全文获取类型
收费全文 | 430篇 |
免费 | 13篇 |
国内免费 | 5篇 |
专业分类
林业 | 32篇 |
农学 | 13篇 |
基础科学 | 2篇 |
142篇 | |
综合类 | 54篇 |
农作物 | 27篇 |
水产渔业 | 21篇 |
畜牧兽医 | 116篇 |
园艺 | 8篇 |
植物保护 | 33篇 |
出版年
2023年 | 4篇 |
2022年 | 4篇 |
2021年 | 6篇 |
2020年 | 10篇 |
2019年 | 8篇 |
2018年 | 12篇 |
2017年 | 6篇 |
2016年 | 4篇 |
2015年 | 5篇 |
2014年 | 9篇 |
2013年 | 31篇 |
2012年 | 23篇 |
2011年 | 38篇 |
2010年 | 15篇 |
2009年 | 15篇 |
2008年 | 23篇 |
2007年 | 22篇 |
2006年 | 30篇 |
2005年 | 21篇 |
2004年 | 30篇 |
2003年 | 20篇 |
2002年 | 25篇 |
2001年 | 7篇 |
2000年 | 9篇 |
1999年 | 9篇 |
1997年 | 3篇 |
1996年 | 6篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1993年 | 3篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1986年 | 4篇 |
1985年 | 1篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1975年 | 1篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1966年 | 2篇 |
1965年 | 1篇 |
1961年 | 1篇 |
排序方式: 共有448条查询结果,搜索用时 562 毫秒
431.
Dichelobacter nodosus, the etiological agent of ovine footrot, exists both as virulent and as benign strains, which differ in virulence mainly due to subtle differences in the three subtilisin-like proteases AprV2, AprV5 and BprV found in virulent, and AprB2, AprB5 and BprB in benign strains of D. nodosus. Our objective was a molecular genetic epidemiological analysis of the genes of these proteases by direct sequence analysis from clinical material of sheep from herds with and without history of footrot from 4 different European countries. The data reveal the two proteases known as virulent AprV2 and benign AprB2 to correlate fully to the clinical status of the individuals or the footrot history of the herd. In samples taken from affected herds, the aprV2 gene was found as a single allele whereas in samples from unaffected herds several alleles with minor modifications of the aprB2 gene were detected. The different alleles of aprB2 were related to the herds. The aprV5 and aprB5 genes were found in the form of several alleles scattered without distinction between affected and non-affected herds. However, all different alleles of aprV5 and aprB5 encode the same amino acid sequences, indicating the existence of a single protease isoenzyme 5 in both benign and virulent strains. The genes of the basic proteases BprV and BprB also exist as various alleles. However, differences found in samples from affected versus non-affected herds do not reflect the currently known epitopes that are attributed to differences in biochemical activity. The data of the study confirm the prominent role of AprV2 in the virulence of D. nodosus and shed a new light on the presence of the other protease genes and their allelic variants in clinical samples. 相似文献
432.
Christina von Haaren Christian Albert Jan Barkmann Rudolf S. de Groot Joachim H. Spangenberg Christoph Schröter-Schlaack Bernd Hansjürgens 《Landscape Ecology》2014,29(8):1335-1346
The development and use of the conceptual framework of ecosystem services (ES) has been very successful in supporting the broad diffusion and application of ES within science and policy communities. However, most of the currently proposed interpretations of the framework neither correlate to environmental planning nor to decision-making contexts at the local and regional scale, which is a potential reason for the slow adoption and practice of the ES conceptual framework. This paper proposes a practice-oriented ES evaluation (PRESET) model specifically adapted to the requirements of local and regional planning and decision-making contexts, and discusses its potential benefits and implications for practice. Through the usage of PRESET we suggest making a distinction between ‘offered ES’, ‘utilized ES’, ‘human input’, and ‘ES benefits’ as relevant information for decision-making. Furthermore, we consider it important to link these decision-support categories to different value dimensions relevant in planning and management practice. PRESET provides guidance to inject the ES concept into planning, but needs to be implemented together with concrete assessment methods, indicators and data. The planning strategic benefits of using PRESET include its reference to existing legislative objectives, avoiding the risk that monetized ES values might dominate decision-making, clarification of human contributions, and easier identification of land use conflicts and synergies. Examples are given for offered and utilized ES, as well as for respective evaluation approaches and instruments of implementation. 相似文献
433.
We extend the well-known double sampling for stratification sampling scheme by cluster subsampling to a three-level design and present corresponding estimators based on the infinite population approach in the first phase. After stratification of the sample points (phase I), a second-phase sample is drawn independently among the first-phase points within each stratum. On level III, clusters are formed of those phase II points and a sample of clusters is finally drawn without replacement. We used the forest planning units compartment and subdistrict as clusters and moreover formed clusters with a heuristic for the vehicle routing problem. The precision of the new estimator was compared to that achieved with classical double sampling for stratification in a case study. The results indicate that the expected increase in sampling errors caused by clustering cannot be compensated by the reduced inventory costs under the conditions given in the case study. 相似文献
434.
435.
Telomeric repeat containing RNA and RNA surveillance factors at mammalian chromosome ends 总被引:1,自引:0,他引:1
Azzalin CM Reichenbach P Khoriauli L Giulotto E Lingner J 《Science (New York, N.Y.)》2007,318(5851):798-801
436.
437.
Schmitt JP Kamisago M Asahi M Li GH Ahmad F Mende U Kranias EG MacLennan DH Seidman JG Seidman CE 《Science (New York, N.Y.)》2003,299(5611):1410-1413
Molecular etiologies of heart failure, an emerging cardiovascular epidemic affecting 4.7 million Americans and costing 17.8 billion health-care dollars annually, remain poorly understood. Here we report that an inherited human dilated cardiomyopathy with refractory congestive heart failure is caused by a dominant Arg --> Cys missense mutation at residue 9 (R9C) in phospholamban (PLN), a transmembrane phosphoprotein that inhibits the cardiac sarcoplasmic reticular Ca2+-adenosine triphosphatase (SERCA2a) pump. Transgenic PLN(R9C) mice recapitulated human heart failure with premature death. Cellular and biochemical studies revealed that, unlike wild-type PLN, PLN(R9C) did not directly inhibit SERCA2a. Rather, PLN(R9C) trapped protein kinase A (PKA), which blocked PKA-mediated phosphorylation of wild-type PLN and in turn delayed decay of calcium transients in myocytes. These results indicate that myocellular calcium dysregulation can initiate human heart failure-a finding that may lead to therapeutic opportunities. 相似文献
438.
439.
Arendt D Tessmar-Raible K Snyman H Dorresteijn AW Wittbrodt J 《Science (New York, N.Y.)》2004,306(5697):869-871
For vision, insect and vertebrate eyes use rhabdomeric and ciliary photoreceptor cells, respectively. These cells show distinct architecture and transduce the light signal by different phototransductory cascades. In the marine rag-worm Platynereis, we find both cell types: rhabdomeric photoreceptor cells in the eyes and ciliary photoreceptor cells in the brain. The latter use a photopigment closely related to vertebrate rod and cone opsins. Comparative analysis indicates that both types of photoreceptors, with distinct opsins, coexisted in Urbilateria, the last common ancestor of insects and vertebrates, and sheds new light on vertebrate eye evolution. 相似文献
440.
Lipopeptide Antibiotics Produced by the Engineered Strain Bacillus subtilis GEB3 and Detection of Its Bioactivity 总被引:1,自引:0,他引:1
MALDI-TOF-MS technology was used for identification of lipopeptide antibiotics produced by GEB3 strain,a derivative of Bacillus subtilis 168 which was transformed by lpaB3gene.The result showed GEB3 only produced lipopeptide antibiotic surfactin.The analysis by LC-MS demonstrated that GEB3 produced standard surfactin isoforms with side chain lengths of 13,14 and 15 carbon atoms.The bioactivity detection of surfactin indicated that the surfactin produced by GEB3 had inhibition effect on plant pathogens Rhizoctonia solani and Pyricularia oryzae. 相似文献