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   14030篇
  免费   1091篇
  国内免费   71篇
林业   626篇
农学   822篇
基础科学   125篇
  1999篇
综合类   1666篇
农作物   496篇
水产渔业   1041篇
畜牧兽医   7022篇
园艺   228篇
植物保护   1167篇
  2023年   88篇
  2021年   88篇
  2020年   122篇
  2019年   201篇
  2018年   373篇
  2017年   345篇
  2016年   334篇
  2015年   306篇
  2014年   325篇
  2013年   569篇
  2012年   478篇
  2011年   568篇
  2010年   462篇
  2009年   420篇
  2008年   554篇
  2007年   577篇
  2006年   473篇
  2005年   521篇
  2004年   407篇
  2003年   446篇
  2002年   358篇
  2001年   759篇
  2000年   721篇
  1999年   592篇
  1998年   171篇
  1997年   164篇
  1996年   126篇
  1995年   150篇
  1994年   156篇
  1993年   120篇
  1992年   321篇
  1991年   346篇
  1990年   292篇
  1989年   266篇
  1988年   272篇
  1987年   319篇
  1986年   245篇
  1985年   193篇
  1984年   170篇
  1983年   147篇
  1982年   94篇
  1981年   83篇
  1980年   79篇
  1979年   141篇
  1978年   94篇
  1977年   73篇
  1975年   77篇
  1974年   79篇
  1973年   70篇
  1969年   70篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
The Canadian Cooperative Wildlife Health Centre (CCWHC) was established in 1992 as an organization among Canada's 4 veterinary colleges, with a mandate to apply veterinary medicine to wildlife management and conservation in Canada. A major function of the CCWHC is nation-wide surveillance of wild animal diseases. Disease surveillance is conceived as consisting of 4 different activities: detection, diagnosis, information management, and use of information. In the CCWHC surveillance program, detection of disease is carried out by a wide range of professional and avocational field personnel, and much effort is expended to stimulate and support this activity. Diagnosis is done by personnel of provincial and federal veterinary laboratories and the CCWHC. Information management is achieved through a national database of wildlife disease incidents developed and maintained by the CCWHC. Use of information is enabled through established channels for distribution of information derived from the surveillance program to persons responsible for wildlife programs and policies, and to the public. There has been a high demand for the services of the CCWHC since its establishment. The CCWHC responds to approximately 2000 requests for information annually, distributes its newsletter to over 1700 recipients, examines approximately 1200 wild animal submissions each year, and has accumulated records of over 5000 disease incidents in its database. Technical information from the CCWHC has benefited federal, provincial/territorial, and nongovernment wildlife agencies; endangered species recovery programs; federal and provincial veterinary services; and federal and provincial public health programs.  相似文献   
982.
Propionate utilisation by the liver in spontaneously ketotic dairy cows was investigated by determining blood glucose levels after an intravenous sodium propionate load (2.5 mmol kg-1). In addition, blood ketone body concentrations were measured after propionate loading. Cows were divided into three groups (control, mildly ketotic and severely ketotic) by their blood acetoacetate concentrations. Plasma glucose concentrations increased significantly after sodium propionate injection in all three groups (P less than 0.05). The maximum glucose concentration occurred earlier in the control group than in the ketotic groups. Changes in glucose concentrations following propionate loading of control and ketotic cows differed significantly at 20 minutes and beyond. Differences in the change in glucose concentration between mildly ketotic and severely ketotic cows were not significant. Acetoacetate concentration was significantly decreased at five minutes and beyond after the injection in ketotic cows, whereas beta-hydroxybutyrate concentration decreased more slowly. A decrease in beta-hydroxybutyrate concentration was significant at 40 minutes and beyond in the severely ketotic group and at 10 minutes and beyond in the mildly ketotic group after loading.  相似文献   
983.
984.
985.
986.
In 1988 and 1989 bacterial diseases of potatoes in Central Anatolia were investigated by utilizing the EC method for the detection of ring-rot bacterium (Clavibacter michiganensis ssp. sepedonicus) and using selective medium. 91 samples containing 200 tubers from commercial and farmers’ stores in Central Anatolia were tested for the presence of C.m.sepedonicus and about 50 tubers of each sample were also tested for the presence of soft-rot erwinias. Five different bacteria that cross-reacted with C.m.spedonicus antisera were isolated from heel-end extracts. All cross-reacted bacteria differed from C.m.sepedonicus morphologically and none of them was pathogenic on eggplant. C.m. sepedonicus was not detected, but Erwinia carotouora ssp. carotouora and Erwinia carotovora ssp. atroseptica were present in 7 and 17% of the samples respectively.  相似文献   
987.
The role of peripheral blood mononuclear cell (PBMC) in Theileria sergenti-infected calves was studied by various in vitro assay systems. Proliferation of T cells in mixed lymphocyte protozoa culture (MLPC) increased with parasitemia, and the addition of monoclonal antibodies against T. sergenti merozoites in this MLPC enhanced the response. However, the addition of antibody-positive autologous serum resulted in the suppression of the response. Cell-mediated cytotoxicity of PBMC increased after peak parasitemia. This cytotoxicity increased on co-cultivation of PBMC with T. sergenti merozoites, but the addition of autologous serum suppressed the response.  相似文献   
988.
The prevalence of enzootic bovine leukosis (EBL) in Turkey was investigated by serological screenings using the agargel immunodiffusion test (AGID). A total of 4,047 blood samples obtained from 2,780 cattle between one and 14 years of age and taken in 6-8 month-intervals in three dairy farms were tested for the presence of EBL-specific antibodies. A high prevalence of EBL-sero-positive animals was found amongst cattle in two of the farms. Furthermore, recommendations based upon the regulation implemented by an expert group of the European Commission and considering the local dairy management conditions were presented.  相似文献   
989.
Within a German-Turkish university partnership documentation of reproductive data of brood-mares was performed as a part project of the cooperation contract. In the study Arab, Haflinger and cross-breed mares were included. The mares mainly were housed in big studfarms and a smaller part was kept under small private farms. Almost three quarters of both the Arab and Haflinger mares exhibited an estrous length of 1-4 days, whereas the others showed a heat duration of a period of 5-10 days. In the same group of probands a mean length of sexual cycle of 18-24 days could be observed in 38.2% of the Haflinger. The majority of the other mares in both races documented a cycle duration of more than 25 days. The remarkable short duration of heat is discussed as caused by the sharp change from winter to spring environment conditions in that area. An explanation of the marked long mean cycle interval is difficult and might be caused by inadequate documentation of the data. Conception results and foaling data as 83.4% resp. 78.8% in the Arabs and 76.6% resp. 74.8% in the Haflinger mares are within the international standard. Conception rate and foaling data in the cross-breed (72.3% resp. 55.3%) are low compared with data (96.9% 70.8%) of Arab brood-mares kept under stud condition in that area. These data point out the necessity of improving pre- and postconceptional care of the mares under stud conditions as well as in private keeping.  相似文献   
990.
Two hundred fifty-two steers (366 kg) were assigned to a 3 x 2 x 2 factorial arrangement of three densities of steam-flaked sorghum grain (bulk [flake] density of 437, 360, and 283 g/liter, B34, B28, and B22, respectively), two roughage levels (9 [R9] and 18% [R18]) and two feeding strategies (ad libitum [AD] or multiple of maintenance [MM], 2.3, 2.5, and 2.7 MM for wk 1, 2, and 3, and 2.9 MM thereafter). Steers fed R18-AD gained faster than steers fed R18-MM (1.59 vs 1.52 kg/d, P = .10); for R9 diets, no difference (P greater than .25) was found between steers fed AD and MM (interaction, P = .07). Flake density did not affect ADG (1.53 kg, P greater than .2). Dry matter intake decreased (9.8, 9.3, and 9.0 kg/d, linear, P less than .001) and gain efficiency (G/DMI, kg of gain/100 kg of DMI) increased (15.7, 16.5, and 16.9, linear, P less than .001; quadratic, P = .19) as processing degree increased (B34 to B22). Percentage of choice carcasses for B34 (67.0%) was higher (linear, P = .05) than for B28 (51.9%) and B22 (52.3%). Fecal starch and pH were 10.8, 5.7, and 4.0%, and 6.11, 6.23, and 6.37 for B34, B28, and B22, respectively (linear, P less than .001). The correlation between fecal starch and pH was -.51 (P less than .001, n = 252). Enzymatic glucose release, in vitro 6-h gas production, microbial protein synthesis, and protein degradability were 375, 483, and 559 mg/g; 24.7, 28.2, and 31.1 ml/.2 g; 6.15, 6.88, and 7.84 g/100g; and 61.4, 56.6, and 42.2% for B34, B28, and B22, respectively (linear, P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)  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