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   16611篇
  免费   481篇
  国内免费   28篇
林业   1298篇
农学   464篇
基础科学   131篇
  2481篇
综合类   1933篇
农作物   862篇
水产渔业   1277篇
畜牧兽医   6942篇
园艺   468篇
植物保护   1264篇
  2022年   101篇
  2021年   159篇
  2020年   216篇
  2019年   217篇
  2018年   319篇
  2017年   398篇
  2016年   377篇
  2015年   411篇
  2014年   445篇
  2013年   602篇
  2012年   982篇
  2011年   1001篇
  2010年   473篇
  2009年   422篇
  2008年   695篇
  2007年   658篇
  2006年   631篇
  2005年   1325篇
  2004年   1250篇
  2003年   1009篇
  2002年   613篇
  2001年   228篇
  2000年   122篇
  1999年   240篇
  1998年   87篇
  1992年   174篇
  1991年   194篇
  1990年   225篇
  1989年   196篇
  1988年   213篇
  1987年   157篇
  1986年   176篇
  1985年   149篇
  1984年   126篇
  1983年   121篇
  1979年   156篇
  1978年   116篇
  1977年   106篇
  1976年   97篇
  1975年   159篇
  1974年   145篇
  1973年   129篇
  1972年   144篇
  1971年   121篇
  1970年   88篇
  1969年   105篇
  1968年   117篇
  1967年   132篇
  1966年   105篇
  1965年   72篇
排序方式: 共有10000条查询结果,搜索用时 718 毫秒
41.
The purpose of this study was to define normal gross anatomic structures in the equine stifle with magnetic resonance images. Magnetic resonance (MR) images were made in sagittal, 15° supinated, transverse, and dorsal planes of two equine stifles. The MR images were scrutinized by comparing MR images to dissection specimens and frozen cross sections of stifle joints. Sagittal and 15° supinated images were the most valuable in assessing articular cartilage, subchondral bone, and soft tissue structures within the joint. Cranial and caudal cruciate ligaments, medial and lateral menisci, meniscotibial and meniscofemoral ligaments, long digital extensor tendon, and patellar ligaments were easily evaluated. MR images provided substantially more gross anatomical information than the currently available imaging modalities.  相似文献   
42.
43.
In faeces and ileal digesta samples of 31 intact (INT) as well as 73 surgically differently prepared pigs bacterial fractionations and 2.6-diaminopimelic acid (DAP) estimations were carried out in order to calculate the bacterial N proportion in faeces N and digesta N after feeding various diets. Because of a high individual variability and the analytical variation width of the DAP/N-ratios no distinct influences of the fed diets could be found. The average DAP/N-values in the faeces (0.224) of INT pigs ranged in the same magnitude as in the digesta (0.0272) of ileorectostomized (IRA) pigs with open colon descendens (IRAo), where a digesta backflow is possible. Distinct lower DAP/N-ratios (0.0125 resp. 0.0043), however, were found in the digesta of pigs with ileo-caecal cannulae (IZB) or IRA pigs with closed colon (IRAg). On the base of various premises (N of the "bacterial fraction" C is only bacterial N; the DAP found in fraction A originates from intestinal bacteria adhering to feed particles) conducted calculations of the bacterial N proportions (in per cent of total N) led to the following data: Faeces of INT pigs: 43.0 ... 68.2 vs. 69.6 ... 89.0; digesta of operated pigs (except protein free diet) IRAo: 22.3 ... 57.0 vs. 46.2 ... 73.8; IZB: 17.0 ... 35.7 vs. 25.2 ... 53.6; IRAg (only 3 pigs): 23.6 vs. 24.2. The proportion of bacterial N in the digesta N of protein free fed IRAo pigs was 22.0 vs. 22.6%.  相似文献   
44.
A paper published byKniehase & Zoebelein (1990) describes a new laboratory method to test the side effects of pesticides on the predatory mitePhytoseiulus persimilis and criticizes the laboratory test developed by the International Working Group pesticides and beneficial organisms of the International Organization for Biological Control (IOBC), West Palaearctic Regional Section (WPRS). The present publication discusses the advantages and disadvantages of both methods, responds to the criticism and mention the overall concept of the IOBC/WPRS Working Group including semifield and field test methods.In einer Arbeit vonKniehase undZoebelein (1990) wird ein neues Laborverfahren zur Prüfung der Nebenwirkung von Pflanzenschutzmitteln auf die RaubmilbePhytoseiulus persimilis beschrieben. Die genannten Autoren äußern sich kritisch über das seither von der Arbeitsgruppe Pflanzenschutzmittel und Nutzorganismen der International Organization for Biological Control (IOBC), West Palaearctic Regional Section (WPRS) praktizierte Verfahren. In der vorliegenden Arbeit werden die Vor- und Nachteile der beiden Prüfmethoden diskutiert. Einer Reaktion auf die Kritik folgt eine kurze Beschreibung der gesamten Konzeption der genannten Arbeitsgruppe, die auf einer Kombination aus Labor-, Halbfreiland- und Feldprüfverfahren beruht.  相似文献   
45.
In a study of susceptibilities of sows from 2 herds to experimentally induced Escherichia coli mastitis, a marked difference was seen. The "susceptible" sows were from a conventional herd and "resistant" sows were from a specific-pathogen-free herd. The purpose of the study was to determine whether deficient neutrophil function was associated with increased susceptibility to E coli-induced mastitis. Four in vitro procedures were used to evaluate polymorphonuclear leukocyte (PMN) function: (i) random migration under agarose, (ii) ingestion of 125I-iododeoxyuridine-labeled Staphylococcus aureus, (iii) quantitative nitroblue tetrazolium reduction, and (iv) iodination. After parturition and intramammary inoculation with E coli, sows from the susceptible herd were neutropenic and the neutrophils which were present in the peripheral blood had reduced function. Specifically, there were depressed random migration under agarose, S aureus ingestion, and iodination when compared with PMN function in resistant sows. These data indicate that susceptibility to E coli mastitis was associated with deficiencies in PMN numbers and function. Potential causes of the neutrophil dysfunction are discussed and include possible systemic hormonal aberrations or the presence of an inapparent viral or bacterial infection.  相似文献   
46.
47.
48.
Atrophic rhinitis is caused by toxigenic Pasteurella multocida strains. The infection is supported by Bordetella bronchiseptica and other widespread agents and by non-infectious factors damaging the nasal epithelium. The term "infectious multifactorial disease" means in German, that ubiquitous low-virulent agents cause disease when intensified by non-infectious factors. Atrophic rhinitis does not belong to this group but is an infectious disease, caused by a specific agent and influenced by several factors.  相似文献   
49.
50.
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