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   567篇
  免费   11篇
  国内免费   2篇
林业   45篇
农学   21篇
基础科学   1篇
  88篇
综合类   38篇
农作物   18篇
水产渔业   45篇
畜牧兽医   279篇
园艺   6篇
植物保护   39篇
  2023年   2篇
  2022年   9篇
  2021年   16篇
  2020年   5篇
  2019年   3篇
  2018年   11篇
  2017年   11篇
  2016年   13篇
  2015年   10篇
  2014年   21篇
  2013年   33篇
  2012年   27篇
  2011年   43篇
  2010年   16篇
  2009年   19篇
  2008年   40篇
  2007年   42篇
  2006年   35篇
  2005年   25篇
  2004年   32篇
  2003年   47篇
  2002年   20篇
  2001年   21篇
  2000年   10篇
  1999年   8篇
  1998年   5篇
  1997年   1篇
  1996年   1篇
  1995年   2篇
  1994年   5篇
  1993年   3篇
  1992年   4篇
  1991年   6篇
  1990年   2篇
  1989年   4篇
  1988年   6篇
  1987年   4篇
  1986年   5篇
  1985年   3篇
  1984年   2篇
  1983年   3篇
  1977年   1篇
  1976年   1篇
  1975年   1篇
  1973年   1篇
  1966年   1篇
排序方式: 共有580条查询结果,搜索用时 9 毫秒
41.
The mutual control of the electric and magnetic properties of a solid is currently of great interest because of the possible application for novel electronic devices. We report on the low-magnetic-field (for example, B values of +/-30 milliteslas) control of the polarization (P) vector in a hexaferrite, Ba2Mg2Fe12O22, which shows the helimagnetic spin structure with the propagation vector k0 parallel to [001]. The B-induced transverse conical spin structure carries the P vector directing perpendicular to both B and k0, in accord with the recently proposed spin-current model. Then, the oscillating or multidirectionally rotating B produces the cyclic displacement current via the flexible handling of the magnetic cone axis.  相似文献   
42.
The causes of early degeneration and calcification of the nucleus pulposus in the chondrodystrophoid dog are poorly understood, and the underlying molecular mechanism of this process has not yet been clearly defined. Type X collagen is one of the key molecules in endochondral bone growth and development, especially matrix calcification. The relationship between type X collagen and disc degeneration and calcification in chondrodystrophoid dogs has not yet been studied. We analyzed the expression of type X collagen in degeneration and calcification of the intervertebral disc in chondrodystrophoid dogs, using type X collagen immunohistochemistry. Control intervertebral discs were collected from five dogs (4 female, 1 male, average age 1.3 years, beagle breed). Degenerated intervertebral discs were surgically removed from 11 canine patients with intervertebral disc extrusion (1 female, 10 male, average age 5.1 years, dachshund breed) in Nippon Veterinary and Animal Science University. All extruded disc samples showed hypertrophic changes and clustering of cells, typical features observed in the degenerated nucleus pulposus. The relative expression of type X collagen in the degenerated nucleus pulposus (84.3 +/- 11.0%) was significantly increased compared to the control nucleus pulposus (5.4 +/- 5.4%). Our findings suggest that type X collagen might contribute to the development of degeneration or calcification in the nucleus pulposus of the chondrodystrophoid dog.  相似文献   
43.
For Apicomplexa (members) the host cell invasion is realized with the help of the organelles located at the apical tip of parasites. In this research paper the characterization of five chicken monoclonal antibodies (mabs) produced against Eimeria acervulina sporozoites is described. All mabs reacted with molecules belonging to the apical complex of chicken Eimeria sporozoites. On immunofluorescence assay (IFA) one mab, 8E-1, recognized an apical tip molecule present on all chicken Eimeria sporozoites, two mabs (8D-2 and HE-4) recognized an antigen present on the apical tip of the same two Eimeria species (E. acervulina and E. brunetti), another mab (5D-11) recognized an antigen present on the apical tip of other two species (E. acervulina and E. maxima) while one mab (8C-3) identified antigens present on the sporozoites and sporocysts wall of only E. acervulina. Besides the apical tip antigens, two mabs (HE-4 and 8D-2) recognized some proteins located in the anterior half of the sporozoites. Collectively, these mabs proved that the apical complex of chicken Eimeria sporozoites share one or more antigens that are expected to play a role in host cell recognition and invasion.  相似文献   
44.
45.
A 12-year-old, 3.5-kg spayed female domestic shorthair cat had a tracheal mass identified as malignant B-cell lymphoma. The cat had tracheal resection and subsequently developed laryngeal paralysis. Due to multiple episodes of respiratory distress the cat subsequently had tracheal surgeries. Finally, the cat had a sudden onset of severe respiratory distress and collapsed. Computed tomography imaging and arterial blood gas analysis supported a diagnosis of acute lung injury.  相似文献   
46.
The thrombocyte extracts (TE) and thrombocyte-secretion products (TSP) prepared from chicken peripheral blood were examined for the growth activity of chicken embryo fibroblasts (CEF). When the cells were incubated with TE and TSP, the enhancement of cell spreading was observed within one hour after seeding, but the control culture showed little spreading. Three to six days after cell seeding, the increase of the cell densities in the culture supplemented with TE and TSP was noticed in comparison with the culture without thrombocyte materials. The results strongly indicate the possibility for the presence of thrombocyte-derived growth factor(s) to CEF.  相似文献   
47.
48.
Uncertainties in the assessment of critical loads for acidic deposition are caused by the choice of biological indicators (BI), critical chemical values (CCV), the current methods used to determine critical loads for an ecosystem, and deficient field data. This paper focuses on the present steady-state mass balance (SSMB) approach, dynamic models and the importance of changes in atmospheric base-cation deposition (BCD), particularly in China. It is argued that 1) for the SSMB approach much uncertainty may come from the choice of BI and the related CCV, and long-term and large-scale monitoring data on weathering rates and growth uptake are urgently needed, especially in China, 2) significant uncertainty may be caused by changes in BCD during SO2 emission controls, particularly in China, 3) constructing a mechanistic Al submodel may be a promising direction for dynamic models, and 4) the nutrient cycle in the vegetation through biogeochemical processes should be incorporated into dynamic models but the input requirements should be moderate for broad application considerations. Generally higher BCD, different soil components and characteristics and different vegetation types in China compared to Europe and North America suggest that more field investigations on BI and their corresponding CCV be carried out before application of current approaches to specific areas, particularly in China.  相似文献   
49.
This is the first report for secondary metabolites in an African medicinal plant, Pachyelasma tessmannii (Leguminosae). Four novel saponins, pachyelasides A-D, were isolated from the methanol extract of the root bark by using recycling HPLC. These compounds showed molluscicidal activity (LD(50) < or =8.0 mug/mL) against the South American snail, Biomphalaria glabratus. The structures were determined on the basis of extensive nuclear magnetic resonance spectroscopic and matrix-assisted laser desorption/ionization time-of-flight mass spectrometric studies.  相似文献   
50.
Pollen records from the annually laminated sediment sequence in Lake Suigetsu, Japan, suggest a sequence of climate changes during the Last Termination that resembles that of the North Atlantic region but with noticeable differences in timing. An interstadial interval commenced a few centuries earlier [approximately 15,000 years before the present (yr B.P.)] than the North Atlantic GI-1 (B?lling) event. Conversely, the onset of a Younger Dryas (YD)-like cold reversal (12,300 to 11,250 yr B.P.) postdated the North Atlantic GS-1 (YD) event by a few centuries. Climate in the Far East during the Last Termination reflected solar insolation changes as much as Atlantic influences.  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