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91.
利用负散度和不可约合作(竞争)系统的单调性质,分别研究二维和三维合作(竞争)系统的全局渐近稳定性.所得结果推广了已有文献的相关结论. 相似文献
92.
将研究重点放在农村信用社和农户之间的暗箱交易上,借助寻租理论的原理,从全新的视角对农村信用社与农户之间非规范融资交易进行了动态的分析。解释了农村信用社和借款农户之间存在的较为严重的寻租行为和道德风险的原因。 相似文献
93.
Regional Sediment Deficits in the Dutch Lowlands: Implications for Long-Term Land-Use Options (8 pp)
Michiel J. van der Meulen Ad J. F. van der Spek Ger de Lange Stephan H. L. L. Gruijters Serge F. van Gessel Buu-Long Nguyen Denise Maljers Jeroen Schokker Jan P. M. Mulder Rob A. A. van der Krogt 《Journal of Soils and Sediments》2007,7(1):9-16
Background, Aim and Scope
Coastal and river plains are the surfaces of depositional systems, to which sediment input is a parameter of key-importance.
Their habitation and economic development usually requires protection with dikes, quays, etc., which are effective in retaining
floods but have the side effect of retarding sedimentation in their hinterlands. The flood-protected Dutch lowlands (so-called
dike-ring areas) have been sediment-starved for up to about a millennium. In addition to this, peat decomposition and soil
compaction, brought about by land drainage, have caused significant land subsidence. Sediment deficiency, defined as the combined
effect of sediment-starvation and drainage-induced volume losses, has already been substantial in this area, and it is expected
to become urgent in view of the forecasted effects of climate change (sea-level rise, intensified precipitation and run-off).
We therefore explore this deficiency, compare it with natural (Holocene) and current human sediment inputs, and discuss it
in terms of long-term land-use options.
Materials and Methods:
We use available 3D geological models to define natural sediment inputs to our study area. Recent progress in large-scale
modelling of peat oxidation and compaction enables us to address volume loss associated with these processes. Human sediment
inputs are based on published minerals statistics. All results are given as first-order approximations.
Results:
The current sediment deficit in the diked lowlands of the Netherlands is estimated at 136 ± 67 million m3/a. About 85% of
this volume is the hypothetical amount of sediment required to keep up with sea-level rise, and 15% is the effect of land
drainage (peat decomposition and compaction). The average Holocene sediment input to our study area (based on a total of 145
km3) is ~14 million m3/a, and the maximum (millennium-averaged) input ~26 million m3/a. Historical sediment deficiency has
resulted in an unused sediment accommodation space of about 13.3 km3. Net human input of sediment material currently amounts
to ~23 million m3/a.
Discussion:
As sedimentary processes in the Dutch lowlands have been retarded, the depositional system's natural resilience to sea-level
rise is low, and all that is left to cope is human countermeasure. Preserving some sort of status quo with water management
solutions may reach its limits in the foreseeable future. The most viable long-term solutions therefore seem a combination
of allowing for more water in open country (anything from flood-buffer zones to open water) and raising lands that are to
be built up (enabling their lasting protection). As to the latter, doubling or tripling the use of filling sand in a planned
and sustained effort may resolve up to one half of the Dutch sediment deficiency problems in about a century.
Conclusions:
Conclusions, Recommendations and Perspectives. We conclude that sediment deficiency – past, present and future – challenges
the sustainable habitation of the Dutch lowlands. In order to explore possible solutions, we recommend the development of
long-term scenarios for the changing lowland physiography, that include the effects of Global Change, compensation measures,
costs and benefits, and the implications for long-term land-use options.
Recommendations and Perspectives:
- 相似文献
94.
Global forest systems: An uncertain response to atmospheric pollutants and global climate change? 总被引:1,自引:0,他引:1
Forest systems cover more than 4.1×109 ha of the Earth's land area. The future response and feedbacks of forest systems to atmospheric pollutants and projected climate change may be significant. Boreal, temperate and tropical forest systems play a prominent role in carbon (C), nitrogen (N) and sulfur (S) biogeochemical cycles at regional and global scales. The timing and magnitude of future changes in forest systems will depend on environmental factors such as a changing global climate, an accumulation of CO2 in the atmosphere, and increase global mineralization of nutrients such as N and S. The interactive effects of all these factors on the world's forest regions are complex and not intuitively obvious and are likely to differ among geographic regions. Although the potential effects of some atmospheric pollutants on forest systems have been observed or simulated, large uncertainty exists in our ability to project future forest distribution, composition and productivity under transient or nontransient global climate change scenarios. The potential to manage and adapt forests to future global environmental conditions varies widely among nations. Mitigation practices, such as liming or fertilization to ameliorate excess NOx or SOx or forest management to sequester CO2 are now being applied in selected nations worldwide.The U.S. Government's right to a non-exclusive, royalty free licence in and to any copyright is acknowledged. 相似文献
95.
96.
运用西方经济学的相关观点,分析了深圳市盐田区供水企业的市场特征,指出了供水垄断会产生一定的社会成本并且在一定程度上遏制技术创新。继而提出了一种产权重组的模式,并运用福利经济学、西方经济学及公共经济学的若干观点,对该模式的优缺点进行了分析。 相似文献
97.
Linking knowledge among spatial and temporal scales: Vegetation,atmosphere, climate and remote sensing 总被引:2,自引:0,他引:2
Global scale modeling is reviewed with respect to global circulation models, biosphere-atmosphere models, and climate-biosphere models. These different models focus on short to long time scale interactions between atmospheric and surface systems. Remote sensing is shown to play a central role in acquisition of data for these models, and an experiment, termed FIFE, is described, which is the first attempt to take simultaneous land surface observations of meteorological and biophysical parameters at sufficient resolution to test hypotheses linking the vegetated surface and circulation within the lower atmosphere. 相似文献
98.
王静海 《河北北方学院学报(自然科学版)》1996,(1)
考虑一类非线性发展方程u_t-u_(xxt) f(u) g(u_x)_x=h(x,t)的初边值问题,证明了整体强解的存在唯一性,并进一步讨论了对应非负初值其解的非负性质。 相似文献
99.
X.?Cui R.?HarlingEmail author 《European journal of plant pathology / European Foundation for Plant Pathology》2005,111(4):327-339
Quorum sensing is a bacterial communication mechanism by which bacteria sense their own population size and couple specific gene expression to cell density. In Gram-negative bacteria, the most commonly used quorum sensing signals are N-acyl homoserine lactones (AHLs). It is now apparent that many pathogenic bacteria employ quorum sensing to control premature expression of virulence factors. This control is thought to decrease the likelihood that the plant host would detect the pathogens presence and activate its defense system. Novel strategies that target bacterial quorum sensing systems in order to control plant bacterial diseases are discussed. 相似文献
100.
为了更进一步明确未来家具设计的必然趋势,引入设计思潮全球化和非物质设计2种观点,并以此为基础进行分析,发现了两者共同忽视的用户需求问题。结合家具与建筑特殊的历史渊源关系,从建筑学领域引入新现代概念,通过对家具这一特殊工业产品的需求分析,总结出一条特定的设计流程,并初步提出了家具设计的新现代形态观,最后以家居饰品中的创新性设计应用来诠释此观点。 相似文献