首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   110182篇
  免费   4797篇
  国内免费   1557篇
林业   8925篇
农学   5897篇
基础科学   1696篇
  13437篇
综合类   20736篇
农作物   6131篇
水产渔业   5790篇
畜牧兽医   43624篇
园艺   2546篇
植物保护   7754篇
  2021年   931篇
  2020年   934篇
  2019年   1027篇
  2018年   3904篇
  2017年   4045篇
  2016年   2542篇
  2015年   1610篇
  2014年   1654篇
  2013年   3567篇
  2012年   3460篇
  2011年   5141篇
  2010年   4357篇
  2009年   3388篇
  2008年   4236篇
  2007年   4546篇
  2006年   2830篇
  2005年   2726篇
  2004年   2326篇
  2003年   2377篇
  2002年   2103篇
  2001年   2653篇
  2000年   2676篇
  1999年   2349篇
  1998年   1105篇
  1997年   1056篇
  1996年   914篇
  1995年   1107篇
  1994年   903篇
  1993年   911篇
  1992年   1749篇
  1991年   1828篇
  1990年   1871篇
  1989年   1840篇
  1988年   1695篇
  1987年   1581篇
  1986年   1621篇
  1985年   1566篇
  1984年   1310篇
  1983年   1195篇
  1979年   1305篇
  1978年   1020篇
  1975年   959篇
  1974年   1256篇
  1973年   1305篇
  1972年   1290篇
  1971年   1223篇
  1970年   1136篇
  1969年   1045篇
  1968年   899篇
  1967年   940篇
排序方式: 共有10000条查询结果,搜索用时 922 毫秒
91.
Restriction endonuclease analysis and DNA hybridization revealed five ovine strains of Mycobacterium paratuberculosis from South Africa had identical DNA patterns to an ovine strain from Canada. Genetically this strain type has features in common with the two major groups of M. paratuberculosis.  相似文献   
92.
Inhalt: An 81 Versuchs- und 92 Kontrolltieren der Rasse “Potnische Schwarzbunte” aus 3 Problembetrieben wurde ein Versuch zur Sterilitätsprophylaxe rnit der PRID-Spirale durchgeführt. Anhand klinischer Befunde und Milchprogesteronwerten wurde die Untergruppe aus Kühen mit Ovardystrophie (18 Versuchs- und 22 Kontrolltiere) gebildet und extra ausgewertet. Der Behandlungsbeginn lag zwischen 60 und 80 Tage post partum. Die Versuchstiere wurden mit der PRID-Spirale 12 Tage lang behandelt, die Kontrolltiere erhielten Injcktionen rnit Kochsalzlösung und solche rnit Ovardystrophie wurden zusätzlich mit einer Eierstocksmassage behandelt. Die Versuchstiere wurden 56 und 72 Stunden nach Entfernung der Spirale blind besamt. Die Brunstin-duktionsrate betrug insgesamt 90,1%, bei denen rnit Ovardystrophie 77,7%. Die An-wendung der PRID-Spirale führte zur Verbesserung der Fertilitätslage. Die Gesamt-trächtigkeitsrate lag mit 87,6% bei den Versuchskühenüber derjenigen der Kontrollkü-he mit 79,3%. Die Behandlung der Tiere rnit Ovardystrophie erbrachte eine Gesamt-trächtigkeitsrate von 88,8% bei den Versuchs- und 72,7% bei den Kontrolltieren. Die Zwischentragezeit betrug bei den Versuchstieren 101,2 Tage und bei den Kontrolltieren 113,3 Tage (p ≤ 0,05). Bei den azyklischen Tieren lag die Zwischentragezeit bei 104,6 Tage bzw. 134,7 Tage (p ≤ 0,05). In einem anderen Versuch wurde 20 Hybriden zwischen Wisent und Hausrind rwecks Zyklussynchronisation die PRID-Spirale verabreicht. Die Brunstinduktionsrate betrug 66,6%, das Erstbesamungsergebnis nach Doppelbesamung 30%, die Gesamtträchtig-keitsrate nach dem Decken der umrindernden Kreuzungstiere rnit einem Bullen 90%. Die Deckperiode konnte verkürzt werden. Contents: Investigations on the synchronization of estrus cycle in cattle from farms with fertility problems and in cross-breeds between bison and cattle with a PRID-de-vice In 81 experimental and 92 control animals of the “Polish Black and White” breed derived from 3 farms with fertility problems an investigation was carried out for sterility prophylaxis using the PRID-device. Based on clinical findings and milk progesterone values cattle with ovarian dystrophy (18 experimental and 22 control animals) from a special group were used. The begin of treatment was between 60 and 80 days post partum. All experimental animals had received a PRID-device for a duration of 12 days. Control animals were injected with physiological saline solution and animals with ovarian dystrophy were treated additionally with ovarian massage. Experimental animals were inseminated 56 and 72 hrs after removal of the device. All animals taken, estrus was induced in 90.1% of the animals, while only 77.7% of animals with ovarian dystrophy came to estrus. Application of the PRID-device led to an improvement of fertility. Pregnancy rates in experimental animals were 87.6%, while only 79.3% of the control animals were pregnant. Treatment of animals with ovarian dystrophy resulted in 88.8% pregnancies for treated and 72.7% for control animals. Experimental animals were non-pregnant for a duration of 101.2 days, while control animals remained non-pregnant for 113.3 days (p < 0.05). Acyclic cattle had a non-pregnant period of 104.6 days and 134.7 days (p < 0.05) respectively. In a second experiment 20 cross-breeds between bison and domestic cattle were treated with a PRID-device for synchronization of the estrus cycle. The rate of estrus induction was 66.6%, the fertility after double insemination 30%, the total pregnancy rate improved after mating with a bull of animals that had not conceived to 90%.  相似文献   
93.
Flavonoids are important dietary constituents owing to their health-promoting properties. As a result, simplified analytic techniques are required for the population of databases with food values so that associations between dietary intake and disease risk/incidence can be established. The current research provides a simplified sample preparation procedure for the accurate estimation of food anthocyanidins, flavones, and flavonols as aglycons. Traditionally, flavonoid aglycons have been formed by acidic hydrolysis. However, some flavonoid aglycons are slowly degraded by acid. A procedure has been developed whereby anthocyanidins and flavonols are deglycosylated with HCl in 50% aqueous methanol and the resulting aglycons subsequently quantified by application of pseudo-first-order kinetics to their degradation. Flavones are also deglycosolated under similar conditions but, at appropriate temperatures, their aglycons are stable in acid, so kinetics were not required for the quantitation of this subclass of flavonoids. Catechins and flavanones were rapidly degraded under the hydrolytic conditions used in these studies.  相似文献   
94.
Salivary or secreted carbonic anhydrase (CA), which constitutes a new class of CA, designated CA-VI, was isolated. Swine CA-VI purified from swine saliva by inhibitor-affinity chromatography and ion exchange chromatography had a specific activity of 5,468 units/mg. The molecular weight was 250,000, as determined by gel filtration under non-denaturing conditions, and the subunit molecular weight was found to be 37,000 by sodium dodecyl sulfate polyacrylamide gel electrophoresis, indicating that swine CA-VI consists of 7 subunits. The treatment of the enzyme with endo-N-acetylglucosaminidase F reduced its subunit molecular weight from 37,000 to 35,000 and 32,000. We raised a rabbit antibody against purfied swine CA-VI. Double immunodiffusion showed that anti-swine CA-VI serum reacted with swine CA-VI and swine saliva, but not with hemolysate (containing CA-I and CA-Il) or muscle extracts (containing CA-III). The concentration of CA-VI in swine saliva, measured using single radial immunodiffusion, was 0.027 +/- 0.017 mg/mg total protein.  相似文献   
95.
Results are given of a survey on the occurrence of pathotypes (races) of Synchytrium endobioticum (potato wart) in both parts of re-unified Germany. An assortment of six differential cultivars appears to be sufficient to distinguish between the seven presently important German wart pathotypes. A total of ten pathotypes was recorded. Two West and two East German pathotypes seem to be identical, based on the results obtained with presently available cultivars. In contrast to pathotype 1 (common race) which prior to 1945 was distributed over the whole German territory, the 'new' pathotypes seem to prefer the central and south German mountain areas.  相似文献   
96.
Ovarian follicular dynamics and embryo yield were studied during 2 different FSH regimens for superovulation of cattle. Twenty heifers were given intramuscular injections of FSH (total of 35 mg NIH) either once daily for 3 days (Group 3×1) or twice daily for 4 days (Group 4×2). At 72 h after the first FSH injection, each animal was injected with 0.75 mg cloprostenol. Inseminations were performed at 12 h and 24 h after the onset of heat. Transrectal ultrasonography was performed on the day of the first FSH injection, the day of cloprostenol injection, the day of insemination and finally on the day of embryo recovery (day 6 or 7 after heat). The numbers of small (2–4 mm), medium (5–9 mm) and large (>10 mm) size follicles were recorded. The total number of corpora lutea, eggs and transferable embryos were recorded on the day of embryo recovery. No differences were found between the 2 groups in either of the parameters studied (p>0.05). It can be concluded that treatment with this FSH preparation once daily for 3 days gives a folliculogenic and superovulatory response similar to a treatment regimen where it is given twice daily for 4 days.  相似文献   
97.
Summary The suitability of blood collected on filter papers in comparison with corresponding conventional serum samples in the diagnosis of bovine anaplasmosis was studied using the complement fixation test, DOT-ELISA, Western immunoblot and rapid card agglutination test. Dried blood on Whatman filter paper no. 1 was eluted in PBS 0·05% Tween 20 giving an initial dilution of 1∶10. The reactivity of the eluted samples in both DOT-ELISA and Western immunoblotting were similar to those obtained with the corresponding straight serum sample dilutions. Filter paper samples gave lower reactivity in the remaining tests when compared with corresponding serum samples. There was no significant difference in the reactivity between the eluates from filter papers stored at temperatures ranging between 15·5 and 24°C and those kept refrigerated. Storage at 15·5 to 24°C did not significantly affect reactivity for up to six months. Eluates from filter papers stored for six months at 15·5 to 24°C continued to give similar reactivity as those from freshly prepared filter papers in both DOT-ELISA and Western blot, and in the rapid card agglutination test. It is concluded that collecting blood on filter papers is a suitable technique for large scale seroepidemiological studies on anaplasmosis and offers many advantages in developing countries where transport and cold chain facilities are a major constraint.
Resumen Se estudió la efectividad de muestras de sangre colectadas en papel filtro, en comparación con las correspondientes muestras convencionales du suero, en el diagnóstico de anaplasmosis bovina, utilizando fijación de complemento, DOT-ELISA, Western, immunoblot y la prueba rápida de la tarjeta. La sangre seca en papel Whatman No 1 fue removida con PBS 0·05% entre 20, dando una dilución inicial de 1∶10. La reactividad de las muestras removidas de papel filtro, en la prueba de DOT-ELISA y Western immunoblotting, fueron similares a la obtenida con la correspondiente muestra de suero. Las muestras de papel filtro reaccionaron menos en las otras pruebas, cuando se compararon con las correspondients muestras du suero. No hubo diferencia significativa en la reactividad entre los lavados del papel filtro guardados a temperaturas entre 15·5 y 24°C y aquellos guardados en refrigeración. El almacenaje entre 15·5 y 24°C, no afectó la reactividad hastas seis meses. Los lavados de papel filtro guardados por seis meses entre 15·5 y 24°C, dieron la misma reactividad como los lavados frescos, en la prueba DOT-ELISA y Western blot, lo mismo que en la prueba de aglutinación rápida de tarjeta. Se concluye, qu la colección de sangre en papel filtro, es una buena técnica para estudios epidemiológicos de cierta magnitud, sobre anaplasmosis, ofreciendo ventajas considerables en paises en desarrollo en donde las cadenas de frío son deficientes.

Résumé La fiabilité du sang récolté sur papier filtre comparée à celle des prélèvements conventionnels de sérum pour le diagnostic de l'anaplasmose a été étudiée à l'aide des tests suivants: fixation du complément, ELISA, immunoblot de Western, test rapide d'agglutination sur carte. Du sang séché sur papier filtre Whatman No 1 a fait l'object d'une élution dans une solution de PBS à 0,05 p. 100 (Tween 20) pour donner une dilution de base au dilution de base au 1∶10. Le réactivité des échantillons, autant avec le test ELISA que l'immunoblot Western, a été identique à celle obtenue par dilution directe de sérums homologue. Les échantillons sur papier filtre ont donné une réactivité plus faible pour les autres tests, comparée à celle des échantillons de sérum semblables. Aucune différence significative n'a été décelée quant à leur réactivité les éluats provenant de papiers filtres stockés à des températures comprises entre 15,5 et 24°C at ceux conservés au réfrigérateur. Le stockage entre 15,5 et 24°C n'a pas non plus affecté la réactivité de fa?on significative; les éluats conservés à partir des papiers filtres, à cette même température durant 6 mois, ont montré des réactions identiques que ceux provenant de papiers filtres fra?chement préparés, à la fois avec le test ELISA, celui de Western Blot et le test d'agglutination rapide sur carte. On peut conclure que la collecte du sang sur papier filtre est une technique adaptée à l'étude épidémiologique de l'anaplasmose à grande échelle. Elle offre de nombreux avantages dans les pays en développement où offre de nombreux avantages dans les pays en développement où les moyens de transports et la cha?ne du froid constituent des contraintes majeures.
  相似文献   
98.
Dermal microfilariae recovered from specimens obtained from umbilical and cervical sites of cattle infected with adult Onchocerca gutturosa alone or with adults of O gutturosa and O lienalis were measured and compared with uterine microfilariae obtained directly from gravid female worms of each species. Uterine microfilariae of O gutturosa were longer than dermal microfilariae obtained from cattle harboring only adults of O gutturosa. Dermal microfilariae were recovered from umbilical and cervical sites in these cattle. Those found at the cervical site had lengths equal to or greater than lengths of microfilariae recovered from the umbilical site. There was a significant (P less than 0.0001) shift in length across populations of microfilariae of O gutturosa from various sites in its bovine host, with a progressive decrease in length between microfilariae recovered from the worm's uterus, microfilariae from the cervical dermis, and microfilariae from the umbilical dermis, respectively. A similar direct comparison was not possible for microfilariae of O lienalis, because none of the cattle was infected with only adult worms of this species. In an indirect comparison, microfilariae of O lienalis were identified at the umbilicus, but their presence in the cervical region could not be determined unequivocally because of confounding of microfilariae length by concurrent infection with O gutturosa. Uterine microfilariae from O lienalis were longer than uterine microfilariae of O gutturosa, although a degree of overlap in the range of measurements existed between species.  相似文献   
99.
Little is known about the effect of fertilization on the N uptake of sunflowers. A 42 factorial trial with 0, 60, 120 and 180 kg N ha−1 and 0, 15, 30 and 45 kg P ha−1 was conducted over three years. The N content and concentration of leaves, stems and capitula were determined at three growth stages. High N levels increased the N content and concentration of all plant parts at all growth stages sharply. High P levels increased the N content of all plant components through better growth. P has an inconsistent effect on N concentration but tended to decrease it. After flowering the crop assimilated 20 to 25 % of the total N. This implies that N applied can still be applied and utilized by the crop at a late stage. This should be substantiated by further research.  相似文献   
100.
湖南省果梅品种资源种质杂化状况的初步研究   总被引:8,自引:0,他引:8  
刘连森  贺善文 《园艺学报》1993,20(3):225-230
  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号