全文获取类型
收费全文 | 5903篇 |
免费 | 313篇 |
国内免费 | 7篇 |
出版年
2023年 | 87篇 |
2022年 | 73篇 |
2021年 | 263篇 |
2020年 | 152篇 |
2019年 | 178篇 |
2018年 | 188篇 |
2017年 | 158篇 |
2016年 | 274篇 |
2015年 | 302篇 |
2014年 | 327篇 |
2013年 | 481篇 |
2012年 | 439篇 |
2011年 | 479篇 |
2010年 | 269篇 |
2009年 | 239篇 |
2008年 | 329篇 |
2007年 | 293篇 |
2006年 | 272篇 |
2005年 | 219篇 |
2004年 | 202篇 |
2003年 | 181篇 |
2002年 | 175篇 |
2001年 | 51篇 |
2000年 | 45篇 |
1999年 | 41篇 |
1998年 | 30篇 |
1997年 | 32篇 |
1996年 | 16篇 |
1995年 | 28篇 |
1994年 | 30篇 |
1993年 | 25篇 |
1992年 | 20篇 |
1991年 | 20篇 |
1990年 | 18篇 |
1989年 | 20篇 |
1988年 | 20篇 |
1987年 | 22篇 |
1986年 | 9篇 |
1985年 | 23篇 |
1984年 | 21篇 |
1983年 | 17篇 |
1982年 | 25篇 |
1981年 | 13篇 |
1980年 | 16篇 |
1979年 | 9篇 |
1978年 | 13篇 |
1977年 | 10篇 |
1975年 | 6篇 |
1974年 | 7篇 |
1966年 | 7篇 |
排序方式: 共有6223条查询结果,搜索用时 109 毫秒
1.
Mohamed M. Eid Samy I. El-Kowrany Ahmad A. Othman Dina I. El Gendy Eman M. Saied 《The Korean journal of parasitology》2015,53(1):51-58
Toxocariasis is a soil-transmitted helminthozoonosis due to infection of humans by larvae of Toxocara canis. The disease could produce cognitive and behavioral disturbances especially in children. Meanwhile, in our modern era, the incidence of immunosuppression has been progressively increasing due to increased incidence of malignancy as well as increased use of immunosuppressive agents. The present study aimed at comparing some of the pathological and immunological alterations in the brain of normal and immunosuppressed mice experimentally infected with T. canis. Therefore, 180 Swiss albino mice were divided into 4 groups including normal (control) group, immunocompetent T. canis-infected group, immunosuppressed group (control), and immunosuppressed infected group. Infected mice were subjected to larval counts in the brain, and the brains from all mice were assessed for histopathological changes, astrogliosis, and IL-5 mRNA expression levels in brain tissues. The results showed that under immunosuppression, there were significant increase in brain larval counts, significant enhancement of reactive gliosis, and significant reduction in IL-5 mRNA expression. All these changes were maximal in the chronic stage of infection. In conclusion, the immunopathological alterations in the brains of infected animals were progressive over time, and were exaggerated under the effect of immunosuppression as did the intensity of cerebral infection. 相似文献
2.
Anti-coccidial and anti-apoptotic activities of palm pollen grains on Eimeria papillata-induced infection in mice 总被引:1,自引:0,他引:1
The present work aimed to study the effect of palm pollen extract (PPE) as an anticoccidial and anti-apoptotic modulator during the course of murine intestinal Eimeria papillata infection. The fact that PPE has an anticoccidial efficacy against intestinal E. papillata infection in mice has been clarified by the reduction of faecal output of oocysts on day five post infection from 49.5 × 103 to 34 × 103 oocyst/g. Moreover, the number of intracellular eimerian stages of zygots and developing oocysts decreased by about 89% and that of schizonts and gamonts to 42% and 72%, respectively. E. papillata infection also induced an increase in the number of apoptotic cells from 17.5 to 122.8 apoptotic nuclei/10 villous crypt units (VCU). In addition, it caused a state of systemic inflammatory response as revealed by an elevation in levels of the pro-inflammatory biomarkers, inducible nitric oxide synthase (iNOs) and tumor necrosis factor alpha (TNF-α) from 5.3 and 78.3 to 33 pmol ml?1 and 96.3 pg ml?1 in blood, respectively, with concurrent duplication in the total leucocytic number. Upon treatment of infected mice with the aqueous PPE, the activity of iNOs was reduced by 55% and the level of TNF-α was decreased by 30%. Moreover, the total leucocytic count was significantly reduced from 9.05 × 103 to 7.8 × 103 cells/mm3. Based on our results, PPE showed both anti-coccidial, anti-inflammatory and anti-apoptotic activities. So it can be used in developing new herbal medicine against animal coccidiosis and may be suitable agent for treating eimeriosis associated inflammatory response. 相似文献
3.
Maizura Ithnin Yang Xu Marhalil Marjuni Norhalida Mohamed Serdari Mohd Din Amiruddin Eng-Ti Leslie Low Yung-Chie Tan Soon-Joo Yap Leslie Cheng Li Ooi Rajanaidu Nookiah Rajinder Singh Shizhong Xu 《Tree Genetics & Genomes》2017,13(5):103
Palm oil has a balanced fatty acid composition and has no trans fat. As a result, its use in food has increased as food-labeling laws have changed to specify trans fat content. Increasing oil production is the main goal in oil palm breeding. Genetic mapping and genomic studies in palm trees are necessary to understand the genetic architecture of economic traits of importance for palm oil production. To help achieve this, we sampled 422 oil palms from MPOB (Malaysian Palm Oil Board)Angola germplasm collection and measured 13 economic traits from these palms. Multi-locus genome-wide association studies (GWAS) were conducted using least absolute shrinkage and selection operator (LASSO) and genome-wide efficient mixed model analysis. We identified 19 quantitative trait loci (QTLs) for 8 traits. Of these, four Angola-specific QTLs associated with bunch components were detected on chromosomes 4, 8, and 11. These QTLs are potentially useful for introgression of desirable genes from the Angola palms to advanced breeding populations for improvement of bunch and oil yield traits. The majority of the QTLs were detected by LASSO-A, in which the p values of individual markers were calculated based on bootstrapped standard errors. Many of the detected QTLs are nearby known QTLs detected from linkage studies reported by other research groups. We also conducted genomic selection (GS) for the 13 traits and concluded that GS can be an effective tool for oil palm breeding. This is the first GWAS and GS study conducted on oil palm germplasm from Angola, and the results can be very useful in oil palm genetic studies and breeding. 相似文献
4.
Khalid Alanazi Bassam A. Alahmadi Ahmed Alhimaidi Faisal M. Abou-Tarboush Mohammad Abul Farah Ahmed Mahmoud Mohamed Alfaifi 《Saudi Journal of Biological Sciences》2016,23(1):87-91
A spermatic granuloma is a chronic inflammatory reaction produced in response to extravasated sperm within the intertubular connective tissue. The present study investigates the possible toxic effects of water extract of Heliotropium bacciferum on the reproductive system of male albino rats and the associated potential for the development of spermatic granulomas. H. bacciferum is a herbal plant used in traditional medicine and reported to have cytotoxic effects due to pyrrolizidine alkaloids. Histological examinations revealed no changes in the tissues of the testes, although, some changes were detected in the cauda epididymis, the most important of which was the development of small lesions of spermatic granulomas. Clear gaps were observed between the epithelial linings of the epididymal tubules. 相似文献
5.
Aina Hazimah Bahaman Azzmer Azzar Abdul Hamid Khairul Bariyyah Abd Halim Yilmaz Kaya Mohamed Faraj Edbeib 《Journal of biomolecular structure & dynamics》2020,38(14):4246-4258
Abstract Fungi of the Trichoderma species are valued industrial enzymes in support of the ‘zero-waste’ technology to convert agro-industrial biomass into valuable products, i.e. nanocellulose (NC). In this study, an in silico approach using substrate docking and molecular dynamic (MD) simulation was used to predict the order of which the multilayers of cellulosic polymers, i.e. lignin, hemicellulose and cellulose in oil palm leaves (OPL) are degraded by fungal enzymes, endocellulase and exocellulase. The study aimed to establish the catalytic tendencies of the enzymes to optimally degrade the cellulosic components of OPL for high yield production of NC. Energy minimized endocellulase and exocellulase models revealed satisfactory scores of PROCHECK (90.0% and 91.2%), Verify3D (97.23% and 98.85%) and ERRAT (95.24% and 91.00%) assessments. Active site prediction by blind docking, COACH meta-server and multiple sequence alignment indicated the catalytic triads for endocellulase and exocellulase were Ser116–His205–Glu249 and Ser382–Arg124–Asp385, respectively. Binding energy of endocellulase docked with hemicellulose (?6.0 ? kcal mol?1) was the most favourable followed by lignin (?5.6 ? kcal mol?1) and cellulose (?4.4 ? kcal mol?1). Exocellulase, contrarily, bonded favorably with lignin (?8.7 ? kcal mol?1), closely followed by cellulose (?8.5 ? kcal mol?1) and hemicellulose (?8.4 ? kcal mol?1). MDs simulations showed that interactions of complexes, endocellulase–hemicellulose and the exocellulase–cellulose being the most stable. Thus, the findings of the study successfully identified the specific actions of sugar-acting enzymes for NC production. Communicated by Ramaswamy H. Sarma 相似文献
6.
Tirupapuliyur V Damodaran Ali Abdel-Rahman Maie H El-Sourady Mohamed B Abou-Donia 《Neurochemistry international》2002,40(4):371-379
A single dose (1.7 mg/kg, s.c.) of diisopropylphosphorofluoridate (DFP) causes organophosphorus ester-induced delayed neurotoxicity (OPIDN) in susceptible species. We studied the effects of DFP administration on the mRNA expression of glyceraldehyde-3-phosphate dehydrogenase (GAPDH), an important glycolytic protein at different time points (1, 2, 5, 10 and 20 days) post-treatment. Total RNA was extracted from cerebrum, cerebellum, brainstem, midbrain, and spinal cord of the control and DFP-treated hens, and northern blots were prepared using standard protocols and hybridized with GAPDH, as well as beta-actin and 28S RNA cDNA (control) probes. There was a distinct spatial/temporal mRNA expression pattern for the different tissues studied. Non-susceptible tissue, cerebrum showed a dramatic increase in GAPDH mRNA at day 1, post-treatment and levels remained high at all time points, suggestive of protective mechanisms from the beginning. In contrast, highly susceptible tissues like brainstem, spinal cord and midbrain showed either no elevation or slight down-regulation at day 1, suggesting trauma and cell injury/cell death. Overall, there was moderate level of induction during the subsequent time points in these tissues, indicative of pathways of either recovery or degeneration. Cerebellum being the less susceptible tissue showed moderate increase initially, followed by higher induction, suggestive of rapid recovery. Our current data on GAPDH provides an important link in this complex network of molecular changes involving pathways identified by our group and others, such as nitric oxide (NO), CaM kinase-II (CaMK-II), protein kinase-A (PKA), c-fos, and phosphorylated-CREB (p-CREB) in DFP-induced OPIDN. 相似文献
7.
Mohamed Faraj Edbeib Roswanira Abdul Wahab Yilmaz Kaya Fahrul Huyop 《Annals of microbiology》2017,67(5):371-382
Halogenated compounds represent potential long-term threats to human well-being and health and, therefore, the quest for microorganisms capable of degrading these hazardous substances merits urgent consideration. We have isolated a novel dehalogenase-producing bacterium from the hypersaline environment of Tuz Gölü Lake, Turkey and subsequently identified this isolate as Pseudomonas halophila HX. Under optimal culture conditions (pH 8.0, 15% NaCl, 30 °C, 200 rpm, 96 h culture time), the strain almost completely degraded (99.3%) 2,2-dichloropropionic acid (20 mM). The dehalogenase gene (dehHX) of the bacterium was amplified by PCR, and the deduced amino acid sequence of the DehHX was found to belong to a Group I dehalogenase and to share an 82% sequence identity to the dehalogenase DehI of Pseudomonas putida strain PP3. Interestingly, the pI of DehHX was more acidic (pI 3.89) than those of the non-halophilic dehalogenases (average measured pI 5.95). Homology-based structural modeling revealed that the surface of DehHX was unusually negatively charged due to the higher presence of acidic residues, which accounts for the uncommonly low pI seen in DehHX and explains the mechanism of adaptation that contributes to the exceptional halotolerance of the enzyme. The excess surface acidic residues were beneficial in enhancing the water-binding capacity, a crucial feature for preserving the stability and solubility of DehHX in highly saline conditions. In summary, we suggest that bio-prospecting for halogenated compound-degrading microorganisms in highly saline environments is a practical and safe strategy for the bioremediation of contaminated coastal areas. 相似文献
8.
Cell Migration associated with cell shape changes are of central importance in many biological processes ranging from morphogenesis to metastatic cancer cells. Cell movement is a result of cyclic changes of cell morphology due to effective forces on cell body, leading to periodic fluctuations of the cell length and cell membrane area. It is well-known that the cell can be guided by different effective stimuli such as mechanotaxis, thermotaxis, chemotaxis and/or electrotaxis. Regulation of intracellular mechanics and cell’s physical interaction with its substrate rely on control of cell shape during cell migration. In this notion, it is essential to understand how each natural or external stimulus may affect the cell behavior. Therefore, a three-dimensional (3D) computational model is here developed to analyze a free mode of cell shape changes during migration in a multi-signaling micro-environment. This model is based on previous models that are presented by the same authors to study cell migration with a constant spherical cell shape in a multi-signaling substrates and mechanotaxis effect on cell morphology. Using the finite element discrete methodology, the cell is represented by a group of finite elements. The cell motion is modeled by equilibrium of effective forces on cell body such as traction, protrusion, electrostatic and drag forces, where the cell traction force is a function of the cell internal deformations. To study cell behavior in the presence of different stimuli, the model has been employed in different numerical cases. Our findings, which are qualitatively consistent with well-known related experimental observations, indicate that adding a new stimulus to the cell substrate pushes the cell to migrate more directionally in more elongated form towards the more effective stimuli. For instance, the presence of thermotaxis, chemotaxis and electrotaxis can further move the cell centroid towards the corresponding stimulus, respectively, diminishing the mechanotaxis effect. Besides, the stronger stimulus imposes a greater cell elongation and more cell membrane area. The present model not only provides new insights into cell morphology in a multi-signaling micro-environment but also enables us to investigate in more precise way the cell migration in the presence of different stimuli. 相似文献
9.
Activity of salivary glands in secreting honey‐elaborating enzymes in two subspecies of honeybee (Apis mellifera L) 下载免费PDF全文
Aliaa A. Al‐Sherif Adel M. Mazeed Mohamed A. Ewis Emad A. Nafea El‐Seid E. Hagag Ahmed A. Kamel 《Physiological Entomology》2017,42(4):397-403
The activity of invertase, glucose oxidase and amylase in the cephalic (post‐cerebral) and thoracic salivary glands is determined in Egyptian and Carniolan honeybees (Apis mellifera L). For this purpose, three ages of worker bees are selected for enzyme assays. The results show that the three target enzymes are detected in the two glands during the three worker ages, except invertase, which cannot be detected in the cephalic gland of newly emerged bees of both subspecies. In both glands, the secretion of invertase is highest, followed by amylase and then glucose oxidase. In Carniolan bees, invertase secretion of the cephalic and thoracic glands increases gradually with age. In Egyptian bees, invertase increases with age only in the cephalic gland, whereas, in the thoracic gland, the highest secretion activity is detected in 10–15‐day‐old bees. The highest amounts of glucose oxidase and amylase in the cephalic gland are detected in newly emerged individuals of both Egyptian and Carniolan bees. In the thoracic gland, however, the highest activity of both enzymes is recorded only in newly emerged Egyptian bees. The results are discussed in the light of bee management and biological aspects of the two subspecies. 相似文献
10.
A Neuro-Comparative Study between Single/Successive Thorium Dose Intoxication and Alginate Treatment
Mohamed M. Rezk 《Biological trace element research》2018,185(2):414-423
The adult male albino rats were grouped into five groups (control group and four variably treated groups with thorium (Th) in single or successive with or without alginate treatment). The IP administration of thorium nitrate (13.6 mg/kg b.wt.) induced a regional distribution and accumulation ordered as cerebellum > cerebral cortex > brain stem > hippocampus > hypothalamus > striatum. Also, it induces a significant increase in Na+, Ca2+, and Fe3+ ion content and malondialdehyde (MDA) level while K+ ions and glutathione (GSH) level were significantly decreased. On the other hand, the daily oral administration of 5% alginate showed a significant decreasing in the accumulation of thorium in the different brain areas and mitigated its hazardous effects. By the alginate treatment, Na+, Ca2+, Fe3+, and level of MDA were declined while K+ ions and GSH level showed a significant increase. The improvement of the investigated parameters was attributed to the specific chelating, regeneration, and antioxidant properties of the alginate. So, alginate administration could ameliorate the hazardous effects of thorium nitrate. 相似文献