首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   6941篇
  免费   498篇
  国内免费   467篇
  2024年   8篇
  2023年   60篇
  2022年   184篇
  2021年   332篇
  2020年   200篇
  2019年   280篇
  2018年   255篇
  2017年   211篇
  2016年   276篇
  2015年   443篇
  2014年   500篇
  2013年   517篇
  2012年   620篇
  2011年   565篇
  2010年   385篇
  2009年   321篇
  2008年   377篇
  2007年   329篇
  2006年   294篇
  2005年   263篇
  2004年   224篇
  2003年   175篇
  2002年   167篇
  2001年   118篇
  2000年   97篇
  1999年   102篇
  1998年   50篇
  1997年   62篇
  1996年   64篇
  1995年   53篇
  1994年   38篇
  1993年   43篇
  1992年   52篇
  1991年   47篇
  1990年   36篇
  1989年   27篇
  1988年   16篇
  1987年   28篇
  1986年   21篇
  1985年   17篇
  1984年   5篇
  1983年   7篇
  1982年   6篇
  1981年   5篇
  1980年   4篇
  1973年   3篇
  1971年   3篇
  1968年   2篇
  1967年   2篇
  1962年   2篇
排序方式: 共有7906条查询结果,搜索用时 109 毫秒
281.
ObjectiveTo study the changes of ginsenoside content in different proportion of Panax ginseng-Angelica sinensis (GA) co-decoction, and to explore the amelioration of hematopoietic function in mice after combined use of the two drugs. The active ingredient profiles in P. ginseng single decoction and co-decoction of GA were determined by high performance liquid chromatography (HPLC). The experimental pharmacology method was used to explore the effect of GA co-decoction on the hematopoietic function of chemotherapy mice.ResultsThe active ingredient profiles of the co-decoction of GA significantly changed compared with those of the single decoction. Compared with GA1:0 (single decoction of Panax ginseng), the routine ginsenosides of all proportions of GA decreased significantly, but the proportion of rare ginsenosides increased significantly. The changes of contents of rare ginsenosides of GA were basically consistent with the trends of effects on the myelosuppression induced by CY. Compared with the model group, GA significantly increased the number of bone marrow nucleated cells, thymus index, peripheral blood leukocytes and platelets, and significantly reduced the spleen index. Moreover, GA could promote G1 phase bone marrow cells to enter the cell cycle, increase the proportion of S phase cells and G2/M phase cells, and increase the cell proliferation index.ConclusionGA can ameliorate the hematopoietic function of mice after chemotherapy, and GA2:3, GA3:2 were the best, which may be due to the changes of the pharmacodynamic material basis of GA after compatibility. All these results implied that GA may be an ideal drug and food supplement for the treatment of toxic and side effects of chemotherapeutic drugs.  相似文献   
282.
283.
In this review, we summarize the rational design and versatile application of organic/inorganic hybrid gene carriers as multifunctional delivery systems. Organic/inorganic nanohybrids with both organic and inorganic components in one nanoparticle have attracted intense attention because of their favorable properties. Particularly, nanohybrids comprising cationic polymers and inorganic nanoparticles are considered to be promising candidates as multifunctional gene delivery systems. In this review, we begin with an introduction of gene delivery and gene carriers to demonstrate the incentive for fabricating nanohybrids as multifunctional carriers. Next, the construction strategies and morphology effects of organic/inorganic hybrid gene carriers are summarized and discussed. Both sections provide valuable information for the design and synthesis of hybrid gene carriers with superior properties. Finally, an overview is provided of the application of nanohybrids as multifunctional gene carriers. Diverse therapies and versatile imaging‐guided therapies have been achieved via the rational design of nanohybrids. In addition to a simple combination of the functions of organic and inorganic components, the performances arising from the synergistic effects of both components are considered to be more intriguing. In summary, this review might offer guidance for the understanding of organic/inorganic nanohybrids as multifunctional gene delivery systems.  相似文献   
284.
285.
Verticillium dahliae is a soil-borne fungus that causes vascular wilt on numerous plants worldwide. The fungus survives in the soil for up to 14 years by producing melanized microsclerotia. The protective function of melanin in abiotic stresses is well documented. Here, we found that the V. dahliae tetraspan transmembrane protein VdSho1, a homolog of the Saccharomyces cerevisiae Sho1, acts as an osmosensor, and is required for plant penetration and melanin biosynthesis. The deletion mutant ΔSho1 was incubated on a cellophane membrane substrate that mimics the plant epidermis, revealing that the penetration of ΔSho1 strain was reduced compared to the wild-type strain. Furthermore, VdSho1 regulates melanin biosynthesis by a signalling mechanism requiring a kinase-kinase signalling module of Vst50-Vst11-Vst7. Strains, ΔVst50, ΔVst7 and ΔVst11 also displayed defective penetration and melanin production like the ΔSho1 strain. Defects in penetration and melanin production in ΔSho1 were restored by overexpression of Vst50, suggesting that Vst50 lies downstream of VdSho1 in the regulatory pathway governing penetration and melanin biosynthesis. Data analyses revealed that the transmembrane portion of VdSho1 was essential for both membrane penetration and melanin production. This study demonstrates that Vst50-Vst11-Vst7 module regulates VdSho1-mediated plant penetration and melanin production in V. dahliae, contributing to virulence.  相似文献   
286.
Improving genetic resistance is a preferred method to manage Verticillium wilt of cotton and other hosts. Identifying host resistance is difficult because of the dearth of resistance genes against this pathogen. Previously, a novel candidate gene involved in Verticillium wilt resistance was identified by a genome-wide association study using a panel of Gossypium hirsutum accessions. In this study, we cloned the candidate resistance gene from cotton that encodes a protein sharing homology with the TIR-NBS-LRR receptor-like defence protein DSC1 in Arabidopsis thaliana (hereafter named GhDSC1). GhDSC1 expressed at higher levels in response to Verticillium wilt and jasmonic acid (JA) treatment in resistant cotton cultivars as compared to susceptible cultivars and its product was localized to nucleus. The transfer of GhDSC1 to Arabidopsis conferred Verticillium resistance in an A. thaliana dsc1 mutant. This resistance response was associated with reactive oxygen species (ROS) accumulation and increased expression of JA-signalling-related genes. Furthermore, the expression of GhDSC1 in response to Verticillium wilt and JA signalling in A. thaliana displayed expression patterns similar to GhCAMTA3 in cotton under identical conditions, suggesting a coordinated DSC1 and CAMTA3 response in A. thaliana to Verticillium wilt. Analyses of GhDSC1 sequence polymorphism revealed a single nucleotide polymorphism (SNP) difference between resistant and susceptible cotton accessions, within the P-loop motif encoded by GhDSC1. This SNP difference causes ineffective activation of defence response in susceptible cultivars. These results demonstrated that GhDSC1 confers Verticillium resistance in the model plant system of A. thaliana, and therefore represents a suitable candidate for the genetic engineering of Verticillium wilt resistance in cotton.  相似文献   
287.
288.
角质颚是研究头足类渔业生态学的重要材料.基于2018年9—11月中国鱿钓船在西北太平洋生产调查期间采集的268尾北方拟黵乌贼样本,对其角质颚外部形态生长特性进行了研究.主成分分析表明: 北方拟黵乌贼角质颚的上头盖长(UHL)、上脊突长(UCL)、上喙长(URL)、下头盖长(LHL)、下脊突长(LCL)和下喙长(LRL)可作为研究其角质颚外形变化的特征因子.协方差分析表明: 各特征因子与胴长和体重的生长关系在性别间均不存显著性差异.赤池信息准则分析显示: UHL、LHL与胴长生长的关系最适于用幂函数表示,UCL、URL、LCL与胴长生长的关系最适于用对数函数表示,而LRL与胴长生长的关系则最适于用线性函数表示;各特征参数与体重生长的关系,除LHL最适于用幂函数表示外,其余均最适于用对数函数表示.外形特征因子生长模型的确定,为北方拟黵乌贼的资源评估等研究打下科学基础.  相似文献   
289.
G kinase‐anchoring protein 1 (GKAP1) is a G kinase‐associated protein that is conserved in many eutherians and is mainly expressed in the testis, especially in spermatocytes and round spermatids. The function of GKAP1 in the testis is largely unknown. Here, we revealed that deletion of GKAP1 led to an increase in sperm production with swollen epididymis, and germ cell apoptosis was found to decrease in GKAP1 knock‐out mice. Further investigations showed that a deficiency of GKAP1 could partly change the cellular location of cGK‐Iα and increase the amount of active cAMP response element‐binding protein (CREB) in the nucleus. Therefore, the expression of a particular inhibitor of apoptosis proteins (IAPs) was upregulated because of the activation of CREB, and this increase in IAPs was associated with a decrease in the level of activated caspase‐3. These results suggest that a deficiency of GKAP1 in mouse testis could increase sperm production through a reduction of the spontaneous apoptosis of germ cells in the testis, possibly because of a change in the activity of the cGK‐Iα pathway.  相似文献   
290.
Grazing is an important modulator of both plant productivity and biodiversity in grassland community, yet how to determine a suitable grazing intensity in alpine grassland is still controversy. Here, we explore the effects of different grazing intensities on plant biomass and species composition, both at community level and functional group level, and examines the productivity–species richness relationship under four grazing patterns: no grazing (CK), light grazing (LG), moderate grazing, (MG) and heavy grazing (HG), attempt to determine a suitable grazing intensity in alpine grassland. The results were as follows. The total aboveground biomass (AGB) reduced with increasing grazing intensity, and the response of plant functional groups was different. AGB of both sedges and legumes increased from MG to HG, while the AGB of forbs reduced sharply and the grass AGB remained steady. There was a significant positive relationship between productivity and species richness both at community level and functional group level. In contrast, the belowground biomass (BGB) showed a unimodal relationship from CK to HG, peaking in MG (8,297.72 ± 621.29 g/m2). Interestingly, the grassland community tends to allocate more root biomass to the upper soil layer under increasing grazing intensities. Our results suggesting that moderate levels of disturbance may be the optimal grassland management strategy for alpine meadow in terms of root production.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号