全文获取类型
收费全文 | 118792篇 |
免费 | 5989篇 |
国内免费 | 81篇 |
专业分类
林业 | 5908篇 |
农学 | 3634篇 |
基础科学 | 568篇 |
12975篇 | |
综合类 | 23731篇 |
农作物 | 4684篇 |
水产渔业 | 5352篇 |
畜牧兽医 | 59413篇 |
园艺 | 1389篇 |
植物保护 | 7208篇 |
出版年
2018年 | 1451篇 |
2017年 | 1564篇 |
2016年 | 1442篇 |
2015年 | 1320篇 |
2014年 | 1586篇 |
2013年 | 4044篇 |
2012年 | 2947篇 |
2011年 | 3480篇 |
2010年 | 2294篇 |
2009年 | 2290篇 |
2008年 | 3443篇 |
2007年 | 3476篇 |
2006年 | 3207篇 |
2005年 | 3067篇 |
2004年 | 2918篇 |
2003年 | 2942篇 |
2002年 | 2794篇 |
2001年 | 3438篇 |
2000年 | 3426篇 |
1999年 | 2846篇 |
1998年 | 1072篇 |
1997年 | 1112篇 |
1995年 | 1247篇 |
1993年 | 1112篇 |
1992年 | 2252篇 |
1991年 | 2296篇 |
1990年 | 2394篇 |
1989年 | 2359篇 |
1988年 | 2237篇 |
1987年 | 2206篇 |
1986年 | 2241篇 |
1985年 | 2236篇 |
1984年 | 1844篇 |
1983年 | 1660篇 |
1982年 | 1136篇 |
1981年 | 1065篇 |
1979年 | 1744篇 |
1978年 | 1413篇 |
1977年 | 1222篇 |
1976年 | 1180篇 |
1975年 | 1339篇 |
1974年 | 1775篇 |
1973年 | 1744篇 |
1972年 | 1789篇 |
1971年 | 1712篇 |
1970年 | 1586篇 |
1969年 | 1494篇 |
1968年 | 1231篇 |
1967年 | 1326篇 |
1966年 | 1175篇 |
排序方式: 共有10000条查询结果,搜索用时 16 毫秒
991.
The aim of this work is to evaluate the haemodynamic characteristics of maternal and fetal vessels during normal pregnancy in bitches, using Colour and Pulsed wave Doppler ultrasonography, in order to obtain more information about maternal and fetal circulation. The blood waveforms of the uteroplacental arteries, aorta, caudal cava vein and umbilical cord of the fetuses were recorded weekly in 16 pregnant bitches. Also, the measurements of Peak Systolic, End Diastolic Velocities, Resistance and Pulsatility Indices were carried out. Uteroplacental blood flow was biphasic while the ones of the umbilical artery and aorta were first systolic and then diastolic. The cava showed a typical waveform of venous vessels. During gestation the EDV and PSV of fetal vessels increased (alpha<0.05) while the PI and RI of all vessels examined decreased (alpha<0.05) except for the IP of the Aorta. The Doppler ultrasonography was used to study the characteristics of maternal and fetal vessel flow and their progressive changes during pregnancy. This study can be considered a further contribution in diagnosing and monitoring high-risk pregnancies in Veterinary Medicine. 相似文献
992.
993.
Effects of domperidone, a peripheral dopamine receptor antagonist, on secretion of LH and prolactin were studied during the luteal phase and following administration of PGF2 alpha. Since hyperprolactinemia has been reported to inhibit secretion of LH in ewes, effects of thyrotropin-releasing hormone (TRH) also were examined. Ewes 8-10 days post-estrus were assigned to be treated with: 1) vehicle (n = 5); 2) 0.3 mg domperidone (n = 6); 3) 1.0 mg domperidone (n = 6); 4) 3 micrograms TRH (n = 6); or 5) 10 micrograms TRH (n = 6) every 4 hours for 60 hr. Luteal regression was induced with PGF2 alpha at 12 hr after initiation of treatments. During the luteal phase, pulses of LH were more frequent (P less than .05) and the amplitudes of these were higher (P less than .05) in ewes treated with domperidone or TRH than in control ewes. These changes in LH occurred even though each treatment elevated markedly concentrations of prolactin in plasma. After induction of luteal regression, mean of LH and frequency of LH discharges were similar in all groups. However, in ewes treated with the 1.0 mg/4 hr dose of domperidone the pulse amplitude was greater than in the other groups (2.3 vs 1.1 ng/ml). Dose-response relationships and the magnitude of the prolactin release following domperidone or TRH varied with time. Treatments did not affect the timing of the LH surge or the increase in progesterone associated with the subsequent cycle.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
994.
995.
Adams CL Bonnett BN Meek AH 《Journal of the American Veterinary Medical Association》2000,217(9):1303-1309
OBJECTIVE: To identify predictors of grief and client desires and needs as they relate to pet death. DESIGN: Cross-sectional mail survey. SAMPLE POPULATION: 177 clients, from 14 randomly selected veterinary practices, whose cat or dog died between 6 and 43 days prior to returning the completed questionnaire. PROCEDURE: Veterinary practices were contacted weekly to obtain the names of clients whose pets had died until approximately 200 clients were identified. Clients were contacted by telephone, and a questionnaire designed to measure grief associated with pet death was mailed to those willing to participate within 1 to 14 days of their pet's death. The questionnaire measured potential correlates and modifiers of grief and included three outcome measures: social/emotional and physical consequences, thought processes, and despair. Demographic data were also collected. RESULTS: Approximately 30% of participants experienced severe grief. The most prominent risk factors for grief included level of attachment, euthanasia, societal attitudes toward pet death, and professional support from the veterinary team. CONCLUSIONS AND CLINICAL RELEVANCE: Bivariate and multivariate analyses highlighted the impact owners' attitudes about euthanasia and professional intervention by the veterinary team had on reactions to pet death. Owners' perceptions of societal attitudes, also a predictor of grief, indicate that grief for pets is different than grief associated with other losses. 相似文献
996.
997.
Hüttner K Seelmann M Feldhusen F 《Berliner und Münchener tier?rztliche Wochenschrift》2010,123(11-12):463-467
Despite indications of a considerable spread of Maedi-Visna among sheep flocks in Germany, prevalence studies of this important infection are hardly available. Prior to any health schemes and guidelines, knowledge about regional disease distribution is essential. Depending upon herd size, 70 farms were randomly selected, of which 41 cooperated. A total of 2229 blood samples were taken at random and serologically examined. For assessment of selected farm characteristics a questionnaire exercise was conducted at all farms involved. The average herd prevalence is 51.2%, the within-herd prevalence is 28,8%. In the unvariate analysis of risk factors, small (10-100 sheep) and large (> 250 sheep) farms are more MVV-affected than medium sized farms. The average stable and pasture space per sheep is larger at non-infected- compared to infected farms. Owners judgement on general herd health turns out to be better at non-infected compared to infected farms. Taking infected farms only, the risk of within-herd prevalence above 20% is significant higher in crossbred than in purebred flocks. 相似文献
998.
H. Doornenbal 《Canadian journal of veterinary research》1965,29(7):179-182
A 5 year history of swine dysentery and treatment has been described. 相似文献
999.
Five commercial dairy herds with 269 lactating cows participated for 12 months in a field trial to determine the effectiveness of a barrier teat dip containing chlorous acid/chlorine dioxide germicide. The right quarters of the cows in two herds and the left quarters of the cows in three herds were dipped in the experimental teat dip after the removal of the milking machine. The other quarters were dipped in a conventional 0.5 per cent iodophor product. Compared with this control product, teat dipping with the experimental dip reduced the number of new intramammary infections by 18.8 per cent, infections with major pathogens by 13.6 per cent, infections with minor pathogens by 16.8 per cent and clinical mastitis by 33.3 per cent. Statistical analysis indicated a trend towards decreased intramammary infections with coliforms and coagulase-negative staphylococci when the experimental teat dip was used. It was concluded that under the conditions of this investigation it was effective in preventing new infections due to both contagious and some environmental pathogens. However, the data suggested that it could adversely affect the condition of the skin of the teat when it was used after incorrect preparation of the udder. 相似文献
1000.
The eye of the marine mollusc Bulla contains a circadian pacemaker which, along with critical entrainment pathways, is located among a small group of neurons at the base of the retina. Long-term intracellular recording from cells of the organized photoreceptor layer, which constitutes most of the retinal volume, indicates that these cells are not involved in generating the rhythm since rhythmic changes in membrane potential were not observed. In addition, surgical removal of the entire photoreceptor layer does not alter the period of the circadian rhythm and does not prevent phase shifts by light pulses. 相似文献