全文获取类型
收费全文 | 776篇 |
免费 | 18篇 |
国内免费 | 3篇 |
专业分类
林业 | 78篇 |
农学 | 35篇 |
基础科学 | 2篇 |
328篇 | |
综合类 | 88篇 |
农作物 | 14篇 |
水产渔业 | 11篇 |
畜牧兽医 | 194篇 |
园艺 | 9篇 |
植物保护 | 38篇 |
出版年
2023年 | 5篇 |
2022年 | 7篇 |
2021年 | 8篇 |
2020年 | 7篇 |
2019年 | 9篇 |
2018年 | 12篇 |
2017年 | 9篇 |
2016年 | 15篇 |
2015年 | 12篇 |
2014年 | 12篇 |
2013年 | 47篇 |
2012年 | 38篇 |
2011年 | 50篇 |
2010年 | 22篇 |
2009年 | 25篇 |
2008年 | 41篇 |
2007年 | 51篇 |
2006年 | 50篇 |
2005年 | 54篇 |
2004年 | 33篇 |
2003年 | 32篇 |
2002年 | 40篇 |
2001年 | 15篇 |
2000年 | 26篇 |
1999年 | 17篇 |
1998年 | 13篇 |
1997年 | 13篇 |
1996年 | 14篇 |
1995年 | 5篇 |
1994年 | 12篇 |
1993年 | 8篇 |
1992年 | 7篇 |
1991年 | 6篇 |
1990年 | 8篇 |
1989年 | 6篇 |
1988年 | 9篇 |
1987年 | 8篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1978年 | 2篇 |
1974年 | 3篇 |
1973年 | 6篇 |
1970年 | 3篇 |
1969年 | 2篇 |
1968年 | 3篇 |
1966年 | 3篇 |
1958年 | 2篇 |
1955年 | 2篇 |
1863年 | 1篇 |
排序方式: 共有797条查询结果,搜索用时 73 毫秒
81.
Kauffold J Amer HA Bergfeld U Weber W Sobiraj A 《The Journal of reproduction and development》2005,51(3):325-332
This study investigated the relationship between follicle size (FS) and developmental competence of calf oocytes. Cumulus-oocyte-complexes (COCs) from follicles>8 (L-COCs; n=19), 4-8 (M-COCs; n=54), and 2-3 mm (S-COCs; n=155) were recovered from non-stimulated 1-4 months old dairy calves post mortem and ex vivo (laparoscopy), and in parallel from slaughtered adult cows from follicles of identical size categories [>8 (n=91); 4-8 (n=138); 2-3 mm (n=193)]. Morphologically intact COCs were subjected to in vitro maturation, fertilization, and embryo culture. Cleavage rate (CR; 46 h post-insemination=p.i.), rate of morulae/blastocysts (M/Bl; day 7 p.i.), and blastocysts (Bl; day 9 p.i.) were recorded. FS had no effect on the CR in calves. However, calf L-COCs yielded the highest rates of M/Bl and Bl compared with the two other size categories (P<0.05). In contrast, calf S- and M-COCs gave similar rates of M/Bl, whereas the proportion of Bl was lowest for S-COCs (P<0.05). This was almost identical to findings in cows, except that the CR was highest for L-COCs and M/Bl yields were lowest for S-COCs (P<0.05). There were no differences between calf and cows with regard to CR for the respective FS categories. L-COCs from calves and cows yielded similar rates of M/Bl and Bl, whereas calf S- and M-COCs yielded lower rates of Bl than S- and M-COCs from cows and a lower rate of M/Bl when S-and M-COCs were analyzed as one group (P<0.05). Whereas the CR was similar in calves and cows, calf COCs yielded lower rates of M/Bl and Bl (P<0.05). In conclusion, the results show that the developmental competence of calf oocytes is higher in those derived from follicles larger than 8 mm, and thus are almost equally as competent as cow oocytes derived from follicles of identical size. This suggests that calf oocytes acquire developmental competence within the large follicle, potentially due to a process similar to prematuration of the oocyte in the adult cow. It is proposed that procedures that facilitate prematuration, such as "coasting" following a preceding superstimulation, might increase the developmental competence of calf oocytes. 相似文献
82.
Zusammenfassung Gefäßkulturen von Hafer in Sand und Erde mit abgestuftem, jeweils gleichbleibend gehaltenem Wasserangebot von 100, 75, 50, 30 und 15% der Boden wasserkapazität ergaben die höchsten Erträge an Gesamttrockenmasse in der Regel bei voller Wassersättigung des Bodens in Verbindung mit gleichzeitig maximalem Wasserverbrauch (bestimmt durch tägliches Wägen der Gefäße). Abnehmende Wasserversorgung verringerte auch Trockenmasse und Wasserverbrauch der Pflanzen. In trockenem Boden und bei reichlicher Wasserzufuhr entwickelte sich die Wurzelmasse im Vergleich mit den oberirdischen Organen stärker als bei mittlerer Bodenfeuchtigkeit. Klimatische Einflüsse, Aussaatzeit und Witterung sowie die Bodenart modifizierten die vom Wasserzustand des Bodens ausgehenden Wirkungen auf Trockenmasseproduktion und Wasserverbrauch, z. B. wurde bei Sommeraussaat gegenüber der Frühjahrsaussaat die Blattentwicklung bedeutend gefördert.Mit registrierenden Infrarot-Gasanalysatoren wurden Tagesgänge von CO2-Aufnahme, Nachtatmung und Transpiration unter natürlichen Bedingungen gemessen. Bei trockenem Boden war die photosynthetische Leistung der Pflanzen zu Beginn ihrer Entwicklung deutlich gehemmt; sie steigerte sich allmählich und war später merklich größer als bei hohen Wassergaben. Die Transpiration verlief im allgemeinen gleichsinnig wie die Netto-Assimilationsrate, wurde jedoch auch nachts meist auf einer gewissen Höhe fortgesetzt. Die Nachtatmung der sehr trocken gehaltenen Pflanzen war gegenüber den anderen Wasserstufen meist erhöht. Die Trockenkulturen zeigten einen größeren Lichtbedarf; der Lichtkompensationspunkt wurde gewöhnlich erst bei höherer Beleuchtungsstärke erreicht als bei guter Wasserversorgung. Daraus wird auf erhöhten Energiebedarf der sehr trocken kultivierten Pflanzen geschlossen. Das Verhältnis zwischen CO2-Aufnahme und Transpiration wurde durch unterschiedliche Bodenwasserversorgung meist nur wenig beeinflußt. Die Ergebnisse der CO2-Assimilationsmessungen stehen im großen und ganzen mit dem wöchentlich festgestellten Trockensubstanzgewinn in Einklang.
Summary Cultures ofAvena sativa L. grown in pots with sand or garden soil with a graduated, in each case fairly constant water supply of 100, 75, 50, 30, and 15% of field capacity yielded maximum total dry weight, as a rule, in fully water-saturated soils combined with maximum water consumption (measured by daily weighing). Decreasing water supply reduced dry matter production and water consumption of plants. In dry soil and at high degrees of water saturation roots developed more dry matter in comparison to the shoots than at medium soil moisture. Results in dry matter production and water consumption, as caused by water relations in soil, are modified additionally by climatic factors, sowing date and weather, and soil type, e.g. sowing in summer considerably favoured leaf development, compared with the spring seed.Daily courses of CO2-uptake, night respiration and transpiration were registered by infrared-gasanalyzers. In very dry soil photosynthetic activity of plants was distinctly hampered during the first weeks of development; it gradually increased, and at a later stage photosynthetic activity was markedly higher than at abundant water supply. In general transpiration followed the net assimilation rate, it was continued, however, even over night on a certain level. Night respiration of plants growing in dry soil was higher in relation to the other water stages. Those plants, too, required more light for dry matter production; their light compensation point arrived at higher light intensity than under abundant water supply. This behaviour seems to indicate higher energy requirement of plants distinctly influenced by water stress. Relations between CO2-uptake and transpiration were but slightly influenced by different soil water level. Results of gas exchange measurements on CO2-assimilation agreed, as a rule, with the weekly dry matter measurements by weighting.
¶rt; 100, 75, 50, 30 15%. , , , ¶rt; ( ). , . ( ) , . , , ; . , . ( ) ( 2, ). ; , . , , , . , , , , . «» ; , . , , ¶rt;. 2 , , . 2 .相似文献
83.
84.
Meinecke M Wagner R Kovermann P Guiard B Mick DU Hutu DP Voos W Truscott KN Chacinska A Pfanner N Rehling P 《Science (New York, N.Y.)》2006,312(5779):1523-1526
Transport of metabolites across the mitochondrial inner membrane is highly selective, thereby maintaining the electrochemical proton gradient that functions as the main driving force for cellular adenosine triphosphate synthesis. Mitochondria import many preproteins via the presequence translocase of the inner membrane. However, the reconstituted Tim23 protein constitutes a pore remaining mainly in its open form, a state that would be deleterious in organello. We found that the intermembrane space domain of Tim50 induced the Tim23 channel to close. Presequences overcame this effect and activated the channel for translocation. Thus, the hydrophilic cis domain of Tim50 maintains the permeability barrier of mitochondria by closing the translocation pore in a presequence-regulated manner. 相似文献
85.
Feger W Brandauer H Gabris P Ziegler H 《Journal of agricultural and food chemistry》2006,54(6):2242-2252
The nonvolatile fractions of cold-pressed peel oils of Key and Persian lime as well as grapefruit were separated by high-speed countercurrent chromatography (HS-CCC). In addition to the isolation of the main coumarins, psoralens and polymethoxyflavones, a number of minor constituents were enriched and successfully characterized by GC-MS and HPLC-UV. 5,7,8-Trimethoxycoumarin and the cyclical acetals of oxypeucedanin hydrate with citral were determined as new nonvolatile trace constituents of lime oils and confirmed by NMR spectroscopy. The citral oxypeucedaninyl acetals were found particularly in Key lime oil type A, which as a result of the juice-oil contact, is exposed to acidic conditions during industrial processing. Some of the confirmed minor constituents, such as pabulenol, isooxypeucedanin, and oxypeucedanin methanolate in lime as well as auraptenol in grapefruit, may have been generated by hydrolysis-sensitive precursors during CCC separation or their respective industrial processing techniques. 相似文献
86.
Kiessling W 《Science (New York, N.Y.)》2006,314(5803):1254-1255
87.
Berkefeld H Sailer CA Bildl W Rohde V Thumfart JO Eble S Klugbauer N Reisinger E Bischofberger J Oliver D Knaus HG Schulte U Fakler B 《Science (New York, N.Y.)》2006,314(5799):615-620
Large-conductance calcium- and voltage-activated potassium channels (BKCa) are dually activated by membrane depolarization and elevation of cytosolic calcium ions (Ca2+). Under normal cellular conditions, BKCa channel activation requires Ca2+ concentrations that typically occur in close proximity to Ca2+ sources. We show that BKCa channels affinity-purified from rat brain are assembled into macromolecular complexes with the voltage-gated calcium channels Cav1.2 (L-type), Cav2.1 (P/Q-type), and Cav2.2 (N-type). Heterologously expressed BKCa-Cav complexes reconstitute a functional "Ca2+ nanodomain" where Ca2+ influx through the Cav channel activates BKCa in the physiological voltage range with submillisecond kinetics. Complex formation with distinct Cav channels enables BKCa-mediated membrane hyperpolarization that controls neuronal firing pattern and release of hormones and transmitters in the central nervous system. 相似文献
88.
Price DC Chan CX Yoon HS Yang EC Qiu H Weber AP Schwacke R Gross J Blouin NA Lane C Reyes-Prieto A Durnford DG Neilson JA Lang BF Burger G Steiner JM Löffelhardt W Meuser JE Posewitz MC Ball S Arias MC Henrissat B Coutinho PM Rensing SA Symeonidi A Doddapaneni H Green BR Rajah VD Boore J Bhattacharya D 《Science (New York, N.Y.)》2012,335(6070):843-847
89.
S Naik N Bouladoux C Wilhelm MJ Molloy R Salcedo W Kastenmuller C Deming M Quinones L Koo S Conlan S Spencer JA Hall A Dzutsev H Kong DJ Campbell G Trinchieri JA Segre Y Belkaid 《Science (New York, N.Y.)》2012,337(6098):1115-1119
Intestinal commensal bacteria induce protective and regulatory responses that maintain host-microbial mutualism. However, the contribution of tissue-resident commensals to immunity and inflammation at other barrier sites has not been addressed. We found that in mice, the skin microbiota have an autonomous role in controlling the local inflammatory milieu and tuning resident T lymphocyte function. Protective immunity to a cutaneous pathogen was found to be critically dependent on the skin microbiota but not the gut microbiota. Furthermore, skin commensals tuned the function of local T cells in a manner dependent on signaling downstream of the interleukin-1 receptor. These findings underscore the importance of the microbiota as a distinctive feature of tissue compartmentalization, and provide insight into mechanisms of immune system regulation by resident commensal niches in health and disease. 相似文献
90.
Fan S Baets R Petrov A Yu Z Joannopoulos JD Freude W Melloni A Popović M Vanwolleghem M Jalas D Eich M Krause M Renner H Brinkmeyer E Doerr CR 《Science (New York, N.Y.)》2012,335(6064):38; author reply 38
We show that the structure demonstrated by Feng et al. (Reports, 5 August 2011, p. 729) cannot enable optical isolation because it possesses a symmetric scattering matrix. Moreover, one cannot construct an optical isolator by incorporating this structure into any system as long as the system is linear and time-independent and is described by materials with a scalar dielectric function. 相似文献