全文获取类型
收费全文 | 21633篇 |
免费 | 1603篇 |
国内免费 | 1345篇 |
专业分类
24581篇 |
出版年
2024年 | 53篇 |
2023年 | 300篇 |
2022年 | 679篇 |
2021年 | 1144篇 |
2020年 | 739篇 |
2019年 | 946篇 |
2018年 | 848篇 |
2017年 | 651篇 |
2016年 | 952篇 |
2015年 | 1375篇 |
2014年 | 1573篇 |
2013年 | 1650篇 |
2012年 | 1915篇 |
2011年 | 1675篇 |
2010年 | 1038篇 |
2009年 | 888篇 |
2008年 | 1059篇 |
2007年 | 872篇 |
2006年 | 828篇 |
2005年 | 665篇 |
2004年 | 613篇 |
2003年 | 541篇 |
2002年 | 489篇 |
2001年 | 396篇 |
2000年 | 360篇 |
1999年 | 328篇 |
1998年 | 236篇 |
1997年 | 200篇 |
1996年 | 190篇 |
1995年 | 174篇 |
1994年 | 125篇 |
1993年 | 115篇 |
1992年 | 144篇 |
1991年 | 122篇 |
1990年 | 113篇 |
1989年 | 76篇 |
1988年 | 57篇 |
1987年 | 61篇 |
1986年 | 28篇 |
1985年 | 40篇 |
1984年 | 26篇 |
1983年 | 35篇 |
1982年 | 29篇 |
1981年 | 24篇 |
1980年 | 18篇 |
1977年 | 12篇 |
1974年 | 13篇 |
1973年 | 12篇 |
1970年 | 13篇 |
1969年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
181.
182.
Conrads TP Tocci GM Hood BL Zhang CO Guo L Koch KR Michejda CJ Veenstra TD Keay SK 《The Journal of biological chemistry》2006,281(49):37836-37843
Antiproliferative factor (APF) is a low molecular weight sialoglycopeptide that is secreted by bladder cells from interstitial cystitis patients and is a potent inhibitor of both normal bladder epithelial and bladder carcinoma cell proliferation. We hypothesized that APF may produce its antiproliferative effects by binding to a transmembrane receptor. This study demonstrates that cytoskeleton-associated protein 4/p63 (CKAP4/p63), a type II transmembrane receptor, binds with high affinity to APF. The antiproliferative activity of APF is effectively inhibited by preincubation with anti-CKAP4/p63-specific antibodies, as well as by short interfering RNA knockdown of CKAP4/p63. Immunofluorescent confocal microscopy showed co-localization of anti-CKAP4/p63 and rhodamine-labeled synthetic APF binding in both cell membrane and perinuclear areas. APF also inhibits the proliferation of HeLa cervical carcinoma cells that are known to express CKAP4/p63. These data indicate that CKAP4/p63 is an important epithelial cell receptor for APF. 相似文献
183.
Chenyang Han Yi Yang Qiaobing Guan Xiaoling Zhang Heping Shen Yongjia Sheng Jin Wang Xiaohong Zhou Wenyan Li Li Guo Qingcai Jiao 《Journal of cellular and molecular medicine》2020,24(14):8078-8090
The present study was designed to investigate the role of β‐amyloid (Aβ1‐42) in inducing neuronal pyroptosis and its mechanism. Mice cortical neurons (MCNs) were used in this study, LPS + Nigericin was used to induce pyroptosis in MCNs (positive control group), and Aβ1‐42 was used to interfere with MCNs. In addition, propidium iodide (PI) staining was used to examine cell permeability, lactate dehydrogenase (LDH) release assay was employed to detect cytotoxicity, immunofluorescence (IF) staining was used to investigate the expression level of the key protein GSDMD, Western blot was performed to detect the expression levels of key proteins, and enzyme‐linked immunosorbent assay (ELISA) was utilized to determine the expression levels of inflammatory factors in culture medium, including IL‐1β, IL‐18 and TNF‐α. Small interfering RNA (siRNA) was used to silence the mRNA expression of caspase‐1 and GSDMD, and Aβ1‐42 was used to induce pyroptosis, followed by investigation of the role of caspase‐1‐mediated GSDMD cleavage in pyroptosis. In addition, necrosulfonamide (NSA), an inhibitor of GSDMD oligomerization, was used for pre‐treatment, and Aβ1‐42 was subsequently used to observe the pyroptosis in MCNs. Finally, AAV9‐siRNA‐caspase‐1 was injected into the tail vein of APP/PS1 double transgenic mice (Alzheimer's disease mice) for caspase‐1 mRNA inhibition, followed by observation of behavioural changes in mice and measurement of the expression of inflammatory factors and pyroptosis‐related protein. As results, Aβ1‐42 could induce pyroptosis in MCNs, increase cell permeability and enhance LDH release, which were similar to the LPS + Nigericin‐induced pyroptosis. Meanwhile, the expression levels of cellular GSDMD and p30‐GSDMD were up‐regulated, the levels of NLRP3 inflammasome and GSDMD‐cleaved protein caspase‐1 were up‐regulated, and the levels of inflammatory factors in the medium were also up‐regulated. siRNA intervention in caspase‐1 or GSDMD inhibited Aβ1‐42‐induced pyroptosis, and NSA pre‐treatment also caused the similar inhibitory effects. The behavioural ability of Alzheimer's disease (AD) mice was relieved after the injection of AAV9‐siRNA‐caspase‐1, and the expression of pyroptosis‐related protein in the cortex and hippocampus was down‐regulated. In conclusion, Aβ1‐42 could induce pyroptosis by GSDMD protein, and NLRP3‐caspase‐1 signalling was an important signal to mediate GSDMD cleavage, which plays an important role in Aβ1‐42‐induced pyroptosis in neurons. Therefore, GSDMD is expected to be a novel therapeutic target for AD. 相似文献
184.
白腐菌对染料脱色和降解作用的研究进展 总被引:2,自引:0,他引:2
白腐菌应用于废水处理始于二十世纪八十年代。本文对印染废水的处理方法、白腐菌及其对污染物的降解机理作了简要概述 ,着重介绍了白腐菌对染料脱色和降解作用的研究进展。白腐菌对染料的脱色解降作用机理有部分尚待进一步研究 ;同时 ,白腐菌的吸附作用亦不容忽视。 相似文献
185.
Jinping Wu Zhenbiao Jiao Jie Zhou Fengling Guo Zili Ding Zhengming Qiu 《World journal of microbiology & biotechnology》2017,33(7):134
The bacterial community and diversity in healthy and diseased konjac rhizosphere soils with different ages of continuous cropping were investigated using next-generation sequencing. The results demonstrated that the number of years of continuous cropping significantly altered soil bacterial community and diversity. Soil bacterial Shannon diversity index and Chao 1 index decreased with the increasing cropping years of konjac. After 1 year of cropping, the soil exhibited the highest bacterial relative abundance and diversity. Of the 44 bacterial genera (relative abundance ratio of genera greater than 0.3%), 14 were significantly affected by the duration of continuous cropping and plant status. With increasing continuous cropping, Alicyclobacillus decreased, while Achromobacter, Lactobacillus, Kaistobacter, Rhodoplanes increased after 3 years continuous cropping. Continuous cropping altered the structure and composition of the soil bacterial community, which led to the reduction in the beneficial bacteria and multiplication of harmful bacteria. These results will improve our understanding of soil microbial community regulation and soil health maintenance in konjac farm systems. 相似文献
186.
Forests play a leading role in regional and global carbon (C) cycles. Detailed assessment of the temporal and spatial changes in C sinks/sources of China’s forests is critical to the estimation of the national C budget and can help to constitute sustainable forest management policies for climate change. In this study, we explored the spatio-temporal changes in forest biomass C stocks in China between 1977 and 2008, using six periods of the national forest inventory data. According to the definition of the forest inventory, China’s forest was categorized into three groups: forest stand, economic forest, and bamboo forest. We estimated forest biomass C stocks for each inventory period by using continuous biomass expansion factor (BEF) method for forest stands, and the mean biomass density method for economic and bamboo forests. As a result, China’s forests have accumulated biomass C (i.e., biomass C sink) of 1896 Tg (1 Tg=1012 g) during the study period, with 1710, 108 and 78 Tg C in forest stands, and economic and bamboo forests, respectively. Annual forest biomass C sink was 70.2 Tg C a?1, offsetting 7.8% of the contemporary fossil CO2 emissions in the country. The results also showed that planted forests have functioned as a persistent C sink, sequestrating 818 Tg C and accounting for 47.8% of total C sink in forest stands, and that the old-, mid- and young-aged forests have sequestrated 930, 391 and 388 Tg C from 1977 to 2008. Our results suggest that China’s forests have a big potential as biomass C sink in the future because of its large area of planted forests with young-aged growth and low C density. 相似文献
187.
Carbon dioxide exchange and canopy conductance of two coniferous forests under various sky conditions 总被引:1,自引:0,他引:1
Sky conditions play an important role in the Earth’s climate system and CO2 uptake by plants. We used eddy covariance and meteorological data, including global and diffuse photosynthetic photon flux
density (PPFD), recorded over the 2008 and 2009 growing season at two Sitka spruce [Picea sitchensis (Bong.) Carr.] forest sites in northern Britain, in order to establish relationships between physiological properties under diverse sky
conditions, i.e. (1) sunny, (2) cloudy, and (3) overcast, and several canopy activity-related properties. These properties
are: (1) response to PPFD, (2) photosynthetic light use efficiency, and (3) canopy stomatal conductance. We found that Sitka
spruce forests utilise PPFD in a more efficient way when solar radiation is dominated by diffuse radiation. Furthermore, our
results show that diffuse radiation enhances canopy stomatal conductance, an effect which may be the result of both blue light
enrichment within the canopy and the reduction in vapour pressure deficit during cloudy and overcast weather. Diffuse radiation
does not only influence short-term (hourly, daily, monthly) canopy activity but also long-term forest growth. 相似文献
188.
189.
二甲基亚砜和吐温80对钝齿棒杆菌产生赖氨酸影响的研究 总被引:2,自引:0,他引:2
以赖氨酸产生菌钝齿捧杆菌(Corynebacteriumcrenatum)E0.7-66(HS ,AECrr,TArr,ESr)为出发菌种,对菌体进行亚硝酸诱变处理,并且通过提高抗七叶苷[1,2]剂量,筛选得到高抗七叶苷突变株E0.8-26,其L-赖氨酸产量较出发菌株提高了13.1%.在发酵至28h时,加入0.2%的吐温80或0.5%的二甲基亚砜,分别又使L-赖氨酸产量提高12.8%和13.3%。因此通过使用表面活性剂来改变细胞质膜造性,可使产酸量大幅度提高,该途径是筛过高产菌株的良好方法. 相似文献
190.
Zheng Fu Xiang Zhang Xinyan Zhou Uzair Ur-Rehman Mengchao Yu Hongwei Liang Hongyuan Guo Xu Guo Yan Kong Yuanyuan Su Yangyang Ye Xiuting Hu Wei Cheng Jinrong Wu Yanbo Wang Yayun Gu Sheng-feng Lu Dianqing Wu Ke Zen Jing Li Chao Yan Chen-Yu Zhang Xi Chen 《Cell research》2021,31(6):631-648
RNAi therapy has undergone two stages of development, direct injection of synthetic siRNAs and delivery with artificial vehicles or conjugated ligands; both have not solved the problem of efficient in vivo siRNA delivery. Here, we present a proof-of-principle strategy that reprogrammes host liver with genetic circuits to direct the synthesis and self-assembly of siRNAs into secretory exosomes and facilitate the in vivo delivery of siRNAs through circulating exosomes. By combination of different genetic circuit modules, in vivo assembled siRNAs are systematically distributed to multiple tissues or targeted to specific tissues (e.g., brain), inducing potent target gene silencing in these tissues. The therapeutic value of our strategy is demonstrated by programmed silencing of critical targets associated with various diseases, including EGFR/KRAS in lung cancer, EGFR/TNC in glioblastoma and PTP1B in obesity. Overall, our strategy represents a next generation RNAi therapeutics, which makes RNAi therapy feasible.Subject terms: RNAi, siRNAs 相似文献