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991.
992.
Wibke Himmelsbach Eduardo J. Treviño-Garza Humberto González-Rodríguez Marco A. González-Tagle Marco V. Gómez Meza Oscar A. Aguirre Calderón A. Eduardo Estrada Castillón Ralph Mitlöhner 《European Journal of Forest Research》2012,131(2):355-367
Water availability and salt excess are limiting factors in Mexican mixed pine-oak forest. In order to characterise the acclimatation
of native species to these stresses, leaf water (Ψw) and osmotic potentials (Ψs) of Juniperus flaccida, Pinus pseudostrobus and Quercus canbyi were measured under natural drought and non-drought conditions under two different aspects in the Sierra Madre Oriental.
Factorial ANOVA revealed significant differences in Ψw and Ψs between two aspects, species and sampling dates. In general, all species showed high predawn and low midday values that declined
progressively with increasing drought and soil–water loss. Seasonal and diurnal fluctuation of Ψw and Ψs were higher for J. flaccida and Q. canbyi than for P. pseudostrobus. Leaf Ψw and Ψs were mainly correlated with soil water content, while Ψs of P. pseudostrobus were hardly correlated with environmental variables. Thus, species have different strategies to withstand drought.
P. pseudostrobus was identified as a species with isohydric water status regulation, while J. flaccida and Q. canbyi presented water potential patterns typical for anisohydric species. The type of water status regulation may be a critical
factor for plant survival and mortality in the context of climate change. Nevertheless, for precise conclusions about the
advantages and disadvantages of each type, further long-term investigations are required. 相似文献
993.
Genome-wide search for segregation distortion loci associated with the expression of complex traits in Populus tomentosa 总被引:1,自引:0,他引:1
Segregation distortion of molecular markers has been reported in a broad range of organisms. It has been detected in an interspecific BC1 Populus pedigree established by controlled crossing between clone “LM50” (Populus tomentosa) and its hybrid clone “TB01” (P. tomentosa×P. bolleana). The study with a total of 150 AFLP markers (approximately 18.9% of the total loci) exhibited significant deviation from the Mendelian ratio (1:1) (p<0.01). Twenty-five percent of the markers were mapped on the pa-rental specific genetic linkage maps of clones “LM50” and “TB01” with a pseudo-test-cross mapping strategy. Twelve linkage groups had markers with skewed segregation ratios, but the major regions were on linkage groups TLG2, TLG4 and TLG6 in the linkage map of clone “LM50”. We also analyzed the association between distorted loci and expression of complex traits with Map-maker/QTL software. A total of 16 putative QTLs affecting 12 traits were identified in the distorted regions on seven linkage groups. Therefore we could detect the distribution of skewed loci along the entire genome and identify the association between quantitative traits and segregation loci via genetic mapping in an interspecific BC1 P. tomentosa family. Furthermore, the genetic nature and pos-sible causes of these segregation distortions for differentiation between female and male parents were also discussed. 相似文献
994.
Madhav Pandey Oliver Gailing Hans H. Hattemer Reiner Finkeldey 《European Journal of Forest Research》2012,131(3):739-746
Knowledge of SGS in plants is vital to understand the ecological and evolutionary dynamics of populations and to plan conservation
strategies. Some of the major factors that can affect spatial genetic structure (SGS) in plants are the level of gene flow,
spatial arrangement and life stages of individuals within populations. Applying six highly variable microsatellite markers,
we investigated the effect of these factors on spatial genetic structure selecting two natural populations of sycamore maple,
which is an insect-pollinated, autotetraploid and an indigenous hardwood species in Germany and in other central European
countries. The two study populations had different shapes (“compact” and “elongated”) and tree densities. Significant SGS
extended to ~180 m in the elongated population and to ~35 m in the compact population. Juvenile plants of the compact population
showed significant SGS up to 40 m. Estimate of Sp statistic in high-density population was almost double of that in the population
with low density. Gene dispersal distance in the low-density population was about 9 times higher than in the population with
high density. The similar level of significant SGS in both adult and juvenile plants suggested minimal or no effect of life
stages of individuals on SGS in the sycamore maple population. The data presented in this study can provide guidelines for
seed collection and to establish populations for the conservation and management of genetic resources of the species. 相似文献
995.
Drought and frost resistance of trees: a comparison of four species at different sites and altitudes
Katline Charra-Vaskou Guillaume Charrier Rémi Wortemann Barbara Beikircher Hervé Cochard Thierry Ameglio Stefan Mayr 《Annals of Forest Science》2012,69(3):325-333
Context
Drought and frost resistances are key factors for the survival and distribution of tree species. 相似文献996.
Ashraful Alam Antti Kilpeläinen Seppo Kellomäki 《European Journal of Forest Research》2012,131(3):655-667
An ecosystem model (Sima) was utilised to investigate the impact of forest management (by changing both the initial stand
density and basal area thinning thresholds from current recommendations) on energy wood production (at energy wood thinning
and final felling) and management-related carbon dioxide (CO2) emissions for the energy wood production in Finnish boreal conditions (62°39′ N, 29°37′ E). The simultaneous effects of
energy wood, timber and C stocks in the forest ecosystem (live and dead biomass) were also assessed. The analyses were carried
out at stand level during a rotation period of 80 years for Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies L. Karst.) growing in different fertility sites. Generally, the results showed that decreased basal area thinning thresholds,
compared with current thinning, reduced energy wood (logging residues) and timber production, as well as carbon stocks in
the forest ecosystem. Conversely, increased thinning thresholds increased energy wood production (ca. 1–27%) at both energy
wood thinning and final felling and reduced CO2 emissions (ca. 2–6%) related to the production chain (e.g. management operations), depending on the thinning threshold levels,
initial stand density, species and site. Increased thinning thresholds also enhanced timber production and carbon stocks in
the forest ecosystem. Additionally, increased initial stand density enhanced energy wood production for energy wood thinning
for both species, but this reduced energy wood production at final felling for Scots pine and Norway spruce. This study concluded
that increases in both initial stand density and thinning thresholds, compared with the current level, could be useful in
energy wood, timber and carbon stocks enhancement, as well as reducing management-related CO2 emissions for energy wood production. Only 2.4–3.3% of input of the produced energy (energy wood) was required during the
whole production chain, depending on the management regime, species and sites. However, a comprehensive substitution analysis
of wood-based energy, in respect to environmental benefits, would also require the inclusion of CO2 emissions related to ecosystem processes (e.g. decomposition). 相似文献
997.
Mathieu Fortin Gaétan Daigle Chhun-Huor Ung Jean Bégin Louis Archambault 《European Journal of Forest Research》2007,126(4):573-585
This study proposes a within-subject variance-covariance (VC) structure to take into account repeated measurements and heteroscedasticity
in a context of growth modeling. The VC structure integrates a variance function and a continuous autoregressive covariance
structure. It was tested on a nonlinear growth model parameterized with data from permanent sample plots. Using a stand-level
approach, basal area growth was independently modeled for red spruce (Picea rubens Sarg.) and balsam fir [Abies balsamea (L.) Mill.] in mixed stands. For both species, the implementation of the VC structure significantly improved the maximum
likelihood of the model. In both cases, it efficiently accounted for heteroscedasticity and autocorrelation, since the normalized
residuals no longer exhibited departures from the assumptions of independent error terms with homogeneous variances. Moreover,
compared with traditional nonlinear least squares (NLS) models, models parameterized with this VC structure may generate more
accurate predictions when prior information is available. This case study demonstrates that the implementation of a VC structure
may provide parameter estimates that are consistent with asymptotically unbiased variances in a context of nonlinear growth
modeling using a stand-level approach. Since the variances are no longer biased, the hypothesis tests performed on the estimates
are valid when the number of observations is large. 相似文献
998.
The fatigue behavior of plywood specimens under shear through thickness was examined on the basis of strain energy to obtain
common empirical equations for the fatigue process and failure criterion under various loading conditions. Specimens were
cut from commercial plywood panels of 9-mm thickness. Loading conditions were set as follows: a square waveform at a loading
frequency of 0.5 Hz, a triangular waveform at 0.5 Hz, and a triangular waveform at 5.0 Hz. Peak stress applied was determined
to be 0.5, 0.7, and 0.9 of static strength, that is, stress levels of 0.5, 0.7, and 0.9. The stress-strain relationships were
measured throughout the fatigue test, and the strain energy was obtained at each loading cycle. Loading conditions apparently
affected the relationship between stress level and fatigue life. On the other hand, the relationship between mean strain energy
per cycle and fatigue life was found to be independent of loading conditions. Mean strain energy per cycle obtained as the
fatigue limit was 5.85 kJ/m3 per cycle. Assuming that the accumulation of strain energy is a fatigue indicator, the fatigue process and failure criterion
for the plywood specimens under the three loading conditions were commonly expressed by the relationship between cumulative
strain energy and loading cycles. 相似文献
999.
Makoto Kiguchi Yutaka Kataoka Hiroshi Matsunaga Koichi Yamamoto Philip D. Evans 《Journal of Wood Science》2007,53(3):234-238
The market for wood-fiber plastic composites (WPCs) is expanding rapidly in many countries including Japan, where WPCs are
mainly used for exterior products. In such applications, WPCs undergo undesirable color change, chalking, and shrinkage and
swelling, and accordingly there is a need to better understand the mechanisms responsible for the weathering of WPC and develop
methods of improving their weathering resistance. In this study, weatherability of WPC was assessed by natural and accelerated
weathering trials. Discoloration (whitening) of WPC during exposure was caused by degradation of both wood and plastic. Darker
color pigments as additives improved the color stability of WPC; however, chalking on the surfaces still occurred. The color
stability of WPC was improved by application of exterior coatings. Preweathering of WPC (before coatings were applied) increased
the absorption of coatings by the WPC and had a positive effect on the color stability and prevented chalking of the composites.
Parts of this study were presented at the IUFRO XXII World Congress Meeting, Brisbane, August 2005 and the IAWPS 2005, Yokohama,
November 2005 相似文献
1000.
Won-Joung Hwang S. Nami Kartal Yuji Imamura Kunio Tsunoda Katsumi Shinoda 《Journal of Wood Science》2007,53(4):332-338
This study describes a laboratory evaluation of the efficacy of two alkylammonium compounds [didecyldimethylammonium tetrafluoroborate
(DBF) and didecyldimethylammonium chloride (DDAC)] when applied via vacuum impregnation or superficial treatment. Treated
wood specimens were tested for their termite and microbial resistance under controlled laboratory conditions. The higher chemical
retentions were needed to suppress the feeding by Coptotermes formosanus ≦3% mass loss in the multichoice test than in the no-choice test. The DBF and DDAC retention levels necessary to meet the
performance requirement ≦3% mass loss after 12-week fungal exposure varied with wood species. The retention level of 3 kg/m3 for DBF and DDAC was generally high to keep the nondurable wood species free of decay. Although there was no difference between
DBF and DDAC in the efficacy against decay and termite attack, the former slightly outperformed the latter as an antimold
and antisapstain agent. 相似文献