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   98685篇
  免费   8552篇
  国内免费   7563篇
林业   11683篇
农学   13425篇
基础科学   7778篇
  15823篇
综合类   28874篇
农作物   4926篇
水产渔业   5692篇
畜牧兽医   16546篇
园艺   3426篇
植物保护   6627篇
  2025年   16篇
  2024年   1086篇
  2023年   1314篇
  2022年   2486篇
  2021年   3595篇
  2020年   3899篇
  2019年   4293篇
  2018年   3016篇
  2017年   3978篇
  2016年   3911篇
  2015年   4686篇
  2014年   4546篇
  2013年   5733篇
  2012年   6104篇
  2011年   6765篇
  2010年   6649篇
  2009年   5831篇
  2008年   5741篇
  2007年   5512篇
  2006年   5108篇
  2005年   4491篇
  2004年   2347篇
  2003年   2057篇
  2002年   1846篇
  2001年   1901篇
  2000年   2099篇
  1999年   2106篇
  1998年   2011篇
  1997年   1701篇
  1996年   1510篇
  1995年   1442篇
  1994年   1250篇
  1993年   1190篇
  1992年   1008篇
  1991年   830篇
  1990年   709篇
  1989年   603篇
  1988年   442篇
  1987年   287篇
  1986年   183篇
  1985年   88篇
  1984年   76篇
  1983年   69篇
  1982年   56篇
  1981年   45篇
  1980年   31篇
  1979年   21篇
  1978年   16篇
  1964年   14篇
  1963年   15篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
为了探索千里光提取物冻干粉(SsE)的药物代谢动力学特征,首次采用耳肿胀度抑制率药理效应法测定SsE药动学参数。结果发现,在一定剂量范围内给小鼠腹腔注射SsE,能较迅速地产生药理效应,使耳肿胀度抑制率显著提高;SsE最低有效量为57.40 mg/kg,在小鼠体内代谢符合一级反应一室模型,模型表达式为:C=1 436.227 e^(-0.133 4 t)-1436.227 e^(-0.237 t),表观药动学参数为:一级消除速率常数Ke=0.133 4 h-1,消除半衰期t1/2Ke=5.194 9 h,一级吸收速率常数Ka=0.237 h-1,吸收半衰期t1/2Ka=2.924 1 h,血药峰浓度Cmax=1 436.227 mg/kg,达峰时间tmax=5.547 4 h,清除率Cl=0.055 3mg/kg.h,药-时曲线下面积AUC=16 826.35 mg/kg.h,表观分布容积V=0.414 2 mg/kg,滞后期t0=0.010 4 h。表明SsE具有良好的抗炎作用,在小鼠体内起效快,消除慢,生物利用度高,在机体内分布有限,较集中于血浆,组织摄入少。  相似文献   
102.
<正>玉米干酒糟及其可溶物(corn distillers dried grains with solubles,DDGS)是玉米加工工业的副产品,是生产工业酒精后,将酒糟醒液经固液分离后的滤渣与蒸发浓缩后的过滤浆液混合干燥而成的。近几年,我国的工业用燃料乙醇生产量大幅度增加,  相似文献   
103.
采用凝血酶原时间(PT-期法)测定、白陶土非特异性粘附试验及加入活化因子等指标,观察了氯化钙抗凝血剂对家兔内、外源凝血系统的影响。结果表明,用0.72mol/LCaCl2作为抗凝剂,血液凝血酶原时间延长,即外源性凝血系统受抑制。白陶土不能激活内源性凝血系统而诱发凝血,即内源性凝血系统亦受到抑制。a因子也不能使之启动  相似文献   
104.
酵母菌生长最适条件和最佳菌种的探讨   总被引:5,自引:0,他引:5  
利用食品工业生产过程中排出的大量废水,培养酵母菌可提高原料的利用率,缓解蛋白质饲料资源的不足,经利用后的废水大大净化,减少了环境污染。酵母菌作为单细胞生物,其蛋白质含量很高,含有8~12种氨基酸,必需氨基酸含量也很高,富含脂肪和维生素,特别是B族维生素多达9种。利用食品工业废水培养酵母菌制成饲料,对发展我国畜牧业、饲料工业有重大的社会经济意义。基于此,我们通过大量试验,尽可能准确地得出了酵母菌生长的最适条件和最佳菌种,为推广工业化大规模生产提供依据。1材料与方法1.1材料1.1.1菌种 白地霉A…  相似文献   
105.
Phenylbutazone (PBZ) is a nonsteroidal anti‐inflammatory drug used in the treatment of chronic pain and arthritis. Topical and transdermal administration of PBZ would be beneficial in large animals in terms of minimizing gastro‐intestinal ulcerations and other side effects, easy administration to legs and joints and minimizing the dose to reduce systemic toxicity of the drug. A topical liposomal preparation with different concentrations of a mono‐substituted alkyl amide (MSA) and PBZ was formulated. The formulations were evaluated by in vitro skin‐permeation kinetics through deer skin using Franz diffusion cells. By increasing drug loading from 1% to 5% w/w, the steady‐state flux (μg/cm2/h) of PBZ was increased twofold (P < 0.001). Similarly, by increasing the MSA concentration from 0% to 4%, the steady‐state flux (μg/cm2/h) of PBZ was increased twofold (P < 0.001). Overall, by increasing the drug load and the use of an appropriate amount of the penetration enhancer, the steady‐state flux of PBZ through skin was increased fourfold (P < 0.001). MSA at both 2% and 4% w/w concentrations significantly increased the skin levels of PBZ as compared with control (P < 0.05). In conclusion, MSA served as an effective skin‐penetration enhancer in the liposomal gel of PBZ for deer.  相似文献   
106.
Reasons for performing study: The nerve‐muscle pedicle graft technique is a treatment for recurrent laryngeal neuropathy (RLN), but the optimal placement of the pedicles within the cricoarytenoideus dorsalis (CAD) muscle is unknown. Hypothesis: The magnitude and direction of force placed on the muscular process of the left arytenoid cartilage affects the magnitude of laryngeal abduction. Methods: Five larynges were harvested from cadavers. Using increments of 0.98 N, a dead‐weight force generator applied a force of 0–14.7 N for 1 min each to the left muscular process at 0, 10, 20, 30, 40, 50, 60 and 70° angles. The rima glottis was photographed digitally 1 min after each force had been applied. Distances between biomarkers (Lines 1–4) and right to left angle quotient (RLQ) were used to assess the degree of left arytenoid abduction. Results: Increasing force from 0–14.7 N progressively and significantly increased the length of all lines and RLQ, indicating abduction. Furthermore, there was a significant interaction between force and angles. Applying forces of 7.84 N or greater (Lines 2–4 and RLQ) or 11.76 N or greater (Line 1) at angles 0, 10, 20 and 30° resulted in significantly greater abduction than applying the same forces at 40, 50, 60 and 70°. Angles of 0–30° correspond with the direction of pull exerted by the lateral compartment of the CAD muscle. Conclusion: In RLN, nerve‐muscle pedicle grafts should be placed preferentially in the lateral rather than in the medial compartment of the CAD muscle. Potential relevance: The information presented can be used to assist surgeons in the planning and application of the nerve‐muscle pedicle graft procedure.  相似文献   
107.
建立富含乳脂肪球膜蛋白乳清粉中测定总磷脂的方法,采用甲醇-三氯甲烷提取,经过高温灼烧,用钼蓝比色法测定无机磷的含量,再乘以系数26.31折算成试样中总磷脂的含量,该法标曲线性关系良好(R2=0.9990),回收率>90%,RSD<3%。该法简单,准确率高,可用于富含乳脂肪球膜蛋白中总磷脂的测定。  相似文献   
108.
Objective: To (1) identify prognostic indicators for stability after stabilization of sacroiliac luxation with screws inserted in lag fashion and (2) report dorsoventral dimensions of the sacrum in cats. Study Design: Multicenter retrospective study. Sample Population: Cats (n=40) with sacroiliac luxation. Methods: Case records and radiographs of cats presented at the Queen's Veterinary School Hospital Cambridge and the Royal Veterinary College Hatfield for screw fixation of sacroiliac luxation were reviewed. Dorsoventral dimensions of 15 feline cadaveric sacral bodies were measured to identify the appropriate implant size for use in fixation with screws inserted in lag fashion. Results: Of 40 cats, 13 had left, 14 right, and 13 bilateral sacroiliac luxations. Of 48 screws analyzed, 42 (87.5%) were placed within the sacral body or exited ventrally and 6 (12.5%) were considered malpositioned. Screw purchase within the sacrum was statistically different between unstable and stable repairs (P=.001). Using confidence intervals for screw length within the sacrum and effect on stability, the lowest screw depth that contained 95% of the screws that did not loosen was ∼60% of the sacral width. Mean dorsoventral sacral dimension at its narrowest point was 5.9±1.14 mm. There was no significant difference in the incidence of implant loosening between those luxations that were 100% reduced and those that were <100% reduced (P=.7837). Conclusions: Screw purchase within the feline sacrum of at least 60% of the sacral width significantly reduces the risk of loosening. Clinical Relevance: Screw placement to a depth of 60% of the width of the feline sacrum is recommended.  相似文献   
109.
以江苏省淮安市樱花园(苏北野生动物园)内人工饲养的1对猞猁为研究对象,对其在人工饲养条件下的日粮组成、饲养环境、日常管理、常见疫病防治及繁殖育幼情况的初步小结,以期为今后猞猁在人工饲养条件下的饲养、繁殖工作提供一定的实践依据。  相似文献   
110.
生物饲料具有质优价廉、吸收利用率高、替代抗生素、保护环境的功能。生物饲料的开发和使用在促进畜牧业健康养殖、动物生产力和繁殖力的提高、改善饲料和动物产品质量等领域具有重要作用,在生态畜牧业发展中前景广阔、意义重大。本文从生物饲料的概念、种类、特点、意义、国内外发展现状、发展趋势等方面进行了综述。结论是人类对食品安全的高质量需求和生态文明的要求,将为生物饲料的发展提供广阔的发展前景。生物饲料开发与应用,将推动畜牧业生产方式转变,实现农业残余物的资源化利用,缓解粮食短缺矛盾,保障食品安全,进一步助推生态畜牧业的高质量发展。  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