combination of extracts from recombinant Escherichia coli cells expressing the lpdB, lpdC, and lpdC genes demonstrated that LpdC is the only protein required to yield gallate decarboxylase activity. However, the disruption of these genes in L. plantarum revealed that the lpdB and lpdC gene products are essential for gallate decarboxylase activity. Similar to L. plantarum tannase, which exhibited activity only in esters derived from gallic and protocatechuic acids, purified His6-LpdC protein from E. coli showed decarboxylase activity against gallic and protocatechuic acids. In contrast to the tannase activity, gallate decarboxylase activity is widely present among lactic acid bacteria. This study constitutes the first genetic characterization of a gallate decarboxylase enzyme and provides new insights into the role of the different subunits of bacterial nonoxidative aromatic acid decarboxylases. 相似文献
988.
José Ragusa‐Netto 《Studies on Neotropical Fauna and Environment》2013,48(2):99-105
I studied Brotogeris chiriri abundance and foraging activity at a dry forest of the Urucum mountains in western Mato Grosso do Sul, Brazil, to evaluate their relationships with food resource production. Brotogeris chiriri abundance sharply increased during the early wet season (mainly October 2001) when it mostly foraged for fleshy fruits. At that time Protium heptaphyllum, one of the most common tree species, bore a large crop of fruits, the arils of which were extensively consumed by B. chiriri. Conversely, only a few parakeets were recorded foraging from the late wet to the late dry season, when dry fruit production predominated. The monthly pattern of parakeet abundance paralleled both its monthly pattern of foraging activity and fleshy fruit availability. Moreover, the variations in foraging activity were highly correlated to fleshy fruit production. Thus, data presented here evidenced the effect of both fruiting pulses and a common tree species that produced a large and ephemeral fruit crop, on the dynamic of a small and mobile canopy forager at a primary dry forest. 相似文献
989.
990.
Rayana Carla Silva de Morais Suênia da Cunha Gonçalves Pietra Lemos Costa Kamila Gaudêncio da Silva Fernando José da Silva Rômulo Pessoa e Silva Maria Edileuza Felinto de Brito Sinval Pinto Brandão-Filho Filipe Dantas-Torres Milena de Paiva-Cavalcanti 《Experimental & applied acarology》2013,59(4):473-481
Visceral leishmaniosis (VL) is a parasitic disease caused by Leishmania infantum, which is primarily transmitted by phlebotomine sandflies. However, there has been much speculation on the role of other arthropods in the transmission of VL. Thus, the aim of this study was to assess the presence of L. infantum in cats, dogs and their ectoparasites in a VL-endemic area in northeastern Brazil. DNA was extracted from blood samples and ectoparasites, tested by conventional PCR (cPCR) and quantitative real time PCR (qPCR) targeting the L. infantum kinetoplast DNA. A total of 280 blood samples (from five cats and 275 dogs) and 117 ectoparasites from dogs were collected. Animals were apparently healthy and not previously tested by serological or molecular diagnostic methods. Overall, 213 (76.1 %) animals and 51 (43.6 %) ectoparasites were positive to L. infantum, with mean parasite loads of 795.2, 31.9 and 9.1 fg in dogs, cats and ectoparasites, respectively. Concerning the positivity between dogs and their ectoparasites, 32 (15.3 %) positive dogs were parasitized by positive ectoparasites. The overall concordance between the PCR protocols used was 59.2 %, with qPCR being more efficient than cPCR; 34.1 % of all positive samples were exclusively positive by qPCR. The high number of positive animals and ectoparasites also indicates that they could serve as sentinels or indicators of the circulation of L. infantum in risk areas. 相似文献