全文获取类型
收费全文 | 19502篇 |
免费 | 1751篇 |
国内免费 | 1428篇 |
专业分类
22681篇 |
出版年
2023年 | 252篇 |
2022年 | 543篇 |
2021年 | 908篇 |
2020年 | 616篇 |
2019年 | 695篇 |
2018年 | 738篇 |
2017年 | 550篇 |
2016年 | 722篇 |
2015年 | 1179篇 |
2014年 | 1303篇 |
2013年 | 1419篇 |
2012年 | 1623篇 |
2011年 | 1551篇 |
2010年 | 1012篇 |
2009年 | 853篇 |
2008年 | 955篇 |
2007年 | 914篇 |
2006年 | 812篇 |
2005年 | 691篇 |
2004年 | 649篇 |
2003年 | 576篇 |
2002年 | 542篇 |
2001年 | 397篇 |
2000年 | 392篇 |
1999年 | 365篇 |
1998年 | 175篇 |
1997年 | 163篇 |
1996年 | 164篇 |
1995年 | 119篇 |
1994年 | 149篇 |
1993年 | 95篇 |
1992年 | 156篇 |
1991年 | 149篇 |
1990年 | 122篇 |
1989年 | 101篇 |
1988年 | 84篇 |
1987年 | 98篇 |
1986年 | 84篇 |
1985年 | 94篇 |
1984年 | 48篇 |
1983年 | 49篇 |
1982年 | 51篇 |
1981年 | 39篇 |
1980年 | 37篇 |
1979年 | 53篇 |
1978年 | 42篇 |
1977年 | 46篇 |
1976年 | 35篇 |
1975年 | 38篇 |
1974年 | 46篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
Plant Cell, Tissue and Organ Culture (PCTOC) - Tree peony (Paeonia sect. Moutan) is a world famous ornamental and economically important species, but it is recalcitrant to in vitro regeneration.... 相似文献
102.
Ding Anqi Bao Fei Zhang Tengxun Yang Weiru Wang Jia Cheng Tangren Zhang Qixiang 《Molecular biology reports》2020,47(9):6635-6647
Molecular Biology Reports - Prunus sibirica and Prunus mume are closely related plant species that differ in cold tolerance. Hybrids of P. sibirica and true mume, belonging to the apricot mei... 相似文献
103.
104.
Conservation is an important organizational focus for zoos and aquariums. Organizational identity theory predicts a relationship between what is central to organizations, such as their mission statements, and their strategic activities. Based on this theory, we tested how organizational missions relate to their conservation strategies and practices. Tax forms and websites provided data from 173 zoos and 38 aquariums in the Association of Zoos and Aquariums in North America. We analyzed conservation mission strength, organizational characteristics, and project features with dependent variables representing the depth of organizational conservation commitments: amount of grants zoos funded, number of partner organizations, and number of projects per zoo. On tax forms, the average amount of total conservation grants donated to partner organizations per zoo was over $650,000, while the average number of partners reported on the tax forms was two. The content analysis of websites revealed an average of 14 conservation partners and 10 projects per zoo. Negative binomial regression models were significant. The financial analysis revealed that only the number of zoo personnel, as a surrogate for organization size, significantly predicted the amount of zoos’ conservation grants. Website analyses found increasing budgets, organizational involvement, and geographic reach of the projects predicted increasing numbers of conservation projects and partnerships. However, our findings did not support the hypothesized relationship—strength of organizational mission did not predict strategy and activities. Zoos could do more to strategically activate their organizational identities and conservation missions to achieve their conservation goals. 相似文献
105.
Zhenpeng Li Zeqiong Cai Weixin Fu Ying Liu Chenglei Tian He Wang Tongtong Fu Zhenzhou Wu Donghai Wu Yongxin Jin Zhihui Cheng Naohiro Terada Lin Liu Weihui Wu Shouguang Jin Fang Bai 《Biotechnology and bioengineering》2020,117(3):816-831
Intracellular delivery of functional proteins is of great interest for basic biological research as well as for clinical applications. Transfection is the most commonly used method, however, it is not applicable to large-scale manipulation and inefficient in important cell types implicated in biomedical applications, such as epithelial, immune and pluripotent stem cells. In this study, we explored a bacterial type III secretion system (Bac-T3SS)-mediated proteofection method to overcome these limitations. An attenuated Pseudomonas aeruginosa vector was constructed, which has features of low toxicity, high T3SS activity, and self-limiting growth. Compared to the method of transfection, the Bac-T3SS showed significantly higher efficiencies of Cre recombinase translocation and target site recombination for hard-to-transfect human cell lines. Furthermore, through the delivery of β-lactamase in live animals, we demonstrated the feasibility and biosafety of in vivo application of the Bac-T3SS. This study provided an efficient and low-cost proteofection strategy for laboratory use as well as for application in large-scale cell manipulations. 相似文献
106.
A variety of epidemiologic studies have focused on the association between macrophage migration inhibitory factor (MIF) gene − 173G/C polymorphism and inflammatory bowel disease (IBD). However, results in different studies have been inconsistent. In order to derive a more precise estimation of the associations, we performed this meta-analysis and systematic searches of electronic databases PubMed and Web of Science (up to April 30, 2013). Based on our search criteria, a total of seven eligible studies concerning the MIF − 173G/C polymorphism and IBD risk were included in the final meta-analysis, comprising 2162 IBD cases and 2134 controls. Significant association was found between MIF − 173G/C polymorphism and the risk of IBD when all studies were pooled into the meta-analysis (for C allele vs. G allele: OR = 1.25, 95% CI = 1.12–1.41, p = 0.000; for C/C vs. G/G: OR = 1.71, 95% CI = 1.23–2.39, p = 0.002; for C/C + G/C vs. G/G: OR = 1.24, 95% CI = 1.09–1.42, p = 0.002; for C/C vs. G/C + G/G: OR = 1.67, 95% CI = 1.20–2.33, p = 0.002). Heterogeneity and publication bias did not exist in the overall comparisons. The present meta-analysis suggests an association between the MIF − 173G/C polymorphism and IBD risk. However, due to few studies and the selection bias existed in some studies, the results should be interpreted with caution. 相似文献
107.
108.
Biao Cheng Hao Gong Xiaochao Li Yue Sun Hong Chen Xin Zhang Qian Wu Ling Zheng Kun Huang 《Proteins》2013,81(4):613-621
The misfolding of human islet amyloid polypeptide (hIAPP) is regarded as one of the causative factors of type 2 diabetes mellitus (T2DM). Salvia miltiorrhiza (Danshen), one of the most commonly used of traditional Chinese medicines, is often used in Compound Recipes for treating diabetes, however with unclear mechanisms. Since salvianolic acid B (SalB) is the most abundant bioactive ingredient of salvia miltiorrhiza water‐extract. In this study, we tested whether SalB has any effect on the amyloidogenicity of hIAPP. Our results clearly suggest that SalB can significantly inhibit the formation of hIAPP amyloid and disaggregate hIAPP fibrils. Furthermore, photo‐crosslinking based oligomerization studies suggest SalB significantly suppresses the toxic oligomerization of hIAPP monomers. Cytotoxicity protection effects on pancreatic INS‐1 cells by SalB were also observed using MTT‐based assays, potentially due to the inhibition on the membrane disruption effects and attenuated mitochondria impairment induced by hIAPP. These results provide evidence that SalB may further be studied on the possible pharmacological treatment for T2DM. Proteins 2013. © 2012 Wiley Periodicals, Inc. 相似文献
109.
Cation-induced conformational changes of peptide as a guide to developing insights into human diseases-related proteins have received a lot of attention. The interactions between poly-l-glutamate (PGA) and different cations, including Na+, K+ and Mg2+, respectively, are studied in solvent at a concentration of 1 M, and the behaviours of peptide with different cations are investigated. For Na+, an oscillatory stabilising process to α-helix PGA is found, in accordance with the uniform free-energy landscape, whereas for K+, an extended α-helix structure is formed by the terminal turns, suggesting a weaker attraction to charged head groups. For Mg2+, the bridged charged side chains are responsible for the maximum probability of helix state. These distinct structural changes can be attributed to the different interactions between charged head groups and cations. Both Na+ and K+ are mainly attracted around head groups by direct ion binding while Mg2+ is centrally trapped among adjacent charged head groups. In addition, a surprising shift of the backbone hydrogen bond, from intact state to intermediate state, is observed. This is opposite to the stabilising effect of Na+ around negatively charged head groups. 相似文献
110.
Jing-Jing Yang Hui Tao Cheng Huang Kai-hu Shi Tao-Tao Ma Er-Bao Bian Lei Zhang Li-Ping Liu Wei Hu Xiong-Wen Lv Jun Li 《Cellular signalling》2013,25(5):1202-1211
Hepatic stellate cell (HSC) activation plays an important role in liver fibrogenesis. Transdifferentiation of quiescent hepatic stellate cells into myofibroblastic-HSCs is a key event in liver fibrosis. The methyl-CpG-binding protein MeCP2 which promotes repressed chromatin structure is selectively detected in myofibroblasts of diseased liver. MeCP2 binds to methylated CpG dinucleotides, which are abundant in the promoters of many genes. Treatment of HSCs with DNA methylation inhibitor 5-aza-2′- deoxycytidine (5-azadC) prevented proliferation and activation. Treatment with 5-azadC prevented loss of Patched (PTCH1) expression that occurred during HSCs activation. In a search for underlying molecular medchanisms, we investigated whether the targeting of epigenetic silencing mechanisms could be useful in the treatment of PTCH1-associated fibrogenesis. It was indicated that hypermethylation of PTCH1 is associated with the perpetuation of fibroblast activation and fibrosis in the liver. siRNA knockdown of MeCP2 increased the expressions of PTCH1 mRNA and protein in hepatic myofibroblasts. These data suggest that DNA methylation and MeCP2 may provide molecular mechanisms for silencing of PTCH1. 相似文献