全文获取类型
收费全文 | 234646篇 |
免费 | 12724篇 |
国内免费 | 201篇 |
专业分类
林业 | 9690篇 |
农学 | 7454篇 |
基础科学 | 1506篇 |
28853篇 | |
综合类 | 41475篇 |
农作物 | 9220篇 |
水产渔业 | 11550篇 |
畜牧兽医 | 119829篇 |
园艺 | 3091篇 |
植物保护 | 14903篇 |
出版年
2019年 | 2226篇 |
2018年 | 3302篇 |
2017年 | 3738篇 |
2016年 | 3429篇 |
2015年 | 2955篇 |
2014年 | 3727篇 |
2013年 | 9098篇 |
2012年 | 6683篇 |
2011年 | 8105篇 |
2010年 | 5445篇 |
2009年 | 5429篇 |
2008年 | 7915篇 |
2007年 | 7638篇 |
2006年 | 7229篇 |
2005年 | 6694篇 |
2004年 | 6443篇 |
2003年 | 6553篇 |
2002年 | 6087篇 |
2001年 | 7384篇 |
2000年 | 7216篇 |
1999年 | 5791篇 |
1998年 | 2448篇 |
1997年 | 2380篇 |
1996年 | 2208篇 |
1995年 | 2608篇 |
1994年 | 2269篇 |
1993年 | 2353篇 |
1992年 | 4712篇 |
1991年 | 4968篇 |
1990年 | 4856篇 |
1989年 | 4950篇 |
1988年 | 4437篇 |
1987年 | 4562篇 |
1986年 | 4603篇 |
1985年 | 4394篇 |
1984年 | 3539篇 |
1983年 | 3229篇 |
1982年 | 2249篇 |
1979年 | 3180篇 |
1978年 | 2526篇 |
1977年 | 2186篇 |
1976年 | 2071篇 |
1975年 | 2261篇 |
1974年 | 2760篇 |
1973年 | 2855篇 |
1972年 | 2741篇 |
1971年 | 2550篇 |
1970年 | 2549篇 |
1969年 | 2371篇 |
1967年 | 2053篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
E. Knoche 《Forstwissenschaftliches Centralblatt》1904,26(7):371-393
Ohne Zusammenfassung 相似文献
993.
994.
995.
996.
M. von Sivers 《Forstwissenschaftliches Centralblatt》1901,23(6):345-348
Ohne Zusammenfassung 相似文献
997.
M. 《Forstwissenschaftliches Centralblatt》1899,21(4):240
Ohne Zusammenfassung 相似文献
998.
Techniques to monitor honey bee (Apis mellifera) egg production in cages allow researchers to study how different environmental factors contribute to reproduction. However, although the conditions required to facilitate queen egg production in a laboratory setting have been established, limited work has addressed the requirements for stimulating and monitoring worker egg laying. Here, we documented that drone laying workers will lay eggs in Queen Monitoring Cages (QMC), specialized cages designed to facilitate queen egg laying under controlled conditions. Egg production and worker mortality were compared between QMCs containing queens and those containing drone laying workers. High-definition images of the last abdominal segments of living first-instar larvae hatched from worker laid eggs and those putatively laid by queens were qualitatively compared to identify candidate characteristics to determine their sex. 相似文献
999.
Nadezhda E. Ustyuzhanina Maria I. Bilan Andrey S. Dmitrenok Eugenia A. Tsvetkova Sofya P. Nikogosova Cao Thi Thuy Hang Pham Duc Thinh Dinh Thanh Trung Tran Thi Thanh Van Alexander S. Shashkov Anatolii I. Usov Nikolay E. Nifantiev 《Marine drugs》2022,20(6)
Fucosylated chondroitin sulfates (FCSs) FCS-BA and FCS-HS, as well as fucan sulfates (FSs) FS-BA-AT and FS-HS-AT were isolated from the sea cucumbers Bohadschia argus and Holothuria (Theelothuria) spinifera, respectively. Purification of the polysaccharides was carried out by anion-exchange chromatography on DEAE-Sephacel column. Structural characterization of polysaccharides was performed in terms of monosaccharide and sulfate content, as well as using a series of non-destructive NMR spectroscopic methods. Both FCSs were shown to contain a chondroitin core [→3)-β-d-GalNAc-(1→4)-β-d-GlcA-(1→]n bearing sulfated fucosyl branches at O-3 of every GlcA residue in the chain. These fucosyl residues were different in pattern of sulfation: FCS-BA contained Fuc2S4S, Fuc3S4S and Fuc4S at a ratio of 1:8:2, while FCS-HS contained these residues at a ratio of 2:2:1. Polysaccharides differed also in content of GalNAc4S6S and GalNAc4S units, the ratios being 14:1 for FCS-BA and 4:1 for FCS-HS. Both FCSs demonstrated significant anticoagulant activity in clotting time assay and potentiated inhibition of thrombin, but not of factor Xa. FS-BA-AT was shown to be a regular linear polymer of 4-linked α-L-fucopyranose 3-sulfate, the structure being confirmed by NMR spectra of desulfated polysaccharide. In spite of considerable sulfate content, FS-BA-AT was practically devoid of anticoagulant activity. FS-HS-AT cannot be purified completely from contamination of some FCS. Its structure was tentatively represented as a mixture of chains identical with FS-BA-AT and other chains built up of randomly sulfated alternating 4- and 3-linked α-L-fucopyranose residues. 相似文献
1000.
A. P. Sclavounos A. E. Voloudakis Ch. Arabatzis P. E. Kyriakopoulou 《European journal of plant pathology / European Foundation for Plant Pathology》2006,115(2):163-172
A severe strain of Cucumber mosaic virus (CMV) originating from an infected tomato plant (Gastouni-Olympia, Greece) was isolated in tobacco (Nicotiana tabacum cv. Xanthi nc), after three serial local lesion passages in Chenopodium quinoa and designated CMV-G. CMV-G induces yellow mosaic (YM) symptoms in tobacco. When CMV-G was passed mechanically through C. quinoa, phenotypic variants inducing YM or green mild mosaic (MM) in tobacco were isolated. Aphid transmission, from different hosts, appears to be an effective approach for separating MM variants of CMV-G from YM variants. In particular, aphid transmission from zucchini proved to be very efficient in selecting for MM variants. In contrast, aphids transmitted only YM variants from tomato plants. Molecular characterization of CMV-G and its progeny resulted in their classification in the CMV subgroup IB, free of satellite RNA, being the first discovery of the subgroup IB in Greece. In the Solanaceae family (tobacco, tomato, pepper) YM variants induced more severe symptoms than the MM variants. YM and MM phenotype was stable in tobacco for all seven passages tried using the obtained YM and MM variants. Cross-protection experiments showed that an isolated MM variant was able to protect tobacco plants against a challenge infection by a YM variant. 相似文献