全文获取类型
收费全文 | 18973篇 |
免费 | 2067篇 |
国内免费 | 17篇 |
出版年
2021年 | 182篇 |
2020年 | 125篇 |
2019年 | 181篇 |
2018年 | 199篇 |
2017年 | 240篇 |
2016年 | 384篇 |
2015年 | 583篇 |
2014年 | 667篇 |
2013年 | 776篇 |
2012年 | 1068篇 |
2011年 | 1043篇 |
2010年 | 716篇 |
2009年 | 665篇 |
2008年 | 946篇 |
2007年 | 1001篇 |
2006年 | 941篇 |
2005年 | 920篇 |
2004年 | 921篇 |
2003年 | 949篇 |
2002年 | 908篇 |
2001年 | 399篇 |
2000年 | 341篇 |
1999年 | 343篇 |
1998年 | 321篇 |
1997年 | 242篇 |
1996年 | 233篇 |
1995年 | 226篇 |
1994年 | 209篇 |
1993年 | 186篇 |
1992年 | 301篇 |
1991年 | 261篇 |
1990年 | 272篇 |
1989年 | 307篇 |
1988年 | 250篇 |
1987年 | 220篇 |
1986年 | 238篇 |
1985年 | 228篇 |
1984年 | 215篇 |
1983年 | 214篇 |
1982年 | 215篇 |
1981年 | 192篇 |
1980年 | 170篇 |
1979年 | 186篇 |
1978年 | 141篇 |
1977年 | 133篇 |
1976年 | 150篇 |
1975年 | 114篇 |
1974年 | 134篇 |
1973年 | 128篇 |
1972年 | 126篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Formate is a major product of mixed-acid fermentation in Escherichia coli. Because formate can act as an uncoupler at high concentration it must be excreted from the cell. The FNT (formate-nitrite transporter) membrane channel FocA ensures formate is translocated across the cytoplasmic membrane. Two glycyl-radical enzymes (GREs), pyruvate formate-lyase (PflB) and 2-ketobutyrate formate-lyase (TdcE), generate formate as a product of catalysis during anaerobic growth of Escherichia coli. We demonstrate in this study that TdcE, like PflB, interacts specifically with FocA. His-tagged variants of two other predicted GREs encoded in the genome of E. coli were over-produced and purified and were shown not to interact with FocA, indicating that interaction with FocA is not a general property of GREs per se. Together, these data show that only the GREs TdcE and PflB interact with the FNT channel protein and suggest that, like PflB, TdcE can control formate translocation by FocA. 相似文献
992.
993.
Metodi?D. Metodiev Kyle Thompson Charlotte?L. Alston Andrew?A.M. Morris Langping He Zarah Assouline Marlène Rio Nadia Bahi-Buisson Angela Pyle Helen Griffin Stefan Siira Aleksandra Filipovska Arnold Munnich Patrick?F. Chinnery Robert McFarland Agnès R?tig Robert?W. Taylor 《American journal of human genetics》2016,99(1):246
994.
995.
996.
997.
998.
Katharine E. T. Thompson Richard J. Bankoff Edward E. LouisJr. George H. Perry 《International journal of primatology》2016,37(2):281-295
The identification of critical, limited natural resources for different primate species is important for advancing our understanding of behavioral ecology and toward future conservation efforts. The aye-aye (Daubentonia madagascariensis) is an Endangered nocturnal lemur with adaptations for accessing structurally defended foods: continuously growing incisors; an elongated, flexible middle finger; and a specialized auditory system. In some seasons, ca. 90% of the aye-aye’s diet consists of two structurally defended resources: 1) the larvae of wood boring insects, extracted after the aye-aye gnaws through decomposing bark (deadwood), and 2) the seeds of Canarium trees. Aye-ayes have very large individual home ranges relative to most other lemurs, possibly owing to limited resource availability. Identification of limiting dietary factor(s) is critical for our understanding of aye-aye behavioral ecology and future conservation efforts. To investigate whether aye-ayes equally access all deadwood resources within their range, we surveyed two 100 × 100 m forest plots within the territories of two aye-ayes at Sangasanga, Kianjavato, Madagascar. Only 2 of 150 deadwood specimens within the plots (1.3%) appeared to have been accessed by the aye-ayes. To test whether any external or internal deadwood properties explain aye-aye foraging preferences we recorded species, height and diameter, and quantified the internal tree density using a 3D acoustic tomograph for each foraged and nonforaged deadwood resource within the plots, plus 13 specimens (5 foraged and 8 nonforaged) outside the plots. We did not detect any statistically significant preferences for species, diameter, or height. However, results from the acoustic analysis tentatively indicated that aye-ayes are more likely to forage in trees with greater internal (≥6 cm from the bark) densities. This interior region may function as a sounding board in the tap-foraging process to help aye-ayes accurately identify potential grub-containing cavities in the outer 1–4 cm of deadwood. 相似文献
999.
Cynthia L. Thompson Susan H. Williams Kenneth E. Glander Christopher J. Vinyard 《International journal of primatology》2016,37(4-5):495-517
Arboreal primates actively navigate a complex thermal environment that exhibits spatial, daily, and seasonal temperature changes. Thus, temperature measurements from stationary recording devices in or near a forest likely do not reflect the thermal microenvironments that primates actually experience. To better understand the thermal variation primates encounter, we attached automated temperature loggers to anklets worn by free-ranging mantled howling monkeys (Alouatta palliata) to record near-animal ambient temperatures. We compared these measures to conventional, stationary temperature measurements taken from within the forest, in nearby open fields, and at a remote weather station 38.6 km from the field site. We also measured temperatures across vertical forest heights and assessed the effects of wind speed, solar radiation, rain, and vapor pressure on primate subcutaneous temperatures (collected via implanted loggers). Ambient temperatures at measurement sites commonly used by researchers differed from those experienced by animals. Moreover, these differences changed between seasons, indicating dynamic shifts in thermal environment occur through space and time. Temperatures increased with height in the forest, with statistically significant, albeit low magnitude, differences between vertical distances of one meter. Near-animal temperatures showed that monkeys selected relatively warmer microhabitats during nighttime temperature lows and relatively cooler microhabitats during the day. Lastly, the thermal variables wind speed, solar radiation, vapor pressure, and rain were statistically associated with primate subcutaneous temperatures. Our data indicate that the temperatures arboreal primates experience are not well reflected by stationary devices. Attaching automated temperature loggers to animals provides a useful tool for more directly assessing primate microhabitat use. 相似文献
1000.
Evidence for different,host‐dependent functioning of Rx against both wild‐type and recombinant Pepino mosaic virus
下载免费PDF全文
![点击此处可从《Molecular Plant Pathology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Celia R. A. Duff‐Farrier Thierry Candresse Andy M. Bailey Neil Boonham Gary D. Foster 《Molecular Plant Pathology》2016,17(1):120-126
The potato Rx gene provides resistance against Pepino mosaic virus (PepMV) in tomato; however, recent work has suggested that the resistance conferred may not be durable. Resistance breaking can probably be attributed to multiple mutations observed to accumulate in the capsid protein (CP) region of resistance‐breaking isolates, but this has not been confirmed through directed manipulation of an infectious PepMV clone. The present work describes the introduction of two specific mutations, A‐T78 and A‐T114, into the coat protein minimal elicitor region of an Rx‐controlled PepMV isolate of the EU genotype. Enzyme‐linked immunosorbent assay (ELISA) and phenotypic evaluation were conducted in three Rx‐expressing and wild‐type solanaceous hosts: Nicotiana benthamiana, Nicotiana tabacum and Solanum lycopersicum. Mutation A‐T78 alone was sufficient to confer Rx‐breaking activity in N. benthamiana and S. lycopersicum, whereas mutation A‐T114 was found to be associated, in most cases, with a secondary A‐D100 mutation to break Rx‐mediated resistance in S. lycopersicum. These results suggest that the need for a second, fitness‐restoring mutation may be dependent on the PepMV mutant under consideration. Both mutations conferred Rx breaking in S. lycopersicum, whereas neither conferred Rx breaking in N. tabacum and only A‐T78 allowed Rx breaking in N. benthamiana, suggesting that Rx may function in a different manner depending on the genetic background in which it is present. 相似文献