全文获取类型
收费全文 | 232177篇 |
免费 | 15061篇 |
国内免费 | 3547篇 |
专业分类
林业 | 25303篇 |
农学 | 16912篇 |
基础科学 | 4780篇 |
42924篇 | |
综合类 | 22098篇 |
农作物 | 18512篇 |
水产渔业 | 16582篇 |
畜牧兽医 | 71977篇 |
园艺 | 7891篇 |
植物保护 | 23806篇 |
出版年
2022年 | 2030篇 |
2021年 | 3644篇 |
2020年 | 3978篇 |
2019年 | 4712篇 |
2018年 | 4459篇 |
2017年 | 5189篇 |
2016年 | 5586篇 |
2015年 | 5634篇 |
2014年 | 7028篇 |
2013年 | 17798篇 |
2012年 | 7187篇 |
2011年 | 8814篇 |
2010年 | 9179篇 |
2009年 | 9595篇 |
2008年 | 7789篇 |
2007年 | 6540篇 |
2006年 | 7131篇 |
2005年 | 5976篇 |
2004年 | 5382篇 |
2003年 | 5083篇 |
2002年 | 4497篇 |
2001年 | 4546篇 |
2000年 | 4118篇 |
1999年 | 4271篇 |
1998年 | 4193篇 |
1997年 | 4238篇 |
1996年 | 3929篇 |
1995年 | 4425篇 |
1994年 | 3785篇 |
1993年 | 3469篇 |
1992年 | 3215篇 |
1991年 | 3338篇 |
1990年 | 2956篇 |
1989年 | 2935篇 |
1988年 | 2549篇 |
1987年 | 2584篇 |
1986年 | 2441篇 |
1985年 | 2841篇 |
1984年 | 2858篇 |
1983年 | 2782篇 |
1982年 | 2491篇 |
1981年 | 2470篇 |
1980年 | 2467篇 |
1979年 | 2396篇 |
1978年 | 2284篇 |
1977年 | 2202篇 |
1976年 | 2051篇 |
1975年 | 1795篇 |
1974年 | 1800篇 |
1973年 | 1750篇 |
排序方式: 共有10000条查询结果,搜索用时 349 毫秒
101.
Vimal Nair Min Cheol Kim James A. Golen Arnold L. Rheingold Gabriel A. Castro Paul R. Jensen William Fenical 《Marine drugs》2020,18(11)
A new cytotoxic thiodepsipeptide, verrucosamide (1), was isolated along with the known, related cyclic peptide thiocoraline, from the extract of a marine-derived actinomycete, a Verrucosispora sp., our strain CNX-026. The new peptide, which is composed of two rare seven-membered 1,4-thiazepane rings, was elucidated by a combination of spectral methods and the absolute configuration was determined by a single X-ray diffraction study. Verrucosamide (1) showed moderate cytotoxicity and selectivity in the NCI 60 cell line bioassay. The most susceptible cell lines were MDA-MB-468 breast carcinoma with an LD50 of 1.26 µM, and COLO 205 colon adenocarcinoma with an LD50 of 1.4 µM. Also isolated along with verrucosamide were three small 3-hydroxy(alkoxy)-quinaldic acid derivatives that appear to be products of the same biosynthetic pathway. 相似文献
102.
103.
社会林业与五指山的自然保护 总被引:1,自引:0,他引:1
五指山自然保护区是世界上现存地势最高的原始热带雨林之一,是我省目前面积最大的自然保护区,也是海南三大河流的发源地。但由于保护区横跨琼中、通什、保亭三县、市,紧邻保护区还生存着众多贫困的黎、苗族村民。因此,保护区与周边社区的联系是十分紧密的,社区的发展也直接影响到五指山热带天然林的保护。海南省林业局中德海南热带林保护和恢复项目在社会林业与五指山森林的保护上做出了有益的尝试,就在全省来说,也是首次对社会林业与森林保护上进行的探索。五指山地区社会林业的研究,对保护海南热带雨林也有着积极的意义。特对社会林业与五指山的森林保护进行了阐述、分析和设想。 相似文献
104.
105.
Osteomyelitis caused by Cryptococcus neoformans was diagnosed in a three-year-old male Irish wolfhound. The case details and radiological findings of radiolucency and periosteal reaction of the left third metatarsal bone had lead to an initial diagnosis of a malignant bone tumour. Biopsy revealed a fungal granuloma and culture identified the causal organism. A four month course of ketaconazole was instigated and the lameness resolved. Twelve months after the end of treatment there was no recurrence of the problem. 相似文献
106.
107.
Differences in gas exchange parameters i.e. carbon exchange rate (CER), transpiration (Tr), water vapor conductance (g) were investigated, under a controlled environment, in a semi-dwarf (SD) Triticum aestivum line, its tall (TL) near isoline and the Payne (PA) variety characterized by small leaves. The plants were maintained in: (a) optimal substrate moisture condition (CTR); (b) salinized by watering with a 0.12 m NaCl solution (SLT); (c) water stressed by withholding waterings during a period of six days (STR); (d) stressed and salinized during the same period and with the same saline solution (S + S). CER and Tr were negatively affected by the stresses; SLT and S + S treatments had a higher WUE compared to their respective controls CTR and STR.
SD line had a better performance in terms of CER and WUE, particularly when water and salt stresses interacted. Leaf anatomy and assimilation/internal CO2 concentration curves contributed to explaining the SD performance. 相似文献
SD line had a better performance in terms of CER and WUE, particularly when water and salt stresses interacted. Leaf anatomy and assimilation/internal CO
108.
109.
Abstract. A humoral antibody response was demonstrated by ELISA in rainbow trout immunized intraperitoneally with extracts from the branchiuran ectoparasite Argulus foliaceus. A similar immunization protocol produced a higher titre response in a rabbit. Both trout and rabbit identified several antigenic components on immunoblots. ELISA and immunoblotting indicated that rainbow trout and rabbit anti-A. foliaceus sera identified components from the parasitic copepods Lepeophtheirus salmonis and Caligus elongatus. 相似文献
110.