全文获取类型
收费全文 | 792篇 |
免费 | 17篇 |
国内免费 | 1篇 |
专业分类
林业 | 103篇 |
农学 | 41篇 |
基础科学 | 1篇 |
125篇 | |
综合类 | 55篇 |
农作物 | 40篇 |
水产渔业 | 84篇 |
畜牧兽医 | 269篇 |
园艺 | 13篇 |
植物保护 | 79篇 |
出版年
2023年 | 2篇 |
2022年 | 13篇 |
2021年 | 33篇 |
2020年 | 11篇 |
2019年 | 10篇 |
2018年 | 17篇 |
2017年 | 13篇 |
2016年 | 18篇 |
2015年 | 31篇 |
2014年 | 29篇 |
2013年 | 77篇 |
2012年 | 39篇 |
2011年 | 52篇 |
2010年 | 18篇 |
2009年 | 28篇 |
2008年 | 59篇 |
2007年 | 40篇 |
2006年 | 44篇 |
2005年 | 50篇 |
2004年 | 42篇 |
2003年 | 42篇 |
2002年 | 37篇 |
2001年 | 25篇 |
2000年 | 19篇 |
1999年 | 15篇 |
1998年 | 17篇 |
1997年 | 10篇 |
1996年 | 5篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1987年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有810条查询结果,搜索用时 171 毫秒
801.
802.
Chondrulelike objects in short-period comet 81P/Wild 2 总被引:1,自引:0,他引:1
Nakamura T Noguchi T Tsuchiyama A Ushikubo T Kita NT Valley JW Zolensky ME Kakazu Y Sakamoto K Mashio E Uesugi K Nakano T 《Science (New York, N.Y.)》2008,321(5896):1664-1667
The Stardust spacecraft returned cometary samples that contain crystalline material, but the origin of the material is not yet well understood. We found four crystalline particles from comet 81P/Wild 2 that were apparently formed by flash-melting at a high temperature and are texturally, mineralogically, and compositionally similar to chondrules. Chondrules are submillimeter particles that dominate chondrites and are believed to have formed in the inner solar nebula. The comet particles show oxygen isotope compositions similar to chondrules in carbonaceous chondrites that compose the middle-to-outer asteroid belt. The presence of the chondrulelike objects in the comet suggests that chondrules have been transported out to the cold outer solar nebula and spread widely over the early solar system. 相似文献
803.
Murase K Shiba H Iwano M Che FS Watanabe M Isogai A Takayama S 《Science (New York, N.Y.)》2004,303(5663):1516-1519
Self-incompatibility (SI) response in Brassica is initiated by haplotype-specific interactions between the pollen-borne ligand S locus protein 11/SCR and its stigmatic S receptor kinase, SRK. This binding induces autophosphorylation of SRK, which is then thought to trigger a signaling cascade that leads to self-pollen rejection. A recessive mutation of the modifier (m) gene eliminates the SI response in stigma. Positional cloning of M has revealed that it encodes a membrane-anchored cytoplasmic serine/threonine protein kinase, designated M locus protein kinase (MLPK). Transient expression of MLPK restores the ability of mm papilla cells to reject self-pollen, suggesting that MLPK is a positive mediator of Brassica SI signaling. 相似文献
804.
Chollet M Guerin L Uchida N Fukaya S Shimoda H Ishikawa T Matsuda K Hasegawa T Ota A Yamochi H Saito G Tazaki R Adachi S Koshihara SY 《Science (New York, N.Y.)》2005,307(5706):86-89
We report that the organic salt (EDO-TTF)2PF6 with 3/4-filled-band (1/4-filled in terms of holes), which forms an organic metal with strong electron and lattice correlation, shows a highly sensitive response to photoexcitation. An ultrafast, photoinduced phase transition from the insulator phase to the metal phase can be induced with very weak excitation intensity at near room temperature. This response makes the material attractive for applications in switching devices with room-temperature operation. The observed photo-induced spectroscopic change shows that this photoinduced phase transition process is caused by the cooperative melting of charge ordering assisted by coherent phonon generation. 相似文献
805.
806.
Kenji?SuzukiEmail author Akira?Goto Masakazu?Mizutani Vichai?Sriboonlue 《Paddy and Water Environment》2003,1(2):91-97
In northeast Thailand, the rapid expansion of rainfed paddy fields has decreased the stability of rice production. This paper describes a model that computes rice production on the basis of the hydrologic conditions of rainfed paddy fields on hill slopes. The model well expressed the hydrologic processes, rice yield, and production at the study site. We simulated rice production as uphill paddy plots are abandoned, increasing catchment area, under various rainfall conditions. The simulation showed that rice yield and stability increase as uphill plots are abandoned, although the total rice production decreases. Thus, the effect of catchment size on rice production in each plot was quantified. The model proved to be useful for analyzing rainfed rice production under various land and water conditions. 相似文献
807.
Tetsuichiro Funamoto Orio Yamamura Tokihiro Kono Tomonori Hamatsu Akira Nishimura 《Fisheries Oceanography》2013,22(3):193-206
Abiotic and biotic factors affecting the recruitment variability of the Japanese Pacific stock (JPS) of walleye pollock (Theragra chalcogramma) were examined using a bivariate regression and multivariate combined model. Of the abiotic variables around Funka Bay (spawning ground), February sea surface temperature (SST) and wind direction index showed significant bivariate relationships with recruitment. February SST was positively related to recruitment, suggesting that warmer water temperature in February favors JPS recruitment. On the other hand, the relationship between February wind direction index and recruitment predicts high JPS recruitment under predominant northwest winds in February. For the biotic variables in the Doto area (nursery ground), significant and negative bivariate relationships with recruitment were observed for catch per unit effort of Kamchatka flounder (Atheresthes evermanni), Pacific cod (Gadus macrocephalus), and walleye pollock, implying an important impact of predation by these groundfishes on JPS recruitment. The overall model incorporating these abiotic and biotic factors successfully reproduced the variability in JPS recruitment. Temperature and wind conditions around the spawning ground along with predator condition in the nursery ground appear to play a dominant role in the recruitment dynamics of JPS. Based on these results and prior knowledge, we propose a new hypothesis to explain the processes controlling JPS recruitment. 相似文献
808.
Kazufumi Osako Akihiko Fujii Yaowalux Ruttanapornvareesakul Naoki Nagano Koichi Kuwahara Akira Okamoto 《Fisheries Science》2007,73(3):660-667
ABSTRACT: For the purpose of clarifying the differences of taste components between the testis and ovary of the sea urchin Anthocidaris crassispina , variations in free amino acid composition in gonadal extract during gonadal development were investigated using chemical and histopathological methods. Sea urchins were collected at Iki Island, Nagasaki, Japan between 30 April and 5 June 2003, and maturation stages and the free amino acid compositions were determined. The sweet amino acids threonine (Thr), glycine (Gly), and alanine (Ala), the umami amino acid glutamic acid (Glu), and the bitter amino acids lysine (Lys) and arginine (Arg) were the main constituents accounting for more than 80% of total free amino acids. In the testis and ovary, Gly levels were the highest among them and increased with gonadal development. The other free amino acids consisted mainly of bitter amino acids and either showed no variation or decreased with gonadal development. These variations in free amino acid composition were observed more clearly in the ovary than the testis. These findings indicate the possibility of differences in the flavor of sea urchin gonad by sex and gonadal development stages. 相似文献
809.
Automated acoustic method for counting and sizing farmed fish during transfer using DIDSON 总被引:1,自引:0,他引:1
Counting and sizing large farmed fish such as tuna is often performed during their transfer from one net cage to another.
Dual-frequency identification sonar (DIDSON) provides an automated fish counting and sizing tool. However, its counter and
sizer are not suitable for measuring farmed fish because of net movements due to currents and subsequent frequent image breakups.
This paper presents a fully automated acoustic method to count and size farmed fish during fish transfer by using DIDSON imaging.
The background is subtracted from the image after being stabilized by an image phase-only correlation method. The segmentation
of the fish is obtained by tracing the edges with a contour tracing method. To prevent recounting the same fish, a Kalman
filter algorithm was designed and adapted to predict fish movements. Automated counting was performed by analyzing the spatiotemporal
trajectory of the track. The separated fish images were searched for and body length was obtained by summing down the centerline
segments from the head to the tail of the fish. The proposed system was verified using farmed yellowtail, Seriola quinqueradiata (mean total length 83.1 cm) to obtain a sizing error of mean total length within 2.4 cm. 相似文献
810.
Kazufumi OSAKO Akira YAMAGUCHI Takao KUROKAWA Koichi KUWAHARA Hiroaki SAITO Yukinori NOZAKI 《Fisheries Science》2002,68(3):587-594
ABSTRACT: The chemical components and body color of horse mackerel caught between July 1997 and May 2000 were studied. The fish were caught with small- to medium-sized purse seine offshore from Nagasaki and from Tsushima, and with bull trawl seine and medium- to large-sized purse seine in the East China Sea. The crude lipid content of the fish caught offshore from Tsushima was higher than that of the others, and there were no significant differences among the other catches. The extractive nitrogen content of the fish caught with bull trawl seine was somewhat lower than that of the others. The body colors of the fish differed from those suggested by their common names: Kuroaji (black) , Kiaji (yellow), and Shiroaji (white). The crude lipid content and body color indicated that there was no difference in quality among the catches, with the exception of the crude lipid content of the Tsushima catch. 相似文献