全文获取类型
收费全文 | 38804篇 |
免费 | 3367篇 |
国内免费 | 4345篇 |
出版年
2024年 | 93篇 |
2023年 | 486篇 |
2022年 | 1093篇 |
2021年 | 1981篇 |
2020年 | 1397篇 |
2019年 | 1773篇 |
2018年 | 1682篇 |
2017年 | 1278篇 |
2016年 | 1670篇 |
2015年 | 2499篇 |
2014年 | 2983篇 |
2013年 | 3197篇 |
2012年 | 3881篇 |
2011年 | 3384篇 |
2010年 | 2143篇 |
2009年 | 2007篇 |
2008年 | 2211篇 |
2007年 | 1992篇 |
2006年 | 1678篇 |
2005年 | 1493篇 |
2004年 | 1230篇 |
2003年 | 1094篇 |
2002年 | 908篇 |
2001年 | 635篇 |
2000年 | 537篇 |
1999年 | 533篇 |
1998年 | 336篇 |
1997年 | 290篇 |
1996年 | 281篇 |
1995年 | 226篇 |
1994年 | 202篇 |
1993年 | 162篇 |
1992年 | 184篇 |
1991年 | 170篇 |
1990年 | 135篇 |
1989年 | 115篇 |
1988年 | 101篇 |
1987年 | 83篇 |
1986年 | 70篇 |
1985年 | 83篇 |
1984年 | 35篇 |
1983年 | 36篇 |
1982年 | 24篇 |
1981年 | 23篇 |
1980年 | 9篇 |
1979年 | 13篇 |
1978年 | 15篇 |
1975年 | 7篇 |
1974年 | 8篇 |
1972年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
Yasuyuki Kurihara Nobumoto Miyashita Kazuo Moriwaki Michael L. Petras François Bonhomme Wang Su Cho Sei-ichi Kohno 《Immunogenetics》1985,22(3):211-218
Allelic distributions of Thy-1, Ly-l, and Ly-2 antigens in wild mice are characteristic of each Mus musculus subspecies. Eastern mice (M.m.molossinus, M.mmusculus, M.m.castaneus, M.m.bactrianus) express the Thy-1.1 antigen, whereas Western mice (M.m. domesticus, M.m.brevirostris) express the Thy-1.2. All mice from wild populations examined in this survey express the Ly-1.2. The Ly-2.1 is distributed in Eastern mice and some Western mice, and the Ly-2.2 is found in the remaining Western mice. Allelic distributions of these antigens were also examined in two other species, Mus spretus and Mus spicilegus. Allelic constitutions of Thy-1 and Ly-1 in these species are similar to those of Eastern mice. Some M.spicilegus, however, express the Ly-1.1 antigen. This antigenic type is not found in M.musculus. Some Eastern mice related to M.m.castaneus react weakly to Ly-1.2-specific and Ly-2.1-specific monoclonal antibodies in both the complement-mediated cytotoxicity test and the absorption test. These results suggest that M.m.castaneus has unique alleles in the Ly-1 and Ly-2 loci. 相似文献
83.
由开花前1—4天的向日葵子房中取出胚珠,在液体培养基上进行漂浮培养,诱导了未受精的卵细胞发育为单倍体的胚状体.亦诱导了珠被绒毡层产生胚状体。对两种胚状体的发生和发育过程及其形态发生特点作了显微观察与描述。 相似文献
84.
Papaya (Carica papaya L.) anther containing microspores in tetrad to early-binucleate stages were successfully cultured on 1/2 strength MS salts and vitamins with full strength Na-Fe-EDTA supplemented with 2 mg/l NAA, 1 mg/l BA and 6% sucrose for callus initiation and formation. Highest frequencies of callus induction were obtained when anthers at the uninucleate stage were cultured in the dark. Haploid plantlets and pollen-derived embryoids were obtained from anthers cultured at the uninucleate stage on solidified MS medium containing 3% sucrose without any growth regulators under a low light intensity (1,500 lux). Large quantities of embryoids were obtained when the original embryoids were transferred to MS medium with 3% sucrose and no growth regulators. Cytology of root tips of embryoid-derived plants confirmed the haploid chromosome number of 9 indicating that the embryoids originated from pollen.Abbreviations MS
Murashige and Skoog (1962)
- MAA
naphthaleneacetic acid
- BA
6-benzyladenine
- 2,4-D
2,4-dichlorophenoxyacetic acid 相似文献
85.
Are Chaoborus larvae more abundant in acidified than in non-acidified lakes in Central Canada? 总被引:2,自引:0,他引:2
Eriksson et al (1980) hypothesized that the abundance of certain macroinvertebrate predators, such as larvae of the phantom midge Chaoborus , should increase in acidified lakes because of the elimination of fish. To examine the influence of pH and presence of fish on Chaoborus abundance, we surveyed Chaoborus populations in 33 lakes in Ontario, Canada which ranged in pH from 4.5 to 7.4. Chaoborus larvae were not more abundant in the acidified lakes that were devoid of fish than in the remaining lakes. Therefore, we concluded that pH and presence of fish are not prime determinants of total Chaoborus abundance in Canadian Shield lakes. We hypothesized that significant increases in Chaoborus abundance should only be anticipated when fish populations are eliminated by acidification of relatively nutrient rich lakes. 相似文献
86.
87.
中国某些野生和栽培茶的核型研究 总被引:9,自引:0,他引:9
研究了茶的4个变种和广东野生毛叶茶等共12个材料的核型。所有材料的染色体数目均是2n=30,为二倍体。所有中国大叶变种(越南大叶除外)(Cametlia sinensis var. macrophylla)和阿萨姆大叶变种(C. sinensis var. assamica)均具比较对称或原始的“2A”核型;中国小叶变种(C.sinensis var.bohea)(“铁观音”品种除外),掸部变种(C.sinensis var. shan form)和广东野生毛叶茶(C. ptilophylla)均具较不对称或较进化的“2B”核型。根据核型特征,植物习性和地理分布,作者认为中国四川和云南可能是茶的起源中心,向东或北迁移,演变为中国小叶变种;向南移则演变为阿萨姆变种和掸部变种。 相似文献
88.
89.
90.