全文获取类型
收费全文 | 17471篇 |
免费 | 1915篇 |
国内免费 | 2428篇 |
出版年
2024年 | 13篇 |
2023年 | 271篇 |
2022年 | 362篇 |
2021年 | 832篇 |
2020年 | 666篇 |
2019年 | 898篇 |
2018年 | 829篇 |
2017年 | 651篇 |
2016年 | 837篇 |
2015年 | 1194篇 |
2014年 | 1441篇 |
2013年 | 1462篇 |
2012年 | 1762篇 |
2011年 | 1584篇 |
2010年 | 1014篇 |
2009年 | 957篇 |
2008年 | 1091篇 |
2007年 | 939篇 |
2006年 | 823篇 |
2005年 | 698篇 |
2004年 | 590篇 |
2003年 | 525篇 |
2002年 | 471篇 |
2001年 | 309篇 |
2000年 | 255篇 |
1999年 | 209篇 |
1998年 | 145篇 |
1997年 | 125篇 |
1996年 | 110篇 |
1995年 | 88篇 |
1994年 | 86篇 |
1993年 | 57篇 |
1992年 | 75篇 |
1991年 | 65篇 |
1990年 | 69篇 |
1989年 | 47篇 |
1988年 | 27篇 |
1987年 | 26篇 |
1986年 | 39篇 |
1985年 | 19篇 |
1984年 | 23篇 |
1983年 | 25篇 |
1982年 | 14篇 |
1981年 | 14篇 |
1980年 | 8篇 |
1979年 | 17篇 |
1977年 | 9篇 |
1976年 | 9篇 |
1975年 | 8篇 |
1973年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
2.
3.
Lauren E. McCullough Erline E. Miller Qiong Wang Jia-yuan Li Li Liu Hui Li Jing Zhang Jennifer S. Smith 《PloS one》2015,10(9)
The incidence of breast cancer has increased in Asian countries and rates of hormone receptor (HR) negative breast cancer exceed those of Western countries. Epidemiologic data suggest that the association between body size and BC risk may vary by HR status, and could differ geographically. While body size may influence BC risk by moderating the synthesis and metabolism of circulating sex-steroid hormones, insulin-like growth factor (IGF)-1 and related binding proteins, there is a dearth of literature among Asian women. We aimed to examine these specific associations in a sample of Chinese women. In Sichuan Province 143 women aged ≥40 years were recruited through outpatient services (2011–2012). Questionnaires, anthropometric measurements, and blood samples were utilized for data collection and linear regression was applied in data analyses. Among women <50 years we observed a non-monotonic positive association between body mass index (BMI) and 17β-estradiol, and a reversed J-shaped association between BMI and IGF-1 (p ≤0.05). We observed similar associations between waist-to-hip ratio and these markers. Our finding of augmented IGF-1 among women with low body mass may have implications for understanding breast tumor heterogeneity in diverse populations and should be evaluated in larger prospective studies with cancer outcomes. 相似文献
4.
Yang Su-Rong Sun Huan-Xin Hu Zhen-Zhen Wang Si-Heng Sun Hui Xue Yin-Jia Ye Chen-Bo 《Sleep and biological rhythms》2017,15(1):57-65
Sleep and Biological Rhythms - Chronic sleep deprivation (SD) is an overwhelming problem in young students. Firstly, we investigated whether different levels of pre-training SD had effects on... 相似文献
5.
6.
Hydroxyacid dehydrogenases are responsible for the conversion of 2-keto acids to 2-hydroxyacids and have a wide range of biotechnological applications. In this study, a D-lactate dehydrogenase (D-LDH) from a Sporolactobacillus inulinus strain was experimentally verified to have both the D-LDH and glutamate dehydrogenase (GDH) activities (reversible deamination). The catalytic mechanism was demonstrated by identification of key residues from the crystal structure analysis and site-directed mutagenesis. The Arg234 and Gly79 residues of this enzyme play a significant role in both D-LDH and GDH activities. His295 and Phe298 in DLDH744 were identified to be key residues for lactate dehydrogenase (LDH) activity only whereas Tyr101 is a unique residue that is critical for GDH activity. Characterization of the biochemical properties contributes to understanding of the catalytic mechanism of this novel D-lactate dehydrogenase enzyme. 相似文献
7.
In this study, we investigated two selection biases that may affect the obesity-mortality link over the life course: mortality selection and healthy participant effects. If these selection mechanisms are stronger among obese adults than among non-obese adults, they may contribute to the weakening obesity-mortality link over the life course. We used data from the National Health and Nutrition Examination Survey 1988–2010 with linked mortality files from 1988–2011. We employed weighted Cox models to test and adjust for these two selection biases. We also used complementary log-log models, adjusted for a normal distribution of frailty, to test for mortality selection effects; accelerated failure-time models to mitigate the mortality selection effect; and ordinary least squares regression to test for healthy participant effects. The link between class II/III obesity and mortality weakens at older ages. We did not find evidence for significant mortality selection or healthy participant effects. Also, even if the healthy participant effects were stronger among obese adults, they are not strong enough to produce a weakening association between obesity and morbidity at higher ages at the time of the survey. Therefore, neither of these selection biases explains the diminishing effect of class II/III obesity on mortality over the life course. 相似文献
8.
Jinjin Shao Zhifei Xu Xueming Peng Min Chen Yuanrun Zhu Li Xu Hong Zhu Bo Yang Peihua Luo Qiaojun He 《PloS one》2016,11(1)
Chemotherapy is the only choice for most of the advanced hepatocellular carcinoma (HCC) patients, while few agents were available, making it an urgent need to develop new chemotherapy strategies. A phase II clinical trial suggested that the efficacy of irinotecan in HCC was limited due to dose-dependent toxicities. Here, we found that gefitinib exhibited synergistic activity in combination with SN-38, an active metabolite of irinotecan, in HCC cell lines. And the enhanced apoptosis induced by gefitinib plus SN-38 was a result from caspase pathway activation. Mechanistically, gefitinib dramatically promoted the ubiquitin–proteasome-dependent degradation of Rad51 protein, suppressed the DNA repair, gave rise to more DNA damages, and ultimately resulted in the synergism of these two agents. In addition, the increased antitumor efficacy of gefitinib combined with irinotecan was further validated in a HepG2 xenograft mice model. Taken together, our data demonstrated for the first time that the combination of irinotecan and gefitinib showed potential benefit in HCC, which suggests that Rad51 is a promising target and provides a rationale for clinical trials investigating the efficacy of the combination of topoisomerase I inhibitors and gefitinib in HCC. 相似文献
9.
10.
Deying Ma Kexin Zhang Mingyue Zhang Shengnan Xin Xiaoli Liu Zongxi Han Yuhao Shao Shengwang Liu 《PloS one》2012,7(10)
In the current study, five novel avian β-defensins (AvBDs) were identified and characterized in tissues from Peking ducks (Anas platyrhynchos). The nucleotide sequences of these cDNAs comprised 198 bp, 182 bp, 201 bp, 204 bp, and 168 bp, and encoded 65, 60, 66, 67, and 55 amino acids, respectively. Homology, characterization and comparison of these genes with AvBD from other avian species confirmed that they were Apl_AvBD1, 3, 5, 6, and 16. Recombinant AvBDs were produced and purified by expressing these genes in Escherichia coli. In addition, peptides were synthesized according to the respective AvBD sequences. Investigation of the antibacterial activity of the Apl_AvBDs showed that all of them exhibited antibacterial activity against all 12 bacteria investigated (P<0.05 or P<0.01). In addition, the antibacterial activity of all of the AvBDs against M. tetragenus and P. multocida decreased significantly in the presence of 150 mM NaCl (P<0.01). None of the AvBDs showed hemolytic activity. Consistent with their broad-spectrum antibacterial activity, the five novel Apl_AvBDs inhibited replication of duck hepatitis virus (DHV) in vitro significantly (P<0.05). The mRNA expression of all five Apl_AvBD in most tissues, including immune organs and the liver, was upregulated in response to DHV infection at different time points. These findings provide evidence that these defensins activate the immune response to combat microbial infection. 相似文献