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81.
Uri Shanas Yunes Abu Galyun Jonathan Cnaani Fares Khoury Khaled Nassar Danny Simon Elad Topel Yaron Ziv 《Biological conservation》2006,132(3):292-299
The peace treaty between Israel and Jordan found the Arava desert ecosystem, shared by the two countries, in a state of developmental dichotomy. On the Israeli side, vast lands have been settled and transformed into agricultural fields, while the Jordanian side has remained relatively intact and inhabited by only a few traditional and pastoral societies. This study examined the effect of different landscape units and proximity to agriculture on reptile diversity and rodent community structure on both sides of the border. It appears that in addition to the effect of proximity to agricultural fields and landscape habitat, the border between the two countries may play a role in determining diversity on the respective sides. While reptile abundance was generally higher on the Israeli side of the border, diversity was found to be significantly higher on the Jordanian side. Rodent community structure also revealed significant differences between the two sides of the border, mainly due to the more favorable conditions for psammophilic gerbils in Jordan. When comparing Western society with pastoral traditional society, it appears that development activities of the former have altered diversity and community structure of the taxa studied in the Arava. We suggest that in addition to the effects of habitats and human disturbances, such as modern agricultural practices, cultural differences between societies should be considered when conservation plans are developed for cross-border ecosystems. 相似文献
82.
Elevated aluminum (Al) availability limits plant growth on acidic soils. Although this element is found naturally in soils, acidic conditions create an environment where Al solubility increases and toxic forms of Al impact plant function. Plant resistance to Al is often attributed to organic acid exudation from plant roots and the chelation of cationic Al in the rhizosphere. The association of arbuscular mycorrhizal (AM) fungi with the roots of plants may alleviate Al toxicity by altering soil Al availability or plant exposure through the binding of Al to fungal structures or through the influence of fungi on exudation from roots. Diverse communities of AM fungi are found in soil ecosystems and research suggests that AM fungi exhibit functional diversity that may influence plant performance under varying edaphic environments. In the present study, we evaluated acidic isolates of six AM species in their responses to Al. Andropogon virginicus (broomsedge), a warm-season grass that commonly grows in a range of stressful environments including acidic soils, was used as a plant host for Acaulospora morrowiae, Glomus claroideum, Glomus clarum, Glomus etunicatum, Paraglomus brasilianum, and Scutellospora heterogama. Fungal spores were germinated and exposed to 0 or 100 μM Al on filter paper in sand culture or were grown and exposed to Al in sand culture in association with A. virginicus. Short- and long-term responses to Al were evaluated using direct measurements of fungal spore germination, hyphal elongation, and measurements of A. virginicus colonization and plant growth as a phytometer of AM function in symbio. Spore germination and hyphal elongation varied among AM species in response to Al, but patterns were not consistent with the influences of these AM species on A. virginicus under Al exposure. Exposure to Al did not influence colonization of roots, although large differences existed in colonization among fungal species. Plants colonized by G. clarum and S. heterogama exhibited the least reduction in growth when exposed to Al, produced the highest concentrations of Al-chelating organic acids, and had the lowest concentrations of free Al in their root zones. This pattern provides evidence that variation among AM fungi in Al resistance conferred to their plant hosts is associated with the exudation of Al-binding organic acids from roots and highlights the role that AM fungal diversity may play in plant performance in acidic soil environments. 相似文献
83.
Amanda R. Taylor Noah D. Cohen Stephen Fletcher John F. Griffin Jonathan M. Levine 《Veterinary radiology & ultrasound》2013,54(4):332-342
The purpose of this study was to describe application and machine accuracy for a new computed tomography (CT) guided, frameless, stereotactic brain biopsy system in dogs. Heads from ten canine cadavers were secured to a bite‐plate with six attached fiducial markers and imaged using CT. Fiducialized CT images were imported into stereotactic software and spherical phantom lesions between 3.9 and 5.5 mm in diameter were created in six locations. Infrared cameras and reflective markers were used to register fiducials to the reconstructed image set. Coordinates in the X, Y, and Z planes were identified for each lesion center. Iohexol (1.5 μl of 240 mgI/ml) was injected into the center of each lesion and CT scans were repeated. Pre‐ and postinjection CT images for each cadaver were fused using the system software. Application accuracy was calculated using the center of each phantom lesion and the center of each injected contrast material location. Machine accuracy was calculated using a phantom with known distances between four fixed points in the X, Y, and Z planes. Mean application accuracy in the first 5 cadavers was 4.3 mm (95% confidence interval [CI] 2.9–4.3 mm) and in the second 5 cadavers was 2.9 mm (95% CI 2–3.9 mm). The more superficial lesions were targeted significantly less accurately than the deeper lesions (P = 0.0183). Median machine accuracy was 0.1 mm and the range was 0.1–0.2 mm. Findings supported use of the new biopsy system for canine brain lesions >3.9 mm in diameter. 相似文献
84.
Barbara Moser Christoph Bachofen Jonathan D. Müller Marek Metslaid Thomas Wohlgemuth 《Annals of Forest Science》2016,73(4):959-970
Key message
Pinus sylvestris seedlings quickly expand their roots to deeper soil layers while Pseudotsuga menziesii concentrates its root system in the topsoil, thereby running the risk of desiccation during long dry spells, as indicated by lower survival after simulated summer drought.Context
Pseudotsuga menziesii (Douglas-fir) is regarded as a promising species to maintain the productivity of Central European lowland forests given the projected increase of long dry spells.Aims
Will the species be able to regenerate from seed and spread outside plantations in a drier temperate Europe?Methods
We measured the relative growth rate, biomass allocation, root architecture, and phenotypic plasticity of Pseudotsuga menziesii seedlings sown in a common garden and grown under current precipitation and prolonged drought, respectively. The species’ competitive ability with respect to Pinus sylvestris L., the most drought-tolerant native conifer in Central Europe, was assessed during three growing seasons.Results
Pinus sylvestris seedlings had higher relative growth rates than did Pseudotsuga menziesii seedlings, first in terms of aboveground biomass and later in terms of shoot height. This resulted in heavier and taller seedlings after three growing seasons under both moist and dry conditions. Shorter vertical roots corresponded with lower survival of Pseudotsuga menziesii seedlings under dry conditions.Conclusion
Fast root proliferation allows Pinus sylvestris seedlings to reach deeper water pools that are less rapidly depleted during transient drought. By contrast, the shallow root system might put Pseudotsuga menziesii seedlings at the risk of desiccation during prolonged dry spells.85.
Jonathan Wadsworth 《Agricultural Systems》1985,16(2):85-107
The economic effect of increased stocking rate permitted by the introduction of dry season feedin is evaluated with reference to the growing/fatening system of beef production in the sub-humid tropics. A widely applicable model is derived which requires few input variables, all of which will be easily obtainable in a specific location. The economic break-even point in terms of feeding cost and dry season length can be determined in order to assess the value of local diets or attempt the formulation of new ones. Increae in profitability due to dry season feeding is assessed taking into account increase in stocking rate, seasonal de-stocking practices, length of dry season, growth rates, feed costs and beef price. The model is appropriate for use in developing countries and can be employed manually to determine rapidly those management options worthy of more detailed consideration. 相似文献
86.
87.
Cultivars of common bean (Phaseolus vulgaris L.) capable of yielding well at low levels of native or added phosphorus (P)
are highly desirable in many tropical production systems. The objective of the present study was to identify geographical
regions which might be sources of such genotypes. A total of 364 landraces, cultivars and wild genotypes, drawn from a broad
geographic range, were divided on the basis of growth habit into four field trials, each comprising two levels of P, stressed
and unstressed, on an infertile Andosol in Popayan, Colombia. The regression relationship between grain yield per plant in
the presence and in the absence of stress was determined, and each genotype's deviation from this relationship was used as
a measure of P-efficiency. There was highly significant variation in efficiency among genotypes in all growth habits, and
in climbing beans there were consistent regional differences, superior genotypes being identified with greater frequency among
those from Bolivia, West Mexico and South Mexico-West Guatemala. The latter region was promising for prostrate bush genotypes
also. Wild beans in general performed relatively poorly; it appears that P-efficiency traits in P. vulgaris have been acquired
during or after domestication. These results confirm that genetic differences in P-efficiency exist among common bean genotypes
and suggest that these are related to geographic origin. Furthermore, the use of a representative sample of germplasm can
help to identify segments of the gene bank that are especially promising as sources of desirable traits.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
88.
89.
Jonathan J. Halvorson Jeffrey L. Smith Robert I. Papendick 《Biology and Fertility of Soils》1996,21(3):207-214
Development of a method to assess and monitor soil quality is critical to soil resource management and policy formation. To be useful, a method for assessing soil quality must be able to integrate many different kinds of data, allow evaluation of soil quality based on alternative uses or definitions and estimate soil quality for unsampled locations. In the present study we used one such method, based on non-parametric geostatistics. We evaluated soil quality from the integration of six soil variables measured at 220 locations in an agricultural field in southeastern Washington State. We converted the continous data values for each soil variable at each location to a binary variable indicator transform based on thresholds. We then combined indicator transformed data for individual soil variables into a single integrative indicator of soil quality termed a multiple variable indicator transform (MVIT). We observed that soil chemical variables, pools of soil resources, populations of microorgansims, and soil enzymes covaried spatially across the landscape. These ensembles of soil variables were not randomly distributed, but rather were systematically patterned. Soil quality maps calculated by kriging showed that the joint probabilities of meeting specific MVIT selection were influenced by the critical threshold values used to transform each individual soil quality variable and the MVIT selection criteria. If MVIT criteria adequately reflect soil quality then the kriging can produce maps of the probabilty of a soil being of good or poor quality. 相似文献
90.
Kopp VI Churikov VM Singer J Chao N Neugroschl D Genack AZ 《Science (New York, N.Y.)》2004,305(5680):74-75
Chiral gratings with double helix symmetry were produced by twisting glass optical fiber with a noncircular core cross section as it passed through a miniature oven. We observed polarization-selective transmission in chiral fibers with pitches of tens of micrometers. Two modes of optical interaction were differentiated. In chirallong-period gratings, dips in transmission were observed at wavelengths associated with scattering into distinct cladding modes mediated by the chiral grating. In chiral intermediateperiod gratings, a broad scattering band was observed. These gratings can be used to produce sharp or broad polarization-selective filters. 相似文献