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   2592篇
  免费   147篇
  国内免费   4篇
林业   74篇
农学   62篇
基础科学   14篇
  279篇
综合类   456篇
农作物   79篇
水产渔业   95篇
畜牧兽医   1517篇
园艺   40篇
植物保护   127篇
  2021年   20篇
  2020年   32篇
  2019年   35篇
  2018年   41篇
  2017年   39篇
  2016年   42篇
  2015年   26篇
  2014年   51篇
  2013年   99篇
  2012年   107篇
  2011年   95篇
  2010年   67篇
  2009年   75篇
  2008年   116篇
  2007年   106篇
  2006年   94篇
  2005年   96篇
  2004年   96篇
  2003年   101篇
  2002年   89篇
  2001年   82篇
  2000年   67篇
  1999年   63篇
  1998年   29篇
  1997年   21篇
  1996年   19篇
  1995年   19篇
  1993年   25篇
  1992年   59篇
  1991年   58篇
  1990年   53篇
  1989年   31篇
  1988年   54篇
  1987年   43篇
  1986年   54篇
  1985年   53篇
  1984年   33篇
  1983年   29篇
  1979年   34篇
  1978年   17篇
  1977年   19篇
  1976年   25篇
  1975年   22篇
  1974年   18篇
  1973年   34篇
  1972年   22篇
  1971年   20篇
  1970年   17篇
  1969年   24篇
  1967年   17篇
排序方式: 共有2743条查询结果,搜索用时 15 毫秒
61.
62.
63.
64.
Single-fiber electromyography (SFEMG), a technique used to investigate neuromuscular transmission, has been described previously in the pelvic limb of dogs. Because preferential involvement of isolated muscle groups can occur in disorders of neuromuscular transmission, SFEMG was done in the peroneus longus (PL), extensor carpi radialis (ECR), and orbicularis oculi (OO) muscles of 10 adult, clinically normal dogs. Jitter was calculated as the mean absolute value of the consecutive differences in latency of 50 single muscle fiber action potentials after stimulation of intramuscular nerve bundles at the level of the motor point in at least 20 muscle fibers per muscle. Bilateral recordings were performed in 3 dogs. Mean jitter values were determined for each muscle, and differences among muscle groups and among dogs were compared. The upper limits of mean consecutive difference (mean plus 3 standard deviations) for the PL, ECR, and OO muscles were 21.94, 22.53, and 23.39 micros, respectively, and the upper limit of mean consecutive difference for individual muscle fibers in the respective fiber pools was 28.62, 36.39, and 35.68 micros. Jitter values for the ECR and OO were significantly higher than the jitter value for the PL muscle (P < .05). Significant differences among muscles or dogs or between sides were not observed for the ECR. Significant differences among dogs were observed for OO jitter values and were attributed to extremely low jitter values in 1 dog. Significant differences were demonstrated between sides for the PL and were attributed to small sample size. Results of this study provide normative data that can be used in the application of the stimulated SFEMG technique to dogs with suspected disorders of neuromuscular transmission.  相似文献   
65.
An 18-month-old domestic short-haired neutered male cat presented with a nodular dermal thickening on a digit. Biopsy demonstrated pyogranulomatous inflammation with moderately frequent acid-fast bacilli. A member of theMycobacterium terrae complex was isolated. There was no evidence of systemic involvement. Treatment was initiated with enrofloxacin, rifampicin and clarithromycin. After 2 months there was no longer any clinically apparent dermal thickening. Treatment was continued for a further 3 months using enrofloxacin and rifampicin.  相似文献   
66.
67.
OBJECTIVE: To characterize the signalment, clinical signs, biological behavior, and response to treatment of carcinoma of the apocrine glands of the anal sac in dogs. DESIGN: Retrospective study. ANIMALS: 113 dogs with histologically confirmed carcinoma of the apocrine glands of the anal sac. PROCEDURE: Data on signalment, clinical signs, and staging were reviewed and analyzed along with treatment modality for potential association with survival time. RESULTS: Sex distribution was approximately equal (54% female, 46% male). One hundred four dogs underwent treatment consisting of surgery, radiation therapy, chemotherapy, or multimodal treatment. Median survival for treated dogs was 544 days (range, 0 to 1,873 days). Dogs treated with chemotherapy alone had significantly shorter survival (median, 212 days) than those receiving other treatments (median, 584 days). Dogs not treated with surgery had significantly shorter survival (median, 402 days) than those that underwent surgery as part of their treatment (median, 548 days). Dogs with tumors > or = 10 cm2 had significantly shorter survival (median, 292 days) than dogs with tumors < 10 cm2 (median, 584 days). Hypercalcemia was identified in 27% (n = 29) of dogs, and those dogs had significantly shorter survival (median, 256 days), compared with those that were normocalcemic (median, 584 days). Dogs with pulmonary metastasis had significantly shorter survival (median, 219 days) than dogs without evidence of pulmonary metastasis (median, 548 days). CONCLUSIONS AND CLINICAL RELEVANCE: Unlike most previous reports, this study revealed an approximately equal sex distribution, and results suggest a more favorable prognosis.  相似文献   
68.
OBJECTIVE: To develop and validate an ELISA for measurement of serum canine pepsinogen A (cPG A) as a diagnostic marker of gastric disorders in dogs and to measure serum cPG A in healthy dogs after food deprivation and after feeding. SAMPLE POPULATION: Sera from 72 healthy dogs. PROCEDURE: A sandwich ELISA was developed and validated. The reference range for serum concentrations of cPG A was determined in 64 healthy dogs. Postprandial changes in serum concentrations of cPG A were evaluated in 8 healthy dogs. RESULTS: Assay sensitivity was 18 microg/L, and the maximum detectable concentration was 1,080 microg/L. The observed-to-expected ratio (O:E) for 3 serial dilutions of 3 serum samples ranged from 69.3 to 104.1%. The O:E for 3 serum samples spiked with 8 concentrations of cPG A ranged from 58.8 to 120.4%. Coefficients of variation for intra- and interassay variability of 3 serum samples ranged from 7.6 to 11.9% and from 10.1 to 13.1%, respectively. Mean +/- SD serum concentration of cPG A in healthy dogs was 63.8 +/- 31.0 microg/L and the reference range was 18 to 129 microg/L. Significant increases in serum concentrations of cPG A were observed between 1 and 7 hours after feeding. CONCLUSIONS AND CLINICAL RELEVANCE: The ELISA for measuring cPG A was sufficiently sensitive, linear, accurate, precise, and reproducible for clinical use. Serum concentrations of cPG A increase substantially after feeding, which should be taken into account when conducting clinical studies.  相似文献   
69.
The association between genetic marker alleles was estimated for two regions of the bovine genome from a random sample of 50 young dairy bulls born in the United Kingdom between 1988 and 1995. Microsatellite marker genotypes were obtained for six markers on chromosome 2 and seven markers on chromosome 6, spanning 38 and 20 cM, respectively. Two different methods, which do not require family information, were used to estimate population haplotype frequencies. Haplotype frequencies were estimated for pairs of loci using the expectation-maximization algorithm and for all linked loci using a Bayesian approach via a Markov chain-Monte Carlo algorithm. Significant (P = 0.0007) linkage disequilibrium was detected between pairs of loci in syntenic groups (that is, loci in the same linkage group), extending to about 10 cM. No significant linkage disequilibrium was detected between markers in nonsyntenic regions. Given the observed level of linkage disequilibrium, mapping methods based on population-wide association might provide a better resolution than traditional quantitative trait loci mapping methods in the U.K. dairy cattle population and may reduce the required sample sizes of the experiments.  相似文献   
70.
Models to predict heat production attributable to maintenance and support metabolism in growing and mature cattle were developed on the basis of three concepts. The first concept is that animals fed fixed amounts of the same diet achieve weight equilibrium over an extended feeding period, and that the ME consumed at weight equilibrium is the maintenance requirement. The second concept is that a part of the heat production resulting from ME consumed above the maintenance requirement is associated with an elevation of vital functions (support metabolism), and this heat production can be modeled as a function of the level of feeding. The third concept is that previous levels of nutrition affect current estimates of heat production, and that this impact can be modeled as a delayed response in heat production associated with support metabolism. Experimental data on feed consumption showed that maintenance requirements varied in simple proportion to BW, not only for different breeds of mature cattle at BW equilibrium, but also for calves and growing steers held at BW stasis. Experimental data in which different breeds of cattle achieved weight equilibrium when fed fixed amounts of a specific diet were used to estimate breed parameters associated with maintenance for 21 breeds of cattle and 15 biological types of crossbred cattle. Level of feeding was estimated as a multiple of the maintenance intake and used to model heat production associated with support metabolism. Other experimental data on growing cattle were used to estimate breed parameters for predicting heat production associated with support metabolism for 21 breeds of cattle and 15 biological types of crossbred cattle. A distributed lag function was used to model the delayed response in heat production associated with support metabolism with changes in plane of nutrition. The models were tested by simulating experimental data for three breeds of weaned steers finished on high-energy diets. Results for the total heat production associated with maintenance and support metabolism expressed on a unit BW basis showed a similar response with stage of maturity when compared with other experimental data.  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