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   304514篇
  免费   17241篇
  国内免费   2384篇
林业   25482篇
农学   16032篇
基础科学   4167篇
  47469篇
综合类   41285篇
农作物   18131篇
水产渔业   18041篇
畜牧兽医   120673篇
园艺   7042篇
植物保护   25817篇
  2021年   3231篇
  2020年   3453篇
  2019年   4225篇
  2018年   4582篇
  2017年   5232篇
  2016年   5418篇
  2015年   5066篇
  2014年   6402篇
  2013年   17146篇
  2012年   8526篇
  2011年   10735篇
  2010年   8820篇
  2009年   9143篇
  2008年   9654篇
  2007年   8888篇
  2006年   9199篇
  2005年   8478篇
  2004年   7828篇
  2003年   7630篇
  2002年   6893篇
  2001年   7655篇
  2000年   7318篇
  1999年   6545篇
  1998年   4490篇
  1997年   4469篇
  1996年   4227篇
  1995年   4756篇
  1994年   4185篇
  1993年   3893篇
  1992年   5237篇
  1991年   5456篇
  1990年   5158篇
  1989年   5126篇
  1988年   4601篇
  1987年   4678篇
  1986年   4711篇
  1985年   4762篇
  1984年   4338篇
  1983年   4017篇
  1982年   3199篇
  1981年   3081篇
  1980年   3006篇
  1979年   3743篇
  1978年   3319篇
  1977年   3003篇
  1976年   2891篇
  1974年   3155篇
  1973年   3088篇
  1972年   2828篇
  1971年   2783篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
43.
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   
44.
45.
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   
46.
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   
47.
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   
48.
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   
49.
Five studies were performed to determine factors affecting progesterone concentration in skim milk. Results of the first study indicated that progesterone concentration was higher in skim milk of samples kept 16 hours in an ice bath (0 C) than of those left at room temperature (21 C). In the second study, this temperature effect was found to be reversible, with skim milk progesterone concentration increasing when whole milk samples were cooled prior to centrifugation. In the third study, [3H]-labeled progesterone was used to determine the relationship between fat content of foremilk (the first milk obtained from the teats), midmilk (milk obtained midway through milking), and strippings (milk obtained immediately after milking machines have been removed) samples and temperature (4 C and 21 C) on the percentage of progesterone in the skim milk fraction. The relationship between percentage of butterfat and percentage of progesterone in skim milk was linear when the log of these variables was used for calculations. In the fourth study, assayable progesterone in the skim milk fraction of foremilk, midmilk, and strippings was affected by temperature. In the fifth study, a multiple-regression procedure was used to determine the amount of variation in percentage of radioactive progesterone in the skim milk fraction. Independent variables (whole milk butterfat and temperature of incubation [1, 3, 13, 22, 37, and 50 C]) and the natural log of each variable, were entered into a stepwise multiple-regression analysis.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
50.
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