全文获取类型
收费全文 | 5503篇 |
免费 | 538篇 |
国内免费 | 115篇 |
出版年
2023年 | 39篇 |
2022年 | 86篇 |
2021年 | 169篇 |
2020年 | 101篇 |
2019年 | 119篇 |
2018年 | 130篇 |
2017年 | 91篇 |
2016年 | 161篇 |
2015年 | 315篇 |
2014年 | 333篇 |
2013年 | 401篇 |
2012年 | 484篇 |
2011年 | 431篇 |
2010年 | 249篇 |
2009年 | 207篇 |
2008年 | 307篇 |
2007年 | 247篇 |
2006年 | 245篇 |
2005年 | 232篇 |
2004年 | 199篇 |
2003年 | 174篇 |
2002年 | 167篇 |
2001年 | 107篇 |
2000年 | 121篇 |
1999年 | 108篇 |
1998年 | 63篇 |
1997年 | 49篇 |
1996年 | 35篇 |
1995年 | 35篇 |
1994年 | 43篇 |
1993年 | 41篇 |
1992年 | 70篇 |
1991年 | 56篇 |
1990年 | 45篇 |
1989年 | 55篇 |
1988年 | 50篇 |
1987年 | 35篇 |
1986年 | 39篇 |
1985年 | 30篇 |
1984年 | 50篇 |
1983年 | 27篇 |
1982年 | 27篇 |
1981年 | 22篇 |
1980年 | 15篇 |
1979年 | 27篇 |
1978年 | 24篇 |
1977年 | 20篇 |
1975年 | 16篇 |
1974年 | 9篇 |
1971年 | 11篇 |
排序方式: 共有6156条查询结果,搜索用时 875 毫秒
161.
A morphometric study on H. armigera antenna showed four styles of sensilla, i.e., styloconica, chaetica, coeloconica, and trichodea, and their numbers were estimated. Sensilla trichodea detect inter and intraspecific communication signals and was the most numerous. They were divided into three types: type I, the longest, with a length of 34.04 ± 3.16 μm and about 2.16 to 2.42 μm in diameter at its base; 2) type II, intermediate, with a length of 22.58 ± 0.77 μm and basal diameter of 1.8–2.52 μm; 3) type III, the shortest sensilla trichodea, with a length of 7.62 ± 0.4 μm and a range in diameter similar to that of type II. The length of the female sensilla trichodea was longer than that of the male. The total number of sensilla trichodea was estimated to be 7520 on the antenna of the female, and 6831 on the male antenna. The lengths of the sensilla trichodea type I and type III were significantly different on male (t = 4.6881, P = 0.0034) and female antenna (t = 18.9852, P = 0.0001). An estimation of the predicted surface area of the most numerous type I on sampled segments between the 12th and 20th segments from a female of H. armigera showed a surface area of 5 × 103 μm2 and a sensillar density of 38 sensilla/103 μm2. The fraction of sensilla-occupied surface area was 0.4 μm2. 相似文献
162.
Timothy A. McCaffrey Constantine Tziros Jannet Lewis Richard Katz Robert Siegel William Weglicki Jay Kramer I. Tong Mak Ian Toma Liang Chen Elizabeth Benas Alexander Lowitt Shruti Rao Linda Witkin Yi Lian Yinglei Lai Zhaoqing Yang Sidney W. Fu 《International journal of biological sciences》2013,9(4):350-360
163.
Ling-Jun Ho Li-Feng Hung Feng-Cheng Liu Tsung-Yun Hou Leou-Chyr Lin Chuan-Yueh Huang Jenn-Haung Lai 《PloS one》2013,8(12)
Osteoarthritis (OA) is a common joint disorder with varying degrees of inflammation. The ideal anti-OA drug should have immunomodulatory effects while at the same time having limited or no toxicity. We examined the anti-inflammatory effects of Ginkgo biloba extract (EGb) in interleukin-1 (IL-1)-stimulated human chondrocytes. Chondrocytes were prepared from cartilage specimens taken from patients with osteoarthritis who had received total hip or total knee replacement. The concentrations of chemokines and the degree of cell migration were determined by ELISA and chemotaxis assays, respectively. The activation of inducible nitric oxide synthase (iNOS), mitogen-activated protein kinases (MAPKs), activator protein-1 (AP-1), and nuclear factor-kappaB (NF-κB) was determined by immunoblotting, immunohistochemistry, and electrophoretic mobility shift assay. We found that EGb inhibited IL-1-induced production of chemokines, which in turn resulted in attenuation of THP-1 cell migration toward EGb-treated cell culture medium. EGb also suppressed IL-1-stimulated iNOS expression and release of nitric oxide (NO). The EGb-mediated suppression of the iNOS-NO pathway correlated with the attenuation of activator protein-1 (AP-1) but not nuclear factor-kappaB (NF-κB) DNA-binding activity. Of the mitogen-activated protein kinases (MAPKs), EGb inhibited only c-Jun N-terminal kinase (JNK). Unexpectedly, EGb selectively caused degradation of c-Jun protein. Further investigation revealed that EGb-mediated c-Jun degradation was preceded by ubiquitination of c-Jun and could be prevented by the proteosome inhibitor MG-132. The results imply that EGb protects against chondrocyte degeneration by inhibiting JNK activation and inducing ubiquitination-dependent c-Jun degradation. Although additional research is needed, our results suggest that EGb is a potential therapeutic agent for the treatment of OA. 相似文献
164.
Kung-Chao Chang Wei-Chao Chang Yao Chang Liang-Yi Hung Chien-Hsien Lai Yu-Min Yeh Yu-Wei Chou Chung-Hsuan Chen 《PloS one》2013,8(11)
Lymphoma-specific biomarkers contribute to therapeutic strategies and the study of tumorigenesis. Diffuse large B-cell lymphoma (DLBCL) is the most common type of malignant lymphoma. However, only 50% of patients experience long-term survival after current treatment; therefore, developing novel therapeutic strategies is warranted. Comparative proteomic analysis of two DLBCL lines with a B-lymphoblastoid cell line (LCL) showed differential expression of Ran GTPase-activating protein 1 (RanGAP1) between them, which was confirmed using immunoblotting. Immunostaining showed that the majority of DLBCLs (92%, 46/50) were RanGAP1+, while reactive lymphoid hyperplasia (n = 12) was RanGAP1+ predominantly in germinal centers. RanGAP1 was also highly expressed in other B-cell lymphomas (BCL, n = 180) with brisk mitotic activity (B-lymphoblastic lymphoma/leukemia: 93%, and Burkitt lymphoma: 95%) or cell-cycle dysregulation (mantle cell lymphoma: 83%, and Hodgkin’s lymphoma 91%). Interestingly, serum RanGAP1 level was higher in patients with high-grade BCL (1.71 ± 2.28 ng/mL, n = 62) than in low-grade BCL (0.75 ± 2.12 ng/mL, n = 52) and healthy controls (0.55 ± 1.58 ng/mL, n = 75) (high-grade BCL vs. low-grade BCL, p = 0.002; high-grade BCL vs. control, p < 0.001, Mann-Whitney U test). In vitro, RNA interference of RanGAP1 showed no effect on LCL but enhanced DLBCL cell death (41% vs. 60%; p = 0.035) and cell-cycle arrest (G0/G1: 39% vs. 49%, G2/M: 19.0% vs. 7.5%; p = 0.030) along with decreased expression of TPX2 and Aurora kinases, the central regulators of mitotic cell division. Furthermore, ON 01910.Na (Estybon), a multikinase inhibitor induced cell death, mitotic cell arrest, and hyperphosphorylation of RanGAP1 in DLBCL cell lines but no effects in normal B and T cells. Therefore, RanGAP1 is a promising marker and therapeutic target for aggressive B-cell lymphoma, especially DLBCL. 相似文献
165.
Yang Liu Qiliang Lai Chunming Dong Fengqin Sun Liping Wang Guangyu Li Zongze Shao 《PloS one》2013,8(11)
Bacteria closely related to Bacillus pumilus cannot be distinguished from such other species as B. safensis, B. stratosphericus, B. altitudinis and B. aerophilus simply by 16S rRNA gene sequence. In this report, 76 marine strains were subjected to phylogenetic analysis based on 7 housekeeping genes to understand the phylogeny and biogeography in comparison with other origins. A phylogenetic tree based on the 7 housekeeping genes concatenated in the order of gyrB-rpoB-pycA-pyrE-mutL-aroE-trpB was constructed and compared with trees based on the single genes. All these trees exhibited a similar topology structure with small variations. Our 79 strains were divided into 6 groups from A to F; Group A was the largest and contained 49 strains close to B. altitudinis. Additional two large groups were presented by B. safensis and B. pumilus respectively. Among the housekeeping genes, gyrB and pyrE showed comparatively better resolution power and may serve as molecular markers to distinguish these closely related strains. Furthermore, a recombinant phylogenetic tree based on the gyrB gene and containing 73 terrestrial and our isolates was constructed to detect the relationship between marine and other sources. The tree clearly showed that the bacteria of marine origin were clustered together in all the large groups. In contrast, the cluster belonging to B. safensis was mainly composed of bacteria of terrestrial origin. Interestingly, nearly all the marine isolates were at the top of the tree, indicating the possibility of the recent divergence of this bacterial group in marine environments. We conclude that B. altitudinis bacteria are the most widely spread of the B. pumilus group in marine environments. In summary, this report provides the first evidence regarding the systematic evolution of this bacterial group, and knowledge of their phylogenetic diversity will help in the understanding of their ecological role and distribution in marine environments. 相似文献
166.
Background
Cataract is the leading cause of blindness worldwide. Many observational studies assessed the relationship between postmenopausal hormone replacement therapy (HRT) and risk of cataract development, but the reported results were controversial. The aim of present meta-analysis was to evaluate the association of postmenopausal hormone replacement therapy with risk of cataract development.Methods
The eligible observational studies, including cross-sectional, case–control and cohort studies, were identified by searching PubMed and Embase during March of 2013. Either a fixed- or a random-effects model was used to calculate the pooled odds ratio (OR) with its 95% confidence interval (95%CI). Subgroup analysis on cataract types was performed.Results
A total of four cohort and five case-control or cross-sectional studies were finally included into this meta-analysis. Overall, a significant decreased risk of developing any type of cataract was found in ever HRT group as compared with non-HRT group among cohort studies (OR 0.83; 95%CI: 0.71,0.97) and case-control or cross-sectional studies (OR 0.74; 95%CI: 0.59,0.93). Subgroup analysis on cataract types determined that the significantly decreased risk of nuclear cataract in current HRT group (OR 0.72; 95%CI: 0.61,0.85) and also a critically reduced risk of nuclear cataract in ever HRT group (OR 0.80; 95% CI: 0.64,1.01) were found among case-control or cross-sectional studies, as compared with non-HRT group. No association of HRT with risk of cortical and posterior subcapsular cataract was observed.Conclusions
The results of present meta-analysis indicate that postmenopausal hormone use may play a protective role in cataract development. 相似文献167.
Introduction
We investigated the changing trend of various toxigenic Clostridium difficile isolates at a 3 500-bed hospital in Taiwan. Genetic relatedness and antimicrobial susceptibility of toxigenic C. difficile isolates were also examined.Methods
A total of 110 non-repeat toxigenic C. difficile isolates from different patients were collected between 2002 and 2007. Characterization of the 110 toxigenic isolates was performed using agar dilution method, multilocus variable-number tandem-repeat analysis (MLVA) genotyping, tcdC genotyping, and toxinotyping.Results
Among the 110 toxigenic isolates studied, 70 isolates harbored tcdA and tcdB (A+B+) and 40 isolates harbored tcdB only (A−B+). The annual number of A+B+ isolates considerably increased over the 6-year study (P = 0.055). A total of 109 different MLVA genotypes were identified, in which A+B+ isolates and A−B+ isolates were differentiated into two genetic clusters with similarity of 17.6%. Twenty-four (60%) of the 40 A−B+ isolates formed a major cluster, MLVA-group 1, with a similarity of 85%. Seven (6.4%) resistant isolates were identified, including two metronidazole-resistant and five vancomycin-resistant isolates.Conclusions
This study indicated a persistence of a MLVA group 1 A−B+ isolates and an increase of A+B+ isolates with diverse MLVA types. Moreover, C. difficile isolates with antimicrobial resistance to metronidazole or vancomycin were found to have emerged. Continuous surveillance is warranted to understand the recent situation and control the further spread of the toxigenic C. difficile isolates, especially among hospitalized patients. 相似文献168.
Chung-Hsu Lai Lin-Li Chang Jiun-Nong Lin Wei-Fang Chen Li-Li Kuo Hsi-Hsun Lin Yen-Hsu Chen 《PloS one》2013,8(10)
Q fever is serologically cross-reactive with other intracellular microorganisms. However, studies of the serological status of Mycoplasma pneumoniae and Chlamydophila pneumoniae during Q fever are rare. We conducted a retrospective serological study of M. pneumoniae and C. pneumoniae by enzyme-linked immunosorbent assay (ELISA), a method widely used in clinical practice, in 102 cases of acute Q fever, 39 cases of scrub typhus, and 14 cases of murine typhus. The seropositive (57.8%, 7.7%, and 0%, p<0.001) and seroconversion rates (50.6%, 8.8%, and 0%, p<0.001) of M. pneumoniae IgM, but not M. pneumoniae IgG and C. pneumoniae IgG/IgM, in acute Q fever were significantly higher than in scrub typhus and murine typhus. Another ELISA kit also revealed a high seropositivity (49.5%) and seroconversion rate (33.3%) of M. pneumoniae IgM in acute Q fever. The temporal and age distributions of patients with positive M. pneumoniae IgM were not typical of M. pneumoniae pneumonia. Comparing acute Q fever patients who were positive for M. pneumoniae IgM (59 cases) with those who were negative (43 cases), the demographic characteristics and underlying diseases were not different. In addition, the clinical manifestations associated with atypical pneumonia, including headache (71.2% vs. 81.4%, p=0.255), sore throat (8.5% vs. 16.3%, p=0.351), cough (35.6% vs. 23.3%, p=0.199), and chest x-ray suggesting pneumonia (19.3% vs. 9.5%, p=0.258), were unchanged between the two groups. Clinicians should be aware of the high seroprevalence of M. pneumoniae IgM in acute Q fever, particularly with ELISA kits, which can lead to misdiagnosis, overestimations of the prevalence of M. pneumoniae pneumonia, and underestimations of the true prevalence of Q fever pneumonia. 相似文献
169.
Gianguglielmo Zehender Erika Ebranati Renata Shkjezi Anna Papa Camilla Luzzago Elena Gabanelli Alessandra Lo Presti Alessia Lai Giovanni Rezza Massimo Galli Silvia Bino Massimo Ciccozzi 《PloS one》2013,8(11)
Crimean-Congo hemorrhagic fever (CCHF) is a zoonosis mainly transmitted by ticks that causes severe hemorrhagic fever and has a mortality rate of 5-60%. The first outbreak of CCHF occurred in the Crimean peninsula in 1944-45 and it has recently emerged in the Balkans and eastern Mediterranean. In order to reconstruct the origin and pathway of the worldwide dispersion of the virus at global and regional (eastern European) level, we investigated the phylogeography of the infection by analysing 121 publicly available CCHFV S gene sequences including two recently characterised Albanian isolates. The spatial and temporal phylogeny was reconstructed using a Bayesian Markov chain Monte Carlo approach, which estimated a mean evolutionary rate of 2.96 x 10-4 (95%HPD=1.6 and 4.7 x 10-4) substitutions/site/year for the analysed fragment. All of the isolates segregated into seven highly significant clades that correspond to the known geographical clades: in particular the two new isolates from northern Albania clustered significantly within the Europe 1 clade. Our phylogeographical reconstruction suggests that the global CCHFV clades originated about one thousand years ago from a common ancestor probably located in Africa. The virus then spread to Asia in the XV century and entered Europe on at least two occasions: the first in the early 1800s, when a still circulating but less or non-pathogenic virus emerged in Greece and Turkey, and the second in the early 1900s, when a pathogenic CCHFV strain began to spread in eastern Europe. The most probable location for the origin of this European clade 1 was Russia, but Turkey played a central role in spreading the virus throughout Europe. Given the close proximity of the infected areas, our data suggest that the movement of wild and domestic ungulates from endemic areas was probably the main cause of the dissemination of the virus in eastern Europe. 相似文献
170.
Mei-Ju Ko Hon-Yen Wu Hung-Yuan Chen Yen-Ling Chiu Shih-Ping Hsu Mei-Fen Pai Ju-YehYang Chun-Fu Lai Hui-Min Lu Shu-Chen Huang Shao-Yu Yang Su-Yin Wen Hsien-Ching Chiu Fu-Chang Hu Yu-Sen Peng Shiou-Hwa Jee 《PloS one》2013,8(8)