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841.
Purpose
The aim of the present study was to investigate the effects of visitors’ activities on soil properties in parks of Tel Aviv-Jaffa city, Israel.Materials and methods
The city was divided into three geographical regions: south, central, and north. This division reflects the course of development of the city from south to north and encompasses various socioeconomic levels of residents. In each region, 9–15 parks were randomly chosen and classified into three groups according to their size (in m2): 2?×?103 to 10?×?103, 11?×?103 to 20?×?103, and 21?×?103 to 50?×?103. In each park soil, 0–2 cm of depth layer was sampled in areas under various levels of visitor pressure from July to August 2011, and organic matter, electrical conductivity, and sodium and chlorine contents were determined. Lawns and path and picnic areas represented low and high visitor pressure, respectively. Observations were conducted to characterize the various land uses of the parks and to estimate the numbers of visitors. Also, questionnaires were used at selected parks to assess visitors’ motivations or reasons for visiting the parks.Results and discussion
Socioeconomic indicators, such as the number of residents, the apartment areas, and the percentages of family households, differed among the regions. Soil properties differed between the areas of high and low visitor pressure: they were influenced by type of human activity, size of the park, and number of visitors.Conclusions
Soil properties are affected by variations in the intensity of park use by visitors and by the type of activities enjoyed by these visitors, both of which depend on the socioeconomic status of the park area.842.
Christine Stark Leo M. Condron Alison Stewart Hong J. Di Maureen O’Callaghan 《Biology and Fertility of Soils》2007,43(5):531-540
Because soil biota is influenced by a number of factors, including land use and management techniques, changing management
practices could have significant effects on the soil microbial properties and processes. An experiment was conducted to investigate
differences in soil microbiological properties caused by long- and short-term management practices. Intact monolith lysimeters
(0.2 m2 surface area) were taken from two sites of the same soil type that had been under long-term organic or conventional crop
management and were then subjected to the same 2.5-year crop rotation [winter barley (Hordeum vulgare L.), maize (Zea mais L.), lupin (Lupinus angustifolius L.), and rape (Brassica napus L. ssp. oleifera)] and two fertilizer regimes (following common organic and conventional practices). Soil samples were taken after crop harvest
and analyzed for microbial biomass C and N, microbial activity (fluorescein diacetate hydrolysis, arginine deaminase activity,
and dehydrogenase activity), and total C and N. The incorporation of the green manure stimulated growth and activity of the
microbial communities in soils of both management histories. Soil microbial properties did not show any differences between
organically and conventionally fertilized soils, indicating that crop rotation and plant type had a larger influence on the
microbial biomass and enzyme activities than fertilization. Initial differences in microbial biomass declined, while the effects
of farm management history were still evident in enzyme activities and total C and N. Links between enzyme activities and
microbial biomass C varied depending on treatment, indicating differences in microbial community composition. 相似文献
843.
Elizabeth Rice 《Genetic Resources and Crop Evolution》2007,54(4):701-713
Using survey data from Jala, Mexico, this case-study evaluates in situ maize conservation of the variety ‘Jala’ (Zea mays L.). Though historically ‘Jala’ was the dominant variety grown in the valley of Jala, today less than 20% of farmers grow
it on only 5% of the maize area. Younger growers of the ‘Jala’ variety specialize in it, growing relatively large amounts
for niche markets. Older, diversified farmers grow small areas for household use and to compete in a local contest. Conservation
of the ‘Jala’ variety has been heavily influenced by shifting ideal concepts of maize, as determined by market and consumption
demands and by a contest designed to promote in situ conservation. The current move away from nationalized purchasing may
favor ‘Jala’s’ continued conservation. 相似文献
844.
Fernando González-Andrés Pedro A. Casquero Cristina San-Pedro Elías Hernández-Sánchez 《Genetic Resources and Crop Evolution》2007,54(1):27-44
All the accessions (35) of white lupin (Lupinus albus L.) landraces collected from northwest Iberian plateau and maintained at the Spanish germplasm collection (CRF of INIA),
were studied with the general objective of assessing the biodiversity of these landraces and to ascertain their value as genetic
resources for the development of germplasm adapted to the areas where they were collected with long and chilly winters. The
characterization study comprised 51 qualitative and 50 quantitative characters. Quantitative parameters were analyzed by Principal
Components Analysis (PCA). The 2-dimensional plot (49.3% of cumulative variability) formed a main group of accessions and
4 outliers (#1, #9, #27 and #28) separated in the first PC. The characters with a higher contribution to the first PC were
inflorescence length, leaf petiole length and leaf central foliole area. The presence of alkaloids, the percentage of plants
killed by soil borne fungal diseases, the phenology, the yield per plant and yield components were also assessed. Twenty six
accessions (the main group in the PCA plot) showed high homogeneity, with the following highlights: bitterness, indeterminate
growth habit, early ripeness and spring sowing with the exception of #18, in which seeding date is unknown and it had a later
phenology. By contrast accessions #9 and #27 were bitter of autumn sowing with determinate growing habit and they had the
longest values of primary inflorescence length and a later phenology when they were sown in spring. Average values for yield
and yield components showed a broad range of variation between accessions. The main yield component was the number of pods
per plant. Accession #22 had the highest mean seed mass, although this had not significant influence in yield. Accession #17
showed the highest yield and #1 the lowest. This last also had the lowest values of inflorescence length, leaf petiole length
and leaf central foliole area. No significant differences of resistance to soil-borne fungi were found between accessions.
The year had a significant effect in the phenology, yield and yield components except for number of seeds per pod. The studied
material might be of interest for the development of spring sowing germplasm adapted to north Iberian peninsula. 相似文献
845.
Steve Cherry Gary C. White Kim A. Keating Mark A. Haroldson Charles C. Schwartz 《Journal of Agricultural, Biological & Environmental Statistics》2007,12(2):195-215
Current management of the grizzly bear (Ursus arctos) population in Yellowstone National Park and surrounding areas requires annual estimation of the number of adult female bears
with cubs-of-the-year. We examined the performance of nine estimators of population size via simulation. Data were simulated
using two methods for different combinations of population size, sample size, and coefficient of variation of individual sighting
probabilities. We show that the coefficient of variation does not, by itself, adequately describe the effects of capture heterogeneity,
because two different distributions of capture probabilities can have the same coefficient of variation. All estimators produced
biased estimates of population size with bias decreasing as effort in creased. Based on the simulation results we recommend
the Chao estimator for model M
h
be used to estimate the number of the female bears with cubs of the year; however, the estimator of Chao and Shen may also
be useful depending on the goals of the research. 相似文献
846.
The simultaneous analysis of mixed discrete and continuous outcomes using nonlinear threshold models
Todd Coffey Chris Gennings 《Journal of Agricultural, Biological & Environmental Statistics》2007,12(1):55-77
Mixed discrete and continuous outcomes are commonly measured on each experimental unit in dose-response studies in toxicology.
The dose-response relationships for these outcomes often have dose thresholds and nonlinear patterns. In addition, the endpoints
are typically correlated, and a statistical analysis that incorporates the association may result in improved precision. We
propose an extension of the generalized estimating equation (GEE) methodology to simultaneously analyze binary, count, and
continuous outcomes with nonlinear threshold models that incorporates the intra-subject correlation. The methodology uses
a quasi-likelihood framework and a working correlation matrix, and is appropriate when the marginal expectation of each outcome
is of primary interest and the correlation between endpoints is a nuisance parameter. Because the derivatives of threshold
models are not continuous at each point of the parameter space, we describe the necessary modifications that result in asymptotically
normal and consistent estimators. Using dose-response data from a neurotoxicity experiment, the methodology is illustrated
by analyzing five outcomes of mixed type with nonlinear threshold models. In this example, the incorporation of the intra-subject
correlation resulted in decreased standard errors for the threshold parameters. 相似文献
847.
Background and Objectives
Soil nitrate nitrogen (NO3 −-N) accumulation is related closely to NO3 − leaching, which is an important issue in groundwater pollution, especially in intensive agricultural areas with saline soils where volumes of water are used in irrigation to avoid salt accumulation in the root zone. However, in the saline environment in Hai River Basin, China, the importance of detailed research into NO3 −-N distribution in the root zone has not been adequately recognized. Considering the impacts of eco-environmental system N and crop production, the present study aimed at contributing to an understanding of the effects of N application rate on soil NO3 −-N distribution, NO3 −-N residue, N loss, and maize (Zea mays L.) yield in this region. 相似文献848.
Joshua M. Tebbs Melinda H. McCann 《Journal of Agricultural, Biological & Environmental Statistics》2007,12(4):534-551
Insect-vectored plant diseases impact the agricultural community each year by affecting the economic value, the quantity,
and the quality of crops. Controlling the spread of disease is an important area in risk assessment, and understanding the
dynamics of vector populations helps researchers to develop effective treatments. In this article, we consider an experimental
design commonly used by researchers who study plant disease and examine large-sample, likelihood-based hypothesis tests that
can be used to characterize disease-transmission behavior in a stratified population. Small-sample size and power results
along with design considerations are provided. We illustrate our testing procedures using two real data examples and provide
recommendations for plant-disease researchers in the field. 相似文献
849.
Abrie J. van der Merwe Albertus L. Pretorius 《Journal of Agricultural, Biological & Environmental Statistics》2003,8(3):328-343
This article applies Bayesian nonparametric techniques of analysis to the mixed linear model. The distribution of the random
effects is specific as a nonparametric prior. A Dirichlet process prior is specified on the space of prior distributions.
A modified Dirichlet process is described and applied using a Gibbs sampler. The approach is demonstrated in an investigation
of the changes over time of packed cell volume in two breeds of cattle. 相似文献
850.
Anthropogenic N-deposition represents a significant input of N into semi-arid chaparral and coastal sage scrub (CSS) shrublands
of southern California. High levels of atmospheric N deposition have the potential to increase soil C and N mineralization,
and we hypothesize that semi-arid shrubland soil exposed to long-term (decades) high N deposition will have significantly
higher C and N mineralization potentials. This hypothesis was tested in a laboratory incubation where the inorganic N (NH4+NO3) and CO2 production of soils maintained at a constant temperature of 25°C and a soil moisture of 0.25 g H2O/g (65% water-filled pore space) were sampled sequentially over a 50-week period. The temporal trend in cumulative C and
N mineralization was well described by a first- and zero-order model, respectively. Long-term atmospheric N deposition significantly
increased potential N mineralization but not C mineralization, and both the rate and total N mineralization were significantly
positively correlated with the surface (0–10 cm) soil δ
15N natural abundance and negatively correlated with the surface soil C:N ratio. While the incubation techniques used here do
not provide realistic estimates of in situ C or N mineralization, these assays indicate that atmospheric N deposition has
significantly altered ecosystem N storage and cycling. 相似文献