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991.
992.
Biodiversity and its fragility in Yunnan, China 总被引:1,自引:0,他引:1
PU Ying-shan ZHANG Zhi-yi PU Li-na HUI Chao-mao 《林业研究》2007,18(1):39-47
In Yunnan, 8 major aspects of biodiversity and fragility in landforms, ecosystems, distribution populations, alien invasion, segregation, pollution and maladministration with various menace factors causing biodiversity loss have been described. It is revealed that the facts that the biodiversity and fragility coexists in this paper. Accordingly, 6 major countermeasures for effective conservation and rational utilization of the provincial biodiversity were suggested on the basis of the scientific development concepts, principles of nature protection, conservation biology, resource management and ethnobotany and present status in Yunnan with rich intangible resources such as climatic, ethnical and cultural diversity, etc. 相似文献
993.
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
994.
The three-dimensional structure of a transverse sawn wood surface was investigated using several methods, to compare techniques,
and to study the types of deformation in tracheids at the saw cut. A sample of spruce sapwood was cut with a fret saw across
the grain. The transverse sawn surface was imaged by confocal microscopy, field emission scanning electron microscopy (FESEM),
and by light microscopy combined with serial sectioning and three-dimensional (3D) reconstruction. Both confocal microscopy
and FESEM were restricted to visualising the cut surface of the wood. However, serial sectioning was able to reveal the internal
structure below the cut surface providing more information on the types of cell deformation present. The wood structure was
deformed to depths of more than 600 μm below the surface with twisting, crushing and tearing deformations. Near the outer
surface, gaps were formed between groups of tracheids where the cell walls had been torn away to form saw dust. The deformation
tended to form groups of tracheids that were twisted relative to each other. Latewood was less distorted, forming a dense
solid surface compared to the highly fibrous earlywood. 相似文献
995.
雷竹四季出笋高效经营技术研究 总被引:3,自引:0,他引:3
对竹园地进行温、肥、水条件的调节控制试验结果表明:在温度适宜、养分充足、水分满足的情况下,竹园竹林一年四季都能出笋,并能在1~2月市场最高价时大量出笋,每公顷鲜笋产量达23.048t,产值达283574.80元,提高了竹林的经济效益。 相似文献
996.
油茶林生物量与养分生物循环的研究 总被引:12,自引:0,他引:12
对不同发育期油茶林生物量与养分的生物循环进行了研究。结果表明,从幼龄期至盛果期油茶林生物量逐步积累,盛果期生物量达到16.139t/hm2,其中经济生物量为1.798t/hm2;不同发育期油茶林分的生产力不同,盛果期油茶林太阳能利用率最高,为0.2%;不同发育期油茶林光合产物在各器官的分配比例不同;不同发育期油茶林系统大量元素(N、P、K、Ca、Mg)的吸收量、存留量、归还量及输出量不同。并提出了油茶林系统施肥的监界量。 相似文献
997.
Lifting for handling and flatbed truck transportation to the job site are important processes during manufacture of prefabri-cated wooden construction units like mini homes and building modules. Significant damage can occur to sections or components of units during these operations. Although damage usually will not impair its structural safety, it is costly to fix and causes the public to perceive prefabricated wooden buildings as low quality products. Field observations and preliminary numerical models for prefabri-cated units subject to lifting and transportation forces are summarized here. Once fully developed and verified, models will support the creation of damage mitigation strategies centered on structural details indicating how units are to be supported during lifting and transportation. 相似文献
998.
999.
Gao Jia-rong Gao Yang 《中国林学(英文版)》2007,9(1):27-32
Mudflow is the principal disturbance in Abies fabri forests. In the Gongga Mountain areas of the upper reaches of the Yangtze River, the intensities and periodicity of different scale mudflows vary. Small-scale mudflows are more frequent, occurring every one or two years while large-scale mudflows may occur once in more than one hundred years. Through a field study of A. fabri forests during different stages of growth, we analyzed their structural characteristics and discovered that after different sizes of mud-flow, poplar and birch often occupy the dominant canopy at the expense of the slow growing A. fabri, for only a small number of saplings are A. fabri that occurs in the first regeneration stage. However, a large number of seed resources can be found in mature A. fabri forests and as a unique regeneration species, A. fabri will gradually replace all the other species and form a stable community of strong shade-tolerant trees. Because of the intimate relationship between growing conditions and soil and water conservation at the upper reaches of the Yangtze River, we should carry out some artificial measurements to control and promote the slow regeneration process of A. fabri. 相似文献
1000.
On mechanical behavior of traditional timber shear wall in Taiwan I: background and theory derivation 总被引:1,自引:0,他引:1
The objectives of this study were to explore the mechanical behavior of traditional timber shear walls in Taiwan and to propose
a theoretical model to predict their lateral force resistance. An extensive field investigation was conducted, and the dimensions,
tectonic detail, and materials used were recorded. The data collected were used as the reference for theoretical derivation
and experimental design. In the theoretical model, the moment resistance of entire shear walls was derived from the contributions
of the moment-resisting capacity supplied not only by embedment and friction action between board units and beams but also
the dowel action of bamboo nails. Timber shear walls with various geometric conditions and material properties are considered.
The theoretical model demonstrated in this study can be used to predict the mechanical behavior of timber shear walls and
will be verified by experiments in our next article. 相似文献