全文获取类型
收费全文 | 16623篇 |
免费 | 6篇 |
专业分类
林业 | 3637篇 |
农学 | 1295篇 |
基础科学 | 138篇 |
2757篇 | |
综合类 | 717篇 |
农作物 | 2101篇 |
水产渔业 | 1814篇 |
畜牧兽医 | 1162篇 |
园艺 | 1111篇 |
植物保护 | 1897篇 |
出版年
2023年 | 1篇 |
2022年 | 4篇 |
2021年 | 7篇 |
2020年 | 2篇 |
2019年 | 2篇 |
2018年 | 2746篇 |
2017年 | 2703篇 |
2016年 | 1188篇 |
2015年 | 77篇 |
2014年 | 22篇 |
2013年 | 22篇 |
2012年 | 800篇 |
2011年 | 2135篇 |
2010年 | 2104篇 |
2009年 | 1260篇 |
2008年 | 1326篇 |
2007年 | 1591篇 |
2006年 | 48篇 |
2005年 | 114篇 |
2004年 | 123篇 |
2003年 | 171篇 |
2002年 | 70篇 |
2001年 | 16篇 |
2000年 | 41篇 |
1999年 | 2篇 |
1998年 | 2篇 |
1995年 | 1篇 |
1993年 | 12篇 |
1992年 | 8篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 5篇 |
1988年 | 11篇 |
1987年 | 1篇 |
1985年 | 1篇 |
1977年 | 4篇 |
1972年 | 1篇 |
1969年 | 1篇 |
1968年 | 4篇 |
1967年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 390 毫秒
91.
Park SJ Yoshida N Nishifuji K Sekiguchi M Momoi Y Fukada T Iwasaki T 《The Journal of veterinary medical science / the Japanese Society of Veterinary Science》2002,64(1):63-65
The effects of non-specific immunotherapy with anti-allergic peptides extracted from the urine of human allergic patients (MS-antigen), in two dogs with allergic dermatitis (AD) have been described. Clinically, severe pruritus accompanied by secondary bacterial pyoderma did not respond to conventional therapy with systemic antibiotics. The first clinical change appeared as a significant reduction in pruritus within 3 months, around the time of the 15th injection in both cases. The clinical condition was stabilized after 5 months, allowing the gradual withdrawal of concurrent therapies and an increase of injection intervals. The correlation between the results of intradermal skin tests before and after treatment and the improvement of clinical signs was not obvious. 相似文献
92.
An introductory study was conducted to investigate the pyrethroid resistance ofHelicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) strains in Turkey, collected from cotton fields in the Adana and Antalya provinces, through
two different synthetic pyrethroid insecticides: lambda-cyhalothrin and esfenvalerate. In addition, the roles of glutathioneS-transferases (GSTs) in this resistance mechanism were analyzed. It was found that whereas resistance ratios for lambda-cyhalothrin
(LD50 levels) were 3- and 98-fold increased in the Adana and Antalya strains, respectively, esfenvalerate ratios were 3.3- and
92.3-fold increased in the Adana and Antalya strains, respectively, with respect to the susceptible strain. Furthermore, Adana
and Antalya strains showed 2.4- and 2.9-fold higher GST activities than the susceptible strain, respectively. In the Antalya
field strain, the minor increase in GST activity compared with the resistance levels implies that GSTs may be not greatly
involved in this resistance. It also provides evidence that they could not be the only metabolic mechanism responsible for
resistance to lambda-cyhalothrin and esfenvalerate inH. armigera from Turkey.
http://www.phytoparasitica.org posting Nov. 16, 2006. 相似文献
93.
94.
M. Lodovica Gullino Riccardo Savigliano Giuliana Gasparrini Corrado Clini 《Phytoparasitica》2007,35(4):321-329
Methyl bromide (MB) was phased out on January 1, 2005, and a Critical Use Exemption (CUE) process has been established in
order to define the rules for allocating the needed amounts of the fumigant. This paper deals with the effects of the CUE
process on Italian horticulture. The actual usage of the amounts of MB allocated to Italy for the year 2005 in the different
areas and on the economically most important crops was monitored and critically evaluated. The usage pattern monitored shows
that already in the first year after MB phaseout, Italy was able to replace it completely on crops such as zucchini, salad
greens, basil and watermelon. However, on crops such as tomato, pepper, melon, eggplant, strawberry, and cut flowers, further
work is required in order fully to replace MB. The emerging problems and research needs are discussed briefly. 相似文献
95.
David White Weidong Chen 《European journal of plant pathology / European Foundation for Plant Pathology》2007,119(1):3-12
Ascochyta blight is a serious disease of cool-season grain legumes (chickpea, faba bean, lentil and pea) caused by fungal
species of the anamorphic genus Ascochyta and related genera. Despite extensive studies on the biology, ecology, epidemiology
and management of the disease, little is known about the pathogenic determinants of these pathogens. This research aims at
using Ascochyta rabiei as a model for the genus in investigating genetic factors of pathogenicity, with the ultimate goal of elucidating pathogenic
mechanisms. Three advances were made: (1) insertional mutants with altered pathogenicity were identified through in vivo screening,
and genomic regions adjacent to the insertion sites in selected mutants were determined; (2) a phage library of A. rabiei genomic DNA was constructed, and the library was estimated to provide complete coverage of the A. rabiei genome. This library was used successfully to recover clones with DNA adjacent to insertional mutation sites and to isolate
specific genes; (3) DNA probes specific for an acyl-CoA ligase (cps1) and a polyketide synthase gene (pks1) were developed and library clones containing the corresponding genomic regions were identified from the phage library.
These advances provide the foundation and necessary tools for experimentation of ectopic complementation assays and targeted
mutagenesis to elucidate the genetic mechanisms of pathogenicity of A. rabiei. 相似文献
96.
Simulating the cumulative effects of multiple forest management strategies on landscape measures of forest sustainability 总被引:1,自引:2,他引:1
While the cumulative effects of the actions of multiple owners have long been recognized as critically relevant to efforts
to maintain sustainable forests at the landscape scale, few studies have addressed these effects. We used the HARVEST timber
harvest simulator to predict the cumulative effects of four owner groups (two paper companies, a state forest and non-industrial
private owners) with different management objectives on landscape pattern in an upper Michigan landscape managed primarily
for timber production. We quantified trends in landscape pattern metrics that were linked to Montreal Process indicators of
forest sustainability, and used a simple wildlife habitat model to project habitat trends. Our results showed that most trends
were considered favorable for forest sustainability, but that some were not. The proportion of all age classes and some forest
types moved closer to presettlement conditions. The trend for the size of uneven-aged patches was essentially flat while the
average size of patches of the oldest and youngest age classes increased and the size of patches of the remaining age classes
decreased. Forest fragmentation generally declined, but edge density of age classes increased. Late seral forest habitat increased
while early successional habitat declined. The owners use different management systems that cumulatively produce a diversity
of habitats. Our approach provides a tool to evaluate such cumulative effects on other landscapes owned by multiple owners.
The approach holds promise for helping landowner groups develop and evaluate cooperative strategies to improve landscape patterns
for forest sustainability. 相似文献
97.
Identification of functional corridors with movement characteristics of brown bears on the Kenai Peninsula,Alaska 总被引:2,自引:1,他引:2
Tabitha A. Graves Sean Farley Michael I. Goldstein Christopher Servheen 《Landscape Ecology》2007,22(5):765-772
We identified primary habitat and functional corridors across a landscape using Global Positioning System (GPS) collar locations
of brown bears (Ursus arctos). After deriving density, speed, and angular deviation of movement, we classified landscape function for a group of animals
with a cluster analysis. We described areas with high amounts of sinuous movement as primary habitat patches and areas with
high amounts of very directional, fast movement as highly functional bear corridors. The time between bear locations and scale
of analysis influenced the number and size of corridors identified. Bear locations should be collected at intervals ≤6 h to
correctly identify travel corridors. Our corridor identification technique will help managers move beyond the theoretical
discussion of corridors and linkage zones to active management of landscape features that will preserve connectivity. 相似文献
98.
Prediction of multinomial probability of land use change using a bisection decomposition and logistic regression 总被引:1,自引:1,他引:1
Land use change is an important research area in landscape ecology and urban development. Prediction of land use change (urban
development) provides critical information for making the right policies and management plans in order to maintain and improve
ecosystem and city functions. Logistic regression is a widely used method to predict binomial probabilities of land use change
when just two responses (change and no-change) are considered. However, in practice, more than two types of change are encountered
and multinomial probabilities are therefore needed. The existing methods for predicting multinomial probabilities have limits
in building multinomial probability models and are often based on improper assumptions. This is due to the lack of proper
methodology and inadequate software. In this study, a procedure has been developed for building models to predict the multinomial
probabilities of land use change and urban development. The foundation of this procedure consists of a special bisection decomposition
system for the decomposition of multiple-class systems to bi-class systems, conditional probability inference, and logistic
regression for binomial probability models. A case study of urban development has been conducted to evaluate this procedure.
The evaluation results demonstrated that different samples and bisection decomposition systems led to very similar quality
and performance in the developed multinomial probability models, which indicates the high stability of the proposed procedure
for this case study. 相似文献
99.
Neutral models for testing landscape hypotheses 总被引:5,自引:0,他引:5
Neutral landscape models were originally developed to test the hypothesis that human-induced fragmentation produces patterns
distinctly different from those associated with random processes. Other uses for neutral models have become apparent, including
the development and testing of landscape metrics to characterize landscape pattern. Although metric development proved to
be significant, the focus on metrics obscured the need for iterative hypothesis testing fundamental to the advancement of
the discipline. We present here an example of an alternative neutral model and hypothesis designed to relate the process of
landscape change to observed landscape patterns. The methods and program, QRULE, are described and options for statistical
testing outlined. The results show that human fragmentation of landscapes results in a non-random association of land-cover
types that can be describe by simple statistical methods. Options for additional landscape studies are discussed and access
to QRULE described in the hope that these methods will be employed to advance our understanding of the processes that affect
the structure and function in human dominated landscapes. 相似文献
100.
Agent-based land-use models: a review of applications 总被引:9,自引:0,他引:9
Robin B. Matthews Nigel G. Gilbert Alan Roach J. Gary Polhill Nick M. Gotts 《Landscape Ecology》2007,22(10):1447-1459
Agent-based modelling is an approach that has been receiving attention by the land use modelling community in recent years,
mainly because it offers a way of incorporating the influence of human decision-making on land use in a mechanistic, formal,
and spatially explicit way, taking into account social interaction, adaptation, and decision-making at different levels. Specific
advantages of agent-based models include their ability to model individual decision-making entities and their interactions,
to incorporate social processes and non-monetary influences on decision-making, and to dynamically link social and environmental
processes. A number of such models are now beginning to appear—it is timely, therefore, to review the uses to which agent-based
land use models have been put so far, and to discuss some of the relevant lessons learnt, also drawing on those from other
areas of simulation modelling, in relation to future applications. In this paper, we review applications of agent-based land
use models under the headings of (a) policy analysis and planning, (b) participatory modelling, (c) explaining spatial patterns
of land use or settlement, (d) testing social science concepts and (e) explaining land use functions. The greatest use of
such models so far has been by the research community as tools for organising knowledge from empirical studies, and for exploring
theoretical aspects of particular systems. However, there is a need to demonstrate that such models are able to solve problems
in the real world better than traditional modelling approaches. It is concluded that in terms of decision support, agent-based
land-use models are probably more useful as research tools to develop an underlying knowledge base which can then be developed
together with end-users into simple rules-of-thumb, rather than as operational decision support tools.
This paper arises from research conducted as part of the UK Research Councils’ RELU Programme (award number RES-224-25-0102).
RELU is funded jointly by the Economic and Social Research Council, the Biotechnology and Biological Sciences Research Council
and the Natural Environment Research Council, with additional funding from the Department for Environment, Food and Rural
Affairs and the Scottish Executive Environment and Rural Affairs Department. 相似文献