全文获取类型
收费全文 | 9730篇 |
免费 | 690篇 |
国内免费 | 827篇 |
专业分类
11247篇 |
出版年
2024年 | 19篇 |
2023年 | 137篇 |
2022年 | 362篇 |
2021年 | 631篇 |
2020年 | 357篇 |
2019年 | 472篇 |
2018年 | 463篇 |
2017年 | 316篇 |
2016年 | 449篇 |
2015年 | 685篇 |
2014年 | 794篇 |
2013年 | 781篇 |
2012年 | 923篇 |
2011年 | 852篇 |
2010年 | 496篇 |
2009年 | 449篇 |
2008年 | 497篇 |
2007年 | 414篇 |
2006年 | 327篇 |
2005年 | 265篇 |
2004年 | 232篇 |
2003年 | 241篇 |
2002年 | 197篇 |
2001年 | 147篇 |
2000年 | 113篇 |
1999年 | 128篇 |
1998年 | 72篇 |
1997年 | 68篇 |
1996年 | 63篇 |
1995年 | 50篇 |
1994年 | 36篇 |
1993年 | 25篇 |
1992年 | 39篇 |
1991年 | 22篇 |
1990年 | 21篇 |
1989年 | 37篇 |
1988年 | 14篇 |
1987年 | 8篇 |
1986年 | 9篇 |
1985年 | 21篇 |
1984年 | 4篇 |
1983年 | 7篇 |
1982年 | 2篇 |
1981年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
基于MATLAB 的花粉形态量化分析 总被引:1,自引:0,他引:1
利用数字照相技术和MATLAB软件测量了5种杨树、3种柏树各50粒花粉的面积、扁圆率、极轴长度、赤道轴长度, 计算了面积标准差和极轴长度/赤道轴长度。对8种花粉的面积作了方差分析。结果显示, 在99%置信水平上用面积能区分8种花粉。用5种杨树花粉的扁圆率平均值、极轴平均值、赤道轴平均值和P/E值作聚类分析, 聚类结果显示, 5种杨树可分成3组, 加拿大杨和小叶杨是一组, 毛白杨和山杨是一组, 青杨单独为一组。电镜观察纹饰特点与以上聚类结果一致。本研究为定量研究花粉形态提供了一种快速有效的方法及更多的有效数据, 比目测精确度提高了10倍。 相似文献
992.
Field cultivation experiments on white sesame (Sesamum indicum L.)seeds implanted with low-energy C ion showed that different dosages of C ion implantation produce different biological effects.Sesame plants in 6 different dosage groups with C ion density respectively at 1×1011,1×1012,1×1015,5×1015,1×1016,5×1016 ion/cm2 were superior to the control group in plant height,leaf number,stalk diameter and leaf size.Further,sesame plants in these groups flower and seed earlier than those in the control group,and single plant yield also increased.Of all the groups,the 5×1015 ion/cm2 dosage group yielded the best effect,whereas the 1×1017/cm2 dosage group showed an evident inhibitory effect of ion implantation on the germination and growth of the sesame seeds. 相似文献
993.
图书馆开展大学生信息素养教育的优势与途径 总被引:3,自引:0,他引:3
论述了对大学生进行信息素养教育的意义,阐明了图书馆在开展大学生信息素养教育过程中起到的优势作用,提出了利用图书馆进行大学生信息素养教育的6种途径。 相似文献
994.
Runan Yang Lin Li Huilong Yuan Hui Liu Yingxin Gong Lifang Zou Shunhua Li Zilin Wang Liran Shi Tianyu Jia Shanhong Zhao Bing Wu Zhihua Yi Yun Gao Guilin Li Hong Xu Shuangmei Liu Chunping Zhang Guodong Li Shangdong Liang 《Journal of cellular physiology》2019,234(3):2756-2764
The upregulation of nociceptive ion channels expressed in dorsal root ganglia (DRG) contributes to the development and retaining of diabetic pain symptoms. The flavonoid quercetin (3,3′,4′,5,7-pentahydroxyflavone) is a component extracted from various fruits and vegetables and exerts anti-inflammatory, analgesic, anticarcinogenic, antiulcer, and antihypertensive effects. However, the exact mechanism underlying quercetin's analgesic action remains poorly understood. The aim of this study was to investigate the effects of quercetin on diabetic neuropathic pain related to the P2X4 receptor in the DRG of type 2 diabetic rat model. Our data showed that both mechanical withdrawal threshold and thermal withdrawal latency in diabetic rats treated with quercetin were higher compared with those in untreated diabetic rats. The expression levels of P2X4 messenger RNA and protein in the DRG of diabetic rats were increased compared with the control rats, while quercetin treatment significantly inhibited such enhanced P2X4 expression in diabetic rats. The satellite glial cells (SGCs) enwrap the neuronal soma in the DRG. Quercetin treatment also lowered the elevated coexpression of P2X4 and glial fibrillary acidic protein (a marker of SGCs) and decreased the upregulation of phosphorylated p38 mitogen-activated protein kinase (p38MAPK) in the DRG of diabetic rats. Quercetin significantly reduced the P2X4 agonist adenosine triphosphate-activated currents in HEK293 cells transfected with P2X4 receptors. Thus, our data demonstrate that quercetin may decrease the upregulation of the P2X4 receptor in DRG SGCs, and consequently inhibit P2X4 receptor-mediated p38MAPK activation to relieve the mechanical and thermal hyperalgesia in diabetic rats. 相似文献
995.
996.
Dandan Jia Lu Hou Yongzhi Lv Lei Xi Zhenjun Tian 《Journal of cellular physiology》2019,234(12):23705-23718
Exercise training mitigates cardiac pathological remodeling and dysfunction caused by myocardial infarction (MI), but its underlying cellular and molecular mechanisms remain elusive. Our present study in an in vivo rat model of MI determined the impact of post-MI exercise training on myocardial fibrosis, mitochondrial biogenesis, antioxidant capacity, and ventricular function. Adult male rats were randomized into: (a) Sedentary control group; (b) 4-week treadmill exercise training group; (c) Sham surgery group; (d) MI group with permanent ligation of left anterior descending coronary artery and kept sedentary during post-MI period; and (e) post-MI 4-week exercise training group. Results indicated that exercise training significantly improved post-MI left ventricular function and reduced markers of cardiac fibrosis. Exercise training also significantly attenuated MI-induced mitochondrial damage and oxidative stress, which were associated with enhanced antioxidant enzyme expression and/or activity and total antioxidant capacity in the heart. Interestingly, the adaptive activation of the SIRT1/PGC-1α/PI3K/Akt signaling following MI was further enhanced by post-MI exercise training, which is likely responsible for exercise-induced cardioprotection and mitochondrial biogenesis. In conclusion, this study has provided novel evidence on the activation of SIRT1/PGC-1α/PI3K/Akt pathway, which may mediate exercise-induced cardioprotection through reduction of cardiac fibrosis and oxidative stress, as well as improvement of mitochondrial integrity and biogenesis in post-MI myocardium. 相似文献
997.
Plant and Soil - Improving our understanding of ecosystem responses to land-use intensification requires explicit consideration of linkages between aboveground and belowground communities. Here, we... 相似文献
998.
Jiang Xue-ru Ren Rui-fen Di Wei Jia Meng-xue Li Ze-di Liu Yan Gao Rong-fu 《Plant Cell, Tissue and Organ Culture》2019,137(3):553-563
Plant Cell, Tissue and Organ Culture (PCTOC) - Programmed cell death (PCD) plays a key role in animal tissue cell death following cryopreservation. However, there are few studies evaluating the... 相似文献
999.
The adsorption of the CO2/CH4 mixture in coal affects the CO2-enhanced coalbed methane recovery project. To gain a better understanding of CH4 and CO2 interaction with middle-rank coal, we developed a molecular concept with support for the sorption of CH4 and CO2 on Ximing-8 coal (XM-8) (1.8% vitrinite reflectance). A XM-8 coal model was built by using molecular dynamic (MD) simulations. The molecular simulations were established by the Grand Canonical Monte Carlo and MD methods to study the effects of the temperature, pressure, and species bulk mole fraction on the pure component adsorption isotherms, isosteric heat and adsorption selectivity. It turns out that the CO2 selectivity decreases as the pressure and its own bulk mole fraction increases, but it increases as temperature increases, and the selectivity values are not always greater than 1. The interactions between the small molecules and XM-8 were determined by using density functional theory. It was found that the interactions between the CO2 and XM-8 surface is greater, particularly for the heteroatoms than CH4. The adsorption selectivity and interaction were simultaneously used to reveal that the advantageously substituted range is high temperature, low pressure and a high content of heteroatoms. 相似文献
1000.
Jiping Sun Liyi Xie Jing Lv Wenjing Zhang Jia Lv Yu Liang Yingzhou Geng Xudong Li 《Journal of cellular biochemistry》2019,120(4):6709-6717
The inhibitor of growth 4 (ING4) is known as a tumor suppressor. The expressions of ING4 were markedly reduced in human renal clear cell carcinoma (ccRCC) tissues. However, the role of ING4 in renal cell carcinoma (RCC) remains unknown. The aim of the current study was to detect the ING4 expression level and its potential role in human RCC cell lines. Our results showed that ING4 was lowly expressed in human RCC cell lines compared with that in proximal tubular cell line. Ectopic overexpression of ING4 inhibited the proliferation, migration, and invasion properties, and as well as prevented epithelial-mesenchymal transition (EMT) phenotype of RCC cells. In addition, ING4 overexpression induced cell apoptosis and autophagy in RCC cells. Furthermore, ING4 overexpression suppressed the activation of PI3K/Akt pathway in RCC cells. The activator of PI3K/Akt, insulin-like growth factor 1, abolished the effects of ING4 on RCC cells. These findings indicated that ING4 presented anticancer activity in RCC cells. The effects of ING4 on RCC cells were mediated by regulating the PI3K/Akt pathway. These findings suggested that ING4 could be used for gene therapy of RCC. 相似文献