全文获取类型
收费全文 | 143846篇 |
免费 | 8308篇 |
国内免费 | 73篇 |
专业分类
林业 | 5654篇 |
农学 | 4608篇 |
基础科学 | 891篇 |
16913篇 | |
综合类 | 25895篇 |
农作物 | 5793篇 |
水产渔业 | 7060篇 |
畜牧兽医 | 74088篇 |
园艺 | 1762篇 |
植物保护 | 9563篇 |
出版年
2018年 | 1871篇 |
2017年 | 2127篇 |
2016年 | 2010篇 |
2015年 | 1780篇 |
2014年 | 2135篇 |
2013年 | 5562篇 |
2012年 | 3933篇 |
2011年 | 4675篇 |
2010年 | 3112篇 |
2009年 | 3087篇 |
2008年 | 4641篇 |
2007年 | 4452篇 |
2006年 | 4175篇 |
2005年 | 4001篇 |
2004年 | 3777篇 |
2003年 | 3884篇 |
2002年 | 3612篇 |
2001年 | 4490篇 |
2000年 | 4298篇 |
1999年 | 3492篇 |
1998年 | 1520篇 |
1997年 | 1484篇 |
1996年 | 1319篇 |
1995年 | 1633篇 |
1994年 | 1423篇 |
1993年 | 1435篇 |
1992年 | 2906篇 |
1991年 | 3045篇 |
1990年 | 2965篇 |
1989年 | 3018篇 |
1988年 | 2741篇 |
1987年 | 2785篇 |
1986年 | 2926篇 |
1985年 | 2792篇 |
1984年 | 2298篇 |
1983年 | 2028篇 |
1982年 | 1442篇 |
1979年 | 2073篇 |
1978年 | 1631篇 |
1977年 | 1468篇 |
1976年 | 1401篇 |
1975年 | 1510篇 |
1974年 | 1861篇 |
1973年 | 1928篇 |
1972年 | 1844篇 |
1971年 | 1756篇 |
1970年 | 1660篇 |
1969年 | 1574篇 |
1968年 | 1263篇 |
1967年 | 1404篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Norman C 《Science (New York, N.Y.)》1981,212(4498):1007
992.
Norman C 《Science (New York, N.Y.)》1981,211(4488):1327
993.
Holden C 《Science (New York, N.Y.)》1981,214(4517):165
994.
Archeological deposits have been discovered in three pimple mounds on the upper Texas coast. Such incorporation indicates that (i) these particular mounds are aggradational rather than erosional in origin; (ii) mound formation continued until at least A.D. 1100 to 1200; (iii) each mound took 300 to 500 years to form; (iv) mounds within the same mound field did not form simultaneously; (v) certain Gulf Coast pimple mounds have archeological research potential; and (vi) archeological data also offer a means for investigating mound formation. 相似文献
995.
996.
Heathcock CH 《Science (New York, N.Y.)》1981,214(4519):395-400
For the scientist who wishes to synthesize complex organic compounds, the most difficult problem is often establishing the correct configuration at the various chiral centers as the synthesis is being carried out. In the past decade, there has been an increasing effort to find direct solutions to this problem, which is particularly acute in the synthesis of acyclic and other conformationally flexible molecules. One of the oldest organic reactions, the aldol condensation, is emerging as a powerful tool for use in achieving such stereocontrol. 相似文献
997.
998.
Abstract Sir, - Andrews'((2)) checklist of helminth parasites of wild ruminants in New Zealand recorded the presence of 10 species of gastrointestinal nematodes in chamois (Rupicapra rupicapra rupicapra L.) from "Central South Island". In October 1978 we examined 28 freshly-shot chamois cadavers from the Harper-Avoca watershed in the headwaters of the Rakaia River. Six of the nematode species reported by Andrews were found again; viz. Ostertagia ostertagi, O. circumcincta, O. trifurcata, Nematodirus filicollis, Oesophagostomum venulosum and Trichuris ovis. The 4 species found by Andrews that were not recovered by us from the animals we examined were: Trichostrongylus axei, T. vitrinus, Spiculotragia spiculoptera and S. asymmetrica. On the other hand we found 4 helminths not encountered by Andrews: 3 nematodes: Nematodirus spathiger (Railliet, 1896), N. abnormalis (May, 1920), and Chabertia ovina (Fabricius, 1794), and 7 specimens of the cestode Moniezia expansa (Rud., 1805). Nematodirus spathiger was the most commonly encountered Nematodirus species, but generally the numbers of all 3 species encountered were low as might be expected in a sample of adult and almost year-old animals. It is probable that most of the adults had acquired some measure of immunity((3)), and the most susceptible group, the kids, would not be born until late November. Because peptic digestion was not used to recover juveniles from the intestinal submucosa, only small numbers of adults were obtained. 相似文献
999.
Strips of rumen wall from bovine fetuses were incubated in an organ bath with prostaglandin F2 alpha (0.13 to 33.76 g/ml). The highest reactivity with a submaximal dose (17.03 g/ml) was observed in the period between 3.0 and 7.9 months of fetal age. A smaller response, but higher than in 1.0 to 2.9 months old fetuses, was observed in the 8.0 to 8.9 months fetuses. The period of the highest reactivity to prostaglandin F2 alpha coincides with the age of onset of papillary morphogenesis and the period of highest reactivity to autonomic and putative transmitter drugs. 相似文献
1000.
A mycoplasma identified asMycoplasma mycoides subspmycoides LC type was isolated from an outbreak of caprine pleuropneumonia and serofibrinous peritonitis. This isolate was the first to be reported in Italy. Experimentally, a rapidly fatal condition followed its inoculation into goats and sheep but inoculation of calves did not lead to clinically apparent infection. Although the organism was recovered for up to 45 days following experimental inoculation of calves, pathological changes were limited to the drainage lymph nodes except in one case where there were histological changes in the lungs. 相似文献