全文获取类型
收费全文 | 1102篇 |
免费 | 97篇 |
专业分类
林业 | 205篇 |
农学 | 59篇 |
基础科学 | 3篇 |
275篇 | |
综合类 | 34篇 |
农作物 | 65篇 |
水产渔业 | 106篇 |
畜牧兽医 | 253篇 |
园艺 | 39篇 |
植物保护 | 160篇 |
出版年
2023年 | 8篇 |
2022年 | 8篇 |
2021年 | 30篇 |
2020年 | 23篇 |
2019年 | 25篇 |
2018年 | 84篇 |
2017年 | 76篇 |
2016年 | 96篇 |
2015年 | 53篇 |
2014年 | 72篇 |
2013年 | 92篇 |
2012年 | 79篇 |
2011年 | 82篇 |
2010年 | 44篇 |
2009年 | 43篇 |
2008年 | 35篇 |
2007年 | 47篇 |
2006年 | 36篇 |
2005年 | 33篇 |
2004年 | 24篇 |
2003年 | 28篇 |
2002年 | 24篇 |
2001年 | 17篇 |
2000年 | 15篇 |
1999年 | 12篇 |
1998年 | 11篇 |
1997年 | 8篇 |
1996年 | 7篇 |
1995年 | 4篇 |
1993年 | 4篇 |
1992年 | 3篇 |
1990年 | 3篇 |
1987年 | 6篇 |
1985年 | 4篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 4篇 |
1976年 | 2篇 |
1975年 | 3篇 |
1973年 | 5篇 |
1972年 | 2篇 |
1971年 | 3篇 |
1970年 | 2篇 |
1969年 | 3篇 |
1967年 | 2篇 |
1966年 | 2篇 |
1965年 | 2篇 |
1963年 | 2篇 |
1926年 | 2篇 |
1918年 | 2篇 |
排序方式: 共有1199条查询结果,搜索用时 109 毫秒
81.
The forested Lysina catchment is situated in an area very susceptible to acid deposition. The stream water is characterized by extremely high concentrations of total dissolved Al (volume weighted mean 66 Μmol L?1) and H+ (average pH=3.87). In a simple two-component model, the surface runoff component contributes only 6% of runoff in winter and 4% of runoff in summer. During flood episodes, the direct runoff contributes up to 20% of streamflow. There is a strong positive correlation between stream acidity and stream discharge. The observed exponential increase in streamwater acidity with discharge during high flow periods cannot be explained by the simple two-component model. A three-component model used for hydrograph separation is based on chemical and18O analysis of precipitation, soil water and runoff. It incorporates a soil water component along with groundwater and rainfall components in streamwater generation. Dissociated organic acids leached during the flow of water through the uppermost soil horizon help to balance an apparent anion deficit. The apparent anion deficit was found to increase exponentially with flow rate. Low variability in streamwaterδ 18O corresponds to a high contribution of indirect components (i.e., soil and ground water) in the runoff. The soil water contribution to indirect runoff calculated from the apparent anion deficit of streamwater, varied from 0 at base flow up to 80% during floods. On average, 40% of the streamwater is derived from soil water (from 31 to 39% in winter and from 47 to 54% in summer). 相似文献
82.
The influence of mesoscale weather patterns on the chemical composition of daily precipitation samples is analysed. The data of pH, sulphur from sulphates and total nitrogen are analysed for two rural sites: Plitvice station in forested part of Central Croatia (1981 to 1990) and Puntijarka suburban station on the mountain near Zagreb, the capital of Croatia (1982–1991). The two prevailing weather types in precipitation days are selected and the comparison of chemical composition of precipitation is made for each of them. The frequency distributions of pH, sulphur and nitrogen show that concentration of major ions in precipitation apparently depends on the regional scale weather type. It is shown that the seasonal variation of deposition is related to the seasonal variation in precipitation amount. In both weather types Plitvice receives more pollution than Puntijarka that is closer to urban and industrial pollution sources. Both locations are under the prevailing influence of regional pollution sources. 相似文献
83.
84.
Salières P Carré B Le Déroff L Grasbon F Paulus GG Walther H Kopold R Becker W Milosević DB Sanpera A Lewenstein M 《Science (New York, N.Y.)》2001,292(5518):902-905
Atoms interacting with intense laser fields can emit electrons and photons of very high energies. An intuitive and quantitative explanation of these highly nonlinear processes can be found in terms of a generalization of classical Newtonian particle trajectories, the so-called quantum orbits. Very few quantum orbits are necessary to reproduce the experimental results. These orbits are clearly identified, thus opening the way for an efficient control as well as previously unknown applications of these processes. 相似文献
85.
Terracciano A Abdel-Khalek AM Adám N Adamovová L Ahn CK Ahn HN Alansari BM Alcalay L Allik J Angleitner A Avia MD Ayearst LE Barbaranelli C Beer A Borg-Cunen MA Bratko D Brunner-Sciarra M Budzinski L Camart N Dahourou D De Fruyt F de Lima MP del Pilar GE Diener E Falzon R Fernando K Ficková E Fischer R Flores-Mendoza C Ghayur MA Gülgöz S Hagberg B Halberstadt J Halim MS Hrebícková M Humrichouse J Jensen HH Jocic DD Jónsson FH Khoury B Klinkosz W Knezević G Lauri MA Leibovich N Martin TA 《Science (New York, N.Y.)》2005,310(5745):96-100
Most people hold beliefs about personality characteristics typical of members of their own and others' cultures. These perceptions of national character may be generalizations from personal experience, stereotypes with a "kernel of truth," or inaccurate stereotypes. We obtained national character ratings of 3989 people from 49 cultures and compared them with the average personality scores of culture members assessed by observer ratings and self-reports. National character ratings were reliable but did not converge with assessed traits. Perceptions of national character thus appear to be unfounded stereotypes that may serve the function of maintaining a national identity. 相似文献
86.
The main objective of this research was to evaluate two possibilities of material feed rate measurement of modern mowing machines equipped with conditioner. The machines are commonly used for harvest of grasses (Lolium multiflorum, Dactylus glomerata, Phleum pratense, etc.), clover (Trifolium pratense, etc.), alfalfa (Medicago sativa) etc.A mowing machine with finger conditioner was equipped with an electronic measuring unit for the purpose of our measurements. The mowing machine's conditioner shaft was supplied with strain gauges placed on a torque-meter and with a RPM optical sensor counter. Together with torque-meter the mowing machine was equipped with a curved impact plate mounted on the machine's material output.It was decided to arrange a laboratory measurement to obtain information about the dependence of conditioner power input and signals from the impact plate on material mass flow. A mixture of grass and alfalfa was used for our measurement.The measurements carried out proved that a very good linear relationship existed between the conditioner's power input, output frequency of the apparatus measuring impact force by means of the impact plate, and material feed rate through the mowing machine. The calculated coefficients of correlation were about 0.95. It is possible to differentiate a material feed rate difference of 0.5kgs–1 using both methods. This accuracy should be sufficient for practical utilisation such as creating yield maps. 相似文献
87.
Zhou M Morgner N Barrera NP Politis A Isaacson SC Matak-Vinković D Murata T Bernal RA Stock D Robinson CV 《Science (New York, N.Y.)》2011,334(6054):380-385
The ability of electrospray to propel large viruses into a mass spectrometer is established and is rationalized by analogy to the atmospheric transmission of the common cold. Much less clear is the fate of membrane-embedded molecular machines in the gas phase. Here we show that rotary adenosine triphosphatases (ATPases)/synthases from Thermus thermophilus and Enterococcus hirae can be maintained intact with membrane and soluble subunit interactions preserved in vacuum. Mass spectra reveal subunit stoichiometries and the identity of tightly bound lipids within the membrane rotors. Moreover, subcomplexes formed in solution and gas phases reveal the regulatory effects of nucleotide binding on both ATP hydrolysis and proton translocation. Consequently, we can link specific lipid and nucleotide binding with distinct regulatory roles. 相似文献
88.
Pavel Šamonil Martin Valtera Stanislav Bek Barbora Šebková Tomáš Vrška Jakub Houška 《European Journal of Forest Research》2011,130(6):1075-1091
Soil variability was assessed in a 74.2-ha area within the Žofínsky prales natural forest. Parameters evaluated for 1765 soil
profiles inside 353 graticule plots were as follows: (1) thickness of organic horizons, (2) thickness and form of mineral
horizons, (3) humus form (HF), (4) soil taxonomic unit (STU) and (5) anomalies. In addition, soil reaction (pHKCl) and oxidizable carbon content (Cox) were measured in the laboratory for 734 samples from the upper mineral (A) and lower mineral (B) horizons. The most frequently
occurring humus form was mor followed by moder, hydromor and peaty T-horizon. Entic Podzols, Dystric Cambisols, Haplic Cambisols,
Albic Podzols, Histic (or Haplic) Gleysols, Endogleyic Stagnosols, Fibric or Hemic or Sapric Histosols and Stagnic Gleysols
were all present at the site despite its homogeneous geological bedrock. Overall coefficient of variance (CV) was lower in
terrestrial soils compared with (semi-)hydromorphic soils. Overall variance decreased in both soil groups with increasing
depth, as did CV differences between the fine (up to 10 m) and the locality scales. The lowest CV values occurred for Cox and pHKCl. The CV values differed between STUs as well. Compared to lower horizons, variograms of upper horizons showed greater autocorrelation
at the intermediate spatial scale (10–320 m)—ranging from 50 to 150 m. Semivariance values, however, reached 70–80% of sill
already at a distance of 10 m. The most significant factor of variability at all studied spatial scales is presumably the
soil disturbance regime, followed by terrain micro-topography and the effect of tree species. 相似文献
89.
Kogovšek P Kladnik A Mlakar J Znidarič MT Dermastia M Ravnikar M Pompe-Novak M 《Phytopathology》2011,101(11):1292-1300
The distribution of Potato virus Y (PVY) in the systemically infected potato (Solanum tuberosum) plants of the highly susceptible cultivar Igor was investigated. Virus presence and accumulation was analyzed in different plant organs and tissues using real-time polymerase chain reaction and transmission electron microscopy (TEM) negative staining methods. To get a complete insight into the location of viral RNA within the tissue, in situ hybridization was developed and optimized for the detection of PVY RNA at the cellular level. PVY was shown to accumulate in all studied leaf and stem tissues, in shoot tips, roots, and tubers; however, the level of virus accumulation was specific for each organ or tissue. The highest amounts of viral RNA and viral particles were found in symptomatic leaves and stem. By observing cell ultrastructure with TEM, viral cytoplasmic inclusion bodies were localized in close vicinity to the epidermis and in trichomes. Our results show that viral RNA, viral particles, and cytoplasmic inclusion bodies colocalize within the same type of cells or in close vicinity. 相似文献
90.
Slobodan Miko Georg Koch Saša Mesić Martina Šparica Miko Marko Šparica Polona Vreča Tadej Dolenec 《Journal of Soils and Sediments》2007,7(5):303-312