全文获取类型
收费全文 | 9215篇 |
免费 | 621篇 |
国内免费 | 623篇 |
出版年
2024年 | 17篇 |
2023年 | 94篇 |
2022年 | 165篇 |
2021年 | 450篇 |
2020年 | 314篇 |
2019年 | 378篇 |
2018年 | 370篇 |
2017年 | 276篇 |
2016年 | 352篇 |
2015年 | 569篇 |
2014年 | 667篇 |
2013年 | 730篇 |
2012年 | 815篇 |
2011年 | 774篇 |
2010年 | 449篇 |
2009年 | 416篇 |
2008年 | 473篇 |
2007年 | 400篇 |
2006年 | 363篇 |
2005年 | 305篇 |
2004年 | 260篇 |
2003年 | 238篇 |
2002年 | 187篇 |
2001年 | 174篇 |
2000年 | 151篇 |
1999年 | 141篇 |
1998年 | 104篇 |
1997年 | 95篇 |
1996年 | 84篇 |
1995年 | 72篇 |
1994年 | 82篇 |
1993年 | 66篇 |
1992年 | 71篇 |
1991年 | 66篇 |
1990年 | 66篇 |
1989年 | 51篇 |
1988年 | 32篇 |
1987年 | 35篇 |
1986年 | 22篇 |
1985年 | 27篇 |
1984年 | 10篇 |
1983年 | 16篇 |
1982年 | 8篇 |
1981年 | 4篇 |
1980年 | 6篇 |
1979年 | 6篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1972年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
Dongmei H Jing L Mei X Ling Z Hongmin Y Zhidong W Li D Zikuan G Hengxiang W 《Cytotherapy》2011,13(8):913-917
Background aimsThe aims of this study were to observe the safety and effectiveness of umbilical cord mesenchymal stromal cells (UC-MSC) in the treatment of spinocerebellar ataxia (SCA) and multiple system atrophy-cerebellar type (MSA-C).MethodsFrom October 2009 to September 2010, 14 cases of SCA and 10 cases of MSA-C were given UC-MSC by weekly intrathecal injection, at a dose of 1 × 106/kg four times as one course. All the patients received one course of treatment, except three patients who received two courses. The movement ability and quality of daily life were evaluated with the International Cooperative Ataxia Rating Scale (ICARS) and Activity of Daily Living Scale (ADL) and the scores compared with those before cell therapy. A follow-up of 6–15 months was carried out for all of the patients.ResultsThe results showed that the ICARS and ADL scores were significantly decreased 1 month after treatment (P < 0.01). The symptoms, including unstable walking and standing, slow movement, fine motor disorders of the upper limbs, writing difficulties and dysarthria, were greatly improved except for one patient, who had no response. The observed side-effects included dizziness (four patients), back pain (two cases) and headache (one case), which disappeared within 1–3 days. During the follow-up, 10 cases remained stable for half a year or longer, while 14 cases had regressed to the status prior to the treatment within 1–14 months (an average of 3 months).ConclusionsIntrathecal injection of UC-MSC is safe and can delay the progression of neurologic deficits for SCA and MSA-C patients. 相似文献
972.
Fairfield H Gilbert GJ Barter M Corrigan RR Curtain M Ding Y D'Ascenzo M Gerhardt DJ He C Huang W Richmond T Rowe L Probst FJ Bergstrom DE Murray SA Bult C Richardson J Kile BT Gut I Hager J Sigurdsson S Mauceli E Di Palma F Lindblad-Toh K Cunningham ML Cox TC Justice MJ Spector MS Lowe SW Albert T Donahue LR Jeddeloh J Shendure J Reinholdt LG 《Genome biology》2011,12(9):R86-12
We report the development and optimization of reagents for in-solution, hybridization-based capture of the mouse exome. By validating this approach in a multiple inbred strains and in novel mutant strains, we show that whole exome sequencing is a robust approach for discovery of putative mutations, irrespective of strain background. We found strong candidate mutations for the majority of mutant exomes sequenced, including new models of orofacial clefting, urogenital dysmorphology, kyphosis and autoimmune hepatitis. 相似文献
973.
Soluble microbial products (SMPs) are considered as the main organic components in wastewater treatment plant effluent from
biological wastewater treatment systems. To investigate and explore SMP metabolism pathway for further treatment and control,
two innovative mechanistically based activated sludge models were developed by extension of activated sludge model no.3 (ASM3).
One was the model by combining SMP formation and degradation (ASM3-SMP model) processes with ASM3, and the other by combining
both SMP and simultaneous substrate storage and growth (SSSG) mechanisms with ASM3 (SSSG-ASM3-SMP model). The detailed schematic
modification and process supplements were introduced for comprehensively understanding all the mechanisms involved in the
activated sludge process. The evaluations of these two models were demonstrated by a laboratory-scale sequencing batch reactor
(SBR) operated under aerated/non-aerated conditions. The simulated and measured results indicated that SMP comprised about
83% of total soluble chemical oxygen demand (SCOD) in which biomass-associated products (BAPs) were predominant compared with
utilization-associated products (UAPs). It also elucidated that there should be a minimum SMP value as the reactive time increases
continuously and this conclusion could be used to optimize effluent SCOD in activated sludge processes. The comparative results
among ASM3, ASM3-SMP and SSSG-ASM3-SMP models and the experimental measurements (SCOD, ammonia and nitrate nitrogen) showed
clearly the best agreement with SSSG-ASM3-SMP simulation values (R = 0.993), strongly suggesting that both SMP formation and degradation and SSSG mechanisms are necessary in biologically activated
sludge modeling for municipal wastewater treatment. 相似文献
974.
Genetic, proteomic and metabolic analysis of the regulation of energy storage in rice seedlings in response to drought 总被引:1,自引:0,他引:1
We used proteomic analysis to determine the response of rice plant seedlings to drought-induced stress. The expression of 71 protein spots was significantly altered, and 60 spots were successfully identified. The greatest down-regulated protein functional category was translation. Up-regulated proteins were mainly related to protein folding and assembly. Additionally, many proteins involved in metabolism (e.g. carbohydrate metabolism) also showed differences in expression. cDNA microarray and GC-MS analysis showed 4756 differentially expressed mRNAs and 37 differentially expressed metabolites. Once these data were integrated with the proteomic analysis, we were able to elucidate the metabolic pathways affected by drought-induced stress. These results suggest that increased energy consumption from storage substances occurred during drought. In addition, increased expression of the enzymes involved in anabolic pathways corresponded with an increase in the content of six amino acids. We speculated that energy conversion from carbohydrates and/or fatty acids to amino acids was increased. Analysis of basic metabolism networks allowed us to understand how rice plants adjust to drought conditions. 相似文献
975.
Screening and evaluating anti- hepatitis C virus (HCV) drugs in vivo is difficult worldwide, mainly because of the lack of suitable small animal models. We investigate whether zebrafish could be a model organism for HCV replication. To achieve NS5B-dependent replication an HCV sub-replicon was designed and created with two vectors, one with HCV ns5b and fluorescent rfp genes, and the other containing HCV's 5'UTR, core, 3'UTR and fluorescent gfp genes. The vectors containing sub-replicons were co-injected into zebrafish zygotes. The sub-replicon amplified in liver showing a significant expression of HCV core RNA and protein. The sub-replicon amplification caused no abnormality in development and growth of zebrafish larvae, but induced gene expression change similar to that in human hepatocytes. As the amplified core fluorescence in live zebrafish was detectable microscopically, it rendered us an advantage to select those with replicating sub-replicon for drug experiments. Ribavirin and oxymatrine, two known anti-HCV drugs, inhibited sub-replicon amplification in this model showing reduced levels of HCV core RNA and protein. Technically, this method had a good reproducibility and is easy to operate. Thus, zebrafish might be a model organism to host HCV, and this zebrafish/HCV (sub-replicon) system could be an animal model for anti-HCV drug screening and evaluation. 相似文献
976.
Hu J Nudelman G Shimoni Y Kumar M Ding Y López C Hayot F Wetmur JG Sealfon SC 《PloS one》2011,6(2):e16614
In the first few hours following Newcastle disease viral infection of human monocyte-derived dendritic cells, the induction of IFNB1 is extremely low and the secreted type I interferon response is below the limits of ELISA assay. However, many interferon-induced genes are activated at this time, for example DDX58 (RIGI), which in response to viral RNA induces IFNB1. We investigated whether the early induction of IFNBI in only a small percentage of infected cells leads to low level IFN secretion that then induces IFN-responsive genes in all cells. We developed an agent-based mathematical model to explore the IFNBI and DDX58 temporal dynamics. Simulations showed that a small number of early responder cells provide a mechanism for efficient and controlled activation of the DDX58-IFNBI positive feedback loop. The model predicted distributions of single cell responses that were confirmed by single cell mRNA measurements. The results suggest that large cell-to-cell variation plays an important role in the early innate immune response, and that the variability is essential for the efficient activation of the IFNB1 based feedback loop. 相似文献
977.
978.
979.
980.
Insect guts represent unique natural biocatalyst systems for biocatalyst discovery and biomass deconstruction mechanism studies. In order to guide the further research for enzyme discovery and biodiversity analysis, we carried out comprehensive xylanase and cellulase activity assays for the gut contents of three insect species representing different orders and food sources. The three insect species are grasshopper (Acrididae sp.), woodborer (Cerambycidae spp.), and silkworm (Bombyx mori) to represent the wood-consuming, grass-consuming, and leaf-consuming insects from Orthoptera, Coleoptera, and Lepidoptera orders, respectively. Generally speaking, the enzyme activity assays have shown that the cellulase and xylanase activities for grasshopper and woodborer guts are significantly higher than those of silkworm under various conditions. In addition, both pH and temperature have a significant impact on the enzyme activities in the gut contents. For the grasshopper gut, the means of xylanase and cellulase activities at pH 7 were 3,397 and 404 μM mg?1 min?1, which are significantly higher than the activities at pH 4 and 10 (P?<?0.05). However, woodborer guts have shown the highest cellulase activity at pH 10. The results suggested that systems similar to woodborer guts could be good resources for discovering alkaline-tolerant enzymes. Moreover, the enzyme activities in response to different substrate concentrations were also analyzed, which indicated that grasshopper gut had particularly high cellulase activity. The enzyme activities in response to the reaction time were also examined, and we found that the enzyme activities (micromolar per milligram per minute) of different insect gut juices in response to the increase of incubation time fit well to the power function equation (E c = K ? t b ) with high coefficients (r 2?>?0.99). The newly developed model serves well to compare the characteristics of the enzyme mixtures among different insect species, which can be applied to other studies of natural biocatalyst systems for the future. Overall, the data indicated that grasshopper and woodborer guts are valuable resources for discovering the novel biocatalysts for various biorefinery applications. 相似文献