全文获取类型
收费全文 | 49002篇 |
免费 | 2690篇 |
国内免费 | 33篇 |
专业分类
林业 | 1708篇 |
农学 | 1661篇 |
基础科学 | 251篇 |
5838篇 | |
综合类 | 8199篇 |
农作物 | 1545篇 |
水产渔业 | 2718篇 |
畜牧兽医 | 26336篇 |
园艺 | 574篇 |
植物保护 | 2895篇 |
出版年
2019年 | 416篇 |
2018年 | 780篇 |
2017年 | 824篇 |
2016年 | 743篇 |
2015年 | 607篇 |
2014年 | 754篇 |
2013年 | 1736篇 |
2012年 | 1349篇 |
2011年 | 1695篇 |
2010年 | 1155篇 |
2009年 | 1099篇 |
2008年 | 1686篇 |
2007年 | 1593篇 |
2006年 | 1497篇 |
2005年 | 1380篇 |
2004年 | 1396篇 |
2003年 | 1371篇 |
2002年 | 1184篇 |
2001年 | 1913篇 |
2000年 | 1984篇 |
1999年 | 1498篇 |
1998年 | 569篇 |
1997年 | 500篇 |
1996年 | 449篇 |
1995年 | 612篇 |
1994年 | 524篇 |
1993年 | 460篇 |
1992年 | 1151篇 |
1991年 | 1211篇 |
1990年 | 1178篇 |
1989年 | 1097篇 |
1988年 | 1056篇 |
1987年 | 1082篇 |
1986年 | 1034篇 |
1985年 | 967篇 |
1984年 | 803篇 |
1983年 | 683篇 |
1982年 | 421篇 |
1981年 | 382篇 |
1979年 | 635篇 |
1978年 | 500篇 |
1977年 | 441篇 |
1976年 | 408篇 |
1975年 | 451篇 |
1974年 | 523篇 |
1973年 | 508篇 |
1972年 | 531篇 |
1971年 | 449篇 |
1970年 | 424篇 |
1969年 | 464篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Schnell RJ Kuhn DN Brown JS Olano CT Phillips-Mora W Amores FM Motamayor JC 《Phytopathology》2007,97(12):1664-1669
ABSTRACT Production of cacao in tropical America has been severely affected by fungal pathogens causing diseases known as witches' broom (WB, caused by Moniliophthora perniciosa), frosty pod (FP, caused by M. roreri) and black pod (BP, caused by Phytophthora spp.). BP is pan-tropical and causes losses in all producing areas. WB is found in South America and parts of the Caribbean, while FP is found in Central America and parts of South America. Together, these diseases were responsible for over 700 million US dollars in losses in 2001 (4). Commercial cacao production in West Africa and South Asia are not yet affected by WB and FP, but cacao grown in these regions is susceptible to both. With the goal of providing new disease resistant cultivars the USDA-ARS and Mars, Inc. have developed a marker assisted selection (MAS) program. Quantitative trait loci have been identified for resistance to WB, FP, and BP. The potential usefulness of these markers in identifying resistant individuals has been confirmed in an experimental F(1) family in Ecuador. 相似文献
102.
Christiansen E Krokene P Berryman AA Franceschi VR Krekling T Lieutier F Lönneborg A Solheim H 《Tree physiology》1999,19(6):399-403
Norway spruce trees (Picea abies (L.) Karst.) pretreated by wounding and fungal infection showed highly enhanced resistance to a subsequent challenge inoculation with the pathogenic bluestain fungus Ceratocystis polonica (Siem.) C. Moreau. This is the first time the effectiveness of the constitutive and inducible defenses has been shown to depend on prior wounding and infection in conifers, although such acquired resistance has previously been found in several angiosperms. Trees that were pretreated with a combination of 12 bark wounds (1.6 x 10 cm), four fungal inoculations and four sterile inoculations 1-15 days before mass inoculation with C. polonica at 400 inoculations per square meter over a 0.8 m stem section had significantly shorter necroses in the phloem, less bluestained sapwood, and less dead cambium than untreated control trees. Pretreatment with four fungal or sterile inoculations alone did not lead to enhanced resistance. Pretreatment by bark wounding alone seemed to provide an intermediate degree of resistance compared to bark wounding, fungal inoculations and sterile inoculations combined. All trees had a marked increase in the number of resin ducts in the year of inoculation compared with previous years, suggesting that formation of traumatic resin ducts play an important role in the development and maintainance of enhanced resistance. 相似文献
103.
The molecular basis of the sparse fur mouse mutation 总被引:30,自引:0,他引:30
The ornithine transcarbamylase-deficient sparse fur mouse is an excellent model to study the most common human urea cycle disorder. The mutation has been well characterized by both biochemical and enzymological methods, but its exact nature has not been revealed. A single base substitution in the complementary DNA for ornithine transcarbamylase from the sparse fur mouse has been identified by means of a combination of two recently described techniques for rapid mutational analysis. This strategy is simpler than conventional complementary DNA library construction, screening, and sequencing, which has often been used to find a new mutation. The ornithine transcarbamylase gene in the sparse fur mouse contains a C to A transversion that alters a histidine residue to an asparagine residue at amino acid 117. 相似文献
104.
105.
106.
107.
Toxoplasmosis in two cats with inflammatory intestinal disease 总被引:1,自引:0,他引:1
J L Peterson M D Willard G E Lees M R Lappin T Dieringer E Floyd 《Journal of the American Veterinary Medical Association》1991,199(4):473-476
Lymphocytic-plasmacytic enteritis, a chronic inflammatory intestinal disease, was diagnosed in 2 cats. In 1 cat, recurrence of clinical signs after initiating treatment was attributed to relapse of the inflammatory intestinal disease, but was found to be attributable to relapsing toxoplasmosis secondary to immunosuppressive drug therapy. Treatment with clindamycin resolved the recurrent toxoplasmosis. In the second cat, clinical signs of toxoplasmosis did not develop, but serologic testing yielded evidence of active toxoplasmosis. Treatment with clindamycin caused the titers to decrease. Relapsing toxoplasmosis may be responsible for apparent resistance to treatment in cats for inflammatory intestinal disease being treated with immunosuppressive drugs. 相似文献
108.
109.
Norway spruce (Picea abies (L.) Karst.) seedlings growing in a growth pouch system were used to investigate the effects of the ectomycorrhizal fungus Hebeloma crustuliniforme (Bull. ex St. Amans) Quél. and various Cs/K ratios on the uptake of (134)Cs, expressed as a percentage of the total amount of (134)Cs supplied. The amount of (134)Cs taken up by seedlings increased with increasing Cs/K ratio. At a Cs/K ratio of 0.1, uptake of (134)Cs ranged between 7.2 and 7.3% and was independent of ectomycorrhizal status, whereas at Cs/K ratios >/= 1 uptake of (134)Cs varied from 8.1 to 11.1% for ectomycorrhizal and from 10.4 to 14.4% for non-inoculated plants. Ectomycorrhizal seedlings contained a lower concentration of (134)Cs than non-inoculated seedlings. Among plant parts, the amount of (134)Cs was significantly lower in needles and lateral roots of ectomycorrhizal seedlings compared with non-inoculated seedlings. Among fungal and seedling tissues, highest X-ray net counts of (133)Cs were measured in fungal hyphae of ectomycorrhizal mantles. X-Ray net counts of (133)Cs in lateral roots of ectomycorrhizal and non-inoculated plants were similar, but 5 to 10 times higher than in main roots and needles, suggesting an accumulation of (133)Cs in lateral roots and slow translocation to other plant parts. In contrast, X-ray net counts of K indicated that K was readily mobilized from lateral roots to main roots and needles. Elemental mapping showed a relatively homogeneous distribution of (133)Cs within the root. 相似文献
110.
Abstract. Incidental observations of Atlantic tomcod during routine laboratory processing revealed that a portion of the adult population collected during the 1977–78 spawning season had enlarged livers containing dark coloured tumours and other abnormalities. Of the total of 264 livers collected between 16 January and 27 February 1978 and grossly examined for prevalence of abnormalities, 25% appeared to contain neoplastic nodules and hepatocellular carcinoma. One liver contained a massive tumour (7 × 12 mm) that involved approximately 60% of the liver. The exact causes of the high prevalence of hepatocellular carcinoma are unknown but poly-chlorinated biphenyls (PCBs) are suspected of having a possible role. The Hudson River is known to contain elevated concentrations of PCBs. Twelve tomcod livers from the 1977–78 spawning population representing both normal and hepatoma conditions contained concentrations of PCBs ranging from 10–9 to 98–2 ppm (mean of 37–5 ppm). 相似文献