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   375391篇
  免费   19482篇
  国内免费   709篇
林业   25802篇
农学   14529篇
基础科学   3033篇
  51308篇
综合类   61356篇
农作物   18010篇
水产渔业   19754篇
畜牧兽医   167266篇
园艺   6794篇
植物保护   27730篇
  2019年   3872篇
  2018年   4893篇
  2017年   5355篇
  2016年   5477篇
  2015年   4751篇
  2014年   6155篇
  2013年   16930篇
  2012年   9688篇
  2011年   12421篇
  2010年   8904篇
  2009年   9125篇
  2008年   11635篇
  2007年   11037篇
  2006年   11068篇
  2005年   10279篇
  2004年   10108篇
  2003年   9905篇
  2002年   9171篇
  2001年   10551篇
  2000年   10139篇
  1999年   8578篇
  1998年   4616篇
  1997年   4633篇
  1996年   4367篇
  1995年   5058篇
  1994年   4549篇
  1993年   4278篇
  1992年   7052篇
  1991年   7336篇
  1990年   7237篇
  1989年   7323篇
  1988年   6607篇
  1987年   6755篇
  1986年   6782篇
  1985年   6711篇
  1984年   5829篇
  1983年   5349篇
  1982年   3981篇
  1981年   3766篇
  1979年   5196篇
  1978年   4415篇
  1977年   3958篇
  1976年   3713篇
  1975年   3726篇
  1974年   4488篇
  1973年   4557篇
  1972年   4323篇
  1971年   4063篇
  1970年   3948篇
  1969年   3674篇
排序方式: 共有10000条查询结果,搜索用时 601 毫秒
31.
32.
In a feeding trial lasting for months Halothane-positive fattening pigs were put on a diet containing different concentrations of vitamin E and selenium. After a Myostress application vitamin E and selenium were additionally injected in order to examine stress resistance (CK-test) and regenerative capacity (histological examination of Musculus longissimus dorsi) of skeletal muscle. The study revealed that neither high dietary levels of vitamin E/selenium nor a vitamin E/selenium treatment applied after stress are capable of preventing stress related myopathy nor can they influence its healing up favourably.  相似文献   
33.
Epidermal growth factor (EGF)-like activity was measured in mares' colostrum and milk by radioreceptor assay. Milk samples were collected from 22 mares 1 or more times during early lactation. Samples of colostrum were taken after parturition and before the foal first suckled (presuckle), within 6 hours after the foal first suckled (postsuckle), and on days 1, 2, 4, and 8 of lactation. In the 5 mares from which milk samples were obtained at each sampling time, presuckle colostral mean EGF-like activity (17.8 ng/ml) was greatest (P less than 0.05). The mean values for EGF-like activity at all other sampling times were not significantly different from each other (postsuckle colostrum, 9.7 ng/ml; day 1, 9.6 ng/ml; day 2, 8.5 ng/ml; day 4, 8.0 ng/ml; day 8, 7.8 ng/ml).  相似文献   
34.
The aerobic bacterial flora of the genital tract was characterized in 15 stud dogs in an 18-month study. The dogs represented 4 breeds and were from 3 kennels. Bacterial samples from the prepuce and semen were collected every month, except in connection with matings, when they were collected weekly (464 samples). The dogs that were included all mated at least once during the study. The mean pregnancy rate, litter size, and pup mortality for the bitches with which they had mated were all within normal limits. The most frequent bacteria isolated from the prepuce and semen were Pasteurella multocida, beta-hemolytic streptococci, and Escherichia coli. There was a tendency for breeds to differ in frequency of the most common bacterial species. Bacterial culture yielded no aerobic growth in 14.2% of the preputial samples and 69.8% of the semen samples. Bacteria were transferred between dog and bitch at mating. In this study of healthy breeding dogs, neither the fertility of the dog nor that of the bitch was affected by the bacteria transferred.  相似文献   
35.
In 11 dogs with nasal adenocarcinoma, IV treatment with 2 to 8 cycles of cisplatin at a dosage of 60 mg/m2 of body surface, given at 3-week intervals, resulted in a survival time of 8 to 128 weeks (mean, 32.7 weeks; median, 20 weeks). Radiography revealed complete remission in 2 dogs and partial remission in 1 dog, for an overall response rate of 27%. Clinical problems such as nasal discharge (n = 11), sneezing (n = 6), and epistaxis (n = 4) resolved in 1 to 2 weeks in all dogs after beginning chemotherapy.  相似文献   
36.
Immune system dysfunction and immunoglobulin deficiency was diagnosed in a 2-year-old horse with disseminated lymphosarcoma. Prolonged (35 days) parenteral nutrition was delivered to support the horse during a period in which immune function studies could be performed. Correction of nutritional compromise by use of parenteral nutrition did not correct the immunoglobulin deficiency, and results of lymphocyte phenotype testing did not indicate abnormal proportions of leukocytes. Lymphoblast transformation studies were suggestive of a circulating immunosuppressive factor in the horse's serum. Normal cell function was detected when the cells were stimulated in precolostral equine serum.  相似文献   
37.
The influence of extruded oilseeds on total tract digestibility and ruminal digestion in dairy cows was studied in three cows fed a hay-concentrate (60.5/39.5; 3.7% fatty acids in diet on DM basis) control diet (C) or the same diet supplemented with raw (R) or extruded (ER) rapeseeds (8.0% fatty acids in diet DM). The experimental design was a 3 x 3 Latin square design. Compared with diet C, diets containing rapeseed decreased ruminal OM digestibility (9.5%, P less than .10) and increased (P less than .05) the proportion of propionate in ruminal fluid VFA. Extrusion had no effect on DM and OM total tract digestibilities and increased (P less than .10) N digestion. Microbial N flow at the duodenum was calculated taking into account solid-adherent bacteria (SAB) and liquid-associated bacteria (LAB). Duodenal flows of total, SAB, and LAB of OM and N did not change with diet. Extrusion of the rapeseeds did not modify (P less than .10) the proportion of bacterial N at the duodenum and had no effect on crude fiber digestibility. This trial demonstrates that rapeseeds in hay-based diets can be fed at levels of up to 14% of the diet without adversely affecting crude fiber digestibility.  相似文献   
38.
Lamb carcasses (n = 278) were selected immediately after slaughter and fat thickness was measured with the SP2 Hennessy grading probe (HP) at the interface of the 12th and 13th ribs, 3.8 cm from the backbone. After a 24-h chilling period, carcasses were graded by a USDA grader and probed with the HP to obtain a fat thickness measure on the chilled carcass. One hundred sixty-five carcasses were fabricated into wholesale cuts (.64 cm of external fat trim), and 113 carcasses were fabricated into tray-ready retail cuts (.25 cm of external fat trim). Carcass weight, fat thickness (metal probe), adjusted fat thickness, hot and chilled carcass HP fat measures, as well as kidney and pelvic fat percentage and USDA yield grade, were highly correlated to cutting yield for both fabrication methods. Regression models developed to predict wholesale cut yields using HP or grader-collected measures were similar with respect to predictive accuracy. Fat thickness explained most of the variation in wholesale and tray-ready cut yields among the variables collected by the grader. Kidney and pelvic fat accounted for more of the variation in yield of wholesale cuts during stepwise regression to determine HP equations, but for predicting tray-ready yields, fat thickness taken with the HP accounted for the largest amount of variation. Equations developed to predict tray-ready retail cut yields using the HP or USDA grader-collected carcass measures were similar in the amount of variation explained. Kidney and pelvic fat percentage must be included in equations to maximize predictive accuracy when this depot site is left in carcasses.  相似文献   
39.
Osteomyelitis caused by Cryptococcus neoformans was diagnosed in a three-year-old male Irish wolfhound. The case details and radiological findings of radiolucency and periosteal reaction of the left third metatarsal bone had lead to an initial diagnosis of a malignant bone tumour. Biopsy revealed a fungal granuloma and culture identified the causal organism. A four month course of ketaconazole was instigated and the lameness resolved. Twelve months after the end of treatment there was no recurrence of the problem.  相似文献   
40.
Findings are presented on the precision of a clinical biochemistry analyser designed specifically for veterinary use. Twenty biochemical analytes have been examined in detail for variation within and between runs. The results indicate that the analyser can provide high precision for all the analytes with the possible exception of calcium, and suggest that the instrument can be used with confidence in the practice laboratory to aid diagnosis and to monitor biochemical changes in animals receiving 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