首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   256301篇
  免费   15366篇
  国内免费   1242篇
林业   23873篇
农学   14381篇
基础科学   3202篇
  44100篇
综合类   25499篇
农作物   17390篇
水产渔业   16759篇
畜牧兽医   97034篇
园艺   6585篇
植物保护   24086篇
  2021年   2719篇
  2020年   3075篇
  2019年   3824篇
  2018年   4157篇
  2017年   4659篇
  2016年   4953篇
  2015年   4569篇
  2014年   5891篇
  2013年   16556篇
  2012年   6878篇
  2011年   8898篇
  2010年   7748篇
  2009年   8227篇
  2008年   7943篇
  2007年   7011篇
  2006年   7491篇
  2005年   6791篇
  2004年   6463篇
  2003年   6275篇
  2002年   5558篇
  2001年   5842篇
  2000年   5642篇
  1999年   5230篇
  1998年   4132篇
  1997年   4145篇
  1996年   3901篇
  1995年   4412篇
  1994年   3848篇
  1993年   3551篇
  1992年   4187篇
  1991年   4479篇
  1990年   4162篇
  1989年   4084篇
  1988年   3610篇
  1987年   3706篇
  1986年   3620篇
  1985年   3826篇
  1984年   3649篇
  1983年   3410篇
  1982年   2860篇
  1981年   2765篇
  1980年   2754篇
  1979年   3146篇
  1978年   2854篇
  1977年   2611篇
  1976年   2550篇
  1975年   2329篇
  1974年   2565篇
  1973年   2477篇
  1972年   2205篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Book reviews     
Recent Advances in Turkey Science. Edited by C. Nixey and T. C. Grey, Poultry Science Symposium Number 21. London, Butterworths, ISBN 0 408 00971 3

Egg and Eggshell Quality. Sally E. Solomon, 1991, 149 pp., illustrated. London, Wolfe Publishing Ltd., £35.00, ISBN 0 7234 1647 8.

Aleen Cust, Veterinary Surgeon, Britain's First Woman Vet. Connie M. Ford, 1990, 109 pp., £5.99, Bristol, Biopress Ltd., The Orchard, Clanage Road, ISBN 0 948737 11 5.

Avian Incubation. Edited by S. G. Tullett, 1991, xiv + 335 pp., illustrated. London, Butterworth‐Heinemann. £00.00, $00.00. ISBN 0–7506–1002–6.

A Colour Atlas of Diseases & Disorders of the Domestic Fowl & Turkey. Edited by C. J. Randall, second edition, 1991, 175 pages, 432 illustrations in colour. London, Wolfe Publishing Ltd, £35, ISBN 0723416281.  相似文献   

992.
993.
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   
994.
Tales retold     
Hull DL 《Science (New York, N.Y.)》1991,252(5008):993-994
  相似文献   
995.
Angular distribution patterns of Auger electrons and of photoelectrons from a Cu (001) surface were measured at the same electron kinetic energy. These measurements reveal that the low kinetic energy angular distributions for Cu Auger electrons and Cu 3p(3/2) photoelectrons differ substantially. This direct comparison between the photoelectron and Auger electron angular distributions demonstrates that, in some circumstances, the Auger process produces a complicated source wave whose nature must be explored before Auger angular distributions can be used for surface structure analysis.  相似文献   
996.
997.
998.
Bacterial isolations were reviewed from equine trachea, guttural pouch, uterus, wounds, abscesses, blood, synovial fluid, and abdominal fluid submitted to the Clinical Bacteriology Laboratory of the School of Veterinary Medicine at the University of Montreal for aerobic bacterial culture from 1986 to 1988. Of the 733 samples submitted, 324 (44%) were positive for bacterial growth, and 233 antimicrobial sensitivity tests were performed. Seventy-six percent of all positive samples yielded one bacterial species and two were isolated from 22% of positive samples. Streptococcus zooepidemicus, Escherichia coli, and Actinobacillus spp. were isolated from 39%, 18%, and 15% of the samples, respectively.

Bacterial growth was most common from guttural pouches, wounds and abscesses, and transtracheal washes (TTW), but was less common from uterus, blood, abdominal fluid, and synovial fluids. Streptococcus zooepidemicus was the most common bacterium recovered from guttural pouches, TTW, uterus, and wounds and abscesses. Escherichia coli predominated in abdominal fluids, blood, and synovia. Bacterial sensitivities to common antimicrobials are presented.

  相似文献   
999.
Sporidesmin-dosed hoggets which developed photosensitisation were shown to have enlarged adrenal glands and premature involution of the thymus. These sheep also developed high concentrations of plasma cortisol after the onset of photosensitisation. Sporidesmin-dosed sheep which did not show photosensitisation showed less or no adrenal associated changes.  相似文献   
1000.
Six Friesian calves from a pedigree herd died or were killed within 1 week of birth because of progressive central nervous disease in which the only consistent lesion was cerebral oedema. The cause was citrullinaemia, resulting from an autosomally inherited dysfunction of the urea cycle enzyme arginosuccinate synthetase. Citrullinaemia was diagnosed by demonstrating markedly elevated concentrations of citrulline in the blood of one calf and in the cerebral spinal fluid of another. One of two sires used in the herd was a heterozygous carrier of the disease. Heterozygocity was demonstrated using a polymerase chain reaction/restriction endonuclease test designed to detect the genetic mutation that causes citrullinaemia in cattle.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号