全文获取类型
收费全文 | 19368篇 |
免费 | 1488篇 |
国内免费 | 1092篇 |
专业分类
21948篇 |
出版年
2024年 | 53篇 |
2023年 | 226篇 |
2022年 | 578篇 |
2021年 | 905篇 |
2020年 | 601篇 |
2019年 | 738篇 |
2018年 | 826篇 |
2017年 | 548篇 |
2016年 | 845篇 |
2015年 | 1153篇 |
2014年 | 1308篇 |
2013年 | 1464篇 |
2012年 | 1766篇 |
2011年 | 1555篇 |
2010年 | 964篇 |
2009年 | 847篇 |
2008年 | 1067篇 |
2007年 | 933篇 |
2006年 | 821篇 |
2005年 | 731篇 |
2004年 | 584篇 |
2003年 | 548篇 |
2002年 | 472篇 |
2001年 | 357篇 |
2000年 | 295篇 |
1999年 | 288篇 |
1998年 | 180篇 |
1997年 | 137篇 |
1996年 | 105篇 |
1995年 | 111篇 |
1994年 | 78篇 |
1993年 | 70篇 |
1992年 | 96篇 |
1991年 | 96篇 |
1990年 | 87篇 |
1989年 | 68篇 |
1988年 | 56篇 |
1987年 | 53篇 |
1986年 | 39篇 |
1985年 | 44篇 |
1984年 | 23篇 |
1983年 | 23篇 |
1982年 | 21篇 |
1981年 | 13篇 |
1979年 | 20篇 |
1978年 | 16篇 |
1977年 | 19篇 |
1976年 | 15篇 |
1975年 | 14篇 |
1972年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
Han YW Aleyas AG George JA Kim SJ Kim HK Yoo DJ Kang SH Eo SK 《Immunology and cell biology》2009,87(1):91-99
The CC chemokine receptor 7 (CCR7) and cognate CCR7 ligands, CCL19 and CCL21, help establish microenvironments in lymphoid tissue that can facilitate encounters between naive T cells and mature dendritic cells (DCs). This study was conducted to determine if CCR7 ligands can augment the immunogenicity of a DNA vaccine that expresses glycoprotein B (gB) of the pseudorabies virus (PrV). The genetic co-transfer of CCR7 ligands along with a PrV DNA vaccine increased the levels of serum PrV-specific immunoglobulin (Ig) G by 2- to 2.5-fold. In addition, the level of PrV-specific IgG2a isotype was significantly enhanced by co-injection of CCR7 ligand DNA, which indicates that CCR7 ligand biases the humoral immunity toward the Th1-type pattern. The co-injection of CCR7 ligand DNA consistently enhanced the level of Th1-type cytokines (IL-2 and IFN-gamma) produced by stimulated immune cells when compared with a group that was vaccinated with the PrV DNA vaccine. Also, the genetic co-transfer of CCR7 ligand DNAs with PrV DNA vaccine provided prolonged survival against a virulent challenge by PrV. Moreover, the co-administration of CCR7 ligand DNA increased the number of mature DCs into the secondary lymphoid tissues, which appeared to enhance the proliferation of PrV-immune CD4(+) T cells. Taken together, these findings indicate that CCR7 ligands are an attractive adjuvant for a PrV DNA vaccine that can offer protective immunity against the PrV. 相似文献
92.
93.
94.
Effects of Melatonin on Growth,Physiology and Gene Expression in Rice Seedlings Under Cadmium Stress
Xiachen Lv Yunxia Fang Lantian Zhang Weiyi Zhang Ling Xu Jingjin Han Bailing Jin Xian Zhang Xiaoqin Zhang Dawei Xue 《Phyton》2019,88(2):91-100
Melatonin (MLT) is a hormonal substance found in many organisms and can improve plant stress resistance. In this study, the japonica rice variety Y32 and indica rice variety NJ6 were cultivated in hydroponics under different concentrations of CdCl2 at the two-leaf stage. The growth, physiological and biochemical responses of the seedlings and the expression of cadmium (Cd)-related genes under exogenous melatonin (MLT) treatment were assessed. The results indicated that Cd stress destroyed the dynamic balance between reactive oxygen species (ROS) production and removal, resulting in ROS accumulation, membrane lipid peroxidation, and impaired growth and development. Following the application of exogenous MLT to rice seedlings, increases in plant biomass including both underground and above-ground areas were observed. MLT also scavenged the inhibition of superoxide dismutase (SOD) and peroxidase (POD) in a concentration dependent manner in response to Cd stress. Catalase (CAT) activity and malondialdehyde (MDA) expression also decreased following MLT treatment. Amongst the six Cd-related genes assessed, five genes were down-regulated and one was up-regulated in response to MLT treatment. Taken together, these data demonstrate that MLT improves the resilience of rice seedlings at the biochemical, physiological, and molecular levels, and diminishes the damage caused by Cd stress. 相似文献
95.
Fusions between the green fluorescent protein (GFP) and the Cauliflower mosaic virus (CaMV) movement protein (MP) induce the formation of fluorescent foci and surface tubules in Arabidopsis thaliana leaf mesophyll protoplasts. Tubules elongate coordinately and progressively in an assembly process approximately 6 to 12 h following transfection of protoplasts with GFP-MP constructs. Tubules are not formed in protoplasts transfected by GFP-MP(ER2A), a MP mutation that renders CaMV noninfectious. A small number of short tubules are formed on protoplasts transfected by GFP-MP(N6) and GFP-MP(N13), two second-site revertants of ER2A that partially restore infectivity. Protoplasts cotransfected with cyan fluorescent protein (CFP)-MP(WT) and GFP-MP(ER2A) form tubules containing both MP fusions, indicating that although the GFP-MP(ER2A) cannot induce tubule formation, GFP-MP(ER2A) can coassemble or colocalize with CFP-MP(WT) in tubules. Thus, CaMV MP-induced tubule formation in protoplasts correlates closely with the infectivity of mutation ER2A and its revertants, suggesting that tubule-forming capacity in plant protoplasts reflects a process required for virus infection or movement. 相似文献
96.
Associations between different agonistic and affiliative behavioural patterns of female domestic cats (Felis silvestris catus) were studied. In three groups of intact cats living in confinement frequencies of fourteen agonistic and affiliative behavioural
patterns were recorded. The technique of factor analysis (Principal Components Analysis followed by varimax rotation on a
dyads X behavioural patterns matrix) was used to detect clusters in these behavioural patterns. Five factors (or types of
interindividual relationships) were extracted per group. They accounted collectively for at least 77% of the total variance
present in the data. Although differences existed between groups with respect to behavioural patterns included in each factor,
four clusters of behaviours could be discriminated: (I) social rubbing, lordosis and rolling in front of partner (sexual behaviour),
(II) allogrooming, social sniffing, nosing, sniffing rear and treading (inspection-affiliative behaviour), (III) offensive
behaviour and staring, and (IV) defensive behaviour and staring. The role of these clusters in group living is discussed. 相似文献
97.
The sectioned thin cell layers (TCL) of flower stalk of Cichorium intybus L. were cultured in MS medium supplemented with NAA and BA or IAA and BA where floral and vegetative buds were developed from the explant. Endogenous IAA, DHZ+DHZR, iPA increased significantly during the floral bud formation, while Z+ZR remained changed. The levels of cytokinins, DHZ +DHZR, iPA, and Z-f-ZR all increased significantly during the vegetative bud formation, however IAA level was reduced during the first 7 days of culture and increased to two-thirds of initial values on the day when the bud primordia were formed. The results suggested that the initiation of floral buds was associated with a high IAA/CTK ratio, whereas the induction of vegetative bud differentiation was related to a low IAA/CTK ratio. 相似文献
98.
Novobiocin blocks the Drosophila heat shock response 总被引:12,自引:0,他引:12
99.
Pei-pei Han Shi-ru Jia Ying Sun Zhi-lei Tan Cheng Zhong Yu-jie Dai Ning Tan Shi-gang Shen 《World journal of microbiology & biotechnology》2014,30(9):2407-2418
The application of antibiotic treatment with assistance of metabolomic approach in axenic isolation of cyanobacterium Nostoc flagelliforme was investigated. Seven antibiotics were tested at 1–100 mg L?1, and order of tolerance of N. flagelliforme cells was obtained as kanamycin > ampicillin, tetracycline > chloromycetin, gentamicin > spectinomycin > streptomycin. Four antibiotics were selected based on differences in antibiotic sensitivity of N. flagelliforme and associated bacteria, and their effects on N. flagelliforme cells including the changes of metabolic activity with antibiotics and the metabolic recovery after removal were assessed by a metabolomic approach based on gas chromatography–mass spectrometry combined with multivariate analysis. The results showed that antibiotic treatment had affected cell metabolism as antibiotics treated cells were metabolically distinct from control cells, but the metabolic activity would be recovered via eliminating antibiotics and the sequence of metabolic recovery time needed was spectinomycin, gentamicin > ampicillin > kanamycin. The procedures of antibiotic treatment have been accordingly optimized as a consecutive treatment starting with spectinomycin, then gentamicin, ampicillin and lastly kanamycin, and proved to be highly effective in eliminating the bacteria as examined by agar plating method and light microscope examination. Our work presented a strategy to obtain axenic culture of N. flagelliforme and provided a method for evaluating and optimizing cyanobacteria purification process through diagnosing target species cellular state. 相似文献
100.
Fengjiao Meng Hui Li Huijuan Shi Qingxu Yang Fenfen Zhang Yang Yang Lili Kang Tiantian Zhen Sujuan Dai Yu Dong Anjia Han 《PloS one》2013,8(4)
The present study was aimed at investigating the expression of metastasis-associated in colon cancer 1 (MACC1) in nasopharyngeal carcinoma (NPC), its relationship with β-catenin, Met expression and the clinicopathological features of NPC, and its roles in carcinogenesis of NPC. Our results showed that MACC1 expression was higher in NPC cells and tissues than that in normal nasopharyngeal cells and chronic inflammation of the nasopharynx tissues, respectively. MACC1 expression was closely related to the clinical stage (p = 0.005) and the N classification (p<0.05) of NPC. Significant correlations between MACC1 expression and Met expression (p = 0.003), MACC1 expression and β-catenin abnormal expression (p = 0.033) were found in NPC tissues. MACC1 knockdown dramatically inhibited cellular proliferation, migration, invasion, and colony formation, but induced apoptosis in NPC cells compared with the control group. Furthermore, MACC1 down-regulation inhibited phosphorylated-Akt (Ser473) and β-catenin expression in NPC cells, but phosphorylated-Erk1/2 expression was not altered. Further study showed that phosphotidylinsitol-3-kinase inhibitor downregulated β-catenin and Met expression in NPC cells. There was a significant relationship between MACC1 expression and phosphorylated-Akt expression (p = 0.03), β-catenin abnormal expression and phosphorylated-Akt expression (p = 0.012) in NPC tissue, respectively. In addition, Epstein Barr virus-encoded oncogene latent membrane protein 1 upregulated MACC1 expression in NPC cells. Our results firstly suggest that MACC1 plays an important role in carcinogenesis of NPC through Akt/β-catenin signaling pathway. Targeting MACC1 may be a novel therapeutic strategy for NPC. 相似文献