全文获取类型
收费全文 | 150734篇 |
免费 | 8565篇 |
国内免费 | 94篇 |
专业分类
林业 | 5412篇 |
农学 | 4480篇 |
基础科学 | 976篇 |
17115篇 | |
综合类 | 28184篇 |
农作物 | 5952篇 |
水产渔业 | 7251篇 |
畜牧兽医 | 78671篇 |
园艺 | 1792篇 |
植物保护 | 9560篇 |
出版年
2018年 | 1931篇 |
2017年 | 2254篇 |
2016年 | 2055篇 |
2015年 | 1810篇 |
2014年 | 2209篇 |
2013年 | 5644篇 |
2012年 | 4070篇 |
2011年 | 4982篇 |
2010年 | 3174篇 |
2009年 | 3262篇 |
2008年 | 4784篇 |
2007年 | 4563篇 |
2006年 | 4399篇 |
2005年 | 4052篇 |
2004年 | 3900篇 |
2003年 | 3953篇 |
2002年 | 3728篇 |
2001年 | 4830篇 |
2000年 | 4788篇 |
1999年 | 3786篇 |
1998年 | 1560篇 |
1997年 | 1515篇 |
1996年 | 1408篇 |
1995年 | 1724篇 |
1994年 | 1550篇 |
1993年 | 1504篇 |
1992年 | 3229篇 |
1991年 | 3372篇 |
1990年 | 3182篇 |
1989年 | 3279篇 |
1988年 | 2982篇 |
1987年 | 3179篇 |
1986年 | 3244篇 |
1985年 | 3097篇 |
1984年 | 2483篇 |
1983年 | 2187篇 |
1982年 | 1537篇 |
1981年 | 1346篇 |
1979年 | 2197篇 |
1978年 | 1817篇 |
1977年 | 1573篇 |
1976年 | 1491篇 |
1975年 | 1601篇 |
1974年 | 2014篇 |
1973年 | 2073篇 |
1972年 | 1989篇 |
1971年 | 1857篇 |
1970年 | 1779篇 |
1969年 | 1607篇 |
1967年 | 1402篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Cystic alterations of the canine endometrium compromise reproduction and fertility of the bitch and may lead to life-threatening diseases, such as pyometra. Even without clinical evidence, reduction of the uterine lumen by cysts implicates disturbances during migration, nidation and development of the embryo. Several studies point to the high variability of morphology of uterine endometrial cysts but they lack detailed analyses of alterations. In the present study, immunohistochemistry was used to investigate the expression of steroid hormone receptors (oestrogen, progesterone), proliferation activity, inflammation and infection in the cystic affected tissue regions in contrast to the normal endometrium. Oestrogen receptor expression showed a high density of receptors throughout the surface epithelial cells, crypt epithelial cells, glandular epithelial cells and stromal cells of the normal endometrium as well as the cystic affected regions. Proliferation in the cysts was verified in the middle and basal cells of the crypts. Neither in the endometrium nor in the cysts inflammatory processes or evidence of infection could be detected. Furthermore, lectin histochemistry and electron microscopic methods showed that lectin binding patterns and cell morphology of internal epithelial lining and surface epithelium of the cysts can be used to characterize and distinguish different types of cystic alterations. Analogies between epithelial cells of the glandular chambers of the canine placenta and the cystic cellular morphology, steroid hormone receptor distribution as well as lectin binding patterns of the endometrial cysts, as observed in this study, suggest to introduce the term 'pseudo-placentational endometrial cysts'. 相似文献
992.
R. C. Regan K. M. Rassnick C. E. Balkman D. B. Bailey S. P. McDonough 《Veterinary and comparative oncology》2010,8(1):1-10
Second-opinion histopathology is intended to detect clinically significant discrepancies that have a direct impact on patient care. We sought to determine if this practice at our institution affected patient management and prognosis. First- and second-opinion histopathology reports from cases were retrospectively reviewed. Reports were considered to be in diagnostic agreement, partial diagnostic disagreement or complete diagnostic disagreement. Four hundred and thirty cases were studied. In 70% of cases there was a diagnostic agreement. In 20% of cases, there was partial diagnostic disagreement, where diagnoses were the same but information such as grade or lymphatic and/or vascular invasion was changed. In 10% of cases, complete diagnostic disagreement resulted from a change in degree of malignancy (malignant to benign, or converse; 7%) or a change in cell type (3%). In 17% of the cases evaluated, the histopathology review prompted a change in treatment or prognosis. These findings support the use of second-opinion histopathology as an important part of patient care. 相似文献
993.
994.
I J Lean M Anderson M G Kerfoot G C Marten 《Journal of the American Veterinary Medical Association》1989,195(6):768-771
Tryptamine alkaloid toxicosis (Phalaris staggers) was diagnosed in feedlot sheep. Clinical signs of toxicosis, which were exacerbated by excitement, included gait abnormalities, muscular tremors, nystagmus, and convulsions. An estimated 8% of the most severely affected lambs had clinical signs of toxicosis. Gross lesions detected in the brain of affected lambs consisted of focal gray-green discoloration in the brain stem and thalamus; these areas had microscopic evidence of intraneuronal pigment accumulation. Brain specimens obtained at slaughter indicated that 60% of the lambs had lesions consistent with tryptamine alkaloid toxicosis. Tryptamine alkaloids were found in low concentrations in the feed. Lambs exposed to these feeds had higher death losses than those that were not exposed to the feeds. Cobalt concentration in the feed was higher than that previously reported to be associated with Phalaris staggers. 相似文献
995.
S D Johnston L C Buoen A F Weber T L Lin 《Journal of the American Veterinary Medical Association》1989,194(10):1446-1448
Analysis of skin fibroblast cultures from a deformed stillborn female Alaskan Malamute pup revealed a 3n = 117,XXX (normal, 2n = 78,XX) chromosome count. The triploid pup was delivered by cesarean section 5 days after estimated date of parturition, because the bitch failed to start labor. The bitch had been inseminated with thawed frozen semen deposited into the lumen of the uterus approximately 4 days after ovulation. Gross anatomic abnormalities of the pup included omphalocele, diaphragmatic hernia, persistent right aortic arch, atresia ani, and no right forelimb distal to the scapula. The pup also had arthrogryposis of the left carpus, kyphosis of the thoracic vertebrae, widely separated cranial sutures, open fontanelles, hydrocephalus, and cleft palate. Suspected cause of the triploidy was dispermy of an aged oocyte after intrauterine deposition of the thawed frozen semen. Numeric chromosome abnormalities may be causes of fetal deformity or death that can be detected by fetal karyotype. 相似文献
996.
Effect of subchondral drilling on repair of partial-thickness cartilage defects of third carpal bones in horses 总被引:1,自引:0,他引:1
L D Shamis L R Bramlage A A Gabel S Weisbrode 《American journal of veterinary research》1989,50(2):290-295
Arthrotomies of middle carpal joints were done on 13 horses, and a 1-cm partial thickness, round defect was made on the radial facet of both third carpal bones. In one joint, 1-mm diameter 1-cm deep holes were drilled within the defect, and one joint was used as a control. horses were assigned to 2 groups--group 1 (n = 6 horses), 5 drill holes; group 2 (n = 7 horses), 11 drill holes. At 1 and 3 weeks after surgery, differences between joints in synovial fluid total protein values, WBC counts, or results of mucin precipitate tests were not significant (P = 0.005). Physically and radiographically, horses were the same during the 12 initial weeks they were housed in stalls and the 9 weeks they were kept in paddocks. Twenty-one weeks after surgery, horses were euthanatized. Joints with drill holes had a significantly greater area (P less than 0.05) of healthy fibrocartilage new tissue: group 1-33 to 68% new tissue, compared with 0 to 23% new tissue in controls; and group 2-22 to 64% new tissue, compared with 0 to 37% new tissue in controls. Differences between healing of defects with drill holes in groups 1 and 2 were not significant. Thickness of new tissue over drill holes was 33 to 61% of thickness of cartilage adjacent to the defect, and thickness of tissue between drill holes was 11 to 43% (group 1) and 8 to 79% (group 2) of the thickness of cartilage adjacent to the defect.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
997.
Effects of thermal stress and level of feed intake on portal plasma flow and net fluxes of metabolites in lactating Holstein cows 总被引:1,自引:0,他引:1
M A McGuire D K Beede M A DeLorenzo C J Wilcox G B Huntington C K Reynolds R J Collier 《Journal of animal science》1989,67(4):1050-1060
Six Holstein cows (averaging 475 kg body weight, 2.3 parities and 96 d in lactation) fitted with catheters in the hepatic portal vein, mesenteric vein and intercostalis posterior artery were exposed to treatments of thermal comfort environments with libitum or restricted (75% of ad libitum) DM intake and a thermal stress environment with ad libitum intake in two balanced 3 x 3 latin squares to evaluate effects of thermal stress on portal plasma flow and net fluxes of metabolites. Portal plasma flow was measured by administering a primed, continuous infusion of para-aminohippurate into a mesenteric vein and determining its concentration and dilution in portal vein plasma. Thermal stress treatment increased rectal temperatures and respiration rates. Dry matter intake decreased from thermal comfort ad libitum level (15.1 kg/d) to lower levels in thermal comfort restricted (11.5 kg/d) and thermal stress (11.1 kg/d) treatments. Portal plasma flow was related directly to level of DM intake, declining about 14% with thermal comfort restricted intake and thermal stress environment treatments compared with the thermal comfort restricted intake and thermal stress environment treatments compared with the thermal comfort ad libitum intake treatment. Net flux of alpha-amino N was reduced 20 and 35% by thermal comfort restricted intake and thermal stress treatments compared with the thermal comfort ad libitum intake treatment. Net fluxes of urea N, ammonia N and glucose were not affected by experimental treatments. A portion of the negative effects of thermal stress on milk production can be explained by decreased nutrient intake and decreased nutrient uptake by the portal-drained viscera of the cow. 相似文献
998.
O D Olaleye L A Oladosu S A Omilabu S S Baba A H Fagbami 《Revue d'élevage et de médecine vétérinaire des pays tropicaux》1989,42(3):321-325
Sixty-two sera horse collected from two stables at Lagos, Nigeria, were tested for complement fixing antibody to 8 arbovirus antigens; Chikungunya, Igbo-Ora, Yellow fever, Wesselsbron, West Nile, Potiskum, Uganda S and Rift Valley fever. Ten per cent of the horse sera examined contained CF antibody to one or more of the test antigens and indicated considerable arbovirus activity in the two stables. Reactions with flavivirus antigens were most common and the highest antibody titres were obtained with Wesselsbron and Yellow fever viruses. Eleven per cent of the sera tested reacted with alphavirus antigens while 10 per cent were positive for Rift Valley fever virus CF antibodies. 相似文献
999.
1000.
Zientara S Sailleau C Dauphin G Roquier C Rémond EM Lebreton F Hammoumi S Dubois E Agier C Merle G Bréard E 《The Veterinary record》2002,150(19):598-601
In October 2000, bluetongue virus was detected on the French island of Corsica. The disease was also reported in Sardinia, Calabria, Sicily and on the Spanish islands of Majorca and Minorca. This paper describes the use of molecular techniques for a rapid identification and serotype determination of serotype 2 of the virus. The nucleotide sequences of segments 2 and 7 of the genome of the Corsican strain were determined and its phylogenetic relationships are described. 相似文献