全文获取类型
收费全文 | 512篇 |
免费 | 60篇 |
出版年
2023年 | 8篇 |
2022年 | 6篇 |
2021年 | 10篇 |
2020年 | 15篇 |
2019年 | 8篇 |
2018年 | 10篇 |
2017年 | 8篇 |
2016年 | 29篇 |
2015年 | 29篇 |
2014年 | 30篇 |
2013年 | 43篇 |
2012年 | 39篇 |
2011年 | 40篇 |
2010年 | 17篇 |
2009年 | 16篇 |
2008年 | 31篇 |
2007年 | 12篇 |
2006年 | 24篇 |
2005年 | 24篇 |
2004年 | 23篇 |
2003年 | 17篇 |
2002年 | 17篇 |
2001年 | 9篇 |
2000年 | 6篇 |
1999年 | 6篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1994年 | 5篇 |
1993年 | 2篇 |
1992年 | 9篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1987年 | 6篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1982年 | 5篇 |
1980年 | 2篇 |
1979年 | 6篇 |
1978年 | 3篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1972年 | 3篇 |
1971年 | 2篇 |
1969年 | 2篇 |
1966年 | 2篇 |
1934年 | 1篇 |
1917年 | 1篇 |
排序方式: 共有572条查询结果,搜索用时 15 毫秒
11.
Bente Christiansen Jens Pete Lomholt Kjell Johansen 《Environmental Biology of Fishes》1982,7(3):291-296
Synopsis Oxygen uptake (Vo
2) was measured in carp of approximately 40 cm length swimming at controlled variable oxygen tensions (Po
2). At Po
2> 120 mm Hg Vo
2 increased with an increase in swimming speed from 5.6 to 11.3 cm · sec–1. Extrapolation of Vo
2 to zero activity at Po
2 = 140 mm Hg revealed a standard O2 uptake of 36.7 ml O2 · kg–1 · h–1 at 20° C. At the lowest swimming speed (5.6 cm · s–1) the oxygen uptake increased when the water Po
2 was reduced. A near doubling in Vo
2 was seen at Po
2 = 70 mm Hg compared to 140 mm Hg. At higher swimming speeds in hypoxic water Vo
2 decreased relative to the values at low swimming speeds. As a result the slope of the lines expressing log Vo
2 as a function of swimming speed decreased from positive to negative values with decreasing Po
2 of the water. pH of blood from the caudal vein drawn before and at termination of swimming at Po
2 = 70 mm Hg and 100 mm Hg did not show any decrease in relation to rest values at Po
2 = 140 mm Hg. Blood lactate concentration did not increase during swimming at these tensions. 相似文献
12.
Potassium tris(oxalato)chromate(III) trihydrate (chromium ixalate) has been shown to be a more useful broadening agent than potassium ferricyanide for the spin label 2,2,6,6-tetramethylpiperidine-N-oxyl-4-amine (Tempamine) in thylakoid suspensions. Our data show that chromium oxalate is less permeable than ferricyanide, does not inhibit thylakoid electron transport or photophosphorylation, and is not photoreduced by thylakoids. 相似文献
13.
Nesbitt D. Brown R.Brickley Sweet John A. Kintzios H.David Cox Bhupendra P. Doctor 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1979,164(1):35-40
A sensitive and specific method for the determination of diamines and polyamines by ion-pair high-performance liquid chromatography is described. The 5-dimethylaminonaphthalene-1-sulfonyl derivatives of putrescine, 1,6-diaminohexane, spermidine and spermine are separated on a μBondapak C15 reversed-phase column with 1-heptanesulfonic acid and acetonitrile as the mobile phase. All compounds are eluted within 30 min using a programmed solvent gradient system. The method has a lower detection limit of 1 pmole on column.Because of the simplicity of the method, its application provides a better means for closely monitoring patients undergoing treatment for various types of genito-urinary neoplastic diseases. 相似文献
14.
Brenda F. Nesbitt P.S. Beevor R.A. Cole R. Lester R.G. Poppi 《Journal of insect physiology》1975,21(5):1091-1096
The female sex pheromones of the red bollworm moth, Diparopsis castanea, were isolated by solvent extraction of the terminal abdominal segments of the female moth followed by purification of the solvent extract by liquid-solid and gas chromatography. The pheromones were identified by gas chromatographic analysis, micro-ozonolysis, infra-red and mass spectroscopy, and comparison with synthetic material. The major pheromone was 9,11-dodecadien-1-yl acetate (80 : 20 trans : cis). Minor components identified were trans 9-dodecen-1-yl acetate, 11-dodecen-1-yl acetate, and dodecan-1-yl acetate. 相似文献
15.
16.
How to measure,report and verify soil carbon change to realize the potential of soil carbon sequestration for atmospheric greenhouse gas removal 总被引:1,自引:0,他引:1
Pete Smith Jean‐Francois Soussana Denis Angers Louis Schipper Claire Chenu Daniel P. Rasse Niels H. Batjes Fenny van Egmond Stephen McNeill Matthias Kuhnert Cristina Arias‐Navarro Jorgen E. Olesen Ngonidzashe Chirinda Dario Fornara Eva Wollenberg Jorge lvaro‐Fuentes Alberto Sanz‐Cobena Katja Klumpp 《Global Change Biology》2020,26(1):219-241
There is growing international interest in better managing soils to increase soil organic carbon (SOC) content to contribute to climate change mitigation, to enhance resilience to climate change and to underpin food security, through initiatives such as international ‘4p1000’ initiative and the FAO's Global assessment of SOC sequestration potential (GSOCseq) programme. Since SOC content of soils cannot be easily measured, a key barrier to implementing programmes to increase SOC at large scale, is the need for credible and reliable measurement/monitoring, reporting and verification (MRV) platforms, both for national reporting and for emissions trading. Without such platforms, investments could be considered risky. In this paper, we review methods and challenges of measuring SOC change directly in soils, before examining some recent novel developments that show promise for quantifying SOC. We describe how repeat soil surveys are used to estimate changes in SOC over time, and how long‐term experiments and space‐for‐time substitution sites can serve as sources of knowledge and can be used to test models, and as potential benchmark sites in global frameworks to estimate SOC change. We briefly consider models that can be used to simulate and project change in SOC and examine the MRV platforms for SOC change already in use in various countries/regions. In the final section, we bring together the various components described in this review, to describe a new vision for a global framework for MRV of SOC change, to support national and international initiatives seeking to effect change in the way we manage our soils. 相似文献
17.
Pamela McElwee Katherine Calvin Donovan Campbell Francesco Cherubini Giacomo Grassi Vladimir Korotkov Anh Le Hoang Shuaib Lwasa Johnson Nkem Ephraim Nkonya Nobuko Saigusa Jean‐Francois Soussana Miguel Angel Taboada Frances Manning Dorothy Nampanzira Pete Smith 《Global Change Biology》2020,26(9):4691-4721
Interlocked challenges of climate change, biodiversity loss, and land degradation require transformative interventions in the land management and food production sectors to reduce carbon emissions, strengthen adaptive capacity, and increase food security. However, deciding which interventions to pursue and understanding their relative co‐benefits with and trade‐offs against different social and environmental goals have been difficult without comparisons across a range of possible actions. This study examined 40 different options, implemented through land management, value chains, or risk management, for their relative impacts across 18 Nature's Contributions to People (NCPs) and the 17 Sustainable Development Goals (SDGs). We find that a relatively small number of interventions show positive synergies with both SDGs and NCPs with no significant adverse trade‐offs; these include improved cropland management, improved grazing land management, improved livestock management, agroforestry, integrated water management, increased soil organic carbon content, reduced soil erosion, salinization, and compaction, fire management, reduced landslides and hazards, reduced pollution, reduced post‐harvest losses, improved energy use in food systems, and disaster risk management. Several interventions show potentially significant negative impacts on both SDGs and NCPs; these include bioenergy and bioenergy with carbon capture and storage, afforestation, and some risk sharing measures, like commercial crop insurance. Our results demonstrate that a better understanding of co‐benefits and trade‐offs of different policy approaches can help decision‐makers choose the more effective, or at the very minimum, more benign interventions for implementation. 相似文献
18.
Jorge Assis Nelson Castilho Coelho Filipe Alberto Myriam Valero Pete Raimondi Dan Reed Ester Alvares Serr?o 《PloS one》2013,8(7)
The genetic consequences of living on the edge of distributional ranges have been
the subject of a largely unresolved debate. Populations occurring along
persistent low latitude ranges (rear-edge) are expected to retain high and
unique genetic diversity. In contrast, currently less favourable environmental
conditions limiting population size at such range-edges may have caused genetic
erosion that prevails over past historical effects, with potential consequences
on reducing future adaptive capacity. The present study provides an empirical
test of whether population declines towards a peripheral range might be
reflected on decreasing diversity and increasing population isolation and
differentiation. We compare population genetic differentiation and diversity
with trends in abundance along a latitudinal gradient towards the peripheral
distribution range of
Saccorhiza
polyschides
, a large brown
seaweed that is the main structural species of kelp forests in SW Europe.
Signatures of recent bottleneck events were also evaluated to determine whether
the recently recorded distributional shifts had a negative influence on
effective population size. Our findings show decreasing population density and
increasing spatial fragmentation and local extinctions towards the southern
edge. Genetic data revealed two well supported groups with a central contact
zone. As predicted, higher differentiation and signs of bottlenecks were found
at the southern edge region. However, a decrease in genetic diversity associated
with this pattern was not verified. Surprisingly, genetic diversity increased
towards the edge despite bottlenecks and much lower densities, suggesting that
extinctions and recolonizations have not strongly reduced diversity or that
diversity might have been even higher there in the past, a process of shifting
genetic baselines. 相似文献
19.
James Hansen Pushker Kharecha Makiko Sato Valerie Masson-Delmotte Frank Ackerman David J. Beerling Paul J. Hearty Ove Hoegh-Guldberg Shi-Ling Hsu Camille Parmesan Johan Rockstrom Eelco J. Rohling Jeffrey Sachs Pete Smith Konrad Steffen Lise Van Susteren Karina von Schuckmann James C. Zachos 《PloS one》2013,8(12)
We assess climate impacts of global warming using ongoing observations and paleoclimate data. We use Earth’s measured energy imbalance, paleoclimate data, and simple representations of the global carbon cycle and temperature to define emission reductions needed to stabilize climate and avoid potentially disastrous impacts on today’s young people, future generations, and nature. A cumulative industrial-era limit of ∼500 GtC fossil fuel emissions and 100 GtC storage in the biosphere and soil would keep climate close to the Holocene range to which humanity and other species are adapted. Cumulative emissions of ∼1000 GtC, sometimes associated with 2°C global warming, would spur “slow” feedbacks and eventual warming of 3–4°C with disastrous consequences. Rapid emissions reduction is required to restore Earth’s energy balance and avoid ocean heat uptake that would practically guarantee irreversible effects. Continuation of high fossil fuel emissions, given current knowledge of the consequences, would be an act of extraordinary witting intergenerational injustice. Responsible policymaking requires a rising price on carbon emissions that would preclude emissions from most remaining coal and unconventional fossil fuels and phase down emissions from conventional fossil fuels. 相似文献
20.
Dola Das Ehsan Fayazzadeh Xin Li Nischal Koirala Akshay Wadera Min Lang Maximilian Zernic Catherine Panick Pete Nesbitt Gordon McLennan 《Journal of cellular physiology》2020,235(9):6167-6182
Hepatocellular carcinoma (HCC) is a major health problem worldwide and in the United States as its incidence has increased substantially within the past two decades. HCC therapy remains a challenge, primarily due to underlying liver disorders such as cirrhosis that determines treatment approach and efficacy. Activated hepatic stellate cells (A-HSCs) are the key cell types involved in hepatic fibrosis/cirrhosis. A-HSCs are important constituents of HCC tumor microenvironment (TME) and support tumor growth, chemotherapy resistance, cancer cell migration, and escaping immune surveillance. This makes A-HSCs an important therapeutic target in hepatic fibrosis/cirrhosis as well as in HCC. Although many studies have reported the role of A-HSCs in cancer generation and investigated the therapeutic potential of A-HSCs reversion in cancer arrest, not much is known about inactivated or quiescent HSCs (Q-HSCs) in cancer growth or arrest. Here we report that Q-HSCs resist cancer cell growth by inducing cytotoxicity and enhancing chemotherapy sensitivity. We observed that the conditioned media from Q-HSCs (Q-HSCCM) induces cancer cell death through a caspase-independent mechanism that involves an increase in apoptosis-inducing factor expression, nuclear localization, DNA fragmentation, and cell death. We further observed that Q-HSCCM enhanced the efficiency of doxorubicin, as measured by cell viability assay. Exosomes present in the conditioned media were not involved in the mechanism, which suggests the role of other factors (proteins, metabolites, or microRNA) secreted by the cells. Identification and characterization of these factors are important in the development of effective HCC therapy. 相似文献