全文获取类型
收费全文 | 147807篇 |
免费 | 8285篇 |
国内免费 | 90篇 |
专业分类
林业 | 6237篇 |
农学 | 5052篇 |
基础科学 | 960篇 |
19327篇 | |
综合类 | 21049篇 |
农作物 | 5787篇 |
水产渔业 | 7789篇 |
畜牧兽医 | 78375篇 |
园艺 | 1951篇 |
植物保护 | 9655篇 |
出版年
2020年 | 1311篇 |
2019年 | 1558篇 |
2018年 | 2424篇 |
2017年 | 2718篇 |
2016年 | 2473篇 |
2015年 | 2145篇 |
2014年 | 2667篇 |
2013年 | 6236篇 |
2012年 | 4679篇 |
2011年 | 5606篇 |
2010年 | 3770篇 |
2009年 | 3797篇 |
2008年 | 5525篇 |
2007年 | 5334篇 |
2006年 | 4967篇 |
2005年 | 4535篇 |
2004年 | 4384篇 |
2003年 | 4453篇 |
2002年 | 4061篇 |
2001年 | 5044篇 |
2000年 | 4917篇 |
1999年 | 3965篇 |
1998年 | 1577篇 |
1997年 | 1591篇 |
1996年 | 1457篇 |
1995年 | 1721篇 |
1994年 | 1429篇 |
1993年 | 1469篇 |
1992年 | 2945篇 |
1991年 | 3129篇 |
1990年 | 3075篇 |
1989年 | 3113篇 |
1988年 | 2804篇 |
1987年 | 2771篇 |
1986年 | 2749篇 |
1985年 | 2572篇 |
1984年 | 2104篇 |
1983年 | 1870篇 |
1982年 | 1248篇 |
1979年 | 1823篇 |
1978年 | 1400篇 |
1977年 | 1254篇 |
1976年 | 1204篇 |
1975年 | 1293篇 |
1974年 | 1538篇 |
1973年 | 1619篇 |
1972年 | 1574篇 |
1971年 | 1387篇 |
1970年 | 1417篇 |
1969年 | 1302篇 |
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
991.
992.
Prevalence and geographic distribution of Fanconi syndrome in Basenjis in the United States 总被引:1,自引:0,他引:1
A survey was conducted to ascertain the prevalence of Fanconi syndrome in Basenjis and to determine in which geographic regions the greatest number of affected dogs resided. A thousand questionnaires were distributed nationally, and 624 (62%) were returned. Through this survey, prevalence, geographic distribution, and breeder involvement were successfully correlated with the overall association of the disease with the Basenji breed. Ten percent (96/959) of all Basenjis involved in the survey had Fanconi syndrome. Half (50%; 48/96) of the Basenjis affected were between 4 and 8 years old. Seventy-six percent (44/58) of owners of Basenjis with Fanconi syndrome were breeding their dogs, and 93% (52/56) had owned other Basenjis before the survey was conducted. Females outnumbered males (3:1) in frequency of the disease. This ratio reflected the higher breeder participation in the survey, rather than being a true gender predilection for the disease. 相似文献
993.
Y R el-Baghdady E S Fattouh K I el-Ekhnawy M M Ayoub L H Bedeir 《The British veterinary journal》1990,146(6):577-581
A study was conducted on 40 buffalo-cows, assigned randomly, immediately after calving into three groups: group I (n = 10) injected with saline and taken as control; group II (n = 15) received 25 mg PGF2 alpha/animal (Lutalyse); group III (n = 15) received 25 mg PGF2 alpha + 25 i.u. oxytocin/animal (Syntocinon), single i.m. dose. Oxytocin and/or PGF2 alpha significantly (P less than 0.01) shortened the interval from calving to first service (38.33 and 31.53 days for groups II and III respectively, versus 91.60 days for controls). The treatment reduced the service period (38.29 and 35.87 days for groups II and III respectively, versus 45.40 days for controls). Concomitantly a significant (P less than 0.01) decrease in the open-days post partum was achieved (76.62 and 67.40 days for groups II and III respectively, versus 137.00 days for controls). In addition, the treated buffaloes needed significantly (P less than 0.01) fewer services per conception (1.67 and 1.20 S/C for groups II and III respectively) than the untreated ones (2.70 S/C), besides a substantial improvement (P less than 0.01) in their conception rate either at 60 or 85 days post partum. Significantly improved (P less than 0.05) results were obtained in the oxytocin and PGF2 alpha treated animals, than in those receiving PGF2 alpha alone for all the previous parameters, except for the service period. Buffaloes therefore seemed to respond better to such treatment than dairy cows. 相似文献
994.
Effect of exogenous porcine somatotropin administration on nitrogen and energy metabolism in three genotypes of pigs 总被引:2,自引:0,他引:2
M W Verstegen W van der Hel A M Henken J Huisman E Kanis P van der Wal E J van Weerden 《Journal of animal science》1990,68(4):1008-1016
Effects of exogenous administration of porcine recombinant somatotropin (rpST) on protein gain and metabolic rate were measured in three genotypes (castrated males) of pigs (Pietrain, Duroc and a crossbreed between Dutch Yorkshire and Dutch Landrace). Six pigs of each genotype were assigned at approximately 60 kg to receive pST doses of either 0 (C) or 14 mg (T) administered i.m. twice weekly over 10 wk. Pigs were housed in individual metabolism cages at a room temperature of 20 to 22 degrees C and received feed at 2.6 times maintenance. Protein gain (N x 6.25) was measured over the final 6 wk of the 10-wk test period. For 2 wk in the test period (wk 2 and wk 5), six pigs of each treatment x genotype group were placed in a large respiration chamber and energy balances (in protein and fat) and metabolic rate were measured. Rate of weight gain measured over the final 6 wk of the experimental period increased by 105 g/d (13%) with rpST administration (P less than .01). Daily protein gain over 6 wk was increased by 48 g/animal with application of rpST (P less than .001). There was a genotype x treatment interaction (P less than .01) for protein gain. Daily protein gain in Durocs with pST treatment was increased (39%) more than in crossbreds (31%). Daily fat gain was decreased by 42 g/animal (P less than .001) by T. Daily heat production with rpST was increased by 12 kcal/kg.75, which is comparable to a 12% increase in the maintenance energy requirement. 相似文献
995.
Relationship between oocyte maturation and fertilization on zygotic diversity in swine 总被引:1,自引:0,他引:1
Two experiments were conducted to examine how oocyte maturation and fertilization influence zygotic diversity in swine. In the first experiment, the distribution of oocyte maturation was compared to that of zygotic development. Oocytes were aspirated from follicles of 31 gilts and classified into stages of meiosis. Zygotes were flushed from oviducts of 19 additional gilts and classified into stages of meiosis and fertilization. The second experiment examined whether the time from ovulation to fertilization was constant among all oocytes. To test this premise, four to six oocytes from follicles of 10 mated gilts were aspirated just before or during ovulation, stained and transferred back into the oviducts of these same gilts. Zygotes were recovered 10 h later to determine whether the first oocytes ovulated were the more developed zygotes and, conversely, whether the last oocytes to be ovulated represented the lesser developed contemporaries. The skewed (P less than .05) distribution of oocyte maturation was similar to that of zygotic development. Regression of the frequency distribution describing early oocyte maturation resulted in a line with a slope (.59) that was similar to the slope (.58) of the regressed distribution of zygotic development. Likewise, the order of ovulation and order of subsequent stages of zygotic development were similar. These data suggest that variation in zygotic development in swine was due to variability in oogenesis; the time from ovulation to fertilization appeared to be constant. 相似文献
996.
T Itabisashi R Horino K Hirano M Maeda 《Nippon juigaku zasshi. The Japanese journal of veterinary science》1990,52(3):551-558
Nine Suffolk sheep and 4 Holstein cattle were employed to observe electroencephalographic changes in experimental cerebrocortical necrosis. Amprolium (600 mg/kg/day) alone was given intraruminally 6 sheep and 4 cattle, all of which showed neurological signs and abnormal electroencephalograms. Both amprolium and thiamine (200 mg/day) and thiamine (50 mg/day) alone were given 2 and 1 sheep, respectively, as controls, which did not show any abnormal signs. Abnormal electroencephalograms included continuous slow waves and long-lasting spindles, both of which appeared diffusely and were seen subclinically or with neurological signs. The spindles consisted of slow waves or sharp- (or spike-) and-slow-wave complexes with or without convulsive seizures even during the convulsion stage. Conversely, the seizures occurred with the spindles or slow waves. 相似文献
997.
998.
Colloid goitre was diagnosed in adult camels in the Kordofan region of the Sudan. The disease is characterized by gross enlargement of the thyroid, histopathological follicular changes, reproductive disorders, low concentrations of circulating thyroid hormones (T3, T4) and normocytic normochromic anaemia. The possible cause of the condition is discussed and iodine supplementation is recommended. 相似文献
999.
Establishment of an attenuated strain of bovine respiratory syncytial virus for live virus vaccine 总被引:1,自引:0,他引:1
M Kubota S Fukuyama K Kodama N Sasaki 《Nippon juigaku zasshi. The Japanese journal of veterinary science》1990,52(4):695-703
To develop a live virus vaccine for the prevention of bovine respiratory syncytial (BRS) virus infection in calves, an attempt was made to produce an attenuated virus. The RS-52 strain of BRS virus, isolated from the nasal secretions of a naturally infected calf, was subjected to serial passages in adult hamster lung established (HAL) cells at 30 degrees C and the attenuated rs-52 strain as a live virus vaccine was established. The rs-52 strain multiplied better at 30 degrees C than at 34 or 37 degrees C in HAL cells. The differences in the highest virus titers of this strain between the culture temperature of 30 degrees C and that of 34 or 37 degrees C were more than 2.25 log TCID50. Colostrum-deprived newborn calves and 2 approximately 4 months old calves inoculated with the rs-52 strain manifested no abnormal clinical sings at all. However, all inoculated calves produced serum neutralization antibody. When the colostrum-deprived newborn calves immunized with the rs-52 strain were challenged with the virulent NMK7 strain of BRS virus, they exhibited no pyrexia or other abnormal clinical signs at all. An attempt was made to recover the virus from nasal secretions of these calves, but in vain. On the other hand, a nonimmunized control colostrum-deprived newborn calf developed slight fever, mild cough, and slight serous nasal discharge after challenge exposure. The virus was recovered from nasal secretions of this calf. From these results, it was considered that the rs-52 strain could be used as an attenuated live virus vaccine for prevention of BRS virus infection. 相似文献
1000.
Nucleotide sequence of hog cholera virus RNA: properties of the polyprotein encoded by the open reading frame spanning the viral genomic RNA 总被引:2,自引:0,他引:2
Hog cholera virus RNA was cloned and sequenced. A single major open reading frame (ORF), encoding an amino acid sequence of 3898 residues, was found in the second reading frame of the sequence of one of the cDNA strands. We demonstrated that the ORF spans the length of the viral sense RNA, which implies that it is translated into a precursor polyprotein. Several properties of this polyprotein, like hydrophobicity, position of putative protease cleavage sites, distribution of N-linked glycosylation sites, distribution of cysteines and distribution of acidic and basic residues are described and discussed. 相似文献