全文获取类型
收费全文 | 10663篇 |
免费 | 805篇 |
国内免费 | 596篇 |
专业分类
12064篇 |
出版年
2024年 | 20篇 |
2023年 | 139篇 |
2022年 | 273篇 |
2021年 | 429篇 |
2020年 | 295篇 |
2019年 | 345篇 |
2018年 | 360篇 |
2017年 | 291篇 |
2016年 | 479篇 |
2015年 | 629篇 |
2014年 | 747篇 |
2013年 | 817篇 |
2012年 | 979篇 |
2011年 | 909篇 |
2010年 | 561篇 |
2009年 | 489篇 |
2008年 | 582篇 |
2007年 | 539篇 |
2006年 | 461篇 |
2005年 | 414篇 |
2004年 | 361篇 |
2003年 | 346篇 |
2002年 | 315篇 |
2001年 | 138篇 |
2000年 | 136篇 |
1999年 | 116篇 |
1998年 | 84篇 |
1997年 | 82篇 |
1996年 | 66篇 |
1995年 | 56篇 |
1994年 | 63篇 |
1993年 | 49篇 |
1992年 | 62篇 |
1991年 | 55篇 |
1990年 | 51篇 |
1989年 | 37篇 |
1988年 | 26篇 |
1987年 | 18篇 |
1986年 | 32篇 |
1985年 | 22篇 |
1984年 | 29篇 |
1983年 | 10篇 |
1982年 | 14篇 |
1981年 | 14篇 |
1980年 | 13篇 |
1979年 | 8篇 |
1978年 | 8篇 |
1977年 | 12篇 |
1976年 | 11篇 |
1975年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Estimation of a novel method to produce bio-oil from sewage sludge by microwave pyrolysis with the consideration of efficiency and safety 总被引:2,自引:0,他引:2
This paper presented a feasible method to produce bio-oil from sewage sludge by microwave pyrolysis. The results showed that oils derived under 400 W obtained an attractive yield (49.8 wt.%) with favorable characteristics such as high calorific value (35.0 MJ/kg), low density (929 kg/m3) and preferable chemical composition (29.5 wt.% of monoaromatics). A model to study the relationship between microwave power and mass balance of product fractions was developed, and the results indicated that the power range of the highest transforming efficiency for organics in sludge into oils was 400-600 W, the subsequent increase of power to the range of 600-800 W favored gases formation at the expense of oils, and increase of power to above 800 W led to the conversion of solids into gases, while oils remained unchanged. The analysis of sulfur and nitrogen compounds in oils showed that bio-oil should be extracted before being used as fuel. 相似文献
992.
刺桐胰蛋白酶抑制剂亲和填料的制备及纯化瑞替普酶 总被引:2,自引:0,他引:2
刺桐属胰蛋白酶抑制剂(ETI)是一种丝氨酸蛋白酶抑制剂,能特异性的抑制胰蛋白酶、组织纤溶酶原激活剂(tPA)、瑞替普酶(rPA)等丝氨酸蛋白酶。实验利用ETI工程菌,经诱导表达、体外复性及纯化获得ETI蛋白,并将该蛋白键合到CNBr活化的琼脂糖凝胶,制备ETI亲和填料,纯化瑞替普酶 。 相似文献
993.
Dynamics of ligand-induced, Rac1-dependent anchoring of cadherins to the actin cytoskeleton 总被引:1,自引:0,他引:1 下载免费PDF全文
Cadherin receptors are key morphoregulatory molecules during development. To dissect their mode of action, we developed an approach based on the use of myogenic C2 cells and beads coated with an Ncad-Fc ligand, allowing us to mimic cadherin-mediated adhesion. We used optical tweezers and video microscopy to investigate the dynamics of N-cadherin anchoring within the very first seconds of bead-cell contact. The analysis of the bead movement by single-particle tracking indicated that N-cadherin molecules were freely diffusive in the first few seconds after bead binding. The beads rapidly became diffusion-restricted and underwent an oriented rearward movement as a result of N-cadherin anchoring to the actin cytoskeleton. The kinetics of anchoring were dependent on ligand density, suggesting that it was an inducible process triggered by active cadherin recruitment. This anchoring was inhibited by the dominant negative form of Rac1, but not that of Cdc42. The Rac1 mutant had no effect on cell contact formation or cadherin-catenin complex recruitment, but did inhibit actin recruitment. Our results suggest that cadherin anchoring to the actin cytoskeleton is an adhesion-triggered, Rac1-regulated process enabling the transduction of mechanical forces across the cell membrane; they uncover novel aspects of the action of cadherins in cell sorting, cell migration, and growth cone navigation. 相似文献
994.
995.
Solution processed polymer:fullerene solar cells on opaque substrates have been fabricated in conventional and inverted device configurations. Opaque substrates, such as insulated steel and metal covered glass, require a transparent conducting top electrode. We demonstrate that a high conducting (900 S cm?1) PEDOT:PSS layer, deposited by a stamp‐transfer lamination technique using a PDMS stamp, in combination with an Ag grid electrode provides a proficient and versatile transparent top contact. Lamination of large size PEDOT:PSS films has been achieved on variety of surfaces resulting in ITO‐free solar cells. Power conversion efficiencies of 2.1% and 3.1% have been achieved for P3HT:PCBM layers in inverted and conventional polarity configurations, respectively. The power conversion efficiency is similar to conventional glass/ITO‐based solar cells. The high fill factor (65%) and the unaffected open‐circuit voltage that are consistently obtained in thick active layer inverted geometry devices, demonstrate that the laminated PEDOT:PSS top electrodes provide no significant potential or resistive losses. 相似文献
996.
Xiongfeng Ma Zhenyu Wang Wei Li Yuzhou Zhang Xiaojian Zhou Yangai Liu Zhongying Ren Xiaoyu Pei Kehai Zhou Wensheng Zhang Kunlun He Fei Zhang Junfang Liu Wenyu Ma Guanghui Xiao Daigang Yang 《Plant biotechnology journal》2019,17(4):762-775
Upland cotton (Gossypium hirsutum) is the world's largest source of natural fibre and dominates the global textile industry. Hybrid cotton varieties exhibit strong heterosis that confers high fibre yields, yet the genome‐wide effects of artificial selection that have influenced Upland cotton during its breeding history are poorly understood. Here, we resequenced Upland cotton genomes and constructed a variation map of an intact breeding pedigree comprising seven elite and 19 backbone parents. Compared to wild accessions, the 26 pedigree accessions underwent strong artificial selection during domestication that has resulted in reduced genetic diversity but stronger linkage disequilibrium and higher extents of selective sweeps. In contrast to the backbone parents, the elite parents have acquired significantly improved agronomic traits, with an especially pronounced increase in the lint percentage. Notably, identify by descent (IBD) tracking revealed that the elite parents inherited abundant beneficial trait segments and loci from the backbone parents and our combined analyses led to the identification of a core genomic segment which was inherited in the elite lines from the parents Zhong 7263 and Ejing 1 and that was strongly associated with lint percentage. Additionally, SNP correlation analysis of this core segment showed that a non‐synonymous SNP (A‐to‐G) site in a gene encoding the cell wall‐associated receptor‐like kinase 3 (GhWAKL3) protein was highly correlated with increased lint percentage. Our results substantially increase the valuable genomics resources available for future genetic and functional genomics studies of cotton and reveal insights that will facilitate yield increases in the molecular breeding of cotton. 相似文献
997.
998.
细菌脂多糖(LPS)可诱导宿主对LPS的耐受,但对细菌脂蛋白(BLP)是否存在交叉耐受,目前报道不一。采用人单核细胞株(THP-1),建立小剂量LPS诱导THP-1对LPS耐受的细胞模型;观察细胞肌动蛋白骨架、炎症因子TNF-α、IL-1β、IL-6的浓度及NF-κB的DNA结合活力的变化情况;探讨BLP交叉耐受及细胞骨架在其中的作用。结果显示,THP-1细胞经小剂量(10ng/ml)LPS、大剂量(100ng/ml)LPS或BLP刺激后,细胞形态严重变形,肌动蛋白重组,细胞周边肌动蛋白丝带消失,出现明显的肌动蛋白收缩团块及伪足,细胞核内NF-κB的DNA结合活性显著升高,培养上清液中炎症因子(TNF-α、IL-1β及IL-6)的释放显著增加;而小剂量LPS预刺激12h后,再用大剂量的LPS或BLP刺激6h,上述指标明显改善;采用细胞骨架肌动蛋白聚集破坏剂鬼笔环肽预处理后的THP-1细胞,可取消由小剂量LPS诱导的自身耐受及对BLP的交叉耐受;可见,细菌LPS、BLP(100ng/ml)可诱导THP-1细胞肌动蛋白骨架的改变,激活NF-κB信号通路,诱导炎性细胞因子TNF-α、IL-1、IL-6过度释放,激活宿主炎症细胞的炎症反应;而小剂量LPS预刺激后可诱导出THP-1细胞对LPS的自身耐受和对BLP的交叉耐受;细胞骨架肌动蛋白参与了小剂量LPS诱导THP-1细胞对LPS自身耐受和对BLP交叉耐受的形成。 相似文献
999.
Examination of both macro‐ and micro‐morphological characters have shown that Ligularia yui S. W. Liu is conspecific with Senecio spathiphyllus Franch., and is here reduced to a synonym of the latter species. 相似文献
1000.
Chen A Cauchon E Chefson A Dolman S Ducharme Y Dubé D Falgueyret JP Fournier PA Gagné S Gallant M Grimm E Han Y Houle R Huang JQ Hughes G Jûteau H Lacombe P Lauzon S Lévesque JF Liu S Macdonald D Mackay B McKay D Percival MD St-Jacques R Toulmond S 《Bioorganic & medicinal chemistry letters》2011,21(13):3976-3981
The design and optimization of a novel series of renin inhibitor is described herein. Strategically, by committing the necessary resources to the development of synthetic sequences and scaffolds that were most amenable for late stage structural diversification, even as the focus of the SAR campaign moved from one end of the molecule to another, highly potent renin inhibitors could be rapidly identified and profiled. 相似文献