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   234篇
  免费   24篇
林业   4篇
农学   1篇
  16篇
综合类   40篇
农作物   3篇
水产渔业   6篇
畜牧兽医   182篇
园艺   2篇
植物保护   4篇
  2021年   5篇
  2020年   2篇
  2019年   3篇
  2018年   2篇
  2016年   2篇
  2015年   5篇
  2014年   5篇
  2013年   15篇
  2012年   5篇
  2011年   2篇
  2010年   7篇
  2008年   13篇
  2007年   6篇
  2006年   11篇
  2005年   7篇
  2004年   10篇
  2003年   11篇
  2002年   8篇
  2001年   7篇
  2000年   8篇
  1999年   4篇
  1998年   6篇
  1997年   2篇
  1996年   5篇
  1994年   4篇
  1993年   2篇
  1992年   7篇
  1991年   10篇
  1990年   10篇
  1989年   4篇
  1988年   8篇
  1987年   8篇
  1986年   3篇
  1985年   3篇
  1984年   2篇
  1976年   4篇
  1974年   7篇
  1973年   3篇
  1972年   2篇
  1971年   4篇
  1967年   3篇
  1953年   1篇
  1931年   1篇
  1924年   1篇
  1918年   1篇
  1916年   1篇
  1907年   1篇
  1886年   1篇
  1883年   1篇
  1881年   3篇
排序方式: 共有258条查询结果,搜索用时 15 毫秒
21.
22.
Peer ratings of the quality of doctoral program faculties were obtained in a 1975 national survey of chemistry, history, and psychology programs. The ratings were then compared to those obtained 6 and 11 years earlier by the American Council on Education. In general, the rankings obtained from the ratings proved to be highly stable over the 11-year period, particularly in chemistry and history. Some ratings were also obtained for subspecialties within the three disciplines. Though it is clear that variations in quality among subspecialty faculties do exist and are important for individual program evaluations, it is unlikely that such subspecialty ratings would be feasible or useful in national surveys of the reputations of doctoral programs. The ratings were found to be highly related to a number of research-oriented variables of departments (such as size, productivity, percentage of alumni holding academic positions at Ph.D.-granting universities), but unrelated or very weakly related to such features as the student-reported quality of teaching and degree of faculty concern for students, or faculty-reported degree of departmental effort toward the career development of junior members of the faculty.  相似文献   
23.
24.
25.
Pulsed laser deposition (PLD) is a conceptually and experimentally simple yet highly versatile tool for thin-film and multilayer research. Its advantages for the film growth of oxides and other chemically complex materials include stoichiometric transfer, growth from an energetic beam, reactive deposition, and inherent simplicity for the growth of multilayered structures. With the use of PLD, artificially layered materials and metastable phases have been created and their properties varied by control of the layer thicknesses. In situ monitoring techniques have provided information about the role of energetic species in the formation of ultrahard phases and in the doping of semiconductors. Cluster-assembled nanocrystalline and composite films offer opportunities to control and produce new combinations of properties with PLD.  相似文献   
26.
27.
The nutritional implications and adaptive processes resulting from resection of 75% of the length of the large colon in ponies were investigated. Ten ponies in good physical condition were divided into two groups: six in the experimental group and four in the control group. During the sixth postoperative month, two digestibility studies were conducted, and phosphate fractional renal excretion and serum biochemical profiles were determined in both groups. The ponies (N = 10) were euthanized six months postoperatively, and gross and histopathological examinations were performed. Results of the serum biochemical profiles, phosphate fractional renal extraction and digestibility studies showed no statistically significant difference between groups except for the serum phosphate concentration. However, large colon resection was associated with hypophosphatemia in three of the six ponies and produced an overall significantly lower phosphate concentration in the experimental ponies. This hypophosphatemia suggests that some dietary modifications may be needed postoperatively in ponies or horses undergoing this surgical procedure. Postmortem examination and histopathological examination failed to demonstrate differences between groups. Adaptive mechanisms, specifically mucosal hypertrophy or hyperplasia, were not observed.  相似文献   
28.
29.
30.
Tissue drug residue research often involves the killing of an animal every time tissue concentrations are determined. To decrease the number of animals required to perform tissue depletion studies and to circumvent the statistical problems associated with determining tissue depletion kinetic properties, using multiple animals, the renal depletion profile of gentamicin from individual sheep was studied, using a bilateral renal translocation technique. Seven ewes were surgically altered, allowed to stabilize, and then allocated into 2 groups; group-1 sheep (n = 4) were given 3 mg of gentamicin/kg, IM, q 12 h for 10 days, and group-2 sheep (n = 3) were not given gentamicin. The kidneys from all ewes were biopsied 9 times over 74 days after the termination of gentamicin treatment. The renal concentrations of gentamicin were measured by use of a validated tissue digestion procedure coupled with a liquid-phase fluorescence polarization immunoassay. On days 75 and 77 after the end of gentamicin treatment, all ewes were euthanatized and necropsied. The concentrations of gentamicin in the biopsy specimens ranged from 71.9 to 183 micrograms/g on days 1 and 2 after dosing, and decreased to concentrations ranging from 3.99 to 7.35 micrograms/g on days 73 and 74 after the end of dosing. The decrease in renal gentamicin concentrations was best described by a biexponential equation. The early phase half-life was 2.8 days, whereas the terminal phase half-life was 59 days (harmonic means). There was no difference in the appearance or histologic features of the kidneys from groups 1 and 2. The only lesions noticed were linear fibroses that were attributed to the biopsy procedure.  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