全文获取类型
收费全文 | 1876篇 |
免费 | 39篇 |
专业分类
1915篇 |
出版年
2024年 | 9篇 |
2023年 | 35篇 |
2022年 | 21篇 |
2021年 | 39篇 |
2020年 | 41篇 |
2019年 | 28篇 |
2018年 | 74篇 |
2017年 | 71篇 |
2016年 | 86篇 |
2015年 | 57篇 |
2014年 | 66篇 |
2013年 | 123篇 |
2012年 | 139篇 |
2011年 | 138篇 |
2010年 | 88篇 |
2009年 | 57篇 |
2008年 | 97篇 |
2007年 | 117篇 |
2006年 | 101篇 |
2005年 | 87篇 |
2004年 | 87篇 |
2003年 | 98篇 |
2002年 | 84篇 |
2001年 | 31篇 |
2000年 | 42篇 |
1999年 | 19篇 |
1998年 | 8篇 |
1997年 | 5篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1994年 | 5篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1978年 | 2篇 |
1975年 | 7篇 |
1974年 | 3篇 |
1973年 | 4篇 |
1972年 | 2篇 |
1971年 | 3篇 |
1969年 | 2篇 |
1967年 | 2篇 |
1966年 | 2篇 |
1965年 | 1篇 |
1964年 | 2篇 |
1959年 | 1篇 |
1933年 | 1篇 |
排序方式: 共有1915条查询结果,搜索用时 15 毫秒
41.
Sahin M Sahin E Gümüşlü S Erdoğan A Gültekin M 《Biochemical and biophysical research communications》2011,(1):145-148
Metastasis is a leading cause of mortality and morbidity in cancer. One of the steps in metastasis process is the formation of new blood vessels. Aberrant DNA methylation patterns are common in cancer cells. In recent studies, S-adenosylmethionine (SAM), which is a DNA methylating agent, has been found to have inhibitory effects on some carcinoma cells in vivo and in vitro. In the present study, we have used SAM to investigate whether it is effective against angiogenesis in vitro. Our results have shown that SAM can reduce the formation and organization of capillary-like structures of endothelial cells in tumoral environment. Besides, we have found SAM can block endothelial cell proliferation and the migration of cells towards growth factors-rich media. In conclusion, our study suggests that SAM may be used against angiogenesis as a natural bio-product. 相似文献
42.
Theta oscillations are related to cognitive functions and reflect functional integration of frontal and medial temporal structures into coherent neurocognitive networks. This study assessed event-related theta oscillations in medication-free, euthymic patients with bipolar disorder upon auditory oddball paradigm. Twenty-two DSM-IV euthymic bipolar I (n = 19) and II (n = 3) patients and twenty-two healthy subjects were included. Patients were euthymic for at least 6 months, and psychotropic-free for at least 2 weeks. EEG was recorded at 30 electrode sites. Auditory oddball paradigm and sensory stimuli were used. Event-related Oscillations were analyzed using adaptive filtering in two different theta frequency bands (4–6 Hz, 6–8 Hz). In healthy subjects, slow theta (4–6 Hz) responses were significantly higher than those of euthymic patients upon target, non-target and sensory stimuli (p < 0.05). Fast theta (6–8 Hz) responses of healthy subjects were significantly higher than those of euthymic patients upon target-only stimuli (p < 0.05). Reduced theta oscillations during auditory processing provide strong quantitative evidence of activation deficits in related networks in bipolar disorder. Fast theta responses are related to cognitive functions, whereas slow theta responses are related to sensory processes more than cognitive processes. 相似文献
43.
Sinan Anlaş 《Zoology in the Middle East.》2013,59(2):153-160
Tetartopeus frischi sp. n. from the U?ak Province in western Anatolia, Turkey, is described and illustrated. Additional records of ten species of Tetartopeus are reported from the West Palaearctic region, among them several new country records. An updated key to the Turkish species of Tetartopeus is presented.http://www.zoobank.org/urn:lsid:zoobank.org:pub:8B832717-E48D-444A-9E1A-2946DA1BCA68 相似文献
44.
BACKGROUND: Papillary carcinoma arising from a thyroglossal duct cyst (TDC) is the most frequent malignancy arising from this embryologic remnant of the thyroglossal duct. The preoperative fine needle aspiration cytology (FNAC) of such neoplasms has rarely been cited. Approximately 170 TDC cases have been reported in the literature worldwide, diagnosed solely on histopathology. CASE: A 63-year-old woman presented with an anterior midline neck mass of years' duration. A hypodense cyst was located at the level of the hyoid bone. FNAC of the midline neck mass showed bloody, mucoid material and numerous atypical, elongated cells. The aspirated material was reported as "papillary carcinoma possibly arising from the thyroglossal duct," and the diagnosis was confirmed by histopathologic investigation on resection material. CONCLUSION: Tall cell variant is a rare variant of papillary carcinoma and has a poor prognosis. The differential diagnosis includes Hürthle cell lesions, oncocytic papillary thyroid carcinoma and Warthin-like papillary carcinoma. 相似文献
45.
46.
Abdelmagid SM Barbe MF Rico MC Salihoglu S Arango-Hisijara I Selim AH Anderson MG Owen TA Popoff SN Safadi FF 《Experimental cell research》2008,314(13):2334-2351
Osteoactivin (OA) is a novel glycoprotein that is highly expressed during osteoblast differentiation. Using Western blot analysis, our data show that OA protein has two isoforms, one is transmembranous and the other is secreted into the conditioned medium of primary osteoblasts cultures. Fractionation of osteoblast cell compartments showed that the mature, glycosylated OA isoform of 115 kDa is found in the membranous fraction. Both OA isoforms (secreted and transmembrane) are found in the cytoplasmic fraction of osteoblasts. Overexpression of EGFP-tagged OA in osteoblasts showed that OA protein accumulates into vesicles for transportation to the cell membrane. We examined OA protein production in primary osteoblast cultures and found that OA is maximally expressed during the third week of culture (last stage of osteoblast differentiation). Glycosylation studies showed that OA isoform of 115 kDa is highly glycosylated. We also showed that retinoic acid (RA) stimulates the mannosylation of OA protein. In contrast, tunicamycin (TM) strongly inhibited N-glycans incorporation into OA protein. The functional role of the secreted OA isoform was revealed when cultures treated with anti-OA antibody, showed decreased osteoblast differentiation compared to untreated control cultures. Gain-of-function in osteoblasts using the pBABE viral system showed that OA overexpression in osteoblast stimulated their differentiation and function. The availability of a naturally occurring mutant mouse with a truncated OA protein provided further evidence that OA is an important factor for terminal osteoblast differentiation and mineralization. Using bone marrow mesenchymal cells derived from OA mutant and wild-type mice and testing their ability to differentiate into osteoblasts showed that differentiation of OA mutant osteoblasts was significantly reduced compared to wild-type osteoblasts. Collectively, our data suggest that OA acts as a positive regulator of osteoblastogenesis. 相似文献
47.
Nisin production of Lactococcus lactis N8 with hemin‐stimulated cell respiration in fed‐batch fermentation system 下载免费PDF全文
In this study, nisin production of Lactococcus lactis N8 was optimized by independent variables of glucose, hemin and oxygen concentrations in fed‐batch fermentation in which respiration of cells was stimulated with hemin. Response surface model was able to explain the changes of the nisin production of L. lactis N8 in fed‐batch fermentation system with high fidelity (R2 98%) and insignificant lack of fit. Accordingly, the equation developed indicated the optimum parameters for glucose, hemin, and dissolved oxygen were 8 g L?1 h?1, 3 μg mL?1 and 40%, respectively. While 1711 IU mL?1 nisin was produced by L. lactis N8 in control fed‐batch fermentation, 5410 IU mL?1 nisin production was achieved within the relevant optimum parameters where the respiration of cell was stimulated with hemin. Accordingly, nisin production was enhanced 3.1 fold in fed‐batch fermentation using hemin. In conclusion the nisin production of L. lactis N8 was enhanced extensively as a result of increasing the biomass by stimulating the cell respiration with adding the hemin in the fed‐batch fermentation. © 2015 American Institute of Chemical Engineers Biotechnol. Prog., 31:678–685, 2015 相似文献
48.
Karataş M Akgöl S Yavuz H Say R Denizli A 《International journal of biological macromolecules》2007,40(3):254-260
Magnetic poly(ethylene glycol dimethacrylate-N-methacryloyl-(L)-histidine methyl ester) [mag-poly(EGDMA-MAH) beads, 50-100 microm in diameter, were produced by suspension polymerization for affinity depletion of immunoglobulin G (IgG) from human serum. Cu2+ ions were complexed directly via MAH groups (Cu2+ loading: 4.1 micromol/g). IgG depletion studies were performed by magnetically stabilized fluidized bed column. Acetate, Tris-HCl, MES and phosphate buffers all allow adsorption of similar quantities of IgG (27.3-45.6 mg/g). MOPS and HEPES allow higher adsorption quantities (79.6 mg/g and 74.1mg/g, respectively). Maximum adsorption capacities in MOPS buffer were 46.8 mg/g for mag-poly(EGDMA-MAH) and 102.1mg/g for Cu2+ chelated mag-poly(EGDMA-MAH) beads. The adsorption capacity decreased drastically from 102.1mg/g to 30.7 mg/g with the increase of the flow rate from 0.2 ml/min to 3.5 ml/min. The elution studies were performed by 1.0M NaCl. The elution results demonstrated that the adsorption of IgG to the adsorbent was reversible. To test the efficiency of IgG depletion from human serum, proteins in the serum and eluted portion were analyzed by two-dimensional gel electrophoresis. The depletion efficiency for IgG was above 99.4%. Eluted proteins include mainly IgG, and a small number of non-albumin proteins such as apo-lipoprotein A1, sero-transferrin, haptoglobulin and alpha1-antitrypsin. When anti-HSA-sepharose adsorbent is used together with our metal-chelated mag-beads, IgG and HSA can be depleted in a single step. 相似文献
49.
Macro and micromorphological properties of intact and mature seeds of 12 taxa (species and varieties) belonging to Nigella L. (Ranunculaceae) was investigated using light and scanning electron microscopy. Material studied covers 11 species of 15
Turkish Nigella. Studied taxa were divided into two types. Type I has ovate to orbicular seeds that includes four species. Type II has triquedrous
seeds and includes seven species. Type II was subdivided into two. Type IIa has triquedrous to subpyramidal seeds (five species)
and Type IIb has triquedrous to subglobose seeds (two species). Further segregation was performed micromorphologically and
an identification key of studied Nigella taxa was given. Studied Nigella taxa have a diverse macro and micromorphological characters that utilize to separate them from each other to assess the systematics
of Nigella. 相似文献
50.
Ziver Sahin Muge Bıcakcıgil Kenan Aksu Sevil Kamali Servet Akar Fatos Onen Omer Karadag Zeynep Ozbalkan Askin Ates Huseyin TE Ozer Vuslat Yilmaz Emire Seyahi Mehmet A Ozturk Ayse Cefle Veli Cobankara A Mesut Onat Ercan Tunc Nursen Düzgün Sibel Z Aydin Neslihan Yilmaz İzzet Fresko Yasar Karaaslan Sedat Kiraz Nurullah Akkoc Murat Inanc Gokhan Keser F Aytul Uyar Haner Direskeneli Güher Saruhan-Direskeneli 《Arthritis research & therapy》2012,14(1):R27-5