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   5366篇
  免费   463篇
  国内免费   590篇
林业   331篇
农学   743篇
基础科学   265篇
  718篇
综合类   1921篇
农作物   269篇
水产渔业   505篇
畜牧兽医   928篇
园艺   163篇
植物保护   576篇
  2024年   37篇
  2023年   135篇
  2022年   260篇
  2021年   310篇
  2020年   336篇
  2019年   334篇
  2018年   212篇
  2017年   327篇
  2016年   386篇
  2015年   313篇
  2014年   299篇
  2013年   378篇
  2012年   433篇
  2011年   426篇
  2010年   291篇
  2009年   284篇
  2008年   218篇
  2007年   231篇
  2006年   186篇
  2005年   133篇
  2004年   114篇
  2003年   87篇
  2002年   80篇
  2001年   69篇
  2000年   57篇
  1999年   50篇
  1998年   52篇
  1997年   42篇
  1996年   45篇
  1995年   30篇
  1994年   32篇
  1993年   50篇
  1992年   28篇
  1991年   25篇
  1990年   23篇
  1989年   29篇
  1988年   12篇
  1987年   12篇
  1986年   13篇
  1985年   8篇
  1984年   3篇
  1981年   5篇
  1980年   3篇
  1979年   7篇
  1978年   4篇
  1977年   4篇
  1976年   2篇
  1975年   1篇
  1956年   1篇
  1955年   1篇
排序方式: 共有6419条查询结果,搜索用时 312 毫秒
51.
误差修正是实时洪水预报研究和应用中的重要内容,从修正模型降雨输入角度出发,提出了一种基于微分响应的降雨误差修正方法,并通过实例论证了该方法修正降雨量的适用性。该方法通过计算降雨所对应模型的微分响应来修正降雨,从而修正出口断面流量过程。将该修正方法结合新安江模型,对闽江建阳流域的19场历史洪水进行了有效性检验,结果表明:此方法对洪量、洪峰的修正效果明显,且能够显著提高洪水预报的合格率,修正后合格率由63.2%提高到94.7%。  相似文献   
52.
内质网是真核细胞蛋白合成和折叠的主要细胞器,当内质网内蛋白合成或折叠负担增加,引起未折叠或错误折叠蛋白增多时,可激活内质网几条特定信号通路,启动未折叠蛋白反应,这对维持细胞稳态有重要意义。越来越多研究表明,多种炎性反应疾病与内质网应激有密切联系。一方面,内质网应激引起的未折叠蛋白反应可以诱发或者抑制炎症,另一方面,炎性反应也能影响蛋白折叠,从而促进或缓解内质网应激。2型糖尿病、肿瘤和动脉粥样硬化等多种重大疾病的病理机制都涉及内质网应激与炎性反应的相互作用,对该问题的深入研究不仅能加深人们对这些疾病发病机制的理解,也有助于相关药物的研发。  相似文献   
53.
优化杜仲叶提取物制备的工艺条件,在单因素试验基础上,以杜仲叶提取物浸膏得率和绿原酸转移率为评价指标,采用Box-Behnken中心组合设计法优化杜仲叶提取物制备的工艺条件。杜仲叶提取物制备的最佳工艺条件为乙醇浓度500mL/L,液料比10∶1(mL/g),提取温度97℃,提取4次,每次30min;在此最佳工艺条件下,杜仲叶提取物浸膏得率和绿原酸转移率综合评分均值为99.08,与预测值基本一致。响应面法(RSM)优化的杜仲叶提取物制备工艺稳定可靠。  相似文献   
54.
This study was conducted to determine if humoral antibody response of foot-and-mouth disease (FMD) vaccine improved in 8-week-old growing pigs born to well-vaccinated sows pre-treated with 60 mg of poly-γ-glutamic acid (γ-PGA) three days before vaccination. Antibody against FMD virus serotype O was measured 0, 2, 4 and 6 weeks post-vaccination, using a PrioCHECK FMDV type O ELISA kit. The results showed that positive antibody reactions against FMDV serotype O antigen among a component of the vaccine significantly increased in response to pre-injection with γ-PGA.  相似文献   
55.
56.
Oral infection of goats with Mycobacterium avium subsp. hominissuis (MAH) resulted in a large variety of granulomas in organized gut-associated lymphatic tissues and intestinal lymph nodes. To characterize the cellular composition of granulomas, CD4+, CD8+, γδ, B lymphocytes and plasma, CD25+, CD68+, MHC-II+, Ki67+ and endothelial cells were labeled in consecutive frozen sections by immunohistochemistry and acid fast bacilli (AFB) by Kinyoun stain. Granulomas with extensive necrosis, little mineralization and variable numbers of AFB surrounded by many CD4+ T cells, but only few epitheloid macrophages were observed in severely sick goats at 2–3 mpi. They were interpreted as exuberant immune reaction. Organized granulomas with very few AFB were seen in clinically healthy goats at 13 mpi. The necrotic cores were surrounded by a zone of granulomatous infiltrate with many epitheloid macrophages and few lymphocytes. This zone was initially wide and highly vascularized and became progressively smaller. It was enclosed by an increasing layer of connective tissue. All organized granulomas were surrounded by compartimentalized tertiary lymphoid tissue. The granulomas in experimental infection of goats with MAH reflect the heterogeneity of lesions seen in mycobacterial infections of humans and ruminants and are therefore valuable for comparative research.  相似文献   
57.
58.
59.
The objective of this study was to evaluate the effects of two different probiotic micro‐organisms on the performance, egg quality and blood parameters of organically reared hens. A total of 900 16‐week‐old Hy‐Line layer hybrids were randomly assigned to three groups of 300 birds each. The control (CTR) group was fed a corn–soya bean cake‐based diet; the L group was fed the same diet supplemented with 0.1% Lactobacillus acidophilus, while the B group was fed the same diet supplemented with 0.05% Bacillus subtilis. Data were recorded at the beginning (weeks 5 and 6: T1) and at the end (weeks 19 and 20: T2) of the experiment, and no differences in hen performance were recorded between dietary groups or sampling times. All of the investigated clinical chemistry parameters, except GGT, were affected by diet (p < 0.05), with the best results recorded for the probiotic‐treated groups. The immune‐response values showed higher blood bactericidal activity in the B and L groups at T2 (p < 0.05) and a lower lysozime concentration in the B group at T1. Higher antibody production against Newcastle disease virus was observed in the L group compared to the CTR (p = 0.013). No differences in oxidative status were recorded, and no effects of diet on egg quality were observed. Among the physical egg characteristics, only the Roche scale colour was affected by diet (p < 0.05): the egg yolk was paler in the L group. The age of the hen was the most relevant factor affecting physical egg characteristics. The chemical parameters of the egg were almost unaffected by supplementation with probiotics except for the lipid content, which decreased with the L diet (p < 0.05). Both probiotic inclusions had beneficial effects on hen metabolism and welfare, and L. acidophilus induced the best immune response.  相似文献   
60.
BACKGROUND: A syndrome of relative adrenal insufficiency has been identified in septic humans, and is associated with hypotension and death. Relative adrenal insufficiency is generally associated with basal serum cortisol concentration within or above the reference range and a blunted cortisol response to adrenocorticotropic hormone administration. It is unknown whether relative adrenal insufficiency occurs in septic dogs. HYPOTHESIS: That relative adrenal insufficiency occurs in septic dogs, and that relative adrenal insufficiency is associated with hypotension and mortality. ANIMALS: Thirty-three septic dogs admitted to a small animal intensive care unit. METHODS: Dogs were included in the study if they had a known or suspected infectious disease and had systemic inflammatory response syndrome. Dogs were excluded if they had disease or medication history expected to affect the hypothalamic-pituitary-adrenal axis. Serum cortisol and endogenous plasma adrenocorticotropic hormone concentrations were measured before, and serum cortisol concentration measured 1 hour after, intramuscular administration of 250 microg of cosyntropin/dog. The change in cortisol concentration (delta-cortisol) before and after cosyntropin administration was determined in each dog. RESULTS: Hypotension was associated with lower delta-cortisol values (OR 1.3; CI 1.0-1.9; P = .029). delta-Cortisol cutoff of 3.0 microg/dL was most accurate for predicting hypotension, survival to discharge, and 28-day survival. The rate of death in dogs with delta-cortisol < or = 3 microg/dL was 4.1 times that of dogs with delta-cortisol > 3 microg/dL (RR 4.1; CI 1.5-12.3; P = .01). CONCLUSIONS AND CLINICAL RELEVANCE: Delta-cortisol < or = 3 microg/dL after adrenocorticotropic hormone administration is associated with systemic hypotension and decreased survival in septic dogs.  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