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   76042篇
  免费   4284篇
  国内免费   251篇
林业   3531篇
农学   2938篇
基础科学   539篇
  9644篇
综合类   12211篇
农作物   2987篇
水产渔业   4020篇
畜牧兽医   38444篇
园艺   1024篇
植物保护   5239篇
  2019年   675篇
  2018年   1178篇
  2017年   1287篇
  2016年   1208篇
  2015年   1031篇
  2014年   1294篇
  2013年   2863篇
  2012年   2326篇
  2011年   2753篇
  2010年   1917篇
  2009年   1969篇
  2008年   2872篇
  2007年   2630篇
  2006年   2542篇
  2005年   2345篇
  2004年   2384篇
  2003年   2430篇
  2002年   2352篇
  2001年   2664篇
  2000年   2543篇
  1999年   2056篇
  1998年   955篇
  1997年   860篇
  1996年   818篇
  1995年   898篇
  1994年   884篇
  1993年   801篇
  1992年   1557篇
  1991年   1582篇
  1990年   1704篇
  1989年   1542篇
  1988年   1472篇
  1987年   1371篇
  1986年   1410篇
  1985年   1362篇
  1984年   1174篇
  1983年   1051篇
  1982年   649篇
  1979年   1029篇
  1978年   817篇
  1977年   740篇
  1976年   695篇
  1975年   741篇
  1974年   795篇
  1973年   849篇
  1972年   828篇
  1971年   779篇
  1970年   741篇
  1969年   760篇
  1967年   670篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Wild ring-tailed lemurs (Lemur catta) can be anesthetized with Telazol via blow dart, but improved techniques are needed so that each lemur is reliably induced with a single dart. Medetomidine-butorphanol (MB) is a good supplemental protocol to be administered once the lemurs are captured, but other protocols may provide longer periods of sedation and immobility. One possible way of increasing the efficacy of each dart is to increase the time it is retained in the leg. In this investigation, a "double-sleeve" technique was used to try to increase the time of dart retention. This technique used a standard silicone sleeve on the needle, along with a second sleeve at the needle hub. Induction values were compared between lemurs darted with double-sleeve needles and those induced with needles that each had a single silicone sleeve. Once the lemurs were induced, supplementation with MB (0.04 mg/kg and 0.2 mg/kg) was compared with supplementation with ketamine-medetomidine (KM) (10 mg/ kg and 0.04 mg/kg). Twenty-three lemurs were darted with Telazol by using single-sleeve needles, and 24 were darted with double-sleeve needles. The number of darts per lemur and number of escapes were not different between animals darted with a single sleeve compared with a double-sleeve; thus, there were no significant improvements in induction success with the double-sleeve technique. Adequate sedation and muscle relaxation were achieved with both MB and KM; however, lemurs that received MB were more relaxed and needed fewer additional supplements that those that received KM. Single-sleeve dart needles are recommended for Telazol induction of ring-tailed lemurs via blow dart and MB is preferable to KM for supplemental sedation and muscle relaxation.  相似文献   
993.
994.
Although one study showed lower adiponectin concentrations in obese dogs, other recent studies indicate that adiponectin might not be decreased in obese dogs, raising the possibility that the physiology of adiponectin is different in dogs than in humans. The aim of this study was to investigate possible causes of the discrepancy between the two largest studies to date that assessed the association between adiposity and adiponectin concentration in dogs, including the validity of the assay, laboratory error, and the effects of breed, sex, and neuter status on the relationship between adiposity and adiponectin concentrations. Adiponectin concentrations measured with a previously validated adiponectin ELISA were compared with those estimated by Western blotting analysis of reduced and denatured plasma samples. The possibility of laboratory error and the effect of EDTA anticoagulant and aprotinin were tested. Adiponectin concentration was measured by ELISA in 20 lean dogs (10 male and 10 female, 5 neutered in each sex). There was close correlation between adiponectin concentrations measured by ELISA and those estimated by Western blotting analysis (r = 0.90; P < 0.001). There was no substantial effect of EDTA, aprotinin, or laboratory error on the results. There was confounding by neuter status of the relationship between adiposity and adiponectin concentrations, but adiponectin concentrations were not significantly lower in male than in female lean dogs (females, 36 mg/L; males, 26 mg/L; P > 0.20) and were not significantly lower in intact than in neutered lean male dogs (intact, 28 mg/L; neutered, 23 mg/L; P = 0.49). We conclude that the adiponectin ELISA previously validated for use in dogs appears to be suitable for determination of canine adiponectin concentrations and that testosterone does not appear to have a strong effect on plasma adiponectin concentrations in dogs. Obesity might decrease adiponectin concentrations in intact but not in neutered dogs.  相似文献   
995.
A 4 yr old intact male rat terrier presented with severe bilateral nonresponsive panuveitis. Bilateral uveitis, blepharospasm, conjunctival hyperemia, diffuse corneal edema, peripheral bullous retinal detachment, and secondary ocular hypertension were noted. Ocular lesions progressed despite aggressive medical treatment and were followed by cutaneous depigmentation and crusting along the nasal planum. Intensive oral and topical anti-inflammatory and topical antiglaucoma medications were administered, but the ocular disease progressed. A bilateral enucleation was performed. Uveodermatologic syndrome was diagnosed from histopathologic examination of a skin biopsy as well as histopathology of both globes after bilateral enucleation. To maintain control of the dermatologic lesions, oral azathioprine was initiated, but it was not well tolerated by this patient. Immunosuppressive doses of oral cyclosporine and anti-inflammatory doses of oral prednisone were used to control the depigmentation and crusting skin lesions.  相似文献   
996.
家禽肠道螺旋体病Avain Intestinal spirochaetosis,AIS)被普遍认为是家禽生产中一个越来越严重的疾病。本病由多种螺旋体引起。螺旋体为一类外形呈螺旋状的细菌,它们主要定殖在大多数哺乳动物和家禽(包括猪、人类和家禽)的大肠中。  相似文献   
997.
Bilateral testicular haemorrhage was detected in a 5-year-old Bleu du Maine ram in an abattoir survey of male reproductive tracts in sheep; the ultrasonographic and histologic features of the lesions are described.  相似文献   
998.
Volatile agent-induced hypotension may contribute to anaesthetic-related morbidity and mortality in horses. Dobutamine is commonly used to support arterial blood pressure (ABP) but little is known about its cardiovascular effects under clinical conditions. The aim of this clinical study was to elucidate the relationship between cardiovascular function and dobutamine infusion in isoflurane-anaesthetized horses. Forty-four horses anaesthetized for a variety of surgical procedures were studied. Premedication with acepromazine, methadone and detomidine was followed by induction of anaesthesia with ketamine and midazolam. Anaesthesia was maintained with isoflurane vaporized in oxygen. Routine anaesthetic monitoring was applied and cardiac output was measured by lithium dilution. Dobutamine was infused to maintain mean ABP above 70 mmHg. The relationship between dobutamine infusion rate, heart rate (HR), ABP and cardiac index was investigated immediately prior to ( T 0) and 15 min ( T 1) after dobutamine infusion started, followed at 30 min intervals ( T 2, etc.). Arterial blood pressure increased significantly after dobutamine infusion started, HR and cardiac index increased significantly only with dobutamine infusion in combination with surgical stimulus. Although isoflurane decreases blood pressure mainly by vasodilation, dobutamine is an effective treatment for hypotension under clinical conditions in isoflurane-anaesthetized horses. The effect of dobutamine is not directly proportional to dose and surgical stimulus probably contributes to the cardiovascular improvement.  相似文献   
999.
The aim of this study was to evaluate the histopathological features in tissues of mice infected by human isolates (I, II, and III) or the reference M2903 strain of Leishmania braziliensis complex. BALB/c and C57Bl/6 mice were infected in the hind footpad with 106 stationary-phase promastigotes of L. braziliensis complex. The evolution of lesions was observed for 10 weeks and the animals were then euthanized and liver, spleen and popliteal lymph nodes were collected. Tissues were stained with hematoxylin and eosin and analyzed by immunohistochemistry assay. Increased thickness of infected footpads was observed in all animals, lesions were nodular and non-ulcerated. Mice infected with isolate I presented inflammatory infiltrates consisting predominantly of mononuclear cells in all tissues examined, and also a great number of megakaryocytes, compared with other isolates. Infection with isolate II led to an infected footpad enlargement not seen in other isolates. In addition, mononuclear infiltrates in the liver and hemosiderin in spleen were noted. Conversely, mice infected with either isolate III or M2903 strain only showed an increased number of megakaryocytes in spleen. All tissues examined had detectable amastigote forms of Leishmania by immunohistochemistry in all groups. Taking together, our results showed an unforeseen behavior of different isolates of L. braziliensis complex that led to diverse pathological findings.  相似文献   
1000.
Two oligodendrogliomas in two domestic cats involved mainly the rostral brain stem, midbrain, fourth ventricle, and cerebellum. Both cats were aged neutered males presenting with clinical neurologic deficits suggestive of a brain stem lesion. Magnetic resonance imaging of both tumors demonstrated lesions with a pattern of heterogeneous contrast enhancement and multifocal lesions in one cat. Routine cerebrospinal fluid analysis was normal in one cat and suggestive of an inflammatory disease in the other. Oligodendroglioma cells were seen in cytospin preparations of cerebrospinal fluid from both cats. In each cat, the tumors occurred intraventricularly in the midbrain and fourth ventricle with aggressive intraparenchymal infiltration. There was extensive growth into the basilar subarachnoid space of the midbrain and brain stem in one cat. One tumor was well differentiated, and the other was an anaplastic subtype. Immunostaining for several myelin- and oligodendroglia-specific antigens was negative with formalin-fixed tumors and with unfixed frozen samples from one cat. In both tumors, component cells of the intratumoral vascular proliferations were positive for human von Willebrand factor VIII antigen or smooth muscle actin. Immunocytochemical reactivity for glial fibrillary acidic protein identified both reactive astrocytes and a subpopulation of minigemistocytes in both tumors. Ultrastructurally, the tumor cells were unremarkable except for their prominent desmosomal junctions and paucity of microtubules.  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