全文获取类型
收费全文 | 2307篇 |
免费 | 214篇 |
国内免费 | 159篇 |
专业分类
2680篇 |
出版年
2024年 | 3篇 |
2023年 | 23篇 |
2022年 | 78篇 |
2021年 | 114篇 |
2020年 | 83篇 |
2019年 | 95篇 |
2018年 | 110篇 |
2017年 | 79篇 |
2016年 | 125篇 |
2015年 | 163篇 |
2014年 | 151篇 |
2013年 | 180篇 |
2012年 | 208篇 |
2011年 | 179篇 |
2010年 | 108篇 |
2009年 | 78篇 |
2008年 | 117篇 |
2007年 | 108篇 |
2006年 | 82篇 |
2005年 | 82篇 |
2004年 | 61篇 |
2003年 | 60篇 |
2002年 | 48篇 |
2001年 | 44篇 |
2000年 | 38篇 |
1999年 | 36篇 |
1998年 | 26篇 |
1997年 | 25篇 |
1996年 | 29篇 |
1995年 | 22篇 |
1994年 | 16篇 |
1993年 | 12篇 |
1992年 | 13篇 |
1991年 | 10篇 |
1990年 | 13篇 |
1989年 | 5篇 |
1988年 | 7篇 |
1987年 | 13篇 |
1986年 | 6篇 |
1985年 | 7篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1971年 | 2篇 |
1969年 | 1篇 |
1968年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有2680条查询结果,搜索用时 16 毫秒
41.
Yuanyuan Wang Shanghui Guan Yanhong Bi Sixiang Lin Jianjun Ma Qian Xing Chonghua Liu Rui Zhang Zhen Qu Peng Jiang Xue Chen Yufeng Cheng 《Translational oncology》2018,11(6):1358-1363
The purpose of the current study was to retrospectively assess the effect of postoperative radiotherapy (RT) delay on survival for patients with esophageal cancer. From 2008 to 2011, patients with esophageal cancer who had undergone postoperative RT in five different hospitals in China were reviewed. Clinical data, including time interval between surgery to RT, were prospectively collected. Kaplan-Meier method was conducted to estimate the effect of each variable on progression-free survival (PFS) and overall survival (OS), with differences assessed by log-rank test. Univariate Cox proportional-hazards models were performed for both PFS and OS for all assumed predictor variables. Statistically significant predictor variables (P < .05) on univariate analysis were then included in multivariate Cox proportional-hazards models, which were performed to compare the effects of RT delay on PFS and OS. A total of 316 patients were finally enrolled in this prospectively multicentric study. Time to RT after surgery varied from 12 days to over 60 days (median, 26 days). Multivariate analysis showed that delay to RT longer than the median does not appear to be a survival cost. There was also no statistically difference in PFS (P = .513) or OS (P = .236) between patients stratified by quartiles (≤21 days vs ≧35 days). However, patients with particularly long delays (≧42 days) demonstrated a detrimental impact on OS (P = .021) but not PFS (P = .580). Delaying postoperative RT of esophageal cancer does not impact PFS, but results in a significant reduction on OS if delaying longer than 6 weeks. 相似文献
42.
Jun Zhang Da‐Wei Wang Wei Lv Lei Qin Shuzhang Niu Siwei Zhang Tengfei Cao Feiyu Kang Quan‐Hong Yang 《Liver Transplantation》2018,8(26)
Sodium‐ion batteries (SIBs) have the potential to be practically applied in large‐scale energy storage markets. The rapid progress of SIBs research is primarily focused on electrodes, while electrolytes attract less attention. Indeed, the improvement of electrode performance is arguably correlated with the electrolyte optimization. In conventional lithium‐ion batteries (LIBs), ether‐based electrolytes are historically less practical owing to the insufficient passivation of both anodes and cathodes. As an important class of aprotic electrolytes, ethers have revived with the emerging lithium‐sulfur and lithium‐oxygen batteries in recent years, and are even booming in the wave of SIBs. Ether‐based electrolytes are unique to enabling these new battery chemistries in terms of producing stable ternary graphite intercalation compounds, modifying anode solid electrolyte interphases, reducing the solubility of intermediates, and decreasing polarization. Better still, ether‐based electrolytes are compatible with specific inorganic cathodes and could catalyze the assembly of full SIBs prototypes. This Research News article aims to summarize the recent critical reports on ether‐based electrolytes in sodium‐based batteries, to unveil the uniqueness of ether‐based electrolytes to advancing diverse electrode materials, and to shed light on the viability and challenges of ether‐based electrolytes in future sodium‐based battery chemistries. 相似文献
43.
研究了37种杀虫剂对粘虫、棉铃虫活性的相关性。结果表明,粘虫对杀虫剂的活性和棉铃虫是一致的,其直线回归式:Y=164.36+0.646X相关系数(R)为0.953。R值受棉铃虫对拟菊酯抗性的影响。 相似文献
44.
45.
46.
Melanie Caron Gilda Grard Christophe Paupy Illich Mamfred Mombo Branly Bikie Bi Nso Fabrice Roland Kassa Kassa Dieudonne Nkoghe Eric Maurice Leroy 《PloS one》2013,8(10)
Gabon, in Central Africa, was affected for the first time in 2007 and then in 2010 by simultaneous outbreaks of chikungunya and Dengue serotype 2 (DENV-2) viruses. Through the national surveillance of dengue-like syndromes between 2007 and 2010, we observed continuous circulation of DENV-2 in a southward movement. This rapid spread of DENV-2 was associated with the emergence of DENV-1 in 2007 and DENV-3 in 2010. Interestingly, we detected six DENV-2 infected patients with hemorrhagic signs during the second outbreak in 2010. Although these cases do not meet all standard WHO criteria for severe Dengue with hemorrhage (formerly DHF), this is the first report of several dengue fever cases associated with hemorrhagic signs during a simultaneous circulation of different DENV serotypes in Africa. Together, these findings suggest that DENV is becoming more widely established on this continent and that DHF will likely become a serious public-health problem in the near future. 相似文献
47.
【目的】构建用于比较黄曲霉(Aspergillus flavus,A. flavus)菌株之间致病力差异的小鼠感染模型,并利用该模型评价真菌病毒AfPV1对宿主A. flavus致病力的影响。【方法】用不同浓度环磷酰胺腹腔注射Institute of Cancer Research (ICR)小鼠,根据白细胞的数量判断小鼠免疫抑制程度;通过滴鼻和尾静脉两种感染方法接种不同浓度的A. flavus孢子量,统计14 d以内小鼠的死亡率,确定A. flavus最佳的孢子接种量;通过小鼠组织的菌落负荷量以及肺部组织的病理观察,确定A. flavus感染是否成功;最后利用该小鼠模型评价真菌病毒AfPV1对寄主A. flavus致病力的影响。【结果】腹腔注射环磷酰胺的浓度为250 mg/kg时,能够达到免疫抑制水平;小鼠组织真菌负荷和病理组织切片观察显示A. flavus成功感染接种的ICR小鼠组织;在滴鼻接种模型中,A. flavus的孢子接种量为40μL(1×106CFU/mL)时比较合适评价A. flavus菌株之间的差异;在尾静脉接种的模型中,A. flavus的孢子... 相似文献
48.
Wenzhi Jiang Huanbin Zhou Honghao Bi Michael Fromm Bing Yang Donald P. Weeks 《Nucleic acids research》2013,41(20):e188
The type II CRISPR/Cas system from Streptococcus pyogenes and its simplified derivative, the Cas9/single guide RNA (sgRNA) system, have emerged as potent new tools for targeted gene knockout in bacteria, yeast, fruit fly, zebrafish and human cells. Here, we describe adaptations of these systems leading to successful expression of the Cas9/sgRNA system in two dicot plant species, Arabidopsis and tobacco, and two monocot crop species, rice and sorghum. Agrobacterium tumefaciens was used for delivery of genes encoding Cas9, sgRNA and a non-fuctional, mutant green fluorescence protein (GFP) to Arabidopsis and tobacco. The mutant GFP gene contained target sites in its 5′ coding regions that were successfully cleaved by a CAS9/sgRNA complex that, along with error-prone DNA repair, resulted in creation of functional GFP genes. DNA sequencing confirmed Cas9/sgRNA-mediated mutagenesis at the target site. Rice protoplast cells transformed with Cas9/sgRNA constructs targeting the promoter region of the bacterial blight susceptibility genes, OsSWEET14 and OsSWEET11, were confirmed by DNA sequencing to contain mutated DNA sequences at the target sites. Successful demonstration of the Cas9/sgRNA system in model plant and crop species bodes well for its near-term use as a facile and powerful means of plant genetic engineering for scientific and agricultural applications. 相似文献
49.
Gao X. Zhang Y. Mu J. Q. Chen K. X. Zhang H. F. Bi K. S. 《Russian Journal of Bioorganic Chemistry》2021,47(2):420-431
Russian Journal of Bioorganic Chemistry - Guan-Xin-Shu-Tong capsule is a widely used traditional Chinese medicine for the treatment of cardiovascular diseases. However, little knowledge about the... 相似文献
50.
Regarded as an emerging diarrheal micropathogen, Vibrio cholerae serogroup O139 was first identified in 1992 and has become an important cause of cholera epidemics over the last two decades. O139 strains have been continually isolated since O139 cholera appeared in China in 1993, from sporadic cases and dispersed foodborne outbreaks, which are the common epidemic types of O139 cholera in China. Antibiotic resistance profiles of these epidemic strains are required for development of clinical treatments, epidemiological studies and disease control. In this study, a comprehensive investigation of the antibiotic resistance of V. cholerae O139 strains isolated in China from 1993 to 2009 was conducted. The initial O139 isolates were resistant to streptomycin, trimethoprim-sulfamethoxazole and polymyxin B only, while multidrug resistance increased suddenly and became common in strains isolated after 1998. Different resistance profiles were observed in the isolates from different years. In contrast, most V. cholerae O1 strains isolated in the same period were much less resistant to these antibiotics and no obvious multidrug resistance patterns were detected. Most of the non-toxigenic strains isolated from the environment and seafood were resistant to four antibiotics or fewer, although a few multidrug resistant strains were also identified. These toxigenic O139 strains exhibited a high prevalence of the class I integron and the SXT element, which were rare in the non-toxigenic strains. Molecular subtyping of O139 strains showed highly diverse pulsed-field gel electrophoresis patterns, which may correspond to the epidemic state of sporadic cases and small-scale outbreaks and complex resistance patterns. Severe multidrug resistance, even resistance transfers based on mobile antibiotic resistance elements, increases the probability of O139 cholera as a threat to public health. Therefore, continual epidemiological and antibiotic sensitivity surveillance should focus on the occurrence of multidrug resistance and frequent microbial population shifts in O139 strains. 相似文献