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   6545篇
  免费   533篇
  国内免费   32篇
林业   340篇
农学   461篇
基础科学   59篇
  1045篇
综合类   697篇
农作物   284篇
水产渔业   400篇
畜牧兽医   3058篇
园艺   100篇
植物保护   666篇
  2020年   69篇
  2019年   123篇
  2018年   226篇
  2017年   228篇
  2016年   185篇
  2015年   200篇
  2014年   197篇
  2013年   379篇
  2012年   268篇
  2011年   321篇
  2010年   253篇
  2009年   220篇
  2008年   309篇
  2007年   270篇
  2006年   237篇
  2005年   204篇
  2004年   198篇
  2003年   196篇
  2002年   147篇
  2001年   234篇
  2000年   180篇
  1999年   170篇
  1998年   70篇
  1997年   75篇
  1996年   54篇
  1995年   60篇
  1994年   45篇
  1993年   53篇
  1992年   105篇
  1991年   107篇
  1990年   109篇
  1989年   106篇
  1988年   88篇
  1987年   80篇
  1986年   75篇
  1985年   58篇
  1984年   64篇
  1983年   52篇
  1981年   44篇
  1980年   48篇
  1979年   72篇
  1978年   52篇
  1977年   52篇
  1976年   59篇
  1975年   52篇
  1974年   61篇
  1973年   75篇
  1972年   44篇
  1971年   45篇
  1969年   43篇
排序方式: 共有7110条查询结果,搜索用时 0 毫秒
31.
32.
S WANG  L DUAN  J LI  X TIAN  & Z LI 《Weed Research》2007,47(2):122-128
Depletion of the protective ozone layer in the atmosphere leads to increasing UV‐B radiation on the earth's surface with potential effects on the response of plants to different stresses. Abutilon theophrasti, Amaranthus retroflexus, Digitaria sanguinalis and Chloris virgata are common weeds encountered in most arable fields in China. The effectiveness of herbicides used in controlling these weeds needs to be evaluated with increased UV‐B radiation. Seedlings of these four weeds were therefore grown under ambient and elevated UV‐B radiation to compare the efficacy of paraquat, a commonly used contact herbicide. Irrespective of species sensitivity to radiation, the elevated UV‐B radiation decreased the effectiveness of paraquat. Net photosynthesis rate was adversely affected except for D. sanguinalis, while the chlorophyll content was significantly reduced in A. retroflexus and C. virgata. UV‐B treatment increased the leaf surface wax and decreased the absorption of 14C‐paraquat in A. theophrasti, D. sanguinalis and C. virgata. These results suggest that the response of weeds to paraquat or the use of the herbicide may be affected by increased UV‐B radiation, to the extent that larger doses may be required to achieve desired effects. This may have damaging consequences for the environment.  相似文献   
33.
The aim of this work was to determine levels of carcinoembryonic antigen (CEA) and cancer antigen (CA 15‐3) in the blood serum of 45 bitches. A modified procedure was used to determine the CEA and CA 15‐3 markers with the human kits using the radioimmunoassay method. Samples collected from extirpated tumour of mammary glands were histologically processed and classified as per WHO guidelines. The average age of animals with tumour was 10.00 ± 2.2 years; for healthy bitches average age was 4.2 ± 3.2 years. Values of CEA and CA 15‐3 were considered positive, if they exceeded 0.23 ng mL?1 and 7 IU mL?1, respectively. Average levels of CEA in the tumour group were 0.25 ± 0.06 versus 0.20 ± 0.03 in healthy bitches (P = 0.0001). The average CA 15‐3 value in bitches with tumour was 8.58 ± 1.27 versus 5.14 ± 1.34 in healthy animals (P < 0.0001).  相似文献   
34.
Extract

In Dunedin, feline respiratory infections with a high morbidity, but a low mortality except in very young animals, commonly occur in epizootics and appear to be enzootic between these outbreaks. The affected animals develop a serous ocular discharge which later becomes mucoid, and a mucoid nasal discharge associated with sneezing especially after handling. While these signs of infection are present, the animals are anorexic and listless. The disease may last for two weeks or more and sometimes affected cats develop a chronic snuffle lasting for months despite treatment. The disease is usually referred to as “snuffles”, although it is probably identical with the syndrome called “rhinotracheitis”. In the summer time, it commonly occurs in boarding establishments where large numbers of pets collected from a wide area are left by summer vacationers. In breeding catteries, infections occur most often in the spring and especially at the time of the first warm weather. Young kittens about 5 to 10 days old are usually affected but kittens which escape infection at this stage not infrequently develop symptoms at about 6 weeks of age.  相似文献   
35.
The present study was to determine in vitro effect of levamisole on the immune functions of Barbel chub (Squaliobarbus curriculus), head–kidney‐derived (HKM), spleen‐derived (SM) and peripheral blood monocyte‐derived macrophage (PBM). Macrophages were incubated with levamisole 103, 101, 10−1 and 10−3 ng mL−1 to assay the cell viability, respiratory burst and phagocytosis. The results showed that macrophages treated with levamisole 10−3 ng mL−1 gave a maximum respiratory burst response, whereas levamisole 103 ng mL−1 had no effect. Phagocytosis activity of the macrophages treated with levamisole enhanced significantly when compared to control, maximum response being at 10−3 ng mL−1. While using the methylthiazoletetrazolium method to measure the cell activity for 12, 24, 36, 48, 60 h, there was no significant role on proliferation and the cell viability began to decline after 24 h. In conclusion, levamisole is a potent enhancer of Barbel chub macrophage activity with low concentration.  相似文献   
36.
Gold-induced immune thrombocytopenia in the dog   总被引:1,自引:0,他引:1  
In two seven-year studies with gold compounds in dogs of both sexes, thrombocytopenia was observed after 45 to 72 months of dosing in three of 14 and two of 14 dogs in high-dose groups that received 2.4 to 3.6 mg/kg of auranofin per day orally or 0.5 to 2.0 mg/kg of gold sodium thiomalate intramuscularly once every three days, respectively. An immune basis for the disorder was suggested by the apparent consumptive nature of the thrombocytopenia (increased bone marrow megakaryocytes and large peripheral blood platelets), the response to corticosteroid therapy and the demonstration of increased platelet-associated immunoglobulin. The latter was demonstrated with a solid phase radioimmunoassay and by electron microscopy using a staphylococcal protein A-colloidal gold conjugate. Platelet-associated immunoglobulin decreased as the platelet counts rose, and in one dog monitored over periods of steroid-induced remissions and subsequent relapses, the amount of platelet-associated immunoglobulin G correlated inversely with the platelet count (r = 0.82). These findings suggest that the long-term administration of gold compounds in dogs is associated with a dose-dependent incidence of thrombocytopenia, which is immune-mediated and similar to that associated with parenteral chrysotherapy in man. The application of tests for platelet-associated immunoglobulin to canine patients with immune thrombocytopenia should be useful in the diagnosis of the disorder in clinical practice.  相似文献   
37.
1. This study examined responses of male broilers during a 42-d production cycle to two different rearing and feeding methods. 2. A total of 400 Chinese Yellow male broilers were allotted randomly at 21 d into two groups; the control was a typical indoor commercial rearing method and the treatment had outdoor access with scattered feeding (OS). Each group had 5 replicates with 40 birds per replicate. 3. Growth performance was similar for both groups from 21 to 63 d of age. OS birds had significantly lower abdominal fat percentage, meat shear force, drip loss, breast meat colour b* value and significantly higher pH value compared with the controls. OS birds had significantly lower muscle fibre diameter and greater muscle fibre density. Serum glutathione peroxidase and catalase activities were significantly higher and the contents of cholesterol, lactic acid, glycogen and malondialdehyde of breast muscle were significantly lower in OS birds than controls. 4. The results suggest that the OS feeding method had no negative effects on performance (weight, gain, feed conversion rate, carcase traits) compared with controls, and appeared to be beneficial for meat quality indices and oxidative stability.  相似文献   
38.
One polyclonal antibody against florfenicol and thiamphenicol was produced and a competitive ELISA was developed for the detection of florfenicol and thiamphenicol in swine feed. The ELISA gave a 50% inhibiting concentration of 1.02 ng/mL for florfenicol. For swine feed fortified with 0.05 to 3.0 mg/kg, the interassay recoveries of florfenicol and thiamphenicol ranged from 86.4 to 118.6%, whereas intraassay recoveries of both drug ranged from 90.1 to 126.5% with less than 15% CV. Results obtained from HPLC-tandem mass spectrometry indicated this ELISA procedure could be used as a convenient method for rapid screening of florfenicol and thiamphenicol in swine feed.  相似文献   
39.
40.
By the radiographic examination of pet and wild birds, veterinary clinicians may relatively easily obtain additional information that can be used routinely in their everyday diagnostic and therapeutic work. The first part of the present review summarizes the basic technical conditions of radiological examinations, analyses the radiographic features of healthy birds, and describes the procedure and radiological indications of contrast radiography.  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