全文获取类型
收费全文 | 1582篇 |
免费 | 136篇 |
国内免费 | 6篇 |
出版年
2023年 | 8篇 |
2022年 | 15篇 |
2021年 | 32篇 |
2020年 | 23篇 |
2019年 | 23篇 |
2018年 | 30篇 |
2017年 | 26篇 |
2016年 | 43篇 |
2015年 | 59篇 |
2014年 | 78篇 |
2013年 | 110篇 |
2012年 | 123篇 |
2011年 | 99篇 |
2010年 | 61篇 |
2009年 | 72篇 |
2008年 | 81篇 |
2007年 | 76篇 |
2006年 | 72篇 |
2005年 | 73篇 |
2004年 | 64篇 |
2003年 | 76篇 |
2002年 | 68篇 |
2001年 | 26篇 |
2000年 | 25篇 |
1999年 | 26篇 |
1998年 | 21篇 |
1997年 | 17篇 |
1996年 | 8篇 |
1995年 | 8篇 |
1993年 | 11篇 |
1992年 | 25篇 |
1991年 | 21篇 |
1990年 | 16篇 |
1989年 | 14篇 |
1988年 | 19篇 |
1987年 | 10篇 |
1986年 | 11篇 |
1985年 | 10篇 |
1984年 | 13篇 |
1983年 | 8篇 |
1982年 | 6篇 |
1981年 | 9篇 |
1980年 | 6篇 |
1979年 | 11篇 |
1977年 | 7篇 |
1976年 | 6篇 |
1971年 | 8篇 |
1970年 | 5篇 |
1969年 | 9篇 |
1967年 | 13篇 |
排序方式: 共有1724条查询结果,搜索用时 15 毫秒
41.
The "vectorial model" proposed in 1973 by Berglund et al. certainlyconstitutes an important progress in the field of olfactoryquantitative interaction. An alternative model called "U model",based also upon perceived odorous intensity of a mixture asa function of perceived odorous intensity of the components,is here presented. The "U model" fits the experimental data of Cain and Drexler(1974) and of Cain (1975) slightly better than the "vectorialmodel".
*Presented at the VIth International Symposium Olfaction andTaste, Gif-sur-Yvette, Paris, France, 1517th July, 1977. 相似文献
42.
Claire-Michelle Calberg-Bacq Camille Francois Luc Gosselin Paul M. Osterrieth Francoise Renteir-Delrue 《生物化学与生物物理学报:生物膜》1976,419(3):458-478
Milk fat globule membranes and mammary tumour virus particles (d = 1.17 g/cm3) have been obtained from the milk of a Swiss albino mice strain. Comparitive biochemistry shows that these two structures differ significantly in the phospholipid, polypeptide and glycopolypeptide patterns and enzymatic activities. However, the lipid profile and the morphology of both structures suggest a filiation with the plasma membrane. Density fractions obtained from the crude virus preparation have been thoroughly investigated. The results suggest that most of these fractions represent degraded virus and/or atypical virus assembly. 相似文献
43.
The minicell-producing Escherichia coli strain P 678-54 was transformed with a series of defined PTY chimeric plasmids consisting of yeast 2-μm DNA and E. coli plasmid pCR1. In minicells the integrated 2-μm DNA from yeast directed specifically the synthesis of six polypeptides with apparent molecular weights of 15 000, 17 500, 20 000, 22 000, 37 000, and 48 000. The specificity of five other polypeptides, which cover a molecular weight range of 19 000 to 28 000, has not yet been established with certainty. Neither the orientation of the integrated DNA, nor the inversion which distinguishes the two structural forms of 2-μm DNA affected the polypeptides synthesized. However, integration at a given EcoRI site appeared to be correlated with the absence of one particular polypeptide band; this suggests that at least one of these sites is located in an expressed region of the DNA. 相似文献
44.
45.
Suzanne M. Marselis Katharine Abernethy Alfonso Alonso John Armston Timothy R. Baker Jean‐Francois Bastin Jan Bogaert Doreen S. Boyd Pascal Boeckx David F. R. P. Burslem Robin Chazdon David B. Clark David Coomes Laura Duncanson Steven Hancock Ross Hill Chris Hopkinson Elizabeth Kearsley James R. Kellner David Kenfack Nicolas Labrire Simon L. Lewis David Minor Herv Memiaghe Abel Monteagudo Reuben Nilus Michael O'Brien Oliver L. Phillips John Poulsen Hao Tang Hans Verbeeck Ralph Dubayah 《Global Ecology and Biogeography》2020,29(10):1799-1816
46.
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
47.
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
48.
Esterhuizen Karien Lindeque J. Zander Mason Shayne van der Westhuizen Francois H. Rodenburg Richard J. de Laat Paul Smeitink Jan A. M. Janssen Mirian C. H. Louw Roan 《Metabolomics : Official journal of the Metabolomic Society》2021,17(1):1-11
Metabolomics - Studies investigating crop resistance to abiotic and biotic stress have largely focused on plant responses to singular forms of stress and individual biochemical pathways that only... 相似文献
49.
Francois Korbmacher Benjamin Drepper Theo Sanderson Peer Martin Thomas Stach Alexander G. Maier Kai Matuschewski Joachim M. Matz 《Cellular microbiology》2021,23(1)
Malaria parasites are fast replicating unicellular organisms and require substantial amounts of folate for DNA synthesis. Despite the central role of this critical co‐factor for parasite survival, only little is known about intraparasitic folate trafficking in Plasmodium. Here, we report on the expression, subcellular localisation and function of the parasite's folate transporter 2 (FT2) during life cycle progression in the murine malaria parasite Plasmodium berghei. Using live fluorescence microscopy of genetically engineered parasites, we demonstrate that FT2 localises to the apicoplast. In invasive P. berghei stages, a fraction of FT2 is also observed at the apical end. Upon genetic disruption of FT2, blood and liver infection, gametocyte production and mosquito colonisation remain unaltered. But in the Anopheles vector, FT2‐deficient parasites develop inflated oocysts with unusual pulp formation consisting of numerous single‐membrane vesicles, which ultimately fuse to form large cavities. Ultrastructural analysis suggests that this defect reflects aberrant sporoblast formation caused by abnormal vesicular traffic. Complete sporogony in FT2‐deficient oocysts is very rare, and mutant sporozoites fail to establish hepatocyte infection, resulting in a complete block of parasite transmission. Our findings reveal a previously unrecognised organellar folate transporter that exerts critical roles for pathogen maturation in the arthropod vector. 相似文献
50.