全文获取类型
收费全文 | 9594篇 |
免费 | 185篇 |
国内免费 | 12篇 |
专业分类
9791篇 |
出版年
2024年 | 67篇 |
2023年 | 138篇 |
2022年 | 363篇 |
2021年 | 499篇 |
2020年 | 401篇 |
2019年 | 555篇 |
2018年 | 460篇 |
2017年 | 324篇 |
2016年 | 452篇 |
2015年 | 483篇 |
2014年 | 573篇 |
2013年 | 758篇 |
2012年 | 701篇 |
2011年 | 699篇 |
2010年 | 383篇 |
2009年 | 329篇 |
2008年 | 371篇 |
2007年 | 370篇 |
2006年 | 332篇 |
2005年 | 270篇 |
2004年 | 241篇 |
2003年 | 173篇 |
2002年 | 159篇 |
2001年 | 60篇 |
2000年 | 46篇 |
1999年 | 43篇 |
1998年 | 42篇 |
1997年 | 32篇 |
1996年 | 23篇 |
1995年 | 21篇 |
1994年 | 15篇 |
1993年 | 23篇 |
1992年 | 24篇 |
1991年 | 30篇 |
1990年 | 13篇 |
1989年 | 17篇 |
1988年 | 17篇 |
1987年 | 17篇 |
1986年 | 24篇 |
1985年 | 27篇 |
1984年 | 21篇 |
1983年 | 13篇 |
1982年 | 12篇 |
1981年 | 15篇 |
1980年 | 15篇 |
1979年 | 11篇 |
1978年 | 14篇 |
1976年 | 12篇 |
1974年 | 16篇 |
1973年 | 13篇 |
排序方式: 共有9791条查询结果,搜索用时 15 毫秒
1.
Viqar Uddin Ahmad Mohammad Ghani Shah Faryal Vali Mohammad Nargis Ismail Mushtaq Noorwala 《Phytochemistry》1991,30(12)
A new flavone glucoside macrophylloside has been isolated from the whole plant of Primula macrophylla and its structure was determined by spectroscopic methods as 2′-hydroxy-7-O-β-
-glucopyranosyloxyflavone. Sitosterol glucoside was also isolated for the first time from this plant. 相似文献
2.
R. John Dobbs Sylvia M. Dobbs Clive Weller ré Charlett Ingvar T. Bjarnason Alan Curry David S. Ellis Mohammad A. A. Ibrahim Maria V. McCrossan John O'Donohue Robert J. Owen Norman L. Oxlade Ashley B. Price Jeremy D. Sanderson Malur Sudhanva John Williams 《Helicobacter》2008,13(5):309-322
We challenge the concept of idiopathic parkinsonism (IP) as inevitably progressive neurodegeneration, proposing a natural history of sequential microbial insults with predisposing host response. Proof-of-principle that infection can contribute to IP was provided by case studies and a placebo-controlled efficacy study of Helicobacter eradication. "Malignant" IP appears converted to "benign", but marked deterioration accompanies failure. Similar benefit on brady/hypokinesia from eradicating "low-density" infection favors autoimmunity. Although a minority of UK probands are urea breath test positive for Helicobacter , the predicted probability of having the parkinsonian label depends on the serum H. pylori antibody profile, with clinically relevant gradients between this "discriminant index" and disease burden and progression. In IP, H. pylori antibodies discriminate for persistently abnormal bowel function, and specific abnormal duodenal enterocyte mitochondrial morphology is described in relation to H. pylori infection. Slow intestinal transit manifests as constipation from the prodrome. Diarrhea may flag secondary small-intestinal bacterial overgrowth. This, coupled with genetically determined intense inflammatory response, might explain evolution from brady/hypokinetic to rigidity-predominant parkinsonism. 相似文献
3.
4.
Houssen ME Haron MM Metwally SS Ibrahim TM 《Journal of physiology and biochemistry》2011,67(1):115-120
Atherosclerosis is a chronic disease of the arterial wall where both innate and adaptive immuno-inflammatory mechanisms are involved. Inflammatory cytokines are implicated in the development and progression of atherosclerotic lesions. Immunomodulatory therapies have been proposed for the treatment of atherosclerosis. Therefore, the aim of this study was to investigate the systemic anti-inflammatory and immunomodulatory effects of atorvastatin, cyclosporine A (CsA), and tacrolimus (FK506) on plasma inflammatory markers in atherosclerotic rabbits. Male New Zealand rabbits were randomized into five groups each of 12 animals. Standard diet-fed group served as control, and the cholesterol-fed group received a diet supplemented with 1% cholesterol alone, cholesterol + atorvastatin, cholesterol + FK506, and cholesterol + CsA. Serum levels of lipid profile parameters (triglycerides, cholesterol, and high-density lipoprotein) were measured using colorimetric methods. Serum levels of C-reactive protein (CRP), interleukin-6 (Il-6), and interferon-gamma (INF-γ) were measured in all studied groups using ELISA techniques. Our results revealed a significant decrease (p < 0.001) in the serum levels of lipid profile parameters, CRP, Il-6, and INF-γ in atorvastatin-treated group compared with the cholesterol-fed group. On the other hand, a non-significant difference was observed for the same parameters in either FK506- or CsA-treated groups compared with the cholesterol-fed group. In conclusion, atorvastatin has a systemic anti-inflammatory role that far surpassed the cholesterol reduction effect alone. FK506 or CsA failed to suppress elevated plasma inflammatory markers. Thus, low doses of these two immunomodulating drugs could not have generalized systemic anti-inflammatory or immunosuppressive effects. 相似文献
5.
Ali Reza Jafarnejadi Mehdi Homaee Gholamabbas Sayyad Mohammad Bybordi 《Soil & Sediment Contamination》2011,20(1):98-113
Cadmium (Cd) accumulation in edible crops is undesirable due to its hazardous influences on human health. The objectives of this study were: i) to evaluate the spatial variability of grain Cd and its relationships with soil properties in 4000 km2 wheat farms; ii) to evaluate the effect of wheat cultivar on the soil properties vs. grain Cd relationships. A number of 255 soil (0–20 cm) and grain samples were taken and Cd concentrations in grain samples and some soil properties were measured. Grain Cd concentrations in 95 percent of the samples exceeded the threshold of 0.2 mg kg?1. Durum wheat had more potential to accumulate Cd in grain (0.76 mg kg?1) than bread (0.69 mg kg?1). There was significant (p < 0.01) correlation between grain Cd and organic carbon (r = 0.66), CEC (r = 0.77) and DTPA-extractable Cd (p < 0.05) (r = 0.57) of the soils. Greater Pearson coefficient values for durum wheat showed that, in the studied calcareous soils, organic carbon, CEC, Cd-DTPA had more effects on durum wheat than bread wheat cultivar. The obtained Kriging map of grain Cd identified three hotspots at the east (durum wheat cultivation), the west (intensive irrigated wheat farms), and south (wheat farms around petrochemical industries) of the region. Agricultural mismanagement due to overusing P-fertilizers increased Cd concentration in the topsoils and grains of wheat farms in the study area. 相似文献
6.
Somayeh Solhjoo Mohammad Akbari Heidar Toolee Keywan Mortezaee Mahshid Mohammadipour Seyed Noureddin Nematollahi-Mahani Amene Shahrokhi Mahtab Sayadi Tayebeh Rastegar 《Journal of cellular biochemistry》2019,120(4):4924-4934
Spermatogonial cells (SCs) are key cells for spermatogenesis. These cells are affected by paracrine signals originated from nearby somatic cells, among them Leydig cells have receptors for osteocalcin, a hormone known for exerting positive roles in the promotion of spermatogenesis. The aim of this study was to evaluate roles for osteocalcin on SCs proliferative and differentiation features after coculture with Leydig cells. SCs and Leydig cells were isolated from neonate NMRI offspring mice and adult NMRI mice, respectively. SCs population were then enriched in a differential attachment technique and assessed for morphological features and identity. Then, SCs were cocultured with Leydig cells and incubated with osteocalcin for 4 weeks. Evaluation of proliferation and differentiation-related factors were surveyed using immunocytochemistry (ICC), Western blot, and quantitative real-time polymerase chain reaction (PCR). Finally, the rate of testosterone release to the culture media was measured at the end of 4th week. Morphological and flow cytometry results showed that the SCs were the population of cells able to form colonies and to express ID4, α6-, and β1-integrin markers, respectively. Leydig cells were also able to express Gprc6α as a specific marker for the cells. Incubation of SCs/Leydig coculture with osteocalcin has resulted in an increase in the rate of expressions for differentiation-related markers. Levels of testosterone in the culture media of SCs/Leydig was positively influenced by osteocalcin. It could be concluded that osteocalcin acts as a positive inducer of SCs in coculture with Leydig cells probably through stimulation of testosterone release from Leydig cells and associated signaling. 相似文献
7.
Nourbakhsh N Soleimani M Taghipour Z Karbalaie K Mousavi SB Talebi A Nadali F Tanhaei S Kiyani GA Nematollahi M Rabiei F Mardani M Bahramiyan H Torabinejad M Nasr-Esfahani MH Baharvand H 《The International journal of developmental biology》2011,55(2):189-195
Stem cells from human exfoliated deciduous teeth (SHED) are highly proliferative, clonogenic and multipotent stem cells with a neural crest cell origin. Additionally, they can be collected with minimal invasiveness in comparison with other sources of mesenchymal stem cells (MSCs). Therefore, SHED could be a desirable option for potential therapeutic applications. In this study, SHEDs were established from enzyme-disaggregated deciduous dental pulp obtained from 6 to 9 year-old children. The cells had typical fibroblastoid morphology and expressed antigens characteristic of MSCs, STRO1, CD146, CD45, CD90, CD106 and CD166, but not the hematopoietic and endothelial markers, CD34 and CD31, as assessed by FACS analysis. Differentiation assessment revealed a strong osteogenic and adipogenic potential of SHEDs. In order to further evaluate the in vitro differentiation potential of SHED into neural cells, a simple short time growth factor-mediated induction was used. Immunofluorescence staining and flow cytometric analysis revealed that SHED rapidly expressed nestin and b-III tubulin, and later expressed intermediate neural markers. In addition, the intensity and percentages of nestin and b-III tubulin and mature neural markers (PSA-NCAM, NeuN, Tau, TH, or GFAP) increased significantly following treatment. Moreover, RT-PCR and Western blot analyses showed that the neural markers were strongly up-regulated after induction. In conclusion, these results provide evidence that SHED can differentiate into neural cells by the expression of a comprehensive set of genes and proteins that define neural-like cells in vitro. SHED cells might be considered as new candidates for the autologous transplantation of a wide variety of neurological diseases and neurotraumatic injuries. 相似文献
8.
Farjam Goudarzi Adel Mohammadalipour Iraj Khodadadi Sheno Karimi Rezvan Mostoli Majid Bahabadi Mohammad Taghi Goodarzi 《Molecular biotechnology》2018,60(4):279-289
Differentiation process of mesenchymal stem cells (MSCs) into adipocyte is involved in obesity. Multiple factors such as Ca2+ play important roles in different stages of this process. Because of the complicated roles of Ca2+ in adipogenesis, the aim of present investigation was to study the influx and efflux of Ca2+ into and out of the cells during adipogenesis. Adipose-derived MSCs were used to differentiate into adipocytes. MSCs were exposed to 2.5 mM Ca2+ or 1.8 mM Ca2+ plus calcium ionophore, A23187, for 3 days. Lipid staining, triglycerides (TG) content, and glyceraldehyde phosphate dehydrogenase (GAPDH) activity were evaluated to confirm the efficiency of the differentiation. Gene expression of GLUT4, PPARγ2, RAR-α, and calreticulin, as well as the protein levels of GLUT4 and PPARγ2 were determined. Ca2+ and in particular Ca2+ plus A23187 significantly lowered the efficiency of differentiation accompanied by decrease in intracellular TG deposits, GAPDH activity and alleviation of gene, and protein levels of GLUT4 and PPARγ2. While calreticulin and RAR-α were remarkably upregulated in A23187 group. This study showed the inhibitory effects of calcium in adipogenesis. Additionally, it indicated the greater inhibitory effect of calreticulin and RAR-α in controlling adipogenesis by higher levels of calcium. 相似文献
9.
This study focuses on karyological investigation of four taxa of Dianthus (Caryophyllaceae) including D. crossopetalus, D. orientalis subsp. stenocalyx, D. orientalis subsp. gorganicus, and Dianthus sp. distributed in Northeast of Iran. The karyotype asymmetry/symmetry was evaluated using two methods: 1) CVCL (coefficient of variation of chromosome length) and CVCI (heterogeneity of the centromeric index); and 2) MCA (mean centromeric asymmetry). The karyotype asymmetry was also used to investigate the relationships among the taxa. Results obtained from the current study revealed that there are two different ploidy levels (2n = 2x = 30 and 2n = 4x = 60) among the investigated taxa. The indices CVCL and MCA described karyotype asymmetry correctly based on variation in chromosome length. Diagram of CVCL vs. MCA seems to be appropriate for karyological delimitation and taxonomic relationships among the Dianthus taxa under study. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
10.
Reston S. Beyo Lekha Divya Oommen V. Oommen Mohammad A. Akbarsha 《Journal of morphology》2008,269(11):1412-1424
There is a paucity of information on the female reproductive biology of the caecilian amphibians when compared with the other vertebrate groups. Hence, the accumulation of nutrient reserves in the form of yolk and formation of yolk platelets were studied in Gegeneophis ramaswamii, adopting light microscopic histological and transmission electron microscopy analysis. Previtellogenic as well as vitellogenic follicles were observed in appropriate preparations. On the basis of the source and the routes of entry, we identified four types of yolk precursor materials, precursors 1 to 4. The earliest material appearing in the oocyte consists of abundant lipid vesicles during the previtellogenic phase, i.e., much before the follicular epithelium is fully established. This is a contribution from the oocyte mitochondria, which we identified as yolk precursor material 1, and it is autosynthetic. Once the follicle cell‐oocyte interface is fully established, there is an accumulation of the principal component of the heterosynthetic yolk by sequestration from the blood through the intercellular spaces between follicle cells in a pinocytic process. This we identified as yolk precursor material 2. There was also an indication of a lipidic yolk material synthesis in the follicle cells sequestered from maternal blood through the follicle cells in an endocytic process in which the macrovilli of follicle cells and the microvilli of the oocyte play a role. This we identified as yolk precursor material 3. Contribution to the yolk of peptidic, glycosidic, and/or lipidic material synthesized in the vitellogenic oocyte was also indicated. This we identified as yolk precursor material 4. The sequential development of intercellular associations and indications of synthesis/sequestration of the yolk have been traced. Thus, we report the mechanistic details of synthesis/sequestration of the yolk materials in a caecilian. J. Morphol., 2008. © 2008 Wiley‐Liss, Inc. 相似文献