全文获取类型
收费全文 | 82581篇 |
免费 | 3739篇 |
国内免费 | 104篇 |
专业分类
林业 | 7042篇 |
农学 | 3267篇 |
基础科学 | 487篇 |
10406篇 | |
综合类 | 11561篇 |
农作物 | 4319篇 |
水产渔业 | 4823篇 |
畜牧兽医 | 36759篇 |
园艺 | 1885篇 |
植物保护 | 5875篇 |
出版年
2018年 | 3632篇 |
2017年 | 3607篇 |
2016年 | 2115篇 |
2015年 | 1002篇 |
2014年 | 997篇 |
2013年 | 2960篇 |
2012年 | 2731篇 |
2011年 | 4359篇 |
2010年 | 3476篇 |
2009年 | 2573篇 |
2008年 | 3408篇 |
2007年 | 3631篇 |
2006年 | 2040篇 |
2005年 | 1906篇 |
2004年 | 1818篇 |
2003年 | 1888篇 |
2002年 | 1715篇 |
2001年 | 1924篇 |
2000年 | 1941篇 |
1999年 | 1548篇 |
1998年 | 647篇 |
1997年 | 623篇 |
1996年 | 577篇 |
1995年 | 670篇 |
1994年 | 618篇 |
1993年 | 610篇 |
1992年 | 1293篇 |
1991年 | 1443篇 |
1990年 | 1360篇 |
1989年 | 1375篇 |
1988年 | 1266篇 |
1987年 | 1215篇 |
1986年 | 1269篇 |
1985年 | 1272篇 |
1984年 | 1028篇 |
1983年 | 954篇 |
1982年 | 622篇 |
1979年 | 974篇 |
1978年 | 759篇 |
1977年 | 754篇 |
1976年 | 752篇 |
1975年 | 761篇 |
1974年 | 931篇 |
1973年 | 917篇 |
1972年 | 873篇 |
1971年 | 791篇 |
1970年 | 826篇 |
1969年 | 803篇 |
1968年 | 714篇 |
1967年 | 709篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
Laughlin RB 《Science (New York, N.Y.)》1988,242(4878):525-533
The case is made that the spin-liquid state of a Mott insulator, hypothesized to exist by Anderson and identified by him as the correct context for discussing high-temperature superconductors, occurs in these materials and exhibits the principles of fractional quantization identified in the fractional quantum Hall effect. The most important of these is that particles carrying a fraction of an elementary quantum number, in this case spin, attract one another by a powerful gauge force, which can lead to a new kind of superconductivity. The temperature scale for the superconductivity is set by an energy gap in the spin-wave spectrum, which is also the fundamental measure of how "liquid" the spins are. 相似文献
112.
113.
Spinrad BI 《Science (New York, N.Y.)》1988,239(4841):707-708
114.
115.
In a balance trial with 10 pigs (mean body mass 50 kg) the influence of a bacterial protein supplement (Alcaligenes eutrophus) on N-metabolism was investigated. The bacteria were included into the diet at levels of 7 and 14% at the expense of extracted soyabean meal. Thus bacterial "pure protein" (bacterial non-nucleic acid N X X 6.25) amounted to 30 and 60% of the protein of the ration. Consuming 2 kg of feed dry matter per day the animals of the control group (I) and the experimental groups (II and III) ingested 48 g, 52 g and 55 g of total N respectively. The difference in N-intake is explained by the additional nucleic acid-N, amounting to 19,8% of total bacterial N. Daily weight gain (on average 1054 g) and feed conversion efficiency (feed ingested/weight gain; on average 1,9) were relatively improved at the highest dietary level of bacterial cell mass. Faecal N-excretion was increased significantly, whereas renal N-excretion remained unchanged. Mean apparent N-digestibility was 87,4% showing no significant difference between the experimental groups. N-balance values were noticibly increased following the intake of the bacterial protein supplement. The excretion of urinary urea-N was slightly reduced whereas 4-6 times as much allantoin-N was excreted when bacteria were fed. It is calculated that about 80% of the bacterial purines are renally excreted as allantoin and uric acid. 相似文献
116.
Whole bloods from weaned lambs with severe selenium responsive unthriftiness usually contain <5 ng Se/ml. Mildly or moderately affected lambs have blood levels of 5-10 ng/ml. Selenium responsive infertility in ewes appears to be associated with whole blood selenium levels below 10 ng/ml. 相似文献
117.
Endogenous ionic currents traverse intact and damaged bone 总被引:1,自引:0,他引:1
R B Borgens 《Science (New York, N.Y.)》1984,225(4661):478-482
Living bone drives an electric current through itself and into sites of damage. Such "fracture currents" consist of two components: an intense, decaying current dependent on bone deformation and a stable, persistent current driven by a cellular battery. The latter is carried by chloride ions and, to a lesser extent, by sodium, magnesium, and calcium ions. Endogenous fracture currents are of the same polarity and similar magnitude as clinically applied currents that are successful in treating chronic nonunions in fractured bones. This suggests that the defect in biological nonunions may reside in the electrophysiology of repair. 相似文献
118.
B C Flann B A Lodge 《Journal of the Association of Official Analytical Chemists》1986,69(6):1026-1030
The validation of a liquid chromatographic procedure suitable for the determination of calcitriol and alfacalcidol in their respective formulations labeled to contain at least 0.25 micrograms drug per unit is described. The capsule content is diluted and chromatographed in 15-20 min on silica columns (5 micron) with a mobile phase of hexane-tetrahydrofuran-methylene dichloride-isopropanol (72 + 12 + 12 + 4, v/v) with detection at 254 nm. The calibration curve is linear. Recoveries of "spikes" averaged 101% with a standard deviation of 2%. Precision was better than 1.5%. 相似文献
119.
120.