全文获取类型
收费全文 | 8513篇 |
免费 | 637篇 |
国内免费 | 2篇 |
专业分类
9152篇 |
出版年
2023年 | 47篇 |
2022年 | 101篇 |
2021年 | 186篇 |
2020年 | 106篇 |
2019年 | 156篇 |
2018年 | 169篇 |
2017年 | 163篇 |
2016年 | 272篇 |
2015年 | 405篇 |
2014年 | 453篇 |
2013年 | 565篇 |
2012年 | 662篇 |
2011年 | 633篇 |
2010年 | 444篇 |
2009年 | 343篇 |
2008年 | 498篇 |
2007年 | 487篇 |
2006年 | 501篇 |
2005年 | 427篇 |
2004年 | 421篇 |
2003年 | 400篇 |
2002年 | 356篇 |
2001年 | 107篇 |
2000年 | 82篇 |
1999年 | 91篇 |
1998年 | 80篇 |
1997年 | 88篇 |
1996年 | 64篇 |
1995年 | 42篇 |
1994年 | 52篇 |
1993年 | 49篇 |
1992年 | 53篇 |
1991年 | 46篇 |
1990年 | 39篇 |
1989年 | 37篇 |
1988年 | 39篇 |
1987年 | 39篇 |
1986年 | 37篇 |
1985年 | 46篇 |
1984年 | 38篇 |
1983年 | 29篇 |
1982年 | 39篇 |
1981年 | 33篇 |
1980年 | 27篇 |
1979年 | 25篇 |
1978年 | 15篇 |
1977年 | 16篇 |
1976年 | 14篇 |
1975年 | 14篇 |
1973年 | 18篇 |
排序方式: 共有9152条查询结果,搜索用时 15 毫秒
71.
72.
Chromatin investigation in the nucleus using a phasor approach to structured illumination microscopy
Isotta Cainero Elena Cerutti Mario Faretta Gaetano Ivan Dellino Pier Giuseppe Pelicci Paolo Bianchini Giuseppe Vicidomini Alberto Diaspro Luca Lanzanò 《Biophysical journal》2021,120(12):2566-2576
Chromatin in the nucleus is organized in functional sites at variable level of compaction. Structured illumination microscopy (SIM) can be used to generate three-dimensional super-resolution (SR) imaging of chromatin by changing in phase and in orientation a periodic line illumination pattern. The spatial frequency domain is the natural choice to process SIM raw data and to reconstruct an SR image. Using an alternative approach, we demonstrate that the additional spatial information encoded in the knowledge of the position of the illumination pattern can be efficiently decoded using a generalized version of separation of photon by lifetime tuning (SPLIT) that does not require lifetime measurements. In the resulting SPLIT-SIM, the SR image is obtained by isolating a fraction of the intensity corresponding to the center of the diffraction-limited point spread function. This extends the use of the SPLIT approach from stimulated emission depletion microscopy to SIM. The SPLIT-SIM algorithm is based only on phasor analysis and does not require deconvolution. We show that SPLIT-SIM can be used to generate SR images of chromatin organizational motifs with tunable resolution and can be a valuable tool for the imaging of functional sites in the nucleus. 相似文献
73.
74.
75.
Marta Cambra Sergio Madrigal-Mora Isaac Chinchilla Geiner Golfín-Duarte Christopher G. Lowe Mario Espinoza 《Journal of fish biology》2021,99(3):1140-1144
Tiger sharks (Galeocerdo cuvier) play an important ecological role as top predators, yet knowledge of their reproductive ecology is scarce. Here, the authors report the first observation of a potential neonate G. cuvier at Cocos Island, a predator-dominated oceanic island in the Eastern Tropical Pacific (ETP). The individual was detected using baited remote underwater video stations (BRUVS). The cameras also detected female individuals potentially pregnant, suggesting that parturition may take place at or near the island. Nonetheless, it is still unclear if the presence of a single neonate is an isolated event or evidence that the species is using the island for reproduction. 相似文献
76.
Roadways may pose barriers to long-distance migrators such as some ungulates. Highway underpasses mitigate wildlife-vehicle collisions and can be an important management tool for protecting migration corridors. In northern California, 3 underpasses were built on United States Route 395 (Route 395) in Hallelujah Junction Wildlife Area (HJWA) in the 1970s for a migratory mule deer (Odocoileus hemionus) herd that had been negatively affected by highway traffic. To determine whether these underpasses were still reducing mule deer mortalities >40 years after construction, we investigated deer use of the underpasses from 2006–2019 using cameras, global positioning system (GPS) collars, and roadkill records. We used occupancy models, approximations of GPS-collared mule deer movement paths, and roadkill locations to estimate the highway crossing patterns of deer. From camera data, there was higher use of the underpasses by deer during migration (spring [Mar–Jun], fall [Oct–Dec]) than in summer (Jul–Sep), when only resident deer were present. Higher underpass usage occurred in the spring compared to fall migrations. Eleven of 21 GPS-collared migrating mule deer crossed Route 395. We estimated 30% of the crossings (by 7 of the 11 deer) occurred south of the underpasses where deer could easily access the highway because of short (1-m high) and deteriorating highway fencing. Roadkill data confirmed that deer-vehicle collisions were occurring south of the underpasses and at the underpasses. This was likely due to deteriorating infrastructure at the underpasses that allows wildlife access to the highway. Overall, our study indicated that although underpasses can provide safe passage for migratory deer decades (>40 yr) after their construction, deteriorating infrastructure such as fencing and gates can lead to wildlife mortalities on highways near underpasses. © 2021 The Wildlife Society. 相似文献
77.
Mario Rincón-Barrado Sanna Olsson Tamara Villaverde Belén Moncalvillo Lisa Pokorny Alan Forrest Ricarda Riina Isabel Sanmartín 《植物分类学报:英文版》2021,59(5):915-934
Wide-range geographically discontinuous distributions have long intrigued scientists. We explore the role of ecology, geology, and dispersal in the formation of these large-scale disjunctions, using the angiosperm tribe Putorieae (Rubiaceae) as a case study. From DNA sequences of nuclear ITS and six plastid markers, we inferred a phylogeny with 65% of all known Putorieae species. Divergence times, ancestral ranges, and diversification rate shifts were then estimated using Bayesian inference. We further explored species climatic tolerances and performed ancestral niche reconstruction to discriminate among alternative speciation modes, including geographical and ecological vicariance, and ecogeographical, ecological, and dispersal-mediated speciation. As a result, we identified seven major clades in Putorieae, some of which exhibit striking geographical disjunctions, matching the Rand Flora pattern, with sister species in the Canary Islands andeastern and southern Africa. Initial diversification within the tribe occurred in the early Miocene, coincident with a period of climate warming; however, most clades diverged within the last 10 Myr. Aridification and high extinction rates, coupled with ecological vicariance, explain the oldest disjunctions. Adaptation to new environmental conditions, after allopatry, is observed in several clades. Dispersal, either long-distance or via corridors made available by mountain uplift, is behind the most recent disjunctions. Some of these events were followed by ecological speciation and rapid diversification, with species becoming adapted to xeric or increasingly colder continental climates. We show that an integrative approach may help discriminate among speciation modes invoked to explain disjunctions at macroevolutionary time scales, even when extinction has erased the signature of past events. 相似文献
78.
Alberto Cornejo Julio Caballero Mario Simirgiotis Vanessa Torres Luisa Snchez Nicols Díaz Marcela Guimaraes Marcos Hernndez Carlos Areche Sergio Alfaro Leonardo Caballero Francisco Melo 《Journal of enzyme inhibition and medicinal chemistry》2021,36(1):154
Parkinson''s disease (PD) is a neurodegenerative disorder that affects adult people whose treatment is palliative. Thus, we decided to test three dammarane triterpenes 1, 1a, 1b, and we determined that 1 and 1a inhibit β-aggregation through thioflavine T rather than 1b. Since compound 1 was most active, we determined the interaction between α-synuclein and 1 at 50 µM (Kd) through microscale thermophoresis. Also, we observed differences in height and diameter of aggregates, and α-synuclein remains unfolded in the presence of 1. Also, aggregates treated with 1 do not provoke neurites'' retraction in N2a cells previously induced by retinoic acid. Finally, we studied the potential sites of interaction between 1 with α-synuclein fibrils using molecular modelling. Docking experiments suggest that 1 preferably interact with the site 2 of α-synuclein through hydrogen bonds with residues Y39 and T44. 相似文献
79.
80.