全文获取类型
收费全文 | 280517篇 |
免费 | 15846篇 |
国内免费 | 655篇 |
专业分类
林业 | 24250篇 |
农学 | 14179篇 |
基础科学 | 2977篇 |
45452篇 | |
综合类 | 27727篇 |
农作物 | 17595篇 |
水产渔业 | 17645篇 |
畜牧兽医 | 116046篇 |
园艺 | 6399篇 |
植物保护 | 24748篇 |
出版年
2021年 | 2536篇 |
2020年 | 2920篇 |
2019年 | 3702篇 |
2018年 | 4329篇 |
2017年 | 4702篇 |
2016年 | 4994篇 |
2015年 | 4438篇 |
2014年 | 5840篇 |
2013年 | 16403篇 |
2012年 | 7503篇 |
2011年 | 9601篇 |
2010年 | 7911篇 |
2009年 | 8391篇 |
2008年 | 8957篇 |
2007年 | 8170篇 |
2006年 | 8488篇 |
2005年 | 7696篇 |
2004年 | 7514篇 |
2003年 | 7374篇 |
2002年 | 6569篇 |
2001年 | 7507篇 |
2000年 | 7206篇 |
1999年 | 6455篇 |
1998年 | 4246篇 |
1997年 | 4294篇 |
1996年 | 4034篇 |
1995年 | 4598篇 |
1994年 | 4005篇 |
1993年 | 3687篇 |
1992年 | 4990篇 |
1991年 | 5220篇 |
1990年 | 5023篇 |
1989年 | 5025篇 |
1988年 | 4444篇 |
1987年 | 4478篇 |
1986年 | 4337篇 |
1985年 | 4520篇 |
1984年 | 4107篇 |
1983年 | 3818篇 |
1982年 | 3056篇 |
1981年 | 2910篇 |
1980年 | 2860篇 |
1979年 | 3487篇 |
1978年 | 3041篇 |
1977年 | 2812篇 |
1976年 | 2628篇 |
1975年 | 2502篇 |
1974年 | 2670篇 |
1973年 | 2752篇 |
1972年 | 2447篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
981.
W. C. Carefoot 《British poultry science》1995,36(2):205-207
1. An investigation was conducted among the progeny from crosses between Buff Rock and Light Sussex bantams, and between Buff Rock and Gold‐Pencilled Hamburgh bantams in order to ascertain whether the eumelanin restrictor genes Columbian (Co) and Dark‐brown (Db) were present in the genome of the Buff Rock.
2. The Light Sussex and Gold‐Pencilled Hamburgh bantams used in this study were known to be Co/ Co db+ / db+ and co+ / co+ Db/ Db respectively.
3. In both F2 generations the least eumelanin restricted segregants were as the parent mated with the Buff Rock, thus demonstrating the Buff Rock bantam tested to be Co/ Co Db/ Db, or possess similar alleles at these loci.
4. The Buff Rock bantam male was found to be heterozygous for a eumelanin inhibitor gene which appears to be dominant white (I). 相似文献
982.
I. Vloutoglou B. D. L. Fitt J. A. Lucas 《European journal of plant pathology / European Foundation for Plant Pathology》1995,101(6):639-653
Conidia ofAlternaria linicola produced on infected linseed crops were mainly dispersed by wind. The numbers of conidia in the air above linseed crops collected by a Burkard spore sampler were greatest between 1200 h and 1300 h, when the relative humidity was lowest. Although numbers of conidia collected decreased with increasing height within and above the crop canopy, air-borneA. linicola conidia were present up to 80 cm above the crop canopy. Conidia ofA. linicola were transported by wind up to at least 40 m downwind from an artificial line inoculum source, but their numbers decreased with increasing distance from the source. In 1991, 1992, and 1993, the dispersal ofA. linicola conidia above linseed crops followed a seasonal periodicity which was influenced by weather conditions and cultural practices. The greatest numbers of conidia were collected during July, August and early September and coincided with periods favourable for sporulation and with an increase in the incidence of the disease in the senescent crop. Air-borneA. linicola conidia produced on point or line inoculum sources (naturally infected linseed stem debris) were responsible for the spread of the disease in linseed crops. In 1992 and 1993, the disease was first detected downwind from the sources, but by the end of the growing seasons, it had spread in all directions and up to 20 m and 60 m from the sources, respectively. Disease gradients were initially steep near the inoculum sources but they became flatter with time due to the secondary spread of the disease. 相似文献
983.
Losecco JM 《Science (New York, N.Y.)》1984,224(4644):56-58
The 8000-ton water IMB nucleon decay detector has good sensitivity to the neutrino burst associated with the collapse of stars. It is particularly sensitive to the v(e) charged current interactions with protons but can also record other neutrino interactions through ve scattering. Signal, noise, physics objectives, and detector modifications that would enhance burst detection are discussed. The objectives include astrophysical questions about the pulse structure and power. It also may be possible with a distant source to study neutrino masses and neutrino oscillations. 相似文献
984.
985.
Geological rhythms and cometary impacts 总被引:1,自引:0,他引:1
Time-series analysis reveals two dominant, stable long-term periodicities approximately equal to 33 +/- 3 and 260 +/- 25 million years in the known series of geological and biological upheavals during the Phanerozoic Eon. Because the cycles of these episodes agree in period and phase with the cycles of impact cratering on Earth, these results suggest that periodic comet impacts strongly influence global tectonism and biological evolution. These two periodicities could arise from interactions of the solar system with interstellar clouds as the solar system moves cyclically through the Galaxy. 相似文献
986.
987.
988.
Polychlorinated dibenzo-p-dioxins and dibenzofurans were found in sediment from Siskiwit Lake on Isle Royale, Lake Superior, a location which can receive only atmospheric inputs. The source of these compounds is the atmospheric transport of dioxins and furans formed by combustion of domestic and chemical waste. 相似文献
989.
Newly discovered fossils support a Wasatchian (early Eocene) age for the Punta Prieta vertebrate fauna of Baja California and reveal the utility of land mammal ages on a continental scale. Dispersal scenarios for late Paleocene and early Eocene vertebrates usually invoke heterochrony for similar, but geographically separated, faunas or taxa. Such heterochrony is not supported by independent geochronologies or adequate geographic samples. 相似文献
990.
Wallerstein MB 《Science (New York, N.Y.)》1984,224(4648):460-466
The federal government's concern about maintaining the lead of the United States over the Soviet Union and its allies in militarily critical technology has led it to attempt to control unwanted technology transfer. Its attempts have extended to control of open scientific communication as well as the transfer of physical devices and blueprints. In 1982, the Corson Panel (an independent ad hoc committee) reviewed the evidence on the costs and benefits of controls and suggested guiding principles for government policy. This article examines the major policy developments since the Corson Panel completed its work. The stringency and the reach of government restrictions, either proposed or in force, go considerably beyond the panel's recommendations. 相似文献