全文获取类型
收费全文 | 198849篇 |
免费 | 4712篇 |
国内免费 | 276篇 |
专业分类
林业 | 7999篇 |
农学 | 6327篇 |
基础科学 | 1837篇 |
24396篇 | |
综合类 | 32067篇 |
农作物 | 7216篇 |
水产渔业 | 9676篇 |
畜牧兽医 | 99254篇 |
园艺 | 2678篇 |
植物保护 | 12387篇 |
出版年
2020年 | 1877篇 |
2019年 | 2197篇 |
2018年 | 3055篇 |
2017年 | 3428篇 |
2016年 | 3152篇 |
2015年 | 2843篇 |
2014年 | 3402篇 |
2013年 | 7629篇 |
2012年 | 6157篇 |
2011年 | 7377篇 |
2010年 | 5062篇 |
2009年 | 4955篇 |
2008年 | 7034篇 |
2007年 | 6800篇 |
2006年 | 6291篇 |
2005年 | 5816篇 |
2004年 | 5460篇 |
2003年 | 5562篇 |
2002年 | 5141篇 |
2001年 | 6133篇 |
2000年 | 6048篇 |
1999年 | 4882篇 |
1998年 | 1960篇 |
1997年 | 1908篇 |
1996年 | 1779篇 |
1995年 | 2056篇 |
1994年 | 1778篇 |
1993年 | 1802篇 |
1992年 | 3713篇 |
1991年 | 4008篇 |
1990年 | 3927篇 |
1989年 | 3920篇 |
1988年 | 3605篇 |
1987年 | 3634篇 |
1986年 | 3630篇 |
1985年 | 3366篇 |
1984年 | 2801篇 |
1983年 | 2435篇 |
1982年 | 1641篇 |
1979年 | 2427篇 |
1978年 | 1921篇 |
1977年 | 1651篇 |
1976年 | 1658篇 |
1975年 | 1721篇 |
1974年 | 2120篇 |
1973年 | 2181篇 |
1972年 | 2118篇 |
1971年 | 1882篇 |
1970年 | 1915篇 |
1969年 | 1773篇 |
排序方式: 共有10000条查询结果,搜索用时 20 毫秒
951.
952.
U. Ammer G. Einsele W. Arnold O. Klee R. Agerer G. Agster U. Babel J. Behringer W. Böcking F. -H. Evers W. Fleck H. Günzl K. -F. Hofmann H. Janz J. Körner I. Kottke V. Kracht A. Krebs K. Kunzweiler W. -D. Langbein H. -U. Moosmauer S. Müller E. Nickel S. Pfeiffer R. Rausch H. Schmidt-Witte O. Schwarz R. Stegmayer 《European Journal of Forest Research》1983,102(1):282-324
Ohne Zusammenfassung
(Prof. Agerer seit 1982 am Institut für Systematische Botanik, München).
(Weilimdorf)
(zuvor t?tig bei der FVA Stuttgart, siehe oben)
(Hohenheim) 相似文献
953.
Zusammenfassung Es konnten 132Bacillus-Stämme isoliert und gegenüber7 Rhizoctonia-solani- und 6Pythium-Stämmen auf Antagonismusin vitro untersucht werden. Die gefundenen Antagonisten hemmten die Pilzisolate unterschiedlich stark, so daß Gemische von Antagonisten für die Praxis zu empfehlen sind.
Mit 4 Abbildungen und einer Tabelle 相似文献
Antagonismin vitro ofBacillus spp. againstRhizoctonia solani andPythium spp.
There were 132Bacillus-strains isolated and tested for antagonism against 7 strains ofRhizoctonia solani and 6 strains ofPythium spp. The isolated antagonists didn't show a uniform effect against the tested strains ofRhizoctonia solani andPythium spp. For an application in practice it will be better to use a mixture of antagonists.
Mit 4 Abbildungen und einer Tabelle 相似文献
954.
For reasons of unequal distribution of more than one nematode species in wood, and limited availability of wood samples required for the PCR‐based method for detecting pinewood nematodes in wood tissue of Pinus massoniana, a rapid staining‐assisted wood sampling method aiding PCR‐based detection of the pine wood nematode Bursaphelenchus xylophilus (Bx) in small wood samples of P. massoniana was developed in this study. This comprised a series of new techniques: sampling, mass estimations of nematodes using staining techniques, and lowest limit Bx nematode mass determination for PCR detection. The procedure was undertaken on three adjoining 5‐mg wood cross‐sections, of 0.5 × 0.5 × 0.015 cm dimension, that were cut from a wood sample of 0.5 × 0.5 × 0.5 cm initially, then the larger wood sample was stained by acid fuchsin, from which two 5‐mg wood cross‐sections (that adjoined the three 5‐mg wood cross‐sections, mentioned above) were cut. Nematode‐staining‐spots (NSSs) in each of the two stained sections were counted under a microscope at 100× magnification. If there were eight or more NSSs present, the adjoining three sections were used for PCR assays. The B. xylophilus– specific amplicon of 403 bp ( DQ855275 ) was generated by PCR assay from 100.00% of 5‐mg wood cross‐sections that contained more than eight Bx NSSs by the PCR assay. The entire sampling procedure took only 10 min indicating that it is suitable for the fast estimation of nematode numbers in the wood of P. massonina as the prelimary sample selections for other more expensive Bx‐detection methods such as PCR assay. 相似文献
955.
The spectral data of a new Δ7,22 sterol, 24S-ethyl-5α-cholesta-7,22E-dien-3α-ol β-galactopyranoside, isolated from the bulbs of Autonoë madeirensis, are reported. 相似文献
956.
Hal O. Liechty Michael A. Blazier Jason P. Wight Lewis A. Gaston Joshua D. Richardson Robert L. Ficklin 《Forest Ecology and Management》2009
The Southeastern United States has a robust broiler industry that generates substantial quantities of poultry litter as waste. It has historically been applied to pastures close to poultry production facilities, but pollution of watersheds with litter-derived phosphorus and to a lesser extent nitrogen have led to voluntary and in some areas regulatory restrictions on application rates to pastures. Loblolly pine (Pinus taeda L.) forests are often located in close proximity to broiler production facilities, and these forests often benefit from improved nutrition. Accordingly, loblolly pine forests may serve as alternative land for litter application. However, information on the influence of repeated litter applications on loblolly pine forest N and P dynamics is lacking. Results from three individual ongoing studies were summarized to understand the effects of repeated litter applications, litter application rates, and land use types (loblolly pine forest and pasture) on N and P dynamics in soil and soil water. Each individual study was established at one of three locations in the Western Gulf Coastal Plain region. Annual applications of poultry litter increased soil test P accumulation of surface soils in all three studies, and the magnitude of increase was positively and linearly correlated with application rates and frequencies. In one study that was established at a site with relatively high soil test P concentrations prior to poultry litter application, five annual litter applications of 5 Mg ha−1 and 20 Mg ha−1 also increased soil test P accumulation in subsurface soils to a depth of up to 45 cm. Soil test P accumulations were greater in surface soils of loblolly pine stands than in pastures when both land use types received similar rates of litter application. In one study which monitored N dynamics, lower soil organic N, potential net N mineralization, potential net nitrification, and soil water N was found in loblolly pine stands than pastures after two annual litter applications. However, increases in potential net N mineralization, net nitrification, and soil water N with litter application were more pronounced in loblolly pine than in pasture soils. Loblolly pine plantations can be a viable land use alternative to pastures for poultry litter application, but litter application rate and frequency as well as differences in nutrient cycling dynamics between pine plantations and pastures are important considerations for environmentally sound nutrient management decisions. 相似文献
957.
The anti-diarrheal activity of methanol extract of dried bark and aerial parts of Litsea polyantha (MELP) has been evaluated in mice using different models (castor oil-induced diarrhea and propulsive gut motility in mice). MELP (50, 75, 100 mg/kg, p.o.) significantly (P<0.01) reduced the onset of diarrhea, fecal excretion and also showed a significant (P<0.001) reduction in gastrointestinal motility on charcoal meal test in mice. The results of the study support the folklore use of the plant for diarrheal remedies. 相似文献
958.
A simple and modified electrospinning technique was utilized to prepare aligned and heat treated Polyacrylonitrile nanofibers by using a rotating drum fixed on top of syringe needles and applying upward hot air flow which can facilitate to heat nanofibers in electrospinning zone. Polyacrylonitrile nanofibers were electrospun from its 14 wt% solution in dimethylformamide under practical conditions. Angular power spectrum analysis showed better fiber alignment with increasing take up speed, although SEM studies demonstrated wider diameters of nanofibers being produced by modified method. The glass transition temperature of all prepared samples were determined between 70 °C and 90 °C using DSC technique. The Quantitative analysis of WAXD patterns has revealed the positive effect of modified method on the degree of crystallization of nanofibers heat treated at higher take up speed. The maximum chain orientation factor of 0.27 was determined for nanofibers collected at linear velocity of 114.5 m/min in the modified set up using Raman Spectroscopy technique. 相似文献
959.
Rapid ?ōhi?a Death (ROD) is a fungal disease of ?ōhi?a lehua (Myrtaceae: Metrosideros polymorpha) caused by Ceratocystis lukuohia and C. huliohia. ROD is the aetiological agent of widespread mortality of this important tree on Hawai?i Island, but its epidemiology remains unclear. We investigated the prevalence and viability of C. lukuohia in ambrosia beetle frass in ROD‐affected ?ōhi?a trees. A total of 200 frass traps were placed onto C. lukuohia‐infected ?ōhi?a at four locations on the east side of Hawai?i Island. Frass was collected and screened for the presence of C. lukuohia DNA using a diagnostic qPCR assay. In addition, frass samples were screened for viability by carrot baiting. All trapped beetles were of the genus Xyleborus, with the majority being the non‐native X. ferrugineus. Of the frass samples tested, 62% contained C. lukuohia DNA and 17% of carrot baits were positive for the fungus. These results indicate that ambrosia beetle frass releases C. lukuohia into the environment. We discuss the potential role infested frass could play in the ROD pathosystem. 相似文献
960.
We assessed clonal variation in morphological variables, mineral nutrition, root growth capacity, net photosynthesis, tannin distribution, and cuticle and epicuticular wax features within four families of white spruce (Picea glauca (Moench) Voss). Seeds were collected from four families obtained through controlled crosses among selected genotypes. For each family, plants were produced either from seeds (zygotic) or by somatic embryogenesis (clones). Each family was therefore represented by its zygotic seedlings and three clones. Within a family and under similar growth conditions, several clones differed significantly from the zygotic seedlings in height, root-collar diameter, needle dry mass, branch density, shoot dry mass, root dry mass, and length of needles. Branch density (number of first-order branches per cm height) of zygotic seedlings and clones varied from 0.8 to 1.4 branches cm(-1) and from 0.6 to 1.3 branches cm(-1), respectively. Mean needle length of zygotic seedlings and clones ranged from 11 to 14 mm and from 11 to 17 mm, respectively. For many variables (height, dry mass of new roots, needle dry mass and branch density), differences among clones were significantly greater than differences among zygotic seedlings within a family. Tannins were more abundant in needles of clones than in needles of zygotic seedlings. In some clones, tannins occurred as a ribbon along the central vacuole, whereas in others they appeared as aggregates dispersed in the vacuole. Within a family, N, P and K showed considerable variations in their use efficiency. Interclonal variations were observed in root growth potential and net photosynthesis. Variations in growth and physiology reflect genetically determined differences among clones within a family. 相似文献