全文获取类型
收费全文 | 4529篇 |
免费 | 477篇 |
国内免费 | 438篇 |
专业分类
5444篇 |
出版年
2024年 | 10篇 |
2023年 | 53篇 |
2022年 | 124篇 |
2021年 | 192篇 |
2020年 | 155篇 |
2019年 | 228篇 |
2018年 | 184篇 |
2017年 | 170篇 |
2016年 | 190篇 |
2015年 | 278篇 |
2014年 | 293篇 |
2013年 | 333篇 |
2012年 | 362篇 |
2011年 | 327篇 |
2010年 | 231篇 |
2009年 | 202篇 |
2008年 | 224篇 |
2007年 | 207篇 |
2006年 | 172篇 |
2005年 | 155篇 |
2004年 | 172篇 |
2003年 | 197篇 |
2002年 | 226篇 |
2001年 | 137篇 |
2000年 | 117篇 |
1999年 | 92篇 |
1998年 | 81篇 |
1997年 | 57篇 |
1996年 | 36篇 |
1995年 | 32篇 |
1994年 | 22篇 |
1993年 | 17篇 |
1992年 | 14篇 |
1991年 | 26篇 |
1990年 | 20篇 |
1989年 | 23篇 |
1988年 | 9篇 |
1987年 | 11篇 |
1986年 | 12篇 |
1985年 | 8篇 |
1984年 | 9篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1979年 | 5篇 |
1973年 | 4篇 |
1966年 | 2篇 |
1959年 | 1篇 |
1948年 | 1篇 |
1947年 | 1篇 |
排序方式: 共有5444条查询结果,搜索用时 10 毫秒
211.
212.
Qiang Hao Weina Li Cun Zhang Xin Qin Xiaochang Xue Meng Li Zhen Shu Tianjiao Xu Yujin Xu Weihua Wang Wei Zhang Yingqi Zhang 《Biochemical and biophysical research communications》2013,430(1):436-441
Controversial roles of FOXP3 in different cancers have been reported previously, while its role in gastric cancer is largely unknown. Here we found that FOXP3 is unexpectedly upregulated in some gastric cancer cells. To test whether increased FOXP3 remains the tumor suppressor role in gastric cancer as seen in other cancers, we test its function in cell proliferation both at basal and TNFα mimicked inflammatory condition. Compared with the proliferation inhibitory role observed in basal condition, FOXP3 is insufficient to inhibit the cell proliferation under TNFα treatment. Molecularly, we found that TNFα induced an interaction between FOXP3 and p65, which in turn drive the FOXP3 away from the promoter of the well known target p21. Our data here suggest that although FOXP3 is upregulated in gastric cancer, its tumor suppressor role has been dampened due to the inflammation environment. 相似文献
213.
Xiao Wang Zhong-Wei Zhang Shi-Hua Tu Wen-Qiang Feng Fei Xu Feng Zhu Da-Wei Zhang Jun-Bo Du Shu Yuan Hong-Hui Lin 《Biologia》2013,68(1):74-81
Cadmium (Cd) has been identified as a significant pollutant due to its high solubility in water and soil and high toxicity to plants and animals. Rice, as one of the most important food crops, is grown in soils with variable levels of Cd and therefore, is important to discriminate the Cd tolerance of different rice cultivars to determine their suitability for cultivation in Cd-contaminated soils. This study investigates the primary mechanisms employed by four rice cultivars in attaining Cd tolerance. HA63 cultivar reduces Cd uptake by increasing Fe absorption through activation of phytosiderophores. T3028 cultivar accumulates the highest level of Cd in leaves while also activating its reactive oxygen species (ROS) scavenging system, including antioxidant enzymes and phytochelatins. In some rice cultivars (such as HA63), a cyanide-resistant respiration mechanism, important in Cd detoxification, was also promoted under the Cd stress. In conclusion, different rice cultivars may adopt different biochemical strategies and respond with different efficiency to Cd stress. 相似文献
214.
Restoration of a subtropical eutrophic shallow lake in China: effects on nutrient concentrations and biological communities 总被引:1,自引:0,他引:1
Disturbances caused by rainfall are common in streams with the impact on stream inhabitants determined by the frequency, intensity, and predictability of the event. Here, we examine the response of winter-emerging Chironomidae (Diptera) to extreme flooding disturbance. In August of 2007, a severe flood impacted southeastern Minnesota, imparting stress on aquatic communities. Chironomid pupal exuviae collections were obtained biweekly from 18 southeast Minnesota streams during the following winter to assess resistance and resilience of winter-active chironomids to flooding. Streams examined were divided into moderate (2.5–10 cm), heavy (10–20 cm), or extreme (20+ cm) rainfall categories with rainfall amounts in each category representing total precipitation during the 3-day storm. Post-flood samples were compared to samples obtained from the same localities during prior winters. Our findings contradict studies of responses by Chironomidae to flooding during warmer-water conditions and show that winter-emerging Chironomidae are resistant to stress imposed by summer spates. Significantly more taxa emerged during winter after flooding as compared to historic collections, and the number of species emerging in winter was positively correlated with rainfall severity, indicating that 15 species responded opportunistically to disturbance. This indicates that winter-active Chironomidae may be resistant to increased severity of summer spates associated with climate change predictions. 相似文献
215.
Tian-Xing Shi Shu Wang Ke-Wu Zeng Peng-Fei Tu Yong Jiang 《Bioorganic & medicinal chemistry letters》2013,23(21):5904-5908
Five new phenolic glycosides, tenuisides A–E (1?5), and a new megastigmane glycoside, tenuiside F (6), along with seventeen known compounds (7–23) were isolated from the aerial parts of Polygala tenuifolia Willd. Their structures were established by detailed analysis of NMR and HRESIMS spectroscopic data, and the absolute configurations of compounds 5 and 6 were determined by CD spectra and in-NMR-tube Mosher’s method. The inhibitory effects of these compounds were evaluated on NO production in LPS-activated BV-2 microglia cells. Compound 17 showed the strongest activity, with an IC50 value of 7.4 μM, while compounds 1, 8, 14, and 18 showed the moderate activities, with IC50 values of 16.2–38.5 μM. And their primary structure–activity relationships (SARs) of NO inhibitory effects were also briefly discussed. 相似文献
216.
217.
Jun-Wu Shu Naoko Sasaki Hikaru Takahara Yoshitaka Hase 《Vegetation History and Archaeobotany》2013,22(4):285-298
To better understand the response of forest vegetation to climate and fire regimes with reference to human activities over the last deglacial period in the Aso Caldera, central Kyushu, southwestern Japan, a 33.9 m long sediment core was examined in order to reconstruct the vegetational and fire history using pollen and charcoal analyses. The results show that a cool temperate broad-leaved deciduous forest, dominated by Quercus (deciduous oaks) with Carpinus and Fagus, prevailed in the Aso Valley from ca. 14.6 ka cal. b.p., indicating warming since the last glacial period. The landscape was presumably covered by a mosaic of deciduous Quercus forests and terrestrial Artemisia communities. Around 12.8–11.7 ka cal. b.p., Quercus dominated the forest and fires occurred frequently. Co-expansion of distinctive Ulmus–Zelkova and Celtis–Aphananthe forests coupled with a progressive retreat of Quercus in the early Holocene could reflect a strengthening of the East Asian summer monsoon under mild and humid climate conditions. Around 8 ka cal. b.p., significant increases in Cyclobalanopsis (evergreen oaks), Castanopsis/Castanea and Podocarpus indicate a further warming, in particular an increased winter temperature. Warm temperate lucidophyllous forests, dominated by Cyclobalanopsis, flourished after 7.3 ka cal. b.p., probably corresponding to the “Holocene Climatic Optimum” interval. Progressive expansion of Quercus at the expense of Cyclobalanopsis began around 6.4 ka cal. b.p. and paralleled an increase in charcoal until ca. 4.8 ka cal. b.p.; this could be evidence of fire disturbance induced by the early-middle Jomon people. The disturbed evergreen forest experienced a temporary recovery but then opened again from 3.6 ka cal. b.p. due to extensive fire deforestation, as suggested by the high charcoal levels during this time. Human exploitation and buckwheat (Fagopyrum) agriculture may have contributed to the opening of the forest, which allowed secondary forests (primarily Pinus and Quercus) and herbaceous communities (mainly Poaceae) to spread. These results are discussed in comparison with other high-resolution pollen data from western Japan to better elucidate the vegetation and fire history over the last deglacial in the Aso Caldera. 相似文献
218.
目的 探讨SPF和正常鼠下呼吸道菌群多样性区别,为研究洁净环境下呼吸道菌群对免疫耐受形成的影响提供简便的动物模型.方法 采用飞行质谱和DGGE的方法检测正常和SPF BALB/c小鼠及Wistar大鼠呼吸道支气管肺泡灌洗液中菌群多样性的区别.结果 SPF BALB/c小鼠下呼吸道菌群丰度小于普通小鼠,下呼吸道菌群丰度小于消化道.SPF Wistar大鼠下呼吸道菌群丰度小于普通大鼠.结论 SPF环境造成鼠下呼吸道菌群丰度减小. 相似文献
219.
Zhe Liu Dan Dan Hu Shu Juan Shao Juan Yang Jian Fu Wang Jin Qiang Huang 《Genes & genomics.》2013,35(5):587-595
Infectious haematopoietic necrosis virus (IHNV) is detrimental to the farming of rainbow trout (Oncorhynchus mykiss) and other salmonids in the Northern hemisphere. The major histocompatibility complex (MHC) plays a key role in immune response in invertebrates, as evidenced by the close correlation of MHC polymorphisms with disease resistance/susceptibility. To analyse the correlation between rainbow trout resistance and susceptibility to IHNV and genetic variation in exon 2 of MHC class Ia gene, UBA, we employed two approaches, namely, polymerase chain reaction-single strand conformation polymorphism analysis and cloning/sequencing. From 102 resistant and 82 susceptible individuals, a total of 12 alleles in UBA exon 2 (GenBank: JX136662–JX136673) were identified, including 11 novel alleles. The maximum number of these alleles in a single individual was four, suggesting that UBA exon 2 most likely resides on at least two loci in the genome. Most of the variations in UBA exon 2 were located in the peptide-binding region and were determined to have been subject to positive selection during evolution. Correlation analysis revealed that Onmy-UBA*0111 and Onmy-UBA*0107 are highly associated with IHNV susceptibility (P = 0.001), whereas Onmy-UBA*0101, Onmy-UBA*0102, and Onmy-UBA*0103 are highly related to IHNV resistance (P = 0.000). In addition, the three resistant alleles were predominant in the IHNV disease-resistant population; thus, these molecular markers can be used for anti-IHNV breeding of rainbow trout. 相似文献
220.