全文获取类型
收费全文 | 504篇 |
免费 | 5篇 |
国内免费 | 1篇 |
专业分类
林业 | 6篇 |
64篇 | |
综合类 | 198篇 |
农作物 | 1篇 |
水产渔业 | 3篇 |
畜牧兽医 | 220篇 |
园艺 | 3篇 |
植物保护 | 15篇 |
出版年
2023年 | 3篇 |
2022年 | 3篇 |
2016年 | 4篇 |
2015年 | 4篇 |
2012年 | 42篇 |
2011年 | 36篇 |
2010年 | 3篇 |
2009年 | 9篇 |
2008年 | 24篇 |
2007年 | 29篇 |
2006年 | 21篇 |
2005年 | 39篇 |
2004年 | 21篇 |
2003年 | 28篇 |
2002年 | 25篇 |
2001年 | 15篇 |
2000年 | 13篇 |
1999年 | 14篇 |
1998年 | 3篇 |
1995年 | 6篇 |
1994年 | 3篇 |
1993年 | 5篇 |
1991年 | 8篇 |
1990年 | 4篇 |
1989年 | 6篇 |
1983年 | 3篇 |
1981年 | 4篇 |
1979年 | 3篇 |
1969年 | 3篇 |
1963年 | 3篇 |
1960年 | 3篇 |
1955年 | 4篇 |
1954年 | 3篇 |
1953年 | 5篇 |
1948年 | 3篇 |
1947年 | 2篇 |
1946年 | 2篇 |
1945年 | 2篇 |
1943年 | 5篇 |
1940年 | 5篇 |
1938年 | 5篇 |
1936年 | 3篇 |
1933年 | 3篇 |
1911年 | 2篇 |
1908年 | 3篇 |
1905年 | 2篇 |
1904年 | 2篇 |
1895年 | 2篇 |
1885年 | 4篇 |
1884年 | 2篇 |
排序方式: 共有510条查询结果,搜索用时 15 毫秒
1.
A moth egg assignable to the family Noctuidae (Lepidoptera) is described from 75-million-year-old sediments from Martha's Vineyard, Massachusetts. This sample, which extends the fossil record of this farnily and modern heteroneuran moths back to the Cretaceous, may provide insight into the coevolution of moths and flowering plants, as well as have implications for the evolution of bats. 相似文献
2.
3.
4.
Brito LF Barth AD Rawlings NC Wilde RE Crews DH Mir PS Kastelic JP 《Domestic animal endocrinology》2007,33(1):1-18
The objective of the present study was to characterize the effects of nutrition on circulating concentrations of metabolic hormones, gonadotropins, and testosterone during sexual development in bulls. Nutrition regulated the hypothalamus-pituitary-testes axis through effects on the GnRH pulse generator in the hypothalamus and through direct effects on the testes. Pituitary function (gonadotropin secretion after GnRH challenge) was not affected by nutrition. However, nutrition affected LH pulse frequency and basal LH concentration during the early gonadotropin rise (10-26 weeks of age). There were close temporal associations between changes in insulin-like growth factor-I (IGF-I) concentrations and changes in LH pulse frequency, suggesting a role for IGF-I in regulating the early gonadotropin rise in bulls. The peripubertal increase in testosterone concentration was delayed in bulls with lesser serum IGF-I concentrations (low nutrition), suggesting a role for IGF-I in regulating Leydig cell function. Serum IGF-I concentrations accounted for 72 and 67% of the variation in scrotal circumference and paired-testes volume, respectively (at any given age), indicating that IGF-I may regulate testicular growth. Bulls with a more sustained elevated LH pulse frequency during the early gonadotropin rise (high nutrition) had greater testicular mass at 70 weeks of age relative to the control group (medium nutrition), despite no differences in metabolic hormone concentrations after 26 weeks of age. Therefore, gonadotropin-independent mechanism regulating testicular growth might be dependent on previous gonadotropin milieu. 相似文献
5.
Melendez P Goff JP Risco CA Archbald LF Littell R Donovan GA 《Research in veterinary science》2007,82(3):349-357
The objective of this study was to determine the effect of a monensin controlled-release capsule administered intraruminally at drying-off on body condition score (BCS) at calving, milk yield, fertility and concentration of energy-related blood metabolites in Holstein cows dried-off with low BCS (< or = 3.0, scale 1 to 5 with a 0.25 point of increment). Between July and August, 2001, 220 cows from parity 2 or more and dried-off 50-70 days before expected parturition, with a BCS < or = 3.0 were randomly assigned to either a treatment group (n=110; oral capsule of monensin releasing 335 mg/day for 95 days) or a control group (no capsule, n=110). At assignment, on day 21 before expected parturition, at calving, and at 7, 14, and 21 days in milk a blood sample was obtained from a random sub sample of 10 cows per group. Effects of monensin on serum NEFA, BHBA and glucose were measured. Milk yield, milk fat and protein content (%) at DHIA test days during the entire lactation, 305 ME milk production and reproductive responses were compared. Monensin significantly improved BCS at calving, increased milk yield at test days 4 and 8, decreased the percentage of milk protein, did not change the percentage of milk fat, and decreased NEFA and BHBA during the post-partum period. 相似文献
6.
Shubitz LF Matz ME Noon TH Reggiardo CC Bradley GA 《Journal of the American Veterinary Medical Association》2001,218(4):537-40, 526
A 4-year-old castrated male mixed-breed dog with a history of coccidioidomycosis was referred for evaluation of abdominal and pleural effusion. Results of radiography, ultrasonography, cytologic evaluation of thoracic fluid, and serologic testing supported a diagnosis of constrictive pericarditis secondary to infection with Coccidioides immitis. Aggressive treatment for presumptive coccidioidomycosis was begun, but the dog's condition continued to deteriorate, and the dog was euthanatized. At necropsy, the pericardium was thicker than normal and fibrotic and adhered to the epicardium. Microscopically, the pericardium and 1 section of epicardium contained lymphoplasmacytic infiltrates with a few macrophages and neutrophils. Coccidioides immitis was cultured from pericardial fluid. A search of records from the Arizona Veterinary Diagnostic Laboratory for 1988 through 1998 revealed that of 46 dogs in which a diagnosis of coccidioidomycosis was confirmed at necropsy, 13 had involvement of the heart or pericardium. 相似文献
7.
The bioefficacy of a standard domestic aerosol insecticide has been compared with that of a similar spray in which the droplets were electrostatically charged. The aerosol was charged without the need for an external power supply, by enhancing natural charge separation processes that occur during atomisation. The charge-to-mass ratio achieved was 1.1 x 10(-4) C kg-1, compared with 2.2 x 10(-5) C kg-1 for the standard aerosol. Efficiency was assessed for insects in free flight. A direct space-spray application method was used to study the bioefficacy of these aerosols on houseflies, Musca domestica, and an indirect space-spray method on houseflies and mosquitoes, Culex quinquefasciatus. Two levels of concentration of active ingredients were compared. At low concentrations of 1.57 g kg-1 of bioallethrin and 0.29 g kg-1 of bioresmethrin, the charged aerosol achieved a significant reduction in KDT50 (time at which 50% of the flies were knocked down), compared with the standard aerosol. In the direct spray application to houseflies, the KDT50 was reduced by 50%, while in the indirect spray the KDT50 was reduced by 40%. In the indirect spray of mosquitoes, the KDT50 was reduced by 22%. With higher active ingredient concentrations of 2.09 g kg-1 for bioallethrin and 0.39 g kg-1 for bioresmethrin, the charged aerosol also demonstrated faster knockdown than the standard, but the improvement was less marked. In the direct spray application to houseflies, the KDT50 was reduced by 21% compared with the standard aerosol, while in the indirect spray the KDT50 was reduced by 16%. In the indirect spray of mosquitoes, the KDT50 was reduced by 24%. The percentage mortality after 24 h was also increased with the charged aerosol. Charge carried by the droplets results in increased interception of the insecticide, as the droplets are attracted to the insects in flight and space charge effects within the aerosol could cause improved dispersion in the test chamber. 相似文献
8.
Human scabies of wombat origin 总被引:2,自引:0,他引:2
9.
10.
Zerbe H Castilho LF Engelke F Mattos RC Schuberth HJ Klug E Leibold W 《Journal of veterinary medicine. A, Physiology, pathology, clinical medicine》2003,50(4):179-184
Sufficient numbers of functionally competent polymorphonuclear neutrophil granulocytes (PMN) seem to be of major importance during the course of equine endometritis. In this study, we wanted to establish a method for cryopreservation of functionally competent neutrophils for an intended local endometritis therapy in mares. The separation of leucocytes by hypotonic lysis of whole blood from clinically healthy mares was superior to the separation by dextrose sedimentation. After suspension of the cells in the cryoprotective solution [equine plasma with 5% (v/v) dimethyl sulphoxide (DMSO)], the leucocytes were frozen in liquid nitrogen. A temperature gradient with low cooling velocity (1 degree C/min between 4 and -70 degrees C) resulted in highest numbers of viable cells after thawing. Thawed PMN had a high phagocytic capacity for opsonized streptococci. Their ability to generate reactive oxygen species (ROS) after stimulation with a phorbol ester was even higher than that of freshly isolated PMN and was preserved up to 6 h after thawing. The results of this study indicate that cryopreservation of PMN may provide viable and functionally competent neutrophils for therapeutic use in mares susceptible to endometritis. 相似文献