全文获取类型
收费全文 | 1057篇 |
免费 | 57篇 |
出版年
2023年 | 6篇 |
2022年 | 13篇 |
2021年 | 22篇 |
2020年 | 12篇 |
2019年 | 10篇 |
2018年 | 15篇 |
2017年 | 21篇 |
2016年 | 27篇 |
2015年 | 31篇 |
2014年 | 33篇 |
2013年 | 50篇 |
2012年 | 67篇 |
2011年 | 78篇 |
2010年 | 49篇 |
2009年 | 47篇 |
2008年 | 63篇 |
2007年 | 42篇 |
2006年 | 36篇 |
2005年 | 37篇 |
2004年 | 40篇 |
2003年 | 45篇 |
2002年 | 41篇 |
2001年 | 39篇 |
2000年 | 39篇 |
1999年 | 38篇 |
1998年 | 15篇 |
1997年 | 7篇 |
1996年 | 7篇 |
1995年 | 8篇 |
1994年 | 4篇 |
1993年 | 7篇 |
1992年 | 17篇 |
1991年 | 12篇 |
1990年 | 19篇 |
1989年 | 19篇 |
1988年 | 9篇 |
1987年 | 12篇 |
1986年 | 11篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 10篇 |
1982年 | 4篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1977年 | 7篇 |
1975年 | 5篇 |
1973年 | 4篇 |
1972年 | 4篇 |
1970年 | 3篇 |
1968年 | 2篇 |
排序方式: 共有1114条查询结果,搜索用时 15 毫秒
61.
Multiple matings result in varying paternity share based on mating interval and order. Thus, assessing the effect of mating interval and order on patterns of sperm usage and paternity is crucial. We designed consecutive and delayed double-mating experiments to investigate paternity variation in ladybird, Menochilus sexmaculatus (Fabricius) (Coleoptera: Coccinellidae), using two distinct morphs of the species as phenotypic markers of paternity. The time to commence mating, copulation duration and reproductive output were recorded. The morphs of the offspring from the two setups were taken as a measure of paternity accumulated by the males. The time to commence mating decreased for the second mating in the consecutive mating treatment, while the reverse was observed in the delayed mating treatment. Consecutive double matings reduced the mating duration. Fecundity increased when second mating occurred after a few days, though percent egg viability remained unaffected. The second male accrued higher paternity (P2?=?0.61) than the first male (P1?=?0.39) in the consecutive mating treatment, while in the delayed mating treatment, the overall paternity share of the first 0.49 (P1) and last male was equal 0.51 (P2). Thus, our study revealed that both mating order and the time interval between successive matings regulate the male paternity share. This finding is reported for the first time in this ladybird species. 相似文献
62.
63.
Visceral leishmaniasis caused by the protozoan Leishmania donovani is the most severe form of leishmaniasis and it is potentially lethal if untreated. Despite the availability of drugs for treating the disease, the current drug regime suffers from drawbacks like antibiotic resistance and toxicity. New drugs have to be discovered in order to overcome these limitations. Our aim is to identify natural compounds from plant sources as putative inhibitors considering the occurrence of structural diversity in plant sources. Spermidine Synthase (SpdS) was chosen as the target enzyme as it plays a vital role in growth, survival, and due to its contribution in virulence. Our initial investigation started with a literature survey in identifying natural compounds that showed antileishmanial activity. Subsequently, we identified two monoterpenoid compounds, namely Geraniol and Linalool, that were structurally analogous to one of the substrates (putrescine) of SpdS. In the present study, homology model of L. donovani SpdS was generated and the binding affinity of the identified compounds was analyzed and also compared with the putrescine through molecular docking and dynamic studies. The pharmacokinetic properties of the identified compounds were validated and the binding efficiency of these ligands over the original substrate has been demonstrated. Based on these studies, Geraniol and Linalool can be considered as lead molecules for future investigations targeting SpdS. This study further emphasizes the choice of natural compounds as a good source of therapeutic agents. 相似文献
64.
Antibody Detection and Molecular Characterization of Toxoplasma gondii from Bobcats (Lynx rufus), Domestic Cats (Felis catus), and Wildlife from Minnesota,USA 下载免费PDF全文
Shiv K. Verma Larissa Minicucci Darby Murphy Michelle Carstensen Carolin Humpal Paul Wolf Rafael Calero‐Bernal Camila K. Cerqueira‐Cézar Oliver C.H. Kwok Chunlei Su Dolores Hill Jitender P. Dubey 《The Journal of eukaryotic microbiology》2016,63(5):567-571
Little is known of the epidemiology of toxoplasmosis in Minnesota. Here, we evaluated Toxoplasma gondii infection in 50 wild bobcats (Lynx rufus) and 75 other animals on/near 10 cattle farms. Antibodies to T. gondii were assayed in serum samples or tissue fluids by the modified agglutination test (MAT, cut‐off 1:25). Twenty nine of 50 bobcats and 15 of 41 wildlife trapped on the vicinity of 10 farms and nine of 16 adult domestic cats (Felis catus) and six of 14 domestic dogs resident on farms were seropositive. Toxoplasma gondii oocysts were not found in feces of any felid. Tissues of all seropositive wild animals trapped on the farm were bioassayed in mice and viable T. gondii was isolated from two badgers (Taxidea taxus), two raccoons (Procyon lotor), one coyote (Canis latrans), and one opossum (Didelphis virginiana). All six T. gondii isolates were further propagated in cell culture. Multi‐locus PCR‐RFLP genotyping using 10 markers (SAG1, SAG2 (5′‐3′SAG2, and alt.SAG2), SAG3, BTUB, GRA6, c22‐8, c29‐2, L358, PK1, and Apico), and DNA from cell culture derived tachyzoites revealed three genotypes; #5 ToxoDataBase (1 coyote, 1 raccoon), #1 (1 badger, 1 raccoon, 1 opossum), and #2 (1 badger). This is the first report of T. gondii prevalence in domestic cats and in bobcats from Minnesota, and the first isolation of viable T. gondii from badger. 相似文献
65.
66.
We report here a PCR-based cloning methodology that requires no post-PCR modifications such as restriction digestion and phosphorylation of the amplified DNA. The advantage of the present method is that it yields only recombinant clones thus eliminating the need for screening. Two DNA amplification reactions by PCR are performed wherein the first reaction amplifies the gene of interest from a source template, and the second reaction fuses it with the designed expression vector fragments. These vector fragments carry the essential elements that are required for the fusion product selection. The entire process can be completed in less than 8 hours. Furthermore, ligation of the amplified DNA by a DNA ligase is not required before transformation, although the procedure yields more number of colonies upon transformation if ligation is carried out. As a proof-of-concept, we show the cloning and expression of GFP, adh, and rho genes. Using GFP production as an example, we further demonstrate that the E. coli T7 express strain can directly be used in our methodology for the protein expression immediately after PCR. The expressed protein is without or with 6xHistidine tag at either terminus, depending upon the chosen vector fragments. We believe that our method will find tremendous use in molecular and structural biology. 相似文献
67.
Dharmendra Singh Chandan Kumar Singh Ram Sewak Singh Tomar Jyoti Taunk Ranjeet Singh Sadhana Maurya Ashish Kumar Chaturvedi Pal Madan Singh Rajendra Dubey Sarawan Kumar 《PloS one》2016,11(1)
The success of drought tolerance breeding programs can be enhanced through molecular assortment of germplasm. This study was designed to characterize molecular diversity within and between Lens species with different adaptations to drought stress conditions using SSR markers. Drought stress was applied at seedling stage to study the effects on morpho-physiological traits under controlled condition, where tolerant cultivars and wilds showed 12.8–27.6% and 9.5–23.2% reduction in seed yield per plant respectively. When juxtaposed to field conditions, the tolerant cultivars (PDL-1 and PDL-2) and wild (ILWL-314 and ILWL-436) accessions showed 10.5–26.5% and 7.5%–15.6% reduction in seed yield per plant, respectively under rain-fed conditions. The reductions in seed yield in the two tolerant cultivars and wilds under severe drought condition were 48–49% and 30.5–45.3% respectively. A set of 258 alleles were identified among 278 genotypes using 35 SSR markers. Genetic diversity and polymorphism information contents varied between 0.321–0.854 and 0.299–0.836, with mean value of 0.682 and 0.643, respectively. All the genotypes were clustered into 11 groups based on SSR markers. Tolerant genotypes were grouped in cluster 6 while sensitive ones were mainly grouped into cluster 7. Wild accessions were separated from cultivars on the basis of both population structure and cluster analysis. Cluster analysis has further grouped the wild accessions on the basis of species and sub-species into 5 clusters. Physiological and morphological characters under drought stress were significantly (P = 0.05) different among microsatellite clusters. These findings suggest that drought adaptation is variable among wild and cultivated genotypes. Also, genotypes from contrasting clusters can be selected for hybridization which could help in evolution of better segregants for improving drought tolerance in lentil. 相似文献
68.
Autonomously replicating sequence (ARS) elements are the genetic determinants of replication origin function in yeasts. They
can be easily identified as the plasmids containing them transform yeast cells at a high frequency. As the first step towards
identifying all potential replication origins in a 73-kb region of the long arm of fission yeast chromosome II, we have mapped
five new ARS elements using systematic subcloning and transformation assay. 2D analysis of one of the ARS plasmids that showed
highest transformation frequency localized the replication origin activity within the cloned genomic DNA. All the new ARS
elements are localized in two clusters in centromere proximal 40 kb of the region. The presence of at least six ARS elements,
including the previously reported ars727, is suggestive of a higher origin density in this region than that predicted earlier using a computer based search. 相似文献
69.
Dubey JP Alvarado-Esquivel C Liesenfeld O Herrera-Flores RG Ramírez-Sánchez BE González-Herrera A Martínez-García SA Bandini LA Kwok OC 《The Journal of parasitology》2007,93(5):1033-1035
Toxoplasma gondii and Neospora caninum are structurally similar parasites, with many hosts in common. The prevalence of antibodies to T. gondii and N. caninum was determined in sera from dogs from Durango City, Mexico. Using a modified agglutination test, antibodies to T. gondii were found in 52 (51.5%) of the 101 dogs with titers of 1:25 in 27, 1:50 in 11, 1:100 in 5, 1:200 in 4, 1:400 in 2, 1:800 in 2, and 1:3,200 or higher in 1. Antibodies to N. caninum were determined by the indirect immunofluorescent antibody test (IFAT) and the Neospora sp. agglutination test (NAT). Two of the 101 dogs had N. caninum antibodies; these dogs did not have T. gondii antibodies, supporting the specificity of the tests used. The N. caninum antibody titers of the 2 dogs were: 1:400 by IFAT and 1:200 by NAT in 1, and 1:25 by NAT and IFAT in the other. Results indicate that these 2 structurally similar protozoans are antigenically different. 相似文献
70.
Dubey JP Morales JA Sundar N Velmurugan GV González-Barrientos CR Hernández-Mora G Su C 《The Journal of parasitology》2007,93(3):710-711
Toxoplasma gondii infection in marine mammals is of interest because of mortality and mode of transmission. It has been suggested that marine mammals become infected with T. gondii oocysts washed from land to the sea. We report the isolation and genetic characterization of viable T. gondii from a striped dolphin (Stenella coeruleoalba), the first time from this host. An adult female dolphin was found stranded on the Pacific Coast of Costa Rica, and the animal died the next day. The dolphin had a high (1:6400) antibody titer to T. gondii in the modified agglutination test. Severe nonsuppurative meningoencephalomyelitis was found in its brain and spinal cord, but T. gondii was not found in histological sections of the dolphin. Portions of its brain and the heart were bioassayed in mice for the isolation of T. gondii. Viable T. gondii was isolated from the brain, but not from the heart, of the dolphin. A cat fed mice infected with the dolphin isolate (designated TgSdCol) shed oocysts. Genomic DNA from tachyzoites of this isolate was used for genotyping at 10 genetic loci, including SAG1, SAG2, SAG3, BTUB, GRA6, c22-8, c29-2, L358, PK1, and Apico, and this TgSdCo1 isolate was found to be Type II. 相似文献