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   17354篇
  免费   1298篇
  国内免费   39篇
林业   1208篇
农学   1060篇
基础科学   560篇
  3219篇
综合类   561篇
农作物   1143篇
水产渔业   1672篇
畜牧兽医   7325篇
园艺   709篇
植物保护   1234篇
  2023年   202篇
  2022年   199篇
  2021年   241篇
  2020年   405篇
  2019年   173篇
  2018年   534篇
  2017年   665篇
  2016年   611篇
  2015年   504篇
  2014年   610篇
  2013年   1079篇
  2012年   756篇
  2011年   981篇
  2010年   805篇
  2009年   724篇
  2008年   825篇
  2007年   721篇
  2006年   691篇
  2005年   566篇
  2004年   466篇
  2003年   445篇
  2002年   443篇
  2001年   435篇
  2000年   349篇
  1999年   385篇
  1998年   234篇
  1997年   211篇
  1996年   198篇
  1995年   181篇
  1994年   177篇
  1993年   178篇
  1992年   233篇
  1991年   208篇
  1990年   192篇
  1989年   200篇
  1988年   268篇
  1987年   228篇
  1986年   235篇
  1985年   220篇
  1984年   225篇
  1983年   171篇
  1982年   151篇
  1981年   146篇
  1980年   155篇
  1979年   139篇
  1978年   119篇
  1977年   116篇
  1976年   116篇
  1975年   68篇
  1974年   71篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Samples of two Andisols and two Ultisols from southern Chile were incubated with acid or with lime for up to 60 d at 25°C or for 1 day at 40°C or at 60°C. The changes in positive and negative charge were measured. The Andisols reacted slowly at 25°C. They lost protons to the solution at high pH, thus increasing the negative charge on the soils and decreasing the pH of the solution. They gained protons at low pH, thus increasing the positive charge on the soils and increasing the pH of the solution. The Ultisols reacted more quickly but again charge and pH changed through time. For all samples, the rate of reaction was increased by incubating at 60°C. Brief incubation at 60°C produces a similar relation to that obtained after longer incubation at 25°C. This provides a convenient means by which measurements can be made more quickly.  相似文献   
22.
Six bullmastiffs with congenital heart disease were evaluated over a three-year period. In all the cases the problem was shown to be dysplasia of the pulmonary valve. Five cases were male, one was female. All dogs available to follow-up developed signs of cardiac decompensation. Bullmastiffs must be added to the list of breeds in which valvular pulmonic stenosis is encountered frequently.  相似文献   
23.
The lipid class and fatty acid (FA) composition of juvenile Artemia fed continuously on four diets—the microalga Tetraselmis suecica , a mix of oat bran-wheat germ-lecithin (OWL), OwL-eicosapentaenoic acid (EPA), and OWL-EPA-arachidonic acid (AA)—were examined over a 9-d experiment in an attempt to approximate the FA profile of phyllosoma larvae of wild southern rock lobster Jasus edwardrii . The main difference in lipid class composition of Artemia fed the four diets was the relative level of polar lipid (PL) and triacylglycerol (TAG). By day 9, the algal-fed Artemia were highest in PL (95% of total lipid) and lowest in TAG (2%), whereas the remaining diets resulted in Artemia with 16–30% PL and 41–82% TAG. After 2 d, the relative FA composition of all Artemia treatments closely reflected those of the diets, with no marked change after further feeding (to day 9). In terms of the content of essential polyunsaturated fatty acids (PUFA), by day 5 Artemia fed: 1) with the algal diet contained 7 mg/g FA dry mass (0.3% DHA, 6.3% EPA, 3.4% AA of total FA); 2) with the OWL diet contained 3 mg/g (0.3% DHA, 0.9% EPA, 0.7% AA); 3) with the OWL-EPA diet contained 55 mg/g (6.2% DHA, 11.6% EPA, 1.1% AA); and 4) with the OWL-EPA-AA contained 83 mg/g (3.8% DHA, 7.5% EPA, 17.4% AA). The PUFA profiles of Artemia using the OWL-oil diets were similar to wild rock lobster phyllmmata, although levels of doco-sahexaenoic acid (DHA) were lower (10% DHA) than in J. edwardsii larvae. On the basis of PUFA composition data alone, the results suggest the suitability of the OWL-oil mixed diets for consideration for feeding to Artemia used in the culture of southern rock lobster larvae, particularly if the level of DHA can be further enhanced.  相似文献   
24.
25.
26.
Genetic diversity estimates in Cicer using AFLP analysis   总被引:2,自引:0,他引:2  
Amplified fragment length polymorphism (AFLP) analysis was used to evaluate the genetic variation among cultivated chickpea and wild Cicer relatives. In total, 214 marker loci were assessed, of which 211 were polymorphic (98.6%) across the 95 accessions that represented 17 species of Cicer. The genetic variation within a species was highest in C. pinnatifidum followed by C. reticulatum and lowest in C. macracanthum. Three main species groups were identified by UPGMA clustering using Nei's pair‐wise distance calculations. Group I included the cultivated species C. arietinum, C. reticulatum and C. echinospermum. Within this group, C. reticulatum accessions were clustered closest to the C. arietinum cultivars ‘Lasseter’, ‘Kaniva’ and ‘Bumper’, supporting the hypothesis that C. reticulatum is the most probable progenitor of the cultivated species. Cicer bijugum, C. judaicum and C. pinnatifidum were clustered together creating group II. Group III contained all nine perennial species assessed and two annual species C. yamashitae and C. cuneatum. The genetic distance detected between group I and group III (0.13) was equivalent to the genetic distance detected between group I and group II (the primary and annual tertiary species, respectively; 0.14). This indicated that the perennial tertiary species may be as valuable for increasing variation to incorporate novel germplasm in the cultigen as the annual tertiary species.  相似文献   
27.
BOOK REVIEW     
Manual of Canine and Feline Wound Management and Reconstruction. Edited by Fowler D and Williams JM  相似文献   
28.
29.
30.
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