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   1247篇
  免费   71篇
  国内免费   1篇
林业   27篇
农学   24篇
基础科学   2篇
  76篇
综合类   280篇
农作物   42篇
水产渔业   43篇
畜牧兽医   759篇
园艺   12篇
植物保护   54篇
  2021年   15篇
  2020年   11篇
  2019年   14篇
  2018年   18篇
  2017年   12篇
  2016年   13篇
  2015年   18篇
  2014年   20篇
  2013年   31篇
  2012年   54篇
  2011年   58篇
  2010年   22篇
  2009年   26篇
  2008年   49篇
  2007年   54篇
  2006年   28篇
  2005年   31篇
  2004年   33篇
  2003年   33篇
  2002年   44篇
  2001年   33篇
  2000年   47篇
  1999年   40篇
  1997年   10篇
  1996年   17篇
  1992年   17篇
  1991年   21篇
  1990年   32篇
  1989年   29篇
  1988年   15篇
  1987年   22篇
  1986年   22篇
  1985年   22篇
  1984年   21篇
  1983年   20篇
  1982年   11篇
  1981年   10篇
  1980年   10篇
  1979年   12篇
  1978年   14篇
  1977年   12篇
  1976年   9篇
  1975年   12篇
  1974年   25篇
  1973年   18篇
  1972年   26篇
  1971年   15篇
  1970年   16篇
  1969年   10篇
  1966年   11篇
排序方式: 共有1319条查询结果,搜索用时 31 毫秒
41.
Arthrodesis of the right stifle was performed in a 21 kg German shepherd dog that had sustained a comminuted fracture of the lateral femoral condyle as a result of a gunshot wound. The arthrodesis was stabilised with a circular external skeletal fixator. A simplified technique to facilitate creation of the osteotomies of the femur and tibia, and positioning of the stifle at the desired angle, is described. Compression of the subchondral bone surfaces of the distal femur and proximal tibia was achieved using tensioned coiled transarticular Kirschner wires. Arthrodesis of the stifle was confirmed radiographically 21 weeks following surgery, and the fixator was removed. After union of the arthrodesis and removal of the fixator, the dog was fully weightbearing when standing or walking, and intermittently weightbearing or non-weightbearing at faster gaits.  相似文献   
42.
The efficacy of 5 drugs was tested against experimental Babesia felis infection in domestic cats. Two of the drugs, rifampicin and a sulphadiazine-trimethoprim combination, appeared to have an anti-parasitic effect, but were inferior to primaquine. The other 3 drugs, buparvaquone, enrofloxacin and danofloxacin, had no significant anti-babesial effect.  相似文献   
43.
44.
Highly comminuted supracondylar humeral fractures were stabilised in six large-breed dogs with a modified type I external fixator using a craniomedial acrylic connecting column and an Intramedullary pin which was incorporated into the connecting frame. This construct provided sufficient stability to allow satisfactory bone healing in five of the six dogs, while premature removal of the intramedullary pin and external fixator resulted in subsequent refracture of the humerus in the remaining dog. Limb function at the time of final assessment was considered excellent in two dogs, good in three dogs and poor in one dog. The craniomedial acrylic connecting column simplified application of this modified type 1(a) configuration to the humerus by reducing the number of clamps required; the acrylic column also facilitated contouring of the cranlomedial connecting column to the brachium and was readily extended proxlmally to engage the intramedullary pin. In addition, the acrylic connecting column allowed placement of intramedullary pins of varying diameter.  相似文献   
45.
46.
A study was conducted to determine the persistence of antibiotic preparations for use in nonlactating cows in bovine mammary secretions following intramammary infusion at cessation of milking. Five commercially available antibiotic formulations were evaluated using 311 cows. All quarters of each cow were sampled once only during the nonlactating period and most cows were sampled at or near parturition. Antibiotic residues were detected qualitatively by the Bacillus stearothermophilus disc assay. Great variation between different antibiotics in persistence in mammary secretion was observed. In general, mammary secretions from most mammary glands infused with cloxacillin or penicillin-dihydrostreptomycin were positive at 28–35 days after infusion and some were positive at 42–49 days after infusion. On the other hand, <13% of mammary secretions at 7 days after infusion of novobiocin and 50% of mammary secretions at 14 days after infusion of penicillin-novobiocin were positive for antibiotics. Cephapirin benzathine persisted for about 21 days after infusion. Some samples that were positive for antibiotics after initial testing were negative following heating of samples, suggesting that component(s) of dry secretion can inhibit growth of B. stearothermophilus and influence the interpretation of results. Colostrum samples from all quarters except one were negative for antibiotics. These data suggest that nonlactating-cow antibiotic formulations persist primarily during the early to mid-nonlactating period. Based upon present methods of formulation, it would appear that antibiotic preparations for use in nonlactating cows most likely provide little protection during the periparturient period, at a time when mammary glands are highly susceptible to new intramammary infections.  相似文献   
47.
Three experiments were conducted to determine the effects of ethanol extraction and duration of heat treatment of soybean flakes on the utilization of soybean protein by growing rats and pigs. In the first experiment, the treatments were no extraction or extraction with a 55% ethanol-water mixture (v/v), and heat treatments of 0, 5, 10, 20 and 40 min in an autoclave. Ethanol extraction improved rate (P less than .002) and efficiency of gain (P less than .001) of rats. As heat treatment was increased from 0 to 20 min, rate of gain increased, but it decreased again as heating time was increased from 20 to 40 min (P less than .03). In Exp. 2 and 3, 45 pigs were used in a growth assay and 54 were used in a N balance experiment to determine the effects of ethanol extraction on under-, intermediate- and over-processed soybean flakes (i.e., 5, 20 and 60 min of autoclaving). The heat treatments were applied either without, before or after extraction with ethanol. Responses in rate and efficiency of gain to ethanol extraction were greater for soybean flakes heated for either 5 or 60 min than for the soybean flakes heated for 20 min. When pooled across heat treatment, pigs fed the soybean flakes heated before or after extraction with ethanol gained faster (P less than .001), had greater gain:feed (P less than .001) and lower plasma urea concentrations (P less than .002) than pigs fed soybean flakes heated without extraction. Feeding soybean flakes heated and extracted with ethanol also resulted in greater apparent N retention (P less than .003), apparent N digestibility (P less than .001) and apparent biological value (P less than .03) than soybean flakes that were heated without extraction. Ethanol extraction improved the protein quality of soybean flakes, especially when the flakes were under- or overprocessed with heat.  相似文献   
48.
A retrospective study of banked sera from 19 cats with the eosinophilic granuloma complex revealed that 68% of affected cats had circulating antibodies to components of normal cat epithelium. Seemingly, the eosinophilic granuloma complex of cats may be an autoimmune disease; however, epidermal damage caused by the eosinophilic granuloma complex may release altered self-antigens to which the cat's immune system responds.  相似文献   
49.
The effects of source of energy and energy restriction during lactation on sow and litter performance were investigated in an experiment with 90 primiparous sows. At parturition, the sows were randomly assigned to diets containing either tallow or cornstarch as a major energy source. Energy intake was restricted to 8 Mcal of metabolizable energy X sow-1 X d-1 during a 28-d lactation. All sows received equal amounts of crude protein, vitamins and minerals daily, which met or exceeded standard recommendations. Sows fed the diet with tallow lost more weight (P less than .05) during lactation than those fed the diet with cornstarch. Litter size at d 28 was greater (P less than .07) for sows fed cornstarch than for sows fed tallow. However, pig and litter weights on d 14 and 28 of lactation were similar between dietary treatments. Sows were bled on d 110 of gestation and d 14 and 28 of lactation and blood plasma was analyzed for urea. A significant treatment X time interaction was found for plasma urea. Sows fed the diet with tallow appeared to catabolize more protein than those fed the diet with cornstarch. Energy digestibility was lower (P less than .01) in the diet containing tallow, but protein digestibility was not affected by source of energy. Percentages of sows in estrus by 7, 14 and 70 d post-weaning were not different between treatments.  相似文献   
50.
Two experiments were conducted with ewes 9 to 11 days after estrus to determine whether the secretion of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) are controlled differentially. In experiment 1, gonadotropin-releasing hormone (GnRH) was injected (100 (μg/ewe) at time = 0 min into ewes in four treatment groups. The treatment groups (9 ewes/group) were: 1) periodic iv sodium pentobarbital (NaPen) vehicle from 0 min; 2) periodic iv NaPen from 0 min; 3) vehicle iv for 120 min then iv NaPen from 120 min; 4) vehicle iv for 150 min then iv NaPen from 150 min. A surgical plane of anesthesia was maintained from the initiation of NaPen injection until the experiment ended. Jugular blood was sampled at 30-min intervals from ?30 to + 210 min for LH and FSH assays, and profiles of hormone concentrations were compared by time-trend analyses. GnRH released LH (P<.001) and FSH (P<.001), but NaPen did not affect the profiles of hormone concentrations; this indicated that NaPen did not reduce the ability of the pituitary to secrete gonadotropins in response to GnRH. Experiment 2 was a 2x2 factorial with ovariectomy (time = 0 hr) and NaPen as the main effects. One group of ovariectomized (n = 6) and one group of sham ovariectomized (n = 6) ewes were anesthetized only during surgery, while a group of ovariectomized (n = 7) and a group of sham ovariectomized (n = 6) ewes were kept at a surgical plane of anesthesia until 10 hr after surgery. Patterns of LH and FSH were compared in jugular blood collected hourly from 0 hr until 10 hr after surgery and in samples collected at 24 hr intervals from -24 to +72 hr of surgery. After ovariectomy, LH increased (P<.001) hourly and daily, but anesthesia suppressed (hourly, <.001 and daily, P<.005) these increases, which resulted in an interaction (hourly, P<.001 and daily, P<.01) of ovariectomy and anesthesia. FSH after ovariectomy increased hourly and daily (hourly, P<.02 and daily, P<.001), but the effect of anesthesia and interaction of ovariectomy and anesthesia were not significant. Because NaPen did not alter secretion of LH or FSH after exogenous GnRH in experiment 1 while it blocked the postovariectomy increase in LH but not FSH in experiment 2, we concluded that the postovariectomy increase in LH resulted from increased hypothalamic secretion of GnRH. The mechanisms responsible for the postovariectomy increase in FSH secretion are not identical to those for LH. The mechanisms that control the postovariectomy secretion of FSH might involve factors that are not suppressible by NaPen or, alternatively, the differences in LH and FSH release after ovariectomy might reflect the removal of ovarian factors that suppress FSH but not LH secretion in intact ewes.  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