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   121467篇
  免费   6841篇
  国内免费   88篇
林业   4327篇
农学   3627篇
基础科学   752篇
  13969篇
综合类   21154篇
农作物   4252篇
水产渔业   6116篇
畜牧兽医   65439篇
园艺   1370篇
植物保护   7390篇
  2018年   1632篇
  2017年   1830篇
  2016年   1657篇
  2015年   1410篇
  2014年   1732篇
  2013年   4414篇
  2012年   3116篇
  2011年   3954篇
  2010年   2556篇
  2009年   2622篇
  2008年   3864篇
  2007年   3616篇
  2006年   3542篇
  2005年   3165篇
  2004年   3139篇
  2003年   3140篇
  2002年   2902篇
  2001年   4154篇
  2000年   4305篇
  1999年   3290篇
  1998年   1269篇
  1997年   1213篇
  1996年   1142篇
  1995年   1478篇
  1994年   1312篇
  1993年   1207篇
  1992年   2776篇
  1991年   2960篇
  1990年   2817篇
  1989年   2775篇
  1988年   2629篇
  1987年   2753篇
  1986年   2731篇
  1985年   2610篇
  1984年   2116篇
  1983年   1812篇
  1982年   1209篇
  1979年   1873篇
  1978年   1510篇
  1977年   1338篇
  1976年   1256篇
  1975年   1344篇
  1974年   1698篇
  1973年   1697篇
  1972年   1653篇
  1971年   1489篇
  1970年   1413篇
  1969年   1345篇
  1968年   1118篇
  1967年   1174篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
The clinical course of a feline leukaemia virus (FeLV)-negative and feline immunodeficiency virus (FIV)-positive cat affected with a large granular lymphocyte lymphoma is presented. Cyto-logical examination showed neoplastic cells in the pleural effusion and in two abdominal masses. Bone marrow and peripheral blood were moderately involved and chemotherapy was used to control the tumour. Cytochemistry, immunohis-tochemistry and ultrastructural studies were applied to define the cellular lineage; cytochemistry suggested a T-cell lineage.  相似文献   
32.
We have developed an antibody detection enzyme-linked immunosorbent assay (ELISA) for the identification of animals infected by feline immunodeficiency virus (FIV). The ELISA solid-phase antigen consists of recombinant FIV gag proteins expressed in bacteria. The proteins are purified from bacterial lysates as insoluble inclusion bodies. In the case of bacterially expressed p24gag, it is shown that all of the linear, sequential epitopes presented by viral p24 during infection are retained. Purified preparations can be substituted for solid-phase whole virus in the IDEXX PetChektm immunoassay. The antibody ELISA duplicates the sensitivity and specificity of the whole virus based PetChek plate assay.  相似文献   
33.
Preparations of duck (Anas platyrhynchos) spleen and blood lymphocytes depleted of cells capable of phagocytosing carbonyl iron gave lower transformation responses to the mitogens phytohaemagglutinin (PHA), concanavalin A (Con A), Bandeiraea simplicifolia seed lectin (BSS), wheat germ agglutinin (WGA), lentil lectin (LL) and phorbol ester (PMA) than intact cell preparations. When cell populations were fractionated on the basis of their adherence to plastic, it was found that the adherent cells were responsive to PHA, Con A, BSS, WGA and PMA, while the non-adherent cells responded to LL. These observations confirm the expected requirement for phagocytic accessory cells in the induction of in vitro mitogen-driven duck lymphocyte responses. The responses of plastic-adherent populations of cells to most mitogens are believed to reflect the generally close physical relationship between the adherent accessory cells and the lymphocytes, although it remains possible that duck monocytes respond to some of the mitogens employed. The data also suggest that LL stimulates a population of cells different to those responding to other mitogens.  相似文献   
34.
The immunofunctional response of the gland of Harder (GH) was compared in chickens and turkeys using an in vivo assay previously developed for use in chickens. The GH were surgically removed (GHx) from leghorn chicks at 1 day of age and from poults at 2 days of age. Intact birds of each species served as controls. During the fourth week of age, both GH-intact and GHx chicks were exposed to killed Brucella abortus antigen by the ocular or intraperitoneal route. One week later, serum and tears were collected and assayed for antibodies to B. abortus. In addition, all birds were killed at the end of the trial period, and the heads were fixed and processed for histologic examination. Various components of the head-associated lymphoid tissue (HALT) including the GH, nasal glands, lacrimal glands, lacrimal ducts, eyelid conjunctiva, and nasal cavity mucosa/submucosa, were evaluated microscopically using a scoring system to estimate quantity and degree of development of immune tissue in those sites. Results of all analyses indicate that functional response and morphology of the HALT are comparable in turkeys and chickens.  相似文献   
35.
36.
A good correlation exists between specific neutralising antibody titre and protection against challenge with foot-and-mouth disease virus (FMDV) in infected or virus-vaccinated cattle, but not in the case of animals immunised with synthetic FMDV peptides. Therefore, mechanisms other than simple neutralisation are likely to be important in vivo. Antibody affinity may influence the protective capacity of sera from immunised animals and experiments were carried out to measure the functional affinity for synthetic FMDV peptide of sera from guinea pigs and cattle given various synthetic vaccines. In guinea pigs given a single dose of synthetic vaccine, antibody affinity increased with time after immunisation. In cattle, however, administration of a second dose of peptide 21 days after the first markedly retarded the process of affinity maturation. For guinea pig sera of equivalent neutralising activity, those of higher functional affinity had higher protective indices than those of lower functional affinity. Knowledge of the importance of antibody affinity in protection against FMD is important for an improved understanding of the mechanisms of protection and for the design of novel vaccines.  相似文献   
37.
A sensitive and precise immunoassay for equine serum amyloid A protein (SAA) was established and used to determine, for the first time, the circulating concentration of this protein in health and disease. As in other species, equine SAA was present only at trace levels in healthy animals but behaved as an extremely sensitive and rapidly responding acute phase reactant following most forms of tissue injury, infection and inflammation, objectively reflecting the extent and activity of disease. Measurements of SAA should make a significant contribution to diagnosis and management of viral and bacterial infection in horses, and routine serial assays could provide an objective criterion for monitoring prospectively the general health of horses in training and racing.  相似文献   
38.
1. The incidence of microscopically detectable degenerative characteristics in 5 skeletal muscles (m. pectoralis thoracicus, m. supracoracoideus, m. biceps femoris, m. semitendinosus, m. femorotibialis medius) of turkeys was investigated. 2. Samples were obtained from 30 Large White turkey males 14, 16 and 18 weeks old. Hyaline degeneration, infiltration of mononuclear cells and necrotic fibres were observed. 3. Individual fibres varied greatly in size and muscle fibre nuclei were often shrunken and pyknotic. 4. Weak and/or uniform reaction for Ca++-ATPase and SDH in all types of muscle fibres and loss of alkaline phosphatase activity in cell membranes were noted. A positive reaction for acid phosphatase occurred in regions of perivascular infiltration and in necrotic muscle fibres. The majority of muscle fibres possessed high activity for phosphorylase a and b. 5. Based on the use of fluorescein alpha-bungarotoxin conjugate, motor end-plates appeared to be morphologically intact. Direct immunofluorescence with anti-chicken IgG showed positive reaction in muscle fibres undergoing necrosis and in the involved connective tissue. 6. Degenerative changes varied with age and were most marked in the oldest birds. 7. Because gross degenerative symptoms were absent from both the birds and the meat from them, the condition appears to be either different from or a precursor to the degenerative myopathy characterised by other authors.  相似文献   
39.
A urinary bladder mass in a 12-year-old spayed female West Highland White Terrier was diagnosed after exploratory surgery and biopsy as a transitional cell carcinoma. Four months later the dog presented with an ulcerated plaque-like cutaneous lesion at the previous surgical incision site; concurrent inguinal lymphadenopathy and recurrence of the urinary bladder mass were identified. Transitional cell carcinoma was diagnosed at all 3 sites. Although a definitive relationship cannot be established between the initial surgery for urinary bladder mass and the resultant subcutaneous lesion, surgical implantation should be considered as a source for the neoplastic cells.  相似文献   
40.
Monoclonal antibody c143 against tumor-associated antigen (TAA) expressed on bovine leukemia cells was conjugated to liposomes containing adriamycin (ADM), and therapeutic effects of conjugates were examined in leukemic or preleukemic cows to prevent the progression of the disease. Five cows with TAA-positive in their peripheral blood lymphocytes were divided into two groups. Each group of cows received 4 injections of ADM alone (0.4 mg/kg) or c143-conjugated liposomes containing the same dose of ADM (L-AMD-c143) through the jugular vein at about 4 day intervals. In three animals treated with L-ADM-c143, the TAA-positive cells gradually decreased with treatment and finally two animals became TAA-negative during a 6 week period and a 14 week period after treatment, respectively. In the control, two animals treated with ADM alone showed only a slight decrease of TAA-positive cells.  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