全文获取类型
收费全文 | 1817篇 |
免费 | 109篇 |
国内免费 | 6篇 |
出版年
2023年 | 8篇 |
2022年 | 27篇 |
2021年 | 72篇 |
2020年 | 51篇 |
2019年 | 42篇 |
2018年 | 64篇 |
2017年 | 67篇 |
2016年 | 89篇 |
2015年 | 102篇 |
2014年 | 105篇 |
2013年 | 149篇 |
2012年 | 138篇 |
2011年 | 139篇 |
2010年 | 88篇 |
2009年 | 69篇 |
2008年 | 74篇 |
2007年 | 80篇 |
2006年 | 60篇 |
2005年 | 63篇 |
2004年 | 48篇 |
2003年 | 39篇 |
2002年 | 36篇 |
2001年 | 26篇 |
2000年 | 23篇 |
1999年 | 21篇 |
1998年 | 14篇 |
1997年 | 11篇 |
1996年 | 13篇 |
1995年 | 8篇 |
1994年 | 10篇 |
1992年 | 13篇 |
1991年 | 8篇 |
1990年 | 7篇 |
1989年 | 6篇 |
1988年 | 8篇 |
1987年 | 7篇 |
1986年 | 5篇 |
1985年 | 8篇 |
1984年 | 18篇 |
1983年 | 10篇 |
1982年 | 10篇 |
1980年 | 5篇 |
1979年 | 11篇 |
1978年 | 6篇 |
1976年 | 6篇 |
1975年 | 6篇 |
1974年 | 9篇 |
1973年 | 6篇 |
1972年 | 11篇 |
1967年 | 5篇 |
排序方式: 共有1932条查询结果,搜索用时 15 毫秒
71.
72.
Nazmul Haque Noor Hayaty Abu Kasim Mohammad Tariqur Rahman 《International journal of biological sciences》2015,11(3):324-334
Mesenchymal stem cells (MSCs) are considered a potential tool for cell based regenerative therapy due to their immunomodulatory property, differentiation potentials, trophic activity as well as large donor pool. Poor engraftment and short term survival of transplanted MSCs are recognized as major limitations which were linked to early cellular ageing, loss of chemokine markers during ex vivo expansion, and hyper-immunogenicity to xeno-contaminated MSCs. These problems can be minimized by ex vivo expansion of MSCs in hypoxic culture condition using well defined or xeno-free media i.e., media supplemented with growth factors, human serum or platelet lysate. In addition to ex vivo expansion in hypoxic culture condition using well defined media, this review article describes the potentials of transient adaptation of expanded MSCs in autologous serum supplemented medium prior to transplantation for long term regenerative benefits. Such transient adaptation in autologous serum supplemented medium may help to increase chemokine receptor expression and tissue specific differentiation of ex vivo expanded MSCs, thus would provide long term regenerative benefits. 相似文献
73.
Identifying qualitative effects of different grazing types on below‐ground communities and function in a long‐term field experiment 下载免费PDF全文
Catriona A. Macdonald Michael J. Crawley Denis J. Wright Justin Kuczynski Lucinda Robinson Rob Knight Waleed Abu Al‐Soud Søren J. Sørensen Ye Deng Jizhong Zhou Brajesh K. Singh 《Environmental microbiology》2015,17(3):841-854
Herbivory is an important modulator of plant biodiversity and productivity in grasslands, but our understanding of herbivore‐induced changes on below‐ground processes and communities is limited. Using a long‐term (17 years) experimental site, we evaluated impacts of rabbit and invertebrate grazers on some soil functions involved in carbon cycling, microbial diversity, structure and functional composition. Both rabbit and invertebrate grazing impacted soil functions and microbial community structure. All functional community measures (functions, biogeochemical cycling genes, network association between different taxa) were more strongly affected by invertebrate grazers than rabbits. Furthermore, our results suggest that exclusion of invertebrate grazers decreases both microbial biomass and abundance of genes associated with key biogeochemical cycles, and could thus have long‐term consequences for ecosystem functions. The mechanism behind these impacts are likely to be driven by both direct effects of grazing altering the pattern of nutrient inputs and by indirect effects through changes in plant species composition. However, we could not entirely discount that the pesticide used to exclude invertebrates may have affected some microbial community measures. Nevertheless, our work illustrates that human activity that affects grazing intensity may affect ecosystem functioning and sustainability, as regulated by multi‐trophic interactions between above‐ and below‐ground communities. 相似文献
74.
75.
76.
Boonfei Tan S Jane Fowler Nidal Abu Laban Xiaoli Dong Christoph W Sensen Julia Foght Lisa M Gieg 《The ISME journal》2015,9(9):2028-2045
Methanogenic hydrocarbon metabolism is a key process in subsurface oil reservoirs and hydrocarbon-contaminated environments and thus warrants greater understanding to improve current technologies for fossil fuel extraction and bioremediation. In this study, three hydrocarbon-degrading methanogenic cultures established from two geographically distinct environments and incubated with different hydrocarbon substrates (added as single hydrocarbons or as mixtures) were subjected to metagenomic and 16S rRNA gene pyrosequencing to test whether these differences affect the genetic potential and composition of the communities. Enrichment of different putative hydrocarbon-degrading bacteria in each culture appeared to be substrate dependent, though all cultures contained both acetate- and H2-utilizing methanogens. Despite differing hydrocarbon substrates and inoculum sources, all three cultures harbored genes for hydrocarbon activation by fumarate addition (bssA, assA, nmsA) and carboxylation (abcA, ancA), along with those for associated downstream pathways (bbs, bcr, bam), though the cultures incubated with hydrocarbon mixtures contained a broader diversity of fumarate addition genes. A comparative metagenomic analysis of the three cultures showed that they were functionally redundant despite their enrichment backgrounds, sharing multiple features associated with syntrophic hydrocarbon conversion to methane. In addition, a comparative analysis of the culture metagenomes with those of 41 environmental samples (containing varying proportions of methanogens) showed that the three cultures were functionally most similar to each other but distinct from other environments, including hydrocarbon-impacted environments (for example, oil sands tailings ponds and oil-affected marine sediments). This study provides a basis for understanding key functions and environmental selection in methanogenic hydrocarbon-associated communities. 相似文献
77.
Muhammad A. Aqueel Abu‐bakar M. Raza Rashad M. Balal Muhammad A. Shahid Irfan Mustafa Muhammad M. Javaid Simon R. Leather 《Insect Science》2015,22(6):813-820
Host plant nutritional quality can directly and indirectly affect the third trophic levels. The aphid–parasitoid relationship provides an ideal system to investigate tritrophic interactions (as the parasitoids are completely dependent for their development upon their hosts) and assess the bottom up forces operating at different concentrations of nitrogen applications. The effects of varying nitrogen fertilizer on the performance of Aphidius colemani (V.) reared on Sitobion avenae (F.) and Aphidius rhopalosiphi (D.) reared on Rhopalosiphum padi (L.) were measured. Parasitism and percent emergence of parasitoids were positively affected by nitrogen fertilizer treatments while developmental duration (egg, larval, and pupal stages) was not affected by increasing nitrogen inputs. In males and females of both parasitoid species, adult longevity increased with the increasing nitrogen fertilizer. Hind tibia length and mummy weight of both parasitoid species increased with nitrogen fertilizer concentrations, as a result of larger aphids. This study showed that nitrogen application to the soil can have important consequences for aboveground multitrophic interactions. 相似文献
78.
Deepak P. Edward Hind Alkatan Qundeel Rafiq Charles Eberhart Saleh Al Mesfer Nicola Ghazi Leen Al Safieh Altaf A. Kondkar Khaled K. Abu Amero 《PloS one》2015,10(3)
Purpose
To study the differential expression of microRNA (miRNA) profiles between intraocular medulloepithelioma (ME) and normal control tissue (CT).Material and Methods
Total RNA was extracted from formalin fixed paraffin embedded (FFPE) intraocular ME (n=7) and from age matched ciliary body controls (n=8). The clinical history and phenotype was recorded. MiRNA profiles were determined using the Affymetrix GeneChip miRNA Arrays analyzed using expression console 1.3 software. Validation of significantly dysregulated miRNA was confimed by quantitaive real-time PCR. The web-based DNA Intelligent Analysis (DIANA)-miRPath v2.0 was used to perform enrichment analysis of differentially expressed (DE) miRNA gene targets in Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway.Results
The pathologic evaluation revealed one benign (benign non-teratoid, n=1) and six malignant tumors (malignant teratoid, n=2; malignant non-teratoid, n = 4). A total of 88 miRNAs were upregulated and 43 miRNAs were downregulated significantly (P<0.05) in the tumor specimens. Many of these significantly dysregulated miRNAs were known to play various roles in carcinogenesis and tumor behavior. RT-PCR validated three significantly upregulated miRNAs and three significantly downregulated miRNAs namely miR-217, miR-216a, miR-216b, miR-146a, miR-509-3p and miR-211. Many DE miRNAs that were significant in ME tumors showed dysregulation in retinoblastoma, glioblastoma, and precursor, normal and reactive human cartilage. Enriched pathway analysis suggested a significant association of upregulated miRNAs with 15 pathways involved in prion disease and several types of cancer. The pathways involving significantly downregulated miRNAs included the toll-like receptor (TLR) (p<4.36E-16) and Nuclear Factor kappa B (NF-κB) signaling pathways (p<9.00E-06).Conclusions
We report significantly dysregulated miRNAs in intraocular ME tumors, which exhibited abnormal profiles in other cancers as well such as retinoblastoma and glioblastoma. Pathway analysis of all dysregulated miRNAs shared commonalities with other cancer pathways. 相似文献79.
Sudip?Biswas Samsad?Razzaque Sabrina?M.?Elias U.?S.?Mahzabin?Amin Taslima?Haque S.?M.?Touhidul?Islam Laisa?A.?Lisa Farhana?Naznin Noorain?M.?Rasul Zeba?I.?SerajEmail author 《Acta Physiologiae Plantarum》2015,37(1):1730
The vacuolar Na+/H+ antiporter is known to alleviate saline stress by sequestering Na+ in both wild-type Arabidopsis and rice and when over-expressed in many transgenic plants. Here we report on the effect of the NHX1 transgene on the salt tolerance properties it confers to a rice landrace and a commercial cultivar suitable for the dry winter season, but which suffers loss due to seasonal stresses, particularly in the coastal areas. The Nipponbare Na+/H+ antiporter 1.9 kb cDNA was cloned into pCAMBIA1305.1 under the control of the CaMV35S promoter and transformed into tissue-culture-responsive rice landrace Binnatoa (BA). The best-expressing transgenic line at T2 was found to be significantly tolerant at the seedling stage and was advanced to T3. The transgene was then transferred to the tissue-culture recalcitrant farmer-popular commercial rice genotype, BRRIdhan 28 (BR28) by crossing. The data generated both from semi-quantitative RT-PCR and western blot hybridization revealed that the transgene showed similar expression in the crossbred BR28 plants and BA transgenic line. Comparative stress tolerance tests, however, revealed that the BR28 crossbred lines were significantly less tolerant than its transgenic parent BA at both seedling and reproductive stages. A single successful transgenic event may therefore not show the same performance in the recipient genetic background, if introgressed by crossing. 相似文献
80.
Debbie C. Crans Samantha Schoeberl Ernestas Gaidamauskas Bharat Baruah Deborah A. Roess 《Journal of biological inorganic chemistry》2011,16(6):961-972
The interactions of metabolites of the antidiabetic vanadium-containing drug bis(maltolato)oxovanadium(IV) (BMOV) with lipid
interface model systems were investigated and the results were used to describe a potentially novel mechanism by which these
compounds initiate membrane-receptor-mediated signal transduction. Specifically, spectroscopic studies probed the BMOV oxidation
and hydrolysis product interaction with interfaces created from cetyltrimethylammonium bromide (CTAB) which mimics the positively
charged head group on phosphatidylcholine. 1H and 51V NMR spectroscopies were used to determine the location of the dioxobis(maltolato)oxovanadate(V) and the maltol ligand in
micelles and reverse micelles by measuring changes in the chemical shift, signal linewidth, and species distribution. Both
micelles and reverse micelles interacted similarly with the complex and the ligand, suggesting that interaction is strong
as anticipated by Coulombic attraction between the positively charged lipid head group and the negatively charged complex
and deprotonated ligand. The nature of the model system was confirmed using dynamic light scattering studies and conductivity
measurements. Interactions of the complex/ligand above and below the critical micelle concentration of micelle formation were
different, with much stronger interactions when CTAB was in the form of a micelle. Both the complex and the ligand penetrated
the lipid interface and were located near the charged head group. These studies demonstrate that a lipid-like interface affects
the stability of the complex and raise the possibility that ligand exchange at the interface may be important for the mode
of action for these systems. Combined, these studies support recently reported in vivo observations of BMOV penetration into
3T3-L1 adipocyte membranes and increased translocation of a glucose transporter to the plasma membrane. 相似文献