全文获取类型
收费全文 | 371篇 |
免费 | 18篇 |
专业分类
林业 | 13篇 |
农学 | 8篇 |
基础科学 | 4篇 |
40篇 | |
综合类 | 43篇 |
农作物 | 24篇 |
水产渔业 | 13篇 |
畜牧兽医 | 201篇 |
园艺 | 12篇 |
植物保护 | 31篇 |
出版年
2021年 | 4篇 |
2020年 | 2篇 |
2019年 | 3篇 |
2018年 | 4篇 |
2017年 | 4篇 |
2016年 | 8篇 |
2015年 | 3篇 |
2014年 | 7篇 |
2013年 | 20篇 |
2012年 | 16篇 |
2011年 | 16篇 |
2010年 | 9篇 |
2009年 | 6篇 |
2008年 | 19篇 |
2007年 | 13篇 |
2006年 | 10篇 |
2005年 | 12篇 |
2004年 | 19篇 |
2003年 | 16篇 |
2002年 | 12篇 |
2001年 | 15篇 |
2000年 | 17篇 |
1999年 | 6篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1995年 | 9篇 |
1994年 | 5篇 |
1993年 | 7篇 |
1992年 | 13篇 |
1991年 | 12篇 |
1990年 | 8篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1987年 | 7篇 |
1986年 | 8篇 |
1985年 | 8篇 |
1984年 | 2篇 |
1983年 | 8篇 |
1982年 | 4篇 |
1979年 | 4篇 |
1977年 | 2篇 |
1974年 | 2篇 |
1973年 | 6篇 |
1972年 | 4篇 |
1968年 | 5篇 |
1967年 | 3篇 |
1966年 | 2篇 |
1914年 | 1篇 |
1902年 | 1篇 |
1896年 | 1篇 |
排序方式: 共有389条查询结果,搜索用时 15 毫秒
31.
Matthews RG 《Science (New York, N.Y.)》1989,246(4933):1064-1065
32.
Bockelée-Morvan D Biver N Moreno R Colom P Crovisier J Gérard E Henry F Lis DC Matthews H Weaver HA Womack M Festou MC 《Science (New York, N.Y.)》2001,292(5520):1339-1343
The gas activity of comet C/1999 S4 (LINEAR) was monitored at radio wavelengths during its disruption. A runaway fragmentation of the nucleus may have begun around 18 July 2000 and proceeded until 23 July. The mass in small icy debris (=30-centimeter radius) was comparable to the mass in the large fragments seen in optical images. The mass budget after breakup suggests a small nucleus ( approximately 100- to 300-meter radius) that had been losing debris for weeks. The HNC, H2CO, H2S, and CS abundances relative to H2O measured during breakup are consistent with those obtained in other comets. However, a deficiency in CH3OH and CO is observed. 相似文献
33.
34.
Replacements of Pro86 in phage T4 lysozyme extend an alpha-helix but do not alter protein stability 总被引:10,自引:0,他引:10
T Alber J A Bell D P Sun H Nicholson J A Wozniak S Cook B W Matthews 《Science (New York, N.Y.)》1988,239(4840):631-635
To investigate the relation between protein stability and the predicted stabilities of individual secondary structural elements, residue Pro86 in an alpha-helix in phage T4 lysozyme was replaced by ten different amino acids. The x-ray crystal structures of seven of the mutant lysozymes were determined at high resolution. In each case, replacement of the proline resulted in the formation of an extended alpha-helix. This involves a large conformational change in residues 81 to 83 and smaller shifts that extend 20 angstroms across the protein surface. Unexpectedly, all ten amino acid substitutions marginally reduce protein thermostability. This insensitivity of stability to the amino acid at position 86 is not simply explained by statistical and thermodynamic criteria for helical propensity. The observed conformational changes illustrate a general mechanism by which proteins can tolerate mutations. 相似文献
35.
Creutzfeldt-Jakob disease (spongiform encephalopathy): transmission to the chimpanzee 总被引:48,自引:0,他引:48
C J Gibbs D C Gajdusek D M Asher M P Alpers E Beck P M Daniel W B Matthews 《Science (New York, N.Y.)》1968,161(839):388-389
Biopsy material taken from the brain of a patient with CreutzfeldtJakob disease with status spongiosus induced a similar fatal encephalopathy in a chimpanzee 13 months after inoculation. 相似文献
36.
Matthews KR 《Science (New York, N.Y.)》2011,331(6021):1149-1153
Vector-borne parasites cause major human diseases of the developing world, including malaria, human African trypanosomiasis, Chagas disease, leishmaniasis, filariasis, and schistosomiasis. Although the life cycles of these parasites were defined over 100 years ago, the strategies they use to optimize their successful transmission are only now being understood in molecular terms. Parasites are now known to monitor their environment in both their host and vector and in response to other parasites. This allows them to adapt their developmental cycles and to counteract any unfavorable conditions they encounter. Here, I review the interactions that parasites engage in with their hosts and vectors to maximize their survival and spread. 相似文献
37.
The large variation in the ratio of uranium-234 to uranium-238 (234U/238U) in rivers is not well understood, but may provide information about past weathering and rainfall and is important because it controls seawater (234U/238U). Here, we demonstrate the importance of physical weathering and rainfall for (234U/238U), using rivers from South Island, New Zealand. These data allow interpretation of an existing speleothem (234U/238U) record and suggest that New Zealand glacier advance 13,000 years ago was influenced by increased rainfall rather than by Younger Dryas-like cooling. A model of seawater (234U/238U) during glacial cycles indicates that rejection of corals based on modern (234U/238U) +/- <0.01 is not merited and may reject the highest quality ages. 相似文献
38.
39.
The attenuation of residual industrial loads of chloride (Cl-) and total ammonia (T-NH3) from Solvay waste bedsto Ninemile Creek, New York, and downstream polluted Onondaga Lake, is characterized and quantified based on fourteen years ofmonitoring following closure of a soda ash manufacturing facility. Concentrations of these constituents were monitored atleast bi-weekly at two sites on Ninemile Creek that bound the waste bed inputs, and at the mouths of the two other major tributaries to the lake, to quantify inputs from the industrial deposits and to place these residual loads in the perspective of contributions to total lake loading. Variations in the concentrations of these constituents in Ninemile Creek downstreamof the industrial inputs within individual years are well represented by a dilution model; i.e., linearity of concentrationversus inverse stream flow. A relatively uniform ratio of T-NH3 to Cl- has been maintained in the residual loading, about 0.42 g T-NH3 per kg Cl-. Substantial decreases (~40%) in loading of these constituents fromthe waste beds to Ninemile Creek over the post-closure period are documented through shifts in the dilution model. As a result,the contribution of this source to the total lake loading has decreased from ~45% to <30%. The estimated total residual Cl- load received from the waste beds since closure of the industry (~1 million metric tons) corresponds to ~1.6 yr of the full operating load of the industry before closure. The time required to reach a Cl- concentration goal for Ninemile Creek is considered, based onprojections of the post-closure trend. 相似文献
40.
The response of 3-year-old grapevines (Vitis vinifera L. cultivar ‘Thompson Seedless’) to furrow and drip irrigation was quantified in terms of water status, growth, and water use efficiency (WUE). Drip irrigation was applied daily according to best estimates of vineyard evapotranspiration while furrow irrigations were applied when 50% of the plant available soilwater content had been depleted. Drip and furrow irrigated vines showed similar water status (midday leaf water potential, Ψ1) and shoot growth patterns throughout the season. Dry weight partitioning was not significantly different between treatments but root mass was somewhat larger for the furrow than drip irrigated vines. Nitrogen concentrations of the fruit and roots were significantly (P < 0.05) less for the drip irrigated vines when compared with the furrow treatment. Similar WUE (kg water kg−1 fresh fruit wt.) were obtained for both treatments indicating that furrow irrigation was as efficient as drip irrigation under the conditions of this study. The data indicate that drip irrigation may increase the potential for control of vine growth by making vines more dependent on irrigation and N fertilization than furrow irrigation. 相似文献