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   6269篇
  免费   451篇
  国内免费   698篇
林业   217篇
农学   350篇
基础科学   51篇
  296篇
综合类   2351篇
农作物   301篇
水产渔业   469篇
畜牧兽医   2918篇
园艺   277篇
植物保护   188篇
  2024年   14篇
  2023年   87篇
  2022年   198篇
  2021年   237篇
  2020年   214篇
  2019年   270篇
  2018年   178篇
  2017年   265篇
  2016年   338篇
  2015年   315篇
  2014年   336篇
  2013年   384篇
  2012年   445篇
  2011年   464篇
  2010年   394篇
  2009年   366篇
  2008年   323篇
  2007年   381篇
  2006年   306篇
  2005年   260篇
  2004年   215篇
  2003年   190篇
  2002年   150篇
  2001年   151篇
  2000年   121篇
  1999年   99篇
  1998年   79篇
  1997年   82篇
  1996年   52篇
  1995年   76篇
  1994年   65篇
  1993年   70篇
  1992年   52篇
  1991年   52篇
  1990年   59篇
  1989年   40篇
  1988年   25篇
  1987年   12篇
  1986年   7篇
  1985年   8篇
  1983年   4篇
  1982年   2篇
  1981年   3篇
  1980年   4篇
  1979年   6篇
  1975年   1篇
  1973年   3篇
  1962年   1篇
  1956年   10篇
  1955年   1篇
排序方式: 共有7418条查询结果,搜索用时 15 毫秒
991.
AIM: To identify fungi isolated from infections of the bovine mammary gland, and establish their possible sources.

METHODS: From a herd of 420 cows, milk samples were collected from all quarters at calving and cultured to detect causative organisms. Quarters identified as infected with fungi were further sampled during early lactation. Samples from feedstuffs, the feed pad and ends of teats were also collected and analysed for the presence of fungi.

RESULTS: Eleven of 420 cows were diagnosed with intramammary infections (IMI) caused by yeasts (nine cows, 10 quarters) and moulds (two cows, three quarters). Six of the yeast species had previously been reported as being responsible for mastitis. Elevated somatic cell counts (SCC) were observed in many quarters, but most infections were eliminated spontaneously. Two of the fungi isolated from milk samples were also isolated from feedstuffs and teat swabs, and seven other fungi isolated from milk samples were not isolated from feed, the feed pad or cows' teats.

CONCLUSIONS: Isolation of fungi from the udder is rarely reported in dairy cows in New Zealand. In this herd, contamination of the end of the teat originating from feedstuffs and possibly exacerbated by the use of a feed pad may have led to the establishment of IMI caused by fungi.

CLINICAL RELEVENCE: Fungi are infrequently if ever reported in mastitis trial data or surveys in New Zealand and are probably of little clinical significance.  相似文献   
992.
We histopathologically and immunohistochemically investigated a case of malignant lymphoma that spontaneously developed in a male common marmoset at two years of age. Beginning at two years four months of age, the animal had an enlargement of the submandibular and inguinal lymph nodes, small subcutaneous nodules near the right breast and an approximately fivefold increase in peripheral lymphocyte count compared with the previous examination value. The postmortem findings at two years eight months of age showed lymphadenopathy with enlargement of the thymus and spleen. Small- to intermediate-sized neoplastic lymphocytes had diffusely proliferated in the enlarged nodes. The neoplastic cells were pleomorphic and had irregularly shaped nuclei. The nuclear chromatin staining revealed hyperchromatism in the small-sized cells, and the intermediate-sized cells exhibited vesicular staining. An immunohistochemical examination indicated that the neoplastic lymphocytes were positive for CD3 and negative for CD20, thus suggesting that they had originated from T cells. In addition, the proliferation of high endothelial venules and reactive epithelioid histiocytes was observed. Scattered tingible body-laden macrophages were infrequently detected. Neoplastic lymphocytes were also observed in the thymus, spleen, heart, lungs, liver, kidneys, adrenal glands and femoral and sternal bone marrow. This malignant lymphoma in a young male common marmoset was considered to fit the category of “peripheral T-cell lymphoma, not otherwise specified (PTCL-NOS)” according to the new WHO system of classification.  相似文献   
993.
The first joint Japanese Society of Toxicologic Pathology (JSTP) and National Toxicology Program (NTP) Satellite Symposium, entitled “Pathology Potpourri,” was held on January 29th at Okura Frontier Hotel in Tsukuba, Ibaraki, Japan, in advance of the JSTP’s 29th Annual Meeting. The goal of this Symposium was to present current diagnostic pathology or nomenclature issues to the toxicologic pathology community. This article presents summaries of the speakers’ presentations, including diagnostic or nomenclature issues that were presented, select images that were used for audience voting or discussion, and the voting results. Some lesions and topics covered during the symposium include: treatment-related atypical hepatocellular foci of cellular alteration in B6C3F1 mice; purulent ventriculoencephalitis in a young BALB/c mouse; a subcutaneous malignant schwannoma in a RccHan:WIST rat; spontaneous nasal septum hyalinosis/eosinophilic substance in B6C3F1 mice; a rare pancreatic ductal cell adenoma in a young Lewis rat; eosinophilic crystalline pneumonia in a transgenic mouse model; hyaline glomerulopathy in two female ddY mice; treatment-related intrahepatic erythrocytes in B6C3F1 mice; treatment-related subendothelial hepatocytes in B6C3F1 mice; spontaneous thyroid follicular cell vacuolar degeneration in a cynomolgus monkey; congenital hepatic fibrosis in a 1-year-old cat; a spontaneous adenocarcinoma of the middle ear in a young Crl:CD(SD) rat; and finally a series of cases illustrating some differences between cholangiofibrosis and cholangiocarcinoma in Sprague Dawley and F344 rats.  相似文献   
994.
This study aimed to investigate the role of epithelial cells in regulating innate immunity in bovine oviduct epithelial cell (BOEC) culture. We studied the effect of Escherichia coli lipopolysaccharide (LPS) and its interaction with ovarian steroids, estradiol (E2) and progesterone (P4), and luteinizing hormone (LH) at concentrations observed during the preovulatory period on immune responses in BOEC culture. Immunohistochemistry of oviduct tissue showed intensive expression of Toll-like receptor-4 (TLR-4) and TLR-2 in epithelial cells. A dose of 10 ng/ml LPS stimulated TLR-4, cyclooxygenase-2 (COX-2), nuclear factor kappa B inhibitor A (NFKBIA), interleukin 1β (IL-1β) and tumor necrosis factor α (TNF-α) expression, indicating an early pro-inflammatory response. A dose of 100 ng/ml LPS did not induce expression of these genes but stimulated TLR-2, IL-10,IL-4 and microsomal prostaglandin E synthase-1 (mPGES-1) expression and PGE2 secretion, indicating an anti-inflammatory response. Ovarian steroids and LH completely block LPS (10 ng/ml)-induced TLR-4, IL-1β and TNF-α expression as well as LPS (100 ng/ml)-induced TLR-2 expression. Taken together, this study suggests the existence of an early signaling system to respond to infection in the BOEC. In addition, ovarian steroids and LH may play a critical role in inducing homeostasis and in controlling hyperactive pro-inflammatory responses detrimental to epithelial cells, sperm and the embryo.  相似文献   
995.
The present experiments were undertaken to examine whether oxytocin cells in the supraoptic nucleus receive synaptic inputs from the contralateral supraoptic nucleus or paraventricular nucleus. Using urethane-anesthetized lactating rats, extracellular action potentials were recorded from single oxytocin or vasopressin cells in the supraoptic nucleus. Electrical stimulation was applied to the contralateral supraoptic nucleus or paraventricular nucleus, and responses of oxytocin or vasopressin cells were analyzed by peri-stimulus time histogram or by change in firing rate of oxytocin or vasopressin cells. Electrical stimulation of the contralateral supraoptic nucleus or paraventricular nucleus did not cause antidromic excitation in oxytocin or vasopressin cells but caused orthodromic responses. Although analysis by peri-stimulus time histogram showed that electrical stimulation of the contralateral supraoptic nucleus or paraventricular nucleus caused orthodromic excitation in both oxytocin and vasopressin cells, the proportion of excited oxytocin cells was greater than that of vasopressin cells. Train stimulation applied to the contralateral supraoptic nucleus or paraventricular nucleus at 10 Hz increased firing rates of oxytocin cells and decreased those of vasopressin cells. The results of the present experiments suggest that oxytocin cells in the supraoptic nucleus receive mainly excitatory synaptic inputs from the contralateral supraoptic nucleus and paraventricular nucleus. Receipt these synaptic inputs to oxytocin cells may contribute to the synchronized activation of oxytocin cells during the milk ejection reflex.  相似文献   
996.
The objective of this study was to explore the underlying mechanism of insulin‐like growth factor 1 (IGF‐1)–caused cell proliferation of rumen epithelium in goats fed a high metabolizable energy (ME) diet. In this study, young goats were fed either a low ME [LL, n = 9, ME: 0.57 MJ/kg0.75/day] or high ME [HL, n = 9, ME: 1.00 MJ/(kg0.75/day)] diet for 42 day. The time duration of G1‐phase was shortened as a result of enhanced expression of cyclin D1 mRNA in the HL group (p < 0.05). It was suggested that a high ME diet promoted cell transition from G0/G1 to S‐phase via cyclin D1. The level of phosphorylation of ERK was higher in HL than LL group (p < 0.05). In cell culture, the ERK was phosphorylated by IGF‐1 treatment. The proliferative effects of insulin‐like growth factor 1 (IGF‐1, 25 ng/ml) on [3H] thymidine (TdR) incorporation into DNA and on cyclin D1 protein expression of rumen epithelial cells were inhibited by PPP (the inhibitor of type 1 IGF receptor) (p < 0.05) and ERK inhibitor (p < 0.05) in vitro. Thus, IGF‐1 up‐regulated cyclin D1 expression and accelerated G1‐phase progression in the cell cycle through Ras/Raf/MEK/ERK pathway in rumen epithelium of goats.  相似文献   
997.
The aim of this study was to estimate heritabilities of and genetic correlations between pathogen‐specific subclinical mastitis (SCM) traits and lactation mean somatic cell score (LSCS) in Norwegian Red cattle. Based on data from 130 733 first‐lactation cows four binary pathogen‐specific SCM traits, Staphylococcus aureus, Streptococcus dysgalactiae, Streptococcus uberis and coagulase‐negative staphylococci SCM, were analysed together with unspecific SCM and LSCS using a multivariate sire model with threshold models for binary traits and a linear model for LSCS. Posterior means (SD) of heritabilities were 0.17 (0.01) for LSCS, 0.11 (0.01) for liability to unspecific SCM and ranged from 0.04 (Staph. aureus) to 0.14 (Strep. dysgalactiae) for liability to pathogen‐specific SCM. Genetic correlations were positive and moderate to high, ranging from 0.37 to 0.98. All genetic correlations except the one between LSCS and unspecific SCM were lower than 1, indicating that SCM caused by different pathogens can be considered as partly different traits.  相似文献   
998.
李莉  徐律  李连军  杨最素  孙瑜  丁国芳 《安徽农业科学》2013,(14):6280-6281,6284
[目的]探讨菲律宾蛤仔酶解多肽的制备及体外抗肺癌H1299细胞的活性。[方法]选择胰蛋白酶酶解菲律宾蛤仔,经超滤得到3kD以下的酶解多肽,应用MTT法、HE染色和AO/EB染色等方法检测其体外抗H1299细胞的活性。[结果]3 kD以下的酶解多肽作用于H1299细胞后,MTT法检测结果表明该多肽能抑制该细胞增殖,呈剂量和时间依赖;经HE染色和AO/EB染色发现H1299细胞出现凋亡的形态学改变。[结论]菲律宾蛤仔酶解多肽能明显抑制H1299细胞的增殖并诱导细胞凋亡。  相似文献   
999.
为了筛选和鉴定猪链球菌3个保护性抗原GAPDH、MRP、DLDH的优势B细胞抗原表位,设计表位串联方案,研究重组串联表位蛋白(简称GMD蛋白)免疫小鼠后对猪链球菌攻击的免疫保护效力。采用生物信息学分析工具对优势B细胞抗原表位进行筛选,并将表位串联并构建重组质粒pET28a-GMD,诱导表达且纯化后将GMD蛋白配合弗氏佐剂免疫BALB/c小鼠,并评价该蛋白对2型猪链球菌的免疫保护效力。发现经SDS-PAGE鉴定该重组蛋白大小为43.3 kDa;小鼠免疫保护实验结果显示,免疫小鼠血清中针对猪链球菌HA9801菌株抗体效价最高可达1∶102 400,GMD蛋白对小鼠的免疫保护率可达90%。上述结果表明面对猪链球菌HA9801菌株的攻击,GMD蛋白可以为机体提供良好的免疫保护,本研究结果为猪链球菌新型表位亚单位疫苗的研制提供了基础数据。  相似文献   
1000.
为探讨低温贮藏下不同包装方式对平菇生理特性及细胞壁变化的影响,将平菇置于5℃冰箱中冷藏,分别以敞口PE保鲜袋和封口PE保鲜袋进行试验,以完全裸露放置作为对照,分析贮藏期间不同包装方式对平菇的感官品质、丙二醛(MDA)含量、可溶性蛋白质含量、抗氧化物酶活性,细胞壁代谢相关酶活性等指标的影响,并对平菇进行石蜡切片,观察其细胞壁的微观结构变化。结果表明,随着贮藏时间的延长,与对照相比,PE保鲜袋处理的平菇保鲜效果显著提升,明显抑制了失重率、MDA含量的增加,减缓了硬度、白度(HW)值的增大,降低了蛋白质含量的损失,延缓了过氧化物酶(POD)、过氧化氢酶(CAT)和纤维素酶(Cx)活性峰值的出现,更好地保持了平菇的品质。在整个处理组中,平菇的HW值、失重率、MDA含量不断增大且封口处理低于敞口处理;硬度值逐渐减小,封口处理硬度较敞口处理低;蛋白质含量呈现先升高后降低的趋势,封口处理蛋白质含量显著低于敞口处理;POD活性先升后降,在0~4 d,封口处理POD活性高于敞口处理,4~8 d急速下降且低于敞口处理;CAT活性呈现先降再增的趋势,贮藏前期0~2 d与贮藏后期第6至第8天CAT活性较高,0~6 d敞口处理高于封口处理,后低于封口。通过对平菇菌褶石蜡切片发现,伴随着采后贮藏天数的增加,平菇子实体细胞结构变得杂乱无序、模糊不清,细胞间隙变大,且封口处理比敞口处理细胞结构有序、规整。由此可知,低温贮藏下,PE包装处理贮藏效果明显优于全部裸露放置,封口包装保鲜效果优于敞口保鲜效果。  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