全文获取类型
收费全文 | 99877篇 |
免费 | 3285篇 |
国内免费 | 1623篇 |
出版年
2022年 | 535篇 |
2021年 | 1002篇 |
2020年 | 700篇 |
2019年 | 804篇 |
2018年 | 1637篇 |
2017年 | 1574篇 |
2016年 | 3513篇 |
2015年 | 7210篇 |
2014年 | 7013篇 |
2013年 | 6796篇 |
2012年 | 6237篇 |
2011年 | 3307篇 |
2010年 | 2882篇 |
2009年 | 2771篇 |
2008年 | 1358篇 |
2007年 | 1206篇 |
2006年 | 1177篇 |
2005年 | 7210篇 |
2004年 | 5760篇 |
2003年 | 3939篇 |
2002年 | 1412篇 |
2001年 | 1366篇 |
2000年 | 582篇 |
1999年 | 1723篇 |
1998年 | 486篇 |
1992年 | 2028篇 |
1991年 | 2115篇 |
1990年 | 2148篇 |
1989年 | 2068篇 |
1988年 | 1998篇 |
1987年 | 1865篇 |
1986年 | 1660篇 |
1985年 | 1679篇 |
1984年 | 1123篇 |
1983年 | 850篇 |
1982年 | 471篇 |
1979年 | 1075篇 |
1978年 | 759篇 |
1977年 | 606篇 |
1976年 | 629篇 |
1975年 | 872篇 |
1974年 | 994篇 |
1973年 | 1005篇 |
1972年 | 953篇 |
1971年 | 928篇 |
1970年 | 820篇 |
1969年 | 830篇 |
1968年 | 734篇 |
1967年 | 751篇 |
1966年 | 584篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
The present study has shown that on the level of the parasitic system the epidemic process is a biological system, wherein the host population serves as the internal regulator, the mechanism of transmission serves as the external regulator and the parasite population, as the regulated object. The biological regulating mechanisms of the epidemic process have fundamental differences in the groups of infectious with various mechanisms of transmission, and the specific nature of the mechanism of transmission determines the peculiar features of the biological mechanism which governs the self-regulation of the epidemic process. In contrast, on a higher level of the organization of the epidemic process, i. e. on the level of the socio-ecological system, the epidemic process is a biosocial system, wherein the human society serves as the regulator, the parasitic system serves as the regulated object and the mechanism of transmission plays the role of the filter which determines the scope of social factors, most important in the regulation of the epidemic process in a given infection. The spontaneous regulation of the epidemic process is the freed forward channel from the regulator to the regulated object, and the controlled regulation is the feedback channel. 相似文献
82.
83.
Protoplasts of Schizosaccharomyces pombe, grown on a rich nutrient medium, were treated with a peptide factor isolated from cultures of the protozoan Tetrahymena pyriformis. The peptide factor is known to inhibit RNA synthesis in Tetrahymena. It has now been shown that the peptide factor also inhibits RNA synthesis in yeast protoplasts without affecting protein synthesis. 相似文献
84.
Peng Wang Ronghua Luo Min Zhang Yaqing Wang Tianzhang Song Tingting Tao Zhongyu Li Lin Jin Hongyi Zheng Wenwen Chen Mengqian Zhao Yongtang Zheng Jianhua Qin 《Cell death & disease》2020,11(12)
COVID-19, caused by SARS-CoV-2, is an acute and rapidly developing pandemic, which leads to a global health crisis. SARS-CoV-2 primarily attacks human alveoli and causes severe lung infection and damage. To better understand the molecular basis of this disease, we sought to characterize the responses of alveolar epithelium and its adjacent microvascular endothelium to viral infection under a co-culture system. SARS-CoV-2 infection caused massive virus replication and dramatic organelles remodeling in alveolar epithelial cells, alone. While, viral infection affected endothelial cells in an indirect manner, which was mediated by infected alveolar epithelium. Proteomics analysis and TEM examinations showed viral infection caused global proteomic modulations and marked ultrastructural changes in both epithelial cells and endothelial cells under the co-culture system. In particular, viral infection elicited global protein changes and structural reorganizations across many sub-cellular compartments in epithelial cells. Among the affected organelles, mitochondrion seems to be a primary target organelle. Besides, according to EM and proteomic results, we identified Daurisoline, a potent autophagy inhibitor, could inhibit virus replication effectively in host cells. Collectively, our study revealed an unrecognized cross-talk between epithelium and endothelium, which contributed to alveolar–capillary injury during SARS-CoV-2 infection. These new findings will expand our understanding of COVID-19 and may also be helpful for targeted drug development.Subject terms: Mechanisms of disease, Viral infection 相似文献
85.
86.
87.
88.
89.
The cytotoxic and radiosensitizing effects of hyperthermia was shown on Ehrlich ascites tumor cells heated in vitro. The effect of hyperthermia resulted in the formation of local lesions in membranes of dying cells. 相似文献
90.
Molecular dynamics (MD) simulations of phosphatidylinositol (4,5)-bisphosphate (PIP2) and phosphatidylinositol (3,4,5)-trisphosphate (PIP3) in 1-palmitoyl 2-oleoyl phosphatidylcholine (POPC) bilayers indicate that the inositol rings are tilted ∼40° with respect to the bilayer surface, as compared with 17° for the P-N vector of POPC. Multiple minima were obtained for the ring twist (analogous to roll for an airplane). The phosphates at position 1 of PIP2 and PIP3 are within an Ångström of the plane formed by the phosphates of POPC; lipids in the surrounding shell are depressed by 0.5-0.8 Å, but otherwise the phosphoinositides do not substantially perturb the bilayer. Finite size artifacts for ion distributions are apparent for systems of ∼26 waters/lipid, but, based on simulations with a fourfold increase of the aqueous phase, the phosphoinositide positions and orientations do not show significant size effects. Electrostatic potentials evaluated from Poisson-Boltzmann (PB) calculations show a strong dependence of potential height and ring orientation, with the maxima on the −25 mV surfaces (17.1 ± 0.1 Å for PIP2 and 19.4 ± 0.3 Å for PIP3) occurring near the most populated orientations from MD. These surfaces are well above the background height of 10 Å estimated for negatively charged cell membranes, as would be expected for lipids involved in cellular signaling. PB calculations on microscopically flat bilayers yield similar maxima as the MD-based (microscopically rough) systems, but show less fine structure and do not clearly indicate the most probable regions. Electrostatic free energies of interaction with pentalysine are also similar for the rough and flat systems. These results support the utility of a rigid/flat bilayer model for PB-based studies of PIP2 and PIP3 as long as the orientations are judiciously chosen. 相似文献