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991.
The Effectiveness of Capillary Barriers to Hydraulically Isolate Salt Contaminated Soils 总被引:1,自引:0,他引:1
The use of capillary barriers overlayed with topsoil to hydraulically isolate highly saline soils was investigated in a greenhouse study. Capillary barriers of 8 cm or greater thickness effectively prevented salt from migrating upward into the topsoil, thus allowing vegetation to be established. The water which drained from the capillary barrier had electrical conductivities on the order of one third that of the underlying saline soil, and should be acceptable for stream discharge. The capillary barriers reduced the flux of water and salt to the groundwater to about one third of that of the control. The results of the study show that capillary barriers can be used effectively to contain salt contaminated soils. 相似文献
992.
J. J. Jiménez A. G. Moreno T. Decaëns P. Lavelle M. J. Fisher R. J. Thomas 《Biology and Fertility of Soils》1998,28(1):101-110
The structure and seasonal changes of earthworm communities were evaluated in a natural savanna and in a improved grass-legume
pasture in a Colombian oxisol over a period of 18 months. One plot of 90×90 m was isolated in each of the systems and each
month five samples of 1 m2×0.5 m and ten of 20×20×20 cm were randomly selected from a stratified block design. Species richness was similar in the two
evaluated plots (seven species), whereas diversity measured by the index, H (Shannon and Weaver 1949) was clearly different, i.e. H=2.89 in natural savanna and H=1.29 in pasture. This is explained by differences in earthworm community structure. The average annual density in the savanna
was 49.8, ranging from 10.8 to 135.8 individuals (ind) m–2, and biomass was 3.3 g m–2 (hand-sorting method), ranging from 0.9 to 11.5 g m–2. In the man-made pasture, density was 80.1 ind m–2 on average, ranging from 24 to 215.8 ind m–2 and biomass was more than tenfold higher, ranging from 29.2 to 110.4 g m–2. This was especially due to the presence of a large glossoscolecid anecic species, Martiodrilus carimaguensis Jiménez and Moreno, which has been greatly favoured by conversion of savanna to pasture. Endogeic species were dominant in
the natural savanna whereas the anecic species accounted for 88% of total earthworm biomass in the pasture. Total earthworm
density and biomass were significantly different in the two systems studied (t-test). The results indicate a clearly positive response of earthworm communities to improved pastures, a type of land use
that is being increasingly adopted in moist neotropical savannas.
Received: 20 October 1997 相似文献
993.
W Zhou JM Thomas DS Shephard BFG Johnson D Ozkaya T Maschmeyer RG Bell Q Ge 《Science (New York, N.Y.)》1998,280(5364):705-708
The anionic ruthenium cluster carbonylates [Ru6C(CO)16]2- or [H2Ru10(CO)25]2- interspersed with bis(triphenylphosphino)iminium counterions (PPN+) are incorporated from solution into the pores of MCM-41 mesoporous silica (3 nanometers in diameter), where they form tightly packed arrays. These arrays were shown by high-resolution transmission electron microscopy, Fourier transform optical diffraction, and computer simulations to be well ordered both along and perpendicular to the axis of the cylindrical pores. In their denuded state produced by gentle thermolysis, the cluster carbonylates yield nanoparticles of ruthenium that are less well ordered than their assimilated precursors but show good activity as hydrogenation catalysts for hexene and cyclooctene. In both their as-prepared and denuded states, these encapsulated clusters are likely to exhibit interesting electronic and other properties. 相似文献
994.
A dielectric omnidirectional reflector 总被引:3,自引:0,他引:3
Y Fink JN Winn S Fan C Chen J Michel JD Joannopoulos EL Thomas 《Science (New York, N.Y.)》1998,282(5394):1679-1682
A design criterion that permits truly omnidirectional reflectivity for all polarizations of incident light over a wide selectable range of frequencies was used in fabricating an all-dielectric omnidirectional reflector consisting of multilayer films. The reflector was simply constructed as a stack of nine alternating micrometer-thick layers of polystyrene and tellurium and demonstrates omnidirectional reflection over the wavelength range from 10 to 15 micrometers. Because the omnidirectionality criterion is general, it can be used to design omnidirectional reflectors in many frequency ranges of interest. Potential uses depend on the geometry of the system. For example, coating of an enclosure will result in an optical cavity. A hollow tube will produce a low-loss, broadband waveguide, whereas a planar film could be used as an efficient radiative heat barrier or collector in thermoelectric devices. 相似文献
995.
It was nearly 100 years ago that the decline in quality and yield observed in potato crops was attributed to the accumulation of pathogens in seed tubers saved from one field generation to the next. As a direct result of this realization, seed potato certification programs have been initiated throughout the world. While these programs have different administrative structures and employ various methodologies, they are all dedicated to the primary goal of producing a sufficient volume of high quality seed tubers as free from disease causing organisms as possible. Viral diseases are especially problematic because they have serious economic affects and their physical and biological properties make them difficult to control. Until recently, certification programs have relied on methodologies including the use of virus-free material obtained from tissue culture, strict adherence to practices that minimize the mechanical and insect spread of virus, physical inspection of seed increase plots to identify and minimize the number of virus-infected plants, and the increase of seed materials for only a limited number of years to insure that any infected materials are “flushed out” of the system. Approximately 10 years ago, it was first observed that virus resistance can be obtained by using transformation techniques to insert viral genes into the genome of plants. Subsequently, researchers in private and public laboratories have shown that potato plants produced in this way are highly resistant or immune to several viral diseases. The effect that the deployment of these materials may have on the seed potato certification process is the subject of this paper. 相似文献
996.
Carbon and nitrogen dynamics in ageing earthworm casts in grasslands of the eastern plains of Colombia 总被引:5,自引:0,他引:5
The effects of a large species of anecic earthworm, Martiodrilus carimaguensis Jiménez and Moreno, on soil C and N dynamics were investigated in a native savanna and a man-made pasture of the eastern
plains of Colombia. We compared, across time (11 months), the total C, total N, NH+
4 and NO–
3 contents in the earthworm casts, the underlying soil and the adjacent soil. Additional sampling of root biomass and macrofauna
was performed. In the two management systems, the total C and N contents were higher in casts (4.33–7.50%) than in the bulk
soil (2.81–4.08%), showing that the earthworms selected food substrates with high organic contents. In general, C contents
significantly increased during cast ageing (+100%), possibly because of CO2 fixation processes, dead root accumulation and/or macrofaunal activities in casts. In fresh casts, NH+
4 levels were very high (294.20–233.98 μg g–1 dry cast) when compared to the soil (26.96–73.95 μg g–1 dry soil), due to the intense mineralisation processes that occurred during the transit of soil and organic matter through
the earthworm gut. During the first week of cast ageing, NH+
4 levels sharply decreased, while NH–
3 levels showed successive peaks in the casts, the underlying soil and the adjacent soil. These results suggested the rapid
production of NO–
3 by nitrification processes in the fresh casts, followed by diffusion to the nearby soil, first vertically, then horizontally.
After 2 weeks of cast ageing, NH+
4 and NO–
3 levels only showed slight variations, likely because of organic matter protection in stable dry casts. The root biomass was
higher (1.6–4.7 times) below the old earthworm casts. The ecological significance of these results is discussed.
Received: 22 October 1998 相似文献
997.
Julie A. Churchill Daniel A. Feeney Thomas F. Fletcher Carl A. Osborne David J. Polzin 《Veterinary radiology & ultrasound》1999,40(6):642-647
Under controlled, but varied dietary conditions 35 geriatric, uninephrectomized, spayed Beagle bitches (dogs) observed for 4 years, renal cortical and renal medullary echogenicity was measured relative to hepatic and splenic echogenicity. Regardless of the diet fed, 60-75% of these aged dogs had renal cortical echogenicity less than that of either the liver or spleen across time; 25-35% of these dogs had renal cortical echogenicity equal to that of the liver, but less than that of the spleen across time. Less than 3% of these dogs had renal cortical echogenicity greater than that of the liver, but less than that of the spleen. Only 1 (one) of these dogs had renal cortical echogenicity equal to that of the spleen and that occurred at only one of the 14 chronologic assessments. Therefore, in either mature or aged dogs imaged with 4.0 to 5.0 MHz equipment, the renal cortical echogenicity should be considered normal if it is less than or equal to that of the liver and less than that of the spleen. In 29 dogs imaged with the 4.0/5.0 MHz equipment and 6 dogs imaged with 7.5 MHz equipment, there was no significant diet or individual dog effect. The 7.5 MHz (6 dog) group had significantly higher average cortical echogenicity scores than the 4.0/5.0 MHz (29 dog) group. However, the occurrence of renal cortical echogenicity greater than liver echogenicity was seen in only 5 of 83 samples (approximately 6.0%) made on 6 dogs imaged with 7.5 MHz equipment and only 1 of 375 samples (approximately 0.27%) made on 29 dogs with 4.0/5.0 MHz equipment. With the exception of one occurrence, all dogs had renal medullary echogenicity less than that of the liver or spleen regardless of imaging equipment frequency. The renal medulla was always hypoechoic compared to the cortex. 相似文献
998.
Thomas J. Doherty MVB MSc Diplomate ACVA Frank M. Andrews DVM MS Diplomate ACVIM Melanie K. Provenza BS Donita L. Frazier DVM PhD Diplomate ABVT 《Veterinary surgery : VS》1999,28(5):375-379
OBJECTIVE: The effect of sedation on gastric emptying was evaluated in six ponies by monitoring serum concentrations of acetaminophen (AP) after intragastric administration. EXPERIMENTAL DESIGN: Prospective randomized experimental study. ANIMALS: Six adult ponies, 135 to 275 kg. METHODS: Fifteen minutes after the intravenous administration of xylazine (1 mg/kg), butorphanol (0.05 mg/kg), acepromazine (0.05 mg/kg) or saline, ponies were given AP (20 mg/kg in 350 mL water) by stomach tube. Blood for AP analysis was collected at baseline and 15, 30, 45, 75, 90, 105, and 120 minutes after AP administration. The time (Tmax) to reach peak serum concentration (Cmax), and the area under the AP serum concentration versus time curve (AUC) were determined for each treatment group. RESULTS: Tmax was 31 mins in the control group, and this increased significantly (P<.05) after sedation. Cmax decreased (P<.05) after xylazine administration, and AUC decreased (P<.05) after acepromazine. CONCLUSIONS: This study indicated that sedation has a significant effect on the gastric emptying rate of a liquid in ponies. 相似文献
999.
1000.
Christian?Jeudy Marielle?Adrian Christophe?Baussard Céline?Bernard Eric?Bernaud Virginie?Bourion Hughes?Busset Lloren??Cabrera-Bosquet Frédéric?Cointault Simeng?Han Mickael?Lamboeuf Delphine?Moreau Barbara?Pivato Marion?Prudent Sophie?Trouvelot Hoai?Nam?Truong Vanessa?Vernoud Anne-Sophie?Voisin Daniel?Wipf Christophe?SalonEmail author 《Plant methods》2016,12(1):31