全文获取类型
收费全文 | 7681篇 |
免费 | 728篇 |
国内免费 | 68篇 |
出版年
2023年 | 52篇 |
2022年 | 49篇 |
2021年 | 203篇 |
2020年 | 133篇 |
2019年 | 190篇 |
2018年 | 196篇 |
2017年 | 212篇 |
2016年 | 254篇 |
2015年 | 447篇 |
2014年 | 425篇 |
2013年 | 560篇 |
2012年 | 668篇 |
2011年 | 608篇 |
2010年 | 435篇 |
2009年 | 386篇 |
2008年 | 458篇 |
2007年 | 393篇 |
2006年 | 370篇 |
2005年 | 314篇 |
2004年 | 355篇 |
2003年 | 260篇 |
2002年 | 272篇 |
2001年 | 85篇 |
2000年 | 61篇 |
1999年 | 72篇 |
1998年 | 66篇 |
1997年 | 57篇 |
1996年 | 46篇 |
1995年 | 45篇 |
1994年 | 41篇 |
1993年 | 52篇 |
1992年 | 41篇 |
1991年 | 36篇 |
1990年 | 46篇 |
1989年 | 39篇 |
1988年 | 28篇 |
1987年 | 27篇 |
1986年 | 23篇 |
1985年 | 34篇 |
1984年 | 36篇 |
1983年 | 28篇 |
1982年 | 34篇 |
1981年 | 24篇 |
1980年 | 23篇 |
1979年 | 21篇 |
1978年 | 26篇 |
1977年 | 26篇 |
1976年 | 30篇 |
1975年 | 29篇 |
1971年 | 16篇 |
排序方式: 共有8477条查询结果,搜索用时 578 毫秒
1.
2.
D. S. Coffman Ben H. Leichtling H. V. Rickenberg 《Journal of cellular biochemistry》1981,15(4):369-385
The phosphoproteins of Dictyostelium discoideum were compared at different stages of development by polyacrylamide gel electrophoresis. Certain phosphoproteins of vegetative amoebae were conserved while others appeared and disappeared during development. Four major phosphoproteins with apparent subunit molecular weights of 50,000, 47,000, 38,000, and 34,000 disappeared precociously in response to exogenous cAMP. Two membranal phosphoproteins, with apparent subunit molecular weights of 80,000 and 81,000, appeared precociously in response to added cAMP. One of these phosphoproteins, molecular weight of 80,000, has been identified tentatively as the “contact site A” glycoprotein. Another membranal protein, with apparent subunit molecular weight of 42,000, unaffected in its appearance by cAMP, has been identified tentatively as phosphoactin. 相似文献
3.
4.
5.
Climatic forcing and larval dispersal capabilities shape the replenishment of fishes and their habitat‐forming biota on a tropical coral reef 下载免费PDF全文
Shaun K. Wilson Martial Depcyznski Rebecca Fisher Thomas H. Holmes Mae M. Noble Ben T. Radford Michael Rule George Shedrawi Paul Tinkler Christopher J. Fulton 《Ecology and evolution》2018,8(3):1918-1928
Fluctuations in marine populations often relate to the supply of recruits by oceanic currents. Variation in these currents is typically driven by large‐scale changes in climate, in particular ENSO (El Nino Southern Oscillation). The dependence on large‐scale climatic changes may, however, be modified by early life history traits of marine taxa. Based on eight years of annual surveys, along 150 km of coastline, we examined how ENSO influenced abundance of juvenile fish, coral spat, and canopy‐forming macroalgae. We then investigated what traits make populations of some fish families more reliant on the ENSO relationship than others. Abundance of juvenile fish and coral recruits was generally positively correlated with the Southern Oscillation Index (SOI), higher densities recorded during La Niña years, when the ENSO‐influenced Leeuwin Current is stronger and sea surface temperature higher. The relationship is typically positive and stronger among fish families with shorter pelagic larval durations and stronger swimming abilities. The relationship is also stronger at sites on the coral back reef, although the strongest of all relationships were among the lethrinids (r = .9), siganids (r = .9), and mullids (r = .8), which recruit to macroalgal meadows in the lagoon. ENSO effects on habitat seem to moderate SOI–juvenile abundance relationship. Macroalgal canopies are higher during La Niña years, providing more favorable habitat for juvenile fish and strengthening the SOI effect on juvenile abundance. Conversely, loss of coral following a La Niña‐related heat wave may have compromised postsettlement survival of coral dependent species, weakening the influence of SOI on their abundance. This assessment of ENSO effects on tropical fish and habitat‐forming biota and how it is mediated by functional ecology improves our ability to predict and manage changes in the replenishment of marine populations. 相似文献
6.
7.
8.
Xu Liu Ben Chen Lulan Chen Wan-Ting Ren Juan Liu Guoxiang Wang Wei Fan Xin Wang Yun Wang 《PloS one》2013,8(4)
Phenol red is widely used in cell culture as a pH indicator. Recently, it also has been reported to have estrogen-like bioactivity and be capable of promoting cell proliferation in different cell lines. However, the effect of phenol red on primary neuronal culture has never been investigated. By using patch clamp technique, we demonstrated that hippocampal pyramidal neurons cultured in neurobasal medium containing no phenol red had large depolarization-associated epileptiform bursting activities, which were rarely seen in neurons cultured in phenol red-containing medium. Further experiment data indicate that the suppressive effect of the phenol red on the abnormal epileptiform burst neuronal activities was U-shape dose related, with the most effective concentration at 28 µM. In addition, this concentration related inhibitory effect of phenol red on the epileptiform neuronal discharges was mimicked by 17-β-estradiol, an estrogen receptor agonist, and inhibited by ICI-182,780, an estrogen receptor antagonist. Our results suggest that estrogen receptor activation by phenol red in the culture medium prevents formation of abnormal, epileptiform burst activity. These studies highlight the importance of phenol red as estrogen receptor stimulator and cautions of careful use of phenol red in cell culture media. 相似文献
9.
The distribution of forty-four coccolithophore species in one hundred deep-sea core-tops from the southwest Indian Ocean is described. Three coccolith assemblages have been recognised (Maputo, Agulhas Current and deep water) by the relative abundances of four ecologically significant coccolithophore species (Gephyrocapsa oceanica, Emiliania huxleyi, Calcidiscus leptoporus and Umbilicosphaera sibogae). Their biogeographical distribution appears to be related to water temperature, nutrient concentration and dissolution.The degree of preservation of coccoliths and foraminifera indicates that the carbonate lysocline lies somewhere between 3500 and 4000 m, resulting in the concentration of dissolution-resistant microfossils below this depth.Stable oxygen isotope ratios of the planktonic foraminiferal species Globigerinoides sacculifer range between −1.5 to −1.0‰ PDB (equal to 22.8–25.1°C) and occur in a narrow band on the sea floor beneath the “A” route of the Agulhas Current.These values are about 0.5 per mil PDB lighter than samples analyzed on either side of this band and can be explained by the Agulhas Current's elevated temperature at the ocean surface of 2–3°C. Thus an oxygen isotope imprint of the Agulhas Current exists beneath it on the sea floor.The Agulhas Current is probably the major factor influencing sedimentation, sediment-distribution patterns and geological features in the study area. At present it is voluminous and fast flowing, possibly eroding sediments up to 2500 m below the surface.The oxygen-isotope ratios and nannoplankton counts obtained in this study indicate, however, that the majority of samples are most probably recent or at least not older than 85,000 years. This implies that sediments are accumulating on the ocean floor and that the Agulhas Current does not have a pronounced erosional influence, at least in areas from which cores were retrieved for this study. 相似文献
10.