全文获取类型
收费全文 | 4934篇 |
免费 | 445篇 |
国内免费 | 2篇 |
专业分类
5381篇 |
出版年
2024年 | 6篇 |
2023年 | 47篇 |
2022年 | 104篇 |
2021年 | 175篇 |
2020年 | 93篇 |
2019年 | 143篇 |
2018年 | 153篇 |
2017年 | 100篇 |
2016年 | 214篇 |
2015年 | 327篇 |
2014年 | 345篇 |
2013年 | 358篇 |
2012年 | 473篇 |
2011年 | 477篇 |
2010年 | 251篇 |
2009年 | 217篇 |
2008年 | 293篇 |
2007年 | 303篇 |
2006年 | 233篇 |
2005年 | 201篇 |
2004年 | 163篇 |
2003年 | 136篇 |
2002年 | 125篇 |
2001年 | 34篇 |
2000年 | 32篇 |
1999年 | 31篇 |
1998年 | 19篇 |
1997年 | 18篇 |
1996年 | 14篇 |
1995年 | 18篇 |
1994年 | 11篇 |
1993年 | 14篇 |
1992年 | 18篇 |
1991年 | 15篇 |
1990年 | 18篇 |
1989年 | 13篇 |
1988年 | 10篇 |
1987年 | 11篇 |
1986年 | 12篇 |
1985年 | 14篇 |
1984年 | 8篇 |
1983年 | 6篇 |
1982年 | 13篇 |
1981年 | 6篇 |
1978年 | 7篇 |
1977年 | 9篇 |
1971年 | 6篇 |
1968年 | 8篇 |
1966年 | 5篇 |
1965年 | 7篇 |
排序方式: 共有5381条查询结果,搜索用时 0 毫秒
111.
Plenderleith Fiona A. Irrazabal Valentina A. Burslem David F. R. P. Travis Justin M. J. Powell Priscila Ana 《Biological invasions》2022,24(7):2201-2216
Biological Invasions - Understanding the drivers of invasive species spread is key to designing optimal management programmes for controlling them. Population models, parameterized from demographic... 相似文献
112.
Long‐term trends in restoration and associated land treatments in the southwestern United States 下载免费PDF全文
Stella M. Copeland Seth M. Munson David S. Pilliod Justin L. Welty John B. Bradford Bradley J. Butterfield 《Restoration Ecology》2018,26(2):311-322
Restoration treatments, such as revegetation with seeding or invasive species removal, have been applied on U.S. public lands for decades. Temporal trends in these management actions have not been extensively summarized previously, particularly in the southwestern United States where invasive plant species, drought, and fire have altered dryland ecosystems. We assessed long‐term (1940–2010) trends in restoration using approximately 4,000 vegetation treatments conducted on Bureau of Land Management lands across the southwestern United States. We found that since 1940, the proportions of seeding and vegetation/soil manipulation (e.g. vegetation removal or plowing) treatments have declined, while the proportions of prescribed burn and invasive species treatments have increased. Treatments in pinyon‐juniper and big sagebrush communities declined in comparison to treatments in desert scrub, creosote bush, and riparian woodland communities. Restoration‐focused treatment objectives increased relative to resource extraction objectives. Species richness and proportion of native species used in seeding treatments also increased. Inflation‐adjusted costs per area rose 750% for vegetation/soil manipulation, 600% for seeding, and 400% for prescribed burn treatments in the decades from 1981 to 2010. Seeding treatments were implemented in warmer and drier years when compared to the climate conditions of the entire study period and warmer and wetter years relative to several years before and after the treatment. These results suggest that treatments over a 70‐year period on public lands in the southwestern United States are shifting toward restoration practices that are increasingly large, expensive, and related to fire and invasive species control. 相似文献
113.
Kline J Zhang L Battaglia L Cohen KS Gajewski TF 《Journal of immunology (Baltimore, Md. : 1950)》2012,188(6):2630-2642
We have recently demonstrated that adoptive transfer of regulatory T cell-depleted polyclonal T cells into lymphopenic mice leads to rejection of B16 melanoma, which generated an opportunity to study host requirements for tumor rejection when it effectively occurred. CD8(+) T cell priming and tumor rejection required tumor Ag cross-presentation, as evidenced by tumor outgrowth in Kb(-/-) bone marrow chimeric or B71/2(-/-) mice. CD4(+) T cells were additionally required for optimal tumor control, although not through classical CD4 "help," as the frequency of primed CD8(+) T cells was similar in the absence of CD4(+) T cells, and tumor rejection did not depend upon CD40-CD40L interactions or on IL-2 production by CD4(+) T cells. Rather, CD4(+) T cells appeared to act at the effector phase of tumor rejection and responded to B16-derived Ags in vitro. At the effector phase, IFN-γ production by transferred T cells, but not host cells, was necessary. IFN-γ acted either on host or tumor cells and was associated with reduced tumor vascularity. Finally, tumor rejection occurred after transfer of TNF-α, perforin, or FasL-deficient T cells. However, perforin/FasL double-knockout T cells failed to reject, arguing that the killing of B16 melanoma cells could occur either via the cytotoxic granule or Fas pathways. Collectively, these results support a model in which host tumor Ag cross-presentation primes adoptively transferred T cells, which remain functional in the setting of homeostatic proliferation and regulatory T cell depletion, and which promote tumor rejection via IFN-γ and lysis via cytotoxic granules and/or FasL. 相似文献
114.
115.
116.
Mathieu E. Wimmer Justin Rising Raymond J. Galante Abraham Wyner Allan I. Pack Ted Abel 《PloS one》2013,8(12)
One of the most significant problems facing older individuals is difficulty staying asleep at night and awake during the day. Understanding the mechanisms by which the regulation of sleep/wake goes awry with age is a critical step in identifying novel therapeutic strategies to improve quality of life for the elderly. We measured wake, non-rapid eye movement (NREM) and rapid-eye movement (REM) sleep in young (2–4 months-old) and aged (22–24 months-old) C57BL6/NIA mice. We used both conventional measures (i.e., bout number and bout duration) and an innovative spike-and-slab statistical approach to characterize age-related fragmentation of sleep/wake. The short (spike) and long (slab) components of the spike-and-slab mixture model capture the distribution of bouts for each behavioral state in mice. Using this novel analytical approach, we found that aged animals are less able to sustain long episodes of wakefulness or NREM sleep. Additionally, spectral analysis of EEG recordings revealed that aging slows theta peak frequency, a correlate of arousal. These combined analyses provide a window into the mechanisms underlying the destabilization of long periods of sleep and wake and reduced vigilance that develop with aging. 相似文献
117.
Laura A. McAllister Justin I. Montgomery Joseph A. Abramite Usa Reilly Matthew F. Brown Jinshan M. Chen Rose A. Barham Ye Che Seung Won Chung Carol A. Menard Mark Mitton-Fry Lisa M. Mullins Mark C. Noe John P. O’Donnell Robert M. Oliver Joseph B. Penzien Mark Plummer Loren M. Price Veerabahu Shanmugasundaram Andrew P. Tomaras Daniel P. Uccello 《Bioorganic & medicinal chemistry letters》2012,22(22):6832-6838
The synthesis and antibacterial activity of heterocyclic methylsulfone hydroxamates is presented. Compounds in this series are potent inhibitors of the LpxC enzyme, a key enzyme involved in the production of lipopolysaccharide (LPS) found in the outer membrane of Gram-negative bacteria. SAR evaluation of compounds in this series revealed analogs with potent antibacterial activity against challenging Gram-negative species such as Pseudomonas aeruginosa and Klebsiella pneumoniae. 相似文献
118.
Tra-My N. Duong Thanh-Van Le Khanh-Linh H. Tran Phuong-Tuyen Nguyen Bich-Phuong T. Nguyen Thu-Anh Nguyen Huong-Lan P. Nguyen Bich-Ngoc T. Nguyen Matthew C. Fisher Johanna Rhodes Guy Marks Greg J. Fox Sharon C.-A. Chen Michael G. Walsh Vanessa R. Barrs Jessica Talbot Catriona L. Halliday Tania C. Sorrell Jeremy N. Day Justin Beardsley 《Environmental microbiology》2021,23(12):7632-7642
Azole-resistant environmental Aspergillus fumigatus presents a threat to public health but the extent of this threat in Southeast Asia is poorly described. We conducted environmental surveillance in the Mekong Delta region of Vietnam, collecting air and ground samples across key land-use types, and determined antifungal susceptibilities of Aspergillus section Fumigati (ASF) isolates and azole concentrations in soils. Of 119 ASF isolates, 55% were resistant (or non-wild type) to itraconazole, 65% to posaconazole and 50% to voriconazole. Azole resistance was more frequent in A. fumigatus sensu stricto isolates (95%) than other ASF species (32%). Resistant isolates and agricultural azole residues were overrepresented in samples from cultivated land. cyp51A gene sequence analysis showed 38/56 resistant A. fumigatus sensu stricto isolates carried known resistance mutations, with TR34/L98H most frequent (34/38). 相似文献
119.
120.