全文获取类型
收费全文 | 7622篇 |
免费 | 674篇 |
国内免费 | 847篇 |
出版年
2024年 | 14篇 |
2023年 | 149篇 |
2022年 | 193篇 |
2021年 | 444篇 |
2020年 | 336篇 |
2019年 | 466篇 |
2018年 | 390篇 |
2017年 | 274篇 |
2016年 | 389篇 |
2015年 | 528篇 |
2014年 | 595篇 |
2013年 | 626篇 |
2012年 | 694篇 |
2011年 | 596篇 |
2010年 | 367篇 |
2009年 | 338篇 |
2008年 | 375篇 |
2007年 | 324篇 |
2006年 | 298篇 |
2005年 | 208篇 |
2004年 | 242篇 |
2003年 | 205篇 |
2002年 | 163篇 |
2001年 | 154篇 |
2000年 | 116篇 |
1999年 | 93篇 |
1998年 | 73篇 |
1997年 | 54篇 |
1996年 | 80篇 |
1995年 | 64篇 |
1994年 | 50篇 |
1993年 | 27篇 |
1992年 | 42篇 |
1991年 | 32篇 |
1990年 | 31篇 |
1989年 | 21篇 |
1988年 | 24篇 |
1987年 | 16篇 |
1986年 | 12篇 |
1985年 | 18篇 |
1984年 | 6篇 |
1983年 | 7篇 |
1982年 | 5篇 |
1981年 | 4篇 |
排序方式: 共有9143条查询结果,搜索用时 750 毫秒
991.
Improved volatile fatty acids production from proteins of sewage sludge with anthraquinone-2,6-disulfonate (AQDS) under anaerobic condition 总被引:1,自引:0,他引:1
Organic matters in sewage sludge can be converted into volatile fatty acids (VFAs) as renewable carbon sources. This work for the first time applied anthraquinone-2,6-disulfonate (AQDS) for enhancing VFA production from sewage sludge. With 0.066 or 0.33 g AQDS g−1 dried solids (DS), the yields for VFAs peak at 403 or 563 mg l−1, 1.9- or 2.7-fold to the control. The accumulated VFAs were principally composed of acetate and propionate. The AQDS enhances degradation rates of model proteins (bovine serum albumin), but had little enhancement on that of model polysaccharides (dextrans). The acidification step is proposed the rate-limiting step for VFA production from sewage sludge, in which the AQDS molecules shuttle electrons to accelerate the redox reactions associated with amino acid degradation. Methanogenic activities are inhibited in the presence of AQDS. The AQDS-assisted VFAs are renewable organic carbon sources, although their direct use for anaerobic digestion is not advised. 相似文献
992.
J Malmström J Viklund C Slivo A Costa M Maudet C Sandelin G Hiller LL Olsson A Aagaard S Geschwindner Y Xue M Vasänge 《Bioorganic & medicinal chemistry letters》2012,22(18):5919-5923
4-(1,3-Benzothiazol-2-yl)thiophene-2-sulfonamide (4a) was found to be a moderately potent inhibitor of cyclin-dependent kinase 5 (cdk5) from a HTS screen. The synthesis and SAR around this hit is described. The X-ray coordinates of ligand 4a with cdk5 are also reported, showing an unusual binding mode to the hinge region via a water molecule. 相似文献
993.
994.
Xue F Ji W Wang C Zhang H Yang B 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2012,124(8):1549-1560
Powdery mildew, caused by Blumeria graminis f. sp. tritici, is an important foliar disease of wheat worldwide. The dominant powdery mildew resistance gene PmAS846 was transferred to the hexaploid wheat lines N9134 and N9738 from wild emmer wheat (Triticum dicoccoides) in 1995, and it is still one of the most effective resistance genes in China. A high resolution genetic map for PmAS846 locus was constructed using two F2 populations and corresponding F2:3 families developed from the crosses of N9134/Shaanyou 225 and N9738/Huixianhong. Synteny between wheat and Brachypodium distachyon and rice was used to develop closely linked molecular markers to reduce the genetic interval around PmAS846. Twenty-six expressed sequence tag-derived markers were mapped to the PmAS846 locus. Five markers co-segregated with PmAS846 in the F2 population of N9134/Shaanyou 225. PmAS846 was physically located to wheat chromosome 5BL bin 0.75–0.76 within a gene-rich region. The markers order is conserved between
wheat and Brachypodium distachyon, but rearrangements are present in rice. Two markers, BJ261635 and CJ840011 flanked PmAS846 and narrowed PmAS846 to a region that is collinear with 197 and 112 kb genomic regions on Brachypodium chromosome 4 and rice chromosome 9, respectively. The genes located on the corresponding homologous regions in Brachypodium, rice and barley could be considered for further marker saturation and identification of potential candidate genes for PmAS846. The markers co-segregating with PmAS846 provide a potential target site for positional cloning of PmAS846, and can be used for marker-assisted selection of this gene. 相似文献
995.
CED-1, CED-7, and TTR-52 regulate surface phosphatidylserine expression on apoptotic and phagocytic cells 总被引:1,自引:0,他引:1
Highlights? PS is expressed on the surface of apoptotic and phagocytic cells during apoptosis ? CED-7 and TTR-52 mediate time-dependent loss of PS from surface of apoptotic cells ? CED-7 and TTR-52 promote generation of extracellular PS vesicles ? CED-7/TTR-52/CED-1 promote phagocyte PS expression, important for corpse engulfment 相似文献
996.
Interleukin-7 receptor α chain (IL-7Rα)-derived signals are critical for normal T cell development, mature T cell homeostasis,
and longevity of memory T cells. IL-7Rα expression in T cells is dynamically regulated at different developmental and antigen-responding
stages. However, the molecular mechanism underlying the dynamic regulation is not completely understood. Here we describe
generation of a bacterial artificial chromosome (BAC)-based reporter transgenic mouse strain, which contains 210 kb DNA sequence
flanking the Il7r locus. We used in vitro validated EGFP reporter and insulator sequences to facilitate the reporter transgene expression.
Consistent with endogenous IL-7Rα expression, the BAC transgene was expressed in mature T cells, a portion of natural killer
cells but not in mature B cells. In the thymus, the EGFP reporter and endogenous IL-7Rα showed synchronized silencing in CD4+CD8+ double positive stage, were both upregulated in CD4+ or CD8+ single positive thymocytes, and both continued to be co-expressed in na?ve T cells in the periphery. Upon encountering antigen,
the antigen-specific effector CD8+ T cells downregulated both endogenous IL-7Rα and the EGFP reporter, which were upregulated in synchrony in antigen-specific
memory CD8 T cells. These results indicate that the BAC-EGFP transgene reports endogenous IL-7Rα regulation with high fidelity,
and further suggest that the 210 kb sequence flanking the Il7r locus contains sufficient genetic information to regulate its expression changes in T lineage cells. Our approach thus represents
a critical initial step towards systematic dissection of the cis regulatory elements controlling dynamic IL-7Rα regulation during T cell development and cellular immune responses. 相似文献
997.
998.
Zou Q Hu Y Xue J Fan X Jin Y Shi X Meng D Wang X Feng C Xie X Zhang Y Kang Y Liang X Wu B Wang M Wang B 《PloS one》2012,7(4):e34865
Background
H5N1 is a highly pathogenic influenza A virus, which can cause severe illness or even death in humans. Although the widely used killed vaccines are able to provide some protection against infection via neutralizing antibodies, cytotoxic T-lymphocyte responses that are thought to eradicate viral infections are lacking.Methodology/Principal Findings
Aiming to promote cytotoxic responses against H5N1 infection, we extended our previous finding that praziquantel (PZQ) can act as an adjuvant to induce IL-17-producing CD8+ T cells (Tc17). We found that a single immunization of 57BL/6 mice with killed viral vaccine plus PZQ induced antigen-specific Tc17 cells, some of which also secreted IFN-γ. The induced Tc17 had cytolytic activities. Induction of these cells was impaired in CD8 knockout (KO) or IFN-γ KO mice, and was even lower in IL-17 KO mice. Importantly, the inoculation of killed vaccine with PZQ significantly reduced virus loads in the lung tissues and prolonged survival. Protection against H5N1 virus infection was obtained by adoptively transferring PZQ-primed wild type CD8+ T cells and this was more effective than transfer of activated IFN-γ KO or IL-17 KO CD8+ T cells.Conclusions/Significance
Our results demonstrated that adding PZQ to killed H5N1 vaccine could promote broad Tc17-mediated cytotoxic T lymphocyte activity, resulting in improved control of highly pathogenic avian influenza virus infection. 相似文献999.
Background
Many studies showed a moderate cholesterol-lowering effect of plant sterols (PS), but increased circulating PS might be atherogenic. We evaluated the associations between natural dietary intake of PS and carotid intima–media thickness (IMT) and serum lipids.Methodology/Principal Findings
This community-based cross-sectional study included 1160 men and 2780 women aged 31–75 years. Dietary intakes were assessed using a food-frequency questionnaire. The IMTs at the common, bifurcation and internal carotid artery segments, and fasting serum total (TC), LDL (LDLc) and HDL (HDLc) cholesterol, and triglycerides (TG) were determined. After adjusting for potential covariates, multivariate analysis showed a dose-dependent inverse association of total PS intake with serum TC, LDLc, non-HDLc in women (P<0.001) and in men (P<0.05). As compared to the lowest quartile of PS intake (<206 mg/d), the multivariate-adjusted means of TC, LDLc and non-HDLc in the highest quartile of PS intake (447 mg/d) decreased by 5.0%, 6.2% and 6.5% in women (P<0.005), and by 6.4%, 7.1% and 6.7% (P>0.05) in men. Although the IMTs tended to be lower with greater intake of dietary PS, only small differences in the left internal IMT between the highest and lowest groups were observed among men (−7.6%) and women (−5.1%) (P<0.05). The multivariate analysis showed no significant mean differences among the PS groups in HDLc, TG and IMTs at other studied sites among men and women (all P>0.05).Conclusions
Greater PS consumption from natural diets is associated with lower serum total, LDL, non-HDL cholesterol and with thinner left internal IMT in women and men. 相似文献1000.
Bu Q Yang Y Yan G Hu Z Hu C Duan J Lv L Zhou J Zhao J Shao X Deng Y Li Y Li H Zhu R Zhao Y Cen X 《Journal of Proteomics》2012,75(4):1330-1342
It has been known that the reinforcing effects and long-term consequences of morphine are closely associated with nucleus accumbens (NAc) in the brain, a key region of the mesolimbic dopamine pathway. However, the proteins involved in neuroadaptive processes and withdrawal symptom in primates of morphine dependence have not been well explored. In the present study, we performed proteomes in the NAc of rhesus monkeys of morphine dependence and withdrawal intervention with clonidine or methadone. Two-dimensional electrophoresis was used to compare changes in cytosolic protein abundance in the NAc. We found a total of 46 proteins differentially expressed, which were further identified by mass spectrometry analysis. The identified proteins can be classified into 6 classes: metabolism and mitochondrial function, synaptic transmission, cytoskeletal proteins, oxidative stress, signal transduction and protein synthesis and degradation. Importantly, we discovered 14 proteins were significantly but similarly altered after withdrawal therapy with clonidine or methadone, revealing potential pharmacological strategies or targets for the treatment of morphine addiction. Our study provides a comprehensive understanding of the neuropathophysiology associated with morphine addiction and withdrawal therapy in primate, which is helpful for the development of opiate withdrawal pharmacotherapies. 相似文献