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   70905篇
  免费   3965篇
  国内免费   34篇
林业   3229篇
农学   2529篇
基础科学   477篇
  8702篇
综合类   11428篇
农作物   2607篇
水产渔业   3643篇
畜牧兽医   36615篇
园艺   909篇
植物保护   4765篇
  2018年   1053篇
  2017年   1129篇
  2016年   1057篇
  2015年   907篇
  2014年   1137篇
  2013年   2631篇
  2012年   2060篇
  2011年   2464篇
  2010年   1684篇
  2009年   1751篇
  2008年   2597篇
  2007年   2363篇
  2006年   2329篇
  2005年   2124篇
  2004年   2194篇
  2003年   2168篇
  2002年   2038篇
  2001年   2366篇
  2000年   2376篇
  1999年   1925篇
  1998年   912篇
  1997年   824篇
  1996年   783篇
  1995年   862篇
  1994年   843篇
  1993年   768篇
  1992年   1523篇
  1991年   1543篇
  1990年   1662篇
  1989年   1507篇
  1988年   1450篇
  1987年   1342篇
  1986年   1384篇
  1985年   1336篇
  1984年   1128篇
  1983年   1025篇
  1982年   628篇
  1979年   1004篇
  1978年   795篇
  1977年   717篇
  1976年   676篇
  1975年   719篇
  1974年   767篇
  1973年   830篇
  1972年   803篇
  1971年   748篇
  1970年   730篇
  1969年   744篇
  1967年   658篇
  1966年   631篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
191.
The effects of subcutaneous administration of a commercially available estradiol 17 beta implant on hematologic values and the chemiluminescence response of neutrophils were evaluated in 14 steers. Chemiluminescence and hematologic values were measured in treated (n = 8) and nontreated (n = 6) steers on days -14, -7, and -1 prior to implantation. Estradiol 17B was implanted into the treated group of steers on day 0, and blood samples were obtained from all steers on days 1, 2, 3, 4, 8, 15, 22, 29, 36, 43, and 50. The concentration of estrogen in serum was significantly (P = 0.0120) higher following implantation. Chemiluminescence and hematologic indices were not significantly affected by either implant status or serum concentrations of estrogen. The results of this study suggested that the use of implants containing estradiol 17 beta for promotion of weight gain in steers will not result in alterations of hematologic values or the neutrophil respiratory burst.  相似文献   
192.
A 14-month-old Arabian colt was admitted for treatment of an articular fracture of the supraglenoid tubercle of the right forelimb. Successful repair was achieved by use of three 5.5-mm cortical screws placed in lag fashion across the fracture line. In other reports of supraglenoid tubercle fractures in horses, investigators have preferred conservative management or surgical removal of the fragment, because of limited success with internal fixation. Use of three 5.5-mm screws placed in lag fashion may offer an alternative method of treatment in selected cases of supraglenoid tubercle fractures.  相似文献   
193.
Properties of threshold model predictions   总被引:4,自引:0,他引:4  
Estimation of genetic parameters and accuracy of threshold model genetic predictions were investigated. Data were simulated for different population structures by using Monte Carlo techniques. Variance components were estimated by using threshold models and linear sire models applied to untransformed data, logarithmically transformed data, and transformation to Snell scores. Effects of number of categories (2, 5, and 10), incidence of categories (extreme, moderate, and normal), heritability in the underlying scale (.04, .20, and .50), and data structure (unbalanced and balanced) on accuracy of genetic prediction were investigated. The real importance of using a threshold model was to estimate genetic parameters. An expected heritability of .20 was estimated to be .22 and .10 by a threshold model and a linear model, respectively. Accuracy increased significantly with a larger number of categories, a more normal distribution of incidences, increased heritability, and more balanced data. Even threshold models were shown to be more efficient with more than two categories (e.g., binomial). Transformation of scale did not accomplish the purpose intended.  相似文献   
194.
195.
Some biochemical indices in naturally occurring fascioliasis in goats   总被引:2,自引:0,他引:2  
Some biochemical indices were assayed in goats naturally harbouring Fasciola gigantica infection and compared with uninfected control goats. Infected goats had significantly lower levels of serum glucose (47.6 +/- 1.8 mg dl-1) and albumin (3.1 +/- 0.1 g dl-1) and reduced albumin:globulin ratio (1.1 +/- 0.1). Total lipid (526.8 +/- 2.4 mg dl-1), serum glutamate dehydrogenase (15.3 +/- 0.9 iu litre-1) and serum alkaline phosphatase (31.6 +/- 1.9 Kind's and King's unit dl-1) were high in infected goats. No significant changes could be recorded in serum total protein, cholesterol and phospholipids.  相似文献   
196.
Forty-two Beagles, 14 to 15 weeks of age, were injected subcutaneously with 50 infective larvae of Dirofilaria immitis and were allotted by weight, within sex, to 6 treatment groups. Group 1 served as nonmedicated vehicle-treated controls; groups 2 through 5 were given an oral tablet form of ivermectin at dosages of 0.3 micrograms/kg, 1.0 micrograms/kg, 2.0 micrograms/kg, and 3.3 micrograms/kg at 30 days after inoculation; group 6 was given the 2.0 micrograms/kg dosage at 45 days after inoculation. Dogs were euthanatized and necropsied 154 days after treatment (day 139 for dogs in group 6) and examined for heartworms. On the numerical bases of helminths recovered in the groups, the efficacies for preventing heartworm maturation were 0% (group 2), 53.2% (group 3), 97.2% (group 4), 98.1% (group 5), and 63.8% (group 6). Drug-related adverse reactions were not detected.  相似文献   
197.
198.
Cellular morphology of Clostridium spiroforme   总被引:1,自引:0,他引:1  
The helically-coiled bacterium, Clostridium spiroforme, has been shown to consist of an ordered aggregation of numerous individual semi-circular cells joined end to end.  相似文献   
199.
A manual, ultrasound-guided biopsy technique was compared to a new automatic method using a new biopsy device. The liver and the left kidney of 10 dogs were biopsied using the two methods. The specimens from the biopsies were compared for size and quality. Results demonstrate that larger and higher quality samples were obtained with the new automatic method.  相似文献   
200.
The importance of the adrenergic nervous system in supporting the failing heart has long been known. The adrenergic drive on cardiac structure and function has however some adverse effects, which include myocardial beta-adrenoceptor (beta-AR) downregulation and decreased beta-adrenergic responsiveness to cathecolamines. In dog lymphocytes, beta(1)-AR and beta(2)-AR populations are almost equally represented (with a slight prevalence of beta(2)) and a significant correlation between cardiac and lymphocytic adrenoceptors has been found. The aim of the present study was to investigate possible differences between the concentration of lymphocytic beta-AR in healthy dogs, dogs with dilated cardiomyopathy (DCM) and dogs with occult DCM. Three groups of great danes were considered: a control group (n =10), dogs with DCM (n =9) and dogs with occult DCM (n =4). Lymphocytic beta-AR populations were determined in all dogs. A substantial and significant decrease (P<0.05) in total-AR, beta(1)-AR and beta(2)-AR concentrations in the lymphocytes of dogs with symptomatic DCM and occult DCM compared to the control group was found. Although the mean value of the lymphocyte beta(1)-AR number in the asymptomatic group was double compared to the DCM group, this difference was not statistically significant. We conclude that in dogs beta-AR downregulation occurs early in the course of dilated cardiomyopathy. This finding may suggest the value of early use of a beta-blocker in the therapeutic regimen. Moreover, the continuous monitoring of lymphocytic beta-AR may represent a useful tool for the development of a more effective individual therapy.  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