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   59393篇
  免费   3198篇
  国内免费   5693篇
林业   6582篇
农学   7286篇
基础科学   3977篇
  8378篇
综合类   21226篇
农作物   3818篇
水产渔业   2472篇
畜牧兽医   7958篇
园艺   2859篇
植物保护   3728篇
  2024年   180篇
  2023年   722篇
  2022年   1864篇
  2021年   2352篇
  2020年   2212篇
  2019年   2229篇
  2018年   1517篇
  2017年   2228篇
  2016年   1846篇
  2015年   2680篇
  2014年   2597篇
  2013年   3249篇
  2012年   3976篇
  2011年   4144篇
  2010年   3865篇
  2009年   3773篇
  2008年   3586篇
  2007年   3582篇
  2006年   3153篇
  2005年   2974篇
  2004年   1509篇
  2003年   1130篇
  2002年   1092篇
  2001年   1094篇
  2000年   1200篇
  1999年   1387篇
  1998年   1099篇
  1997年   940篇
  1996年   899篇
  1995年   796篇
  1994年   739篇
  1993年   731篇
  1992年   596篇
  1991年   527篇
  1990年   432篇
  1989年   358篇
  1988年   274篇
  1987年   174篇
  1986年   134篇
  1985年   79篇
  1984年   48篇
  1983年   41篇
  1982年   41篇
  1981年   56篇
  1980年   33篇
  1979年   24篇
  1978年   11篇
  1965年   10篇
  1964年   13篇
  1963年   12篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
AIM: To observe the immunoregulation of allogeneic cornea on the human peripheral blood T lymphocytes in vitro. METHODS: After Co-culture of human peripheral blood lymphocytes and allogeneic cornea in vitro, T lymphocytes were labeled by monoclonal antibody, and analyzed by fluorescent activated cell sorter (FACS). RESULTS: CD25 expression on T lymphocytes in control was 25.2%, after stimulated by the allogeneic cornea or PDB, CD25 expression on T lymphocytes was 56.8% and 80.9%, respectively. After stimulated by the allogeneic cornea, CD25 expression on CD4+ or CD8+ T lymphocytes were 67.3% and 52.3%, respectively. CONCLUSION: Allageneic cornea stimulates CD25 expression on human peripheral blood T lymphocytes, and the CD25 expression on CD4+ T lymphocytes is more prominent than CD8+ T lymphocytes.  相似文献   
992.
AIM: To observe the effects of ginkgolide B on the neuron apoptosis induced by glutamate and explore whether this effects are related to the changes of calcium in neurons. METHODS: Primary neuron culture was prepared according to a previously reported procedure with slight modification. Neuron damage was induced by 0.8 mmol/L glutamate. The cell survival rate was examined by 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assays. The neuron morphological changes, Hoechst 33258 unclear-staining analysis and agarose gel electrophoresis of DNA were measured as the indexes of cell apoptosis. Intracellular free Ca2+ concentration in neurons was measured by using the fluorescent Ca2+ indicator Fura-2/AM. RESULTS: The cells, exposed to glutamate (0.8 mmol/L), showed characteristic change of apoptosis and calcium overload, which were relieved by the treatment of ginkgolide B (10-250 μmol/L), with survival increasing and cell morphology restoring and DNA fragment decreasing. CONCLUSIONS: Ginkgolide B prevents the neurons from glutamate neurotoxicity by inhibiting glutamate-induced apoptosis. The potential mechanism of its action may be related to the competitive PAF receptor binding of ginkgolide B and decreasing the intracellular calcium concentration in neurons.  相似文献   
993.
AIM: To investigate the influence of the cornus officinalis glycosides (COG) on immunological function of corneal transplantation model of rats, and to clarify the immunosuppressive mechanism of COG through observing the activation of lymphocytes in blood. METHODS: Wister rats were used as recipients and SD rats were used as corneal graft donors, then the corneal allografts transplantation model on the closed colony rats were set up. Splenocytes proliferation and mixed lymphocyte reaction of Wister rats activated by ConA were observed. The phenotype change of CD4, CD8, CD25 in blood in different time postoperatively were observed by the di-sign flow cytometry, and the rate of CD4/CD8 was calculated. RESULTS: 1. The COG suppressed the proliferation of T lymphocytes and one-way mixed lymphocyte reaction on the corneal allografting. 2. The phenotype change of lymphocytes in boold was as follows: there was no significant difference between the different time of the CD4, CD8 expression and the CD4/CD8 rate in blood of the control group. The CD4 positive cells expressed CD25 postoperatively increased obviously. The CD4/CD8 rate of medicine group had the tendency to decrease. The CD4 positive cells expressed CD25 postoperation in the medicine group were less than that in the control group obviously. CONCLUSION: The suppression of the T lymphocyte proliferation, mixed lymphocyte reaction, CD molecule expressed by the activated T lymphocytes and the IL-2 receptor expression may be the main immunosuppressive mechanisms of Cornus officinalis glycosides on the cell-mediated immunity.  相似文献   
994.
AIM: To investigate the influence of hepatic portal interdicting on gastric mucosa of the liver cirrhosis rats and the protective effect of famotidine on gastric mucosa. METHODS: Fifty Wistar rats were randomly divided into 5 groups; group A (healthy rats), group B (healthy rats with interdicted hepatic portal), group C (liver cirrhosis rats without interdicted hepatic portal), group D (liver cirrhosis rats with interdicted hepatic portal) and group E (liver cirrhosis rats without interdicted hepatic portal and use of famotidine); The gastricfluid pH, gastric mucous content (GMC), gastric mucosa blood flow (GMBF) and the damage index of gastric mucosa (DIGM) of the every group were observed. RESULTS: There is no significant difference in the above parameters between group A and group B (P>0.05). Compared with group A, GMBF of group C, D, and E were reduced (P<0.01), pH, GMC of group C, D and E were also reduced (P<0.05); DIGM of group C, D and E were increased (P<0.01). All the changes of group D were more obvious than those of group C (P<0.01); While there was no significant difference in all the parameters between group E and group C (P>0.05). CONCLUSION: Hepatic portal interdicting can aggravate the gastric mucosa damage of the liver cirrhosis rat, and famotidine can protect against such gastric mucosa injury through improving the microcirculation of gastric mucosa.  相似文献   
995.
AIM: To investigate the relation between the time- spatiotemporal expression of caspase-9 and photoreceptor apoptosis as well as electroretinography (ERG) in Royal College of Surgeons (RCS) rats. METHODS: Twelve non-pigmented degenerative RCS rats at age of 15, 20, 25, 30 days were sacrificed after ERG examination. The caspase-9 expression was analyzed with immunohistochemical staining, fluoro-metric activity assay and Western blotting. Apoptotic retinal neurons were detected by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) technique. RESULTS: The latency and amplitude of b-wave were (58.60±3.42) ms and (109.07±14.50) mV, (56.45±1.08) ms and (109.00±7.35) mV, respectively, in 15 and 20 days old degenerative RCS rats. The ERG resembled flat form in the degenerative RCS rats at age of 25 and 30 days. TUNEL-positive cells were located only in the outer nuclear layer, mostly prevailed in 25-day-old group. Caspase-9 protein expressed in the rat retina started to be found immunohistochemically in 25-day-old and was most predominant in the inner segment. Fluorometric activity assay showed that caspase-9 activity reached its peak, (10.98±0.13) nmol·g-1·min-1 at 20th day. Western blot assay revealed the small cleavage fragmentation at 20th day. No cleavage fragmentation was revealed in the 15-day-old degenerative RCS rats and all other control rats. CONCLUSION: The activation and time-spatiotemporal expression of caspase-9 are coincidence with photoreceptor apoptosis as well as the loss of vision function in RCS degenerative rats, which implicates the important role of caspase-9 in photoreceptor apoptosis.  相似文献   
996.
茄科植物内生细菌的分离及拮抗菌的筛选   总被引:4,自引:0,他引:4  
从番茄和辣椒植株中共分离到9株对植物病原真菌具有拈抗作用的内生细菌。其中,来自樱桃番茄的内生细菌株系BS-1和湘研辣椒的内生细菌株系BS-4对辣椒根腐病菌等具有较强的拈抗作用,两者在植株体内均可以定殖。BS-1和BS-4均属于芽孢杆菌。  相似文献   
997.
陈凤英  何寿斌  徐国平 《江西植保》2005,28(2):86-86,85
5%除虫菊素乳油(云菊)是一种天然除虫菊杀虫剂,由除虫菊植物中提取的杀虫活性物质叫除虫菊素。使用该农药对环境无污染,对蔬菜无残留,防治斜纹夜蛾使用的适宜浓度1500——2000倍液,药后3天、7天防效分别为90.14%、94.03%,94.12%、96.89%。  相似文献   
998.
对广东省鹤山和东莞莲花山自然保护区的小蛾类昆虫进行调查,计有8科35属43种。其中广东新记录种14种。  相似文献   
999.
Trans-resveratrol is a biologically active compound present in certain foods that has anti-inflammatory and anticancer properties. These beneficial effects are derived from both the immune system and cytokines. The purpose of this study was to determine the immunomodulatory effect of trans-resveratrol on the ex vivo production of inflammatory and anti-inflammatory cytokines stimulated by lipopolysaccharides (LPS). Trans-resveratrol (0, 0.01, 0.1, 1, and 10 microM) was added to blood samples from male Sprague-Dawley rats (n = 6) along with 100 U of LPS (Escherichia coli serotype, 055B5). The samples were then incubated for 4 h at 37 degrees C and centrifuged. Finally, concentrations of tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta), and IL-6 in the plasma were analyzed using an enzyme-linked immunosorbent assay (ELISA). The production of inflammatory (TNF-alpha and IL-1beta) and anti-inflammatory (IL-6) cytokines was suppressed by trans-resveratrol in a concentration-dependent manner. These results support the hypothesis that the immunomodulatory effect of trans-resveratrol plays an important role in disease conditions that involve an overproduction of inflammatory cytokines.  相似文献   
1000.
Calcidiol (25-hydroxyvitamin D) values are reported for 22 wild Ricord's iguanas (Cyclura ricordii) and seven wild rhinoceros iguanas (Cyclura cornuta cornuta). Calcitriol (1,25-hydroxyvitamin D) values are reported for 12 wild Ricord's iguanas and seven wild rhinoceros iguanas. These animals were captured as part of a larger health assessment study being conducted on Ricord's iguanas in Isla Cabritos National Park, Dominican Republic. A total of 13 captive rhinoceros iguanas held outdoors at Parque Zoológico Nacional were also sampled for comparison. Mean concentrations of 25-hydroxyvitamin D were 554 nmol/L (222 ng/ml) with a range of 250-1,118 nmol/L (100-448 ng/ml) for wild Ricord's iguanas, 332 nmol/L (133 ng/ml) with a range of 260-369 nmol/L (104-148 ng/ml) for wild rhinoceros iguanas, and 317 nmol/L (127 ng/ml) with a range of 220-519 nmol/L (88-208 ng/ml) for captive rhinoceros iguanas. On the basis of these results, serum concentrations of at least 325 nmol/L (130 ng/ml) for 25-hydroxyvitamin D should be considered normal for healthy Ricord's and rhinoceros iguanas.  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