全文获取类型
收费全文 | 130776篇 |
免费 | 9252篇 |
国内免费 | 298篇 |
专业分类
140326篇 |
出版年
2023年 | 679篇 |
2022年 | 726篇 |
2021年 | 1505篇 |
2020年 | 1307篇 |
2019年 | 1474篇 |
2018年 | 3055篇 |
2017年 | 2708篇 |
2016年 | 3835篇 |
2015年 | 5750篇 |
2014年 | 5884篇 |
2013年 | 7914篇 |
2012年 | 9542篇 |
2011年 | 8872篇 |
2010年 | 5728篇 |
2009年 | 4488篇 |
2008年 | 7318篇 |
2007年 | 7274篇 |
2006年 | 6676篇 |
2005年 | 6338篇 |
2004年 | 5971篇 |
2003年 | 5602篇 |
2002年 | 5223篇 |
2001年 | 2545篇 |
2000年 | 2423篇 |
1999年 | 2214篇 |
1998年 | 1136篇 |
1997年 | 893篇 |
1996年 | 802篇 |
1995年 | 804篇 |
1994年 | 779篇 |
1993年 | 614篇 |
1992年 | 1498篇 |
1991年 | 1340篇 |
1990年 | 1224篇 |
1989年 | 1154篇 |
1988年 | 1059篇 |
1987年 | 917篇 |
1986年 | 866篇 |
1985年 | 970篇 |
1984年 | 836篇 |
1983年 | 711篇 |
1982年 | 636篇 |
1981年 | 626篇 |
1979年 | 768篇 |
1978年 | 606篇 |
1977年 | 545篇 |
1976年 | 524篇 |
1975年 | 534篇 |
1974年 | 581篇 |
1973年 | 606篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Psychodid sand flies are blood-sucking fly vectors of several parasitic diseases. The oldest definitive record of this group is from the Lower Cretaceous amber of Lebanon (circa-135 to -125 My), but the high diversity within this group supports the idea that the psychodoids originated much earlier in history. The palaeontology demonstrates that the Lower Creataceous representatives of the different subfamilies of Psychodidae had similar morphology and were blood-feeders, which supports Hennig's hypothesis on the ground plan structure of this family. Historical relationship between sand flies and diseases is unclear up to the present time, but this relationship could be as old as the origin of psychodoids because of the blood-feeding life mode. 相似文献
992.
Pascal Fournier Christian Maizeret David Jimenez Jean-Pierre Chusseau Stéphane Aulagnier François Spitz 《Acta theriologica》2007,52(1):1-12
The European minkMustela lutreola Linnaeus, 1761 and the European polecatMustela putorius Linnaeus, 1758 are related species sympatric in southwestern France. The European mink is rapidly disappearing whereas the
polecat maintains good populations. Seasonal habitat use of both species was compared in the Landes de Gascogne region to
identify if some vulnerability factors of the European mink were associated with habitats occupied by this mustelid. Potential
habitats were mapped using a satellite picture and 12 main types of habitats were defined. Animal locations were recorded
by radiotracking 9 European mink and 14 polecats from March 1996 to August 1999. Resting animals were located by triangulation,
and, when possible, resting places were described. Animals in activity were tracked by continuous monitoring. Data collected
revealed a strong preference of European mink for flooded habitats, particularly open marshes, flooded woodlands and moorlands.
They seldom left the corridor of the riparian forest and their resting places were mainly in flooded environments, above ground
(under herbs or bushes) or in cavities between tree roots. European polecats were less tightly linked to wetlands. Most of
their locations were in the pine forests outside the valleys and their resting places were mainly in burrows. The strong specialisation
of European mink in aquatic habitats is probably one of the main reasons for its decline because wetlands suffer drastic damages
throughout all of its range. Maintaining adequate water levels is crucial for satisfying habitat requirements of mink. 相似文献
993.
Genetic diversity at 13 equine microsatellite loci was compared in five endangered Spanish donkey breeds: Andaluza, Catalana, Mallorquina, Encartaciones and Zamorano-Leonesa. All of the equine microsatellites used in this study were amplified and were polymorphic in the domestic donkey breeds with the exception of HMS1, which was monomorphic, and ASB2, which failed to amplify. Allele number, frequency distributions and mean heterozygosities were very similar among the Spanish donkey breeds. The unbiased expected heterozygosity (HE) over all the populations varied between 0.637 and 0.684 in this study. The low GST value showed that only 3.6% of the diversity was between breeds (P < 0.01). Significant deviations from Hardy-Weinberg equilibrium were shown for a number of locus-population combinations, except HMS5 that showed agreement in all analysed populations. The cumulative exclusion probability (PE) was 0.999 in each breed, suggesting that the loci would be suitable for donkey parentage testing. The constructed dendrogram from the DA distance matrix showed little differentiation between Spanish breeds, but great differentiation between them and the Moroccan ass and also with the horse, used as an outgroup. These results confirm the potential use of equine microsatellite loci as a tool for genetic studies in domestic donkey populations, which could also be useful for conservation plans. 相似文献
994.
Joubert DA Kars I Wagemakers L Bergmann C Kemp G Vivier MA van Kan JA 《Molecular plant-microbe interactions : MPMI》2007,20(4):392-402
Six endopolygalacturonases from Botrytis cinerea (BcPG1 to BcPG6) as well as mutated forms of BcPG1 and BcPG2 were expressed transiently in leaves of Nicotiana benthamiana using agroinfiltration. Expression of BcPG1, BcPG2, BcPG4, BcPG5, and mutant BcPG1-D203A caused symptoms, whereas BcPG3, BcPG6, and mutant BcPG2-D192A caused no symptoms. Expression of BcPG2 caused the most severe symptoms, including wilting and necrosis. BcPG2 previously has been shown to be essential for B. cinerea virulence. The in vivo effect of this enzyme and the inhibition by a polygalacturonase-inhibiting protein (PGIP) was examined by coexpressing Bcpg2 and the Vvpgipl gene from Vitis vinifera in N. benthamiana. Coinfiltration resulted in a substantial reduction of the symptoms inflicted by the activity of BcPG2 in planta, as evidenced by quantifying the variable chlorophyll fluorescence yield. In vitro, however, no interaction between pure VvPGIP1 and pure BcPG2 was detected. Specifically, VvPGIP1 neither inhibited BcPG2 activity nor altered the degradation profile of polygalacturonic acid by BcPG2. Furthermore, using surface plasmon resonance technology, no physical interaction between VvPGIP1 and BcPG2 was detected in vitro. The data suggest that the in planta environment provided a context to support the interaction between BcPG2 and VvPGIP1, leading to a reduction in symptom development, whereas neither of the in vitro assays detected any interaction between these proteins. 相似文献
995.
T. Corrêa de Souza P. César Magalhães F. José Pereira E. Mauro de Castro S. Netto Parentoni 《Acta Physiologiae Plantarum》2011,33(5):1877-1885
This study was carried out to evaluate maize plants of different recurrent selection cycles of the variety (Zea mays L.—Saracura-BRS-4154) regarded to genetic gains, morphophysiology, and grain yield, achieved over the selection cycles under
intermittent flooding of the soil. This variety has the capacity to survive and produce in temporarily flooded soils and was
developed by the National Maize and Sorghum Research Center (EMBRAPA). The experiment was conducted in greenhouse by using
ten alternating selection cycles (Cycle 1–18) and BR 107 a variety known for its susceptibility to flooding. The flooding
initiated at six-leaf stage by applying 50 mm of water three times a week. At flowering, the following parameters were evaluated:
rate of leaf photosynthesis, stomatal conductance, intercellular CO2 concentration, transpiration rate, photosynthetically active leaf area, root porosity, relative chlorophyll content, grain
yield, harvest index, ear length, and interval between male and female flowering. Yield as a function of root porosity and
photosynthesis were also evaluated. An index was created in this study, in order to help the discussion of the characteristics
evaluated, it was called “Relative Tolerance Value—RTV”, only gaseous exchange measurements was not included in this index.
By the way, it was observed throughout the selection cycles an increase in all gaseous exchange parameters, being the cycle
18, the one which presented the greatest averages. RTV for leaf area showed the greatest values for cycles 7 and 18, whereas
root porosity, chlorophyll relative content, and harvest index, the greater RTV values were found in cycles 17 and 18. The
largest grain yield RTV was observed in cycle 7, followed by cycles 13, 15, and 18. Flooding resulted in longer Anthesis-Silking
Interval, especially for the first cycles. At flooding condition, grain yield was strongly related to root porosity (R
2 = 0.66). These results showed that the selection cycles of “Saracura” maize improved some morphophysiologic characters, which
favor their survival in flooded environments, also resulting in higher productivity. 相似文献
996.
Under mild conditions (Lewis acid/solvent/room temperature), the reaction of unprotected glucose, deoxyribose or xylose with hydroxylalkylthymine gives selectively nucleoside analogs with a spacer arm between sugar and base moiety. Experimental conditions (Lewis acid, solvent) for this new strategy leading to nucleoside analogs synthesis are discussed. 相似文献
997.
998.
M. Crispo A. P. Mulet L. Tesson N. Barrera F. Cuadro P. C. dos Santos-Neto T. H. Nguyen A. Crénéguy L. Brusselle I. Anegón A. Menchaca 《PloS one》2015,10(8)
While CRISPR/Cas9 technology has proven to be a valuable system to generate gene-targeted modified animals in several species, this tool has been scarcely reported in farm animals. Myostatin is encoded by MSTN gene involved in the inhibition of muscle differentiation and growth. We determined the efficiency of the CRISPR/Cas9 system to edit MSTN in sheep and generate knock-out (KO) animals with the aim to promote muscle development and body growth. We generated CRISPR/Cas9 mRNAs specific for ovine MSTN and microinjected them into the cytoplasm of ovine zygotes. When embryo development of CRISPR/Cas9 microinjected zygotes (n = 216) was compared with buffer injected embryos (n = 183) and non microinjected embryos (n = 173), cleavage rate was lower for both microinjected groups (P<0.05) and neither was affected by CRISPR/Cas9 content in the injected medium. Embryo development to blastocyst was not affected by microinjection and was similar among the experimental groups. From 20 embryos analyzed by Sanger sequencing, ten were mutant (heterozygous or mosaic; 50% efficiency). To obtain live MSTN KO lambs, 53 blastocysts produced after zygote CRISPR/Cas9 microinjection were transferred to 29 recipient females resulting in 65.5% (19/29) of pregnant ewes and 41.5% (22/53) of newborns. From 22 born lambs analyzed by T7EI and Sanger sequencing, ten showed indel mutations at MSTN gene. Eight showed mutations in both alleles and five of them were homozygous for indels generating out-of frame mutations that resulted in premature stop codons. Western blot analysis of homozygous KO founders confirmed the absence of myostatin, showing heavier body weight than wild type counterparts. In conclusion, our results demonstrate that CRISPR/Cas9 system was a very efficient tool to generate gene KO sheep. This technology is quick and easy to perform and less expensive than previous techniques, and can be applied to obtain genetically modified animal models of interest for biomedicine and livestock. 相似文献
999.
Christian G. Blumentrath Martin P. Grobusch Pierre-Blaise Matsiégui Friedrich Pahlke Rella Zoleko-Manego Solange Nzenze-Aféne Barthélemy Mabicka Maurizio Sanguinetti Peter G. Kremsner Frieder Schaumburg 《PLoS neglected tropical diseases》2015,9(10)
Background
Rhinoentomophthoromycosis, or rhino-facial conidiobolomycosis, is a rare, grossly disfiguring disease due to an infection with entomophthoralean fungi. We report a case of rhinoentomophthoromycosis from Gabon and suggest a staging system, which provides information on the prognosis and duration of antifungal therapy.Methods
We present a case of rhinoentomophthoromycosis including the histopathology, mycology, and course of disease. For the suggested staging system, all cases on confirmed rhinoentomophthoromycosis published in the literature without language restriction were eligible. Exclusion criteria were missing data on (i) duration of disease before correct diagnosis, (ii) outcome, and (iii) confirmation of entomophthoralean fungus infection by histopathology and/or mycology. We classified cases into atypical (orbital cellulitis, severe pain, fever, dissemination), early, intermediate, and late disease based on the duration of symptoms before diagnosis. The outcome was evaluated for each stage of disease.Findings
The literature search of the Medpilot database was conducted on January 13, 2014, (updated on January 18, 2015). The search yielded 8,333 results including 198 cases from 117 papers; of these, 145 met our inclusion criteria and were included in the final analysis. Median duration of treatment was 4, 3, 4, and 5 months in atypical, early, intermediate, and late disease, respectively. Cure rates were clearly associated with stage of disease and were 57%, 100%, 82%, and 43% in atypical, early, intermediate, and late disease, respectively.Conclusion
We suggest a clinical staging system that underlines the benefit of early case detection and may guide the duration of antifungal treatment. The scientific value of this classification is its capacity to structure and harmonize the clinical and research approach towards rhinoentomophthoromycosis. 相似文献1000.