全文获取类型
收费全文 | 1658篇 |
免费 | 103篇 |
国内免费 | 14篇 |
专业分类
林业 | 150篇 |
农学 | 68篇 |
基础科学 | 6篇 |
209篇 | |
综合类 | 161篇 |
农作物 | 77篇 |
水产渔业 | 156篇 |
畜牧兽医 | 808篇 |
园艺 | 35篇 |
植物保护 | 105篇 |
出版年
2023年 | 4篇 |
2022年 | 4篇 |
2021年 | 51篇 |
2020年 | 25篇 |
2019年 | 23篇 |
2018年 | 49篇 |
2017年 | 45篇 |
2016年 | 52篇 |
2015年 | 58篇 |
2014年 | 56篇 |
2013年 | 109篇 |
2012年 | 95篇 |
2011年 | 120篇 |
2010年 | 55篇 |
2009年 | 67篇 |
2008年 | 97篇 |
2007年 | 109篇 |
2006年 | 113篇 |
2005年 | 129篇 |
2004年 | 88篇 |
2003年 | 94篇 |
2002年 | 67篇 |
2001年 | 47篇 |
2000年 | 42篇 |
1999年 | 28篇 |
1998年 | 18篇 |
1997年 | 5篇 |
1996年 | 14篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1993年 | 4篇 |
1992年 | 12篇 |
1991年 | 6篇 |
1990年 | 7篇 |
1989年 | 10篇 |
1988年 | 11篇 |
1987年 | 7篇 |
1986年 | 10篇 |
1985年 | 11篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1971年 | 1篇 |
1970年 | 7篇 |
1969年 | 2篇 |
1967年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有1775条查询结果,搜索用时 15 毫秒
1.
本研究以黑河下游额济纳旗成熟的河岸胡杨林为对象,分析不同年龄胡杨(Populus euphratica)的年轮宽度序列与不同时间尺度环境因子的关系。结果表明:①在年尺度上,气温是影响胡杨径向生长的主要因子,但不同年龄胡杨对气温的响应有所不同。②在季节尺度上,休眠季气温越高越有利于壮龄胡杨的径向生长,而生长季气温越高越不利于老龄胡杨的径向生长。③在月尺度上,前一年3月和当年9月的平均气温越高,对壮龄胡杨的径向生长越有利,而当年10月平均气温越高,对老龄胡杨的径向生长越不利;前一年7月径流量的增加对老龄胡杨的径向生长有利,而当年2月径流量的增加对壮龄胡杨径向生长有利。综上所述,在季节和年等相对较长的时间尺度上,气温是影响胡杨径向生长量的主要因素,随着时间尺度的缩小,胡杨对环境因子的响应更为细化,并且表现出一定的滞后效应。径流量作为重要的环境因子在月尺度上才突显出来,前一年7月和当年2月的径流补给对胡杨径向生长有极大的促进作用。因此,在黑河统一调度管理过程中,可通过适度调增2月和7月洪水的下泄量来满足胡杨径向生长对水分的需求。 相似文献
2.
Hiroto Miura Kazuhisa Mukai Keigo Sudo Satoshi Haga Yutaka Suzuki Yasuo Kobayashi Satoshi Koike 《Journal of animal science》2021,99(1)
Trehalose, a nonreducing disaccharide consisting of d-glucose with α,α-1,1 linkage, was evaluated as a functional material to improve the gut environment in preweaned calves. In experiment 1, 173 calves were divided into two groups; the trehalose group was fed trehalose at 30 g/animal/d with milk replacer during the suckling period, and the control group was fed nonsupplemented milk replacer. Medication frequency was lower in the trehalose group (P < 0.05). In experiment 2, calves (n = 20) were divided into two groups (control group [n = 10] and trehalose group [n = 10]) based on their body weight and reared under the same feeding regimens as in experiment 1. Fresh feces were collected from individual animals at the beginning of the trial (average age 11 d), 3 wk after trehalose feeding (experimental day 22), and 1 d before weaning, and the fecal score was recorded daily. Fecal samples were analyzed for fermentation parameters and microbiota. The fecal score was significantly lower in the trehalose group than in the control group in the early stage (at an age of 14 to 18 d; P < 0.05) of the suckling period. Calves fed trehalose tended to have a higher proportion of fecal butyrate on day 22 than calves in the control group (P = 0.08). Population sizes of Clostridium spp. were significantly lower (P = 0.036), whereas those of Dialister spp. and Eubacterium spp. tended to be higher in the feces of calves in the trehalose group on day 22 (P = 0.060 and P = 0.083). These observations indicate that trehalose feeding modulated the gut environment and partially contributed to the reduction in medication frequency observed in experiment 1. 相似文献
3.
Kikumi OGIHARA Ken ONDA Reiichiro SATO Yuko NAYA Hideharu OCHIAI 《The Journal of veterinary medical science / the Japanese Society of Veterinary Science》2015,77(1):85-88
L-type amino acid transporter
1 (LAT1), the first isotype of amino acid transport system L, transports aromatic and
branched amino acids pivotal for fundamental cellular activities such cellular growth and
proliferation. LAT1 expression was high only in the brain in contrast to its limited
distribution and low level of expression in normal tissues. We found potent LAT1
expression in canine caput epididymis by quantitative RT-PCR and Western blotting
analysis. Immnuno-histochemical examination revealed observable LAT1 in microvillous
epithelial cells. 相似文献
4.
Masato HIYAMA Ken Takeshi KUSAKABE Ai TAKESHITA Sinji SUGI Nobue KUNIYOSHI Hiroyuki IMAI Kiyoshi KANO Yasuo KISO 《The Journal of veterinary medical science / the Japanese Society of Veterinary Science》2015,77(3):305-311
LC3 − the mammalian homolog of Atg8 − was found as autophagosome membrane binding protein
in mammals and widely used as an autophagosomal marker. LC3A, B and C show different
expression patterns in each tissue. The aim of this study was to reveal the differences of
expression patterns among LC3 families in mouse placenta under normal condition and
nutrient starving condition. LC3A and B were highly expressed in decidual cells. LC3A and
B were increased in D14 compared with D12 and D16 in mouse placenta, while LC3C was
decreased. Starvation induced increase in LC3B expression specifically.
Immunohistochemistry showed different expression patterns among LC3A, B and C. LC3A
expression in syncytiotrophoblast was vanished by starvation. The results of real time
RT-PCR suggested differences between D12 and D16 in autophagic cascade induced by
starvation. Taken together, this study suggests that autophagy could play a role in
placental invasion system and that nutrient starvation affects LC3B expression. 相似文献
5.
Rei NAKANO Kazuya EDAMURA Tomohiro NAKAYAMA Kenji TESHIMA Kazushi ASANO Takanori NARITA Ken OKABAYASHI Hiroshi SUGIYA 《The Journal of veterinary medical science / the Japanese Society of Veterinary Science》2015,77(1):27-35
We investigated the in
vitro differentiation of canine bone marrow stromal cells (BMSCs) into voltage-
and glutamate-responsive neuron-like cells. BMSCs were obtained from the bone marrow of
healthy beagle dogs. Canine BMSCs were incubated with the basal medium for neurons
containing recombinant human basic fibroblast growth factor (bFGF; 100
ng/ml). The viability of the bFGF-treated cells was
assessed by a trypan blue exclusion assay, and the morphology was monitored. Real-time
RT-PCR was performed to evaluate mRNA expression of neuronal, neural stem cell and glial
markers. Western blotting and immunocytochemical analysis for the neuronal markers were
performed to evaluate the protein expression and localization. The Ca2+
mobilization of the cells was evaluated using the Ca2+ indicator Fluo3 to
monitor Ca2+ influx. To investigate the mechanism of bFGF-induced neuronal
differentiation, the fibroblast growth factor receptor inhibitor, the phosphoinositide
3-kinase inhibitor or the Akt inhibitor was tested. The bFGF treatment resulted in the
maintenance of the viability of canine BMSCs for 10 days, in the expression of neuronal
marker mRNAs and proteins and in the manifestation of neuron-like morphology. Furthermore,
in the bFGF-treated BMSCs, a high concentration of KCl and L-glutamate induced an increase
in intracellular Ca2+ levels. Each inhibitor significantly attenuated the
bFGF-induced increase in neuronal marker mRNA expression. These results suggest that bFGF
contributes to the differentiation of canine BMSCs into voltage- and glutamate-responsive
neuron-like cells and may lead to the development of new cell-based treatments for
neuronal diseases. 相似文献
6.
The eating quality of cooked rice is important and determines its market price and consumer acceptance. To comprehensively describe the variation of eating quality in 183 rice germplasm accessions, we evaluated 33 eating-quality traits including amylose and protein contents, pasting properties of rice flour, and texture of cooked rice grains. All eating-quality traits varied widely in the germplasm accessions. Principal-components analysis (PCA) revealed that allelic differences in the Wx gene explained the largest proportion of phenotypic variation of the eating-quality traits. In 146 accessions of non-glutinous temperate japonica rice, PCA revealed that protein content and surface texture of the cooked rice grains significantly explained phenotypic variations of the eating-quality traits. An allelic difference based on simple sequence repeats, which was located near a quantitative trait locus (QTL) on the short arm of chromosome 3, was associated with differences in the eating quality of non-glutinous temperate japonica rice. These results suggest that eating quality is controlled by genetic factors, including the Wx gene and the QTL on chromosome 3, in Japanese rice accessions. These genetic factors have been consciously selected for eating quality during rice breeding programs in Japan. 相似文献
7.
Managing fisheries presents trade‐offs between objectives, for example yields, profits, minimizing ecosystem impact, that have to be weighed against one another. These trade‐offs are compounded by interacting species and fisheries at the ecosystem level. Weighing objectives becomes increasingly challenging when managers have to consider opposing objectives from different stakeholders. An alternative to weighing incomparable and conflicting objectives is to focus on win–wins until Pareto efficiency is achieved: a state from which it is impossible to improve with respect to any objective without regressing at least one other. We investigate the ecosystem‐level efficiency of fisheries in five large marine ecosystems (LMEs) with respect to yield and an aggregate measure of ecosystem impact using a novel calibration of size‐based ecosystem models. We estimate that fishing patterns in three LMEs (North Sea, Barents Sea and Benguela Current) are nearly efficient with respect to long‐term yield and ecosystem impact and that efficiency has improved over the last 30 years. In two LMEs (Baltic Sea and North East US Continental Shelf), fishing is inefficient and win–wins remain available. We additionally examine the efficiency of North Sea and Baltic Sea fisheries with respect to economic rent and ecosystem impact, finding both to be inefficient but steadily improving. Our results suggest the following: (i) a broad and encouraging trend towards ecosystem‐level efficiency of fisheries; (ii) that ecosystem‐scale win–wins, especially with respect to conservation and profits, may still be common; and (iii) single‐species assessment approaches may overestimate the availability of win–wins by failing to account for trade‐offs across interacting species. 相似文献
8.
Okajima Kenji Nagaoka Seiya Islam Mohammad Raihanul Ito Ryouei Watanabe Ken 《Paddy and Water Environment》2020,18(2):345-353
Paddy and Water Environment - Repairs of concrete irrigation channels in Japan are guided to a large extent by the degree to which their walls have degraded over decades of use. Current methods of... 相似文献
9.
为研究硒浸种对春小麦种子活力和幼苗生长特性的影响,分别设置0,0.5,1.0,2.5,3.5,5.0,10.0,50.0 mg/L共8个亚硒酸钠溶液浓度,通过发芽试验,比较研究了不同浓度的亚硒酸钠浸种对春小麦种子萌发和幼苗生长的影响.结果表明:随着亚硒酸钠溶液浓度升高,春小麦种子的发芽率、发芽势、发芽指数、活力指数、幼苗和根长以及干鲜重等指标均呈先升高后下降的趋势;1.0 mg/L的亚硒酸钠溶液对小麦种子萌发和幼苗生长有促进作用;随着亚硒酸钠浓度的升高(≥2.5 mg/L),其各项指标显著下降,并对根和苗的生长表现出抑制作用;因此在实际生产中,掌握合适的硒浸种浓度非常关键. 相似文献
10.