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   11087篇
  免费   876篇
  国内免费   4篇
林业   987篇
农学   443篇
基础科学   89篇
  2912篇
综合类   300篇
农作物   567篇
水产渔业   1223篇
畜牧兽医   4281篇
园艺   187篇
植物保护   978篇
  2024年   16篇
  2023年   97篇
  2022年   155篇
  2021年   309篇
  2020年   305篇
  2019年   280篇
  2018年   565篇
  2017年   577篇
  2016年   574篇
  2015年   425篇
  2014年   496篇
  2013年   712篇
  2012年   867篇
  2011年   803篇
  2010年   468篇
  2009年   377篇
  2008年   623篇
  2007年   623篇
  2006年   507篇
  2005年   487篇
  2004年   414篇
  2003年   367篇
  2002年   308篇
  2001年   227篇
  2000年   229篇
  1999年   187篇
  1998年   34篇
  1997年   48篇
  1996年   31篇
  1995年   26篇
  1994年   19篇
  1993年   20篇
  1992年   62篇
  1991年   47篇
  1990年   46篇
  1989年   56篇
  1988年   38篇
  1987年   40篇
  1986年   46篇
  1985年   53篇
  1984年   37篇
  1983年   35篇
  1982年   19篇
  1979年   31篇
  1978年   32篇
  1977年   28篇
  1974年   26篇
  1973年   45篇
  1972年   30篇
  1971年   26篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
991.
In 1990 three experiments were performed in heifers 184 to 505 day-old with the weight 190 to 390 kg to test some biotechnical methods while studying the level of reproduction functions. Heifers were examined in 4 to 24-hour intervals by direct observations of animal behaviour, by clinical and gynaecological examinations of larger animals. The progesterone concentration in the peripheral blood was determined by the RIA method and simultaneously with the blood samplings, the values of impedance of vaginal mucosa were measured by means of several types of the Estral device (CSFR) for cattle. To detect the functional responses to prostaglandins administered, the following forms of substances were used: racemic mixture of optically active forms D (+) and L (-) in the Czechoslovak preparation Oestrophan inj. Spofa (0.25 mg of cloprostenol in 1 ml of solution) and the dextrorotatory D isomer--cloprostenol (0.075 mg in 1 ml of solution) in the Czechoslovak preparation Remophan inj. Spofa. Evaluating the results of the group 1 based on clinical and ethological examinations, the values of impedance of vaginal mucosa and progesterone levels (Tab. I), the functional maturity of sexual organs in heifers were determined. No significant differences were found while compared the luteolytic effects between D-cloprostenol in the Remophan preparation and the conventional mixture of optically active forms of Oestrophan. All methods used confirm the functional maturity of sexual organs (including a response to prostaglandin analogues administered) in heifers 11-12 month old. The values of impedance of vaginal mucosa varied during oestrus in some heifers and this fact is to be taken into account in practice.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
992.
993.
Epizootic of wild water birds caused by the toxin Clostridium botulinum of C type occurred in extensive shallow artificial lakes of the Nové Mlyny dam system from May to October 1988 and later on from February to early April 1989. In total more than 3,000 dead or dying birds of 44 species were found, the following orders were prevailing: Anseriformes (56%), Lariformes (33%), Charadriiformes (6%) and Ralliformes (4%). Botulotoxin was detected at high concentrations in sarcophagic fly larvae of Calliphora vomitoria and Lucilia sericata which were collected in bird cadavers, but it was not found in different components of the aquatic environment (water, submersed vegetation, phytoplankton, zooplankton, Gastropoda, Crustacea, Oligochaeta, larvae of Odonata, Chironomidae and Ceratopogonidae). Future development of the epizootic situation in the Nové Mlyny artificial lakes will depend on the water level and meterological conditions in the critical period (May to September).  相似文献   
994.
51 gnotobiotic and 63 conventional, one-, or two-days-old piglets were divided into five groups and infected orally either with Isospora suis or rotavirus alone, or with both agents simultaneously or successively with alternative sequences and various intervals. 15 gnotobiotic and 10 conventional piglets served as controls. The development of small intestinal lesions after infection with I. suis was biphasic. The dominant alteration resulting from rotavirus infection was villus atrophy, considerably more pronounced and extensive in gnotobiotic than in conventional piglets. Synergistic action of I. suis and rotavirus was manifested both clinically, and morphologically. This action culminated at the time of the actual, or presumed development of merogony of I. suis, i.e. on DPI 3 to 5. The action develops only if the intestinal epithelium is damaged functionally and morphologically by a preceding rotavirus infection. It is concluded that the synergistic action is based on a competition of rotavirus and I. suis for mature, enzymatically active absorptive cells.  相似文献   
995.
Non‐steroidal anti‐inflammatory drugs may potentiate the opioid induced reduction in volatile anaesthetic requirements ( Gomez de Segura et al. 1998 ). This study determined the reduction in the MAC of isoflurane (ISO) produced by ketoprofen (KETO) in dogs anaesthetized with fentanyl (FENT) and ISO. Six healthy female crossbred dogs, weighing 13.5 ± 1.3 (mean ± SD) kg and aged 3.0 ± 0.9 years were studied. Approval of the study was obtained from the institutional ethics committee. Anaesthesia was induced in all dogs via a facemask with 5% ISO in 5 L minute?1 oxygen. The dogs' trachea were intubated and lungs were ventilated to maintain normocapnia (Pe ′CO2 4.7–6 kPa, 35–45 mm Hg). A heating pad was used to maintain body temperature. The animals were anaesthetized four times at one week intervals with the following anaesthetic and analgesic protocols randomly administered. Study 1, MAC (ISO); Isoflurane MAC. Study 2, MAC (ISO + FENT); dogs anaesthetized with ISO received a loading dose of 30 µg kg?1 FENT IV over 20 minutes followed by a maintenance infusion of 0.2 µg kg?1 minute?1 FENT. Study 3, MAC (ISO + FENT + KETO1); as study 2 plus 1 mg kg?1 KETO. Study 4, MAC (ISO + FENT + KETO2); as study 2 plus 2 mg kg?1 KETO. The MAC was determined in duplicate by applying a standard electrical stimulus (50 V, 50 H2 over 60 seconds via two needles placed SC over the tarsus). The stimulus was applied 15 minutes after every step change in anesthetic concentration. The Wilcoxon test was applied to data to determine significant differences among MAC measurements. Fentanyl significantly decreased MAC (ISO) from 1.27% ± 0.02% to 0.73% ± 0.08%, a reduction of 42% (p < 0.05). Ketoprofen 1 mg kg?1 further decreased the MAC value (although not statistically significantly) with a reduction of 47% from MAC (ISO) (0.67% ± 0.13%) and 8% from MAC (ISO + FENT). When KETO 2 mg kg?1 was given, the reduction in MAC was 50% compared to MAC (ISO) (0.63% ± 0.08%; p < 0.05) and 14% compared to MAC (ISO + FENT) p < 0.05. Administration of KETO further reduces MAC (ISO) compared to levels observed with FENT alone. The observed reduction may have clinical advantages.  相似文献   
996.
A 17-mo-old captive-born female red panda (Ailurus fulgens fulgens) presented with a sudden onset of lameness in its left hind leg was diagnosed radiographically as having possible severe, bilateral Legg-Calve-Perthes disease with fracture of the great trochanter of the left femur. Surgical repair of the fracture was performed using pins and a tension band wire through a lateral approach to the hip. This is the first case reported at Madrid Zoo-Aquarium, where 63 individuals have been bred over 15 yr.  相似文献   
997.
Febantel at a dose level of 5 mg kg-1 had a lethal efficacy of 54.1% against the adult worm and 69.5% against the migrating larvae of Trichinella spiralis in rats. When administered at 15 mg kg-1, it demonstrated lethal effects of 94.4, 92.5 and 74.7% against adult, young and encysted larvae, respectively. Infected rats treated with 300 mg kg-1 died. Thiabendazole had efficiencies of 96.4 and 83.3% against intestinal and migrating early muscle phases, respectively, and was 42% effective against the encysting phase.  相似文献   
998.
999.
The dynamics of hematological, protein, mineral and electrolytic profile was examined clinically in nine calves when the hemoconcentration was induced experimentally. The hemoconcentration occurred after diarrhea caused by the per os application of 12 g saccharose per one kg of live weight. The hemoconcentration culminated six hours after application. The calves where the hemoconcentration did not exceed the critical value were included in the first group, and the calves with the extreme hemoconcentration values in the other group. In the first group (with the increasing hemoconcentration degree), a statistically significant increase was found in the values of hematocrit, erythrocytes, hemoglobin, total protein in blood serum and total immunoglobins and a statistically insignificant increase in the levels of leucocytes, inorganic phosphorus, serum calcium and sodium. Serum potassium and magnesium showed the inverse dynamics, i. e. the decrease. In the second group (with the extreme hemoconcentration), hyperkalemia and slight hypermagnesemia were identified, while the other parameters showed deviations similar to those observed in the first group. After the rehydration of animals by a preparation without any influence on the studied parameters, the hemoconcentration and the parameters under study stabilized, while in the second group the hemoconcentration was increasing even during the rehydration and the levels of serum potassium and magnesium showed different tendencies. As follows from the results, in the calves suffering from scours accompanied by hemoconcentration the correction of the parameters of metabolic profile is necessary.  相似文献   
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