全文获取类型
收费全文 | 165380篇 |
免费 | 9103篇 |
国内免费 | 9945篇 |
专业分类
林业 | 12368篇 |
农学 | 14566篇 |
基础科学 | 7727篇 |
22716篇 | |
综合类 | 44284篇 |
农作物 | 7607篇 |
水产渔业 | 6573篇 |
畜牧兽医 | 53810篇 |
园艺 | 4598篇 |
植物保护 | 10179篇 |
出版年
2023年 | 1206篇 |
2022年 | 2764篇 |
2021年 | 4016篇 |
2020年 | 3684篇 |
2019年 | 3868篇 |
2018年 | 3382篇 |
2017年 | 4482篇 |
2016年 | 4100篇 |
2015年 | 5149篇 |
2014年 | 5214篇 |
2013年 | 7330篇 |
2012年 | 8348篇 |
2011年 | 9319篇 |
2010年 | 8118篇 |
2009年 | 7519篇 |
2008年 | 7982篇 |
2007年 | 8017篇 |
2006年 | 7404篇 |
2005年 | 6768篇 |
2004年 | 4317篇 |
2003年 | 4279篇 |
2002年 | 3891篇 |
2001年 | 4152篇 |
2000年 | 4259篇 |
1999年 | 3890篇 |
1998年 | 2495篇 |
1997年 | 2245篇 |
1996年 | 2050篇 |
1995年 | 2004篇 |
1994年 | 1742篇 |
1993年 | 1773篇 |
1992年 | 2399篇 |
1991年 | 2439篇 |
1990年 | 2254篇 |
1989年 | 2081篇 |
1988年 | 1855篇 |
1987年 | 1753篇 |
1986年 | 1696篇 |
1985年 | 1461篇 |
1984年 | 1231篇 |
1983年 | 1053篇 |
1979年 | 1067篇 |
1978年 | 830篇 |
1975年 | 749篇 |
1974年 | 1005篇 |
1973年 | 985篇 |
1972年 | 954篇 |
1971年 | 880篇 |
1970年 | 854篇 |
1969年 | 806篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
981.
Brownlie J Nuttall PA Stott EJ Taylor G Thomas LH 《Veterinary immunology and immunopathology》1980,1(4):371-378
Certain immunological responses of 4-6 month old calves experimentally inoculated with either cytopathic or non-cytopathic bovine virus diarrhoea virus (BVDV) were compared with those of uninfected control calves. The tests used to demonstrate the immunological responses were the transformation of lymphocytes by PHA mitogen, the percentage of lymphocytes with surface immunoglobulin, and the antibody titres induced by an intravenous inoculation of killed Brucella abortus. There were no significant differences between the two groups of calves and therefore, the mild experimental disease produced by BVDV did not appear to affect adversely the immunological response. 相似文献
982.
B.J. Bergot K.J. Judy D.A. Schooley L.W. Tsai 《Pesticide biochemistry and physiology》1980,13(2):95-104
Several species of insects, exhibiting varying responsiveness to the juvenile hormone antagonist precocene II (6,7-dimethoxy-2,2-dimethylchromene), were challenged topically with a tritiated preparation of the title compound. Metabolism of [3H]precocene II was subsequently examined by withdrawing hemolymph samples from treated animals at appropriate time intervals and characterizing the extractable radiolabel chromatographically. Quantitative (or qualitative) differences observed between the respective metabolic profiles were found not correlative with specimen sensitivity to precocene. Production of two heretofore unreported metabolites, identified by spectral and chemical means as O-β-glucosides of 6- and 7-monodemethylated precocene II, was demonstrated in both sensitive and insensitive species. No evidence for the presence of a hemolymphborne, biologically effective “activated metabolite” produced in vivo by precocene-susceptible insects could be found. The latter finding may well argue for in situ bioactivation of precocene at the target tissue(s) by these sensitive insects. 相似文献
983.
Although the molluscicide Frescon is a strong neurotoxin to the Lymnaea stagnalis central nervous system in vitro, it is probable that the exposure of the whole animal to this molluscicide fails to result in central nervous system abnormalities: Frescon does not appear to reach the brain in sufficient quantity to disrupt its normal activity. However, only those Frescon analogs found to be neurotoxic were molluscicidal, suggesting some related mode, if not site, of action. Frescon and its analogs may act by affecting excitable tissues other than the nervous system (e.g., the snail musculature) by altering certain functional and/or structural membrane properties. 相似文献
984.
985.
胡桃长足象是核桃果实的大害虫,为害损失很大。1975年以来,我们在四川平武地区进行了生活习性观察和防治试验,初步明确了以下几个问题。1.胡桃长足象一年一代。11月份以成虫越冬,次年4月上旬开始活动,为害果、芽、嫩枝、叶柄,5月上旬交尾产卵于果中,一般一果一粒,8月中旬产卵结束,10月陆续死亡。当年成虫6月中旬羽化,进行为害。2.成虫有假死性和向阳性,飞翔力弱,具有与核桃树芽苞相似的保护色。3.防治胡桃长足象,应抓住越冬成虫大量出现和卵孵化盛期时进行。用每毫升含孢量二至五亿的白僵菌液或50%的三硫磷乳油、50%速灭松乳剂、82%磷胺乳剂加水一千倍喷雾,效果良好。 相似文献
986.
987.
Perlman ML 《Science (New York, N.Y.)》1978,202(4367):469-470
988.
989.
Silicon monoxide solid was evaporated in a bell jar containing reducing, neutral, or oxidizing atmospheres at pressures of a few torr. The vapor invariably condensed as smoke-sized particles of silicon sesquioxide, Si(2)O(3). The condensation of a solid whose composition differs from that of the parent gas and is apparently the least stable of the three solid species illustrates the importance of specific nucleation effects in the condensation process. This result has significant implications for theories of formation of grains in space. 相似文献
990.
A Fluorite Isotype of SnO2 and a New Modification of TiO2: Implications for the Earth's Lower Mantle
Liu LG 《Science (New York, N.Y.)》1978,199(4327):422-425
The existence of a cubic fluorite-type SnO(2) and a hexagonal TiO(2) (which may be related to the fluorite structure) have been demonstrated by an in situ x-ray diffraction study in which a diamond-anvil pressure cell was used after the samples had been heated by a continuous yttrium-aluminum-garnet laser. At room temperature, the lattice parameter for SnO(2) (fluorite) is a = 4.925 +/- 0.005 angstroms and those for TiO(2) (fluorite-related) are a = 9.22 +/- 0.01 angstroms and c = 5.685 +/- 0.006 angstroms at about 250 kilobars. The volume change associated with the transition from rutile to fluorite (or related structure) is about -8 percent for SnO(2) and -10.5 percent for TiO(2) at transition. Upon release of pressure, both the fluorite-type SnO(2) and the TiO(2) reverted to the alpha-PbO(2) structure at room temperature. The hypothesis that the earth's lower mantle is composed of oxide phases might be feasible if it were possible for SiO(2) to possess the fluorite structure or its related forms at high pressure, as shown for SnO(2) and TiO(2) in this study. The oxide hypothesis proposed here differs from that postulated by Birch in that the primary coordination of silicon is 6 for Birch's hypothesis and 8 for the hypothesis presented here. 相似文献