全文获取类型
收费全文 | 16796篇 |
免费 | 16篇 |
专业分类
林业 | 3676篇 |
农学 | 1308篇 |
基础科学 | 139篇 |
2820篇 | |
综合类 | 720篇 |
农作物 | 2137篇 |
水产渔业 | 1823篇 |
畜牧兽医 | 1168篇 |
园艺 | 1123篇 |
植物保护 | 1898篇 |
出版年
2024年 | 3篇 |
2023年 | 4篇 |
2022年 | 7篇 |
2021年 | 17篇 |
2020年 | 17篇 |
2019年 | 17篇 |
2018年 | 2751篇 |
2017年 | 2715篇 |
2016年 | 1195篇 |
2015年 | 77篇 |
2014年 | 34篇 |
2013年 | 36篇 |
2012年 | 815篇 |
2011年 | 2161篇 |
2010年 | 2117篇 |
2009年 | 1266篇 |
2008年 | 1349篇 |
2007年 | 1597篇 |
2006年 | 49篇 |
2005年 | 111篇 |
2004年 | 115篇 |
2003年 | 159篇 |
2002年 | 72篇 |
2001年 | 6篇 |
2000年 | 41篇 |
1999年 | 2篇 |
1996年 | 2篇 |
1995年 | 3篇 |
1993年 | 13篇 |
1992年 | 9篇 |
1989年 | 5篇 |
1988年 | 12篇 |
1987年 | 2篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1979年 | 2篇 |
1977年 | 6篇 |
1972年 | 3篇 |
1971年 | 1篇 |
1969年 | 1篇 |
1968年 | 4篇 |
1967年 | 1篇 |
1943年 | 2篇 |
1939年 | 2篇 |
1935年 | 1篇 |
1933年 | 1篇 |
1929年 | 1篇 |
1928年 | 1篇 |
1926年 | 1篇 |
1924年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
A facile and inexpensive way to prepare self-crosslinkable poly(dimethylsiloxane) (PDMS) for superhydrophobic treatment of cotton fabrics is reported in the study. Through thiol-ene click reaction between mercaptopropyltrimethoxysilane (MPTMOS) and vinyl-containing poly(dimethylsiloxane) (VPDMS), PDMS-g-TMOS can be simply and quickly synthesized. The trimethoxysilane group of PDMS-g-TMOS can react with hydroxyl group on cotton fabric and other -Si(OCH3)3 groups. The synthesized polysiloxane (PDMS-g-TMOS) was identified by FT-IR and 1H-NMR. The morphology of the treated cotton fabric was observed by SEM and XPS was used to analyze the elemental composition on the surface of cotton fabric. The analysis results indicated that the surface was fully covered with PDMS. Due to the low surface energy of PDMS and the rough surfaces of cotton fabric, the optimized water contact angle (WCA) and sliding angle were respectively 154°±0.4° and 14°±0.5°, indicating superhydrophobicity. Moreover, water spray test (AATCC Test Method 22-2010) was also applied to evaluate the water repellency of treated cotton fabric and a score of 90 was assigned according to AATCC Test Method 22-2010. The durability of treated cotton fabric was tested by 50 laundering cycles. The resultant WCA barely decreased and the score of water spray test dropped from 90 to 80, showing the reasonable wash durability. 相似文献
992.
Philina A. English Joseph J. Nocera Bruce A. Pond David J. Green 《Landscape Ecology》2017,32(2):343-359
Context
Conservation research often focuses on individual threats at a single spatial scale, but population declines can result from multiple stressors occurring at different spatial scales. Analyses incorporating alternative hypotheses across spatial scales allow more robust evaluation of the ecological processes underlying population declines.Objectives
Populations of many aerially insectivorous birds are declining, yet conservation efforts remain focused on habitat due to an absence of data on changes in prey availability. We evaluate the potential for prey and habitat availability at multiple spatial scales to influence a population of eastern whip-poor-wills (Antrostomus vociferous).Methods
We assess relationships between landcover (topographical map and satellite imagery) and insect abundance (moths and beetles from blacklight traps), and whip-poor-will distribution and abundance within eastern Canada using Ontario breeding bird atlas data (1980s and 2000s), acoustic recordings (regional), and point counts (local).Results
Whip-poor-will occurrence in both atlas time periods was positively associated with forest area and fragmentation, but only a delayed effect of urban area explained reductions in detection. Contemporary regional whip-poor-will presence was positively related to moth abundance, and local whip-poor-will abundance was best predicted by area of open-canopy forest, anthropogenic linear disturbance density, and beetle abundance. Our finding that bird presence and abundance were associated with human activity and insect abundance across spatial scales suggests factors beyond habitat structure are likely driving population declines in whip-poor-wills and other aerial insectivores.Conclusions
This study demonstrates the importance of examining multiple hypotheses, including seasonally and locally variable food availability, across a range of spatial scales to direct conservation efforts.993.
994.
Hordeum chilense Roem. et Schult. is a diploid wild South American barley that contains genes of interest for cereal breeding, many of them
located on chromosome 1Hch. In the current study, two H. chilense-wheat addition lines with deletions in the 1Hch chromosome were used for sub-arm localization of five prolamin (glutenin and gliadin) loci and 33 EST-SSR marker loci on
chromosome 1Hch. The two sets of markers were distributed across five sub-arm chromosome regions. Three glutenin loci (Glu-H
ch
2, Glu-H
ch
3, Glu-H
ch
4) together with the gliadin locus Gli-H
ch
1 were located on the distal 20% of the 1HchS arm, whereas the glutenin locus Glu-H
ch
1 was on the proximal 88% region of 1HchL. Among 33 EST-SSR marker loci, 7 (21.2%) were on the 1HchS arm and, of them, 3 (9.1%) were on the distal 20% end and 4 (12.1%) on the proximal 80% region. The 26 loci (78.8%) on 1HchL were distributed across three different regions: 18 (78.8%) in the proximal 88%, 3 (9.1%) in the distal 12% and 5 (15.2%)
in a region less than 12% from the distal end. The deletions in the 1Hch chromosome added to the common wheat background were thus shown to be useful for determining the sub-arm location of EST-SSR
and prolamin loci. This could facilitate the identification of molecular markers linked to genes of agronomic interest and
the isolation of such genes for use in common wheat improvement. 相似文献
995.
This study is part of an effort to improve the quality of dried shiitake mushrooms (Lentinula edodes) in accordance with consumer preference. Results are presented of a trend survey that examined the preferences of consumers
using questionnaires combined with sensory evaluation. From the original preference (OP) survey, the distributions of OP divided
by age class (AC) were statistically equal to the results obtained in 2000. The medians of OP for teenagers and twenties were
“neutral” and “slightly like,” respectively. A firm preference change occurred between teenagers and those in their twenties.
It is empirically realized that sensory intensity (SI) scores that were too high or too low led to a low hedonic preference
(HP) score. The same tendency was seen for “neutralists” and “likers.” In addition, almost all distributions concerned with
HP had no significant difference between 2000 and 2005; for example, that of SI divided by AC. These results showed that the
preference for dried shiitake mushroom has been unaffected by the passage of the past 5 years. Dried shiitake mushrooms have
been used from ancient times and for many dishes; therefore, the overall preference appears to have remained unchanged. 相似文献
996.
The aim of this study was to determine changes in crystallinity and crystalline unit cell type of heat-treated Scots pine
(Pinus sylvestris L.) and Uludağ fir (Abies nordmanniana stev. subsp. bornmuelleriana Mattf.) wood samples by means of FT-IR spectroscopic method. Heat treatment was applied on the test samples in an oven at
three different temperatures (120, 150, and 180°C) and for two different periods of time (6 and 10 h) under atmospheric pressure.
It was designated that crystallinity of both Scots pine and Uludağ fir wood samples increased during heat treatment depending
on the duration. However, monoclinic structure in crystalline unit cells of Scots pine and Uludağ fir wood samples converted
to triclinic structure when heat treated. It was estimated that monoclinic structure was dominant in the crystalline unit
cell. It was established that the crystalline structure of Scots pine wood samples was more affected by heat treatment than
that of Uludağ fir wood samples. 相似文献
997.
Mohammad R. Sabzalian Aghafakhr Mirlohi Ghodratollah Saeidi Mohammad T. Rabbani 《Genetic Resources and Crop Evolution》2009,56(8):1057-1064
Wild species of safflower, Carthamus oxyacanthus Bieb., is highly crossable with cultivated species, C. tinctorius L. and could be directly exploited in broadening safflower gene pool and improving the crop for biotic and abiotic stress
environments. In this study, genetic diversity among accessions of C. oxyacanthus and their relationships with cultivated safflower were evaluated using agro-morphological traits and polymorphic inter-simple
sequence repeats (ISSR) markers. Significant variation was observed among accessions particularly for seeds per capitulum,
seed yield per plant, harvest index and capitula per plant. Cluster analysis based on agro-morphological traits classified
the wild accessions in two groups according to their geographical regions, and separated them from the cultivated genotypes.
ISSR marker also revealed a high genetic variation among the accessions, and cluster analysis based on this marker divided
genotypes into four groups, with cultivated ones in a separate clade. Genetic variation observed among the wild safflower
germplasm at the DNA level was higher than the agro-morphological traits, indicating that ISSR is an effective marker system
for detecting diversity among safflower genotypes and their genetic relationships. Accessions of C. oxyacanthus with high genetic relationship to cultivated species could be used for interspecific hybridization in breeding programs of
safflower. 相似文献
998.
Growth and ontogeny of digestive function were studied in pikeperch (Sander lucioperca) larvae weaned on artificial food at different ages. Three weaning treatments initiated respectively on day 9 (W9), day 15
(W15) or day 21 (W21) post-hatching (p.h.) were compared with a control group, fed Artemia nauplii from first feeding until the end of the rearing trial on day 36 p.h. The digestive enzyme activities and the ontogeny
of digestive structures were investigated using enzymatic assays and histological methods. Growth of pikeperch larvae was
significantly affected by precocious weaning. Pancreatic (trypsin and amylase) and intestinal (leucine-alanine peptidase,
leucine aminopeptidase N and alkaline phosphatase) enzyme activities were detected from hatching onwards, increased at the
moment of first feeding and then decreased. Pepsin secretion occurred at day 29 p. h. only, concurrently with the stomach
development and differentiation of gastric glands. In the early weaning group (W9) the maturation process of intestinal enterocytes
seems to be impaired and/or delayed and several signs of malnutrition were recorded. Except for alkaline phosphatase activity,
no differences in enzyme activities and development of digestive structures were observed among the control, W21, and W15
groups. Moreover, at the end of the experiment, no differences in proteolytic activities were observed among larvae from the
different treatments, indicating that, in surviving individuals, the digestive structures were properly developed and the
larvae had acquired an adult mode of digestion. Based on the artificial diet used, our results suggested that pikeperch larvae
can be weaned from day 15 p.h. without significant adverse effect on digestive capacities (except for alkaline phosphatase)
or development of digestive tract, while earlier weaning impaired the onset of the maturation processes of the digestive system,
both in terms of morphological structures and enzymatic activities. 相似文献
999.
Three species of wireworms (Coleoptera: Elateridae) known to cause severe damage to potatoes in Europe and Asia have been introduced to Canada and are now well established as pests in the westernmost province of British Columbia (BC) (Agriotes obscurus and A. lineatus) and the eastern provinces of Nova Scotia and Prince Edward Island (A. obscurus, A. lineatus and A. sputator). Conventional insecticide-based efforts to control these invasive pests have had serious environmental impacts, or are failing to prevent severe economic damage from occurring to potatoes in some key potato production areas. Research toward developing an IPM programme for these exotic species has been completed or is underway in Canada, including the following: biological and ecological studies, development of monitoring and risk assessment programmes, and development of insecticidal and alternative control strategies. This research is summarized and implications for wireworm management in Europe are discussed. In addition to wireworms, one of the primary economic insect pests of potatoes in BC is the tuber flea beetle, Epitrix tuberis (Coleoptera: Chrysomelidae). The larvae of this beetle feed on developing or mature daughter tubers, producing surface channels or tracks and holes directly into the tuber. In the past, growers would apply 7–10 foliar sprays of broad-spectrum insecticides per growing season, which was not always successful in controlling this pest. In the EU, a newly identified flea beetle, Epitrix papa sp. n., as well as the North American species, E. cucumeris, have been identified as attacking potatoes initially in Portugal (2004) and later also in Spain. The potential spread of these emergent pests to various EU and non-EU countries is of concern, and if established would require the development of management strategies. The former development of a highly effective IPM programme developed in BC for E. tuberis is discussed, as is its potential for E. papa and E. cucumeris management in Europe. 相似文献
1000.
Arben Q. Alla J. Julio Camarero Pilar Rivera Gabriel Montserrat-Martí 《Annals of Forest Science》2011,68(7):1245-1254