全文获取类型
收费全文 | 46665篇 |
免费 | 5089篇 |
国内免费 | 5857篇 |
出版年
2024年 | 36篇 |
2023年 | 622篇 |
2022年 | 879篇 |
2021年 | 2224篇 |
2020年 | 1892篇 |
2019年 | 2375篇 |
2018年 | 2146篇 |
2017年 | 1681篇 |
2016年 | 2184篇 |
2015年 | 3141篇 |
2014年 | 3801篇 |
2013年 | 3923篇 |
2012年 | 4769篇 |
2011年 | 4339篇 |
2010年 | 2720篇 |
2009年 | 2493篇 |
2008年 | 2774篇 |
2007年 | 2491篇 |
2006年 | 2126篇 |
2005年 | 1779篇 |
2004年 | 1525篇 |
2003年 | 1452篇 |
2002年 | 1246篇 |
2001年 | 884篇 |
2000年 | 736篇 |
1999年 | 650篇 |
1998年 | 412篇 |
1997年 | 348篇 |
1996年 | 304篇 |
1995年 | 238篇 |
1994年 | 235篇 |
1993年 | 168篇 |
1992年 | 173篇 |
1991年 | 154篇 |
1990年 | 118篇 |
1989年 | 102篇 |
1988年 | 75篇 |
1987年 | 57篇 |
1986年 | 59篇 |
1985年 | 72篇 |
1984年 | 21篇 |
1983年 | 29篇 |
1982年 | 30篇 |
1981年 | 22篇 |
1979年 | 17篇 |
1978年 | 9篇 |
1977年 | 7篇 |
1974年 | 8篇 |
1973年 | 11篇 |
1971年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Zi Shi Wei Song Jinfeng Xing Minxiao Duan Fengge Wang Hongli Tian Liwen Xu Shuaishuai Wang Aiguo Su Chunhui Li Ruyang Zhang Yanxin Zhao Meijie Luo Jidong Wang Jiuran Zhao 《Molecular breeding : new strategies in plant improvement》2017,37(9):108
Kernel size and kernel weight are important factors possibly involved in the determination of grain yield in maize, so identifying the genetic basis of kernel-related traits provides insights into the breeding of high-yield maize varieties. Kernel length (KL), kernel width (KW) and hundred kernel weight (HKW) were evaluated in three various planting conditions for the 240 field-grown double haploid (DH) lines derived from the single-cross hybrid Xianyu335. Variations in KL, KW and HKW were observed among DH lines, and all three traits showed a broad sense heritability of 76%. A total of 964 single nucleotide polymorphisms (SNPs) from the MaizeSNP3072 chip was utilised to create a high-density genetic map of 1546.4 cM and to identify quantitative trait loci (QTLs). Using composite interval mapping, a total of five, seven and five QTLs have been mapped for KL, KW and HKW, respectively. qkl1-2 and qkl4-1 explained 17.8% and 14.2% of the phenotypic variation in KL, respectively, and the other three QTLs contributed 3.2–4.0%. The phenotypic variation explained (PVE) of seven QTLs responsible for KW ranged from 3.3 to 9.5%. Three QTLs for HKW, qhkw1, qhkw5 and qhkw10 each explained more than 10% of the phenotypic variation, and qhkw4 and qhkw9 accounted for 3.0% and 6.0%, respectively. Due to their detection in multiple planting environments, the loci mapped here appear to be potential targets for the improvement of maize grain yield. 相似文献
2.
3.
Neuroprotective Effect of Chitosan Oligosaccharide on Hypoxic-Ischemic Brain Damage in Neonatal Rats
Wei Wu Wei Wei Min Lu Xiaoyun Zhu Ning Liu Yang Niu Tao Sun Yuxiang Li Jianqiang Yu 《Neurochemical research》2017,42(11):3186-3198
Neonatal hypoxic-ischemic brain damage (HIBD) is one of the leading causes of neonatal mortality and permanent neurological disability worldwide and the effective treatment strategies are not yet available. It has been demonstrated that Chitosan oligosaccharide (COS) exerts protective effect in vitro ischemic brain injury. However, no information is available on possible effects of COS on neonatal HIBD. To investigate the hypothesis of the potential neuroprotective effect of COS on the brain injury due to HIBD, 7-day-old Sprague–Dawley rats were treated with left carotid artery ligation followed by exposure to 8% oxygen (balanced with nitrogen) for 2.5 h at 37?°C. After COS treatment, the cerebral damage was measured by behavior tasks, 2,3,5-triphenyltetrazolium chloride(TTC), Hematoxyline-Eosin(HE), Nissl and Fluoro-Jade B(FJB)staining. In addition, the oxidative stress were assayed with ipsilateral hemisphere homogenates. Immunofluorescence staining were used to examine the activation of the astrocyte and microglia. Expression of inflammatory-related proteins were analyzed by western-blot analysis. In this study we found that administration of COS ameliorated early neurological reflex behavior, significantly reduce brain infarct volume and attenuated neuronal cell injury and degeneration. Furthermore, COS markedly decreased the level of MDA, lactic acid and increased SOD, GSH-Px and T-AOC. COS attenuated hypoxic-ischemic induced up-regulation of expressions of interleukin-1β (IL-1β), tumor necrosis factor alpha (TNF-α), meanwhile it dramatically increased the interleukin-10 (IL-10). These results suggest that COS exerts neuroprotection on hypoxic-ischemic brain damage in neonatal rats, it implies COS might be a potential therapeutic for the treatment of HIBD. 相似文献
4.
Jingzheng Ren Xusheng Ren Hanwei Liang Liang Dong Long Zhang Xiao Luo Yingkui Yang Zhiqiu Gao 《The International Journal of Life Cycle Assessment》2017,22(9):1397-1405
Purpose
Life cycle sustainability assessment is meaningful for the decision-makers/stakeholders to select the most sustainable option among multiple alternatives; however, there are usually various severe uncertainty problems in sustainability-oriented decision-making, i.e., the vagueness and ambiguity that existed in human judgments and the lack of information. This study aims at developing a novel life cycle multi-criteria sustainability assessment method for helping the decision-makers/stakeholders to determine the sustainability level of the industrial and energy systems. In part 1, an improved interval analytic hierarchy process (AHP) which allows multiple decision-makers/stakeholders to participate in the decision-making was developed to determine the weights of the criteria which were used in life cycle sustainability assessment.Methods
It is usually difficult for the decision-makers/stakeholders to use the numbers from 1 to 9 and their reciprocals for determining the comparison matrix when using the traditional AHP method for weight calculation, because human judgments usually involve various uncertainties. In order to the overcome this weak point of the traditional AHP, an improved AHP, so-called interval AHP, in which, multiple decision-makers/stakeholders are allowed to participate in the decision-making and allowed to use interval numbers instead of crisp numbers to establish the comparison matrix for determining the weights of the criteria for life cycle sustainability assessment, has been developed.Results and discussion
The proposed method was used to determine the weights of the four aspects for life cycle sustainability assessment including economic, safety, social, and environmental aspects. Five representative stakeholders were invited to participate in the decision-making. After Monte Carlo simulation, the final weights of the four aspects have been determined with the proposed interval AHP.Conclusions and perspectives
An interval AHP method was developed for determining the weights of the criteria for life cycle sustainability assessment; the decision-makers are allowed to use interval numbers to establish the comparison matrix for weight calculation. The weighting coefficients determined by Monte Carlo method can accurately reflect the preferences and willingness of multi-actor comparing with the traditional AHP method. This paper merely presents a novel method to calculate the weights of the criteria for life cycle sustainability assessment, but the method for determining the sustainability performance has been presented in part 2.5.
6.
7.
8.
9.
Dongxue Yin Wei Liu Ningning Zhai Yongzhong Feng Gaihe Yang Xiaojiao Wang Xinhui Han 《PloS one》2015,10(5)
This study investigated the effect of sunlight-dark conditions on volatile fatty acids (VFAs), total ammonium nitrogen (TAN), total alkalinity (TA) and pH during pig manure (PM) digestion and then the subsequent influence on biogas yield of PM. PM1 and PM2 were performed in a transparent reactor and a non-transparent reactor, respectively. Two sets of experiments were conducted with a temperature of 35.0±2.0 °C and a total solid concentration of 8.0% to the digestion material. The dynamic change of the four parameters in response to sunlight-dark conditions resulted in variations of the physiological properties in the digester and affected the cumulative biogas production (CBP). PM1 obtained higher CBP (15020.0 mL) with a more stable pH and a lower TAN concentration (1414.5 mg/L) compared to PM2 (2675.0 mL and 1670.0 mg/L, respectively). The direct path coefficients and indirect path coefficients between the four parameters and CBP were also analyzed. 相似文献
10.
Cathepsin D (Cath D) is overexpressed and secreted in a number of solid tumors and involved in the progress of tumor invasion, proliferation, metastasis, and apoptosis. Inhibition of Cath D is regarded as an attractive pathway for the development of novel anticancer drugs. Our previous studies revealed that tasiamide B, a cyanobacterial peptide that contained a statine‐like unit, exhibited good inhibition against Cath D and other aspartic proteases. Using this natural product as prototype, we designed and synthesized three new analogs, which bear isophthalic acid fragment at the N‐terminus and isobutyl amine ( 1 ), cyclopropyl amine ( 2 ), or 3‐methoxybenzyl amine ( 3 ) moiety at the C‐terminus. Enzymatic assays revealed that all these three compounds showed moderate‐to‐good inhibition against Cath D, with IC50s of 15, 884, and 353 nM, respectively. Notably, compound 1 showed extreme selectivity for Cath D with 576‐fold over Cath E and 554‐fold over BACE1, which could be a valuable template for the design of highly potent and selective Cath D inhibitors. Additionally, compound 1 showed moderated activity against HeLa cell lines with IC50 of 41.8 μM. Copyright © 2017 European Peptide Society and John Wiley & Sons, Ltd. 相似文献