全文获取类型
收费全文 | 1576篇 |
免费 | 90篇 |
国内免费 | 1篇 |
专业分类
林业 | 77篇 |
农学 | 57篇 |
基础科学 | 7篇 |
288篇 | |
综合类 | 100篇 |
农作物 | 77篇 |
水产渔业 | 126篇 |
畜牧兽医 | 755篇 |
园艺 | 31篇 |
植物保护 | 149篇 |
出版年
2024年 | 3篇 |
2023年 | 24篇 |
2022年 | 33篇 |
2021年 | 67篇 |
2020年 | 52篇 |
2019年 | 72篇 |
2018年 | 46篇 |
2017年 | 47篇 |
2016年 | 46篇 |
2015年 | 28篇 |
2014年 | 68篇 |
2013年 | 71篇 |
2012年 | 129篇 |
2011年 | 134篇 |
2010年 | 75篇 |
2009年 | 69篇 |
2008年 | 102篇 |
2007年 | 103篇 |
2006年 | 82篇 |
2005年 | 73篇 |
2004年 | 57篇 |
2003年 | 50篇 |
2002年 | 53篇 |
2001年 | 18篇 |
2000年 | 15篇 |
1999年 | 9篇 |
1998年 | 7篇 |
1997年 | 11篇 |
1996年 | 14篇 |
1995年 | 10篇 |
1994年 | 8篇 |
1993年 | 4篇 |
1992年 | 8篇 |
1991年 | 7篇 |
1990年 | 5篇 |
1989年 | 6篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1980年 | 3篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1975年 | 4篇 |
1970年 | 2篇 |
1969年 | 4篇 |
1966年 | 2篇 |
排序方式: 共有1667条查询结果,搜索用时 140 毫秒
101.
Nanominerals, mineral nanoparticles, and Earth systems 总被引:4,自引:0,他引:4
Hochella MF Lower SK Maurice PA Penn RL Sahai N Sparks DL Twining BS 《Science (New York, N.Y.)》2008,319(5870):1631-1635
Minerals are more complex than previously thought because of the discovery that their chemical properties vary as a function of particle size when smaller, in at least one dimension, than a few nanometers, to perhaps as much as several tens of nanometers. These variations are most likely due, at least in part, to differences in surface and near-surface atomic structure, as well as crystal shape and surface topography as a function of size in this smallest of size regimes. It has now been established that these variations may make a difference in important geochemical and biogeochemical reactions and kinetics. This recognition is broadening and enriching our view of how minerals influence the hydrosphere, pedosphere, biosphere, and atmosphere. 相似文献
102.
Vanhollebeke B De Muylder G Nielsen MJ Pays A Tebabi P Dieu M Raes M Moestrup SK Pays E 《Science (New York, N.Y.)》2008,320(5876):677-681
The protozoan parasite Trypanosoma brucei is lysed by apolipoprotein L-I, a component of human high-density lipoprotein (HDL) particles that are also characterized by the presence of haptoglobin-related protein. We report that this process is mediated by a parasite glycoprotein receptor, which binds the haptoglobin-hemoglobin complex with high affinity for the uptake and incorporation of heme into intracellular hemoproteins. In mice, this receptor was required for optimal parasite growth and the resistance of parasites to the oxidative burst by host macrophages. In humans, the trypanosome receptor also recognized the complex between hemoglobin and haptoglobin-related protein, which explains its ability to capture trypanolytic HDLs. Thus, in humans the presence of haptoglobin-related protein has diverted the function of the trypanosome haptoglobin-hemoglobin receptor to elicit innate host immunity against the parasite. 相似文献
103.
Despite concerns of consumer protection andenvironmental groups that the use of geneticallyproduced growth hormone in milk-producing cows mayadversely impact the safety of the milk supply,scientific evidence and governmental findings from theUSA appear to indicate that milk fromtreated cows is identical in quality, taste, andnutritional value to milk from untreated cows. Limitedexperience to date in the USA demonstrateslittle consumer resistance to milk from cows that havereceived the growth hormone, which can lead to a 15%increase in milk production. In fact, if there is noperceived differentiation between the two forms ofmilk, the issue offers little choice to consumers atlarge, and may result in economic benefit only toselected dairy farmers, as well as the producers ofthe genetically produced growth hormone. Thissituation in the USA may be an example ofdysfunctional technology transfer, with desirablebenefits to a few, and as yet unknown benefits to thesociety. The USA has taken a bold move inapproving the use of bovine growth hormone in milk-producing cows, while the European Union has takena divergent approach by enacting lengthy moratoriumsagainst its use. The basic lesson to be learned fromthe bST case is that lack of awareness amonggovernment officials and the public at large serves asa significant impediment to the adoption of newtechnologies. Accordingly, delays may occur indelivery of significant social benefits to thepopulation as a whole. Obviously, the issue extendsbeyond bST. 相似文献
104.
Willingham S Outeiro TF DeVit MJ Lindquist SL Muchowski PJ 《Science (New York, N.Y.)》2003,302(5651):1769-1772
Genome-wide screens were performed in yeast to identify genes that enhance the toxicity of a mutant huntingtin fragment or of alpha-synuclein. Of 4850 haploid mutants containing deletions of nonessential genes, 52 were identified that were sensitive to a mutant huntingtin fragment, 86 that were sensitive to alpha-synuclein, and only one mutant that was sensitive to both. Genes that enhanced toxicity of the mutant huntingtin fragment clustered in the functionally related cellular processes of response to stress, protein folding, and ubiquitin-dependent protein catabolism, whereas genes that modified alpha-synuclein toxicity clustered in the processes of lipid metabolism and vesicle-mediated transport. Genes with human orthologs were overrepresented in our screens, suggesting that we may have discovered conserved and nonoverlapping sets of cell-autonomous genes and pathways that are relevant to Huntington's disease and Parkinson's disease. 相似文献
105.
106.
Samanta A Costa MH Nunes EL Vieira SA Xu L Myneni RB 《Science (New York, N.Y.)》2011,333(6046):1093; author reply 1093
Zhao and Running (Reports, 20 August 2010, p. 940) reported a reduction in global terrestrial net primary production (NPP) from 2000 through 2009. We argue that the small trends, regional patterns, and interannual variations that they describe are artifacts of their NPP model. Satellite observations of vegetation activity show no statistically significant changes in more than 85% of the vegetated lands south of 70°N during the same 2000 to 2009 period. 相似文献
107.
In mammals, fertilization typically involves the ovulation of one or a few eggs at one end of the female reproductive tract and the entry of millions of sperm at the other. Given this disparity in numbers, it might be expected that the more precious commodity-eggs-would be subject to more stringent quality-control mechanisms. However, information from engineered mutations of meiotic genes suggests just the opposite. Specifically, the available mutants demonstrate striking sexual dimorphism in response to meiotic disruption; for example, faced with adversity, male meiosis grinds to a halt, whereas female meiosis soldiers on. This female "robustness" comes with a cost, however, because aneuploidy appears to be increased in the resultant oocytes. 相似文献
108.
D H Hsu R de Waal Malefyt D F Fiorentino M N Dang P Vieira J de Vries H Spits T R Mosmann K W Moore 《Science (New York, N.Y.)》1990,250(4982):830-832
Cytokine synthesis inhibitory factor (CSIF; interleukin-10), a product of mouse TH2 T cell clones that inhibits synthesis of cytokines by mouse TH1 T cell clones, exhibits extensive sequence similarity to an uncharacterized open reading frame in the Epstein-Barr virus BCRF1. Recombinant BCRF1 protein mimics the activity of interleukin-10, suggesting that BCRF1 may have a role in the interaction of the virus with the host's immune system. 相似文献
109.
Davis ST Benson BG Bramson HN Chapman DE Dickerson SH Dold KM Eberwein DJ Edelstein M Frye SV Gampe RT Grifffen RJ Harris PA Hassell AM Holmes WD Hunter RN Knick VB Lackey K Lovejoy B Luzzio MJ Murray D Parker P Rocque WJ Shewchuk-Chapman L Veal JM Walker DH Kuyper LF 《Science (New York, N.Y.)》2002,298(5602):2327
110.
Gelfand MJ Raver JL Nishii L Leslie LM Lun J Lim BC Duan L Almaliach A Ang S Arnadottir J Aycan Z Boehnke K Boski P Cabecinhas R Chan D Chhokar J D'Amato A Ferrer M Fischlmayr IC Fischer R Fülöp M Georgas J Kashima ES Kashima Y Kim K Lempereur A Marquez P Othman R Overlaet B Panagiotopoulou P Peltzer K Perez-Florizno LR Ponomarenko L Realo A Schei V Schmitt M Smith PB Soomro N Szabo E Taveesin N Toyama M Van de Vliert E Vohra N Ward C Yamaguchi S 《Science (New York, N.Y.)》2011,332(6033):1100-1104
With data from 33 nations, we illustrate the differences between cultures that are tight (have many strong norms and a low tolerance of deviant behavior) versus loose (have weak social norms and a high tolerance of deviant behavior). Tightness-looseness is part of a complex, loosely integrated multilevel system that comprises distal ecological and historical threats (e.g., high population density, resource scarcity, a history of territorial conflict, and disease and environmental threats), broad versus narrow socialization in societal institutions (e.g., autocracy, media regulations), the strength of everyday recurring situations, and micro-level psychological affordances (e.g., prevention self-guides, high regulatory strength, need for structure). This research advances knowledge that can foster cross-cultural understanding in a world of increasing global interdependence and has implications for modeling cultural change. 相似文献