首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   6907篇
  免费   556篇
  国内免费   715篇
林业   280篇
农学   391篇
基础科学   51篇
  313篇
综合类   2590篇
农作物   305篇
水产渔业   496篇
畜牧兽医   3079篇
园艺   481篇
植物保护   192篇
  2024年   5篇
  2023年   89篇
  2022年   158篇
  2021年   253篇
  2020年   261篇
  2019年   313篇
  2018年   202篇
  2017年   316篇
  2016年   374篇
  2015年   357篇
  2014年   383篇
  2013年   446篇
  2012年   492篇
  2011年   526篇
  2010年   440篇
  2009年   404篇
  2008年   362篇
  2007年   442篇
  2006年   334篇
  2005年   301篇
  2004年   237篇
  2003年   199篇
  2002年   160篇
  2001年   156篇
  2000年   127篇
  1999年   102篇
  1998年   84篇
  1997年   85篇
  1996年   54篇
  1995年   78篇
  1994年   65篇
  1993年   72篇
  1992年   53篇
  1991年   54篇
  1990年   60篇
  1989年   42篇
  1988年   26篇
  1987年   12篇
  1986年   7篇
  1985年   9篇
  1983年   4篇
  1982年   2篇
  1981年   3篇
  1980年   4篇
  1979年   6篇
  1975年   1篇
  1973年   3篇
  1962年   1篇
  1956年   10篇
  1955年   1篇
排序方式: 共有8178条查询结果,搜索用时 31 毫秒
991.
研究了茶树油及其组分干预树突状细胞后,采用MTT法检测药物对树突状细胞活力的抑制,并通过倒置显微镜观察细胞形态学变化,以探讨茶树油及其主要组分对小鼠骨髓来源树突状细胞体外生长的影响。结果表明:茶树油、Terpin-4-ol、1.8-Cineole和Terpinolene在实验浓度范围内(0.002~1.000μL/mL)对树突状细胞活力均有不同程度的抑制,抑制率与药物浓度呈剂量依赖关系,其中,茶树油对树突状细胞活力抑制率为25.60%(1.000μL/mL),而同等浓度下的Terpinene-4-ol抑制率为97.20%(P<0.01),表明Terpinene-4-ol对树突状细胞有较强的细胞毒性;结果还表明,在进行茶树油对树突状细胞活性评价研究时,应控制安全实验浓度在0.310μL/mL以下。  相似文献   
992.
为建立欧洲鳗鲡病毒性疾病分离、鉴定的细胞模型,以欧洲鳗鲡胸鳍细胞人工培养适应株(第21代)为试验材料,采用人工培养基体外传代培养的方法,探讨欧洲鳗鲡胸鳍传代细胞体外培养的最适条件。观察比较不同培养基(L-15、RPMI-1640、高糖型DMEM)、血清成分(BS和FBS)及其浓度(5%、10%、15%、20%)对欧洲鳗鲡胸鳍细胞生长状态的影响。结果表明:含有10%胎牛血清(FBS)的L-15培养基最适合欧洲鳗鲡胸鳍细胞的生长。  相似文献   
993.
AIM: To observe the effects of interleukin-32γ (IL-32γ)on the proliferation and cell cycle of rat vascular smooth muscle cells (VSMCs). METHODS: The VSMCs were isolated from the thoracic aorta of SD rats by the method of tissue-piece inoculation. The cells were cultured and treated with different concentrations of IL-32γ. The proliferation of the cells was examined by MTT assay. The cell cycles were analyzed by flow cytometry. The protein levels of NF-κB p65 and cyclin D1 were detected by Western blotting. The expression of proliferating cell nuclear antigen (PCNA)was examined by immunocytochemical staining. RESULTS: Administration of IL-32γ at the concentrations of 10~50 μg/L for 24~48 h significantly promoted the proliferation of VSMCs in a dose- and time-dependent manner. After stimulation with IL-32γ at the concentration of 50 μg/L for 24 h, the cell cycle transition from G1 phase to S/G2 phase was accelerated and the expression levels of NF-κB p65, cyclin D1 and PCNA increased as compared with those in control group. CONCLUSION: IL-32γ promotes the proliferation of rat VSMCs and accelerates the cell cycle transition via upregulating the expression of NF-κB p65 and cyclin D1.  相似文献   
994.
AIM: To evaluate the relationship between epithelial cell adhesion molecule (EPCAM)/cluster of differentiation 44 (CD44)/cluster of differentiation 24 (CD24) expression and the clinicopathological characteristics/prognosis in 95 gastric cancer patients. METHODS: The expression levels of EPCAM, CD44 and CD24 were detected using the two-step method of immunohistochemistry in 95 gastric cancer patients who underwent surgical excision and were pathologically diagnosed as gastric cancer. RESULTS: There were 56 EPCAM-positive patients (58.95%), 41 CD44-positive patients (43.16%) and 56 CD24-positive patients (58.95%). Thirty patients were both EPCAM and CD44 positive (31.58%), 45 patients were both EPCAM and CD24 positive (47.37%), 32 patients were both CD44 and CD24 positive (33.68%), and 25 patients were EPCAM, CD44 and CD24 positive (26.32%). EPCAM expression was correlated with age, depth of tumor infiltration and WHO histological classification. CD44 expression was correlated with BORRMANN and WHO histological classification as well as CEA value. CD24 expression was correlated with the depth of infiltration, location of the tumor, WHO histological classification and viscera invasion. All positive expression of EPCAM, CD44 and CD24 was correlated with the depth of infiltration, location of the tumor and WHO histological classification (P<0.05). The difference of survival rate between EPCAM positive group and negative group was observed, and the CD44 positive group and negative group had the same result (P<0.05 and P<0.01, respectively). The difference of survival rate between EPCAM+CD44+CD24+ group and EPCAM-CD44-CD24- group was statistically significant (P<0.05). The difference of survival rate between EPCAM-CD44+CD24+ group and EPCAM-CD44-CD24- group was also significant (P<0.05). CONCLUSION: The positive rates of EPCAM, CD44 and CD24 expression are high in gastric cancer tissues and these 3 proteins can be used as primary screening targets.  相似文献   
995.
在研制猪细小病毒灭活疫苗时,应用了超滤浓缩技术,提高了合毒细胞培养液中的抗原含量。为了保证浓缩的流量,减少对滤膜的污染,对含毒细胞培养液作了预处理一离心及微滤,以便除去细胞培养液中的细胞碎片、蛋白质等大分子物质及固形微粒。超滤时选用50000Da滤膜,在20psig压力下,经过5倍浓缩的PPV细胞培养液,血凝滴度提高2个滴度以上。病毒含量测定表明,TCID50/0.2mL由107左右升至109以上,以其配制疫苗,能显著地提高疫苗的免疫原性。超滤技术具有易于操作、高效、分离精度高、没有二次污染等优点,可以根据需要选择不同的浓缩浓度,对保证疫苗的质量具有重要作用。  相似文献   
996.
The anatomy characteristics of cell wall and lignin distribution in different anatomical regions for 12-month-old bamboo species Pseudosasa amabilis was investigated.The lignin distribution was studied by means of optical microscope and confocal laser scanning microscope and the color reaction. In addition,the distribution of lignin in different tissues(fiber,parenchyma and vessel) was investigated by visible-light microspectrophotometry coupled with the Wiesner and Maule reaction.The cell walls of different tissues were all lignified and the lignin was widely distributed in different tissues, in which there was a difference between tissues and anatomical regions in lignin content.Guaiacyl lignin and syringyl lignin unit could be found in cell wall of fiber,parenchyma and vessel through Wiesner and Maule reaction and the absorbance peak of spectrum. There was no regular variation in lignin content with different radial location of culms and different location in fiber strands.The lamellation of the fiber cell wall was generally had as alternating broad and narrow layers with alternating low and high concentration of lignin.  相似文献   
997.
Mast cell tumors (MCT) are the most common cutaneous tumors in dogs. Our purpose was to describe the magnetic resonance (MR) imaging characteristics of cutaneous MCT and to identify imaging characteristics that allow differentiation of metastatic from normal lymph nodes. Eight dogs with a total of nineMCT were imaged as were their presumed draining and associated contralateral lymph nodes. The signal intensity of tumors and lymph nodes was compared to adjacent musculature. On T2-W images, 7/9 MCT were hyperintense to muscle and 2/9 were isointense. On T1-W images, 8/9 MCT were isointense and 1/9 were mildly hypointense. All tumors were strongly contrast enhancing; 5/9 were homogeneous and 4/9 heterogeneous in their enhancement patterns. Six lymph node pairs were included in the evaluation (five sentinel lymph nodes with metastases, one without, and six contralateral lymph nodes). Metastatic lymph nodes were significantly larger than their contralateral lymph nodes (P = 0.039). All lymph nodes were isointense on T1-W images and hyperintense on T2-W images. 5/5 metastatic and 2/7 normal lymph nodes were heterogeneously T2-hyperintense. All lymph nodes were moderately to strongly contrast enhancing. 4/5 metastatic and 2/7 normal lymph nodes had heterogeneous enhancement patterns. While heterogeneity was more common in metastatic than in normal lymph nodes, this difference was not significant (P = 0.058 for T2-W images; P = 0.234 for postcontrast images). MR imaging may be useful in the presurgical evaluation and clinical staging of cutaneous MCT.  相似文献   
998.
The association of cryptorchidism, functional Sertoli cell tumors, and spermatic cord torsion has been rarely reported in the literature. Two dogs were admitted for bilateral skin alopecia and weight loss. Both animals were cryptorchid and displayed a pendulous preputial sheath, prostate hypertrophy, and increased levels of circulating oestrogen. Transabdominal palpation and ultrasonography revealed the presence of neoplastic retained gonads. During surgery, spermatic cord torsion was also detected in the enlarged neoplastic testes of both dogs. Histologic examination confirmed the presence of Sertoli cell tumors that were primarily responsible for the feminizing syndrome. Complete remission of all symptoms occurred within 3 months after orchiectomy.  相似文献   
999.
Alternative sources of mesenchymal stem cells (MSCs) for replacing bone marrow (BM) have been extensively investigated in the field of bone tissue engineering. The purpose of this study was to compare the osteogenic potential of canine MSCs derived from adipose tissue (AT), BM, umbilical cord blood (UCB), and Wharton''s jelly (WJ) using in vitro culture techniques and in vivo orthotopic implantation assays. After canine MSCs were isolated from various tissues, the proliferation and osteogenic potential along with vascular endothelial growth factor (VEGF) production were measured and compared in vitro. For the in vivo assay, MSCs derived from each type of tissue were mixed with β-tricalcium phosphate and implanted into segmental bone defects in dogs. Among the different types of MSCs, AT-MSCs had a higher proliferation potential and BM-MSCs produced the most VEGF. AT-MSCs and UCB-MSCs showed greater in vitro osteogenic potential compared to the other cells. Radiographic and histological analyses showed that all tested MSCs had similar osteogenic capacities, and the level of new bone formation was much higher with implants containing MSCs than cell-free implants. These results indicate that AT-MSCs, UCB-MSCs, and WJ-MSCs can potentially be used in place of BM-MSCs for clinical bone engineering procedures.  相似文献   
1000.
为寻找奶牛乳腺上皮细胞亚细胞结构中与泌乳相关的重要蛋白质、从蛋白质水平揭示乳蛋白合成的调控机制,应用双向凝胶电泳技术分离体外培养的蛋氨酸处理组与正常组奶牛乳腺上皮细胞蛋白质,利用Image Maser 2D软件对图谱进行对比分析,基质辅助激光解析电离飞行时间质谱(MALDI-TOF-MS)和数据库检索鉴定,并采用实时荧光定量PCR技术在mRNA水平上验证2-DE结果。质谱鉴定出8个表达上调的差异蛋白质,大多数差异蛋白质的功能涉及细胞骨架构成、能量代谢等过程。这些差异点的发现为研究奶牛泌乳机理提供了有益的线索。  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号