全文获取类型
收费全文 | 100396篇 |
免费 | 18695篇 |
国内免费 | 30101篇 |
专业分类
林业 | 11162篇 |
农学 | 11307篇 |
基础科学 | 10235篇 |
37292篇 | |
综合类 | 40136篇 |
农作物 | 8061篇 |
水产渔业 | 7295篇 |
畜牧兽医 | 11915篇 |
园艺 | 3721篇 |
植物保护 | 8068篇 |
出版年
2024年 | 1086篇 |
2023年 | 1449篇 |
2022年 | 2325篇 |
2021年 | 2506篇 |
2020年 | 3986篇 |
2019年 | 7280篇 |
2018年 | 6624篇 |
2017年 | 7695篇 |
2016年 | 8307篇 |
2015年 | 8774篇 |
2014年 | 7851篇 |
2013年 | 8464篇 |
2012年 | 8729篇 |
2011年 | 7883篇 |
2010年 | 6614篇 |
2009年 | 6024篇 |
2008年 | 5008篇 |
2007年 | 5008篇 |
2006年 | 4770篇 |
2005年 | 4254篇 |
2004年 | 3419篇 |
2003年 | 2924篇 |
2002年 | 2654篇 |
2001年 | 2270篇 |
2000年 | 2085篇 |
1999年 | 2178篇 |
1998年 | 1923篇 |
1997年 | 1813篇 |
1996年 | 1581篇 |
1995年 | 1655篇 |
1994年 | 1564篇 |
1993年 | 1313篇 |
1992年 | 1276篇 |
1991年 | 1090篇 |
1990年 | 846篇 |
1989年 | 810篇 |
1988年 | 688篇 |
1987年 | 503篇 |
1986年 | 446篇 |
1985年 | 238篇 |
1984年 | 222篇 |
1983年 | 203篇 |
1982年 | 204篇 |
1981年 | 246篇 |
1980年 | 197篇 |
1979年 | 157篇 |
1978年 | 130篇 |
1975年 | 110篇 |
1965年 | 138篇 |
1964年 | 141篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
J. Cabaret H. M. Baudet J. Devos J. Hubert J. Cortet C. Sauv 《Veterinary parasitology》1995,60(3-4):331-337
Multispecific resistance to benzimidazoles was studied in three selected farms. These farms had bred dairy goats for more than 15 years. The helminths were introduced with the goats at the establishment of the farms which afterwards remained isolated. Nematode resistance could then be related to their own management practices. Faecal egg count tests and egg hatch assays were performed to assess intensity of resistance. The generic (infective larvae in faecal cultures) and specific richness (adult worms) were assessed. The resistant species were Trichostrongylus colubriformis, Teladorsagia circumcincta, Haemonchus contortus and Oesophagostomum venulosum. Faecal egg count reduction tests and egg-hatch assays did not match exactly. Faecal larval counts after treatments gave a distorted picture of multispecific resistance: Haemonchus and Oesophagostomum were very largely over represented. The number of species found in the three farms was relatively low compared with other reports in goat farms of the area. This reduction of diversity might also be due in part to characteristics of breeding management and history (use of permanent pasture and introduction of goats at the establishment of farm). 相似文献
12.
J Tetens S A Barker M Waguespack G Hosgood 《Canadian journal of veterinary research》2001,65(2):133-135
The objectives were to use high performance liquid chromatography (HPLC) to validate an established method for adenine nucleotide separation in equine colonic mucosal tissue, to determine the inherent variability in the tissue and extraction method, and to determine the stability of ATP, ADP, and AMP in the tissue with time. Equine colonic mucosal tissue obtained from a single horse was immediately submersed in liquid nitrogen, and stored at -70 degrees C. Samples were lyophilized, extracted, and separated by HPLC. The limit of quantitation was 0.05 microg/mL. The coefficient of variation for the instrument was less than 10% for all nucleotides measured. When the tissue was not homogenized prior to sampling, there were significant differences in adenine nucleotide content between samples. However, when the tissue was homogenized prior to analysis, these differences were no longer significant. There was no significant decrease in ATP, ADP, or AMP content over a 54-day analysis period. 相似文献
13.
14.
15.
16.
1月见草的引种驯化
1.1用于人工驯化的品种
①柔毛②小花③003④拉马克⑤英国一号⑥英国二号⑦夜来香⑧蒙科9001
1.2驯化内容
从品种的分枝习性、现蕾与开花时间、成熟与生育期情况、株高和生长动态、单株开展度与叶面积系数,产量表现等几个方面对引进月见草品种进行试验研究. 相似文献
17.
ABSTRACT: The reproductive traits and the monthly larval abundance of the mantis shrimp Oratosquilla oratoria were investigated in Tokyo Bay, Japan, in 2002. The goal of the study was to elucidate the cause of changes in the monthly pattern of larval abundance from the 1980s to the 1990s as these changes relate to variation in the stock size of the adult shrimp. Oogenesis was divided into 10 stages by histological observation. The developmental stage of oocytes in an individual's ovary was synchronous, suggesting that almost all the oocytes in an ovary are spawned at the same time. The size at first maturity was estimated to be 7 ≤ body length ( BL ) < 8 cm. Fecundity was expressed as a function of BL , ranging from 19 300 eggs for 8 cm BL to 92 100 eggs for 14 cm BL . Small female shrimps (<10 cm BL ) spawned around August. Most large female shrimps (≥10 cm BL ) spawned around May, and some large female shrimps also spawned until September. Although most large female shrimps spawned in spring, the larval abundance was low before July and high from August onwards. The results suggest that a substantial decrease in the stock size of large individuals causes the low larval abundance before July. 相似文献
18.
19.
CERES-Maize (Vl. 0) predicted no grain yield when 100% defoliation occurred during vegetative growth. This result conflicted with field observations where 100% defoliation early in the vegetative stage did not materially reduce grain yield. CERES-Maize was modified to realistically predict yields when defoliation greater than 50% occurred during vegetative growth by taking into account stem (stem proper and sheath) photosynthesis and translocation of dry matter from the stem to the developing leaves. With these modifications, predictions from CERES-Maize were in good agreement with field measurements when defoliation occurred both early and later in the vegetative stage. This modified version of CERES-Maize can be the basis of a decision support system for defoliating pests of corn where yields can be evaluated under different management strategies and climate scenarios. 相似文献
20.
对N×特青示范田中试区与肥料试验田各处理小区稻株分析结果表明:抽穗后,亚种间杂交稻N×特青比常规稻特青干物质生产能力强,灌浆速度快;地上部各器官占植株干重比例,前者叶片比重大于茎,后者茎比重大于叶。亚种间杂交稻对肥料反应敏感,抽穗后,干物质累积,植株高度,每穗总粒数和粒重均随施肥量增加而增加,在高肥区有利于进一步提高产量,但增施氮肥后,灌浆速度明显滞后。 相似文献