全文获取类型
收费全文 | 11381篇 |
免费 | 864篇 |
国内免费 | 545篇 |
专业分类
12790篇 |
出版年
2024年 | 22篇 |
2023年 | 113篇 |
2022年 | 276篇 |
2021年 | 441篇 |
2020年 | 326篇 |
2019年 | 399篇 |
2018年 | 445篇 |
2017年 | 353篇 |
2016年 | 480篇 |
2015年 | 707篇 |
2014年 | 755篇 |
2013年 | 903篇 |
2012年 | 1066篇 |
2011年 | 930篇 |
2010年 | 547篇 |
2009年 | 507篇 |
2008年 | 592篇 |
2007年 | 519篇 |
2006年 | 442篇 |
2005年 | 386篇 |
2004年 | 355篇 |
2003年 | 294篇 |
2002年 | 253篇 |
2001年 | 201篇 |
2000年 | 187篇 |
1999年 | 170篇 |
1998年 | 86篇 |
1997年 | 98篇 |
1996年 | 93篇 |
1995年 | 76篇 |
1994年 | 72篇 |
1993年 | 73篇 |
1992年 | 89篇 |
1991年 | 87篇 |
1990年 | 66篇 |
1989年 | 55篇 |
1988年 | 47篇 |
1987年 | 48篇 |
1986年 | 36篇 |
1985年 | 39篇 |
1984年 | 22篇 |
1983年 | 21篇 |
1982年 | 12篇 |
1981年 | 12篇 |
1979年 | 11篇 |
1978年 | 15篇 |
1975年 | 7篇 |
1974年 | 7篇 |
1972年 | 13篇 |
1971年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
82.
83.
84.
85.
The miscibility and mechanical properties of poly vinyl alcohol (PVA) and poly acrylic acid (PAA)-composited membranes were studied with molecular simulation. The Flory–Huggins parameters (δ) were calculated to prove the good miscibility of PVA and PAA. The radial distribution functions of hydroxyl and carboxyl atoms and the average number of H-bonds were observed to indicate the degree of physical cross-linking between PVA and PAA. The influences of intermolecular physical cross-linking on the glass transition temperature and mechanical properties were estimated. The results revealed that the PVA/PAA membrane with a composition of 2:3 has the best plastic properties, which exhibits a good application value. All of the simulated results showed good agreement with the experimental data. It indicates that the method presented in this work has a promising application prospect. 相似文献
86.
Zhai Xiaofeng Zhao Wen Li Kemang Zhang Cheng Wang Congcong Su Shuo Zhou Jiyong Lei Jing Xing Gang Sun Haifeng Shi Zhiyu Gu Jinyan 《中国病毒学》2019,34(6):601-609
Since late 2011, outbreaks of pseudorabies virus(PRV) have occurred in southern China causing major economic losses to the pig industry. We previously reported that variant PRV forms and recombination in China could be the source of continued epidemics. Here, we analyzed samples from intensive pig farms in eastern China between 2017 and 2019, and sequenced the main glycoproteins(gB, gC, gD, and gE) to study the evolution characteristics of PRV. Based on the g C gene, we found that PRV variants belong to clade 2 and detected a founder effect during by the PRV epidemic. In addition,we detected inter-and intra-clade recombination; in particular, inter-clade recombination in the g B genes of strains FJ-ZXF and FJ-W2, which were recombinant with clade 1 strains. We also found specific amino-acid changes and positively selected sites, possibly associated with functional changes. This analysis of the emergence of PRV in China illustrates the need for continuous monitoring and the development of vaccines against specific variants of PRV. 相似文献
87.
88.
Jin Ding Hang Su Fan Wang Taiwei Chu 《Bioorganic & medicinal chemistry letters》2019,29(14):1791-1798
During the last four decades, nuclear medicine has undergone enormous growth, and positron emission tomography (PET) has been in the driving seat for most of the time. 18F-fluorodeoxyglucose (18F-FDG) is the most widely used agent for the detection of hibernating myocardium and metabolically active cancer tissue. But its cost and limited availability are the main limitations. For a long time different researchers and groups of pharmacists have tried to label glucose with a cheaper and long-acting radionuclide like 99mTc. However, they failed to achieve this goal owing to the chemical complexity of 99mTc and the lack of maintaining the physiological activity of diagnostic compounds. A pre-targeting strategy based on strain-promoted [3 + 2] azide-alkyne cycloaddition (SPAAC) reaction was applied to solve this problem. Functional click synthons were synthesized: 2-azido-2-deoxy-d-glucose (GlucN3) as a glucose analogue, and N- (2- (2- (2- (bis (pyridin-2-ylmethyl) amino) ethoxy) ethoxy) ethyl-2- (6H-11,12-didehydrodibenzo [a,e] cycloocten-5-ylideneaminooxy) acetamide (C7) as a 99mTc(CO)3 labeling and azido-binding group. The results of biodistribution experiments in mice bearing S180 tumor show the relatively high tumor/blood ratio (up to 2.95) and tumor/muscle ratio (up to 6.37), and both of them decreases significantly in the glucose blocking experiment. It indicates that GlucN3 behaves similarly to glucose and that in vivo SPAAC reactions can occur effectively. It is supposed that this pre-targeting strategy can indeed enhance target specificity and may be used for glucose metabolism imaging in tumor diagnosis. 相似文献
89.
90.