全文获取类型
收费全文 | 709篇 |
免费 | 35篇 |
国内免费 | 54篇 |
专业分类
林业 | 64篇 |
农学 | 60篇 |
基础科学 | 52篇 |
101篇 | |
综合类 | 232篇 |
农作物 | 31篇 |
水产渔业 | 28篇 |
畜牧兽医 | 116篇 |
园艺 | 88篇 |
植物保护 | 26篇 |
出版年
2024年 | 4篇 |
2023年 | 14篇 |
2022年 | 28篇 |
2021年 | 34篇 |
2020年 | 27篇 |
2019年 | 40篇 |
2018年 | 30篇 |
2017年 | 34篇 |
2016年 | 43篇 |
2015年 | 33篇 |
2014年 | 40篇 |
2013年 | 44篇 |
2012年 | 40篇 |
2011年 | 42篇 |
2010年 | 43篇 |
2009年 | 36篇 |
2008年 | 31篇 |
2007年 | 37篇 |
2006年 | 37篇 |
2005年 | 22篇 |
2004年 | 28篇 |
2003年 | 19篇 |
2002年 | 12篇 |
2001年 | 11篇 |
2000年 | 9篇 |
1999年 | 10篇 |
1998年 | 7篇 |
1997年 | 6篇 |
1996年 | 6篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1993年 | 5篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 1篇 |
排序方式: 共有798条查询结果,搜索用时 687 毫秒
181.
182.
利用多重马尔可夫链提高林业预测精度 总被引:1,自引:0,他引:1
本文对多重马尔可夫链的应用进行了讨论。利用马尔可夫链和多重马尔可夫链对陕西省五倍子的年产量进行了预测,分析了它们的预测精度。预测结果的分析表明多重马尔可夫链明显地提高了预测精度。 相似文献
183.
AIM: To explore the effect of neuroepithelial cell transforming gene-1 (NET-1) expression on the metastasis of lung squamous-cell carcinoma (LSC) and the underlying molecular mechanism. METHODS: Immunohistochemistry was used to detect the expression of NET-1 protein in 53 cases of lung squamous-cell carcinoma (LSC group), 24 cases of normal lung epithelium (NLE group) and 27 cases of lung squamous intraepithelial lesions (SIL group). The correlation of clinical and pathological factors was analyzed. The protein expression of NET-1 in human lung squamous-cell carcinoma cell lines H226, H1703, H2170, SK-MES-1, H520 and YTMLC-90 was determined by Western blot. The RNA interference recombinant adenovirus against NET-1 gene (Ad-NET-siRNA) and Ad-control with control sequence were constructed and infected with human lung squamous cell carcinoma cell YTMLC-90 to silence the expression of NET-1 gene. The protein expression of NET-1, E-cadherin, vimentin and Snail1 in the BEAS-2B cells and the YTMLC-90 cells was determined by Western blot. The mRNA expression of E-cadherin and vimentin in each group of the cells was detected by qPCR. The invasive ability of the cells in each group was detected by Transwell chamber assay. RESULTS: The positive expression rate of NET-1 in LSC group was significantly higher than that in NLE group and SIL group(P<0.05). The distribution of NET-1 protein positive expression population was correlated with histological grade, lymph node metastasis, and TNM stage. The NET-1 expression rate of LSC with lymph node metastasis was significantly higher than that without lymph node metastasis. Over-expression of NET-1 protein in YTMLC-90 cells was observed. The expression of E-cadherin was decreased, and the protein expression of vimentin and Snail1 was increased in YTMLC-90 cells. Knock-down of NET-1 expression increased the expression of E-cadherin, and decreased the expression of vimentin and Snail1 in the YTMLC-90 cells. CONCLUSION: The expression of NET-1 promotes the lymphatic metastasis of lung squamous-cell carcinoma. This promotion may be achieved through the activation of epithelial-mesenchymal transition (EMT) by NET-1 expression. 相似文献
184.
Fibrosis is a common clinical disease that occurs in a variety of organs, and mainly manifests increased connective tissue of organ tissue and decreased parenchymal cells. Continuous progression may lead to organ structural damage, dysfunction and even depletion, seriously threatening human health and life safety. Therefore, in-depth study of the pathogenesis of fibrosis and the development of effective therapeutic drugs are of great importance for the prevention and treatment of fibrosis. Recent studies provide evidence that AMP-activated protein kinase (AMPK) plays an important role in the development of fibrosis. In combination with related literatures, this paper reviews the structure and biological function of AMPK, AMPK in inflammatory response associated with fibrosis, epithelial-mesenchymal transition, extracellular matrix and myofibroblasts, and the therapeutic role of AMPK as a new target in treating fibrosis diseases. 相似文献
185.
AIM:To investigate the effect of interleukin-6 (IL-6) on epithelial-mesenchymal transition (EMT), migration and invasion of papillary thyroid carcinoma TPC-1 cells by inducing the expression of long noncoding RNA lncTCF7. METHODS:The effects of IL-6 on the expression of lncTCF7 in the TPC-1 cells were detected by RT-qPCR after the TPC-1 cells were treated with IL-6 at 0, 5, 10, 20 and 50 μg/L for 24 h or with IL-6 at 50 μg/L for 0, 6, 12 and 24 h. After the TPC-1 cells were treated with IL-6 at 50 μg/L for 24 h, the effect of IL-6 on the protein expression of E-cadherin and vimentin in the TPC-1 cells was detected by Western blot. The TPC-1 cell line with lncTCF7 over-expression was established, and the effects of lncTCF7 over-expression on EMT, migration and invasion of the TPC-1 cells were measured by Western blot and Transwell assay. After knockdown of lncTCF7 expression and exposure to IL-6 at 50 μg/L, the effects of lncTCF7 on EMT, migration and invasion of TPC-1 cells treated with IL-6 were observed. RESULTS:The expression of lncTCF7 in the TPC-1 cells was induced by IL-6 in a dose-and time-dependent manner. The expression of E-cadherin was down-regulated, the expression of vimentin was up-regulated, and the migration and invasion abilities of the TPC-1 cells were enhanced by lncTCF7 over-expression (P<0.05). The expression of E-cadherin was decreased, the expression of vimentin, Snail and Slug was increased, and the migration and invasion abilities of the TPC-1 cells and intercellular space were enhanced by IL-6. The above changes induced by IL-6 were significantly inhibited by knockdown of lncTCF7 expression. CONCLUSION:IL-6 promotes the EMT, migration and invasion of papillary thyroid carcinoma TPC-1 cells by inducing the expression of lncTCF7. 相似文献
186.
幅度平滑变化的QAM调制 总被引:1,自引:0,他引:1
为了压缩QAM调制方式的频带宽度,提高频谱利用效率,提出了一种新的幅度平滑变化的QAM调制和解调方式,即将已调制信号的幅度在相邻码元之间由跳变改变为平滑变化,在计算机上仿真了幅度平滑变化的QAM调制和解调过程,从中分析并找出了幅度平滑变化最佳的过渡时间。 相似文献
187.
188.
189.
长白山云冷杉针阔混交林最优直径结构的构建 总被引:2,自引:0,他引:2
以长白山云冷杉针阔混交林两个大区内274个固定样点为研究对象,样地内每木检尺;从1987年至今,每两年复查一次。利用不同模型拟合该地区林分每公顷胸高断面积和每公顷蓄积的关系,求得林分能够生长达到的每公顷最大胸高断面积,并以此为界将现有林分胸高断面积分成10、10~20、30~40、40~50 m2/hm24个胸高断面积区间,分别计算各胸高断面积蓄积生长量。结果表明:林分进阶率和枯损率随胸高断面积的增加而减少;林分蓄积生长量随胸高断面积增加而先增大后减少。林分能够生长达到的最大胸高断面积大约为60 m2/hm2,但当林分胸高断面积为40 m2/hm2,平均Q值为1.4时,林分蓄积生长量最大(10.5 m3/(hm2.a))。利用呈负指数模型,结合林木径阶能够持续生长的转移情况,拟合出该地区林分最优直径结构。 相似文献
190.