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   228篇
  免费   3篇
  国内免费   2篇
林业   10篇
农学   5篇
基础科学   7篇
  9篇
综合类   80篇
农作物   2篇
水产渔业   1篇
畜牧兽医   112篇
园艺   3篇
植物保护   4篇
  2022年   3篇
  2018年   2篇
  2016年   3篇
  2015年   2篇
  2014年   4篇
  2012年   11篇
  2011年   13篇
  2010年   6篇
  2009年   8篇
  2008年   17篇
  2007年   4篇
  2006年   17篇
  2005年   10篇
  2004年   12篇
  2003年   11篇
  2002年   6篇
  2001年   8篇
  2000年   9篇
  1999年   8篇
  1998年   5篇
  1997年   2篇
  1995年   4篇
  1994年   5篇
  1993年   3篇
  1990年   5篇
  1989年   4篇
  1986年   2篇
  1979年   3篇
  1974年   3篇
  1971年   1篇
  1970年   2篇
  1969年   1篇
  1966年   1篇
  1960年   1篇
  1958年   2篇
  1957年   3篇
  1956年   3篇
  1955年   1篇
  1954年   2篇
  1948年   1篇
  1947年   1篇
  1942年   1篇
  1941年   2篇
  1939年   2篇
  1937年   1篇
  1936年   1篇
  1935年   2篇
  1932年   1篇
  1931年   1篇
  1893年   1篇
排序方式: 共有233条查询结果,搜索用时 15 毫秒
171.
172.
Rocks of the rim and upper walls of Scripps Submarine Canyon are intensely burrowed by marine invertebrates. Important excavators are bivalves, polychaetes, and sipunculoids whose activities culminate in a network of passageways and eventual disintegration of the rocks. In many localities erosion by animals is more important than erosion by physical and chemical processes.  相似文献   
173.
174.
BACKGROUND: Lidocaine is most frequently used to treat ventricular arrhythmias. However, lidocaine may have an antiarrhythmic effect for certain supraventricular arrhythmias. HYPOTHESIS: We hypothesized that lidocaine would be effective in converting experimentally induced atrial fibrillation (AF) to sinus rhythm and that a decrease in the dominant frequency (DF) and an increase in the organization as judged by the spectral entropy (SE) would occur over the course of the conversion. ANIMALS: Seven German Shepherd (GS) Dogs. METHODS: Dogs were anesthetized with fentanyl and pentobarbital. AF was induced with standard pacing protocols while left and right atrial monophasic action potentials (MAP) were recorded. The power spectra from the MAP recordings were analyzed to determine DF and SE during treatment with boluses of 2 mg/kg lidocaine. RESULTS: Lidocaine converted AF to sinus rhythm in all dogs and all episodes (n = 19). Conversion time was 27-87 seconds. After atropine, sustained AF was not induced; however, 5 episodes of atrial tachycardia resulted, and 3 were converted with lidocaine. Frequency domain analysis of 12 conversion sequences showed that left and right DF of the MAP signals decreased from the time of injection to conversion to sinus rhythm (P < .001). Mean SE indicated a gradient between the left and right atria (P = .003) that did not change during conversion. CONCLUSIONS AND CLINICAL IMPORTANCE: Vagally associated AF in GS dogs is terminated with lidocaine. Lidocaine is likely an effective treatment in clinical dogs with vagally associated AF.  相似文献   
175.
Mycoplasma hyosynoviae has never been reported to cause arthritis in pigs younger than 10 weeks of age. In order to investigate whether a strict age-related resistance exists, four 6-week-old pigs and four 13-week-old pigs, all immunologically na?ve with respect to M. hyosynoviae, were inoculated intranasally with the agent and autopsied at day 11 or 13 after infection. One uninoculated pig per age group was included as a negative control. Just as the 13-week-old pigs, the 6-week-old piglets were susceptible to blood, joint and tonsillar infection with M. hyosynoviae and developed clinical arthritis following inoculation with the agent. Thus, we found no evidence of an age-related resistance to the infection.  相似文献   
176.
文章作者详细分析工程量清单计价的意义、概念、作用及基本特征,并提出应注意的问题。  相似文献   
177.
178.
OBJECTIVE: To determine whether argyrophilic nucleolar organizing regions (AgNORs), Ki-67, and proliferating cell nuclear antigen (PCNA) scores were associated with histologic grade and survival in dogs with soft tissue sarcomas (STSs). DESIGN: Retrospective study. ANIMALS: 60 dogs with STSs. PROCEDURE: Medical records were examined and histologic specimens were reviewed. Tissue specimens obtained from archival materials were used to prepare sections for histologic staining for AgNOR and immunohistochemical staining for Ki-67 and PCNA labeling. Follow-up monitoring was obtained by reevaluation or telephone conversations with referring veterinarians or owners. RESULTS: 27 (45%) STSs were grade 1, 23 (38%) were grade 2, and 10 (17%) were grade 3. The mean and median AgNOR, Ki-67, and PCNA scores were determined, and significant positive associations among AgNOR and Ki-67 scores with histologic grade and mitotic score were detected. Fifty-four dogs had adequate follow-up examinations and were included in survival analysis and evaluation of prognostic factors. Overall median survival time was > 1,306 days. Twelve of 54 (22%) dogs died of tumor-related causes. Metastatic disease developed in 8 of 54 (15%) dogs. Results of univariate analysis indicated that increased mitotic score, increased AgNOR score, increased Ki-67 score, incomplete surgical margins, noncurative intent surgery, Ki-67 score greater than the median Ki-67 score, and AgNOR score greater than the median AgNOR score were prognostic factors for decreased survival time. Results of multivariate analysis indicated that increased AgNOR score was the only prognostic factor for decreased survival time. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested that AgNORs and possibly Ki-67 should be routinely evaluated with histologic grading for STSs in dogs.  相似文献   
179.
Magnetic field studies by Voyager 1 have confirmed and refined certain general features of the Saturnian magnetosphere and planetary magnetic field established by Pioneer 11 in 1979. The main field of Saturn is well represented by a dipole of moment 0.21 +/- 0.005 gauss-R(s)(3) (where 1 Saturn radius, R(s), is 60,330 kilometers), tilted 0.7 degrees +/- 0.35 degrees from the rotation axis and located within 0.02 R(s) of the center of the planet. The radius of the magnetopause at the subsolar point was observed to be 23 R(s) on the average, rather than 17 R(s). Voyager 1 discovered a magnetic tail of Saturn with a diameter of approximately 80 R(s). This tail extends away from the Sun and is similar to type II comet tails and the terrestrial and Jovian magnetic tails. Data from the very close flyby at Titan (located within the Saturnian magnetosphere) at a local time of 1330, showed an absence of any substantial intrinsic satellite magnetic field. However, the results did indicate a very well developed, induced magnetosphere with a bipolar magnetic tail. The upper limit to any possible internal satellite magnetic moment is 5 x 10(21) gauss-cubic centimeter, equivalent to a 30-nanotesla equatorial surface field.  相似文献   
180.
The Texas A&M University Medical Sciences Library (MSL) supports lifelong learning for Texas veterinarians and College of Veterinary Medicine and Biomedical Sciences (CVMBS) alumni through several ongoing outreach efforts. The MSL provides free document delivery and literature search services to practicing veterinarians in support of patient care. The MSL also responded to unique opportunities to expand services and increase its visibility through collaborations with the American Association of Equine Practitioners and CABI, provider of VetMed Resource. The MSL continues to explore ways to expand its mission-critical veterinary outreach work and market library services to veterinarians through participation in continuing education, regional meetings, and veterinary student instruction.  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