全文获取类型
收费全文 | 1467篇 |
免费 | 98篇 |
国内免费 | 2篇 |
专业分类
林业 | 64篇 |
农学 | 27篇 |
基础科学 | 16篇 |
244篇 | |
综合类 | 253篇 |
农作物 | 48篇 |
水产渔业 | 85篇 |
畜牧兽医 | 653篇 |
园艺 | 40篇 |
植物保护 | 137篇 |
出版年
2023年 | 7篇 |
2022年 | 8篇 |
2021年 | 16篇 |
2020年 | 33篇 |
2019年 | 25篇 |
2018年 | 22篇 |
2017年 | 24篇 |
2016年 | 26篇 |
2015年 | 27篇 |
2014年 | 28篇 |
2013年 | 71篇 |
2012年 | 81篇 |
2011年 | 105篇 |
2010年 | 69篇 |
2009年 | 41篇 |
2008年 | 106篇 |
2007年 | 109篇 |
2006年 | 102篇 |
2005年 | 92篇 |
2004年 | 87篇 |
2003年 | 84篇 |
2002年 | 106篇 |
2001年 | 19篇 |
2000年 | 21篇 |
1999年 | 15篇 |
1998年 | 20篇 |
1997年 | 15篇 |
1996年 | 18篇 |
1995年 | 6篇 |
1994年 | 10篇 |
1993年 | 13篇 |
1992年 | 12篇 |
1991年 | 6篇 |
1990年 | 8篇 |
1989年 | 15篇 |
1988年 | 4篇 |
1987年 | 12篇 |
1986年 | 7篇 |
1985年 | 4篇 |
1984年 | 9篇 |
1983年 | 12篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1978年 | 7篇 |
1977年 | 8篇 |
1976年 | 3篇 |
1974年 | 5篇 |
1971年 | 3篇 |
1968年 | 3篇 |
1962年 | 3篇 |
排序方式: 共有1567条查询结果,搜索用时 15 毫秒
121.
Foote M Crampton JS Beu AG Marshall BA Cooper RA Maxwell PA Matcham I 《Science (New York, N.Y.)》2007,318(5853):1131-1134
In the time between speciation and extinction, a species' ecological and biogeographic footprint-its occupancy-will vary in response to macroecological drivers and historical contingencies. Despite their importance for understanding macroecological processes, general patterns of long-term species occupancy remain largely unknown. We documented the occupancy histories of Cenozoic marine mollusks from New Zealand. For both genera and species, these show a distinct pattern of increase to relatively short-lived peak occupancy at mid-duration, followed by a decline toward extinction. Thus, species at greatest risk for extinction are those that have already been in decline for a substantial period of time. This pattern of protracted rise and fall stands in contrast to that of incumbency, insofar as species show no general tendency to stay near maximal occupancy once established. 相似文献
122.
123.
Garzione CN Hoke GD Libarkin JC Withers S MacFadden B Eiler J Ghosh P Mulch A 《Science (New York, N.Y.)》2008,320(5881):1304-1307
The surface uplift of mountain belts is generally assumed to reflect progressive shortening and crustal thickening, leading to their gradual rise. Recent studies of the Andes indicate that their elevation remained relatively stable for long periods (tens of millions of years), separated by rapid (1 to 4 million years) changes of 1.5 kilometers or more. Periodic punctuated surface uplift of mountain belts probably reflects the rapid removal of unstable, dense lower lithosphere after long-term thickening of the crust and lithospheric mantle. 相似文献
124.
Bruce WF 《Science (New York, N.Y.)》1935,81(2094):179-180
125.
Engelman JA Zejnullahu K Mitsudomi T Song Y Hyland C Park JO Lindeman N Gale CM Zhao X Christensen J Kosaka T Holmes AJ Rogers AM Cappuzzo F Mok T Lee C Johnson BE Cantley LC Jänne PA 《Science (New York, N.Y.)》2007,316(5827):1039-1043
The epidermal growth factor receptor (EGFR) kinase inhibitors gefitinib and erlotinib are effective treatments for lung cancers with EGFR activating mutations, but these tumors invariably develop drug resistance. Here, we describe a gefitinib-sensitive lung cancer cell line that developed resistance to gefitinib as a result of focal amplification of the MET proto-oncogene. inhibition of MET signaling in these cells restored their sensitivity to gefitinib. MET amplification was detected in 4 of 18 (22%) lung cancer specimens that had developed resistance to gefitinib or erlotinib. We find that amplification of MET causes gefitinib resistance by driving ERBB3 (HER3)-dependent activation of PI3K, a pathway thought to be specific to EGFR/ERBB family receptors. Thus, we propose that MET amplification may promote drug resistance in other ERBB-driven cancers as well. 相似文献
126.
Solforosi L Criado JR McGavern DB Wirz S Sánchez-Alavez M Sugama S DeGiorgio LA Volpe BT Wiseman E Abalos G Masliah E Gilden D Oldstone MB Conti B Williamson RA 《Science (New York, N.Y.)》2004,303(5663):1514-1516
Neuronal death is a prominent, but poorly understood, pathological hallmark of prion disease. Notably, in the absence of the cellular prion protein (PrPC), the disease-associated isoform, PrPSc, appears not to be intrinsically neurotoxic, suggesting that PrPC itself may participate directly in the prion neurodegenerative cascade. Here, cross-linking PrPC in vivo with specific monoclonal antibodies was found to trigger rapid and extensive apoptosis in hippocampal and cerebellar neurons. These findings suggest that PrPC functions in the control of neuronal survival and provides a model to explore whether cross-linking of PrPC by oligomeric PrPSc can promote neuronal loss during prion infection. 相似文献
127.
Fleming DG Arseneau DJ Sukhorukov O Brewer JH Mielke SL Schatz GC Garrett BC Peterson KA Truhlar DG 《Science (New York, N.Y.)》2011,331(6016):448-450
The neutral muonic helium atom may be regarded as the heaviest isotope of the hydrogen atom, with a mass of ~4.1 atomic mass units ((4.1)H), because the negative muon almost perfectly screens one proton charge. We report the reaction rate of (4.1)H with (1)H(2) to produce (4.1)H(1)H + (1)H at 295 to 500 kelvin. The experimental rate constants are compared with the predictions of accurate quantum-mechanical dynamics calculations carried out on an accurate Born-Huang potential energy surface and with previously measured rate constants of (0.11)H (where (0.11)H is shorthand for muonium). Kinetic isotope effects can be compared for the unprecedentedly large mass ratio of 36. The agreement with accurate quantum dynamics is quantitative at 500 kelvin, and variational transition-state theory is used to interpret the extremely low (large inverse) kinetic isotope effects in the 10(-4) to 10(-2) range. 相似文献
128.
Chen CH Huang H Ward CM Su JT Schaeffer LV Guo M Hay BA 《Science (New York, N.Y.)》2007,316(5824):597-600
One proposed strategy for controlling the transmission of insect-borne pathogens uses a drive mechanism to ensure the rapid spread of transgenes conferring disease refractoriness throughout wild populations. Here, we report the creation of maternal-effect selfish genetic elements in Drosophila that drive population replacement and are resistant to recombination-mediated dissociation of drive and disease refractoriness functions. These selfish elements use microRNA-mediated silencing of a maternally expressed gene essential for embryogenesis, which is coupled with early zygotic expression of a rescuing transgene. 相似文献
129.
Dallas DC Martin WF Strum JS Zivkovic AM Smilowitz JT Underwood MA Affolter M Lebrilla CB German JB 《Journal of agricultural and food chemistry》2011,59(8):4255-4263
N-Linked glycans of skim human milk proteins were determined for three mothers. N-Linked glycans are linked to immune defense, cell growth, and cell-cell adhesion, but their functions in human milk are undetermined. Protein-bound N-linked glycans were released with peptidyl N-glycosidase F (PNGase F), enriched by graphitized carbon chromatography, and analyzed with Chip-TOF MS. To be defined as N-glycans, compounds were required, in all three procedural replicates, to match, within 6 ppm, against a theoretical human N-glycan library and be at least 2-fold higher in abundance in PNGase F-treated than in control samples. Fifty-two N-linked glycan compositions were identified, and 24 were confirmed via tandem mass spectra analysis. Twenty-seven compositions have been found previously in human milk, and 25 are novel compositions. By abundance, 84% of N-glycans were fucosylated and 47% were sialylated. The majority (70%) of total N-glycan abundance was composed of N-glycans found in all three milk samples. 相似文献
130.
Ullah SM Murphy B Dorich B Richter B Srinivasan K 《Journal of agricultural and food chemistry》2011,59(6):2169-2174
This paper describes a new in-cell method for pursuing accelerated solvent extraction (ASE) prior to lipid analysis from food samples. It is difficult to pursue direct ASE with acid- or base-hydrolyzed samples due to the corrosive nature of the reagents and material limitations. In this study ion exchange based materials were used to remove acid or base reagents in-cell without compromising the recovery of lipids. The performance data are presented here for the new methods for lipid extraction for a variety of food samples and compared to the Mojonnier method. NIST Standard Reference Materials (SRM-1546 and SRM-1849) were used to validate the ASE methods. Excellent fat recoveries were obtained for the ASE methods. The new methods presented here enhance the utility of ASE and eliminate labor intensive protocols. 相似文献