全文获取类型
收费全文 | 7333篇 |
免费 | 573篇 |
国内免费 | 1篇 |
专业分类
7907篇 |
出版年
2023年 | 72篇 |
2022年 | 125篇 |
2021年 | 232篇 |
2020年 | 157篇 |
2019年 | 184篇 |
2018年 | 225篇 |
2017年 | 214篇 |
2016年 | 334篇 |
2015年 | 458篇 |
2014年 | 452篇 |
2013年 | 500篇 |
2012年 | 661篇 |
2011年 | 597篇 |
2010年 | 318篇 |
2009年 | 317篇 |
2008年 | 402篇 |
2007年 | 346篇 |
2006年 | 321篇 |
2005年 | 309篇 |
2004年 | 290篇 |
2003年 | 259篇 |
2002年 | 218篇 |
2001年 | 82篇 |
2000年 | 68篇 |
1999年 | 81篇 |
1998年 | 71篇 |
1997年 | 56篇 |
1996年 | 42篇 |
1995年 | 42篇 |
1994年 | 47篇 |
1993年 | 28篇 |
1992年 | 36篇 |
1991年 | 30篇 |
1990年 | 29篇 |
1989年 | 22篇 |
1988年 | 17篇 |
1987年 | 13篇 |
1986年 | 17篇 |
1985年 | 30篇 |
1984年 | 18篇 |
1983年 | 13篇 |
1982年 | 20篇 |
1981年 | 18篇 |
1980年 | 11篇 |
1979年 | 12篇 |
1978年 | 15篇 |
1977年 | 10篇 |
1975年 | 12篇 |
1973年 | 10篇 |
1968年 | 10篇 |
排序方式: 共有7907条查询结果,搜索用时 0 毫秒
981.
Paola Navarrete Fabien Magne Pamela Mardones Macarena Riveros Rafael Opazo Antonia Suau Philippe Pochart & Jaime Romero 《FEMS microbiology ecology》2010,71(1):148-156
The aim of this study was to evaluate different molecular tools based on the 16S rRNA gene, internal transcribed spacer, and the rpo B gene to examine the bacterial populations present in juvenile rainbow trout intestines. DNA was extracted from both pooled intestinal samples and bacterial strains. Genes were PCR-amplified and analysed using both temporal temperature gradient gel electrophoresis (TTGE) and restriction fragment length polymorphism methods. Because of the high cultivability of the samples, representative bacterial strains were retrieved and we compared the profiles obtained from isolated bacteria with the profile of total bacteria from intestinal contents. Direct analysis based on rpo B-TTGE revealed a simple bacterial composition with two to four bands per sample, while the 16S rRNA gene-TTGE showed multiple bands and comigration for a few species. Sequencing of the 16S rRNA gene- and rpo B-TTGE bands revealed that the intestinal microbiota was dominated by Lactococcus lactis, Citrobacter gillenii, Kluyvera intermedia, Obesumbacterium proteus , and Shewanella marinus . In contrast to 16S rRNA gene-TTGE, rpo B-TTGE profiles derived from bacterial strains produced one band per species. Because the single-copy state of rpo B leads to a single band in TTGE, the rpo B gene is a promising molecular marker for investigating the bacterial community of the rainbow trout intestinal microbiota. 相似文献
982.
Samuel Gmez-Arcas Francisco Jos Muoz Adriana Ricarte-Bermejo ngela María Snchez-Lpez Marouane Baslam Edurne Baroja-Fernndez Abdellatif Bahaji Goizeder Almagro Nuria De Diego Karel Doleal Ondej Novk Jesús Leal-Lpez Rafael Jorge Len Morcillo Araceli G Castillo Javier Pozueta-Romero 《Plant physiology》2022,190(4):2137
983.
Carolina Lessa-Aquino Camila Borges Rodrigues Jozelyn Pablo Rie Sasaki Algis Jasinskas Li Liang Elsio A. Wunder Jr Guilherme S. Ribeiro Adam Vigil Ricardo Galler Douglas Molina Xiaowu Liang Mitermayer G. Reis Albert I. Ko Marco Alberto Medeiros Philip L. Felgner 《PLoS neglected tropical diseases》2013,7(10)
Background
Leptospirosis is a widespread zoonotic disease worldwide. The lack of an adequate laboratory test is a major barrier for diagnosis, especially during the early stages of illness, when antibiotic therapy is most effective. Therefore, there is a critical need for an efficient diagnostic test for this life threatening disease.Methodology
In order to identify new targets that could be used as diagnostic makers for leptopirosis, we constructed a protein microarray chip comprising 61% of Leptospira interrogans proteome and investigated the IgG response from 274 individuals, including 80 acute-phase, 80 convalescent-phase patients and 114 healthy control subjects from regions with endemic, high endemic, and no endemic transmission of leptospirosis. A nitrocellulose line blot assay was performed to validate the accuracy of the protein microarray results.Principal findings
We found 16 antigens that can discriminate between acute cases and healthy individuals from a region with high endemic transmission of leptospirosis, and 18 antigens that distinguish convalescent cases. Some of the antigens identified in this study, such as LipL32, the non-identical domains of the Lig proteins, GroEL, and Loa22 are already known to be recognized by sera from human patients, thus serving as proof-of-concept for the serodiagnostic antigen discovery approach. Several novel antigens were identified, including the hypothetical protein LIC10215 which showed good sensitivity and specificity rates for both acute- and convalescent-phase patients.Conclusions
Our study is the first large-scale evaluation of immunodominant antigens associated with naturally acquired leptospiral infection, and novel as well as known serodiagnostic leptospiral antigens that are recognized by antibodies in the sera of leptospirosis cases were identified. The novel antigens identified here may have potential use in both the development of new tests and the improvement of currently available assays for diagnosing this neglected tropical disease. Further research is needed to assess the utility of these antigens in more deployable diagnostic platforms. 相似文献984.
985.
Mónica Pérez-Nicolás Heike Vibrans Angélica Romero-Manzanares Alfredo Saynes-Vásquez Mario Luna-Cavazos María Flores-Cruz Rafael Lira-Saade 《Economic botany》2017,71(3):209-223
Medicinal plants continue to play an important role in healthcare, both in Mexico and around the world. We investigated the relationship between various sociodemographic factors, such as age, economic activity, years of schooling, socioeconomic levels, gender, and language proficiency, and the knowledge and frequency of medicinal plant use in Santiago Camotlán, Sierra Norte of Oaxaca, with a mainly Zapotec population. In a first stage, we interviewed specialists in depth and collected and identified plants for a catalogue of the medicinal plant flora (90 species). With this catalogue, we then interviewed a sample of the general population and the specialists on knowledge and frequency of use. The relationship between the sociodemographic variables and knowledge was analyzed by multiple regression. To explore differences of knowledge within the population, we identified three groups with a two-step cluster analysis; the results were compared statistically with a Kruskal-Wallis non-parametric test and then a post hoc Dunn’s test to see if all the differences between groups were significant. Age and occupation explained 54% of the variation of knowledge. Medicinal plant knowledge in the region persists mainly because of the necessity to treat the diseases that the “doctor does not cure,” the culture-bound syndromes, and the most common ailments, malfunctions of the digestive system. 相似文献
986.
Hocking, Bree T. The great reimagining: public art,urban space and the symbolic landscapes of a ‘new’ Northern Ireland. xi, 232 pp., illus., bibliogr. Oxford,New York: Berghahn Books, 2015. £60.00 (cloth) 下载免费PDF全文
Rafael Schacter 《The journal of the Royal Anthropological Institute》2017,23(1):193-194
987.
988.
The effect of inbreeding on genetic diversity is expected to decrease plant defences or vigour-related traits that, in turn,
can modify the pattern of attack by herbivores. The selective damage caused by herbivores can produce variable fitness costs
between inbred and outcrossed progenies influencing the evolution of a species’ plant mating system. By exposing inbred and
outcrossed plants to natural conditions of seed predation, we assessed whether inbreeding increases weevil incidence and infestation,
and how weevil seed predation affects the fitness of inbred and outcrossed progeny. To test if inbreeding affected the host’s
plant quality, we weighed the biomass of weevils developed in inbred and outcrossed progenies. An additional experiment was
carried out to examine whether weevils preferentially attack vigorous plants regardless from the level of inbreeding. The
average value of leaf size was 21% larger in outcrossed plants than in inbred plants. Likewise, weevil incidence and infestation
were 13 and 40%, respectively, higher on outcrossed plants relative to their inbred counterparts. However, the relative impact
of seed predation was significantly lower in outcrossed progeny than in inbred progeny. In contrast, inbreeding did not alter
host plant quality and weevils developed in inbred and outcrossed plants had a similar biomass. Variations in fruit number
were consistently associated with the infestation level in both experiments, whereas leaf size only predicted the number of
weevils in one experiment, suggesting that fruit number is the most influential vigour-related characteristic of a weevil
attack. These findings indicate that the costs of inbreeding of the interaction D. stramonium-T. soror were higher for inbred plants than for outcrossed plants. The interaction between seed predation and inbreeding depression
could prevent the fixation of selfing as a unique reproductive strategy in D. stramonium. 相似文献
989.
Rafael C. Rodrigues Cesar A. Godoy Giandra Volpato Marco A.Z. Ayub Roberto Fernandez-Lafuente Jose M. Guisan 《Process Biochemistry》2009,44(9):963-968
This paper describes the immobilization and stabilization of the lipase from Thermomyces lanuginosus (TLL) on glyoxyl agarose. Enzymes attach to this support only by the reaction between several aldehyde groups of the support and several Lys residues on the external surface of the enzyme molecules at pH 10. However, this standard immobilization procedure is unsuitable for TLL lipase due to the low stability of TLL at pH 10 and its low content on Lys groups that makes that the immobilization process was quite slow. The chemical amination of TLL, after reversible immobilization on hydrophobic supports, has been shown to be a simple and efficient way to improve the multipoint covalent attachment of this enzyme. The modification enriches the enzyme surface in primary amino groups with low pKb, thus allowing the immobilization of the enzyme at lower pH values. The aminated enzyme was rapidly immobilized at pH 9 and 10, with activities recovery of approximately 70%. The immobilization of the chemically modified enzyme improved its stability by 5-fold when compared to the non-modified enzyme during thermal inactivation and by hundreds of times when the enzyme was inactivated in the presence of organic solvents, being both glyoxyl preparations more stable than the enzyme immobilized on bromocyanogen. 相似文献
990.
J?natas S. Abrah?o Maria Isabel M. Guedes Giliane S. Trindade Flávio G. Fonseca Rafael K. Campos Bruno F. Mota Zélia I. P. Lobato André T. Silva-Fernandes Gisele O. L. Rodrigues Larissa S. Lima Paulo C. P. Ferreira Cláudio A. Bonjardim Erna G. Kroon 《PloS one》2009,4(10)