全文获取类型
收费全文 | 44620篇 |
免费 | 1294篇 |
国内免费 | 10篇 |
专业分类
林业 | 4877篇 |
农学 | 2288篇 |
基础科学 | 330篇 |
7471篇 | |
综合类 | 4803篇 |
农作物 | 3190篇 |
水产渔业 | 3260篇 |
畜牧兽医 | 14597篇 |
园艺 | 1379篇 |
植物保护 | 3729篇 |
出版年
2019年 | 253篇 |
2018年 | 3448篇 |
2017年 | 3538篇 |
2016年 | 1760篇 |
2015年 | 419篇 |
2014年 | 480篇 |
2013年 | 970篇 |
2012年 | 1706篇 |
2011年 | 3441篇 |
2010年 | 3235篇 |
2009年 | 2423篇 |
2008年 | 2629篇 |
2007年 | 3024篇 |
2006年 | 839篇 |
2005年 | 869篇 |
2004年 | 759篇 |
2003年 | 899篇 |
2002年 | 695篇 |
2001年 | 811篇 |
2000年 | 857篇 |
1999年 | 634篇 |
1998年 | 275篇 |
1997年 | 282篇 |
1995年 | 260篇 |
1994年 | 227篇 |
1993年 | 253篇 |
1992年 | 463篇 |
1991年 | 516篇 |
1990年 | 435篇 |
1989年 | 431篇 |
1988年 | 421篇 |
1987年 | 411篇 |
1986年 | 363篇 |
1985年 | 388篇 |
1984年 | 339篇 |
1983年 | 287篇 |
1982年 | 243篇 |
1979年 | 383篇 |
1978年 | 289篇 |
1977年 | 308篇 |
1976年 | 300篇 |
1975年 | 317篇 |
1974年 | 332篇 |
1973年 | 302篇 |
1972年 | 291篇 |
1971年 | 246篇 |
1969年 | 292篇 |
1968年 | 287篇 |
1967年 | 333篇 |
1966年 | 304篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
51.
Tiering of benthic marine suspension-feeding communities on soft substrata has varied throughout the Phanerozoic. Epifaunal tiering was most developed during the middle and late Paleozoic and the Triassic to Jurassic, with large-scale reductions in tiering occurring during the Permian-Triassic extinctions and after the Jurassic. Infaunal tiering reached its highest level of organization after the Paleozoic. 相似文献
52.
53.
54.
55.
The death of a 6-week-old alpaca being treated for acute polyarthritis is described. Post-mortem and histological findings included fibrinous mural endocarditis, lung abscessation, acute passive congestion of the liver, embolic suppurative nephritis and chronic nonsuppurative polyarthritis. Actinobacillus suis was isolated from the heart lesion and in pharyngeal swabs from four of six clinically normal alpacas in the same flock. 相似文献
56.
A. Navon 《Phytoparasitica》1992,20(1):S21-S24
Knowledge of the interactions among lepidopterous insects, microbial insecticides and plants is either lacking or incomplete. In some of the interactions, plant allelochemicals antagonized the insecticidal activity of the microbe by means of feeding reduction. In others, microbe activity was enhanced either by causing insect toxicity or by a potentiation of the crystal protein. Nutritional evaluations of the interactions amongHeliothis virescens. Bacillus thuringiensis crystal protein and tannin showed that microbe toxicity in the larva was antagonized by this phytochemical. 相似文献
57.
58.
Radiocarbon dates associated with engraved stones from sealed archeological deposits at Wonderwerk Cave in the northern Cape Province indicate that rock engraving in South Africa is at least 10,000 years old. 相似文献
59.
Antibodies specific for Brucella abortus were purified from the serum of hyperimmunized sheep using immunochemical procedures. They were conjugated to fluorescein isothiocyanate and used in a fluorescent antibody (FA) test for B. abortus. The conjugate did not stain any heterologous bacterial or fungal species tested and background fluorescence associated with its use on smears and sections of abortion materials was particularly low. Of 239 cases of abortion examined fluorescent microscopy demonstrated B. abortus in all 12 cases in which the organism was isolated. A few areas of fluorescence typical of B. abortus were also seen in 3 cases from which the organism was not cultured. B. abortus was demonstrated in lymph nodes from 6 of 36 Brucella reactor cows by culture and 7 by the FA test. However, only very low numbers of B. abortus were isolated or seen and sampling errors would have been significant. Use of the FA test allows diagnosis of Brucellosis to be made in 2 hours, compared to 6 days by the usual cultural procedures. 相似文献
60.
1. The α‐tocopherol (AT) content of abdominal fat and fat stability increased as a function of the duration of α‐tocopheryl acetate (ATA) feeding in broilers fed on diets containing either 40 g acidulated soyabean‐oil soapstock (ASS) or tallow/kg. A linear relationship was observed between AT content of the adipose tissue and its stability with both types of fat supplements.
2. The stabilities of carcass fat and meat of 9‐week‐old broilers fed on diets containing ASS with 300 mg ethoxyquin (EQ)/kg or diets containing tallow with 20 mg ATA/kg from weeks 5 to 9 were comparable with those obtained by feeding these antioxidants and fats throughout the growth period.
3. ATA added to a diet containing ASS, and EQ, added to a diet containing tallow did not improve meat stability despite such an effect on adipose tissue when fed for 9 weeks. The results emphasise the importance of using the dietary antioxidant appropriate to the fat supplement to improve carcass stability. 相似文献