全文获取类型
收费全文 | 13140篇 |
免费 | 883篇 |
国内免费 | 47篇 |
专业分类
林业 | 1139篇 |
农学 | 547篇 |
基础科学 | 129篇 |
3454篇 | |
综合类 | 457篇 |
农作物 | 712篇 |
水产渔业 | 1373篇 |
畜牧兽医 | 4918篇 |
园艺 | 250篇 |
植物保护 | 1091篇 |
出版年
2024年 | 21篇 |
2023年 | 96篇 |
2022年 | 175篇 |
2021年 | 319篇 |
2020年 | 301篇 |
2019年 | 295篇 |
2018年 | 555篇 |
2017年 | 567篇 |
2016年 | 570篇 |
2015年 | 440篇 |
2014年 | 544篇 |
2013年 | 821篇 |
2012年 | 965篇 |
2011年 | 949篇 |
2010年 | 574篇 |
2009年 | 511篇 |
2008年 | 785篇 |
2007年 | 768篇 |
2006年 | 633篇 |
2005年 | 561篇 |
2004年 | 538篇 |
2003年 | 489篇 |
2002年 | 377篇 |
2001年 | 304篇 |
2000年 | 307篇 |
1999年 | 260篇 |
1998年 | 67篇 |
1997年 | 70篇 |
1996年 | 55篇 |
1995年 | 54篇 |
1994年 | 34篇 |
1993年 | 33篇 |
1992年 | 76篇 |
1991年 | 58篇 |
1990年 | 56篇 |
1989年 | 64篇 |
1988年 | 52篇 |
1987年 | 54篇 |
1986年 | 52篇 |
1985年 | 63篇 |
1984年 | 42篇 |
1983年 | 44篇 |
1982年 | 27篇 |
1979年 | 48篇 |
1978年 | 43篇 |
1977年 | 31篇 |
1974年 | 32篇 |
1973年 | 55篇 |
1972年 | 37篇 |
1971年 | 31篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The role of GIS and GPS in precision farming 总被引:2,自引:0,他引:2
M. Nemnyi P. . Mesterhzi Zs. Pecze Zs. Stpn 《Computers and Electronics in Agriculture》2003,40(1-3):45
Examinations in connection with site-specific farming have been carried out by our institute since 1998. Precision farming is a way of agricultural production, which takes into account the in-field variability, a technology where the application-seeding, nutrient replacement, spraying, etc. has taken place to act on the local circumstances of a given field. The geographic information system (GIS) created by computing background makes possible to generate complex view about our fields and to make valid agrotechnological decisions. Our goal was to compare two systems for marking out further research tasks, because in some cases there have been misunderstandings among the researchers, and the information provided by given companies seems to be complicated for potential users (famers). 相似文献
992.
993.
The brain maintains internal models of its environment to interpret sensory inputs and to prepare actions. Although behavioral studies have demonstrated that these internal models are optimally adapted to the statistics of the environment, the neural underpinning of this adaptation is unknown. Using a Bayesian model of sensory cortical processing, we related stimulus-evoked and spontaneous neural activities to inferences and prior expectations in an internal model and predicted that they should match if the model is statistically optimal. To test this prediction, we analyzed visual cortical activity of awake ferrets during development. Similarity between spontaneous and evoked activities increased with age and was specific to responses evoked by natural scenes. This demonstrates the progressive adaptation of internal models to the statistics of natural stimuli at the neural level. 相似文献
994.
Studies suggest that populations of different species do not decline equally after habitat loss. However, empirical tests have been confined to fine spatiotemporal scales and have rarely included plants. Using data from 89,365 forest survey plots covering peninsular Spain, we explored, for each of 34 common tree species, the relationship between probability of occurrence and the local cover of remaining forest. Twenty-four species showed a significant negative response to forest loss, so that decreased forest cover had a negative effect on tree diversity, but the responses of individual species were highly variable. Animal-dispersed species were less vulnerable to forest loss, with six showing positive responses to decreased forest cover. The results imply that plant-animal interactions help prevent the collapse of forest communities that suffer habitat destruction. 相似文献
995.
Kicheva A Pantazis P Bollenbach T Kalaidzidis Y Bittig T Jülicher F González-Gaitán M 《Science (New York, N.Y.)》2007,315(5811):521-525
In the developing fly wing, secreted morphogens such as Decapentaplegic (Dpp) and Wingless (Wg) form gradients of concentration providing positional information. Dpp forms a longer-range gradient than Wg. To understand how the range is controlled, we measured the four key kinetic parameters governing morphogen spreading: the production rate, the effective diffusion coefficient, the degradation rate, and the immobile fraction. The four parameters had different values for Dpp versus Wg. In addition, Dynamin-dependent endocytosis was required for spreading of Dpp, but not Wg. Thus, the cellular mechanisms of Dpp and Wingless spreading are different: Dpp spreading requires endocytic, intracellular trafficking. 相似文献
996.
Francisco J. Pichón 《Agriculture and Human Values》1996,13(1):32-51
One of the most striking features observed throughout tropical agricultural frontiers is the extreme variability in land-use strategies from one farmer to the next. This article analyzes the forest conversion process and predominant land uses associated with smallholder settlement expansion in the Amazon frontier. The discussion seeks to increase understanding of the micro and macro-level forces that propel land-use decisions in the Amazon and offer insights about how farmers' land-use decisions may be altered to bring about forms of resource use that are consistent with the constraints and opportunities of the frontier environment. Recognizing that no frontier area can be truly representative of the Amazon as a whole, this article also introduces some detailed evidence from another Amazon country (Ecuador) within a topic that has been previously dominated by research mainly in Brazil. The analysis suggests that to be effective, any policy or technology-based effort on the part of governments or researchers to alter colonist land-use systems must begin to look systematically at the production systems of agricultural colonist populations already present in frontier environments. This knowledge is essential to understand the social and economic factors affecting present land use and choice of technology. It is also important for understanding factors influencing farmers' demand for more optimal systems of land use that are consistent with varying agroecological potentials, demographic situations, and the management capacity of the farmer. 相似文献
997.
998.
Nepalese porters routinely carry head-supported loads equal to 100 to 200% of their body weight (Mb) for many days up and down steep mountain footpaths at high altitudes. Previous studies have shown that African women carry head-supported loads of up to 60% of their Mb far more economically than army recruits carrying equivalent loads in backpacks. Here we show that Nepalese porters carry heavier loads even more economically than African women. Female Nepalese porters, for example, carry on average loads that are 10% of their Mb heavier than the maximum loads carried by the African women, yet do so at a 25% smaller metabolic cost. 相似文献
999.
The main tasks for climate controllers in potato bulk stores are to keep the storage climate in an appropriate condition for quality conservation. To avoid extra energy costs by using cooling systems the internal climate of potato bulk stores is controlled with outdoor air. A conventionally designed controller is difficult to adapt for an optimal climate control to reduce quality loss. However, a controller designed with fuzzy logic is found as advantageous for adapting control parameters to improve the control process. A test stand is built to ventilate and to control two samples of potato bulks simultaneously with the same outdoor weather conditions for comparisons. Several experiments were carried out to compare climate controllers with different control algorithms, i.e. conventional to a different conventional and conventional to fuzzy. 相似文献
1000.
Changelian PS Flanagan ME Ball DJ Kent CR Magnuson KS Martin WH Rizzuti BJ Sawyer PS Perry BD Brissette WH McCurdy SP Kudlacz EM Conklyn MJ Elliott EA Koslov ER Fisher MB Strelevitz TJ Yoon K Whipple DA Sun J Munchhof MJ Doty JL Casavant JM Blumenkopf TA Hines M Brown MF Lillie BM Subramanyam C Shang-Poa C Milici AJ Beckius GE Moyer JD Su C Woodworth TG Gaweco AS Beals CR Littman BH Fisher DA Smith JF Zagouras P Magna HA Saltarelli MJ Johnson KS Nelms LF Des Etages SG Hayes LS Kawabata TT 《Science (New York, N.Y.)》2003,302(5646):875-878
Because of its requirement for signaling by multiple cytokines, Janus kinase 3 (JAK3) is an excellent target for clinical immunosuppression. We report the development of a specific, orally active inhibitor of JAK3, CP-690,550, that significantly prolonged survival in a murine model of heart transplantation and in cynomolgus monkeys receiving kidney transplants. CP-690,550 treatment was not associated with hypertension, hyperlipidemia, or lymphoproliferative disease. On the basis of these preclinical results, we believe JAK3 blockade by CP-690,550 has potential for therapeutically desirable immunosuppression in human organ transplantation and in other clinical settings. 相似文献