全文获取类型
收费全文 | 3398篇 |
免费 | 264篇 |
国内免费 | 2篇 |
专业分类
林业 | 269篇 |
农学 | 129篇 |
基础科学 | 19篇 |
882篇 | |
综合类 | 254篇 |
农作物 | 151篇 |
水产渔业 | 306篇 |
畜牧兽医 | 1333篇 |
园艺 | 43篇 |
植物保护 | 278篇 |
出版年
2024年 | 5篇 |
2023年 | 57篇 |
2022年 | 37篇 |
2021年 | 97篇 |
2020年 | 108篇 |
2019年 | 47篇 |
2018年 | 101篇 |
2017年 | 107篇 |
2016年 | 153篇 |
2015年 | 127篇 |
2014年 | 173篇 |
2013年 | 262篇 |
2012年 | 306篇 |
2011年 | 232篇 |
2010年 | 115篇 |
2009年 | 78篇 |
2008年 | 224篇 |
2007年 | 212篇 |
2006年 | 205篇 |
2005年 | 191篇 |
2004年 | 144篇 |
2003年 | 163篇 |
2002年 | 125篇 |
2001年 | 80篇 |
2000年 | 73篇 |
1999年 | 40篇 |
1998年 | 25篇 |
1997年 | 17篇 |
1996年 | 10篇 |
1995年 | 9篇 |
1994年 | 9篇 |
1993年 | 15篇 |
1992年 | 6篇 |
1991年 | 5篇 |
1990年 | 5篇 |
1989年 | 6篇 |
1988年 | 7篇 |
1987年 | 3篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1981年 | 6篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1976年 | 4篇 |
1974年 | 5篇 |
1969年 | 4篇 |
1968年 | 6篇 |
1953年 | 3篇 |
1937年 | 2篇 |
排序方式: 共有3664条查询结果,搜索用时 31 毫秒
991.
992.
Roberta Renzo Alexandre P. Ribeiro Miguel L. da Silva Germana Alegro da Silva Kethye P. Ortencio Alexandre A. F. Barros Sobrinho Tiago Wilson Patriarca Mineo José Luiz Laus 《Veterinary ophthalmology》2014,17(4):280-285
This study aimed to evaluate and correlate intraocular pressure (IOP), endothelial cell density (CD), and hexagonality (HEX), and the aqueous humor prostaglandin E2 (PGE2) concentration in dogs with mature (MG, n = 8) and hypermature (HG, n = 8) cataracts. Eight laboratory beagles with no ocular abnormalities were included as a control group (CG). The IOP was measured using a digital applanation tonometer. Noncontact specular microscopy was used to evaluate CD and HEX. Samples of aqueous humor were used to determine prostaglandin E2 concentration using enzyme‐linked immunoassay. Data were compared by anova and Bonferroni's multiple comparison test, and possible correlations among the PGE2 aqueous concentration and corneal endothelium cell parameters were assessed by Person′s test (P < 0.05). Average values of IOP (P = 0.45) and CD (P = 0.39) were not significantly different between MG, HM, and CG. Average values of HEX were lower, and PGE2 concentration was increased in the MG and HG in comparison with CG (P < 0.05); however, such parameters did not change significantly between MG and HG (P > 0.05). PGE2 values did not correlate with IOP, CD, and HEX in any group (P > 0.05). Although there were a small number of dogs studied, our results demonstrated that cataract progression from mature to hypermature did not have a significant change in PGE2 aqueous concentration, IOP, corneal endothelial cell count, or morphology. In addition, PGE2 concentration was not correlated with parameters of the corneal endothelium or IOP in dogs with mature or hypermature cataracts. 相似文献
993.
994.
Fork reversal and ssDNA accumulation at stalled replication forks owing to checkpoint defects 总被引:1,自引:0,他引:1
Checkpoint-mediated control of replicating chromosomes is essential for preventing cancer. In yeast, Rad53 kinase protects stalled replication forks from pathological rearrangements. To characterize the mechanisms controlling fork integrity, we analyzed replication intermediates formed in response to replication blocks using electron microscopy. At the forks, wild-type cells accumulate short single-stranded regions, which likely causes checkpoint activation, whereas rad53 mutants exhibit extensive single-stranded gaps and hemi-replicated intermediates, consistent with a lagging-strand synthesis defect. Further, rad53 cells accumulate Holliday junctions through fork reversal. We speculate that, in checkpoint mutants, abnormal replication intermediates begin to form because of uncoordinated replication and are further processed by unscheduled recombination pathways, causing genome instability. 相似文献
995.
Hinkov V Haug D Fauqué B Bourges P Sidis Y Ivanov A Bernhard C Lin CT Keimer B 《Science (New York, N.Y.)》2008,319(5863):597-600
Electronic phases with symmetry properties matching those of conventional liquid crystals have recently been discovered in transport experiments on semiconductor heterostructures and metal oxides at millikelvin temperatures. We report the spontaneous onset of a one-dimensional, incommensurate modulation of the spin system in the high-transition-temperature superconductor YBa2Cu3O6.45 upon cooling below approximately 150 kelvin, whereas static magnetic order is absent above 2 kelvin. The evolution of this modulation with temperature and doping parallels that of the in-plane anisotropy of the resistivity, indicating an electronic nematic phase that is stable over a wide temperature range. The results suggest that soft spin fluctuations are a microscopic route toward electronic liquid crystals and that nematic order can coexist with high-temperature superconductivity in underdoped cuprates. 相似文献
996.
Le Quéré C Rödenbeck C Buitenhuis ET Conway TJ Langenfelds R Gomez A Labuschagne C Ramonet M Nakazawa T Metzl N Gillett N Heimann M 《Science (New York, N.Y.)》2007,316(5832):1735-1738
Based on observed atmospheric carbon dioxide (CO2) concentration and an inverse method, we estimate that the Southern Ocean sink of CO2 has weakened between 1981 and 2004 by 0.08 petagrams of carbon per year per decade relative to the trend expected from the large increase in atmospheric CO2. We attribute this weakening to the observed increase in Southern Ocean winds resulting from human activities, which is projected to continue in the future. Consequences include a reduction of the efficiency of the Southern Ocean sink of CO2 in the short term (about 25 years) and possibly a higher level of stabilization of atmospheric CO2 on a multicentury time scale. 相似文献
997.
Saint André Av Blackwell NM Hall LR Hoerauf A Brattig NW Volkmann L Taylor MJ Ford L Hise AG Lass JH Diaconu E Pearlman E 《Science (New York, N.Y.)》2002,295(5561):1892-1895
Parasitic filarial nematodes infect more than 200 million individuals worldwide, causing debilitating inflammatory diseases such as river blindness and lymphatic filariasis. Using a murine model for river blindness in which soluble extracts of filarial nematodes were injected into the corneal stroma, we demonstrated that the predominant inflammatory response in the cornea was due to species of endosymbiotic Wolbachia bacteria. In addition, the inflammatory response induced by these bacteria was dependent on expression of functional Toll-like receptor 4 (TLR4) on host cells. 相似文献
998.
Genome-wide insertional mutagenesis of Arabidopsis thaliana 总被引:2,自引:0,他引:2
Alonso JM Stepanova AN Leisse TJ Kim CJ Chen H Shinn P Stevenson DK Zimmerman J Barajas P Cheuk R Gadrinab C Heller C Jeske A Koesema E Meyers CC Parker H Prednis L Ansari Y Choy N Deen H Geralt M Hazari N Hom E Karnes M Mulholland C Ndubaku R Schmidt I Guzman P Aguilar-Henonin L Schmid M Weigel D Carter DE Marchand T Risseeuw E Brogden D Zeko A Crosby WL Berry CC Ecker JR 《Science (New York, N.Y.)》2003,301(5633):653-657
Over 225,000 independent Agrobacterium transferred DNA (T-DNA) insertion events in the genome of the reference plant Arabidopsis thaliana have been created that represent near saturation of the gene space. The precise locations were determined for more than 88,000 T-DNA insertions, which resulted in the identification of mutations in more than 21,700 of the approximately 29,454 predicted Arabidopsis genes. Genome-wide analysis of the distribution of integration events revealed the existence of a large integration site bias at both the chromosome and gene levels. Insertion mutations were identified in genes that are regulated in response to the plant hormone ethylene. 相似文献
999.
Schoell M Schouten S Damsté JS de Leeuw JW Summons RE 《Science (New York, N.Y.)》1994,263(5150):1122-1125
The difference in carbon-13 ((13)C) contents of hopane and sterane biomarkers in the Monterey formation (Naples Beach, California) parallels the Miocene inorganic record of the change in (18)O (delta(18)O), reflecting the Miocene evolution from a well-mixed to a highly stratified photic zone (upper 100 meters) in the Pacific. Steranes (delta(13)C = 25.4 +/- 0.7 per mil versus the Pee Dee belemnite standard) from shallow photic-zone organisms do not change isotopically throughout the Miocene. In contrast, sulfur-bound C(35) hopanes (likely derived from bacterial plankton living at the base of the photic zone) have systematically decreasing (13)C concentrations in Middle and Late Miocene samples (delta(13)C = -29.5 to -31.5 per mil), consistent with the Middle Miocene formation of a carbon dioxide-rich cold water mass at the base of the photic zone. 相似文献
1000.
Monot M Honoré N Garnier T Araoz R Coppée JY Lacroix C Sow S Spencer JS Truman RW Williams DL Gelber R Virmond M Flageul B Cho SN Ji B Paniz-Mondolfi A Convit J Young S Fine PE Rasolofo V Brennan PJ Cole ST 《Science (New York, N.Y.)》2005,308(5724):1040-1042
Leprosy, a chronic human disease with potentially debilitating neurological consequences, results from infection with Mycobacterium leprae. This unculturable pathogen has undergone extensive reductive evolution, with half of its genome now occupied by pseudogenes. Using comparative genomics, we demonstrated that all extant cases of leprosy are attributable to a single clone whose dissemination worldwide can be retraced from analysis of very rare single-nucleotide polymorphisms. The disease seems to have originated in Eastern Africa or the Near East and spread with successive human migrations. Europeans or North Africans introduced leprosy into West Africa and the Americas within the past 500 years. 相似文献