全文获取类型
收费全文 | 105330篇 |
免费 | 1410篇 |
国内免费 | 1032篇 |
出版年
2023年 | 93篇 |
2022年 | 165篇 |
2021年 | 340篇 |
2020年 | 217篇 |
2019年 | 231篇 |
2018年 | 12068篇 |
2017年 | 10842篇 |
2016年 | 7762篇 |
2015年 | 1172篇 |
2014年 | 843篇 |
2013年 | 1004篇 |
2012年 | 5042篇 |
2011年 | 13559篇 |
2010年 | 12447篇 |
2009年 | 8667篇 |
2008年 | 10391篇 |
2007年 | 11871篇 |
2006年 | 753篇 |
2005年 | 970篇 |
2004年 | 1464篇 |
2003年 | 1457篇 |
2002年 | 1184篇 |
2001年 | 652篇 |
2000年 | 492篇 |
1999年 | 331篇 |
1998年 | 151篇 |
1997年 | 115篇 |
1996年 | 112篇 |
1995年 | 127篇 |
1994年 | 102篇 |
1993年 | 117篇 |
1992年 | 190篇 |
1991年 | 231篇 |
1990年 | 145篇 |
1989年 | 168篇 |
1988年 | 155篇 |
1987年 | 144篇 |
1986年 | 110篇 |
1985年 | 133篇 |
1984年 | 114篇 |
1983年 | 105篇 |
1982年 | 60篇 |
1981年 | 65篇 |
1980年 | 63篇 |
1979年 | 70篇 |
1978年 | 72篇 |
1977年 | 63篇 |
1975年 | 58篇 |
1972年 | 278篇 |
1971年 | 312篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
A strain of canine parvovirus (CPV) was isolated from feces of an ill puppy in an animal hospital in Wuhan, China. It was designated as CPV/WH02/06. This isolate was identified as serotype CPV-2a by the hemagglutination test, CPV Ag detection strip, electron microscopy, and PCR. The vp2 gene was cloned and sequenced and assigned GenBank accession number EU377537. A 1242 bp segment of the 5' region of the vp2 gene was cloned and inserted into the binary vector pBI121 and used for Agrobacterium-mediated tobacco transformation. Transgenic tobacco plants were selected on MS medium supplemented with 100 μg/mL kanamycin and 100 μg/mL timentin. Integration of the vp2 gene into the tobacco genome was confirmed by PCR using T1 progeny plants, and the expression of the VP2 protein was confirmed by Western blotting. 相似文献
993.
994.
Current knowledge of microbial community structures in landfills and its cover soils 总被引:2,自引:0,他引:2
Semrau JD 《Applied microbiology and biotechnology》2011,89(4):961-969
Landfills are a vital component of our waste handling processes. Our lack of knowledge on the microbial processes in these
systems, however, hampers our ability to design the next generation of landfills that: (1) enhance the rate and extent of
waste decomposition, (2) produce byproducts of some value (e.g., methane that can be used for energy generation), and, (3)
minimize their overall impact on driving climate change through the emission of greenhouse gases. In this review, the current
state of knowledge the microbial community structure and activity in both the refuse and overlying cover soils is discussed,
and suggestions provided for future research in this critical aspect of our infrastructure. 相似文献
995.
Nostoc flagelliforme, which is distributed on arid and semi-arid steppes of northwestern parts of China, has attracted increasing interest for
its stress tolerance. In order to gain more insight into the genetic background of N. flagelliforme, we sequenced its partial genomic DNA for similarity analyses against current public databases, followed by phylogenetic
comparison of N. flagelliforme and the potentially related species deduced from the similarity analyses. Approximately 430 kb genomic sequence (~5% of genome
as a rough estimate) was determined from 106 distinct genomic clones. Nucleotide BLAST showed that ~23.1% of the partial genomic
sequence was similar to N. punctiforme genomic DNA and ~12.4% to its plasmid DNA. Similar protein search by online FASTA-protein program showed 46.2% of the similar
proteins had their corresponding orthologs in N. punctiforme genome. Furthermore, phylogenetic comparison based on 16S rRNA sequences showed N. flagelliforme and N. punctiforme clustered closer among the deduced related species. These results indicated that N. punctiforme might also be potentially close neighbor species of N. flagelliforme, in addition to the formerly regarded close neighbor species N. commune and N. sphaeroids. In general, these data enriched our recognition of the evolutionary relationship between N. flagelliforme and other Nostoc species, especially N. punctiforme. 相似文献
996.
997.
Xuemei Han Shauna P. Dendy Karen A. Garrett Liang Fang Melinda D. Smith 《Plant Ecology》2008,198(2):197-210
We surveyed the prevalence and amount of leaf damage related to herbivory and pathogens on 12 pairs of exotic (invasive and
noninvasive) and ecologically similar native plant species in tallgrass prairie to examine whether patterns of damage match
predictions from the enemy release hypothesis. We also assessed whether natural enemy impacts differed in response to key
environmental factors in tallgrass prairie by surveying the prevalence of rust on the dominant C4 grass, Andropogon gerardii, and its congeneric invasive exotic C4 grass, A. bladhii, in response to fire and nitrogen fertilization treatments. Overall, we found that the native species sustain 56.4% more
overall leaf damage and 83.6% more herbivore-related leaf damage when compared to the exotic species. Moreover, we found that
the invasive exotic species sustained less damage from enemies relative to their corresponding native species than the noninvasive
exotic species. Finally, we found that burning and nitrogen fertilization both significantly increased the prevalence of rust
fungi in the native grass, while rust fungi rarely occurred on the exotic grass. These results indicate that reduced damage
from enemies may in part explain the successful naturalization of exotic species and the spread of invasive exotic species
in tallgrass prairie. 相似文献
998.
Ho Nam Chang Nag-Jong Kim Jongwon Kang Chang Moon Jeong 《Biotechnology and Bioprocess Engineering》2010,15(1):1-10
The typical biorefinery platforms are sugar, thermochemical (syngas), carbon-rich chains, and biogas platforms, each offering
unique advantages and disadvantages. The sugar platform uses hexose and pentose sugars extracted or converted from plant body
mass. The thermochemical (syngas) platform entails a chemical or biological conversion process using pyrolysis or gasification
of plants to produce biofuels. The carbon-rich chains platform is used to produce biodiesel from long-chain fatty acids or
glycerides. In the present work, we suggest a new platform using volatile fatty acids (VFAs) for the production of biofuels
and biochemicals production. The VFAs are short-chain fatty acids composed mainly of acetate and butyrate in the anaerobic
digestion (AD) process, which does not need sterilization, additional hydrolysis enzymes (cellulose or xylanase), or a high
cost pretreatment step. VFAs are easily produced from almost all kinds of biomass with low lignin content (terrestrial, aquatic,
and marine biomass) by the AD process. Considering that raw material alone constitutes 40∼80% of biofuel production costs,
biofuels made from VFAs derived from waste organic biomass potentially offer significant economical advantage. 相似文献
999.
DNA vaccines consisted of tumor-associated antigen (TAA) are well suited for immunotherapy against tumor. The construct can
contain TAA fused to an appropriate molecule (biologic adjuvant) to improve the efficacy of anti-tumor immune response. Heat
shock protein 70 (HSP70) has been shown to be an excellent candidate, capable of cross-priming TAA by antigen presenting cells
leading to a robust T-cell response. However, the relationship between strong T-cell responses and tumor rejection is not
always mutually exclusive, for which TAA loss or activation of suppressive mechanisms may occur. HSP70 fused to downstream
of Her2/neu as DNA vaccine has been shown to be efficient against Her2-expressing tumors. In this study, we examined if N-terminally
fusion of Her2/neu to HSP70 could also improve efficiency of Her2/neu DNA vaccine. Therefore, mice with an established Her2/neu
expressing tumor were immunized with DNA vaccine consisting of extracellular and trans-membrane domain (EC+TM) of rat Her2/neu
alone or N-terminally fused to HSP70 and immune response was evaluated. Administration of rat Her2/neu led to partial control
of tumor progression. Surprisingly, fusion of HSP70 to N-terminal of rat Her2/neu led to tumor progression. Our result proposes
that fusion direction of biologic adjuvant is an important consideration when Her2/neu is used. 相似文献
1000.
Pangkhi Medhi Ololade Olatunji Atul Nayak Chandra Teja Uppuluri Richard T. Olsson Buchi N. Nalluri Diganta B. Das 《AAPS PharmSciTech》2017,18(5):1488-1494
Microneedle (MN) technology has emerged as an effective drug delivery system, and it has tremendous potential as a patient friendly substitute for conventional methods for transdermal drug delivery (TDD). In this paper, we report on the preparation of lidocaine-loaded biodegradable microneedles, which are manufactured from fish scale-derived collagen. Lidocaine, a common tissue numbing anaesthetic, is loaded in these microneedles with an aim of delivering the drug with controlled skin permeation. Evaluation of lidocaine permeation in porcine skin has been successfully performed using Franz diffusion cell (FDC) which has shown that the drug permeation rate increases from 2.5 to 7.5% w/w after 36 h and pseudo steady state profile is observed from 5.0 to 10.0% w/w lidocaine-loaded microneedle. Swelling experiments have suggested that the microneedles have negligible swellability which implies that the patch would stick to the tissue when inserted. The experiments on MN dissolution have depicted that the lidocaine loaded in the patch is lower than the theoretical loading, which is expected as there can be losses of the drug during initial process manufacture. 相似文献