全文获取类型
收费全文 | 60226篇 |
免费 | 3483篇 |
国内免费 | 35篇 |
专业分类
林业 | 2425篇 |
农学 | 1851篇 |
基础科学 | 301篇 |
6614篇 | |
综合类 | 10218篇 |
农作物 | 2083篇 |
水产渔业 | 2798篇 |
畜牧兽医 | 33005篇 |
园艺 | 705篇 |
植物保护 | 3744篇 |
出版年
2018年 | 895篇 |
2017年 | 912篇 |
2016年 | 808篇 |
2015年 | 772篇 |
2014年 | 839篇 |
2013年 | 2575篇 |
2012年 | 1669篇 |
2011年 | 2019篇 |
2010年 | 1269篇 |
2009年 | 1250篇 |
2008年 | 1879篇 |
2007年 | 1846篇 |
2006年 | 1727篇 |
2005年 | 1580篇 |
2004年 | 1501篇 |
2003年 | 1543篇 |
2002年 | 1470篇 |
2001年 | 1809篇 |
2000年 | 1783篇 |
1999年 | 1462篇 |
1998年 | 620篇 |
1997年 | 606篇 |
1996年 | 546篇 |
1995年 | 641篇 |
1994年 | 600篇 |
1993年 | 571篇 |
1992年 | 1221篇 |
1991年 | 1369篇 |
1990年 | 1258篇 |
1989年 | 1265篇 |
1988年 | 1163篇 |
1987年 | 1136篇 |
1986年 | 1194篇 |
1985年 | 1194篇 |
1984年 | 960篇 |
1983年 | 900篇 |
1982年 | 582篇 |
1979年 | 891篇 |
1978年 | 701篇 |
1977年 | 694篇 |
1976年 | 711篇 |
1975年 | 714篇 |
1974年 | 866篇 |
1973年 | 842篇 |
1972年 | 812篇 |
1971年 | 727篇 |
1970年 | 769篇 |
1969年 | 733篇 |
1968年 | 651篇 |
1967年 | 657篇 |
排序方式: 共有10000条查询结果,搜索用时 781 毫秒
261.
262.
263.
264.
265.
266.
267.
The atomic force microscope (AFM) was used to image an electrode surface at atomic resolution while the electrode was under potential control in a fluid electrolyte. A new level of subtlety was observed for each step of a complete electrochemical cycle that started with an Au(111) surface onto which bulk Cu was electrodeposited. The Cu was stripped down to an underpotential-deposited monolayer and finally returned to a bare Au(111) surface. The images revealed that the underpotential-deposited monolayer has different structures in different electrolytes. Specifically, for a perchloric acid electrolyte the Cu atoms are in a close-packed lattice with a spacing of 0.29 +/- 0.02 nanometer (nm). For a sulfate electrolyte they are in a more open lattice with a spacing of 0.49 +/- 0.02 nm. As the deposited Cu layer grew thicker, the Cu atoms converged to a (111)-oriented layer with a lattice spacing of 0.26 +/- 0.02 nm for both electrolytes. A terrace pattern was observed during dissolution of bulk Cu. Images were obtained of an atomically resolved Cu monolayer in one region and an atomically resolved Au substrate in another in which a 30 degrees rotation of the Cu monolayer lattice from the Au lattice is clearly visible. 相似文献
268.
269.
M D Bishop M E Davis W R Harvey G R Wilson B D VanStavern 《Journal of animal science》1991,69(11):4360-4367
A single generation divergent selection study, replicated four times (1983, 1984, 1985, and 1986), was conducted to assess genetic differences between progeny of high and low feed conversion sires in Angus beef cattle and to determine correlated response for weight gain (ADG140), feed intake (AVFD140), and BW (OFFTSTWT) in a time- (140-d) and fat-constant (8.9 mm) period. Realized heritability estimates for unadjusted (feed/gain; FEFF140; .26) and adjusted feed conversion (adjusted as recommended by the BIF, 1986; ADJFDEFF; .46) were obtained. The difference in heritability estimates reflects variation accounted for by adjustment for BW differences, and thus maintenance requirements, of individual progeny. Phenotypic and "pseudo" realized genetic correlations of FEFF140 with ADG140, AVFD 140, and OFFTSTWT were -.33 and -.66, .49 and -.26, and .15 and -.41, respectively. Phenotypic and "pseudo" realized genetic correlations of ADJFDEFF with ADG140, AVFD140, OFFTSTWT, and FEFF140 were -.54 and -.59, .30 and -.23, .27 and -.36, and .97 and .49, respectively. Subcutaneous fat (as estimated by ultrasonic measurement; BF140) had phenotypic and "pseudo" realized genetic correlations with FEFF140 of -.33 and .66, respectively, and with ADJFDEFF of -.44 and -.58, respectively. 相似文献
270.
Thirty-six mice were inoculated intranasally with Bordetella parapertussis organisms (isolated from sheep with chronic non-progressive pneumonia) to study their deposition and clearance in the lower respiratory tract. The deposition of the organism was greater in the trachea than in the lungs. At 48 hours after inoculation, almost 100% of organisms were cleared from the trachea but only 55% of organisms were cleared from the lungs. This result correlates well with the morphological changes seen previously in the pulmonary parenchyma and airways of mice and lambs experimentally infected with this organism. 相似文献