全文获取类型
收费全文 | 57498篇 |
免费 | 2261篇 |
国内免费 | 285篇 |
专业分类
林业 | 5500篇 |
农学 | 2899篇 |
基础科学 | 497篇 |
9229篇 | |
综合类 | 6851篇 |
农作物 | 3739篇 |
水产渔业 | 3693篇 |
畜牧兽医 | 21263篇 |
园艺 | 1558篇 |
植物保护 | 4815篇 |
出版年
2021年 | 367篇 |
2020年 | 432篇 |
2019年 | 471篇 |
2018年 | 3744篇 |
2017年 | 3819篇 |
2016年 | 2013篇 |
2015年 | 704篇 |
2014年 | 801篇 |
2013年 | 1840篇 |
2012年 | 2199篇 |
2011年 | 3932篇 |
2010年 | 3534篇 |
2009年 | 2804篇 |
2008年 | 3084篇 |
2007年 | 3425篇 |
2006年 | 1290篇 |
2005年 | 1206篇 |
2004年 | 1149篇 |
2003年 | 1222篇 |
2002年 | 997篇 |
2001年 | 1252篇 |
2000年 | 1286篇 |
1999年 | 930篇 |
1998年 | 388篇 |
1997年 | 418篇 |
1996年 | 343篇 |
1995年 | 393篇 |
1994年 | 343篇 |
1992年 | 691篇 |
1991年 | 781篇 |
1990年 | 688篇 |
1989年 | 742篇 |
1988年 | 682篇 |
1987年 | 625篇 |
1986年 | 666篇 |
1985年 | 591篇 |
1984年 | 463篇 |
1983年 | 412篇 |
1979年 | 553篇 |
1978年 | 431篇 |
1977年 | 374篇 |
1976年 | 365篇 |
1975年 | 396篇 |
1974年 | 459篇 |
1973年 | 474篇 |
1972年 | 448篇 |
1970年 | 366篇 |
1969年 | 403篇 |
1968年 | 377篇 |
1967年 | 367篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
D. M. Zhao S. Tateyama N. Miyoshi K. Uchida R. Yamaguchi T. Yamagami T. Hayashi 《Research in veterinary science》1995,59(3)
Cloning of the canine yes oncogene was attempted from a c
library derived from a healthy canine spleen using a human c-yes-1 probe. The nucleotide and amino acid sequences revealed that the canine yes gene contained an open reading frame consisting of 539 amino acids. Its product had a molecular mass of 60,368 Daltons and showed 95·9 per cent and 90·4 per cent homology with human and chick p61c-yes, respectively. Moreover, the product had a myristylation signal, src homology region (SH) 3, SH2, and tyrosine kinase domains showing 98·8 per cent and 96·0 per cent homology with those of human beings and chickens, respectively. These findings indicate that the products of the canine yes gene may have non-receptor-type tyrosine kinase activity on the cell membrane, as is the case in human and chick p61c-yes 相似文献
73.
Ihle JN 《Science (New York, N.Y.)》1987,237(4818):1060-1061
74.
75.
1. Brown egg layers were fed diets differing in oil content, oil source and linoleic acid concentration and the effect on performance from 22 to 69 weeks of age was studied.
2. The birds responded with an increasing mean egg weight up to a linoleic acid intake of 2.75 g/bird d.
3. Increasing the intake of readily absorbable oil without increasing linoleic acid concentration did not increase mean egg weight. 相似文献
76.
77.
78.
79.
"Benchmark" - a large observational study of Ontario beef breeding herds: Study design and collection of data 下载免费PDF全文
McDermott JJ Alves DM Anderson NG Martin SW 《The Canadian veterinary journal. La revue veterinaire canadienne》1991,32(7):407-412
The methods used in a large field study which investigated the health and productivity of Ontario beef breeding herds are described. Beginning in the calving season of 1986, 180 breeding herds on 170 randomly sampled farms were followed for a two year period, using producer records and annual farm visits.
The response (cooperation) rate among the eligible producers initially contacted was 70%. Approximately two-thirds of producers maintained individual animal records, primarily calving season records. Approximately 40% recorded disease occurrences.
The advantages, disadvantages, and interpretation of “on-farm” observational studies are discussed.
相似文献80.
Equivalent salt solution series have been previously defined as solutions with combinations of sodium absorption ratio (SAR) and electrolyte concentration (Ec) producing the same extent of clay swelling in a given soil. The present study shows that there is a high (r2>0.96) positive correlation between log Ec and log SAR of equivalent salt solutions series, in the equation: where a1 and b1 are constants for each equivalent salt solution series for a given soil. Log a1 could also be represented as a linear function of b1 resulting in the equation: where a2 and b2 are constants for a given soil. Solving this equation using any given value of b1 yields the combinations of SAR and Ec which make up each equivalent salt solution series for a given soil. The relationship between log a1 and b2 for three soils from western United States, namely Waukena, Pachappa and Grangeville, was similar, with their combined data having a r2 value of 0.96. This indicated that a single set of equivalent salt solution series values could be used for these three soils which have different clay contents and clay mineralogy. Prediction of hydraulic conductivity decreases with Ec reduction at given values of SAR in red-brown and alluvial soils from southern Tasmania, using the equivalent salt solution series values for Waukena soil, showed similar patterns to measured values and also to those predicted using the equivalent salt solution values applicable to the respective Tasmanian soils. Thus, available data indicate that the same set of equivalent salt series could be applied to the five soils studied. If further testing shows that a single set of equivalent salt solutions values could be applied to all or large groups of soils, this would facilitate the application of the equivalent salt solution concept to predict salt solution flow in the field. 相似文献