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   89390篇
  免费   4942篇
  国内免费   65篇
林业   3364篇
农学   2479篇
基础科学   613篇
  10466篇
综合类   15678篇
农作物   3337篇
水产渔业   4260篇
畜牧兽医   47684篇
园艺   1039篇
植物保护   5477篇
  2018年   1140篇
  2017年   1295篇
  2016年   1215篇
  2015年   1029篇
  2014年   1321篇
  2013年   3308篇
  2012年   2441篇
  2011年   3084篇
  2010年   1886篇
  2009年   1954篇
  2008年   2921篇
  2007年   2738篇
  2006年   2726篇
  2005年   2447篇
  2004年   2367篇
  2003年   2360篇
  2002年   2265篇
  2001年   2787篇
  2000年   2888篇
  1999年   2226篇
  1998年   880篇
  1997年   878篇
  1996年   857篇
  1995年   1060篇
  1994年   911篇
  1993年   884篇
  1992年   1973篇
  1991年   2127篇
  1990年   1973篇
  1989年   1985篇
  1988年   1866篇
  1987年   1966篇
  1986年   2003篇
  1985年   1912篇
  1984年   1511篇
  1983年   1342篇
  1982年   904篇
  1979年   1385篇
  1978年   1147篇
  1977年   998篇
  1976年   956篇
  1975年   998篇
  1974年   1302篇
  1973年   1327篇
  1972年   1263篇
  1971年   1160篇
  1970年   1106篇
  1969年   977篇
  1968年   839篇
  1967年   881篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Aminoglycoside nephrotoxicosis (AGNT) was induced in ewes by daily SC administration of gentamicin. Changes in urinary indices of renal function during the development of AGNT are reported. Measurements from timed, volume-measured urine samples were made on days 0, 7, and 8 and included creatinine clearance, total excretion (TE) rates of electrolytes (Na, K, Cl, P) and urine volume. Measurements from free-catch urine samples (without volume measurement) were made daily and included fractional excretion (FE) rate of electrolytes, urine osmolality, and urine-to-serum osmolality and urine-to-serum creatinine ratios. With the onset of AGNT, FE rates of Na, K, Cl, and P- increased many fold above baseline values (200x, 4 to 5x, 6 to 9x, and 70 to 95x, respectively, on days 7 and 8), indicating decreased tubular reabsorption or increased tubular secretion. The increased FE rates were not representative of increases in total electrolyte excretion rates. The total excretion of Na (TENa) was mildly increased, TEK was decreased, TECl was unchanged, and TEP was significantly increased on days 7 and 8. Abnormal urinalysis results, glucosuria, and increased FEP preceded appreciable increase in serum creatinine concentration. Other abnormal urinary indices of renal function coincided with or followed the increase in serum creatinine concentration. Urinary indices may help characterize renal function associated with the disease state, but did not provide early indication of AGNT.  相似文献   
992.
Three experiments were conducted to determine the effects of ethanol extraction and duration of heat treatment of soybean flakes on the utilization of soybean protein by growing rats and pigs. In the first experiment, the treatments were no extraction or extraction with a 55% ethanol-water mixture (v/v), and heat treatments of 0, 5, 10, 20 and 40 min in an autoclave. Ethanol extraction improved rate (P less than .002) and efficiency of gain (P less than .001) of rats. As heat treatment was increased from 0 to 20 min, rate of gain increased, but it decreased again as heating time was increased from 20 to 40 min (P less than .03). In Exp. 2 and 3, 45 pigs were used in a growth assay and 54 were used in a N balance experiment to determine the effects of ethanol extraction on under-, intermediate- and over-processed soybean flakes (i.e., 5, 20 and 60 min of autoclaving). The heat treatments were applied either without, before or after extraction with ethanol. Responses in rate and efficiency of gain to ethanol extraction were greater for soybean flakes heated for either 5 or 60 min than for the soybean flakes heated for 20 min. When pooled across heat treatment, pigs fed the soybean flakes heated before or after extraction with ethanol gained faster (P less than .001), had greater gain:feed (P less than .001) and lower plasma urea concentrations (P less than .002) than pigs fed soybean flakes heated without extraction. Feeding soybean flakes heated and extracted with ethanol also resulted in greater apparent N retention (P less than .003), apparent N digestibility (P less than .001) and apparent biological value (P less than .03) than soybean flakes that were heated without extraction. Ethanol extraction improved the protein quality of soybean flakes, especially when the flakes were under- or overprocessed with heat.  相似文献   
993.
Three hundred-fourteen domestic animals: 114 goats, 93 sheep, 67 dogs and 30 pigs in the Fontem sleeping sickness focus (Cameroon) were screened for infection with trypanosomes using parasitological and serological tests. Nannomonas was the only sub-genus detected in the animals with a prevalence of 28.3%. The card agglutination test (Testryp CATT) for trypanosomiasis showed a positivity rate of 38.2%, indicating that it allowed a better estimation of animal trypanosomiasis. The absence of trypanosomes of the sub-genus Trypanozoon seems to indicate that human African trypanosomiasis is not a zoonosis in this sleeping sickness focus.  相似文献   
994.
Four pregnant mink and seven pregnant ferrets, including five with previous exposure and specific antibody, were injected intravenously with 10(8)-10(10) colony-forming units of Campylobacter jejuni. All 11 pregnancies failed 1-16 days after infection, with results ranging from fetal resorption to expulsion of dead or premature living kits. In every case, uterine contents (placenta, uterine fluid and/or kits) were culture-positive for C. jejuni. Three pregnant mink and nine pregnant ferrets, including four with previous exposure and antibody, were fed 10(9)-10(11) C. jejuni. Two of the mink aborted; kits of all three were culture-positive, but those of one female survived. Seven of the nine ferrets aborted, with two having culture-positive uterine contents. None of 28 uninfected ferret control pregnancies ended in abortion. The most prominent histological feature observed was severe placentitis, which appears to be a more likely cause of Campylobacter-induced abortion than direct pathogenic effects on infected kits. These results suggest that infection of mink or ferrets with C. jejuni during pregnancy poses a serious risk of reproductive failure, even for previously exposed females.  相似文献   
995.
Five field trials evaluated whether immunization of beef cattle prior to weaning, at weaning, or immediately upon arrival at the feedlot with a commercial bovine respiratory syncytial virus (BRSV) vaccine would reduce subsequent treatment for respiratory disease.

Bovine respiratory syncytial virus vaccination was associated with a significant (p<0.05) reduction in treatment rate in one of three groups of calves immunized prior to weaning (−12%) and in calves immunized upon arrival at the feedlot (−4%).

There was no significant (p>0.05) effect of the BRSV vaccine on treatment rate in calves immunized at weaning, in calves immunized upon arrival at the Saskatoon bull test station, or in yearlings immunized upon arrival at the feedlot.

Although the trend in these field trials was to a sparing effect of the BRSV vaccine, the small reduction in treatment rate may not justify the cost of the vaccination program.

  相似文献   
996.
997.
Uremia unexpectedly developed in five dogs 24 hours after undergoing thoracotomy in a student laboratory. In all dogs general anesthesia had been maintained with methoxyflurane, muscle relaxation had been induced with gallamine, and each dog received a single intravenous dose of 1.0 mg/kg flunixin meglumine for analgesia upon termination of anesthesia. In a subsequent group of dogs undergoing an orthopedic procedure, we assessed the effects on renal function of methoxyflurane anesthesia plus oxymorphone, or of methoxyflurane or halothane anesthesia in combination with a single IM 1.0 mg/kg dose of flunixin meglumine. Significant elevations in serum urea and creatinine values, and necrosis of collecting ducts and loops of Henle, were noted only in the dogs receiving methoxyflurane and flunixin meglumine.

We conclude that the use of combination of methoxyflurane and flunixin meglumine is contraindicated in dogs.

  相似文献   
998.
Watery mouth was diagnosed as the cause of illness and subsequent death in a 3-day-old Romney lamb which had not received early colostrum. The history, clinical signs and post-mortem findings were typical of the disease as seen in other countries, including Great Britain. The diagnosis was based on the clinical signs and was supported by an absence of post-mortem findings of other specific neonatal diseases. The potential importance of watery mouth under conditions of intensive husbandry in New Zealand is discussed.  相似文献   
999.
1000.
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