全文获取类型
收费全文 | 2558篇 |
免费 | 242篇 |
专业分类
2800篇 |
出版年
2021年 | 20篇 |
2020年 | 22篇 |
2019年 | 24篇 |
2018年 | 21篇 |
2017年 | 30篇 |
2016年 | 45篇 |
2015年 | 68篇 |
2014年 | 77篇 |
2013年 | 96篇 |
2012年 | 123篇 |
2011年 | 130篇 |
2010年 | 74篇 |
2009年 | 82篇 |
2008年 | 100篇 |
2007年 | 103篇 |
2006年 | 108篇 |
2005年 | 84篇 |
2004年 | 76篇 |
2003年 | 97篇 |
2002年 | 68篇 |
2001年 | 75篇 |
2000年 | 65篇 |
1999年 | 49篇 |
1998年 | 34篇 |
1997年 | 31篇 |
1996年 | 23篇 |
1995年 | 20篇 |
1992年 | 43篇 |
1991年 | 44篇 |
1990年 | 48篇 |
1989年 | 41篇 |
1988年 | 48篇 |
1987年 | 38篇 |
1986年 | 35篇 |
1985年 | 46篇 |
1984年 | 39篇 |
1983年 | 54篇 |
1982年 | 19篇 |
1981年 | 35篇 |
1980年 | 20篇 |
1979年 | 28篇 |
1978年 | 29篇 |
1977年 | 32篇 |
1976年 | 27篇 |
1975年 | 23篇 |
1974年 | 30篇 |
1973年 | 19篇 |
1972年 | 23篇 |
1971年 | 24篇 |
1969年 | 28篇 |
排序方式: 共有2800条查询结果,搜索用时 9 毫秒
101.
Boccara M Mills CE Zeier J Anzi C Lamb C Poole RK Delledonne M 《The Plant journal : for cell and molecular biology》2005,43(2):226-237
Host cells respond to infection by generating nitric oxide (NO) as a cytotoxic weapon to facilitate killing of invading microbes. Bacterial flavohaemoglobins are well-known scavengers of NO and play a crucial role in protecting animal pathogens from nitrosative stress during infection. Erwinia chrysanthemi, which causes macerating diseases in a wide variety of plants, possesses a flavohaemoglobin (HmpX) whose function in plant pathogens has remained unclear. Here we show that HmpX consumes NO and prevents inhibition by NO of cell respiration, indicating a role in protection from nitrosative stress. Furthermore, infection of Saintpaulia ionantha plants with an HmpX-deficient mutant of E. chrysanthemi revealed that the lack of NO scavenging activity causes the accumulation of unusually high levels of NO in host tissue and triggers hypersensitive cell death. Introduction of the wild-type hmpX gene in an incompatible strain of Pseudomonas syringae had a dramatic effect on the hypersensitive cell death in soya bean cell suspensions, and markedly reduced the development of macroscopic symptoms in Arabidopsis thaliana plants. These observations indicate that HmpX not only protects against nitrosative stress but also attenuates host hypersensitive reaction during infection by intercepting NO produced by the plant for the execution of the hypersensitive cell death programme. 相似文献
102.
G C Mills 《Biochemical medicine and metabolic biology》1989,42(3):240-247
Procedures are described for the isolation and identification of 1-methyladenine from the urine of an adult female with adenosine deaminase deficiency but no immunodeficiency. Evidence is provided indicating that much of the usual urinary excretion product, 1-methyladenosine, is converted to 1-methyladenine in this subject prior to excretion. Since the nucleoside phosphorylases present in normal individuals do not act on 1-methyladenosine, this suggests that a phosphorylase with unusual properties is present in this adenosine deaminase-deficient subject. A possible role for this phosphorylase in removal of deoxyadenosine in this subject is discussed. 相似文献
103.
104.
Dengqun Liu Megan D Radyk Rebecca L Cunningham Joseph Burclaff Greg Sibbel Hei‐Yong G Lo Valerie Blanc Nicholas O Davidson Zhen‐Ning Wang Jason C Mills 《The EMBO journal》2018,37(7)
In 1900, Adami speculated that a sequence of context‐independent energetic and structural changes governed the reversion of differentiated cells to a proliferative, regenerative state. Accordingly, we show here that differentiated cells in diverse organs become proliferative via a shared program. Metaplasia‐inducing injury caused both gastric chief and pancreatic acinar cells to decrease mTORC1 activity and massively upregulate lysosomes/autophagosomes; then increase damage associated metaplastic genes such as Sox9; and finally reactivate mTORC1 and re‐enter the cell cycle. Blocking mTORC1 permitted autophagy and metaplastic gene induction but blocked cell cycle re‐entry at S‐phase. In kidney and liver regeneration and in human gastric metaplasia, mTORC1 also correlated with proliferation. In lysosome‐defective Gnptab?/? mice, both metaplasia‐associated gene expression changes and mTORC1‐mediated proliferation were deficient in pancreas and stomach. Our findings indicate differentiated cells become proliferative using a sequential program with intervening checkpoints: (i) differentiated cell structure degradation; (ii) metaplasia‐ or progenitor‐associated gene induction; (iii) cell cycle re‐entry. We propose this program, which we term “paligenosis”, is a fundamental process, like apoptosis, available to differentiated cells to fuel regeneration following injury. 相似文献
105.
106.
Richard A. Watson Rob Mills C. L. Buckley Kostas Kouvaris Adam Jackson Simon T. Powers Chris Cox Simon Tudge Adam Davies Loizos Kounios Daniel Power 《Evolutionary biology》2016,43(4):553-581
The mechanisms of variation, selection and inheritance, on which evolution by natural selection depends, are not fixed over evolutionary time. Current evolutionary biology is increasingly focussed on understanding how the evolution of developmental organisations modifies the distribution of phenotypic variation, the evolution of ecological relationships modifies the selective environment, and the evolution of reproductive relationships modifies the heritability of the evolutionary unit. The major transitions in evolution, in particular, involve radical changes in developmental, ecological and reproductive organisations that instantiate variation, selection and inheritance at a higher level of biological organisation. However, current evolutionary theory is poorly equipped to describe how these organisations change over evolutionary time and especially how that results in adaptive complexes at successive scales of organisation (the key problem is that evolution is self-referential, i.e. the products of evolution change the parameters of the evolutionary process). Here we first reinterpret the central open questions in these domains from a perspective that emphasises the common underlying themes. We then synthesise the findings from a developing body of work that is building a new theoretical approach to these questions by converting well-understood theory and results from models of cognitive learning. Specifically, connectionist models of memory and learning demonstrate how simple incremental mechanisms, adjusting the relationships between individually-simple components, can produce organisations that exhibit complex system-level behaviours and improve the adaptive capabilities of the system. We use the term “evolutionary connectionism” to recognise that, by functionally equivalent processes, natural selection acting on the relationships within and between evolutionary entities can result in organisations that produce complex system-level behaviours in evolutionary systems and modify the adaptive capabilities of natural selection over time. We review the evidence supporting the functional equivalences between the domains of learning and of evolution, and discuss the potential for this to resolve conceptual problems in our understanding of the evolution of developmental, ecological and reproductive organisations and, in particular, the major evolutionary transitions. 相似文献
107.
The light brown apple moth (Epiphyas postvittana) is a highly polyphagous species that has invaded several geographic regions across the globe and has stimulated substantial
concern over possible impacts for agriculture in the US. We aimed to predict the potential geographic range of E. postvittana to better understand the threat of this species in the US and globally. We used the mechanistic simulation modelling method
CLIMEX and the correlative niche modelling method Maxent to predict the geographic distribution of E. postvittana in its native range and globally and tested model projections using known invasion data. Different predictor variable data
sets and threshold dependent and independent measures of environmental suitability were considered in model evaluation. Models
accurately predicted known invasive localities of E. postvittana across the globe. Overall predictions of environmental suitability were largely congruent across models, although there were
some notable differences. Ephiphyas postvittana clearly has the potential to establish in many regions of the globe, although some previous analyses of the potential distribution
of this species appear overly pessimistic. Additional studies of the biology of this species in invaded areas, including interactions
with natural enemies and the capacity to adapt to novel climatic conditions, are ultimately needed to more fully understand
its potential economic and environmental impacts. 相似文献
108.
Kwame?YeboahEmail authorView authors OrcID profile Daniel?A.?Antwi Ben?Gyan Virginia?Govoni Charlotte?E.?Mills J.?Kennedy?Cruickshank Albert?G.?B.?Amoah 《BMC endocrine disorders》2016,16(1):53
Background
Diabetes and hypertension increase arterial stiffness and cardiovascular events in all societies studied so far; sub-Saharan African studies are sparse. We investigated factors affecting arterial function in Ghanaians with diabetes, hypertension, both or neither.Method
Testing the hypothesis that arterial stiffness would progressively increase from controls to multiply affected patients, 270 participants were stratified into those with diabetes or hypertension only, with both, or without either. Cardio-ankle vascular index (CAVI), heart–ankle pulse wave velocity (haPWV), aortic PWV (PWVao) by Arteriograph, aortic and brachial blood pressures (BP), were measured.Results
In patients with both diabetes and hypertension compared with either alone, values were higher of CAVI (mean?±?SD, 8.3?±?1.2 vs 7.5?±?1.1 and 7.4?±?1.1 units; p?<?0.05), PWVao (9.1?±?1.4 vs 8.7?±?1.9 and 8.1?±?0.9 m/s; p?<?0.05) and haPWV (8.5?±?1 vs 7.9?±?1 and 7.2?±?0.7 m/s; p?<?0.05) respectively. In multivariate analysis, age, having diabetes or hypertension and BMI were independently associated with CAVI in all participants (β?=?0.49, 0.2, 0.17 and -0.2 units; p?<?0.01, respectively). Independent determinants of PWVao were heart rate, systolic BP and age (β?=?0.42, 0.27 and 0.22; p?<?0.01), and for haPWV were systolic BP, age, BMI, diabetes and hypertension status (β?=?0.46, 0.32, -0.2, 0.2 and 0.11; p?<?0.01).Conclusion
In this sub-Saharan setting with lesser atherosclerosis than the western world, arterial stiffness is significantly greater in patients with coexistent diabetes and hypertension but did not differ between those with either diabetes or hypertension only. Simple, reproducibly measured PWV/CAVI may offer effective and efficient targets for intervention.109.
110.
Comparative genetics of invasive populations of walnut aphid,Chromaphis juglandicola,and its introduced parasitoid,Trioxys pallidus,in California 下载免费PDF全文
Coevolution may be an important component of the sustainability of importation biological control, but how frequently introduced natural enemies coevolve with their target pests is unclear. Here we explore whether comparative population genetics of the invasive walnut aphid, Chromaphis juglandicola, and its introduced parasitoid, Trioxys pallidus, provide insights into the localized breakdown of biological control services in walnut orchards in California. We found that sampled populations of C. juglandicola exhibited higher estimates of genetic differentiation (FST) than co‐occurring populations of T. pallidus. In contrast, estimates of both the inbreeding coefficient (GIS) and contemporary gene flow were higher for T. pallidus than for C. juglandicola. We also found evidence of reciprocal outlier loci in some locations, but none showed significant signatures of selection. Synthesis and applications. Understanding the importance of coevolutionary interactions for the sustainability of biological control remains an important and understudied component of biological control research. Given the observed differences in gene flow and genetic differentiation among populations of T. pallidus and C. juglandicola, we suspect that temporary local disruption of biological control services may occur more frequently than expected while remaining stable at broader regional scales. Further research that combines genomewide single nucleotide polymorphism genotyping with measurements of phenotypic traits is needed to provide more conclusive evidence of whether the occurrence of outlier loci that display significant signatures of selection can be interpreted as evidence of the presence of a geographic mosaic of coevolution in this system. 相似文献