全文获取类型
收费全文 | 2343篇 |
免费 | 207篇 |
专业分类
2550篇 |
出版年
2023年 | 13篇 |
2022年 | 28篇 |
2021年 | 77篇 |
2020年 | 41篇 |
2019年 | 41篇 |
2018年 | 42篇 |
2017年 | 42篇 |
2016年 | 52篇 |
2015年 | 118篇 |
2014年 | 121篇 |
2013年 | 114篇 |
2012年 | 133篇 |
2011年 | 152篇 |
2010年 | 99篇 |
2009年 | 79篇 |
2008年 | 105篇 |
2007年 | 140篇 |
2006年 | 104篇 |
2005年 | 91篇 |
2004年 | 87篇 |
2003年 | 87篇 |
2002年 | 73篇 |
2001年 | 37篇 |
2000年 | 27篇 |
1999年 | 20篇 |
1998年 | 26篇 |
1997年 | 18篇 |
1996年 | 14篇 |
1995年 | 15篇 |
1994年 | 12篇 |
1992年 | 15篇 |
1991年 | 17篇 |
1990年 | 18篇 |
1989年 | 18篇 |
1988年 | 13篇 |
1986年 | 17篇 |
1984年 | 14篇 |
1983年 | 15篇 |
1982年 | 18篇 |
1981年 | 12篇 |
1979年 | 10篇 |
1978年 | 15篇 |
1977年 | 11篇 |
1976年 | 18篇 |
1974年 | 15篇 |
1968年 | 13篇 |
1967年 | 10篇 |
1964年 | 14篇 |
1963年 | 10篇 |
1962年 | 11篇 |
排序方式: 共有2550条查询结果,搜索用时 15 毫秒
81.
Small invertebrate consumers produce consistent size spectra across reef habitats and climatic zones
Changes in invertebrate body size-distributions that follow loss of habitat-forming species can potentially affect a range of ecological processes, including predation and competition. In the marine environment, small crustaceans and other mobile invertebrates (‘epifauna') represent a basal component in reef food webs, with a pivotal secondary production role that is strongly influenced by their body size-distribution. Ongoing degradation of reef habitats that affect invertebrate size-distributions, particularly transformation of coral and kelp habitat to algal turf, may thus fundamentally affect secondary production. Here we explored variation in size spectra of shallow epifaunal assemblages (i.e. the slope and intercept of the linear relationship between log abundance and body size at the assemblage level) across 21 reef microhabitats distributed along an extensive eastern Australian climatic gradient from the tropical northern Great Barrier Reef to cool temperate Tasmania. When aggregated across microhabitats at the site scale, invertebrate body size spectra (0.125–8 mm range) were consistently log-linear (R2 ranging 0.87–0.98). Size spectra differed between, but not within, major groups of microhabitats, and exhibited little variability between tropical and temperate biomes. Nevertheless, size spectra showed significant tropical/temperate differences in slopes for epifauna sampled on macroalgal habitats, and in elevation for soft coral and sponge habitats. Our results reveal epifaunal size spectra to be a highly predictable macro-ecological feature. Given that variation in epifaunal size spectra among groups of microhabitats was greater than variation between tropical and temperate biomes, we postulate that ocean warming will not greatly alter epifaunal size spectra directly. However, transformation of tropical coral and temperate macroalgal habitats to algal turfs due to warming will alter reef food web dynamics through redistribution of the size of prey available to fishes. 相似文献
82.
Saskia von Stillfried Sophia Villwock Roman D. Bülow Sonja Djudjaj Eva M. Buhl Angela Maurer Nadina Ortiz-Brüchle Peter Celec Barbara M. Klinkhammer Dickson W.L. Wong Claudio Cacchi Till Braunschweig Ruth Knüchel-Clarke Edgar Dahl Peter Boor 《Microbial biotechnology》2021,14(4):1627-1641
Virus detection methods are important to cope with the SARS-CoV-2 pandemics. Apart from the lung, SARS-CoV-2 was detected in multiple organs in severe cases. Less is known on organ tropism in patients developing mild or no symptoms, and some of such patients might be missed in symptom-indicated swab testing. Here, we tested and validated several approaches and selected the most reliable RT-PCR protocol for the detection of SARS-CoV-2 RNA in patients’ routine diagnostic formalin-fixed and paraffin-embedded (FFPE) specimens available in pathology, to assess (i) organ tropism in samples from COVID-19-positive patients, (ii) unrecognized cases in selected tissues from negative or not-tested patients during a pandemic peak, and (iii) retrospectively, pre-pandemic lung samples. We identified SARS-CoV-2 RNA in seven samples from confirmed COVID-19 patients, in two gastric biopsies, one small bowel and one colon resection, one lung biopsy, one pleural resection and one pleural effusion specimen, while all other specimens were negative. In the pandemic peak cohort, we identified one previously unrecognized COVID-19 case in tonsillectomy samples. All pre-pandemic lung samples were negative. In conclusion, SARS-CoV-2 RNA detection in FFPE pathology specimens can potentially improve surveillance of COVID-19, allow retrospective studies, and advance our understanding of SARS-CoV-2 organ tropism and effects. 相似文献
83.
Lowell T. Edgar Scott C. Sibole Clayton J. Underwood James E. Guilkey 《Computer methods in biomechanics and biomedical engineering》2013,16(7):790-801
Recent interest in the process of vascularisation within the biomedical community has motivated numerous new research efforts focusing on the process of angiogenesis. Although the role of chemical factors during angiogenesis has been well documented, the role of mechanical factors, such as the interaction between angiogenic vessels and the extracellular matrix, remains poorly understood. In vitro methods for studying angiogenesis exist; however, measurements available using such techniques often suffer from limited spatial and temporal resolutions. For this reason, computational models have been extensively employed to investigate various aspects of angiogenesis. This paper outlines the formulation and validation of a simple and robust computational model developed to accurately simulate angiogenesis based on length, branching and orientation morphometrics collected from vascularised tissue constructs. Microvessels were represented as a series of connected line segments. The morphology of the vessels was determined by a linear combination of the collagen fibre orientation, the vessel density gradient and a random walk component. Excellent agreement was observed between computational and experimental morphometric data over time. Computational predictions of microvessel orientation within an anisotropic matrix correlated well with experimental data. The accuracy of this modelling approach makes it a valuable platform for investigating the role of mechanical interactions during angiogenesis. 相似文献
84.
85.
Erqi Liu Matthew H. Stenmark Matthew J. Schipper James M. Balter Marc L. Kessler Elaine M. Caoili Oliver E. Lee Edgar Ben-Josef Theodore S. Lawrence Mary Feng 《Translational oncology》2013,6(4):442-446
OBJECTIVES: The full potential of stereotactic body radiation therapy (SBRT), in the treatment of unresectable intrahepatic malignancies, has yet to be realized as our experience is still limited. Thus, we evaluated SBRT outcomes for primary and metastatic liver tumors, with the goal of identifying factors that may aid in optimization of therapy. METHODS: From2005 to 2010, 62 patients with 106 primary and metastatic liver tumors were treated with SBRT to a median biologic effective dose (BED) of 100 Gy (42.6-180). The majority of patients received either three (47%) or five fractions (48%). Median gross tumor volume (GTV) was 8.8 cm3 (0.2-222.4). RESULTS: With a median followup of 18 months (0.46-46.8), freedom from local progression (FFLP) was observed in 97 of 106 treated tumors, with 1- and 2-year FFLP rates of 93% and 82%. Median overall survival (OS) for all patients was 25.2 months, with 1- and 2-year OS of 81%and 52%. Neither BED nor GTV significantly predicted for FFLP. Local failure was associated with a higher risk of death [hazard ratio (HR) = 5.1, P = .0007]. One Child-Pugh Class B patient developed radiationinduced liver disease. There were no other significant toxicities. CONCLUSIONS: SBRT provides excellent local control for both primary and metastatic liver lesions with minimal toxicity. Future studies should focus on appropriate selection of patients and on careful assessment of liver function to maximize both the safety and efficacy of treatment. 相似文献
86.
Julie In Valeriy Lukyanenko Jennifer Foulke-Abel Ann L. Hubbard Michael Delannoy Anne-Marie Hansen James B. Kaper Nadia Boisen James P. Nataro Chengru Zhu Edgar C. Boedeker Jorge A. Girón Olga Kovbasnjuk 《PloS one》2013,8(7)
Life-threatening intestinal and systemic effects of the Shiga toxins produced by enterohemorrhagic Escherichia coli (EHEC) require toxin uptake and transcytosis across intestinal epithelial cells. We have recently demonstrated that EHEC infection of intestinal epithelial cells stimulates toxin macropinocytosis, an actin-dependent endocytic pathway. Host actin rearrangement necessary for EHEC attachment to enterocytes is mediated by the type 3 secretion system which functions as a molecular syringe to translocate bacterial effector proteins directly into host cells. Actin-dependent EHEC attachment also requires the outer membrane protein intimin, a major EHEC adhesin. Here, we investigate the role of type 3 secretion in actin turnover occurring during toxin macropinocytosis. Toxin macropinocytosis is independent of EHEC type 3 secretion and intimin attachment. EHEC soluble factors are sufficient to stimulate macropinocytosis and deliver toxin into enterocytes in vitro and in vivo; intact bacteria are not required. Intimin-negative enteroaggregative Escherichia coli (EAEC) O104:H4 robustly stimulate Shiga toxin macropinocytosis into intestinal epithelial cells. The apical macropinosomes formed in intestinal epithelial cells move through the cells and release their cargo at these cells’ basolateral sides. Further analysis of EHEC secreted proteins shows that a serine protease EspP alone is able to stimulate host actin remodeling and toxin macropinocytosis. The observation that soluble factors, possibly serine proteases including EspP, from each of two genetically distinct toxin-producing strains, can stimulate Shiga toxin macropinocytosis and transcellular transcytosis alters current ideas concerning mechanisms whereby Shiga toxin interacts with human enterocytes. Mechanisms important for this macropinocytic pathway could suggest new potential therapeutic targets for Shiga toxin-induced disease. 相似文献
87.
Elizabeth B. Oliveira-Sales Edgar Maquigussa Patricia Semedo Luciana G. Pereira Vanessa M. Ferreira Niels O. Camara Cassia T. Bergamaschi Ruy R. Campos Mirian A. Boim 《PloS one》2013,8(11)
Renovascular hypertension induced by 2 Kidney-1 Clip (2K-1C) is a renin-angiotensin-system (RAS)-dependent model, leading to renal vascular rarefaction and renal failure. RAS inhibitors are not able to reduce arterial pressure (AP) and/or preserve the renal function, and thus, alternative therapies are needed. Three weeks after left renal artery occlusion, fluorescently tagged mesenchymal stem cells (MSC) (2×105 cells/animal) were injected weekly into the tail vein in 2K-1C hypertensive rats. Flow cytometry showed labeled MSC in the cortex and medulla of the clipped kidney. MSC prevented a further increase in the AP, significantly reduced proteinuria and decreased sympathetic hyperactivity in 2K-1C rats. Renal function parameters were unchanged, except for an increase in urinary volume observed in 2K-1C rats, which was not corrected by MSC. The treatment improved the morphology and decreased the fibrotic areas in the clipped kidney and also significantly reduced renal vascular rarefaction typical of 2K-1C model. Expression levels of IL-1β, TNF-α angiotensinogen, ACE, and Ang II receptor AT1 were elevated, whereas AT2 levels were decreased in the medulla of the clipped kidney. MSC normalized these expression levels. In conclusion, MSC therapy in the 2K-1C model (i) prevented the progressive increase of AP, (ii) improved renal morphology and microvascular rarefaction, (iii) reduced fibrosis, proteinuria and inflammatory cytokines, (iv) suppressed the intrarenal RAS, iv) decreased sympathetic hyperactivity in anesthetized animals and v) MSC were detected at the CNS suggesting that the cells crossed the blood-brain barrier. This therapy may be a promising strategy to treat renovascular hypertension and its renal consequences in the near future. 相似文献
88.
89.
90.