全文获取类型
收费全文 | 11413篇 |
免费 | 802篇 |
专业分类
林业 | 1166篇 |
农学 | 421篇 |
基础科学 | 42篇 |
2607篇 | |
综合类 | 737篇 |
农作物 | 477篇 |
水产渔业 | 781篇 |
畜牧兽医 | 4614篇 |
园艺 | 281篇 |
植物保护 | 1089篇 |
出版年
2023年 | 102篇 |
2022年 | 126篇 |
2021年 | 234篇 |
2020年 | 224篇 |
2019年 | 152篇 |
2018年 | 550篇 |
2017年 | 524篇 |
2016年 | 467篇 |
2015年 | 374篇 |
2014年 | 425篇 |
2013年 | 653篇 |
2012年 | 906篇 |
2011年 | 821篇 |
2010年 | 443篇 |
2009年 | 348篇 |
2008年 | 712篇 |
2007年 | 662篇 |
2006年 | 536篇 |
2005年 | 559篇 |
2004年 | 513篇 |
2003年 | 473篇 |
2002年 | 383篇 |
2001年 | 278篇 |
2000年 | 246篇 |
1999年 | 217篇 |
1998年 | 66篇 |
1997年 | 56篇 |
1996年 | 44篇 |
1995年 | 60篇 |
1994年 | 38篇 |
1993年 | 33篇 |
1992年 | 79篇 |
1991年 | 67篇 |
1990年 | 63篇 |
1989年 | 58篇 |
1988年 | 56篇 |
1987年 | 46篇 |
1986年 | 47篇 |
1985年 | 46篇 |
1984年 | 43篇 |
1983年 | 36篇 |
1979年 | 40篇 |
1978年 | 21篇 |
1974年 | 28篇 |
1973年 | 22篇 |
1972年 | 24篇 |
1971年 | 24篇 |
1970年 | 29篇 |
1969年 | 25篇 |
1968年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
Ga?l Caro Anick Abourachid Thibaud Deca?ns Lorenza Buono Jér?me Mathieu 《Biology and Fertility of Soils》2012,48(8):961-965
In this work, we documented the influence of earthworm's galleries on their speed of movements during dispersal events in the soil. We quantified, by using X-rays, the dispersal behaviour of earthworms in the soil. The observations were conducted in mesocosms in controlled conditions for 12?h. Our experiments revealed that during a dispersal sequence of a batch of individuals of the species Aporrectodea terrestris (Savigny 1826): (a) individuals used preferentially existing conspecifics' galleries, (b) individual velocity increased after each dispersal event and (c) the lag time before each dispersal event did not seem to be influenced by previous dispersers. Therefore, dispersal seems to be facilitated by conspecifics' activity, which strongly supports the hypothesis of a feedback between ecosystem engineers' activity and their dispersal speed. 相似文献
132.
Retention processes play a major role in the fate and impact of organic contaminants in soils. The main goal of this study was to determine the influence of soil hydrophobic properties on the retention of diuron by using plots of a long‐term experiment in Versailles. We selected seven plots with pH 3.4 to 8.2 and low organic content. Sorption isotherms were obtained on soil slurries and kinetic measurements of diuron sorption were performed on undisturbed soil samples. The results showed that the Freundlich coefficient kf decreased as pH increased and that the Koc coefficient, kf/TOC, was linearly related to the contact angle measured on the clay fraction over a wide range of pH. A low initial adsorption rate and low adsorption equilibrium were observed for the plot treated with NaNO3. In this case, the structure in micro‐aggregates was assumed to limit the accessibility of adsorption sites. The CaCO3 and CaO treated plots had similar organic matter contents, pHs, CECs and bulk densities, although their < 2 μm:C ratio differed. The higher retention of diuron in the CaCO3 plot is attributed to the higher hydrophobicity of the < 2 μm fraction, probably masking part of the permanent clay negative charges. Thus, in addition to the different treatments, organic matter composition and distribution should also be included as specific soil properties. We conclude that the sorption properties of pesticides such as diuron can be a good tool to obtain greater understanding of soil properties and the degree of soil hydrophobicity/hydrophilicity in particular. 相似文献
133.
Subileau M Schneider R Salmon JM Degryse E 《Journal of agricultural and food chemistry》2008,56(19):9230-9235
The molar conversion yield of Cys-3MH into 3MH, during alcoholic fermentation, was traced using a deuterated isotope of the precursor added to different Sauvignon Blanc musts. This yield is close to that found in synthetic media supplemented with synthetic Cys-3MH, that is, below 1%. Yet, this represents only 3-7% of the total 3MH production in wine. This clearly shows that Cys-3MH is a precursor of 3MH, but not the main one in the different musts tested. The contribution of ( E)-hex-2-enal, which has been suggested as another potential precursor of 3MH, was discarded as well, as shown using also a deuterated analogue. The third suggested precursor of 3MH is a glutathionyl-3MH (G-3MH), which upon proteolytic degradation could release Cys-3MH. The knockout of the OPT1 gene, which encodes the major glutathione transporter, reduces 3MH accumulation by a 2-fold factor in grape must as compared to the wild type strain. Consequently, it is deduced that major 3MH precursor(s) are transported into yeast via Opt1p, which is in favor of G-3MH being a 3MH precursor. This work opens the search for the major natural precursor(s) of 3MH in Sauvignon Blanc must. 相似文献
134.
135.
136.
The spatial distribution patterns of the attack on fresh logs ofPasania edulis was studied for the oak borer,Platypus quercivorus (Murayama), and two species of Scolytid ambrosia beetles,Xylosandrus crassiusculus (Motschulsky) andXyleborus attenuatus Blanford, in 1994 and 1995. On the logs where onlyP. quercivorus attacked, the entry holes were distributed uniformly when attack intensity was low. However, the distribution pattern became
more aggregated with the increase in attack intensity. On logs where bothP. quercivorus and the two Scolytid species attacked, there was a negative association between the spatial distribution of the entry holes
ofP. quercivorus and that of scolytids. Simultaneous attack of two scolytids also increased the degree of aggregation of the entry holes ofP. quercivorus. The entry holes of scolytids were distributed in groups irrespective of the attack intensity of scolytids andP. quercivorus. These results suggest an asymmetrical interspecific relationship betweenP. quercivorus and scolytids. Concentration of the entry holes ofP. quercivorus in a small area may cause a considerable decline in the reproductive success in the galleries constructed there. 相似文献
137.
D. Edwin Swift William Knight Martin Béland Issifi Boureima Charles P.-A. Bourque Fan-Rui Meng 《Scandinavian Journal of Forest Research》2017,32(1):45-59
In the late 1980s, large forest companies began precommercial thinning (PCT) operations in young northern hardwood cutovers in New Brunswick, Canada. To provide supporting growth and yield information, an industrial experiment was established at residual stand densities of 1300, 1600, 1900, and 2200?stems?ha?1. Stand responses were examined for measurements recorded at 0 (1987), 5 (1992), 10 (1997), 16 (2003), and 23 (2010) years after establishment. Average diameter at breast height, quadratic mean diameter, stand basal area, and stand total volume growth increased as stem density decreased from PCT. There were significant linear differences for many of these variables between treatments and time periods (year). No significant differences were detected in tree height between treatments. In 2010, the four PCT thinning treatments did not exhibit any differences in potential sawlogs at 2.4?m (8?ft) and 3.6?m (12?ft) lengths. Significant differences were observed for 4.9?m (16?ft) sawlogs that were produced at the least dense spacing (1300?stems?ha?1). Results from this study and recommendations from the European literature suggest that value-added timber products may be produced from more intense PCT treatments than are currently being practiced on sites dominated by yellow birch (Betula alleghaniensis Britt.). 相似文献
138.
Magali Geay Véronique Marchetti André Clément Bernard Loubinoux Philippe Gérardin 《Journal of Wood Science》2000,46(4):331-333
New materials containing carboxylate groups have been synthesized by grafting polyacrylic acid onto sawdust. These new adsorbents were subjected to continuous extraction of different metal ions using packed columns to determine their maximum binding capacities. They exhibit binding capacities 15–40 times higher than unmodified sawdusts for removal of Cu2+, Ni2+, and Cd2+ chosen as representative heavy metal ions. Cation desorption and adsorbent regeneration could be effected by elution with a diluted HCl solution; water as an eluent has no effect on metal desorption. 相似文献
139.
Lahti M Aphalo PJ Finér L Lehto T Leinonen I Mannerkoski H Ryyppö A 《Tree physiology》2002,22(18):1311-1316
Five-year-old Norway spruce (Picea abies (L.) Karst.) seedlings were subjected to three simulated growing seasons in controlled environment chambers. Plants were acclimated to a soil temperature of 16 degrees C during the first and third growing seasons, but were allocated at random to soil temperature treatments of 9, 13, 18 and 21 degrees C during the second growing season. Low soil temperature during the second growing season depressed stomatal conductance and photosynthetic rate (A) per unit of projected leaf area, although intercellular CO2 concentrations did not differ significantly between treatments. At all soil temperatures, total chlorophyll concentration first decreased and then increased, although the rate of increase and the final concentration increased with soil temperature, which may explain the effect of soil temperature on A. Neither chlorophyll a/b ratio nor leaf nitrogen concentration was significantly affected by soil temperature. Treatment differences disappeared during the third simulated growing season when plants were again acclimated to a soil temperature of 16 degrees C. 相似文献
140.
Brenda Colleen Clifton-Cardoso Marcelo Schramm Mielke José Roberto De Melo Rondinele Nascimento Querino 《New Forests》2008,35(1):15-31
Dimorphandra jorgei MF Silva (Caesalpinaceae) and Swartzia macrostachya Benth. var. riedelii Cowan (Fabaceae) are tree species from the southern Bahian Atlantic Forest, identified for the restoration of degraded areas.
The objective of this research is to study their seed germination and seedling growth to develop simple methods for seedling
production in small scale nurseries. Because the species have distinct dormancy and germination characteristics, the seeds
were submitted to different treatments. D. jorgei seeds were immersed in hot water, scarified and stored for 12 weeks in the laboratory environment (25°C). S. macrostachya seeds were submitted to different combinations of drying and storage in the laboratory environment or refrigerator (4°C).
Seedlings were submitted to two light treatments for 3 months: partial shade (52% of full sun) and full shade (12% of full
sun). In D. jorgei, the highest germination occurred for scarified seeds (87%) and for seeds stored for 12 weeks and then scarified (69%). In
S. macrostachya the undried control seeds had the highest germination, followed by that of the refrigeration storage treatment, without predrying
(99% and 97%, respectively). The average values for the growth parameters were greater in full shade for D. jorgei, while S. macrostachya seedlings showed greater growth rates in partial shade. Two months growth is recommended before D. jorgei seedlings are of the sufficient size and leaf number for field planting. On the other hand, a period of 4 months is recommended
for S. macrostachya, due to its relatively slow growth. 相似文献