全文获取类型
收费全文 | 34530篇 |
免费 | 1227篇 |
国内免费 | 1546篇 |
专业分类
林业 | 4732篇 |
农学 | 3071篇 |
基础科学 | 358篇 |
1932篇 | |
综合类 | 13998篇 |
农作物 | 2288篇 |
水产渔业 | 1242篇 |
畜牧兽医 | 3998篇 |
园艺 | 2392篇 |
植物保护 | 3292篇 |
出版年
2024年 | 95篇 |
2023年 | 255篇 |
2022年 | 411篇 |
2021年 | 470篇 |
2020年 | 548篇 |
2019年 | 587篇 |
2018年 | 428篇 |
2017年 | 685篇 |
2016年 | 1014篇 |
2015年 | 869篇 |
2014年 | 1349篇 |
2013年 | 1635篇 |
2012年 | 2195篇 |
2011年 | 2185篇 |
2010年 | 1802篇 |
2009年 | 1823篇 |
2008年 | 1879篇 |
2007年 | 2155篇 |
2006年 | 1776篇 |
2005年 | 1704篇 |
2004年 | 1262篇 |
2003年 | 1101篇 |
2002年 | 1030篇 |
2001年 | 1140篇 |
2000年 | 924篇 |
1999年 | 912篇 |
1998年 | 697篇 |
1997年 | 617篇 |
1996年 | 678篇 |
1995年 | 757篇 |
1994年 | 761篇 |
1993年 | 481篇 |
1992年 | 487篇 |
1991年 | 419篇 |
1990年 | 450篇 |
1989年 | 386篇 |
1988年 | 416篇 |
1987年 | 271篇 |
1986年 | 130篇 |
1985年 | 106篇 |
1984年 | 92篇 |
1983年 | 65篇 |
1982年 | 44篇 |
1981年 | 38篇 |
1980年 | 36篇 |
1979年 | 27篇 |
1978年 | 32篇 |
1977年 | 45篇 |
1975年 | 8篇 |
1955年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
施德昌 《南京农业大学学报》1989,12(1):118-128
本文提出了串励直流电动机使用新型无触点斩波调速的新方法。通过两组二段式斩波电路,主电路完全无触点化成为可能,而且扩大了调速使用范围,也证明了可应用于双机车牵引同步自动化控制。 相似文献
2.
3.
4.
试验结果表明谷子在—13.9Pa的负压下发芽率只有24.0%,在—16.73Pa时发芽率为16.3%。用0.5%的NM—1号抗旱剂包衣后,在—16.73Pa的负压下发芽率可达65.6%,比对照提高49.3%。同0.5%的NM—1抗旱剂在大豆现蕾期喷施叶面1次,相对收获株率为115.38%,相对千粒量为107.7%,增产率为40,27%。玉米在6叶期喷施0.5%的抗旱剂后,饱和亏减少4.09g,是对照的43.81%;干物质积累比对照快67.19%,蒸腾系数减少8.36g。 相似文献
5.
A field experiment was conducted with different nitrogen regimes to assess the growth and yield performance of wheat genotypes which differ in nitrate assimilation potential. Genotypic differences in biomass accumulation were observed at different growth stages. The nitrogen treatment had little effect on biomass accumulation at early stages of growth, while at later stages of growth there was enhanced biomass accumulation when N was applied in more than two splits. On an average, genotypes with high nitrate reductase activity (the 'HNR' genotypes) accumulated 14.2 % more biomass than the genotypes with low nitrate reductase activity ('LNR' genotypes) when an extra dose (40 kg N ha−1 ) of nitrogen was given at the time of anthesis. The application of nitrogen in more than two splits increased grain yield of both 'HNR' and 'LNR' genotypes mainly by increasing grain weight per ear. The application of an extra dose of nitrogen (40 kg N ha−1 ) at the time of anthesis increased grain yield of 'HNR' genotypes by 38.5 % as compared to 'LNR' genotypes. 相似文献
6.
本文报道了江西三种危害食用菌的绿色霉菌的生物学特性。它们是:绿色木霉(Trichoderma Viride pers exFn)。产黄青霉(Penicillium Chrysoenum Thom)和构巢曲霉(Aspergillus nidulcms(Eidzm)Winter)。 相似文献
7.
8.
M. Özgen 《Journal of Agronomy and Crop Science》1991,166(5):318-325
The purpose of this study was to compare responsiveness to environment as well as the stability of newly developed promising lines with traditional commercial cultivars. Subject research was conducted in Ankara between 1983-1989 on common and durum wheat cultivars and lines. Regression coefficient (b) was used as the criterion of genotypes' responsiveness to environment whereas deviation from regression (S2 d) and coefficient of determination (r2 ) were used as stability parameters. Each experiment year was regarded as an environment and yield average of each year was used as the environmental index.
In consequence of the research, it was determined that new varieties with high yield, adaptable to diverse environments could be developed by means of hybridizations between parents having different genetic characteristics which were provided from diverse ecological regions. 相似文献
In consequence of the research, it was determined that new varieties with high yield, adaptable to diverse environments could be developed by means of hybridizations between parents having different genetic characteristics which were provided from diverse ecological regions. 相似文献
9.
The effect of salinity on seed germination, plant yield parameters, and plant Na, Cl and K concentrations of chickpea and lentil varieties was studied. Results showed that in both crops percentage emergence was significantly reduced by increasing NaCl levels (0–8dSm?1). From the plant growth studies it was found that differences existed among chickpea and lentil varieties in their response to NaCl application. In chickpea, the variety Mariye showed the comparatively lowest germination percentage and the lowest seedling shoot dry weight in response to salinity and was also among the two varieties which had the lowest relative plant height, shoot and root dry weight and grain yield at maturity. Similarly, variety DZ-10-16-2, which was the second best in germination percentage and the highest in terms of seedling shoot dry weight, also had the highest relative plant height, shoot and root dry weights, and grain yield at maturity. In lentil, however, such relationships were less pronounced. Chloride concentration (mg g?1) in the plant parts at salt levels other than the control was about 2–5 times that of Na. K concentration in the plants was significantly reduced by increasing NaCl levels. Chickpea was generally more sensitive to NaCl salinity than lentil. While no seeds were produced at salinity levels beyond 2dSm?1 in chickpea (no seeds were produced at this salt level in the most sensitive variety, Mariye), most lentil varieties could produce some seeds up to the highest level of NaCl application. Overall, varieties R-186 (lentil) and Mariye (chickpea) were the most sensitive of all varieties. On the other hand, lentil variety NEL-2704 and chickpea variety DZ-10-16-2 gave comparatively higher mean relative shoot and root dry weights, and grain yield, thus showing some degree of superiority over the others. The observed variations among the varieties may be useful indications for screening varieties of both crops for salt tolerance. 相似文献
10.
Time course of grain filling pattern in two rice (Oryza sativa L.) cultivars, grown under normal and low light intensities, was studied. The number of spikelets, partially filled grains and high density grains were monitored at a 5 day interval during grain filling period from uniform panicles tagged at anthesis. The low light tolerant cultivar Swarnaprabha had more high density grains and less partially filled grains throughout the grain filling period and at harvest compared to cultivar Ratna under both normal and low light intensities. Further, the opening of spikelets in two flushes in Swarnaprabha seemed to result in a more efficient resource allocation and hence better yield as compared to Ratna, in which the opening of spikelets was in a single flush on day 10. 相似文献