全文获取类型
收费全文 | 4502篇 |
免费 | 563篇 |
国内免费 | 687篇 |
出版年
2024年 | 9篇 |
2023年 | 48篇 |
2022年 | 116篇 |
2021年 | 227篇 |
2020年 | 211篇 |
2019年 | 234篇 |
2018年 | 217篇 |
2017年 | 203篇 |
2016年 | 213篇 |
2015年 | 290篇 |
2014年 | 363篇 |
2013年 | 336篇 |
2012年 | 417篇 |
2011年 | 349篇 |
2010年 | 221篇 |
2009年 | 200篇 |
2008年 | 246篇 |
2007年 | 226篇 |
2006年 | 170篇 |
2005年 | 144篇 |
2004年 | 203篇 |
2003年 | 211篇 |
2002年 | 255篇 |
2001年 | 194篇 |
2000年 | 118篇 |
1999年 | 90篇 |
1998年 | 57篇 |
1997年 | 29篇 |
1996年 | 30篇 |
1995年 | 19篇 |
1994年 | 25篇 |
1993年 | 15篇 |
1992年 | 11篇 |
1991年 | 14篇 |
1990年 | 12篇 |
1989年 | 11篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 1篇 |
排序方式: 共有5752条查询结果,搜索用时 31 毫秒
841.
Oral Hepatoprotective Ability Evaluation of Purple Sweet Potato Anthocyanins on Acute and Chronic Chemical Liver Injuries 总被引:2,自引:0,他引:2
Wencheng Wang Jinlian Li Zhi Wang Hui Gao Li Su Jing Xie Xuehong Chen Hui Liang Chunbo Wang Yantao Han 《Cell biochemistry and biophysics》2014,69(3):539-548
In recent years, chemical liver injury cases increased significantly in Asian countries, and the imbalance in redox system was believed to be the main cause. Purple sweet potato anthocyanins (PSPA) have been shown to exert antioxidant activity and oxidative-stress-associated functional protein modulation through various signaling pathways, so it is considered to have the potential of liver injury preventive activity. In order to evaluate the hepatoprotective potency of PSPA according to its free radical scavenging and antioxidant effects, three acute chemical liver injury models were set up with ethanol, acetaminophen and carbon tetrachloride. PSPA at moderate and high doses obviously attenuated the tested serum biomarker levels and liver index in our experiments. Besides, one chronic liver injury model set up with carbon tetrachloride was also applied, in which PSPA was orally administrated after the liver damage had been formed. Both the serum biomarker levels and histopathological analysis showed that PSPA was able to attenuated chronic liver injury. Our experimental results demonstrated the potential of PSPA as an oral hepatoprotective agent against chemical liver injury from food plant. 相似文献
842.
Association of SLC22A4 Gene Polymorphism with Rheumatoid Arthritis in the Chinese Population 下载免费PDF全文
Tian‐li Ren Zhi‐jun Han Cheng‐jian Yang Yuan‐xing Hang De‐yu Fang Ke Wang Xue Zhu Xiao‐jing Ji Fan‐fan Zhou 《Journal of biochemical and molecular toxicology》2014,28(5):206-210
Rheumatoid arthritis (RA) is a chronic inflammatory disease with complex genetic factors. Single‐nucleotide polymorphisms (SNPs) in the SLC22A4 gene have been previously reported to be associated with RA in Japanese but not European populations. This study further investigated the association of SLC22A4 polymorphisms, in particular slc2F1/slc2F2, with RA in the Chinese population, the largest Asian population. A total of 160 human subjects with 95 RA patients and 65 healthy controls were genotyped for slc2F1‐G/A and slc2F2‐C/T polymorphisms. The results showed that there was a significant difference in the genotype distribution of these two polymorphisms between the two groups. In addition, the presence of slc2F1 A allele and slc2F2 T allele carries a 1.93‐fold and 2.14‐fold increased risk for anticyclic citrullinated peptide (CCP) positivity, respectively. Overall, this study provided evidence that SLC22A4 gene polymorphisms played important roles in the etiology of RA in the largest Asian population, the Chinese population. 相似文献
843.
China is the world's largest producer and consumer of fertilizer N, and decades of overuse has caused nitrate leaching and possibly soil acidification. We hypothesized that this would enhance the soils' propensity to emit N2O from denitrification by reducing the expression of the enzyme N2O reductase. We investigated this by standardized oxic/anoxic incubations of soils from five long‐term fertilization experiments in different regions of China. After adjusting the nitrate concentration to 2 mM, we measured oxic respiration (R), potential denitrification (D), substrate‐induced denitrification, and the denitrification product stoichiometry (NO, N2O, N2). Soils with a history of high fertilizer N levels had high N2O/(N2O+N2) ratios, but only in those field experiments where soil pH had been lowered by N fertilization. By comparing all soils, we found a strong negative correlation between pH and the N2O/(N2O+N2) product ratio (r2 = 0.759, P < 0.001). In contrast, the potential denitrification (D) was found to be a linear function of oxic respiration (R), and the ratio D/R was largely unaffected by soil pH. The immediate effect of liming acidified soils was lowered N2O/(N2O+N2) ratios. The results provide evidence that soil pH has a marginal direct effect on potential denitrification, but that it is the master variable controlling the percentage of denitrified N emitted as N2O. It has been known for long that low pH may result in high N2O/(N2O+N2) product ratios of denitrification, but our documentation of a pervasive pH‐control of this ratio across soil types and management practices is new. The results are in good agreement with new understanding of how pH may interfere with the expression of N2O reductase. We argue that the management of soil pH should be high on the agenda for mitigating N2O emissions in the future, particularly for countries where ongoing intensification of plant production is likely to acidify the soils. 相似文献
844.
Rice straw burning has accompanied paddy management for millennia, introducing black carbon (BC) into soil as the residue of incomplete combustion. This study examined the contribution of BC to soil organic matter and the rate at which it accumulates in paddy soils as a result of prolonged paddy management. Soil depth profiles were sampled along a chronosequence of 0–2000 years of rice–wheat rotation systems and adjacent non‐paddy systems (50–700 years) in the Bay of Hangzhou (Zhejiang province, China). The soil BC content and its degree of condensation were assessed using benzene‐polycarboxylic acids (BPCAs) as geochemical markers. The results showed that despite regular long term BC input, BC only contributed 7–11% of total soil organic carbon (SOC) in the topsoil horizons. Nevertheless, along with SOC, paddy soils accumulated BC with increasing duration of management until 297 years to reach a steady‐state of 13 t BC ha?1. This was 1.8 times more than in non‐paddy soils. The fate of BC in paddy soils (0–1 m) could be modeled revealing an average annual input of 44 kg ha?1 yr?1, and a mean residence time of 303 years. The subsoils contributed at least 50% to overall BC stocks, which likely derived from periods prior to land embankment and episodic burial of ancient topsoil, as also indicated by BPCA pattern changes. We conclude that there is a significant but limited accumulation of C in charred forms upon prolonged paddy management. The final contribution of BC to total SOC in paddy soils was similar to that in other aerobic ecosystems of the world. 相似文献
845.
Melissa Lasaro Zhi Liu Rima Bishar Kathryn Kelly Sujay Chattopadhyay Sandip Paul Evgeni Sokurenko Jun Zhu Mark Goulian 《Journal of bacteriology》2014,196(9):1723-1732
The biology of Escherichia coli in its primary niche, the animal intestinal tract, is remarkably unexplored. Studies with the streptomycin-treated mouse model have produced important insights into the metabolic requirements for Escherichia coli to colonize mice. However, we still know relatively little about the physiology of this bacterium growing in the complex environment of an intestine that is permissive for the growth of competing flora. We have developed a system for studying colonization using an E. coli strain, MP1, isolated from a mouse. MP1 is genetically tractable and does not require continuous antibiotic treatment for stable colonization. As an application of this system, we separately knocked out each two-component system response regulator in MP1 and performed competitions against the wild-type strain. We found that only three response regulators, ArcA, CpxR, and RcsB, produce strong colonization defects, suggesting that in addition to anaerobiosis, adaptation to cell envelope stress is a critical requirement for E. coli colonization of the mouse intestine. We also show that the response regulator OmpR, which had previously been hypothesized to be important for adaptation between in vivo and ex vivo environments, is not required for MP1 colonization due to the presence of a third major porin. 相似文献
846.
847.
848.
849.
Fn14 Promotes Differentiation of Human Mesenchymal Stem Cells into Heart Valvular Interstitial Cells by Phenotypic Characterization 下载免费PDF全文
850.
Rong Li Di‐Dong Xie Jun‐hong Dong Hui Li Kang‐shuai Li Jing Su Lai‐Zhong Chen Yun‐Fei Xu Hong‐Mei Wang Zheng Gong Guo‐Ying Cui Xiao Yu Kai Wang Wei Yao Tao Xin Min‐Yong Li Kun‐Hong Xiao Xiao‐fei An Yuqing Huo Zhi‐gang Xu Jin‐Peng Sun Qi Pang 《Journal of neurochemistry》2014,128(2):315-329
Striatal‐enriched tyrosine phosphatase (STEP) is an important regulator of neuronal synaptic plasticity, and its abnormal level or activity contributes to cognitive disorders. One crucial downstream effector and direct substrate of STEP is extracellular signal‐regulated protein kinase (ERK), which has important functions in spine stabilisation and action potential transmission. The inhibition of STEP activity toward phospho‐ERK has the potential to treat neuronal diseases, but the detailed mechanism underlying the dephosphorylation of phospho‐ERK by STEP is not known. Therefore, we examined STEP activity toward para‐nitrophenyl phosphate, phospho‐tyrosine‐containing peptides, and the full‐length phospho‐ERK protein using STEP mutants with different structural features. STEP was found to be a highly efficient ERK tyrosine phosphatase that required both its N‐terminal regulatory region and key residues in its active site. Specifically, both kinase interaction motif (KIM) and kinase‐specific sequence of STEP were required for ERK interaction. In addition to the N‐terminal kinase‐specific sequence region, S245, hydrophobic residues L249/L251, and basic residues R242/R243 located in the KIM region were important in controlling STEP activity toward phospho‐ERK. Further kinetic experiments revealed subtle structural differences between STEP and HePTP that affected the interactions of their KIMs with ERK. Moreover, STEP recognised specific positions of a phospho‐ERK peptide sequence through its active site, and the contact of STEP F311 with phospho‐ERK V205 and T207 were crucial interactions. Taken together, our results not only provide the information for interactions between ERK and STEP, but will also help in the development of specific strategies to target STEP‐ERK recognition, which could serve as a potential therapy for neurological disorders.