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   83641篇
  免费   4687篇
  国内免费   56篇
林业   2908篇
农学   2279篇
基础科学   564篇
  9185篇
综合类   14867篇
农作物   3081篇
水产渔业   3896篇
畜牧兽医   45666篇
园艺   880篇
植物保护   5058篇
  2018年   1032篇
  2017年   1170篇
  2016年   1084篇
  2015年   935篇
  2014年   1172篇
  2013年   3051篇
  2012年   2119篇
  2011年   2696篇
  2010年   1648篇
  2009年   1754篇
  2008年   2587篇
  2007年   2403篇
  2006年   2403篇
  2005年   2126篇
  2004年   2088篇
  2003年   2077篇
  2002年   1969篇
  2001年   2700篇
  2000年   2806篇
  1999年   2131篇
  1998年   813篇
  1997年   825篇
  1996年   807篇
  1995年   1017篇
  1994年   888篇
  1993年   841篇
  1992年   1930篇
  1991年   2080篇
  1990年   1923篇
  1989年   1934篇
  1988年   1824篇
  1987年   1929篇
  1986年   1975篇
  1985年   1872篇
  1984年   1481篇
  1983年   1299篇
  1982年   880篇
  1979年   1366篇
  1978年   1122篇
  1977年   973篇
  1976年   937篇
  1975年   983篇
  1974年   1272篇
  1973年   1298篇
  1972年   1234篇
  1971年   1147篇
  1970年   1088篇
  1969年   964篇
  1968年   832篇
  1967年   869篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Virucidal efficacy of four new disinfectants   总被引:5,自引:0,他引:5  
Virucidal efficacy was evaluated for four recently available disinfectants: chlorine dioxide, potassium peroxymonosulfate, a quaternary ammonium compound, and citricidal (grapefruit extract). Sodium hypochlorite (3%) and tap water were used as positive and negative controls respectively. Feline herpesvirus, feline calicivirus, and feline parvovirus were exposed to the manufacturers' recommended dilutions of the evaluated disinfectants. Both chlorine dioxide and potassium peroxymonosulfate completely inactivated the three viruses used in this study. These disinfectants can aid in controlling nosocomial transmission of viruses with less of the deleterious effects of sodium hypochlorite. The quaternary ammonium compound evaluated in this study and citricidal were not effective against feline calicivirus and feline parvovirus.  相似文献   
992.
A 13-day-old foal with profound tachypnoea and respiratory distress was examined. Thoracic radiographs revealed a severe, diffuse miliary pattern, and the foal was markedly hypoxaemic. It failed to improve with empirical treatment, and was euthanased. Lesions associated with Coccidioides immitis infection were identified at postmortem examination, and were limited to the lower respiratory tract.  相似文献   
993.
994.
Steers (379 +/- 10 kg) with ruminal, duodenal, and ileal cannulas were used in a 5 x 5 Latin square digestion trial to quantify and evaluate the relationship between intestinal protein supply and intestinal starch disappearance. Treatments were infusions of 0, 50, 100, 150, or 200 g/d of casein along with 1,042 g/d of raw cornstarch. Abomasal infusions were accomplished by passing tubing and a pliable retaining washer through the reticular-omasal orifice into the abomasum. Steers were fed a 93% corn silage, 7% supplement diet that contained 12% crude protein at 1.65% body weight in 12 equal portions/d. Periods lasted 17 d (12 d for adaptation, 2 d of collections, and 3 d of rest). The quantity and percentage of organic matter and protein disappearance from the small intestine increased linearly (P < 0.03) with infused casein. Greater quantities of starch disappeared with increased casein infusion (P < 0.01). The infusion of 200 g/d of casein increased small intestinal starch disappearance by 226 g/d over the control. Casein infusion did not affect the quantity or percent of organic matter, starch, or protein disappearance in the large intestine. Treatments did not change ruminal ammonia N, ruminal pH, or plasma glucose concentrations. Starch disappearance from the small intestine was increased with greater protein flow to the duodenum of steers.  相似文献   
995.
996.
The primary objective of this study was to determine the pharmacokinetic profile of firocoxib, a novel second generation coxib, in horses. Horses were administered either a single oral or intravenous dose of firocoxib at 0.1 mg/kg in a two-period crossover study with 12 animals. The dosage was based on previously determined pharmacodynamic parameters. Oral firocoxib was well absorbed with an average bioavailability (absolute) of 79% and a Cmax of 75 ng/mL at 3.9 h. The average elimination half-life was 30 h. Following intravenous administration the average Cmax was 210 ng/mL and the elimination half-life was 34 h. The area under the curve [AUC(0-tlast)] was 1.8 microg.h/mL for the oral dose and 2.3 microg.h/mL for the intravenous dose. Firocoxib was widely distributed with a volume of distribution value of 1.7 L/kg for the intravenous dose. Biotransformation of firocoxib was via dealkylation and glucuronidation to inactive metabolites, namely descyclopropylmethylfirocoxib and its glucuronide conjugate. Urinary excretion was the major route of elimination, and the clearance rate was 37 mL/h/kg.  相似文献   
997.
Two hundred and twelve dog cadavers belonging to different breeds were examined, to investigate the formation of the femoral, obturator and the sciatic nerve. Besides the commonly described formation patterns of the mentioned nerves, some variations were also found. These variations were not gender-related, but on the other hand we discovered a certain correlation between the variations appearing in the formation of the femoral, obturator and the sciatic nerve. In 74.05% of cases, the femoral nerve was formed from ventral branches of the 4th, 5th and 6th lumbar nerve, and 16.98% of the dogs had the nerve formed from ventral branches of the 3rd, 4th and 5th lumbar nerve. Many dogs (i.e. 2.30%) had the femoral nerve formed from the ventral branches of the 5th, 6th and 7th, the 3rd, 4th, 5th and 6th or the 4th, 5th, 6th and 7th lumbar nerve, respectively. In 1.88% of dogs in particular, the femoral nerve was formed from ventral rami of the 4th and 5th lumbar nerve. In 66.98% of the examined dogs, the obturator nerve was formed from the ventral branches of the 4th, 5th and 6th lumbar nerve, followed by 16.59% of the dogs with the obturator nerve formed from the ventral rami of the 4th and 5th lumbar nerve and 9.43% of dogs in which the nerve was formed from the ventral branches of the 5th and 6th lumbar nerve. In 4.71% of dogs, the obturator nerve was formed from the ventral rami of the 4th, 5th, 6th and 7th lumbar nerve, while only 2.30% of the examined dogs had the same nerve formed from the ventral branches of the 5th, 6th and 7th lumbar nerve. The sciatic nerve was formed from ventral branches of the 6th and 7th lumbar nerve and the 1st sacral nerve in 86.79% of the dogs. In 5.18% of cases, the same nerve was formed from a junction of the ventral branches of the 7th lumbar and the 1st and 2nd sacral nerve, and, in the same percentage of cases, it was formed from a junction of ventral branches of the 6th and 7th lumbar nerve and the 1st and 2nd sacral nerve. In 2.83% of the dogs, it was formed from a junction of the ventral branches of the 6th and 7th lumbar and the 1st sacral nerve. The correlation of variations established in the formation of the femoral, obturator and the sciatic nerve was not statistically significant.  相似文献   
998.
Seventeen cutaneous and oral tumours with light microscopic features of plasmacytomas from 16 dogs were studied. Clinically, most neoplasms were benign, although three recurred after excision and three were locally invasive. Tumours most often arose on the pinnae, digits, gingiva, and inguinal regions near areas of chronic inflammation and exhibited variable degrees of plasmacytic differentiation microscopically. Diagnosis of plasmacytoma was confirmed in paraffin-embedded tissues with a panel of leukocyte differentiation antigen markers that included cross-reactive antibodies for Mb-1 (CD79a), CD3, and vimentin and canine-specific antibodies for CD45RA and CD18. Immunoreactivity for Mb-1 and CD45RA, including staining of multinucleate cells and cells with karyomegaly, confirmed a B-cell origin of neoplasms, while staining for CD3 and CD18 revealed an extensive network of infiltrative T-cells and dendritic cells in tumours suggestive of a directed immune response. These findings (i) demonstrate the value of using a panel of antibodies for leukocyte antigens to differentiate plasmacytomas from other cutaneous and oral round cell tumours, and (ii) suggest that immune recognition and responsiveness within tumours may play a role in the behaviour of plasmacytomas in dogs by affecting tumour cell growth and differentiation.  相似文献   
999.
A study to determine the secretion of Mycobacterium spp. in milk from indigenous cattle was carried out in pastoral cattle reared in the Southern Highlands of Tanzania. The study was aimed at elucidating the dangers associated with milk-borne zoonoses in a society where milk is normally consumed raw. Out of 805 milk samples, 31 (3.9%) were positive for mycobacteria. There was a preponderance of atypical mycobacteria (87%) whereas only two isolates (6.5%) were confirmed as M. bovis. Atypical mycobacteria included: M. terrae (n=7), M. fortuitum (n=2), M. flavescens (n=13), M. gordonae (n=1) and M. smegmatis (n=4). Although the number of M. bovis positive samples was low, the habit of pooling milk may still pose great public health dangers to milk consumers in this part of the world. Moreover, isolation of atypical mycobacteria should also be considered to be a danger to human health in countries such as Tanzania, where the number of people with lowered immunity due to HIV infection is on the increase.  相似文献   
1000.
The study was conducted in a peri-urban agricultural system at Botshabelo, a city in the south-eastern Free State. A questionnaire survey revealed that 88.5% of cattle farmers in the area experienced problems related to ticks and tick-borne diseases. Because of the cost of commercial acaricides the Botshabelo farmers use alternative, cheaper methods of tick control, including the application of used engine oil. The specific aim of the study was to determine whether used engine oil can effectively control ticks on cattle. From March to August 1996 the tick burdens of ten control animals and six animals treated by their owner with used engine oil were compared. The total tick burdens for the 6 month period differed significantly between the two experimental groups. The efficacy of the used engine oil on the treated group varied between 15.1% and 64.8% with a mean of 38.1%. Although commercial acaricides can be more cost-effective, the application of used engine oil can be useful to reduce tick numbers on cattle during periods of peak abundance. Another advantage in that the use of the oil will not influence existing endemic stability of Anaplasma marginale and Babesia bigemina infections because of the residual tick burdens after treatment.  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