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   474篇
  免费   12篇
林业   55篇
农学   4篇
  30篇
综合类   16篇
农作物   13篇
水产渔业   83篇
畜牧兽医   266篇
园艺   3篇
植物保护   16篇
  2023年   1篇
  2022年   2篇
  2021年   9篇
  2020年   9篇
  2019年   7篇
  2018年   10篇
  2017年   3篇
  2016年   11篇
  2015年   10篇
  2014年   12篇
  2013年   34篇
  2012年   22篇
  2011年   32篇
  2010年   16篇
  2009年   17篇
  2008年   30篇
  2007年   33篇
  2006年   33篇
  2005年   30篇
  2004年   19篇
  2003年   22篇
  2002年   21篇
  2001年   15篇
  2000年   10篇
  1999年   6篇
  1998年   4篇
  1995年   1篇
  1993年   1篇
  1992年   4篇
  1991年   3篇
  1990年   10篇
  1989年   5篇
  1988年   18篇
  1987年   6篇
  1986年   9篇
  1985年   7篇
  1984年   1篇
  1980年   2篇
  1979年   1篇
排序方式: 共有486条查询结果,搜索用时 125 毫秒
31.
Technology for storing carbon in the subsoil of agricultural land using organic filter materials in underdrains was evaluated as an activity for sequestering CO2 to mitigate global warming. First, the quantity of carbon remaining in wood chips and rice husks in underdrains was determined over 11 years after construction. Moreover, the quantity of CO2 emissions from the construction of two underdrain types was calculated. Then, a survey was conducted to investigate the effect on greenhouse gas emissions of the filter material. The results indicate that greenhouse gas emissions would not increase. The quantity of storage carbon in the wood chip filter material of underdrains during their 15-year service life was estimated to be 6.76 tCO2eq ha?1. Rice husks, in contrast, were found ineffective in storing carbon. Therefore, the selection of the filter material for underdrains is important. The value of storage carbon in the wood chip filter material is similar to the amount of carbon sequestered by no-till farming, which is now being implemented as a global warming countermeasure based on soil management in agricultural land.  相似文献   
32.
Twenty‐four archival tags were recovered from Pacific bluefin tuna previously released off Tsushima Island in the East China Sea. By analysis of the time‐series data of the pressure and the ambient and internal temperature from the 24 tags, we examined the relationship between the tuna's pattern of diving and the thermocline depth. In the East China Sea, diving and feeding events occurred throughout almost the entire day in both winter and summer, suggesting that the purpose of diving is for feeding. In summer, the feeding frequency was greater than that in winter, which corresponds to the fact that growth is more rapid in summer than in winter. During summer in the Kuroshio–Oyashio transition region, on the other hand, feeding events were much more frequent than those in the East China Sea, in spite of a lower diving frequency. The mean horizontal distance traveled was also significantly higher and it seems that in this area they may move horizontally to feed on prey accumulated at the surface. We conclude that, in addition to the ambient temperature structure, the vertical and horizontal distribution of prey species plays an important role in the feeding behavior of Pacific bluefin tuna. One bluefin tuna migrated to the Oyashio frontal area, where both the horizontal and the vertical thermal gradients are much steeper. The fish spent most of the time on the warmer side of the front and often traveled horizontally to the colder side during the day, perhaps to feed. This implies that there is a thermal barrier effect, in this case from the Oyashio front, on their behavior. The frequency of feeding events was low, although all the monitored fish dived every dawn and dusk, irrespective of the seasons or location. It is possible that these twice‐daily diving patterns occurred in response to the change in ambient light at sunrise and sunset.  相似文献   
33.

Technology for storing carbon in the subsoil of agricultural land using organic filter materials in underdrains was evaluated as an activity for sequestering CO2 to mitigate global warming. First, the quantity of carbon remaining in wood chips and rice husks in underdrains was determined over 11 years after construction. Moreover, the quantity of CO2 emissions from the construction of two underdrain types was calculated. Then, a survey was conducted to investigate the effect on greenhouse gas emissions of the filter material. The results indicate that greenhouse gas emissions would not increase. The quantity of storage carbon in the wood chip filter material of underdrains during their 15-year service life was estimated to be 6.76 tCO2eq ha−1. Rice husks, in contrast, were found ineffective in storing carbon. Therefore, the selection of the filter material for underdrains is important. The value of storage carbon in the wood chip filter material is similar to the amount of carbon sequestered by no-till farming, which is now being implemented as a global warming countermeasure based on soil management in agricultural land.

  相似文献   
34.
35.
本文从林业和环境的可持续性的视点出发,对关系到森林的退耕还林政策的成果和问题以及最近开始的林权制度改革的内容和课题进行了实地考察和探讨,针对今后中国的森林和环境保护的方向进行了论述。  相似文献   
36.
Apoptotic cells expose phosphatidylserine and are swiftly engulfed by macrophages. Milk fat globule epidermal growth factor (EGF) factor 8 (MFG-E8) is a protein that binds to apoptotic cells by recognizing phosphatidylserine and that enhances the engulfment of apoptotic cells by macrophages. We report that tingible body macrophages in the germinal centers of the spleen and lymph nodes strongly express MFG-E8. Many apoptotic lymphocytes were found on the MFG-E8-/- tingible body macrophages, but they were not efficiently engulfed. The MFG-E8-/- mice developed splenomegaly, with the formation of numerous germinal centers, and suffered from glomerulonephritis as a result of autoantibody production. These data demonstrate that MFG-E8 has a critical role in removing apoptotic B cells in the germinal centers and that its failure can lead to autoimmune diseases.  相似文献   
37.
Antigenic and genetic analysis of the hemagglutinin of approximately 13,000 human influenza A (H3N2) viruses from six continents during 2002-2007 revealed that there was continuous circulation in east and Southeast Asia (E-SE Asia) via a region-wide network of temporally overlapping epidemics and that epidemics in the temperate regions were seeded from this network each year. Seed strains generally first reached Oceania, North America, and Europe, and later South America. This evidence suggests that once A (H3N2) viruses leave E-SE Asia, they are unlikely to contribute to long-term viral evolution. If the trends observed during this period are an accurate representation of overall patterns of spread, then the antigenic characteristics of A (H3N2) viruses outside E-SE Asia may be forecast each year based on surveillance within E-SE Asia, with consequent improvements to vaccine strain selection.  相似文献   
38.
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   
39.
A sensitive enzyme immunoassay for cephalexin (CEX) was developed using the rabbit antiserum to CEX, beta-D-galactosidase-labeled CEX, and a double-antibody separation method. The immunogen of CEX was prepared by coupling the amino group of CEX to thiol groups introduced into bovine serum albumin by the use of N-(m-maleimidobenzoyloxy)succinimide as a cross-linker. Highly titered antiserum to CEX was produced in rabbits immunized with the immunogen. Enzyme labeling of CEX with beta-D-galactosidase was done by using N-(gamma-maleimidobutyryloxy)succinimide as the cross-linker. The limit of detection was 30 ng CEX/mL sample solution. Application of the method to CEX drug residues detected 30 ng/mL in milk, 60 ng/g in egg yolk, and 400 ng/g in hen tissue.  相似文献   
40.
In order to confirm the effects of matching of expressed feline major histocompatibility complex (FLA) class II DRB genotype on transplantation immunity in cats, skin-allogeneic transplantation was carried out between cats, in which DRB genes expressed were genotyped by the RT-PCR-RFLP method using group-specific primers. Duration until grafts were rejected was 14.63 +/- 1.69 days (mean +/- standard deviation) in the pairs that had the same type of subgroups, 7.25 +/- 0.71 days in the pairs that had one different type of subgroup and 6.88 +/- 0.35 days in the pairs that had two different types of subgroups. The duration of graft survival in the pairs with the same type of subgroups was significantly longer (P<0.01) than those in the pairs with different types. Although FLA components involved in transplantation immunity should not only be DRB genes, it was suggested that the expressed FLA-DRB genotype might associate with feline transplantation immunity, and that typing and matching of expressed FLA-DRB genes might be one of the important factors in the control of feline transplantation immunity.  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