全文获取类型
收费全文 | 11712篇 |
免费 | 1061篇 |
国内免费 | 1164篇 |
专业分类
13937篇 |
出版年
2024年 | 44篇 |
2023年 | 196篇 |
2022年 | 409篇 |
2021年 | 674篇 |
2020年 | 474篇 |
2019年 | 556篇 |
2018年 | 525篇 |
2017年 | 399篇 |
2016年 | 526篇 |
2015年 | 769篇 |
2014年 | 922篇 |
2013年 | 921篇 |
2012年 | 1093篇 |
2011年 | 980篇 |
2010年 | 556篇 |
2009年 | 541篇 |
2008年 | 620篇 |
2007年 | 533篇 |
2006年 | 419篇 |
2005年 | 333篇 |
2004年 | 318篇 |
2003年 | 268篇 |
2002年 | 259篇 |
2001年 | 186篇 |
2000年 | 168篇 |
1999年 | 155篇 |
1998年 | 116篇 |
1997年 | 97篇 |
1996年 | 101篇 |
1995年 | 74篇 |
1994年 | 84篇 |
1993年 | 59篇 |
1992年 | 69篇 |
1991年 | 72篇 |
1990年 | 51篇 |
1989年 | 34篇 |
1988年 | 43篇 |
1987年 | 24篇 |
1986年 | 33篇 |
1985年 | 32篇 |
1984年 | 21篇 |
1983年 | 26篇 |
1982年 | 17篇 |
1980年 | 14篇 |
1979年 | 14篇 |
1977年 | 12篇 |
1975年 | 13篇 |
1974年 | 12篇 |
1973年 | 11篇 |
1970年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
142.
Guoxu Ma Haifeng Wu Jingquan Yuan Lizhen Wu Qingxia Zheng Zhaocui Sun Xiaoru Fan Hua Wei Junshan Yang Xudong Xu 《Phytochemistry letters》2013,6(1):152-155
Five phenylpropanoids including one new compound balanophonin A (1), one new natural compound balanophonin B (2) were isolated from the seeds of Lithocarpus pachylepis for the first time. Their structures were elucidated by various spectroscopic techniques (UV, IR, MS, CD, 1D and 2D NMR). All compounds were evaluated for their anti-inflammatory activities on lipopolysaccharide (LPS)-induced nitric oxide (NO) production in RAW 264.7. 相似文献
143.
Background
Total hip or knee arthroplasty is an elective procedure that is usually accompanied by substantial blood loss, which may lead to acute anemia. As a result, almost half of total joint arthroplasty patients receive allogeneic blood transfusions (ABT). Many studies have shown that post-operative auto-transfusion (PAT) significantly reduces the need for ABT, but other studies have questioned the efficacy of this method.Methods
The protocol for this trial and supporting CONSORT checklist are available as supporting information; see Checklist S1. To evaluate the efficacy of PAT, we conducted a Cochrane systematic review that combined all available data from randomized controlled trials. Data from the six included trials were pooled for analysis. We then calculated relative risks with 95% confidence intervals (CIs) for dichotomous outcomes and mean differences with 95% CIs for continuous outcomes.Findings and Conclusion
To our knowledge, this is the first meta-analysis to compare the clinical results between PAT and a control in joint replacement patients. This meta-analysis has proven that the use of a PAT reinfusion system reduced significantly the demand for ABT, the number of patients who require ABT and the cost of hospitalization after total knee and hip arthroplasty. This study, together with other previously published data, suggests that PAT drains are beneficial. Larger, sufficiently powered studies are necessary to evaluate the presumed reduction in the incidence of infection as well as DVT after joint arthroplasty with the use of PAT. 相似文献144.
145.
Shumei Li Bin Wang Pengfei Xu Qixiang Lin Gaolang Gong Xiaoling Peng Yuanyuan Fan Yong He Ruiwang Huang 《PloS one》2013,8(8)
Diffusion-weighted MRI (DW-MRI), the only non-invasive technique for probing human brain white matter structures in vivo, has been widely used in both fundamental studies and clinical applications. Many studies have utilized diffusion tensor imaging (DTI) and tractography approaches to explore the topological properties of human brain anatomical networks by using the single tensor model, the basic model to quantify DTI indices and tractography. However, the conventional DTI technique does not take into account contamination by the cerebrospinal fluid (CSF), which has been known to affect the estimated DTI measures and tractography in the single tensor model. Previous studies have shown that the Fluid-Attenuated Inversion Recovery (FLAIR) technique can suppress the contribution of the CSF to the DW-MRI signal. We acquired DTI datasets from twenty-two subjects using both FLAIR-DTI and conventional DTI (non-FLAIR-DTI) techniques, constructed brain anatomical networks using deterministic tractography, and compared the topological properties of the anatomical networks derived from the two types of DTI techniques. Although the brain anatomical networks derived from both types of DTI datasets showed small-world properties, we found that the brain anatomical networks derived from the FLAIR-DTI showed significantly increased global and local network efficiency compared with those derived from the conventional DTI. The increases in the network regional topological properties derived from the FLAIR-DTI technique were observed in CSF-filled regions, including the postcentral gyrus, periventricular regions, inferior frontal and temporal gyri, and regions in the visual cortex. Because brain anatomical networks derived from conventional DTI datasets with tractography have been widely used in many studies, our findings may have important implications for studying human brain anatomical networks derived from DW-MRI data and tractography. 相似文献
146.
In desertified regions, shrub-dominated patches are important microhabitats for ground arthropod assemblages. As shrub age increases, soil, vegetation and microbiological properties can change remarkably and spontaneously across seasons. However, relatively few studies have analyzed how ground arthropods respond to the microhabitats created by shrubs of different plantation ages across seasons. Using 6, 15, 24 and 36 year-old plantations of re-vegetated shrubs (Caragana koushinskii) in the desert steppe of northwestern China as a model system, we sampled ground arthropod communities using a pitfall trapping method in the microhabitats under shrubs and in the open areas between shrubs, during the spring, summer and autumn. The total ground arthropod assemblage was dominated by Carabidae, Melolonthidae, Curculionidae, Tenebrionidae and Formicidae that were affected by plantation age, seasonal changes, or the interaction between these factors, with the later two groups also influenced by microhabitat. Overall, a facilitative effect was observed, with more arthropods and a greater diversity found under shrubs as compared to open areas, but this was markedly affected by seasonal changes. There was a high degree of similarity in arthropod assemblages and diversity between microhabitats in summer and autumn. Shrub plantation age significantly influenced the distribution of the most abundant groups, and also the diversity indices of the ground arthropods. However, there was not an overall positive relationship between shrub age and arthropod abundance, richness or diversity index. The influence of plantation age on arthropod communities was also affected by seasonal changes. From spring through summer to autumn, community indices of ground arthropods tended to decline, and a high degree of similarity in these indices (with fluctuation) was observed among different ages of shrub plantation in autumn. Altogether the recovery of arthropod communities was markedly affected by seasonal variability, and they demonstrated distinctive communal fingerprints in different microhabitats for each plantation age stage. 相似文献
147.
Liulin Chen Junming Zhu Yuhong Li Jie Lu Li Gao Huibi Xu Mingwen Fan Xiangliang Yang 《PloS one》2013,8(8)
The design of optimized nanoparticles offers a promising strategy to enable DNA vaccines to cross various physiological barriers for eliciting a specific and protective mucosal immunity via intranasal administration. Here, we reported a new designed nanoparticle system through incorporating anionic liposomes (AL) into chitosan/DNA (CS/DNA) complexes. With enhanced cellular uptake, the constructed AL/CS/DNA nanoparticles can deliver the anti-caries DNA vaccine pGJA-P/VAX into nasal mucosa. TEM results showed the AL/CS/DNA had a spherical structure. High DNA loading ability and effective DNA protection against nuclease were proved by gel electrophoresis. The surface charge of the AL/CS/DNA depended strongly on pH environment, enabling the intracellular release of loaded DNA via a pH-mediated manner. In comparison to the traditional CS/DNA system, our new design rendered a higher transfection efficiency and longer residence time of the AL/CS/DNA at nasal mucosal surface. These outstanding features enable the AL/CS/DNA to induce a significantly (p<0.01) higher level of secretory IgA (SIgA) than the CS/DNA in animal study, and a longer-term mucosal immunity. On the other hand, the AL/CS/DNA exhibited minimal cytotoxicity. These results suggest that the developed nanoparticles offer a potential platform for DNA vaccine packaging and delivery for more efficient elicitation of mucosal immunity. 相似文献
148.
149.
Plant and Soil - Although the linkages between aboveground photosynthates production and belowground respiration processes have been well studied, doubts remain as to the extent that photosynthate... 相似文献
150.
Limei Yuan Qinghai Li Zhiguo Zhang Qingle Liu Xuechen Wang Lihua Fan 《Journal of cellular biochemistry》2020,121(2):1400-1408
Atherosclerosis is a kind of chronic cardiovascular disease, characterized by oxidized low-density lipoprotein (ox-LDL) accumulation in macrophage. Tanshinone IIA (Tan), a lipophilic pharmacologically activate compound from Salvia miltiorrhiza Bunge, has been indicated to exert cardioprotective roles. Nevertheless, the biological role of Tan and regulatory mechanism in atherosclerosis are not fully established. In present study, atherosclerosis model was established in THP-1-derived macrophages by treatment of ox-LDL. The adipogenesis was measured by Nile red staining. The expressions of inflammatory factors, microRNA-130b (miR-130b) and WNT5A were measured by quantitative real-time polymerase chain reaction or Western blot. The target association between miR-130b and WNT5A was explored via luciferase activity and RNA immunoprecipitation assay. The results showed that exposure of Tan inhibited ox-LDL-induced adipogenesis and expressions of interleukin-1β (IL-1β), IL-6, and tumor necrosis factor-alpha in THP-1-derived macrophages. miR-130b expression was decreased in THP-1-derived macrophages treated by ox-LDL and its overexpression attenuated adipogenesis as well as inflammatory response. miR-130b knockdown reversed the regulatory effect of Tan on adipogenesis and inflammatory response in THP-1-derived macrophages stimulated by ox-LDL. In addition, WNT5A acted as a functional target of miR-130b and inhibited by Tan and miR-130b. As a conclusion, Tan decreased the adipogenesis and inflammatory response by mediating miR-130b and WNT5A, providing a novel theoretical foundation for treatment of atherosclerosis. 相似文献