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   6099篇
  免费   321篇
  国内免费   612篇
林业   641篇
农学   838篇
基础科学   492篇
  991篇
综合类   1871篇
农作物   312篇
水产渔业   266篇
畜牧兽医   1018篇
园艺   198篇
植物保护   405篇
  2024年   18篇
  2023年   83篇
  2022年   201篇
  2021年   279篇
  2020年   210篇
  2019年   260篇
  2018年   175篇
  2017年   210篇
  2016年   204篇
  2015年   283篇
  2014年   282篇
  2013年   317篇
  2012年   382篇
  2011年   434篇
  2010年   424篇
  2009年   368篇
  2008年   321篇
  2007年   318篇
  2006年   361篇
  2005年   272篇
  2004年   133篇
  2003年   126篇
  2002年   121篇
  2001年   141篇
  2000年   116篇
  1999年   144篇
  1998年   91篇
  1997年   106篇
  1996年   108篇
  1995年   103篇
  1994年   86篇
  1993年   70篇
  1992年   63篇
  1991年   49篇
  1990年   49篇
  1989年   42篇
  1988年   18篇
  1987年   19篇
  1986年   13篇
  1985年   4篇
  1984年   7篇
  1983年   5篇
  1982年   2篇
  1981年   3篇
  1972年   3篇
  1971年   3篇
  1965年   1篇
  1964年   2篇
  1948年   1篇
  1947年   1篇
排序方式: 共有7032条查询结果,搜索用时 15 毫秒
101.
磷对板栗结实性能及产量的影响   总被引:26,自引:2,他引:24  
试验结果表明,磷对板栗(Castanea mollissima Blume)雌花的形成数量有重要影响,结果母枝含磷量与母枝抽生结果枝数量和着生雌花数量呈显著正相关。板栗结果母枝含磷量比雄花母枝和营养枝分别高5.19%和5.27%。树体磷素含量水平与板栗雌、雄花枝比例和结果枝结栗苞数量也存在密切的相关性。在不同施磷水平下,结果枝粗度与果枝结栗苞数均具有显著的回归关系,但b值差异大。本研究结果在鄂东大别山区进行了大面积施磷肥示范,生产实践证明,施磷肥对板栗具有一致的增产效益。  相似文献   
102.
Thirty-three cases of enzootic bovine leukosis (EBL) and 14 cases of sporadic bovine leukosis (SBL) were examined by immunohistochemistry using 6 monoclonal antibodies against leukocyte differentiation molecules of bovine leukocytes. There were 17 cases of B-1a cell type, 10 cases of B-1b cell type and 6 cases of B-2 cell type in EBL, and 5 cases originating from B cells (B-2 cell type) and 9 cases originating from immature T cells in SBL. The average age for the EBL cases of B-1a cell type was 8.6 years, B-1b cell type was 6.5 years, and of B-2 cell type was 4.5 years. In cases of SBL, immature T cell type patients were younger than B-2 cell type ones. The lymphoma originating from B cells differed from that originating from T cells in morphology. In T cell tumors, the nucleus of tumor cells was round, the edge of the cytoplasm obvious, and tumor cells were sporadically present and proliferated. When compared with T cells, the region among B cells was obscure. But, there was no relation between phenotype and the histologic classification of tumor cells. In EBL, beyond the lymph node, tumors of B-1a and B-1b types had developed in the heart and abomasum, and those of the B-2 type tended to occur in liver. In SBL, B-2 type and T type cells formed tumors in the liver, kidney, thymus, and one case of T-cell type tumor formed on the skin. We would like to propose a new classification of bovine leukosis as EBL, calf type B-cell lymphoma, juvenile T-cell lymphoma and skin type T-cell lymphoma.  相似文献   
103.
Ma M  Guan G  Lu B  Liu A  Liu Z  Chang Z  Li F  Chang F  Luo J  Lu W  Zhang Q  Yuan G  Yin H  Boulard C 《Veterinary parasitology》2003,117(1-2):147-151
A chemotherapy trial was conducted to determine the lowest dosage of injectable preparation of ivermectin against Hypoderma spp. infestation in yaks in Tibetan areas in Tianzhu county, Gansu province, in northwest of China. One hundred and sixty yaks were randomly divided into four groups of 40 yaks for the trial. The first three groups were treated by subcutaneous injection in the neck with 0.1% ivermectin (respectively, 1, 5, 10 microg/kg body weight). The fourth group was not treated and considered as control group. All the experiments were performed in November 2000 and the animals were examined for the presence of warbles in the next March and May. The results indicated that there was no warbles found on the back of treated animal while third stage larvae were palpated on back of some of the yaks in control group. It is concluded that dosage of 1 microg/kg ivermectin injectable was sufficient to kill or stop development of larvae of Hypoderma spp. in naturally infected yaks if administrated in November.  相似文献   
104.
Epidemiology and control of brucellosis in China   总被引:8,自引:0,他引:8  
The paper describes the history and evolvement of brucellosis in China. It presents the variation of epidemic situation, epidemiological characteristics, application of vaccines and control in brief. Before 1980s, human and animal brucellosis was quite severe; during 1980s, the incidence of human and animal brucellosis was relatively low, and seemed to decrease during the decade. During 1990s, there were no obvious changes in the incidence of animal brucellosis, but the incidence of human brucellosis increased, especially from 1995 to 2001. There are not only some common characteristics but also some differences in brucellosis epidemiology relative to that reported in the rest of the world. For the entire country, B. melitensis was the predominant strain associated with outbreaks, and the epidemic peak is from February to June. Several Brucella vaccines have been used in China for prevention and control of brucellosis. such as B. abortus 104 M in humans, B. suis S2 in animals. The introduction of comprehensive measures has allowed great progress in the prevention and control of brucellosis in China. Surveillance points were set-up countrywide to estimate the epidemic situation. In addition, we discussed the new characteristics of brucellosis in China, the influence of the El Nino phenomenon on brucellosis epidemic situation, the phenomenon of antigenic interference between Brucella species and some disadvantages of live Brucella vaccines.  相似文献   
105.
Antioxidant activities of seven phenolic agents against Fe(2+)-induced lipid oxidation were compared with alpha-tocopherol, beta-carotene, and vitamin C in human erythrocyte membrane ghosts and liposome systems. The antioxidant activity of five test flavonoids followed the order catechin > epicatechin > rutin > quercetin > myricetin in both systems (p < 0.05), which was negatively correlated with their partition coefficients. The antioxidant interaction of these phenolic agents with alpha-tocopherol, beta-carotene, or vitamin C in inhibiting Fe(2+)-induced lipid oxidation was examined. Synergistic effects were present in the combinations of alpha-tocopherol plus caffeic acid, catechin, or epicatechin as well as in all combinations of vitamin C plus phenolic antioxidants. On the basis of the stronger individual and combined effects present in caffeic acid, catechin, and epicatechin, the application of these three phenolic agents with or without alpha-tocopherol, beta-carotene, and vitamin C may provide stronger protective benefits against lipid oxidation, which may be helpful for oxidation-related diseases prevention.  相似文献   
106.
他——挚爱警犬事业,挚爱着警犬队说到吴世林,整个刑警支队是无人不知,无人不晓。领导说:“他是个雷厉风行、办事严谨、闲不住的大忙人。”民警说:“他是个没有假日的好民警。”妻子说:“他从当兵到当警察20多年来没有真正与家人逛过街。”的确,吴世林是个出了名的“工作狂”,20多年来,他刻苦钻研警犬业务知识,精益求精。他曾说:“只要一天没见犬心里就痒痒,3天不牵犬则手痒痒了”。似乎只有在训练场上,吴世林才能找到人生最大的乐趣。  相似文献   
107.
一、犬现场搜索物证能力的培养(一)基础搜索能力的培养在训练初期,训犬员拿一些在实际现场中比较常见的作案工具(如刀具、钳子、木棍等),让犬进行搜  相似文献   
108.
为了了解植酸酶在包埋状态下酶活及酶性的变化,分别对酶的释放情况和热稳定性进行了研究.结果表明,随着时间的延长,包埋酶释放出的酶活逐渐上升(P<0.01),60min时达到最大值;而未包埋酶释放出的酶活逐渐下降(P<0.01),60 min时达到最小值.包埋酶和未包埋酶在30、40、50、60、70、80、90和100℃的条件下,随着温度的升高,残留的植酸酶活力下降(P<0.01).对于包埋酶,当温度升高到70℃时,植酸酶相对酶活仍保持在93%(P>0.05);当温度升高到80℃时,植酸酶的相对酶活才明显下降(P<0.01),不过在100℃时,仍能保持67%的酶活(P<0.01).对于未包埋酶,当温度升高到60℃时,植酸酶相对酶活明显下降(P<0.01);当温度升高到100℃时,植酸酶相对酶活仅有23%(P<0.01).通过在统一温度条件下,对包埋酶和未包埋酶处理组的相对酶活的对比发现,在50℃以下时,二者差异不显著,当温度超过60℃时,包埋酶的相对酶活极显著高于未包埋酶.  相似文献   
109.
苏州大学蚕桑研究所发明现行蚕品种转育成荧光茧色判性蚕品种的方法,新育成的蚕品种“雄晓”雄茧为黄荧光,雌茧为紫荧光,判性率100%。茧质成绩:全茧量1.499g,茧层量0.366g,茧层率24.42%,具生产实用性。  相似文献   
110.
寡糖取代抗生素对泌乳母猪血清生化指标的影响   总被引:4,自引:0,他引:4  
将24头长×大二元母猪随机分为4组,每组6头,以研究基础日粮添加吉它霉素、维吉尼亚霉素和半乳甘露寡糖对其泌乳期结束时血清生化指标的影响。试验结果表明:与对照组相比,半乳甘露寡糖可以显著降低血清中甘油三酯、磷酸肌酸激酶和谷草转氨酶的活性,显著提高血清中IgM的含量,进而间接地起到提高母猪免疫能力和健康水平的作用,总体效果要好于吉它霉素,和维吉尼亚霉素相当。  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