全文获取类型
收费全文 | 2717篇 |
免费 | 245篇 |
国内免费 | 2篇 |
出版年
2024年 | 5篇 |
2023年 | 31篇 |
2022年 | 45篇 |
2021年 | 122篇 |
2020年 | 68篇 |
2019年 | 86篇 |
2018年 | 93篇 |
2017年 | 67篇 |
2016年 | 125篇 |
2015年 | 167篇 |
2014年 | 174篇 |
2013年 | 209篇 |
2012年 | 222篇 |
2011年 | 191篇 |
2010年 | 127篇 |
2009年 | 121篇 |
2008年 | 159篇 |
2007年 | 135篇 |
2006年 | 117篇 |
2005年 | 132篇 |
2004年 | 92篇 |
2003年 | 66篇 |
2002年 | 68篇 |
2001年 | 30篇 |
2000年 | 16篇 |
1999年 | 18篇 |
1998年 | 20篇 |
1997年 | 11篇 |
1996年 | 8篇 |
1995年 | 14篇 |
1994年 | 10篇 |
1993年 | 12篇 |
1992年 | 16篇 |
1991年 | 12篇 |
1990年 | 11篇 |
1989年 | 14篇 |
1988年 | 16篇 |
1987年 | 9篇 |
1986年 | 9篇 |
1985年 | 7篇 |
1984年 | 4篇 |
1981年 | 5篇 |
1980年 | 7篇 |
1979年 | 7篇 |
1972年 | 7篇 |
1971年 | 6篇 |
1968年 | 4篇 |
1964年 | 3篇 |
1963年 | 4篇 |
1950年 | 3篇 |
排序方式: 共有2964条查询结果,搜索用时 281 毫秒
1.
2.
Luke L. M. Heaton Eduardo López Philip K. Maini Mark D. Fricker Nick S. Jones 《Proceedings. Biological sciences / The Royal Society》2010,277(1698):3265-3274
Cord-forming fungi form extensive networks that continuously adapt to maintain an efficient transport system. As osmotically driven water uptake is often distal from the tips, and aqueous fluids are incompressible, we propose that growth induces mass flows across the mycelium, whether or not there are intrahyphal concentration gradients. We imaged the temporal evolution of networks formed by Phanerochaete velutina, and at each stage calculated the unique set of currents that account for the observed changes in cord volume, while minimizing the work required to overcome viscous drag. Predicted speeds were in reasonable agreement with experimental data, and the pressure gradients needed to produce these flows are small. Furthermore, cords that were predicted to carry fast-moving or large currents were significantly more likely to increase in size than cords with slow-moving or small currents. The incompressibility of the fluids within fungi means there is a rapid global response to local fluid movements. Hence velocity of fluid flow is a local signal that conveys quasi-global information about the role of a cord within the mycelium. We suggest that fluid incompressibility and the coupling of growth and mass flow are critical physical features that enable the development of efficient, adaptive biological transport networks. 相似文献
3.
Enterochelin synthetase activity is controlled by both repression and feed-back inhibition mechanisms. Inclusion of iron in growth media results in synthesis of all four (D, E, F and G) components of enterochelin synthetase being repressed. The specific inhibition of L-serine activation (partial reaction catalyzed by the F component) by the end products, ferric-enterochelin and 2,3-dihydroxybenzoylserine, is shown to inhibit overall enterochelin synthetase activity. 相似文献
4.
D C Rideout M Lambert D A Kendall G R Moe D G Osterman H P Tao I B Weinstein E T Kaiser 《Journal of cellular physiology》1985,124(3):365-371
Four amphiphilic peptides, each with net charges of +2 or more at neutrality and molecular weights under 4 kilodaltons, were found to mediate the adhesion of normal rat kidney fibroblasts to polystyrene surfaces. Two of these peptides, a model for calcitonin (peptide 1, MCT) and melittin (peptide 2, MEL), form amphiphilic alpha-helical structures at aqueous/nonpolar interfaces. The other two, a luteinizing hormone-releasing hormone model (peptide 3, LHM) and a platelet factor model (peptide 4, MPF) form beta-strand structures in amphiphilic environments. Although it contains only 10 residues, LHM mediated adhesion to surfaces coated with solutions containing as little as 10 pmoles/ml of peptide. All four of these peptides were capable of forming monolayers at air-buffer interfaces with collapse pressures greater than 20 dynes/cm. None of these four peptides contains the tetrapeptide sequence Arg-Gly-Asp-Ser, which has been associated with fibronectin-mediated cell adhesion. Ten polypeptides that also lacked the sequence Arg-Gly-Asp-Ser but were nonamphiphilic and/or had net charges less than +2 at neutrality were all incapable of mediating cell adhesion (Pierschbacher and Ruoslahti, 1984). The morphologies of NRK cells spread on polystyrene coated with peptide LHM resemble the morphologies on fibronectin-coated surfaces, whereas cells spread on surfaces coated with MCT or MEL exhibit strikingly different morphologies. The adhesiveness of MCT, MEL, LHM, and MPF implies that many amphiphilic cationic peptides could prove useful as well defined adhesive substrata for cell culture and for studies of the mechanism of cell adhesion. 相似文献
5.
6.
7.
8.
9.
10.