全文获取类型
收费全文 | 549篇 |
免费 | 25篇 |
国内免费 | 2篇 |
专业分类
576篇 |
出版年
2022年 | 15篇 |
2021年 | 27篇 |
2020年 | 21篇 |
2019年 | 28篇 |
2018年 | 36篇 |
2017年 | 19篇 |
2016年 | 16篇 |
2015年 | 28篇 |
2014年 | 20篇 |
2013年 | 41篇 |
2012年 | 42篇 |
2011年 | 33篇 |
2010年 | 15篇 |
2009年 | 13篇 |
2008年 | 21篇 |
2007年 | 23篇 |
2006年 | 12篇 |
2005年 | 15篇 |
2004年 | 10篇 |
2003年 | 15篇 |
2002年 | 7篇 |
2001年 | 17篇 |
2000年 | 8篇 |
1998年 | 4篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1993年 | 4篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 5篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 6篇 |
1980年 | 4篇 |
1978年 | 3篇 |
1975年 | 2篇 |
1972年 | 3篇 |
1971年 | 5篇 |
1970年 | 5篇 |
1969年 | 2篇 |
1968年 | 1篇 |
1960年 | 1篇 |
1948年 | 1篇 |
排序方式: 共有576条查询结果,搜索用时 15 毫秒
51.
Fathi GH Eshtiaghi H Kheiri A Okhovat M 《Communications in agricultural and applied biological sciences》2004,69(3):393-396
In this research, control of tomato root- knot nematode (Meloidogyne incognita) was conducted using tea dust residues at different rates. First, the species and race of nematode were identified by employing diagnostic keys. Then, with 5 replications in complete randomized design. Tea dust residues were used at 9 treatments (0, 5, 10, 15, 20, 25, 30, 35 and 40 g/kg of soil). Statistical analysis on mean treatments rates showed that treatment with 25 g/kg soil economically was effective in growth rates and reduction in gall index. 相似文献
52.
DeCarr LB Buckholz TM Coish PD Fathi Z Fisk SE Mays MR O'Connor SJ Lumb KJ 《Bioorganic & medicinal chemistry letters》2007,17(2):538-541
Activation of the NPY2 receptor to reduce appetite while avoiding stimulation of the NPY1 and NPY5 receptors that induce feeding provides a pharmaceutical approach to modulate food intake. The naturally occurring peptide PYY(3-36) is a nonselective NPY1, NPY2, and NPY5 agonist. N-terminal truncation of PYY to abrogate affinity for the NPY1 and NPY5 receptors and subsequent N-terminal modification with aminobenzoic analogs to restore NPY2 receptor potency results in a series of highly selective NPY2 receptor peptide agonists. 相似文献
53.
54.
Sallam SM Abdelgaleil SA Bueno IC Nasser ME Araujo RC Abdalla AL 《Archives of animal nutrition》2011,65(3):203-214
The objectives of this study were to characterise four essential oils (EO) chemically and to evaluate their effect on ruminal fermentation and methane emission in vitro. The investigated EO were isolated from Achillea santolina, Artemisia judaica, Schinus terebinthifolius and Mentha microphylla, and supplemented at four levels (0, 25, 50 and 75 microl) to 75 ml of buffered rumen fluid plus 0.5 g of substrate. The main components of the EO were piperitone (49.1%) and camphor (34.5%) in A. judaica, 16-dimethyl 15-cyclooactdaiene (60.5%) in A. santolina, piperitone oxide (46.7%) and cis-piperitone oxide (28%) in M. microphylla, and gamma-muurolene (45.3%) and alpha-thujene (16.0%) in S. terebinthifolius. The EO from A. santolina (at 25 and 50 j1), and all levels of A. judaica increased the gas production significantly, but S. terebinthifolius (at 50 and 75 microl), A. santolina (at 75 microl) and all levels of M. microphylla decreased the gas production significantly in comparison with the control. The highest levels of A. santolina and A. judaica, and all doses from M. microphylla EO inhibited the methane production along with a significant reduction in true degradation of dry matter and organic matter, protozoa count and NH3-N concentration. It is concluded that the evaluated EO have the potential to affect ruminal fermentation efficiency and the EO from M. microphylla could be a promising methane mitigating agent. 相似文献
55.
Ticks are monophyletic and composed of the hard (Ixodidae) and soft (Argasidae) tick families, as well as the Nuttalliellidae, a family with a single species, Nuttalliella namaqua. Significant biological differences in lifestyle strategies for hard and soft ticks suggest that various blood-feeding adaptations occurred after their divergence. The phylogenetic relationships between the tick families have not yet been resolved due to the lack of molecular data for N. namaqua. This tick possesses a pseudo-scutum and apical gnathostoma as observed for ixodids, has a leathery cuticle similar to argasids and has been considered the evolutionary missing link between the two families. Little knowledge exists with regard to its feeding biology or host preferences. Data on its biology and systematic relationship to the other tick families could therefore be crucial in understanding the evolution of blood-feeding behaviour in ticks. Live specimens were collected and blood meal analysis showed the presence of DNA for girdled lizards from the Cordylid family. Feeding of ticks on lizards showed that engorgement occurred rapidly, similar to argasids, but that blood meal concentration occurs via malpighian excretion of water. Phylogenetic analysis of the 18S nuclear and 16S mitochondrial genes indicate that N. namaqua grouped basal to the main tick families. The data supports the monophyly of all tick families and suggests the evolution of argasid-like blood-feeding behaviour in the ancestral tick lineage. Based on the data and considerations from literature we propose an origin for ticks in the Karoo basin of Gondwanaland during the late Permian. The nuttalliellid family almost became extinct during the End Permian event, leaving N. namaqua as the closest living relative to the ancestral tick lineage and the evolutionary missing link between the tick families. 相似文献
56.
Lima ES Bonini MG Augusto O Barbeiro HV Souza HP Abdalla DS 《Free radical biology & medicine》2005,39(4):532-539
Nitric oxide-derived oxidants such as nitrogen dioxide and peroxynitrite have been receiving increasing attention as mediators of nitric oxide toxicity. Indeed, nitrated and nitrosated compounds have been detected in biological fluids and tissues of healthy subjects and in higher yields in patients under inflammatory or infectious conditions as a consequence of nitric oxide overproduction. Among them, nitrated lipids have been detected in vivo. Here, we confirmed and extended previous studies by demonstrating that nitrolinoleate, chlolesteryl nitrolinoleate, and nitrohydroxylinoleate induce vasorelaxation in a concentration-dependent manner while releasing nitric oxide that was characterized by chemiluminescence-and EPR-based methodologies. As we first show here, diffusible nitric oxide production is likely to occur by isomerization of the nitrated lipids to the corresponding nitrite derivatives that decay through homolysis and/or metal ion/ascorbate-assisted reduction. The homolytic mechanism was supported by EPR spin-trapping studies with 3,5-dibromo-4-nitrosobenzenesulfonic acid that trapped a lipid-derived radical during nitrolinoleate decomposition. In addition to provide a mechanism to explain nitric oxide production from nitrated lipids, the results support their role as endogenous sources of nitric oxide that may play a role in endothelium-independent vasorelaxation. 相似文献
57.
Hassan AE Wang P McBrayer TR Tharnish PM Stuyver LJ Schinazi RF Otto MJ Watanabe KA 《Nucleosides, nucleotides & nucleic acids》2005,24(5-7):961-964
A series of N3, 5-Anhydro-4-(beta-D-ribofuranosyl)-8-azapurin-2-ones were prepared in multistep reactions from uridine as potential anti-hepatitis C virus (HCV) agents. The synthetic details as well as biological evaluations are discussed. 相似文献
58.
A genome walking strategy based on annealing and ligation of single-stranded DNA primers to 3′ overhangs following restriction
endonuclease digestion was developed. A set of primers contains 4 nucleotides at the 3′ end that are complementary to overhangs
formed by restriction endonucleasesApaI;PstI;SacI andSphI. Following ligation, 5′ end overhangs are formed on the DNA, which serves as sites for the adaptor primers and nested primers
for PCR amplification in combination with the gene-specific primers. This strategy was verified by the amplification of up
to 4 kb of a potato leafroll virus full-length infectious clone. The procedure could be adopted to target any upstream and
downstream regions flanking known sequences within the plant genome. 相似文献
59.
I Ben Charfeddine FG Riepe E Clauser A Ayedi S Makni MT Sfar H Sboui N Kahloul H Ben Hamouda S Chouchane S Trimech N Zouari S M'rabet F Amri A Saad PM Holterhus M Gribaa 《Gene》2012,507(1):20-26
Congenital adrenal hyperplasia (CAH) is an autosomal recessive disease of steroid biosynthesis in humans. More than 90% of all CAH cases are caused by mutations of the 21-hydroxylase gene (CYP21A2), and approximately 75% of the defective CYP21A2 genes are generated through an intergenic recombination with the neighboring CYP21A1P pseudogene. In this study, the CYP21A2 gene was genotyped in 50 patients in Tunisia with the clinical diagnosis of 21-hydroxylase deficiency. CYP21A2 mutations were identified in 87% of the alleles. The most common point mutation in our population was the pseudogene specific variant p.Q318X (26%). Three novel single nucleotide polymorphism (SNP) loci were identified in the CYP21A2 gene which seems to be specific for the Tunisian population. The overall concordance between genotype and phenotype was 98%. With this study the molecular basis of CAH has been characterized, providing useful results for clinicians in terms of prediction of disease severity, genetic and prenatal counseling. 相似文献
60.
Morsy MA Abdalla AM Mahmoud AM Abdelwahab SA Mahmoud ME 《Journal of physiology and biochemistry》2012,68(1):29-35
Liver fibrosis is a major health problem that can lead to the development of liver cirrhosis and hepatocellular carcinoma.
On the other hand, several antioxidants have been shown to possess protective effect against liver fibrosis. Therefore, in
the present work, the effectiveness of curcumin, α-lipoic acid, and N-acetylcysteine in protecting against carbon tetrachloride (CCl4)-induced liver fibrosis as well as the mechanism(s) implicated in this protective effect was studied. The antioxidants used
in this study resulted in hepatoprotective effect as evident by substantial decreases in collagen deposition in histopathological
examinations in addition to significant decrease in serum levels of alanine aminotransferase, aspartate aminotransferase,
gamma glutamyl transpeptidase, bilirubin, and transforming growth factor-alpha (TGF-α) as well as hepatic malondialdehyde
concentration, with a concurrent increase in serum matrix metalloproteinase-13 (MMP-13) and hepatic reduced glutathione (GSH)
levels as compared to CCl4 fibrotic group. In conclusion, curcumin, α-lipoic acid, and N-acetylcysteine protect rats against CCl4-induced liver fibrosis most possibly through their antioxidant activities and their capacities to induce MMP-13 and to inhibit
TGF-α levels. 相似文献